Mating and spermatophore morphology of water (: Parasitengona)

HEATHER C. PROCTOR*

Department of

Received June 1991, accepted March 1992

In this paper I synthesize original and published studies of sperm transfer behaviour of 23 genera of water mitrs from 15 families. The morphology of spermatophores from 16 genera (12 families) is described. Behaviour and/or spermatophores are described for the first time for the following species: Hydrachna magniscutata Marshall, Hydrachna hesperia Lundblad, Hydrachna sp. nr. leegk Koenike, ampricana Lundblad, undulata (Miiller), distincta Marshall, (three species in the I/. crassipes-complex), 'Thyas stolli Koenike, Lcbertia annae Habeeb, Lcbertia sp., Piona sp. nr. debilis (Wolcott), Tip$s uernalis (Habeeb), Arrenurus dentipctiolatus Marshall, Arrmurus marshalli Piersig and Arrenurus birgei Marshall. On the basis of proximity of male and female during sperm transfer, 1 divide water mites into four groups: complete dissociation, involving no physical or chemical contact between the sexes (nine genera); incomplete dissociation, requiring distance- or contact-chemoreception but not involving pairing behaviour (five genera); pairing with indirect transfer, involving pairing behaviour with females controlling sperm uptake (three genera); pairing with direct transfer ( = copulation), involving pairing behaviour and male placement of sperm in the receiving structure of the female (12 genera). Four genera have representative species in more than one category of sperm transfer. Factors possibly leading to the diversity of water mating behaviour include an evolutionarily flexible mode of sperm transfer in the ancestral water mite, and the development of planktonic and endoparasitic habits in many mites. Morphological features of spermatophores that improve physical stability, probability of females taking up sperm and resistance against osmotic stress are discussed. Finally, I present implications of mating behaviour and spermatophore morphology for phylogenetic relationships within water mites and between this group and terrestrial Acari.

KEY WORDS:-Acari - water mites - mating behaviour - spermatophores - evolution.

CONTENTS Introduction ...... 342 Methods ...... 342 Collection and maintenance of mites ...... 342 Spermatophore illustrations ...... 343 Behavioural observations and descriptions ...... 343 Experimental methods ...... 343 Statistical analyses ...... 343 Modes of sperm transfer ...... 343 Complete dissociation...... 346 Incomplete dissociation ...... 356 Pairing with indirect transfer ...... 362 Pairing with direct transfer (copulation) ...... 366

*Present address: Department of Biological Scienres, University of Calgary, Calgary, A1 berta, Canada T2N I N4. 34 I 0024-4082/92/120341+44 SOE.OO/O 0 1992 The Linnean Society of London 342 H. C. PROCTOR Discussion ...... 375 Comparison of mating behaviour between water mites and other . .. 375 Functional morphology of water mite spermatophores ...... 378 Spermatophore structure, mating behaviour and water mite phylogeny. ... 380 Acknowledgements ...... 382 References ...... 382

INTRODUCTION Although arachnids show the greatest diversity of sperm transfer behaviour of all (Thomas & Zeh, 1984), there are few reviews of mating in any groups other than scorpions (Polis & Sissom, 1990), spiders (Austad, 1984) and pseudoscorpions (Weygoldt, 1966, 1970). Within the class Arachnida most orders are monotypic in their mode of sperm transfer (e.g. all spiders copulate); however, one monophyletic group, water mites, exhibits all modes of sperm transfer from complete dissociation of the sexes to intromission. Possibly because there has been no synthesis of early work, water mite behaviour has been overlooked in comparisons of mating systems. In this paper I compile previous studies of mating behaviour, present my own experiments testing the importance of female presence for spermatophore production in non-pairing species, and describe spermatophore morphology (where possible) of water mites in 15 families. Finally, I compare the diversity of water mite mating to that of other arachnids, discuss functional morphology of spermatophores, and describe patterns in behaviour and spermatophore structure that may help to elucidate phylogenetic relationships in this diverse group of .

METHODS Collection and maintenance of mites Water mites were collected from several sites in southern Ontario, Canada, from April to November 1989 and April to September 1990 (Table 1). Samples were taken by sweeping a dipnet (250 pm mesh) through aquatic vegetation or by holding it downstream while disturbing rocks and gravel. I maintained mites

TABLE1. Collection sites in Ontario. Authorities for species' names are in text Location and type of water body Latitude Longitude Species

Burlington, flooded quarry 43" 15' 79" 45' Hydrachna hespcria; Anmum birgei Valens Conservation Area, pond 43" 20' 80" 05' Limnesia marshallac Milton, permanent pond 43" 31' 79" 56' Hydrachna magniscutata; Limnochares americana; Hydrodroma despicicns; Limnesia fulgida; Neumania distincta; Unionicola sp. 4 Erindale Campus, Mississauga 43" 33' 79" 40' (a) permanent 43" 33' 79"40' Limnesia undulata; ; Piona sp. nr. debilis; Anenurw marshalli (b) temporary pond 43" 33' 79" 40' Thyas stolli; uemalis Credit River, river 43" 35' 79" 42' Lcbertia sp.; Atractidcs nodipalpis Warnock Lake, pond 43" 40' 79" 57' Limnesia undulata Caledon Hills, pond 43" 50' 79" 55' Hydrachna baculoscutata Indian Lake, pond 44" 40' 76" 20' Hydrachna sp. nr. lcegei Lake Opinicon, bay 44" 40' 76" 20' Limnesia undulata; Lcbcrtia annac; Unionicola sp. 3 Plastic Lake, lake 45" 11' 78" 50' Unionicola sp. 4 MATING AND SPERMATOPHORES OF WATER MITES 343 individually in 17-mm deep tissue-culture well plates (large: diameter = 35 mm; small: diameter = 11 mm) at 19-21°C, 12 h light: 12 h dark. Except for Thyas and Hydrachna, whose food was unavailable, I fed mites according to their preferences (Proctor & Pritchard, 1989). Representative specimens of new or unidentified species are deposited with Ian Smith at the Biosystematics Division of Agriculture Canada, Ottawa.

Spermatophore illustrations Spermatophores were removed gently from their sites of deposition with minuten pins and pipetted on to a depression slide. Specimens were photographed through a compound microscope. Technical pen drawings were made by projecting slide images on to a mirror angled at 45”C, and placing a glass plate covered with tracing paper above the mirror. Terms applied to spermatophore morphology are illustrated in Fig. 1 a.

Behavioural observations and descriptions Mating and spermatophore deposition were observed under a stereomicroscope or videotaped with a Panasonic CCTV chip camera (model WV-BL200) attached to a stereomicroscope and recorded to a Panasonic SVHS time lapse video cassette recorder (model AG-6720). Morphological terms used in descriptions of mite behaviour include (1) idiosoma: the fused ‘thorax’ and ‘abdomen’ of the mite, i.e. its body exclusive of mouthparts; (2) legs: are numbered from fore to hind with roman numerals (legs I to IV).

Experimental methods When possible, experiments were performed to determine the importance of female presence for spermatophore deposition in non-pairing species or to compare deposition rate of males held with con- and heterospecific females. Details are outlined in Table 2. For each experiment mites were initially maintained individually for several days; I then paired some males with females, maintained other males alone, and sometimes provided males with female chemical cues. Substrates for spermatophore deposition were taken from the species’ habitat (vegetation), except for Hydrodroma (chironomid egg masses) and Unionicola (scratched well bottom). Trial durations were based on preliminary observations of spermatophore deposition.

Statistical analyses Tests were performed with the STATISTIX I1 software package (NH Analytical Software). All measures of central tendency are mean k SE.

MODES OF SPERM TRANSFER With the exclusion of Hydrovolzioidea, water mites comprise a monophyletic group of six superfamilies in the prostigmatid cohort Parasitengona (Barr, 1972; Cook, 1974; but see Witte, 1991). Because water mites evolved from a non- W L TABLE2. Experimental procedures and results from tests of the importance of female presence for spermatophore production by males. Time alone = time mites maintained separately prior to the experiment; duration = duration of treatment; m = male; f = female

Number of males ZkSE Species Time alone (days) Substrate Treatments N Duration depositing Spermatophores/male - H$raCh 3 M~~ophyffumstem m alone 6 3 hours 4 - magniscuhh m+2mL f H20 6 4 - m+f 6 3 - Limnochres americana' I1 Oak leaf m alone 8 5 days' 0 - m+f 9 5 - Limnochres am'cana' 4-9 Oak leaf m alone 12 5 days 0 - m+f 11 5 - m+m I 0 - Limnochres americana' I1 Oak leaf m alone 17 5 days 0 - m+f 14 9 - m+m 9 6 - Limnochres amnicana' 10 Oak leaf m+f 2 5 days 1 - m+m 10 8 - - Hgdrodrmna' 4 chironornid egg mass m alone 9 32 hours 7 &SpiCitnS m+f 6 6 - m+m 8 7 - Limnesia undulah 3 1 x 1 cm reed' m alone 23 I hour 22 17.1k3.3 m+f 23 23 49.1 k8.6 Limnesia undulah 13 1 x 1 cm reed' m+f 5 1.5 hours 5 158f39.2 m in vacated well off 5 5 105.6 f 23.4 Thyas shlli' 4 IxIcmoakIed m alone 7 18 hours 0 - m+f 9 5 - m+m 3 0 - Unwnicola sp. 1 6 - m+sp.4 224 4 hours 22 55.2k 11.8 m+sp. I 22 12 8.8k3.1

'Treatmenu have unequal sample sizes because mites could not be sexed until after the experiments. 'WeUs checked for spermatophores every day. 30dy spermatophores on the substrate provided were counted. 'Each of the 22 males was paired with one type of female, rested for 6 days, then paired with the other type. MATING AND SPERMATOPHORES OF WATER MITES 345 TABLE3. Taxonomic distribution of sperm transfer modes in water mites. A question mark (?) indicates that expcriments are needed to discriminate between complete and incomplete dissociation for that taxon

~~ Sperm transfer mode

Complete Incomplete Paired, Taxon dissociation dissociation indirect Copulation

Hydrachnidae Hydrachna X Limnochares X Eylaidae Eylais X X Hydryphantidae Hydryphantes X Thyas X Hydrodromidae Hydrodroma Sperchontidae Sperchon Lebertiidae Lebertia X? Limnesia Hygrobatidae Hygrobales Atroctides X? Unionicola X X X X Neumania X X Feltriidae Feltria X Piona X Tiphys X X X Aturidae Brachypoda X Aluru X Kongsbngia X Mideidae Midea X Arrenuridae Ancnurus X

copulating terrestrial parasitengonid, ancestral water mites most likely transferred sperm indirectly by depositing spermatophores on a substrate (Proctor, 199 1 a; Witte, 199 1). Table 3 outlines modes of sperm transfer in taxa in which spermatophore deposition or mating has been observed. Below, the mating behaviour of these taxa is categorized based on proximity of partners during sperm transfer, a classification similar to those of Alexander (1964), Schaller (1971) and Thomas & Zeh (1984). For each taxon I describe whether physical or chemical cues from the females are needed to induce spermatophore deposition by males, how many spermatophores are produced, spermatophore deposition/transfer behaviour, and spermatophore morphology. 346 H. C. PROCTOR

Complete dissociation Complete dissociation occurs when a male deposits spermatophores without having physically contacted a female, and in the absence of chemical cues from females. Females pick up sperm without any direction from males. In this category only those taxa for which it has been demonstrated that female chemicals are unnecessary to trigger spermatophore deposition are included; unclear cases are discussed under incomplete dissociation.

Hydrachna (Hydrachnidae) Davids & Belier (1979) found that isolated male Hydrachna (Diplohydrachna) conjecta Koenike deposit spermatophores within three days of their emergence as adults; mean deposition rate over a 10 day period was 121 per day, and mean lifetime production was 2300 spermatophores (N= 5 males). It was found that Hydrachna (Hydrachna) magniscutata Marshall males require neither presence of females nor of female-conditioned water to deposit spermatophores (Table 2). Deposition rate in Hydrachna species seems to accelerate in the presence of other males (Davids & Belier, 1974, personal observation), in which case deposition is concentrated on a substrate that already has spermatophores. Spermatophore deposition was obtained in five species of Hydrachna: Hydrachna magniscutata, Hydrachna (Rhabdohydrachna) hesperia Lundblad, Hydrachna (Rhabdohydrachna) sp. nr. leegei Koenike, and Hydrachna (Rhabdohydrachna) baculoscutata Crowell. In all species, a depositing male straddles the substrate (often a plant stem), moves his genital plates over the substrate in a sinusoidal path while keeping his legs anchored or moving slightly forward, then rapidly extrudes a spermatophore. He then walks forward a few steps and repeats this process. One spermatophore is deposited every three seconds in H. conjecta (Davids & Belier, 1979) and one every 6.2k0.15 seconds in H. magniscutata (N = 4 males, 4 or 5 spermatophores/male). Individual deposition behaviour, together with the tendency for males to deposit on the same substrate, produces fields of spermatophores in neatly aligned rows. Davids & Belier (1979) observed female H. conjecta picking up sperm packets. A female walks over the spermatophore field touching the substrate with her everted ovipositor; when she finds a spermatophore, she squeezes the sperm capsule with her ovipositor to remove the sperm packet. Females remove packets from several spermatophores, and sometimes push them into their ovipositors with legs IV. Hydrachna spermatophores differ in size but share the same basic morphology (Fig. lb-e). The stalk is relatively short, and in some species has both dorsal and ventral strengthening ridges (e.g. Hydrachna baculosculata, and H. sp. near leegei), while others have only a partial dorsal ridge (e.g. H. hesperia). The stalk of H. magniscutata is unusual in being strongly curved and supported by a dorsal flange that runs to the substrate; the spermatophore morphology of Hydrachna (Hydrachna) cruenta Miiller is very similar (Witte, 1991). Note that both species belong to the same subgenus. Witte (1984, 1991) states that male Hydrachna lay down zigzag threads between spermatophores. Although I did not see these tracks, males of all species do describe a zigzag path with their genital areas before depositing spermatophores. Hydrachna sperm capsules are large, laterally compressed, and bent at 45" to 90" from the stalk. Except for Hydrachna MATING AND SPERMATOPHORES OF WATER MITES 347

sperm packet /-with sperm cells

sperm capsule

Wb a

f h Figure 1. (a) Diagram of a generalized water mite spermatophore showing major morphological features: the sperm packet consists of a membrane and the enclosed sperm cells; the sperm capsule is a chitinous structure that contains the sperm packet; the stalk is a (usually) cylindrical chitinous support for the capsule; and the foot is a continuation ofstalk material that adheres to a substrate. (b) Spermatophore of Hydrachna magniscutafa (total height = 0.16fO.002 mm, N= 6 from 1 male). (c) Spermatophore of Hydrachna hesperia (total height = 0.17f0.007 mm, N = 6 from 2 males). (d) Spermatophore of Hydrachna sp. nr. leegci (total height = 0.22f0.005 mm, N= 7 from I male). (e) Spermatophore of Hydrachna baculoscutata (total height = 0.25f0.008 mm, N= 6 from 2 males). (0Spermatophore of Limnocharcs amcricana with intact sperm packet (total height = 0.77f0.02 mm, N = 6 from unknown number of males). (9) L. amm'cana spermatophore with empty sperm capsule. (h) Variation in structure of L. americana spermatophore feet. Scale = 50 pm for Hydrachna, 100 pm for Limnochares. 348 H. C. PROCTOR magniscutata, sperm capsules from Ontario species have two horn-like extensions on the dorsal apical margins. Hydrachna cruenta spermatophores have inward- pointing spurs, apparently located in the same place as these horns (Witte, 1984). Sperm packets are large and conform to the subrectangular shape of the capsule. Witte (1984) states that capsules have two openings, one on the dorsal margin and one at the anterior; females grasp the sperm capsule with their ovipositors and remove sperm from the anterior opening as water flows into the capsule through the dorsal one.

Limnochares (Limnocharidae) Male Limnochares (Limnochares) aquatica (Linnaeus) deposit spermatophores when held alone, but the presence of other males appears to incite a higher rate of deposition (Pahnke, 1974). Limnochares (Cyclothrix) americana Lundblad males do not produce spermatophores if held alone; however, presence of either male or female conspecifics appears sufficient to induce deposition (Table 2). Over five days, at most ten spermatophores were deposited in the wells of paired male L. americana; usually only two or three were present. Spermatophores were deposited on leaves, sand cases of chironomids, or on the cuticle of chironomids that had been killed and consumed by the mites. Pahnke (1974) states that L. aquatica males require a cold shock followed by warm temperatures if they are to produce spermatophores. Pahnke (1974) observed spermatophore deposition in L. aquatica. A male pauses in his wanderings and bends legs I11 and IV to lower his genital aperture to the substrate. He rocks from side to side while simultaneously lifting his body, thereby drawing out the spermatophore stalk. This is accompanied by trembling and pumping movements of the male’s body. He pauses briefly, then lifts his posterior idiosoma further to reveal the sperm capsule. I observed neither spermatophore deposition nor sperm uptake behaviour in L. americana. Foot structures in spermatophores of Limnochares americana vary from zigzag, to straight, to splayed (Fig. 1h). produces zigzag feet according to Witte (1984, 1991), although Pahnke (1974) describes the foot as having no particular structure. Stalks of both species are robust and slightly tapering. The sperm capsule is an open cup similar to that of Hydrodroma (see below), and is joined to the stalk slightly off centre so that the side of the capsule opposite to the foot is tilted up (Fig. lg). A seam divides the capsule into halves; the margins of the seam are thickened and on the low side terminate in hooks. The sperm packet is large and is not completely enclosed by the capsule. Spermatophores of L. aquatica and americana differ primarily in size (the former being slightly smaller, 480-600 pm) and in the stalk being much longer in relation to the sperm capsule in the latter.

Hydrodroma (Hydrodromidae) Meyer (1985) found that solitary male Hydrodroma despiciens (Muller) deposit spermatophores 14-21 days after emergence. Males deposited up to 150 spermatophores/day and continued for a month, producing between 350 and 800 spermatophores. Males maintained in male/female pairs did not produce significantly more spermatophores, nor was the duration of deposition different from males kept alone. My studies of North American H. despiciens show that the MATING AND SPERMATOPHORES OF WATER MITES 349 presence of conspecifics, male or female, is unnecessary for spermatophore production (Table 2). Wiles (1982) found that male Hydrodroma despiciens deposit only on the jelly coat of chironomid egg masses. Conversely, Meyer (1985) found only two of many hundreds of spermatophore fields on egg masses; most occurred beneath leaves, or on the bottoms and sides of aquaria. My observations of H.despiciens are equivocal. Males kept alone did not deposit unless egg masses were available, in which case they almost invariably put spermatophores on the jelly coat; if several males were maintained together with an egg mass they deposited both on and off the jelly coat. Wiles (1982) interprets the use of egg masses as deposition substrates as a strategy to increase the probability of female/spermatophore encounter, since females are likely to be attracted to the chironomid eggs as a food source (Proctor & Pritchard, 1989). Similarly, Meyer (1985) argues that her H.despiciens males deposited under plant leaves because these serve as oviposition and resting sites for females. I observed H.despiciens depositing on a chironomid egg mass. The male first vibrates his venter against the substrate; this may anchor the spermatophore base to the jelly or allow tactile hairs on the genital plates to gather information about the deposition site (Barr, 1972). He then taps legs I and/or I1 alternately against the substrate as if marching in place, raises his hind end to draw out a spermatophore, and then moves forward a few steps to start another deposition. Deposition rate for one male was 1 spermatophore per 3.8s (N= 8 spermatophores), while another deposited 1 spermatophore per 4.9 s (N= 13 spermatophores). Meyer (1985) found that European H. despiciens produced 1 spermatophore per 6 s. As in Hydrachna, the presence of previously deposited spermatophores appears to induce further deposition by the same or other males. However, Hydrodroma males tend to deposit directly on top of other spermatophores rather than adjacent to them. When several males are held together this behaviour results in towering spermatophore ‘trees’ composed of hundreds of tangled stalks and capsules (Meyer, 1985; personal observation), Meyer ( 1985) states that males held individually tend to produce spermatophore fields rather than trees. Uptake of sperm packets by female Hydrodroma has not been observed. Hydrodroma spermatophores have a trailing foot of varying length (Fig. 2b). A tapering stalk, sometimes straight, sometimes sinuous, rises from the foot and terminates in an open hemisperical cup. At the base of the cup the stalk is expanded in lateral flanges. The cup is open at the top and one side; the open side has three projections, a lanceolate one from the base of the cup and a tab- shaped lateral projection from each side. These hold the sperm packet in place. Hydrodroma’s sperm packets are unique in consisting of two discoidal sections connected by a median constriction. In the cup the sections are tightly apposed, but liberated sperm packets expand (Fig. 2c). Stalks of European H. despiciens ranged from 439 to 901 pm (2 = 783) (Meyer, 1985), much taller than those of Ontario specimens (Fig. 2b); however, there was little difference in capsule size between these populations.

Sperchon (Sperchontidae) Sperchon setiger (Thor) and S. glandulosus (Koenike) males will deposit spermatophores without females present (Ullrich, 1976), although when they are 350 H. C. PROCTOR present male S. setiger show great interest in them (see below). Sperchon setiger deposits fields of from eight to 30 spermatophores whereas S. glundulosus produces groups of only three or four. Ullrich (1976) found that the period of spermatophore deposition lasted at least nine months in laboratory-held mites. Males of the two species differ in their deposition behaviour (Ullrich, 1976). When in the presence of a female, a Sperchon setiger male immediately clambers onto her back and remains clinging there for a few minutes to a few hours while the female walks about. The female does not appear to alter her behaviour during this period. After dismounting, the male crawls about in circular paths. In the course of circling he often pauses to rock his body back and forth, thereby brushing the tip of his everted ejaculatory complex against the substrate. The rocking grows weaker until the male eventually stands still and presses his body to the substrate, then pauses for one or two minutes. He then swings his body obliquely backwards, to the right or left, while keeping his legs anchored. This likely draws the spermatophore out of the genital aperture. The male then walks forward in a tight half-circle either to the left, if he had originally swung back to the right, and to the right if he had swung back to the left, and deposits another spermatophore. Subsequent depositions alternate between left- and right-hand turns, thereby keeping the male within a small area and resulting in the production of a dense field of spermatophores. Other males encountering such a field often deposit spermatophores on its periphery. Sperchon glundulosus males, in contrast to those of S. setiger, do not alter their behaviour in the presence of females. Rocking and pauses also occur in this species. The spermatophore is drawn out of the genital aperture not by an oblique backward swing, as in S. setiger, but rather by an upward jerk and a sideways swing. The male S. glundulosus then walks about in circles, with rocking movements, for a few minutes before depositing another spermatophore. Ullrich (1976) did not observe uptake of sperm packets in Sperchon. Spermatophores of these two species differ greatly in size, although male body size does not differ (Ullrich, 1976) (Fig. 2d, e). The stalk of S. glundulosus is c. 5 taller than that of S. setiger (715 pm vs 140 pm), but the sperm capsule is only twice as large. Thus the ratio of capsule to stalk is much greater in S. setiger (0.93) than in S. glundulosus (0.22). Stalks in both species are straight and taper only slightly towards the tip. The sperm capsule completely encloses the sperm packet, and according to Witte (1991) is not fused along its dorsal margin. A thin membrane or “velum” (Witte, 1991) runs from the ventral side of the capsule to the stalk.

Lebertiu (Lebertiidae) Ullrich ( 1976) found that Leberliu sulebrosu (Koenike) males deposit spermatophores in the absence of females. He observed one male depositing. The male swung his posterior idiosoma from side-to-side in arcs of decreasing magnitude, never completely coming to rest. After c. 30 s he stepped forward to reveal a spermatophore. Further spermatophores were deposited at intervals of 1/2 to several minutes, with the male walking straight ahead after each deposition. Lebertiu sulebrosu produces spermatophores with bipartite stalks, essentially identical to other Lebertia species (see Fig. 4c-d). The lower half is chambered and rises perpendicularly from the substrate, and the upper half is unchambered MATING AND SPERMATOPHORES OF WATER MITES 35 1

a d

C

h

e

Figure 2. (a) Hydrodroma despiciens spermatophore with intact sperm packet. (b) Spermatophore of H. despiciens with empty sperm capsule (total height = 0.32f0.006 mm, N= 6 from unknown number of males). (c) Liberated sperm packet of H, despicim. (d) Spermatophores of Spnchon setigcr and (e) S. glandulosus both redrawn from Ullrich, 1976). (9 Spermatophore of Limnesiufulgida (total height = 0.36f0.014mm, N=6 from unknown number of males). (9) Spermatophores of Limnesia undulata from Telephone Bay (total height = 0.2f0.01 mm, N= 3 from unknown number of males). (h) Spermatophore of Limnesiu undulata from Erindale Pond (total height = 0.27 f0.03, N = 6 from I male). (i) Spermatophore ofLimnesiu marshullac (total height = 0.28f0.01 mm, N = 3 from I male). 0) Dorsal view of empty sperm capsule of Limnesiu undulutu from Warnock Lake Pond, showing dorsal [d] and anterior [a] openings. (N.B. sperm capsule shape distorted by cover glass in (0,(g) and (h).) Scale = 50 pm for Hydrodroma and Limnesiu, 100 pm for Sperchon. 352 H. C. PROCTOR and is curved backwards. A thin membrane is located at the crook of the stalk where it changes from chambered to unchambered. The sperm capsule has a sharp point on its apex and two wing-shaped processes where it is attached to the stalk.

Limnesiu (Limnesiidae) Male Limnesiu undulatu (Muller) do not require the presence of a female to deposit spermatophores; however, they do produce significantly more spermatophores when held with females than when maintained alone (Wilcoxon's rank sum, two-tailed P = 0.0008) (Table 2). This appears to be due to female chemicals rather than any active role played by the female, since there was no difference in the number of spermatophores produced by males held with a female and those placed in wells that had recently held females (Wilcoxon's rank sum, two-tailed P = 0.2103). Witte (1991) mentions that temperature affects whether male Limnesia maculata (Muller) held individually deposit fewer or more spermatophores than males held with females. Over a 5 day period at 8°C single males deposited no spermatophores, while males held with females deposited about 350 on average; at 20°C single males deposited almost 1200 spermatophores whereas males with females deposited only about 740. These treatments are not directly comparable, however, since in the male + female treatment males were held together in groups of five. Males held in groups of five without females produced similar numbers of spermatophores as did grouped males with females; this suggests that the lower number produced by grouped than by single males may be due to some sort of interference between males. Casual observations only were made of spermatophore deposition behaviour in Limnesiu undulata. A male briefly rubs his venter against the substrate, then rapidly raises his body to the full extension of his fourth legs, thereby drawing out a spermatophore. Deposition was rapid; although the time it took for individual spermatophores to be produced was not monitored, one male L. undulatu produced 279 in 1.5 h, a rate of 1 spermatophore per 19 s. Witte (1984) states that fields of hundreds of spermatophores were produced when several Limnesiu males were kept together. Individual L. undulatu also produce large stands of spermatophores, and tend to deposit in only one or two areas on a substrate. I did not observe spermatophore uptake by Limnesiu females. Spermatophores produced by species in the subgenus Limnesia are fairly uniform in morphology and differ mainly in size (Fig. 2f-h). As in Hydrodroma, there is a foot of varying length. In L. fulgida Koch and L. undulata collected from two sites, spermatophores are bent once at an oblique or right angle about 2/3 up the stalk. Limnesia undulata from Erindale Pond produced spermatophores that bend at 90" then straighten. The round sperm packet is held in a pouch at the tip of the stalk. Like the sperm capsules of Hydrachna, those of this subgenus have a strengthened lower margin and two major openings, one dorsally and one anteriorly. Witte (1984) states that females squeeze the pouches with their genital flaps, removing the sperm packet through the anterior opening while water comes in through the dorsal one. The sperm capsules have a prong on each side that protrudes into the capsule, presumably keeping the sperm packet in place (Witte, 1984) (Fig. 2j). Spermatophores from a species in another subgenus, Limnesia (Limnesiella) marshallae (Viets) have a slightly different shape (Fig. 2i). The foot is thick and sinuous, and the stalk is relatively shorter than MATING AND SPERMATOPHORES OF WATER MITES 353 those from the subgenus Limnesia. It is obliquely bent about halfway up, and flares out as a laterally flattened keel that merges into the base of the spermatophore capsule. I was unable to get a dorsal view of the capsule, so I do not know whether it has the typical two openings; I was also unable to see any inward-pointing prongs. The sperm packet also differs from those of the subgenus Limnesia in having a serrated margin.

Hygrobates (Hygrobatidae) Male Hygrobates calliger Piersig and H. nigromaculatus Lebert will deposit spermatophores in the absence of females; Ullrich (1976) states that four or five H. calliger males maintained together can produce hundreds of spermatophores in a week. Up to 20 spermatophores are laid in a bout, deposited one behind the other to form a row rather than a field. Ullrich (1976) describes the deposition behaviour of H. calliger and H. nigromaculatus. In both species deposition of a single spermatophore takes c. 30 s. Hygrobates calliger moves its body repeatedly to the side and then up and down; it is during a particularly slow upwards movement that the spermatophore is drawn out. The male than gives a vigorous upwards jerk, steps forward a few mm, and begins moving his body again in the above described manner. In this way a single line of spermatophores is formed. Deposition behaviour is similar in H. nigromaculatus. In this species body movements form a distinct figure of 8 pattern that is repeated approximately twice a second. Ullrich (1976) observed males from the side and noticed that during these movement the ejaculatory apparatus was everted and its tip dragged over the substrate. After about 10 s the male presses his body to the substrate, then lifts slowly to reveal the spermatophore. As in H. calliger, the male then steps forward to deposit again, thereby forming a line of spermatophores. Ullrich ( 1976) describes spermatophores of H. calliger and H. nigromaculatus (Fig. 3a-b). The stalk ofH. calliger tapers slightly towards its apex, and is curved backwards in the upper one quarter of its length. The sperm capsule has two wing-like processes at its point of attachment to the stalk. The stalk of H. nigromaculatus is c. 2.5 x longer than that of H. calliger, although capsule sizes are the same. Other differences are the presence of tendrils on the lower part of the stalk and a sharper backwards inclination of the upper quarter in the spermatophore of H. nigromaculatus. The capsule possesses a sharp apical point as well as two wing-like processes at its juncture with the stalk.

Neumania (Unionicolidae) In Neumania ( Tetraneumania) distincta Marshall, males require neither females nor their chemical cues to induce spermatophore deposition. Two males were maintained alone after collection. After four days spermatophores appeared in the well of the first male, and after 21 days in those of both males. Spermatophores were deposited on bottoms and sides of the wells, and were often clumped onto tangled balls; it seems likely that N. distincta, like Hydrodroma, tends to place new spermatophores directly on previously deposited ones. Deposition behaviour was observed in one male. He moved his legs in a scrambling motion on the substrate as if searching for a foothold, then, with all his leg tips gathered beneath himself, he dropped his genital aperture to the substrate, lifted up almost to the full extension of his legs, and rapidly moved the 354 H.- C. PROCTOR

F

b

a e

C

f

Figure 3. (a) Spermatophores of Hygrobates calligcr and (b) H. nigromaculafus (both redrawn from Ullrich, 1976). (c) Diagrammatic representation of Ncumaniu distincta spermatophore (total height = 1.19k0.06 mm. JV = 5 from 1 male). (d) Terminal segments and sperm capsule from JV. disfincfa spermatophore. (e) Segment of N. distincfa spermatophore stalk.(f) Diagrammatic representation of the spermatophore clump of Unionicola sp. 3 (total height = 1.99&0.009 mm, JV= 6 clumps from 1 male). (9) Terminal segments and sperm capsules of Unionicola sp. 3 and (h) Unionicola sp. 1 spermatophores. Scale = 50 pm for (9)and (h), 100 pm for Hygrobates and Neumania, and 200 pm for (4. tips of legs IV near his genital area. He swam off leaving one spermatophore behind, and repeated these behaviours several times. Sperm uptake by females was not observed. The spermatophore of Neumania distincta is complex (Fig. 3c-e). The stalk is tall, slender and of a uniform thickness; there is no apparent foot. A web-like extension originates one-half to three-quarters of the way up each side of the stalk. It flares out at about 45" from its origin and attaches to the substrate MAI'ING AND SPERMATOPHORES OF WAI'ER MITES 355 approximately 100 pm from the base of the stalk. Regularly spaced strands run from the stalk to the main 'guy' strand, sometimes anastomosing with other strands. The stalk tip bends 20" to 90" and expands into a fusiform portion that is drawn out into a thin section terminating in a loosely attached sperm capsule made of two flaps. The sperm packet is relatively small, and rests between the capsule's flaps.

Unionicolu (Unionicolidae) Because the of mites in the Unionicolu crussipes (Muller) complex is not complete for North American species (personal communication, Ian Smith), I will refer to the species that fell into this sperm transfer category as Unionicolu spp. 1 and 3. These species are included under complete dissociation because males deposited spermatophores after having been isolated for several days; however, casual observations indicate that as in Limnesiu, female presence or chemical cues increase rate of deposition. I observed production of spermatophores by Unionicolu sp. 1 males held with females. After contacting a female, the male walks slowly, sometimes in a circular path, and occasionally trembles his forelegs. He eventually pauses and dips his genital aperture to the substrate, drawing it backwards to create the foot of a spermatophore (Fig. 7a). He raises his posterior idiosoma by straightening legs IV, in the process drawing out the spermatophore stalk; when he reaches the greatest extension of legs I11 he pauses but continues producing stalk material, resulting in the tip of the spermatophore being curved like the handle of a cane. The male then brings his hind end down abruptly, drawing out the terminal segment and sperm capsule, and begins depositing another spermatophore directly beside the first. The second spermatophore is produced so that it obliquely contacts the first about halfway up its stalk, resulting in an 'X' pattern. Usually three and sometimes up to six spermatophores were produced per group (mean of means for four males = 2.9f0.2), each subsequent stalk laying across the previous one but angled in the opposite direction (Fig. 7a). After finishing a spermatophore group, the male assumes a normal crawling position but with his front legs trembling and raised higher than normal; he pauses or crawls about slowly in front of the clump for a few seconds while trembling, then moves off to deposit another spermatophore group. Females often clutched males that were trembling; clutching is a typical predatory response to prey vibrations (Proctor & Pritchard, 1990). I observed one male attaching spermatophores to previously deposited clumps. He backed up to the clump, straddled it with his hind legs and rubbed his body up the stalks until it reached the sperm packets, whereupon he rubbed his genital area against them. He then dropped his genital opening to the midpoint of the group and attached a new spermatophore there. Several more spermatophores were deposited in the normal way (i.e. with feet on the substrate). I also observed one Unionicolu sp. 3 male depositing in the presence of a female. Like Unionicolu sp. 1 males, after contacting the female he began walking slowly; however, in a 20 minute observation period in which he deposited 20 spermatophores his forelegs trembled only once. This male also produced spermatophore clumps, but instead of laying spermatophore feet down in the direction of the long axis of his body, the male deposited feet at right angles to this axis (Fig. 39. The first stalk deposited is straight, the second is curved at its 356 H. C. PROCTOR point of attachment to the first, and third and fourth stalks have double curves (2 spermatophores/clump = 4_+0.63, N = 5 clumps). After removing the male, I observed the female’s attempts to pick up sperm packets. She swayed from side to side near a spermatophore clump while walking slowly forwards. She touched the clump while passing, then sidled backwards over it on the side opposite the sperm packets. She rubbed on the spermatophores for a few seconds, then groomed over her back and towards her genital aperture. The female performed these same behaviours on a different clump, but this time backed over it from the packet side. Except for arrangement of spermatophore groups, spermatophore structure of these and other free-living Unionicolu species is similar (see Hevers, 1978). The foot and stalk are long, slender and composed of many small chambers; in the foot and throughout most of the stalk these chambers are rectangular, but in the ‘cane-handle’ they are almost spherical (Fig. 3g, h). A thin tube running through the centre of the chambers is often apparent. The morphology of the apical chamber differs between Unionicolu sp. 1 and 3. In the former it is long and tapers smoothly to a point (Fig. 3h); in the latter it bows out from its attachment point to the stalk, then rapidly narrows to a drawn-out tendril (Fig. 3g). The sperm capsule in both species is small and composed of two flaps that form a partially open slipper-like structure. In Unionicolu sp. 1, fresh sperm packets were teardrop-shaped and tapered to a fine point that emerged from the open part of the capsule; this point was absent in older packets. I did not observe sperm packets in Unionicolu sp. 3 spermatophores.

Incomplete dissociulion Incomplete dissociation is characterized by males requiring contact with a female or female chemicals before depositing spermatophores, but showing no attempt to attract females to them before or after deposition. The presence of a female at the deposition site is not required for spermatophore production. In this category I include species in which males are described as depositing without females nearby but without the source paper controlling for the possibility that female chemical cues are needed to induce deposition.

Thps (Hydryphantidae) Male Thyus stolli Koenike do not deposit spermatophores in the absence of females (Fisher’s Exact two-tailed P = 0.034) (Table 2). All spermatophores in this experiment were found on submerged oak leaves; however, because they were so small (c. 150 pm), spermatophores deposited on well bottoms would have been invisible against the light background. Thyas stolli males did not produce dense fields of spermatophores; I found only two to five spermatophores on the oak leaves of each of the five males that deposited in the above experiment. I observed neither deposition behaviour nor uptake of spermatophores by ‘I: stolli; however, Mullen (1977) saw one female T. burbigera Viets approach spermatophores in the absence of a male. She took up sperm from several spermatophores, spending c. 10 s at each one. My observations in combination with those of Mullen (1977) indicate that female presence is required to elicit spermatophore production in Thyas,but that the male does not court the female to induce her to take up sperm packets. MATING AND SPERMATOPHORES OF WATER MITES 357 The spermatophore of Thyas stolli has a short foot from which a short curved stalk rises (Fig. 4a). A small bracket projects from the concave side of the stalk near its tip. The relatively large sperm capsule is loosely attached to the tip of the stalk, and in situ probably rests against the bracket. Like those of Hydrachna and Limnesia, the capsule of Thyas has a thickened ventral margin and a spine-like projection from each side into the capsule. Although I did not observe the spermatophores of 1. stolli from a dorsal aspect, Witte (1984) noted anterior and dorsal openings like those in Hydrachna and Limnesia capsules in spermatophores of T. barbigera. The sperm packet in T. stolli is ovoid. Mullen (1977) illustrated spermatophores from 1. barbigera that appear very different from those described by Witte (1984) and from those of 1. stolli. Mullen’s illustration shows an extremely long stalk without a bracket, and a relatively small, completely closed, ovoid capsule that adheres to the stalk along its long axis.

Hydryphantes (Hydry phantidae) Bottger (1966) states that male Hydryphantes ruber (Geer) deposit spermatophores in bouts after contact with a female. During a bout, the presence of a female nearby is not necessary for continued spermatophore production. Up to ten spermatophores are produced per bout. This contrasts with Mitchell’s (1958) assertion that males do not require contact with females to deposit spermatophores. Mitchell worked with a North American population of H. Tuber while Bottger observed mites from Europe; it is possible that there are geographical differences in the necessity of female presence in this species, or that the different populations are actually unrecognized species. I include H. ruber in the incomplete dissociation category because of the greater detail of Bottger’s observations. Bottger ( 1966) observed deposition behaviour of Hydryphantes ruber. After contacting a female, the male slows and eventually stops swimming. After 30 s to several min he begins to deposit spermatophores. Legs IV, normally trailed behind, are bent beneath the body, and the male lifts his posterior idiosoma briefly for each spermatophore. Uptake of sperm packets by females was not observed. The spermatophore of H. ruber consists of a tapering stalk that widens slightly at the base but does not form a foot (Fig. 4b). The sperm capsule is a deep cup that does not entirely contain the large, oval sperm packet. Witte (1991) illustrates the sperm capsule of H. ruber as a two-tined structure with two inward pointed spines that hold the large sperm packet in place. Mitchell (1958) did not provide a clear illustration of spermatophores from his population of H. ruber. His measurements indicate that they are c. one-tenth the size of Bottger’s; however, as Bottger suggests, it is likely that Mitchell simply missed a decimal place.

Lebertia (Lebertiidae) I observed spermatophore deposition by Lebertia annae Habeeb males held together with females and saw no pairing behaviour before or after deposition; however, I do not know whether female presence was necessary. Lebertia annae males deposited spermatophores on the underside of water plants. Males of a different, unidentified Libertia species deposited on a piece of waterlogged wood. Efford ( 1966) found spermatophores of Lebertia glabra Thor 358 H. C. PROCTOR on the substrate around conspecifics' egg clutches. When depositing, a male Lebertia annae shudders for about 5 s with his genital aperture held close to the substrate, pauses a few seconds, and then rapidly elevates the hind part of his body; this produces the chambered portion of the stalk (see below). After a pause, the unchambered stalk and sperm capsule are quickly drawn out, and the male goes on to deposit another spermatophore. Mean deposition time for one spermatophore is 8.6f0.13 s (N = 3 spermatophores from each of three males). Deposition by one male appears to elicit it in others. Sperm packet uptake by Lebertia females was not observed. Lebertia spermatophores have a bipartite stalk (Fig. 4c, d). The lower part of the stalk rises from at most a small foot and appears to be constructed of quadrate chambers. About halfivay up, the stalk bends at about 90" and becomes unchambered. There is a ventral seam along the underside of this section of the stalk. The open sperm capsule is attached to the end of the stalk, rather like the bowl of a spoon. A dorsal view indicates that flaps may partially cover the part of the capsule nearest the stalk. These flaps may correspond to the wing-shaped processes described by Ullrich (1976) for Lebertia salebrosa (see complete dissociation). The sperm packet is round and is almost entirely enclosed by the capsule. I saw no major structural differences between the spermatophores of Lebertia annae and the unidentified Lebertia other than size; however, Efford's ( 1966) sketch of L. glabru spermatophores shows no evidence of a chambered lower stalk.

Atractides (Hygrobatidae) Ullrich ( 1976) observed deposition behaviour in Atractides nodipalpis (Thor) from Europe and observed no courtship, but did not determine whether female chemical cues were required. I made similar observations of A. nodipalpis from Ontario. Ullrich (1976) found that when a male Atractides nodipalpis contacts a female he pauses and then wanders about in a agitated manner for 10-20 min. Eventually he stops and proceeds to construct a field of spermatophores. The field is small, at most 1 mm in diameter, because the male keeps his legs anchored to the same place on the substrate while depositing. Males never deposited on a flat substrate, but rather over a crevice or in the angle formed by the wall and bottom of the container. While depositing the male stretches the legs of one side fully, thus causing his body to lean to the opposite side, and the hind idiosoma is then moved backwards, repeatedly tapped on the substrate, and lifted upwards. This last movement prezumably draws out the spermatophore. Each deposition takes about lOs, and usually 10-15 (up to 50) spermatophores are deposited sequentially before the male leaves the field. I also found that A. nodiapalpis produces sharply demarcated fields of evenly spaced spermatophores, ranging from seven to 53 spermatophores per field (X = 20.33 f4.61, N = 8 fields). I watched one male deposit spermatophores. Upon contacting a previously deposited field of spermatophores, he stopped swimming and stood over the field with his legs gripping the substrate close to his sides. He then appeared to grind down these spermatophores with his venter by repeatedly rotating his body about 45" to the left and right. The male then deposited his own spermatophores with elaborate dipping motions of his posterior. I did not observe uptake of sperm packets by females. MATING AND SPERMATOPHORES OF WATER MITES 359

a

f Figure 4. (a) Spermatophore of Thyas stolli (total height = 0.17&0.02 mrn, JV= 6 from unknown number of males). (b) Spermatophore of Hydryphanfes ruber (redrawn from Bottger, 1966). (c) Spermatophores of Lebertia annac (total height = 0.63f0.04 rnm, N = 6 from unknown number of males). (d) Spermatophore of Lcbertia sp. (total height = 0.30&0.01,N = 6 from unknown number of males). (e)Spermatophore of Afractides nodipalpis (total height = 0.068f0.0005 rnm, N= 6 from I male). (9 Interlocking pattern formed by A. nodipalpis spermatophore feet. Scale = 25 pm for Atractides, 50 pm for Thyas, 100 pm for Hydryphanfes and Lcberfia.

Spermatophores of' Atractides nodipalpis from Ontario are unique in their tripedal structure (Fig. 4e). Dipping motions during deposition probably involve construction of this foot. The stalk is slender and tapering, and is approximately the same length as one of the foot segments. The sperm capsule is attached to the tip of the stalk slightly off centre, and dorsal views of empty capsules indicate that they are composed of two flaps that fuse at the end nearest the stalk, leaving the opposite end and the dorsal margin open. The sperm packet is oval. Spermatophore fields of A. nodipalpis have two interesting characteristics, Spermatophores are arranged regularly, so that when viewed from above 360 H. C. PROCTOR (Fig. 49 the tripartite feet form an almost interlocking pattern. As well, rather than simply placing spermatophores on available substrates, male A. nodipalpis males first construct a filmy sheet on which to deposit them. Grinding motions performed by the male prior to spermatophore deposition may involve construction of this sheet; however, I was unable to see it being laid down, and I do not know whether the sheet is made from exudations from the male’s genital opening or from nearby skin glands. Alternatively, grinding may be a form of external sperm competition (see Discussion), and the filmy sheet may be produced during spermatophore deposition. The spermatophore illustrated by Ullrich ( 1976) is similar in shape and size, although it shows bipedal rather than tripedal foot morphology. Ullrich also mentions the filmy substrate on which spermatophores are deposited.

Unionicola (Unionicolidae) Hevers (1978) states that males of many Unionicola species will not deposit spermatophores unless female cues are present. For Unionicola (Pentatax) aculeata (Koenike), Unionicola (Unionicola) crassipes (Muller) and Unionicola (Unionicola) minor (Soar), Hevers did not determine whether the male had to physically contact a female prior to deposition, or if water-borne chemical cues were sufficient. For Unionicola (Unionicola) parvipora Lundblad, he found that males produced spermatophores when placed in containers that previously held females; thus for this species, physical contact is not r uired. In none of these species does the male attempt to induce the female to take up spermatophores. My observations of a species from the U. crassipes complex, Unionicola sp. 4, also showed that males did not produce spermatophores unless held with females. There was no pairing behaviour, but I did not determine whether physical contact with females is required to induce deposition in this species. Hevers ( 1978) observed spermatophore deposition in the four European species mentioned above. When placed together with females, a Unionicola aculeata male cleans his venter with his legs, and moves in short, convulsive leaps or a staggering walk. He also engages in what Hevers terms “fidgety marching- in-place” in which he raises and lowers his legs without moving from the spot. Eventually the male presses his genital aperture to the substrate, lifts himself slightly, and fans his fourth legs so rapidly that they appear blurred. At this point, some males were observed to extrude spermatophores that were not attached to the substrate and that drifted about before coming to lie in a heap on the bottom; however, since other males did deposit well-anchored spermatophores that had feet, Hevers assumed the first type were laboratory artifacts resulting from inappropriate substrate. Unlike Unionicola species described under complete dissociation, U. aculeata did not produce morphologically discrete groupings of spermatophores. Females of this species were not observed to take up sperm packets. When placed with a female, a male Unionicola crassipes cleans his venter, walks slowly about on the substrate (often in a circular path), and makes short convulsive leaps without moving far from one spot. He begins deposition by pressing his genital aperture to the substrate and moving his posterior idiosoma backwards, thereby drawing out the foot. He then lifts himself off the substrate to the full extent of his longest legs (legs I1 and IV) while reaching beneath himself with his shorter legs I and I11 to touch the spermatophore stalk. At MATING AND SPERMATOPHORES OF WATER MITES 36 1 maximal extension he pauses but continues producing stalk material, thereby making a ‘cane-handle’ for the stalk. The sperm capsule is then extruded, and the male immediately dips down to deposit another spermatophore. Hevers says that subsequent spermatophores are bound together by manipulations of legs I and 111, but does not describe morphology of the spermatophore group. Number of spermatophores per group ranged from two to six. Sperm packet uptake by females was not observed. A male Unionicola minor walks in semi-circular paths soon after being placed with a female. He shakes tremulously, and walks in a staggering manner. Eventually he pauses, presses his first legs convulsively against his venter and produces a strand of stalk material that floats free in the water. He then drops his genital aperture to the substrate and produces a short length of adherent foot, then lifts up again to draw out the stalk. At the greatest extension of his legs he pauses, makes the ‘cane-handle’, and waits about three seconds before producing the sperm capsule. He drops down and produces a new spermatophore which is joined with the previous one, but not by leg manipulations as in U. crussipes. Hevers does not describe morphology of the spermatophore group. Three to six spermatophores are produced per group. After finishing a group, the male remains motionless for up to 3 min in front of it, then trembles violently and begins walking about in the manner described above before depositing another group. Hevers records one male depositing 25 spermatophores in 22 min, two groups consisting of 5 and the rest of 3 spermatophores each. He observed females visiting two of these groups while the male still sat in front of them; however, females did not touch males. A female intent on sperm uptake walks over a spermatophore group and rubs her venter against them. Hevers says in this way sperm packets are brought in contact with her genital region, where they stick and are later brushed into the genital aperture by vigorous grooming of the venter with legs I11 and IV. Unionicola puruipora males show spermatophore deposition behaviour almost identical to that of U. crassipes, except that before deposition they march in place like U. aculeata. During deposition males stretch to the utmost extension of legs I1 and IV, and reach back with legs I and I11 to bind spermatophores into a group composed of three spermatophores. Males do not stay in front of spermatophore groups like U. minor. Hevers found that U. parvipora males can deposit spermatophores for five months, producing more than 400 spermatophores before death. Uptake of sperm packets in this species is similar to that in U. minor. Again, sperm appears to be brushed into the genital aperture by grooming movements of the legs rather than taken in directly. A female may visit several spermatophore groups sequentially, and one group may be visited by several different females. Females do not differentiate between full and empty capsules. Hevers found that females maintained in the lab pick up sperm a few days after emergence as adults and repeatedly thereafter for 5 months. I observed spermatophore deposition behaviour in Unionicola sp. 4. When placed with females, a male begins walking slowly in circles. Some males violently vibrate their forelegs while walking although others deposit spermatophores without ever trembling. Trembling does not necessarily predict spermatophore deposition; one male trembled for 14 minutes but did not deposit. Like U. crassipes and U. parvipora, Unionicola sp. 4 reach back to touch the spermatophore stalks with legs I and I11 as they are produced, and 362 H. C. PROCTOR manipulate them into morphologically distinct groups. In these groups the first stalk deposited rises straight from the substrate (Fig. 5a), but each subsequent one has two 90" bends so that they cross over the central stalk and have their capsules on the side opposite to their stalks. Each new spermatophore is deposited on the side opposite to the previous one. In one hour a male deposited 35 spermatophores in three groups of 6, two of 5 and one of 7. Males often return to deposit new spermatophores on old groups, resulting in clumps of up to 14 spermatophores. I did not observe sperm uptake in this species. Hevers ( 1978) reports behavioural reproductive isolation between the morphologically similar species Unionicola crassipes and U. minor. He maintained males of one species with females of the other and observed no deposition in 20 minutes, but when he placed males with conspecific females deposition occurred in two to 12 minutes. I performed a similar experiment with Unionicola sp. 4 males presented with conspecific females and Unionicola sp. 1 females (Table 2). Unlike Hevers I found that males produced spermatophores in the presence of both con- and heterospecific females; however, they produced significantly fewer when paired with Unionicola sp. 1 than with Unionicola sp. 4 females (paired t-test, d.f. = 21, t = 7.12, P < 0.0001). Spermatophores of all five Unionicola species have feet and stalks composed of chambers and a spermatophore capsule made up of two flaps that partially enclose a sperm packet. However, U. aculeata lacks the elongate terminal stalk chamber shown by U. crassipes, U. minor, U.paruipora and Unionicola sp. 4 spermatophores (Fig. 5c). Except for U. minor, which has a terminal capsule like that of Unionicola sp. 1 (see Complete dissociation), the terminal capsules of spermatophores of these species are bowed out on one side (Fig. 5b). In spermatophores of Unionicola sp. 4 a thin strand of stalk material apparently runs through the centres of the chambers; this does not appear in Unionicola spermatophores illustrated by Hevers ( 1978).

Pairing with indirect transfer Pairing with indirect transfer occurs when a male deposits spermatophores on a substrate, remains in the vicinity, and guides a female towards them. Courtship or advertisement may occur before, during, or after deposition.

Eylais (Eylaidae) Lanciani (1972) observed mating behaviour in 15 species of Eylais that pair and transfer spermatophores indirectly. He divided them into three groups based on the type of contact between male and female during spermatophore uptake: (1) Leg-contact-1 1 species fall into this group: Eylais breuijiuca Lanciani, E. rectisulcus Lanciani, E. vernalis Lanciani, E. coptotomi Lanciani, E. harmani Lanciani, E. mitchelli Lanciani, E. peltodytis Lanciani, E. paruiporus Lanciani, E. conformis Lanciani, E. helophori Lanciani, and E. hydraenae Lanciani. After contacting a female, a male crawls in circular paths on the substrate until he contacts her again. The male immediately begins depositing spermatophores on the substrate while walking slowly in a circle; the female maintains contact with the male by touching the tips of her legs to his and walking in the same path. In this way, the female is guided over the freshly deposited spermatophores (up to 20 in a pairing) and picks up one or more sperm packets in her genital opening. MATING AND SPERMATOPHORES OF WATER MITES 363

.:. ., ,---IC

b d

e f Figure 5. (a) Diagrammatic representation of the spermatophore clump of Unionicolu sp. 4 (total height = 2.75f0.5 mm, N= 6 clumps from I male). (b) Terminal segments and sperm capsule of Unionicolu sp. 4 spermatophore. (c) Terminal segments and sperm capsule of Unionicola uculeala spermatophore (redrawn from Hevers, 1978). (d) Spermatophore of Eyluis exlendens (redrawn from Witte, 1991). (e) Diagrammatic representation of the spermatophores of Ncumania pupillutor. (9 Sperm packet and upper half of stalk of N. pupiflalor spermatophore (length of packet = 0.065~0.0058mm, N = 4 packets from unknown number ofmales). Scale = 50 pm for (b) and (c), 100 pn for Neumuniu, 500 pm for (a).

The process lasts less than two minutes, after which the partners separate. Occasionally, pairs swim while maintaining contact with leg tips on both sides of their bodies, thereby spinning about in mid-water. While spinning, the male deposits spermatophores on algal strands caught up between their venters, or simply in the intervening space (venters are not directly apposed). They then crawl about on the algal or spermatophore mass while still touching leg tips and the females pick up sperm. (2) Ventral mount prior to deposition-Eylais falcala Koenike falls in this group. Upon contacting a swimming female, the male immediately wraps his fourth legs around her and rides on her dorsum, both mites facing the same 364 H. C. PROCTOR direction. The mites separate and rejoin repeatedly until the male clasps the female venter to venter, facing the same direction but without genital apertures apposed. The male often touches the female’s genital aperture with his palps during the seven to 15 minute period he remains clasping her venter. After the female lands on the substrate, the male dismounts and crawls a short distance away, where he deposits ten to 20 spermatophores while moving in circular paths; the female maintains contact by touching her leg tips to his on one side and follows the male, picking up sperm packets. (3) Dorsal mount prior to and after deposition-Eyluis ovuliporus Lanciani, E. major Lanciani and E. glundulosu Lanciani fall in this group. As in the second group, upon contacting a female, the male immediately wraps his fourth legs around the hind part of her body. The female swims about for up to 10 min while the male maintains a dorsal hold. When the female pauses on the substrate, the male dismounts and deposits one to three spermatophores directly in front of her. He quickly returns to his position on her back and she then crawls over the spermatophores several times. The female then swims away with the mounted male, and the whole process is repeated two or three times. Mites may remain paired for up to 30 min. Lanciani ( 1972) did not illustrate Eyulais spermatophores; however, he states that spermatophores consist of a stalk, a short foot, and a dorsoventrally flattened head that contains sperm. Most spermatophores have several hairlike extensions from the middle of the stalk. Among the species Lanciani studied, spermatophore stalks ranged from 0.2 to 2.0 mm in length and 0.03 to 0.10 mm wide; heads were 0.08-0.26 mm long and 0.05-0.18 mm wide. Witte’s (1991) illustration of the spermatophore of Eyluis extendens (Muller) (Fig. 5d) conforms to Lanciani’s descriptions. It shows a sinuous foot held to the substrate with wide flat bands of foot material. The stalk is tapering and possesses long filaments that project at right angles from it. Rather than a sperm capsule there is a flat platform on which the oval sperm packet rests.

Neumunia (Unionicolidae) Neumuniu (Neumunia) PuPillutor Marshall are ambush predators of , and during courtship the female is almost always in the hunting posture or ‘net- stance’ in which she rests on a substrate and lifts legs I and I1 into the water column (Proctor, 1991b). Upon contacting a female or the recent resting place of one, the male stops swimming or slows his walking, and begins crawling in a circular path. If he contacts the female again, he vibrates one or both of legs I and/or I1 in c. 1 s bursts. A male can be in front, beside, behind or on top of a female while trembling. As in Unionicolu sp. 1 (see Complete dissociation), the female frequently clutches at the trembling male. After trembling and before depositing spermatophores, the male turns to face away from the female and raises and lowers legs I and I1 as if marching in place. The male then begins spermatophore deposition. He extrudes a spermatophore while lifting up his posterior idiosoma, then quickly lowers his genital aperture to the substrate beside it and produces another one. He leans forward and deposits another two spermatophores in front of the first pair. This is continued until two parallel rows of spermatophores are produced. Deposition time is c. 30s per group (28.67f0.95, N= 12), and the number of spermatophores per group ranges from seven to 18 (2 = 12.24k0.26, N= 67). The male then lifts legs IV MATING AND SPERMATOPHORES OF WATER MITES 365 vertically above his back, makes two sharp upward jerks of his posterior idiosoma, and begins vigorously fanning his fourth legs over the spermatophores. During fanning, paths of particles in the water show that a current is generated over the spermatophores and towards the female. After fanning the male rests briefly and may begin courting again, but usually takes up the net-stance. Virgin females almost invariably picked up sperm packets when males deposited in front of them, but I observed uptake of sperm packets by an egg- bearing female Neumania papillator on only one occasion. When the male begins fanning, the female drops from the net-stance and crawls toward the source of the water current, hence over the spermatophores. She then rubs over the spermatophores. Sperm packets are sticky and adhere to her venter; after dismounting from the spermatophores she grooms by stroking legs I11 and IV over her dorsum and toward her genital aperture like female Unionicola minor (see Incomplete dissociation). I often observed more than one male simultaneously courting a single female. If one male deposited spermatophores and began fanning while another was in the path of the fanned water, the second male became highly agitated and swam or crawled towards the fanning male. The second male then trampled and rubbed on the spermatophores, and on some occasions stood behind the fanning male with legs I and I1 upraised as if blocking the current. Like most Unionicola species (see Complete and Incomplete dissociation), fleumania papillator males produce morphologically distinct spermatophore groupings (Fig. 5e, 9. Each group is composed of slender rib-like spermatophore stalks that angle toward each other in pairs, thus forming two parallel rows of stalks. Each stalk is attached to its neighbours on the same and opposite sides by reticulated webbing made of stalk material. A large, sausage-shaped sperm packet rests loosely on top of each stalk, with its long axis parallel to the rows of s t a1 ks.

Unionicola (Unionicolidae) Hevers ( 1978) describes the mating behaviour of Unionicola (Penlatax) lricuspis (Koenike). Males deposit spermatophores only in the presence of females. A male initially crawls in circular paths with his leg tips constantly trembling. After 5-10 min of this trembling walk he begins spermatophore deposition without necessarily being close to a female. The male presses his genital opening close to the substrate to produce the spermatophore foot, then lifts his posterior idiosoma while poised on legs I and 11. Legs I11 and IV are flailed towards the venter, thereby pushing the spermatophore stalk into a curved shape and pulling out the sperm capsule. The male immediately sinks down and deposits a second spermatophore next to the first. After finishing the second spermatophore the male runs around to the ‘front’ of the spermatophores so that he ends up with the sperm capsules curving over his back. He sits in front of them with legs I1 and I11 and his genital aperture touching the substrate, legs IV held high above his body clasping the spermatophore stalks, and legs I trembling violently. Males remain in this posture for 30 s to 3 min, then leave to possibly deposit new spermatophores. Pairing in U. tricuspis occurs while the male trembles his forelegs. A female attracted by these vibrations climbs over the male, her venter close to his back. In this way she contacts the sperm capsules and rubs her genital area against them. 366 H. C. PROCTOR The spermatophore of U. tricuspis differs from those of previously mentioned Unionicola species (see Complete and Incomplete dissociation) in that each stalk consists of two parallel chambered rows (Fig. 6a). Hevers (1978) describes the stalk as ending in an irregular cord-shaped strand and a likewise irregular open capsule in which the sperm packet lies freely; unfortunately his photograph does not clearly show capsule morphology. The stalk has a short foot and a curved tip like other Unionicola spermatophores.

Pairing with direct transfer (Copulation) Pairing with direct transfer (or Copulation) is characterized by the male actively placing sperm in a female’s sperm-receiving structure (Hinton, 1964). In water mites, copulation can be inferred using morphological modifications of the male even when mating behaviour has not been observed in that taxon (Proctor, 199 la); however, the following section deals only with taxa in which copulation has been witnessed.

Eylais (Eylaidae) Males of Eylais species in the subgenus Syneylais have modified funnel-like genital plates that are used as intromittent organs. Bottger (1962) observed the mating behaviour of Eylais (Syneylais) infundibulifera Koenike. When a receptive female is touched by a male she immediately becomes immobile with her legs stretched out rigidly. Unreceptive females do not become rigid. The male crawls beneath the female and clasps her with legs IV so that they are facing the same direction with their genital apertures apposed. This often takes place in the water column; joined pairs sink to the substrate. Bottger was unable to see sperm transfer because the mites’ venters were so closely apposed; however, by separating males and females at various times after they had paired, he found that sperm transfer takes place within the first five minutes. The ejaculate is composed of sperm cells surrounded by, and scattered irregularly within, a viscous envelope. After ejaculation, the couple stays together for up to 2 hours during which the female’s sides pump rhythmically. Separation is accomplished by the male simply letting go with his fourth legs. Both sexes are almost immediately capable of further copulations.. Lanciani’s (1972) description of the mating behaviour of Eylais discreta Koenike and Eylais belostomatis Lanciani is similar to that for E. infundibulifera, except that in E. belostomatis the couple remains paired for only 2-5 min.

Unionicola (Unionicolidae) The only Unionicola species in which copulation has been observed, Unionicola (Pentatax) intermedia (Koenike) , differs from congeners previously mentioned in that it is lives in mussels where it presumably feeds on host mucus and haemolymph (Baker, 1977). Hevers (1978) found that young male U. intermedia held alone or with other males produce spermatophores, but fewer than when the sexes are together. When a male is placed together with females he grooms the area around his genital opening. Then, even if there has been no physical contact between the sexes, the male begins spermatophore deposition. He reaches back with legs IV (which have modified 4th and 5th segments) to grasp and pull out the emerging MATING AND SPERMATOPHORES OF WATER MITES 367 spermatophore. Once drawn out, the spermatophore stalk is clasped in a groove made by the apposed bristles of the 5th segments. The male wanders about without letting his fourth legs touch the substrate. If he meets another mite, male or female, he turns around and tries to force himself backwards between that mite’s venter and the gill substrate. A male or unreceptive female holds fast to the substrate with its palps and does not raise its idiosoma, or else it moves away. A receptive female leans forward so that the male can creep backwards beneath her. He lifts legs I\’ to press the spermatophore capsule against the female’s venter near her genital aperture so that she can take up sperm. Males produce up to 12 spermatophores in 30 min, but Hevers does not say how many of these depositions are followed by mating attempts. The morphology of U. intermedia spermatophores differs greatly from that of other Unionicola species (Fig. 6b). The stalk is relatively short and is unchambered. It ends in two lateral hornlike projections that point downwards, and a median one to which the sperm capsule is loosely attached. The capsule, unlike most other Unionicola except U. tricuspis, is made of an open shell that does not enclose the sperm packet, which instead lies loosely within.

Feltria (Feltriidae) Uchida ( 1932) briefly describes the pairing posture of Feltria georgei Piersig. The male seizes the anterior margin of the female’s dorsal shield with his palps, and is carried about by the female with his venter apposed to her dorsum. Male Feltria of the subgenus Feltria have modified distal segments of their third legs; possibly these are used for sperm transfer.

Piona (Pionidae) Previous work on Piona deals with species in which the male genital aperture is modified to form a deep, chitinous pocket. Here I also report observations of mating behaviour in a species in which males have the ancestral ‘pocketless’ type of genital aperture. In ‘pocketed’ Piona species males produce spermatophores prior to pairing with females, and swim about with legs I11 curved beneath them so that their modified claws hold the spermatophores inside the pocket (Mitchell, 1957; Bottger, 1962). Piona constricta (Wolcott) and Piona clavicornis (Miiller) require physical contact with a female prior to producing spermatophores (Mitchell, 1957); however, Bottger (1962) states that male Piona nodata (Miiller) swim about with leg I11 tips in their pockets without ever having contacted females. Both authors agree that a male must be holding a spermatophore prior to pairing with a female if he is to successfully transfer sperm. Bottger (1962) states that male Piona nodata recognize females after contacting them while swimming; such males immediately begin to swim in a looping fashion until contact is re-established. The male grasps one of the female’s hind legs in his palps, upon which a receptive female immediately becomes immobile with her legs stretched out rigidly. Unreceptive females struggle vigorously and eventually escape. Once the female goes rigid the pair sinks to the substrate. The male clambers hind-end first along the female’s venter until he ends up with his venter pressed against her head between her eyes (her ‘forehead’). He clasps the bases of the female’s first legs in the notched 4th segments of his legs IV. He extends legs I11 to bring the spermatophore cluster in contact with the female’s 368 H. C. PROCTOR

I

C

a b

d Figure 6. (a) Spermatophore of Unionicola tricurjis (after photograph in Hevers, 1978). (b) Spermatophore of Unionicola inlcrmedia (redrawn from Hevers, 1978). (c) Semi-diagrammatic representation of Piona nodata spermatophore cluster (two sperm packets and the gelatinous hull omitted for clarity) (redrawn from Bottger, 1962). (d) Spermatophore stalk of Arrenurur birgei; the dotted line indicates size and location of the sperm droplet. Scale = 50 pm for Piona and Arrmurus, 100 pm for (b) 200 vrn for (a). genital aperture; if he is misaligned he may miss the correct spot. He rubs the spermatophores against her genital aperture for about 30 min, during which sperm is presumably taken up by the female. Mites remain paired for up to 2 hours. Separation occurs after the male brushes the remnants of the spermatophores from legs I11 and straightens legs IV, thus releasing the female who comes out of her rigidity and swims away. Bottger says it takes a few hours to a few days for a male to produce a new ejaculate. Mitchell (1952) describes essentially the same behaviour for P. constricta and P. clavicornis, except in these species the male clasps the base of leg I1 or I11 of the female with his modified fourth legs, and pairing lasts 5 min on average. ‘Pocketless’ males of a Piona species near debilis (Wolcott) do not swim about holding spermatophores prior to pairing with females. After a male grasps a female that enters the state of rigidity, the mites fall to the substrate and lie venter-to-venter facing in opposite directions, with the male’s palps approximately level with the female’s first coxae. In this position he attempts to gather all of the female’s outstreched legs over her head, where he holds them briefly clasped together (Fig. 7b). Unless he succeeds in doing this, the female grows restless and attempts to escape. He holds her legs this way for a short while, then lets them return to their original outstretched position, The male reaches into his genital opening with his leg I11 claws and, for up to 3 min, works them back and forth until he pulls out a large spermatophore cluster (Fig. 7c). The male usually still has his venter apposed to the female’s while reaching for the spermatophores. After the spermatophores are out of his genital aperture, the MATING AND SPERMATOPHORES OF WATER MITES 369 male either moves slightly backwards (in the most common case) or clambers about on the female (if he had moved away previously) so that he rests his venter against her forehead, and the 4th segments of legs IV clasp the bases of her first legs as in P. nodata. In two matings, males rubbed their spermatophores against the females’ genital apertures for 10 and 15 min respectively. Separation often occurred after the female began swimming. For three pairings, mites were observed to stay together for 15, 20 and more than 60 min. Bottger (1962) describes the intricate morphology of Piona nodata’s spermatophore cluster. Externally it is an irregular gelatinous lump; internally there are six sperm packets arranged alternately on either side of a comblike row of six hard teeth that share a common base (Fig. 6c); this is actually a group of fused spermatophore stalks (Witte, 1991). The base of the comb has two openings at one end into which the male inserts his specialized leg I11 claws. Sperm packets are teardrop-shaped and have long stringlike stalks that are tangled together above the teeth of the comb. Bottger says that the teeth serve to rip open the gelatinous coating of the cluster when the male rubs it against the female’s genital aperture. In spermatophore clusters of P. sp. nr. debilis I have seen teardrop-shaped sperm packets, but not combs.

Tiphys (Pionidae) Viets ( 1914) and Mitchell (1957) observed mating behaviour in Tiphys species of the subgenus Tiphys. Like some Pionu, males of Tiphys ornatus (Koch), T$hys brevzpes Habeeb and Tiphys marshallae Cook carry spermatophore clusters between the tips of legs I11 prior to pairing with a female; both Viets and Mitchell state that previous contact with a female or water with female chemical cues is necessary to induce spermatophore production. T. ornatus males hold their third leg tips inside their genital opening at this stage, and tend to walk more than swim (Viets, 1914). Mitchell ( 1957) illustrates his species in a similar spermatophore-carrying position. After encountering a female, males walk slowly about on the substrate and periodically make short, convulsive springs. According to Mitchell ( 1957), these springs induce a female to pounce on a male; Viets (1914) says only that “mutual grappling” occurs soon after encounter. Once encircled by the female’s legs the male manoeuvres so that he hangs upside down beneath her, facing the opposite direction. His modified fourth legs are bent beneath him so that the curved 5th segments are pressed to the female’s venter near her third or fourth coxae. The 4th segments of legs IV are modified as flattened plates, and reach behind the male near the female’s mouthparts. Mitchell was uncertain how legs IV help the male maintain his grip on the female and postulates the existence of an adhesive secreted by the female. Viets, however, claims that the fourth legs serve only to prop the male against the female, and perhaps prevent him from slipping. He states that males pull themselves towards the female’s venter by grasping the bases of her fourth legs or an area near her genital plates with the claws of legs 11. While hanging beneath the female, the male makes jerking movements with legs I. Sperm transfer occurs when the male repeatedly thrusts his third legs, holding the spermatophore cluster, against the female’s genital opening (Viets, 1914). Eventually the sperm packets are ruptured by the tines of the comb (see below), and the female presumably takes up sperm. I observed three pairings in a Tiphys species of a different subgenus, Tifih~s 370 H. C. PROCTOR (Acercopsis) vernalis (Habeeb). Unlike Viets (1914) and Mitchell (1957), I did not observe males putting their leg I11 tips in their genital apertures until after they had taken up positions beneath females. A male T. vernalis appears to clasp the posterior part of the female’s capitulum with the flattened 4th segments of legs IV as well as holding onto the posterior margin of the female with his leg I1 claws. As Viets observed for T. ornatus, the T. vernalis male makes jerking movements with his forelegs while hanging beneath the female; however, in my observations males grasp the substrate prior to performing these movements and thus, rather than legs I alone moving, the bodies of both male and female are shaken. The sudden jerks seem to calm the female; on many occasions I saw the male jerk in apparent response to restive motions by the female, who immediately spread her legs out stiffly (a posture similar to Piona females) after the jerk was performed. Mites were pressed closely together and I was unable to observe sperm transfer, although I did see males repeatedly move the tips of legs I11 from their genital apertures to the female’s where they vibrated rapidly. The amount of time males spent holding a female was 38, 28 and 27 min for the three pairs. Viets (1914) describes the spermatophore cluster of Tiphys ornatus. It is similar to that of Piona in that it consists of a gelatinous mass enclosing a number of tines (c. 8) that are closely apposed at the bottom, and an equal number of saclike sperm packets. Unlike those of Piona, T+/ys’ spermatophore clumps have no basal openings for the male’s leg I11 claws. As well, the stalk of each sperm packet appears to attach directly to the tip of a tine rather than intertwining above the tips as they do in Piona. When the male thrusts the spermatophore cluster against the female’s genital aperture, the loosely attached sperm packets are punctured by the sharp tines.

Pionopsis (Pionidae) A male Pionopsis lutescens (Hermann) holds his third leg tips in his genital aperture when in the presence of females (Viets, 1914). The position taken by the male on the female is similar to that of Piona; the male rests his venter against the forehead of the female, facing downwards, and holds on by wrapping his fourth legs around the basal segments of her first legs. The modifications of the 4th and 5th segments of leg IV are less extreme than in Piona, often being merely a profusion of setae. Sperm transfer occurs, as is typical in the , by the male tapping the spermatophore packet he holds in his third legs against the female’s genital aperture. One copulation lasted 1 3/4 hours. Viets (1914) does not describe morphology of the spermatophores.

Forelia (Pionidae) Uchida (1940) states that when a male Forelia variegator (Koch) meets a female he immediately grasps her with his palps. At first the female tries to escape, but she soon enters a state of immobility with her legs outstretched. This occurs after the male has moved into a venter-to-venter position, facing the opposite direction to the female, and has attached himself to her with his modified fourth legs. These legs are bent so that the proximal parts of the 4th segments extend above the male’s dorsum, and their distal ends contact the female’s venter. The curved 5th segments lie with their concave sides fitting snugly over the female’s 3rd coxae. The male maintains his grip by extending his palps and legs I forward MATING AND SPERMATOPHORES OF WATER MITES 37 1

b C

a

L

Q h Figure 7. Spermatophore deposition and transfer by water mites. (a) Spermatophore deposition by Unionicola sp. 1. See text for details. (b) Male Piona sp. nr. debilis gathering female’s legs above her head (c) Ventral view of male pulling spermatophore cluster from his genital aperture with his leg 111 claws (all legs except male legs I11 and IV omitted for clarity). (d) Brachypoda ucrsicolor in the ‘handstand’ position; the female balances on the male’s palps while the male holds her in his legs IV and a spermatophore in his leg I11 claws (redrawn from Halik, 1955). (e) Copulatory position of Afurus scaber; the male clasps the female with legs IV (redrawn from Lundblad, 1929a). (0 Copulatory position of Midea orbiculafa; the male is below (redrawn from Lundblad, 1929a). (g) Copulatory position of Arrenurus cuspidifcr; the male is about to strip sperm from the spermatophore with his petiole, which the female touches with her legs IV (b) the female is pushed back so that the petiole with its load of sperm is forced into her genital aperture (redrawn from Cassagne-Mkjean, 1966). 372 H. C. PROCTOR and hooking onto the hind margin of the female’s body with his leg I1 claws. Legs I11 act as gonopods, and their tips move repeatedly from male to female genital openings carrying sperm in the modified claws. Pairing lasts almost an hour. Uchida does not describe spermatophore morphology.

Bruchypodu (Aturidae) Halik ( 1955) describes mating behaviour in Bruchypodu versicolor (Miiller). The presence of a female in the container causes the male to stop swimming and take up a ‘readiness position’ on the substrate. In this position the male reaches into his genital aperture with the tips of legs I11 and orients to vibrations in the water by directing his hind end and legs IV towards the source of vibration (which may be any aquatic organism, not just a conspecific female). After contacting a female he grasps her with his modified fourth legs, and removes legs I11 and the spermatophore from his genital aperture. The posterior of the male’s body is modified as an overhanging shelf so that when he draws the female towards himself, her forehead is wedged beneath this shelf. With the female secured, the male walks about on legs I and I1 until he reaches a suitable place to continue mating. The male then props himself on legs I and I1 in a sort of handstand and moves the female’s body up and down with his fourth legs. During this the female balances herself by resting the tips of legs IV against the fourth segments of the male’s palps (Fig. 7d). After about five pumping movements lasting a total of 2 s, the male rapidly thrusts the female’s forehead back beneath the overhanging shelf. Pumping and thrusting behaviours alternate for up to 2 hours. When the female is ready to be inseminated she clasps the shelflike extension of the male with legs I and 11, and the male taps the spermatophore held in his third legs against her genital opening for several min. Pairing ends when the male makes a violent lateral convulsion, the pair separates, and the female swims away. The male drops the remnants of the spermatophere, grooms, and rests in the sediment. Copulation of the same pair can occur repeatedly. Halik does not describe the spermatophere of B. versicolor.

Alurus (Aturidae) The mating position of Aturus scaber Kramer is described by Lundblad (1929). After contacting a receptive female, the male pushes himself backwards beneath her so that she rides up on his back. The female’s venter fits into a trough on the male’s dorsum, and the long modified fourth legs of the male reach over her back to clasp her. The large leg IV claws fasten onto the hind end of the female’s body (Fig. 7e). Although Lundblad did not observe sperm transfer in A. scuber, on the basis of male morphology the following scenario is probable. Because of the female-above position and the cleft in the male’s body behind his genital aperture, it seems likely that transfer is achieved by the male lowering the female onto substrate-deposited spermatophores that are guided to the female’s genital aperture by the cleft.

Kongsbergiu (Aturidae) Thor (1901) made brief observations of mating behaviour in Kongsbergiu runcznutu (Thor). The male grasps the middle of the female’s body with legs I and I1 while his enlarged palps hold onto the projecting front margin of the female’s head. Thor does not say whether the posture taken up is venter-to-venter or MArING AND SPERMATOPHORES OF WATER MITES 373 male-above-female, though the latter seems likely. Legs I11 of the male move over the female’s genital acaetabula, while legs IV move repeatedly from the male to the female genital aperture. He did not observe sperm transfer, but hypothesized that legs IV serve this function. Lundblad (1929) disagreed, stating that the structure of K. runcinata’s fourth legs indicate that they are more likely grasping structures, and that the third leg (although unmodified for such a purpose) is more likely to aid in sperm transfer.

Midea (Mideidae) Lundblad ( 1929) describes the mating behaviour of Midea orbiculata (Muller). Pairing mites assume a venter-to-venter position facing the same direction, the male clasping the female with legs I and 11. Legs I11 hook over the basal segment of the female’s legs IV with their enlarged claws (Fig. 70. The male maintains a constant hold to the bottom of the female’s capitular bay with his palp tips, while legs I1 stroke between the pair’s genital apertures. Male Midea have triangular genital flaps that are erectable; the male rubs the tips of the flaps back and forth against the genital opening of the female. Rubbing continues for about 2 hours, during which sperm and accessory gland secretions accumulate in the space between the pair’s genital apertures. Lundblad thought the secretions may help to hold the male and female together. After remaining motionless for another 2 hours, the male releases his leg hold on the female. Lundblad was uncertain whether the genital flaps of the male serve to funnel sperm into the female, to wedge open her genital aperture, or simply to stimulate her.

Arrenurus (Arrenuridae) Males in the seven subgenera of Arrenurus exhibit sexual dimorphisms running from a slight elongation of the posterior body to elaborate pygal lobes, a posterior median projection (the petiole) and modified hind legs (Cook, 1974). The hindbody modifications are collectively termed ‘cauda’. Mating behaviour has been described for four subgenera. Males in the subgenus Arrenurus have elaborate cauda typically consisting of pygal lobes, a well-developed petiole between the lobes, modified fourth legs and often medial and/or medio-lateral protrusions of the dorsum. Munchberg ( 1952) and Bottger (1965), respectively, state that male Arrenurus planus Marshall and Arrenurus valdiviensis Viets actively grasp females which, if willing, enter a state of rigidity similar to that of Piona females. I saw similar activity in Arrenurus dentipetiolatus Marshall. However, Cassagne-Mkjean ( 1966) describes female Arrenurus cuspidifer Piersig as taking the active role; males present their cauda to females which in turn grasp the males. In A. valdiviensis and A. dentipetiolatus, the male manipulates the immobile female until she is pushed up onto his back with her venter resting on his dorsal protrusions. Although his observations were fragmentary, Munchberg (1952) states that the male A. planus crawls over the female’s venter and inserts his unusual ventrally directed petiole into her genital aperture. Arrenurus cuspidifer females apparently position themselves by grasping the male’s body with the first three pairs of legs and reaching behind with legs IV to touch the petiole. Males of all species produce a colourless secretion from dorsal glands that glues the partners together. Cassagne-Mkjean ( 1966) states that male A. cuspidifer use the spurs on his fourth legs to smear the secretions over the female’s venter. After the female is securely glued the male walks about. In 374 H. C. PROCTOR A. valdiviensis, the male periodically vibrates legs I11 against the female’s sides and then lowers them to the ground where they thrust up to jerk the male’s hind end with the attached female upwards. The following description excludes A. planus, for which sperm transfer was not observed. When the male finds a spot with secure footing he anchors legs I to 111, leans backwards to bring his genital aperture in contact with the substrate, and slowly lifts up to draw out a spermatophore (Fig. 7g). He then leans forward, dips down, and collects the spermatophore head on the tip of his petiole leaving the stalk behind. Arrenurus cuspidifer males deposit and strip two or three spermatophores at intervals of a few minutes (Cassagne-Mkjean, 1966), whereas A. ualdiviensis males produce up to 20 at intervals of only a few seconds (Bottger, 1965). The sperm collects in a mass on the petiole. At this point the orientation of the pair changes. Bottger (1965) states that the male A. ualdiviensis pushes against the female’s venter with his fourth legs so that she tilts backwards onto the petiole, thereby forcing the petiole with its load of sperm into her genital atrium (Fig. 7h). Cassagne-Mkjean (1966), on the other hand, asserts that the female A. cuspidifer “throws herself backwards” onto the petiole. In A. ualdiviensis, insertion of the petiole is followed by a 1.5-2 hour period in which the male quivers his third legs against the female’s venter near her genital opening (Bottger, 1965). In A. cuspidifer there is a period that lasts up to 7 hours during which the male periodically makes a rapid move forward then stops and shakes the female violently to the left and right. Cassagne-Mkjean (1966) feels this behaviour helps to loosen the glue holding male and female together. This seem unlikely since when the time comes for separation, in both species the male simply presses legs IV firmly against the female’s venter until she is forced off the petiole. In A. cuspidifer, just-mated females are ready to remate almost immediately, whereas males have a refractory period of at least 3 days. Bottger (1965) states that female A. valdiviensis refuse to mate if they have begun the process of egg ripening. Male Arrenurus of the subgenus Megaluracarus typically have their hind end very elongated, often with a dorso-medial projection, lack pygal lobes, and have spurs on their fourth legs. Usually there is no petiole, but if it is present it is small and peglike (Cook, 1974). Both Lundblad (1929) and Bottger (1962) describe the mating behaviour of Arrenurus globator (Muller). After contacting a female, the male stops, and crooks his modified legs IV over the posterior end of his cauda. In this position he turns to direct his cauda to any source of vibration. Lundblad (1929) states that the male tries to push his cauda beneath the female, but Bottger (1962) says the female takes the active part in going to and climbing onto the male’s cauda. Once the female is on the cauda, the male produces a sticky secretion that glues her in place. The projections and tassel-like setae on the male’s fourth legs are used to prevent secretions from running onto the female’s genital plates. For a period of 10 to 15 min after gluing, the male jolts violently every few seconds “as if an electric current had passed through the pair”; Bottger (1962) feels this is to encourage the female to open her genital flaps to accept sperm. Spermatophore deposition and sperm transfer occurs much as it does in the subgenus Arrenurus (see above) except that the male does not strip sperm off the spermatophores with his cauda, but instead drops the female down on a spermatophore and rocks from side to side several times; according to Bottger MATING AND SPERMATOPHORES OF WATER MITES 375 (1962), the male jolts briefly before going on to deposit another spermatophore. Lundblad (1929) observed deposition of up to four spermatophores and Bottger (1962) saw up to six with intervals between deposition of 3-5 min. After completion of this phase there is a large clot of sperm in the cleft between male cauda and female genital aperture. The male then begins to shake the female violently from side-to-side as in A. (Arrenurus) cuspidifer (see above) while beating legs IV against the female’s venter. Bottger (1962) states that this phase of lateral shuttling can go on for 3 to 4 hours. Although Lundblad (1929) considered this behaviour a mere “reflex action”, Bottger (1962) felt that it encouraged the female to take up sperm on her genital flaps. I saw similar behaviour in Arrenurus marshalli Piersig and Arrenurus birgei Marshall except that male A. birgei first brush one side of the female with one fourth leg, then the other side, in between shuttling. To separate, males of this subgenus push their fourth legs against the female’s venter until she is forced off. As in species of the subgenus Arrenurus, females are still receptive after mating while males must wait a few days, during which they cannot be induced to exhibit the crook-legged readiness posture (Bottger, 1962). Males of the subgenus Truncaturus have slightly elongated cauda, no pygal lobes, no fourth leg spurs, and the petiole (if present) is rudimentary. Lundblad ( 1929) briefly describes the mating behaviour of Arrenurus ( Truncaturus) stecki Koenike. An A. stecki male enters a ‘readiness posture’ similar to that of A. (Megaluracarus) globator with legs IV crooked over his very short cauda. He slips his cauda beneath a female, positions her on his back with his fourth legs, and glues her there. Spermatophore deposition and transfer occur in the same way as in A. globator. Up to three spermatophores are produced. After this, instead of shuttling, the male A. stecki repeatedly strikes his cauda, with the attached female, against the substrate. Pairing lasts from 1/2 to 1 h. Males of the subgenus Micruracarus have short cauda with a deep and often elaborate median cleft, a petiole that (when present) varies from rudimentary to complex, no pygal lobes, and fourth leg spurs may be present or absent. Lundblad (1929) made a few observations on the early stages of courtship in Arrenurus (Micruracarus)forcipatus Neuman. The male does not show the crook- legged readiness position upon contacting a female, but rather (like males of the subgenus Arrenurus) grapples with her and tries to manoeuvre her onto his back. Bottger describes the simple spermatophore of A. (Megaluracarus) globator. It has a slender stalk, 170-200 pm long, that tapers from a broad base to a point. There is no sperm capsule and possibly no membrane around the sperm cells; instead, the unencapsulated sperm droplet is held to the stalk by surface tension and rests against small bracket near the tip of the stalk. The spermatophore stalk of A. birgei appears similar to that of A. globator (Fig. 6d).

DISCUSSION Comparison of mating behaviour between water mites and other arachnids Water mites show perhaps the greatest diversity of sperm transfer behaviour in the Arachnida. Most other groups are monotypic in transfer mode: pairing with indirect transfer occurs in all scorpions, uropygids, amblypygids and schizomids; copulation occurs in all spiders, solfugids, ricinuleids and 376 H. C. PROCTOR opilionids (Thomas & Zeh, 1984). Within the Acari, most major taxa are also monotypic (e.g. all ticks copulate) or show rare exceptions to monotypy [e.g. pairing among otherwise dissociated oribatids (Schuster, 1962) or terrestrial parasitengonids (Andrt, 1953)l. Pseudoscorpions come closest to rivaling water mites in diversity of sperm transfer modes, except for the paucity of clear examples of copulation; however, in the pairing species Rhacochelifer disjunctus (Koch), the male opens the female’s genital flaps with his forelegs before pressing her onto the spermatophore (Weygoldt, 1970), behaviour that ranks as copulation in my classification. Why have water mites evolved such diversity in mating behaviour in comparison to other arachnid taxa? I believe that the evolutionarily flexible ancestral state of sperm transfer in water mites together with their radiation into diverse habitats has given these mites the latitude to develop sperm transfer modes not found in other arachnid groups. With regard to the first point, evolution of behavioural diversity can be constrained by the ancestral condition of a trait (van Rhijn, 1990). For arachnid groups derived from ancestors that transferred sperm by copulation, the evolution of indirect sperm transfer may be prevented by phylogenetic constraints (Alexander, 1964). For example, copulating taxa often evolve unstalked spermatophores (e.g. Pionidae) or free sperm (e.g. spiders), and perhaps thereby lose internal organs devoted to the production of stalk material. For such groups to evolve indirect transfer they would first have to re-evolve these organs. There may be other constraints that make the evolution of dissociation in certain non-copulating groups difficult. Arachnids in pairing, non-copulating taxa are often widely dispersed predators, and at least in scorpions (Polis & Sissom, 1990) and uropygids (Weygoldt, 1972), spermatophore construction is a lengthy procedure taking hours or days; dissociated sperm transfer seems unlikely to evolve when spermatophores are costly and spermatophore-female encounter would be rare. Pairing, with or without direct transfer, is likely the ancestral mode of sperm transfer in most arachnid orders (Alexander, 1964; Thomas & Zeh, 1984); however, for pseudoscorpions dissociation may be the ancestral state (Weygoldt, 1966a). For water mites, outgroup analysis indicates that ancestral water mites may not have paired, since all but a few terrestrial relatives of this group have dissociated sperm transfer (for a tentative cladogram, see Proctor, 1991 a). However, there is also some evidence that pairing was ancestral and dissociation evolved many times in terrestrial and aquatic parasitengonids (Witte, 1984). Thomas & Zeh (1984) suggest that for an originally pairing species to evolve dissociated spermatophore transfer (or for dissociation to be maintained), its habitat must be subject to low desiccation stress; this condition is met by many soil-inhabiting arthropods and, obviously, by water mites. However, there are many species of terrestrial arthropods with desiccation-resistant spermatophores (Witte, 1991). Another environmental factor conducive to the evolution of dissociation may be substrate complexity; Witte (1991) states that the intricate spatial structure characterizing soil, litter and vegetation may limit the range of direct signals sent from partner to partner. He suggests that persistent signal threads on the substrate, such as are found in non-pairing millipedes (Schomann, 1956), the pseudoscorpion Serianus carolinensis Weygoldt (Weygoldt, 1986b), and many terrestrial mites, may be a more efficient way of leading females to spermatophores than by pairing with them. In water mites, MATING AND SPERMATOPHORES OF WATER MITES 377 spermatophore-associated pheromones may take the place of signal threads in attracting females, although in many taxa males still deposit reduced threads near deposition sites (see Witte, 1991, for an excellent discussion of the taxonomic distribution and morphology of signalling threads in the Parasitengona). Thomas & Zeh (1984) also mention mortality risk from mating partners as a possible selective force behind the evolution of dissociation. This seems unlikely, since there are more herbivores among non-pairing arthropods than among pairing ones [e.g. oribatid mites, polyxenid millipedes and collembolans (Schaller, 197 I)]. Regardless of whether they originally paired, water mites have clearly descended from an ancestor with an evolutionarily flexible mode of indirect sperm transfer. Whether many losses or many gains of pairing have occurred in the water mites is dependent on the (unknown) plesiomorphic state of indirect sperm transfer (i.e. whether the ancestor showed dissociation or pairing). It is clear, however, that there have been a great number of independent evolutions of copulation in this group. I estimated 91 independent gains of this trait in the 343 genera of water mites, and sought ecological explanations for the repeated development of copulation in aquatic mites when terrestrial parasitengonids have failed to evolve direct transfer even once (Proctor, 1991a). My analysis indicated that copulation evolved more often in swimming than in non- swimming mites. In crawling species, females are likely to come in contact with spermatophores left on the substrate, but in swimming species selection would act on males to either capture a female and bring her down to the substrate to deposit spermatophores (e.g. some Eylais), or to pass the sperm directly to her. I also noted a trend towards evolution of copulation in endoparasitic water mites (Proctor, 1991a). Unsuitability of substrate within hosts may have selected for direct transfer in these species (Hevers, 1978). Relative to scorpions, pseudoscorpions, amblypygids, uropygids and schizomids, there are few examples of pairing with indirect transfer in water mites; this may be due to morphological differences between mites and the other orders. Most non-copulating, pairing arachnids have a courtship dance prior to spermatophore deposition during which males grasp females with their chelate or raptorial palps (e.g. scorpions, pseudoscorpions). Few water mites have palps of suitable length or structure to grasp females while simultaneously depositing spermatophores on the substrate. In water mites, grappling between the sexes is likely to lead to postures more conducive to copulation than to substrate- mediated sperm transfer. In those 8eumania and Unionicola species that pair without copulation, there is no grappling between the sexes. I feel that courtship in these water mite species is feasible because of their adaptations for predation. Mites in both genera are sit-and-wait predators that are very sensitive to vibrations; by using vibratory stimuli, males are able to hold females’ attention during courtship, or to attract them to the site of spermatophore deposition (Proctor, 1991b). Finally, the rarity of pairing with indirect transfer in water mites may simply reflect the paucity of behavioural studies in this group. Almost unique among arachnids is the harem-defense polygyny of some water mites that parasitize the mantle cavities of freshwater mussels. In Unionicola formosa (Dana & Whelpley) and Unionicola ypsilophoru (Bonz), males are highly aggressive towards each other and often fight to the death (Dimock, 1983; Davids el al., 1988). Intermale aggression often results in highly female-biased 378 H. C. PROCTOR sex ratios within mussels; in U. formosa a single male may monopolize up to 78 females (Dimock, 1983). It seems likely that the defensible nature of the host’s mantle cavity has selected for the evolution of harem behaviour in these mites. Sait6 (1990) has a similar explanation for harem mating systems in spider mites. There are several caveats with regard to behaviour and spermatophore morphology described in this paper. Unnatural conditions of light, temperature and density of conspecifics in the laboratory may have affected production of spermatophores, and hence whether a species was included under complete or incomplete dissociation. Deposition behaviour and number of spermatophores produced could also have been affected [e.g. temperature effects on Limnesia maculata (Witte, 199 l)]. Even spermatophore morphology can be influenced by substrate quality; Hevers (1978) found that male Unionicola intermedia slip when depositing on smooth substrates, resulting in bent spermatophore stalks. As well, individual differences in age or nutritional status might affect a male’s willingness or ability to produce spermatophores (e.g. Gwynne & Simmons, 1990; Lederhouse et al., 1900); Hevers ( 1978) describes production of spermless or malformed spermatophores by Unionicola males. In other non-copulating arthropods, males may be limited by either sperm or spermatophore stalk material (e.g. collembolans, Schliwa, 1965; pseudoscorpions, Weygoldt, 1966a).

Functional morphology of water mite spermatophores The diversity of water mite behaviour and ecology provides an opportunity to test how social interactions and environment affect spermatophore structure. In his 1985 book Sexual Selection and Genitalia, William Eberhard suggests that structural complexity of a species’ spermatophore is an adaptation for internal courtship of the female. This hypothesis predicts that spermatophores of dissociated species should be less complex than those of pairing species, because in dissociated species the only time a female would approach a spermatophore would be when she was already fully receptive to fertilization, and complex spermatophore elaborations designed to stimulate her into receptivity would be superfluous. In pairing species, on the other hand, males would have the opportunity to bring slightly unreceptive females in contact with their spermatophores, where morphological features may encourage them to take up sperm. However, a recent test of this ‘female choice’ hypothesis for spermatophore complexity that included spermatophores from many species in addition to water mites found no statistical association between complexity and mode of sperm transfer (Proctor, 1992). Nevertheless, the female choice hypothesis should not be dismissed without further observations of what parts of spermatophores are touched by females during sperm uptake, and how females respond to natural variation in spermatophore structure. One fascinating avenue as yet unexplored is the effect of certainty of uptake on the size and number of spermatophores produced. Here water mites would again be an ideal group for study because of their variation in proximity of male and female during sperm transfer, and because of the relative ease of collecting and measuring their spermatophores. It has been suggested that production of large numbers of spermatophores is an adaptation to uncertain uptake (Eberhard, 1985); assuming a limited amount of sperm, production of many spermatophores would result in a relatively small amount of sperm per spermatophore. It would MATING AND SPERMATOPHORES OF WATER MITES 379 be very interesting to compare sperm packet size, number of spermatophores produced, and likelihood of sperm uptake in a with diverse transfer modes, such as Unionicola, that is also easy to maintain and observe in the laboratory. Conversely, sperm packet size may be an adaptation to female clutch size, as may be the case in pseudoscorpions (Weygoldt, 1966a). It may be pragmatically difficult to measure clutch size in water mites, however, since females of some species can lay fertilized eggs for many months using stored sperm (personal observation for Neumania papillator). There is more evidence of environmental effects on spermatophore morphology. Witte (1984, 1991) suggests that adaptations to low-humidity by terrestrial parasitengonids pre-adapted mites of this cohort to invade water. Fluid surrounding sperm in spermatophores of terrestrial mites is hygroscopic, allowing spermatophores of some species to tolerate very low humidities without desiccating (Wendt & Witte, 1985). To prevent water loss in this hypertonic spermatophore medium, each sperm cell is covered by an impermeable sheath. This adaptation would also have provided protection against the opposite problem, water uptake, for spermatophores deposited in aquatic habitats. Except for water mites, complete invasion of water has not been achieved by any other non-intromitting arthropods. Intromission without exposure of spermatophores to the environment, and hence avoidance of water/sperm contact, is ancestral to that mate in the water (e.g. Coleoptera, Hemiptera). Spermatophore-associated pheromones are another plesiomorphic character of water mites. There is evidence for contact and long-distance chemoattractants in the spermatophores of many terrestrial relatives of water mites (e.g. Bdellidae: Alberti, 1974; Erythraeidae: Putman, 1966; Trombidiidae: Andrt, 1953). In these mites both males and females respond to pheromones, the latter to pick up sperm and the former to deposit their own spermatophores and possibility destroy those of others (e.g. Anystidae: Schuster & Schuster, 1966; Erythraeidae: Turk, 1988). In water mites, production of spermatophore fields by individual males may be a strategy to concentrate pheromones so that spermatophores will be more easily located by females (Witte, 1984). Spermatophore fields are most evident in species whose males deposit in the complete absence of conspecific cues (e.g. Hydrachna, Hydrodroma, Limnesia); dissociated species that require conspecific cues produce scattered individual spermatophores (e.g. Thyas, Limnochares) . Fanning by males in the pairing species Neumania papillator probably sends a phermone-laden current of water from the spermatophores to the female (Proctor, 199 1 b). As in terrestrial mites, spermatophore-associated pheromones appear to be involved with male-male competition in water mites. Non-copulating male water mites engage in external sperm competition either by depositing near or on previously existing spermatophore fields (e.g. Hydrachna, Hydrodroma, Sperchon), or by crushing spermatophores of rivals (e.g. Neumania, Unionicola and possibly Atractides) . Another way spermatophore structure may enhance uptake by females is shown by spermatophores of Hydrachna and Limnochares. Witte (1984) feels that the zigzag secretions males put down prior to spermatophore deposition guide the female to the side of the asymmetrical spermatophore from which sperm is accessible. Unionicolids are unique among water mites in producing groups of 380 H. C. PROCTOR spermatophores with distinct morphologies. Intertwined stalks, as found in most Unionicola species, may enhance the stability of very tall spermatophores. The net-like spermatophore groups of Neumania papillator may be adapted to hydrodynamic stresses produced by male fanning. Spermatopheres not deposited in distinct groups also show modifications to enhance stability. The tall spermatophore of Neumania ( Tetraneumania) distincta is supported by webbed vanes. Atractides constructs its own filmy substrate before depositing tripodal spermatophores. The trailing feet of many spermatophore stalks (e.g. those of Hydrodroma, Limnesia) may increase stability. Males may sometimes be limited by the amount of stalk material available for spermatophore construction. One way to reduce the amount of material without altering spermatophore size would be to construct hollow stalks; however, particularly for tall spermatophores, hollow stalks would be more likely to bend or crimp when disturbed. A solution to both problems is to produce flexible chambered stalks. Tall, chambered spermatophore stalks are deposited by Lebertia and most Unionicola species, and by terrestrial mites of the family Anystidae (Schuster & Schuster, 1966). In two genera, spermatophore capsules are reduced in species with close association between the sexes; compare spermatophores of Neumania papillator with N. distincta, and those of Unionicola intermedia and tricuspis with most other Unionicola. Copulating Arrenurus species produce unencapsulated sperm drops on stalks. Capsule reduction may be an adaptive response to the greater certainty of female presence in pairing species, indicating that there may be a tradeoff between protection of the packet and ease of sperm transfer. Many copulating species have dispensed with stalked spermatophores. Male pionids transfer gelatinous balls that contain several sperm packets and a comblike structure homologous to fused spermatophore stalks (Witte, 1991). Eylais males in copulating species produce ejaculates consisting of individual sperm cells in a gelatinous matrix.

Spermatophore structure, mating behaviour and water mite phylogeny Witte (1991) discusses evolutionary trends in spermatophore structure and sperm transfer behaviour in water mites and terrestrial Parasitengona, and provides a preliminary phylogeny of 15 genera of aquatic mites. He suggests that certain spermatophore characters were present in the ancestral parasitengonid and are still expressed in certain water mite taxa. Zigzag secretions laid down before spermatophore deposition by Hydrachna, Limnochares, Thyas, Lebertia and Limnesia may be homologous to the tracks produced by trombidioid and erythroid parasitengonids like Johnstoniana, Camerothrombium, Charletonia and Abrolophus. These tracks may be produced during the shivering and lateral body movements that occur prior to spermatophore deposition in most of the above water mites. A circular field of signalling threads adjacent to the deposition site is found in most terrestrial parasitengonids, and in their sister-group, the cohort Anystina. Among the water mites, only pairing, non-copulating Eylais produce a full circular field; Thyas, Hydrachna, Lebertia and Limnesia produce much reduced fields. Witte (1991) suggests that ancestral mating behaviour in the Parasitengona included a circling dance in which male and female tap each other with their legs; this dance initiated spermatophore deposition. Subsequent MATING AND SPERMATOPHORES OF WATER MITES 38 I deposition would not require additional male/female contact. He also feels that destruction of previously deposited spermatophores was a behaviour present in the ancestral parasitengonid. Some spermatophore characters are widely-distributed within the water mites and may have been present in the stem species for this group. Witte (1984) points out the morphological similarities of spermatophores in Hydrachna, Thyas and Limnesia; spermatophores of these genera possess sperm capsules characterized by dorsal and apical openings, a thickened ventral keel, and a pair of spines or horns pointing into the capsule. Certain behavioural characters are also common in water mites. In copulating species, female rigidity during sperm transfer is shown in several distantly related families (Eylaidae, Pionidae and Arrenuridae). This may reflect an ancestral tendency to become immobile when physically stimulated; I have noticed that Hydrachna become stiff and fall to the substrate when squeezed lightly with forceps, even though there are no copulating species in this genus. Ullrich (1976) mentions similar responses in females of non-copulating Sperchon species. In many species with direct transfer, males appear to take advantage of this rigidity response by violently striking or shaking females during courtship or when females become restive during copulation ( Tiphys, Brachypoda, Arrenurus) . Finally, “marching-in-place” prior to spermatophore deposition is also shown by two widely divergent families (Hydrodromidae, Unionicolidae); possibly these leg movements are a way of rearranging internal musculature and sclerites to allow deposition. Spermatophore morphology and mating behaviour provide clues about relationships within some water mite families. In the Unionicolidae, it seems likely that the ancestral spermatophore consisted of a tall unchambered stalk tipped by a small encapsulated sperm packet. In Neurnania (Tetraneurnania) distincta the stalk is supported by two lateral webs and spermatophores are deposited singly. In Neumania (Neumania) papillator, webbed stalks are deposited in pairs so that two parallel rows of interconnected spermatophores are produced. This subgenus differs from Tetraneumania and non-pairing Unionicola by producing unencapsulated sausage-shaped sperm packets. In all Unionicola (Unionicola) species, stalks are chambered, deposited in groups of two or more, and have encapsulated sperm. The chambered stalk could have evolved from a progressive melding of the lateral supporting webs of a Tetraneurnania-like spermatophore; I often observed a median internal strand within the stalks of Unionicola spermatophores that could be the remnant of an original unchambered stalk. This hypothesis is best supported by the morphology of U. (Pentatax) tricuspis spermatophores, whose double-chambered stalks look most like modified Telraneumania stalks. The unchambered stalk of U. intermedia is likely an autapomorphy of this species, since LI. aculeata and tricuspis, in the same subgenus, produce more typical chambered stalks (Hevers, 1978). Several sperm transfer behaviours occur both in Neumania papillator and Unionicola species: walking in circles, trembling and marching. Another N. papillator behaviour, fanning, also occurs in U. aculeata, albeit before rather than after spermatophore deposition. In the Pionidae, Piona species can be split into two groups: those whose males have deeply recessed, sclerotized pockets in which spermatophores are held by leg I11 claws prior to pairing, and those without pockets that wait until they have captured a female to draw out spermatophores. The plesiomorphic state in 382 H. C. PROCTOR the Pionidae is lack of a pocket (see Smith, 1976); the pocket and pre-pairing production of spermatophores may be adaptations to reduce the amount of time spent reaching for spermatophores after finding a female, and the concomitant probability of female escape. T$hys species also vary with regard to presence of the pocket (Cook, 1974), indicating that a similar selective process may have occurred in this genus. In the Arrenuridae, the presence of glue glands and the mating position in which the female’s venter is apposed to the male’s dorsum appear to be ancestral characters for Arrenurus. A. (Arrenurus) planus is unique in having a derived venter-to-venter position. The plesiomorphic state for the family was probably sexual monomorphism as in Africasia and Wuria (Cook, 1974). Two trends in male morphology are apparent within Arrenurus: elongation of the caudal area in a grade from subgenus Truncaturus to Megaluracarus; and elaboration of an intromittent petiole in Micruracarus and Arrenurus. There are some behavioural similarities that also characterize these two groups. In Truncaturus and Megaluracarus, females mount males that show a “readiness posture” with legs IV crooked over their backs, and males shake or strike the substrate with their cauda after sperm translocation (although A. (Arrenurus) cuspidifer also does this). In Micruracarus and Arrenurus, the male captures and manipulates the female into the mating position rather than taking up the readiness posture. However, subgenera in Arrenurus are rather arbitary, since there are species with almost every gradation of caudal development (Cook, 1974). Finally, mating biology may provide evidence for or against taxonomic unification of morphologically similar groups. Many nominate species have North American and European populations (e.g. Hydrodroma despiciens, Hydryphantes ruber and Atractides nodipalpis); comparison of deposition behaviour and spermatophore structure may allow finer taxonomic discrimination between these groups. Even within one geographical area, there are sometimes differences between spermatophores produced by a single ‘species’ (see Limnesia undulata, Fig. 6c, d) that may indicate regional diversity in otherwise identical types or that the populations are actually cryptic species.

ACKNOWLEDGEMENTS I thank Ian Smith of the Biosystematics Research Centres in Ottawa for identifying water mites, Criticism from Rob Baker, Darryl Gwyne and two anonymous reviewers greatly improved the manuscript. Research was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) 1967 Science and Engineering Scholarship to H.C.P., and NSERC Operating Grants to Rob Baker and Darryl Gwynne.

REFERENCES ALEXANDER, R. D., 1964. The evolution of mating behaviour in arthropods. Symposium of the Rqal Entomological Socie& of London, 2: 78-94. ALBERTI, G., 1974. Fortpflanzungsverhalten und Fortpflanzungsorgane der Schnabelmilben (Acarina: Bdellidae, ). .t;itschrifr@r Morphologie und (Ikologic der Tiere, 78: 1 11-1 57. ANDRE, M., 1953. Observations sur la Econdation chez Allothrombium fulginosum Herm. Bulletin du Museum Noturel PHistoire Naturelle, 25: 382-386. ARNOLD, S. J., 1976. Sexual behavior, sexual interference and sexual defense in the salamanders Ambysfoma maculatum, Ambystoma tigrinum and Plethodon jordani.

AUSTAD, S. N., 1984. Evolution of sperm priority patterns in spiders. In R. L. Smith (Ed.), Sperm Competition and the Evolution of Animal Mating Systems: 223-249. Toronto: Academic Press. BAKER, R. A., 1977. Nutrition of the mite Unionicola intermedia Koenike and its relationship to the inflammatory response induced in its molluscan host Anodonta anatina L. Parasitology, 75: 301-308. BARR, D., 1972. The ejaculatory complex in water mites (Acari: Parasitengona): morphology and potential value for systematics. L$e Sciences Contributions of the Riyal Ontario Museum, 81: 1-87. BOTTGER, K., 1962. Zur Biologie und Ethologie der einheimischen Wassermilben Arrenurur (Megaluracarur) globator (Mull.), 1776 Piona nodata nodata (Mull.), 1776 und Eylais infundibulqera meridionalis (Thon), 1899 (Hydrachnellae, Acari).

PROCTOR, H. C., 1991b. Courtship in the water mite Neumania papillator: males capitalize on female adaptations for predation. Animal Behauiour, 42: 589-598. PROCTOR, H. C. & PRITCHARD, G., 1990. Prey detection by the water mite Unionicola crassips (Acari: Unionicolidae). Freshwater Biology, 23: 27 1-279. PROCTOR, H. & PRITCHARD, G., 1989. Neglected predators: water mites (Acari: Parasitengona: Hydrachnellae) in freshwater communities. Journal ofthe North American Benthological Son’ep, 8: 100-1 I I. PUTMAN, W. L., 1966. Insemination in Balaustium sp. (Erythraeidae). Acarologia, 8: 424-426. RHIJN, J. G. VAN, 1990. Unidirectionality in the phylogeny of social organization, with special reference to birds. Behauiour, 115: 153-1 74. SAITO, Y., 1990. ‘Harem’ and ‘non-harem’ type mating systems in two species of subsocial spider mites (Acari, Tetranychidae). Researches on Population Ecology, 32: 263-278. SCHLIWA, W., 1965. Vergleichend antomisch-histologische Untersuchungen iiber die Spermatophorenbildung bei Collernbolen (mit Beriicksichtigung der Dipluren und Oribatiden).