MALACOLOGIA, 1970, 10(2) : 283-321

THE NEW ZEALAND SPECIES OF POTAMOPYRGUS (GASTROPODA: HYDROBIIDAE)

Michael Winterbourn1

Department of Zoology Massey University, Palmerston North New Zealand

ABSTRACT

In his revision of the genus, Suter (1905) recognized 6 species and 3 subspecies of Potamopyrgus from the 2 main islands of New Zealand, but the present study has shown that only 3 species exist. They are P. antipodarum (Gray, 1843), P. pupoides Hutton, 1882, and a previously unrecognized species P. estuarinus n. sp. Potamopyrgus estuarinus andP. pupoides are oviparous, possess smooth, unornamented shells and are confined to brackish water, whereasP. antipodarum is ovoviviparous, highly variable in shell size, shape and ornamentation, and inhabits both fresh and brackish water. Populations of P. antipodarum may consist entirely of parthenogenetic females or contain varying numbers of sexually functional males. RearingP. of anti­ podarum in the laboratory has shown that snails do not necessarily breed true with respect to shell ornamentation, and that shell shape and ornamentation are not controlled primarily by environmental factors. The shell ofP. estuarinus is indistinguishable from shells of some P. antipodarum, but P. pupoides is easily recognized by its small, pupiform shell. The radula, operculum, external morphology, body pigmentation and male repro­ ductive system are similar in all species and do not provide useful taxonomic characters. In Potamopyrgus antipodarum the lower section of the female reproductive system is modified to form a brood pouch with the open sperm groove running along its floor. In P. estuarinus andP. pupoides the lower reproductive tract is dominated by the strongly developed capsule gland which is physically separated from the spermathecal duct below. The diploid chromosome number of all 3 species is 24. Ion-exchange chromatography of shell periostracal protein has disclosed no significant differences in amino acid composition between species, but considerable intraspecific variation is found. Potamopyrgus antipodarum is abundant in permanent freshwaters of all kinds and has been found in water up to 26%0 salinity, although experimental work indicates that it is active only in water below 17’5%0 salinity. No clear relationship between shell morphology and type of habitat has been found.P. estuarinus is most abundant in tidal estuaries where considerable fluctuations in salinity are found, and where many snails are regularly exposed to the air for part of each tide cycle. P. pupoides occupies a similar habitat, but normally remains fully aquatic at all times. In the laboratory P. estuarinus andP. pupoides remained active at all salinities from fresh to sea water, but they have not been found in fresh water in the field. Laboratory experiments have shown the existence of behavioural differences between species, which are associated with the different habitats occupied by them.Potamopyrgus estuarinus shows pronounced amphibious tendencies not foundP. in antipodarum and was able to survive in a " dormant ” state when exposed to the air for up to 70 days. The Potamopyrgus antipodarum complex is examined in the light of current concepts of the species, and the high degree of variability found in this species is associated with

1 Current Address: Department of Zoology, University of Canterbury, Christchurch, New Zealand. 283 284 M. WINTER BOU RN

the occurrences of ovoviviparity and parthenogenesis which allow a high degree of divergent evolution to occur independently in individual populations. A comparison between Potamopyrgus antipodarum and the European speciesP. jenkinsi (Smith) shows that the 2 cannot be distinguished on anatomical grounds, and many features of their biology and ecology are similar. It therefore seems probable that the 2 are the same species, the European snails having been introduced from New Zealand (or Australia ?) in the 19th century.

INTRODUCTION Snails were collected from 128 localities throughout the 2 main islands of New Two genera of Hydrobiidae. Potamo­ Zealand, and selected morphological, re­ pyrgus Stimpson 1865 and Opacuincola productive and biochemical factors, as Ponder 1966 are recognised from New well as environmental relationships have Zealand, the latter containing a single, been examined.2 recently discovered subterranean species As a result of this study it is concluded (Ponder, 1966). The genusPotamopyrgus that only 3 species can be recognised on was erected for the New Zealand species the 2 main islands of New Zealand. In Melania corolla Gould 1874. and was addition. 2 species.Potamopyrgus dawbini separated from other hydrobiid genera Powell 1955 and (?) P. melvilli (Hedley, primarily on the basis of radular struc­ 1916)w have been described from the Auck- ture. This study has confirmed the land and Kermadec Islands respectively, generic distinctness ofPotamopyrgus, but and species probably referable to Pota­ its relationships to other hydrobiid genera mopyrgus are found in southern and remain unclear. Taylor (1966) has sug­ eastern Australia (Williams, 1968). A gested it may belong in his subfamily single species, P. jenkinsi (Smith) is Littoridininae in which he placesPyrgo­ widely distributed in Britain and Europe, phorus Ancey 1888. the other genus con­ and was probably introduced from Aus­ taining ovoviviparous, spiny-shelled snails, tralasia in the late 19th century (Boettger, although differences in the verge ofPota­ 1951; and this paper). mopyrgus suggest that it is not close to North American species formerly referred the American hydrobiids familiar to him. to Potamopyrgus are now placed in other In 1882. Hutton assigned all the known genera (Morrison, 1939; Taylor, 1966) but New Zealand Hydrobiidae to Potamo­ the true generic status of central African pyrgus, and in the most recent revision of snails placed inPotamopyrgus by Pilsbry & the genus, Suter (1905) recognised 6 Bequaert (1927) remains problematical. species and 3 subspecies, which he dis­ tinguished primarily on shell characters. REVISED DIAGNOSIS OF Suter's (1905) revision has remained the POTAMOPYRGUS definitive systematic work on Potamopyr­ Potamopyrgus Stimpson 1865 gus in New Zealand, but it is now clear that there is much greater variation in Type (Monotypy): Melania corolla Gould, shell characteristics than was recognised 1847 by him. A thorough investigation of the Shell dextral; height less than 12 mm; systematics of Potamopyrgus in New Zea­ shape variable ovateconical-cylindrical ; land has therefore been undertaken. up to eight whorls, ventricose-flat sided.

2 The raw data on which this account is based may be found in the appendices to a thesis by the author deposited in the Massey University Library. Palmerston North, New Zealand. NEW ZEALAND POTAMOPYRGUS 285

smooth with or without shouldering and/ Amnicola antipodarum. Gray, 1844, Rev. Z o o l, or periostracal spines; body whorl over 7: 356. half height of shell; imperforate; aperture Hydrobia antipodum, von Martens, 1873, M a i Blätter, 19: 14. ovoid, continuous (in fully grown shells). Hydrobia antipodum. Smith, 1875, Z o o l Voy. Operculum ovate, thin, corneous, sub­ “ Erebus " & “ Terror " , 2: 3. spiral, usually possessing a calcareous Bythinella antipoda, Hutton, 1880, M an. N .Z . smear. Radula taenioglossan ; central M o ll, p 81. Potamopyrgus antipodum, Hutton. 1882, Trans. tooth trapezoidal, inferior margin nearly N .Z . Inst. 14: 145. straight, faintly trilobate, basal cups close Potamopyrgus antipodarum, Hedley & Suter, to lateral margins; lateral tooth denticu­ 1893, Proc. Linn. Soc. N.S.W ., 7: 619. late, shank 2 3 times length of subrhom- Potamopyrgus antipodum, Suter, 1893, J. Con­ boidal body which possesses no basal chy Ho I. 41: 221. Potamopyrgus antipodum, Suter, 1905, Trans. peg; marginals finely serrate, long and N.Z. Inst., 37: 263. slender, shanks straight, sharply curved Potamopyrgus antipodum zelandiae (Gray, 1843), . , , (3-5) 1 (3-5) Suter. 1905, Trans. N.Z. Inst., 37: 263 (New at tree ends; cusp formula,— ~ - : (2 5) (2-5) Zealand; in British Museum). (7-13): (14 32): (21 48). Animal with Potamopyrgus corolla (Gould, 1847), Suter, 1905, Trans. N.Z. Inst., 37: 260 (New Zealand: long pointed tentacles. Reproduction U.S. Nat. Museum). sexual or parthenogenetic, ovoviviparous Potamopyrgus badia (Gould. 1848), Suter, 1905, or oviparous. Males with long, narrow Trans. N.Z. Inst., 37: 264 (Banks Peninsula, non-lobate penis containing a single duct, N.Z.; U.S. Nat. Museum). normally coiled beneath the mantle edge Potamopyrgus egenus (Gould, 1848), Suter, 1905, Trans. N.Z. Inst., 37: 265 (Banks Peninsula, and attached to the head on right of mid­ N.Z.; U.S. Nat. Museum). dorsal line; vas deferens strongly coiled: Potamopyrgus corolla salleana (Fischer, 1860), prostate imbedded in visceral mass. Ovo­ Suter, 1905, Trans. N.Z. Inst., 37: 262 (New viviparous females possess a thin walled Zealand; collection ofJ. de Conchyliologie, brood pouch, with the sperm channel Paris). Potamopyrgus spelaeus (Frauenfeld, 1862), Suter, (=ventral channel) incorporated in its 1905 Trans. N.Z. Inst., 37: 266 (caves, Colling- floor; oviparous females with the sper- wood. Nelson, N.Z.; K.K. Hofmuseum, mathecal duct separated from the acces­ Vienna). sory glands above, and probably func­ Potamopyrgus subterraneus, Suter, 1905, Trans. tioning as the palliai oviduct. Habitat, N.Z. Inst.. 37: 267 (well, Ashburton. N.Z.; Dominion Museum. Wellington). fresh and brackish water.

Synonymy Holotype.—Deposited in the British Until further anatomical information is Museum (Natural History). available the synonymy of other genera Type Locality.— New Zealand, in fresh with Potamopyrgus must be considered water. tentative. Such genera may includeAus- tropyrgus Cotton 1942 and Fluviopupa A full account of all earlier synonymies Pilsbry 1911. and the nomenclatural histories of the species recognized by Suter (1905) is given DIAGNOSTIC CHARACTERS OF in his paper and therefore is not repeated THE NEW ZEALAND SPECIES here. However, the full nomenclatural Potamopyrgus antipodarum (Gray, 1843) history of Suter's Potamopyrgus antipodum is given, as the valid spelling of the specific Amnicola antipodanum, Gray, 1843, in Dieffen­ bachi, E., Travels in New Zealand, 2: 241 (New name has been in doubt. This is resolved Zealand; British Museum). as follows. 286 M. VVINTERBOURN

In his original description. Gray mis­ Potamopyrgus estuarinusn. sp. spelled the specific name antipodanum. This was emended in a second description Holotype: Deposited in Dominion Mu­ of the species the following year (Gray, seum. Wellington, New Zealand. 1844) and was also recognized as “ an Paratypes: Auckland, Dominion and Can­ evident and accidental mis-spelling" terbury Museums, New Zealand; Natur- by Hedley & Suter (1893). As Gray's historiska Museet, Goteborg, Sweden. original spelling was clearly an inadver­ Type Locality: Small brackishwater tent error it should be corrected toanti­ stream, Bell Block. Taranaki, New podarum. The emendation of Gray's Zealand. name to antipodum is not justified, and this spelling which has been followed Shell ovate-conic, height up to 7 mm; by most subsequent authors should not whorls 6-7, smooth, flattened; never be used. possessing periostracal ornamentation; Shell ovate-conic, height fully grown sutures sometimes margined below; apical 3-12 mm; shape highly variable, slender whorls frequently eroded. Females ovi­ and elongate to ventricose; spire long or parous, reproduction sexual. Rostral and short, loosely or tightly coiled, whorls mantle pigmentation always very dark. 4 -8 flattened to rounded, with or without The ecological niche of this species is shouldering and variable periostracal spi­ restricted and distinctive, snails inhabiting na t i o n. Females ovoviviparous, the lower the lower tidal reaches of rivers, and oviduct forming a brood pouch. Repro­ particularly harbour mud flats adjacent to duction sexual or parthenogenetic. sex river mouths, where they are alternately ratio variable. Inhabit fresh waters of exposed and covered by water of varying practically every type and also brackish salinity. water, throughout New Zealand. The animals of dried specimens labelled Amnicola antipodarum in the U.S. Potamopyrgus pupoides Hutton. 1882 National Museum were examined by Morrison ( 19393. who reported that the Potamopyrgus pupoides, Hutton, 1882, Trans. males possessed a long, simple, geniculate N.Z. Inst., 14: 146. (Heathcote estuary verge and the females were oviparous. Christchurch; Canterbury Museum). Potamopyrgus spelaeus pupoides (Hutton. 1882). This description indicates that they were Suter. 1905. Trans. N.Z. Inst., 37: 266. my Potamopyrgus estuarinus. However, examination of a photograph of the Holotype.— Deposited in the Canterbury holotype of A. antipodarum in the British Museum. Christchurch. New Zealand. Museum shows that it is definitely not Type Locality.— Heathcote estuary, near estuarinus as it possesses a large, heavily Christchurch. New Zealand. In brack­ built shell unlike that found in the latter ish water. and this is confirmed by Dr. R. K. Dell (pers. comm.) who has examined the type. Shell height less than 2'5 mm, conic- cylindrical. obtuse in apical region; whorls COMPARATIVE SYSTEMATIC 5. flat, smooth, never possessing spines or A C C O U N T ' keels, suture often margined below. Re­ Methods production sexual, females oviparous. Shell ' Inhabits the brackish lower reaches of • • • • * c streams and rivers, and tidal estuaries, Three shell parameters, height, width throughout New Zealand. and height of aperture (Fig. la) were NEW ZEALAND POTAMOPYRGUS 287

measured to the nearest 0-1 mm, with a linear eyepiece micrometer inserted in a stereoscopic microscope at magnifications

of X12-5 and .x 32. For comparative ■ purposes, ratips of shell height to shell width (h/w) and shell height to aperture height (h/ap h) were employed, as well as direct comparisons of measurements. Shells of fully grown snails only were used in comparative studies. The number of snails measured from each population was determined partly by numbers avail­ able and in all cases was sufficient to give a thorough indication of the full range of variation found within the population. In most cases 10 -20 snails were measured. Whorl counts were made to the nearest a complete whorl. Because the apex of 2 many shells was eroded accurate whorl counts could not always be made. Some shell characters such as con­ vexity and shouldering of whorls, and degree of ornamentation cannot be ex­ pressed conveniently as measurements b and so do not lend themselves to bio­ metric examination. Comparisons of such FIG. 1. Measurements made in the study of characters were made from camera lucida shell variation, a. Fully grown shell, b. Em­ tracings. bryonic shell, h. shell height; w, shell width; ap h, aperture height; 1, width of tip of apical whorl; 2, diameter of first whorl. Embryo shell Embryos were taken from the brood pouches of individuals ofPotamopyrgus Radula antipodarum and camera lucida tracings Radulae were extracted in boiling 4% of shell outlines were made at a magni­ KOH, stained in picric acid and perma­ fication of X 120. From the shell tracings nently mounted in PVA. Some radulae the width of the tip of the apical whorl, were mounted intact, whereas the teeth of and the diameter of the first whorl were others were teased apart. Duplicate measured (Fig. lb). counts of cusps, denticles and serrations were made on at least 3 lateral, inner and Operculum outer marginal teeth from each radula. Opercula were removed from snails All measurements were made with a and cleaned in a weak solution of oxalic linear eyepiece micrometer at magnifica­ acid. Permanent mounts were made in tions of X 100 and X400. polyvinyl alcohol (PVA), and examined with a binocular microscope using both top Internal anatomy and bottom lighting. Slides were placed on Anatomy was examined by dissection a dark background so that calcification and serial sections. The most successful within the operculum would be visible. dissections were carried out on fresh 288 M. WINTERBOURN

material. Snails to be sectioned were removed from their shells, or in some fixed in Bouin's fluid, sections were cut cases the animal was separated after at 5-10 /*, stained with Ehrlich's haema- décalcification, and the shells were toxylin and counterstained with eosin. thoroughly cleaned. Shells were decalci­ fied in the presence of 10% trichloracetic Chromosome numbers acid solution by HC1, and the periostra- Chromosome numbers were determined cum remaining was removed, washed and using a squash technique. hydrolysed with 6N HC1 at 110°C for Shells of freshly obtained snails were 24 hours under vacuum. All samples cracked and tissues were examined imme­ consisted of periostracal material pooled diately without fixation, or were fixed for from a number of snails. Amino acids 24 hours at 4°C in Carnoy's fluid (ethyl were analysed using a Beckman/Spinco alcohol: glacial acetic acid: chloroform. Model 120 amino acid analyser. 6:1:3, v/v/v), and stored in 70% alcohol in a refrigerator until required. Salinity relations Small pieces of testis and ovary (plus Snails were kept in the laboratory at digestive gland) were separated and 11 salinities, 0, 10, 20— 100% sea water, stained in acetic-orcein (1% orcein in made up by diluting freshly collected sea 45% acetic acid) for 10 -15 minutes on a water with distilled water. Salinities were cavity slide. Material was transferred to checked by titration with silver nitrate. a plain microscope slide in a minimum of Ten fully-grown individuals ofPotamo­ stain, gently squashed under a cover slip pyrgus estuarinus, 10 of P. pupoides and and examined microscopically using oil 20 of P. antipodarum, half from fresh­ immersion at X 1000 magnification. water and half from water of fluctuating salinity, were placed in glass bowls con­ Laboratory rearing of Potamopyrgus anti­ taining 200 ml of water, at each salinity. podarum Snails were transferred direct to the Potamopyrgus antipodarum was kept in experimental salinity from water taken the laboratory in transparent plastic from their natural habitats. All experi­ boxes ( 1 4 x 1 1 x 6 cm) with loose fitting ments were run at 18-20°C for 24 hours. lids. Boxes were half filled with tap At the end of an experiment all inactivated water, and each contained several grams snails were transferred to water with a of finely sieved pond mud and pieces of salinity of 3-5%» and examined again after Elodea canadensis. No artificial aeration a further 24 hours. All experiments were of the water was required. Water levels run in duplicate. were maintained and small quantities of pond mud were added at infrequent Amphibious behaviour intervals. Under these conditions growth Laboratory experiments were designed of snails was continous and fairly rapid to compare the behaviour of Potamopyr­ (minimum generation time 6 months), gus antipodarum and P. estuarinus when and embryos were released by large offered a choice between submerged and numbers of adult snails. exposed substrata. The experimental ap­ paratus consisted of a rectangular plastic Amino acid composition of shell perio­ box (20x10x7 cm) with a cardboard stracal protein floor covered in a layer of river mud The method of Ghiselin et a!. (1967) forming a sloping “ ramp ”. The floor was used for preparation and analysis of was subdivided into 3 zones, a lower shell material. Snails were completely submerged section, an upper zone of Page Unavailable 290 W. WINTER BOU RN

r------«------1------* 0 1 2 3 4 5 mm

nrinr77r?/j,

FIG. 3. Outline tracings of fully grown, ornamented shells Potamopyrgus of antipodarum from 20 populations, showing variations in size, shape and form of ornamentation.

slightly damp, exposed mud, and a middle the air. One hundred snails were used zone of saturated mud also exposed to in each experimental run. Tap water NEW ZEALAND POTAMOPYRGUS 2 9 1

was employed in experiments on both species and sea water was also used with P. estuarinus. The different salinities did not affect the responses of P. estuarinus in the experimental situation. All experiments were carried out at 18 -20°C.

Effects of desiccation and starvation (1) To determine the time snails can exist in a dry atmosphere before death occurs, experiments similar to those of van der Schalie & Getz (1963) were a b

carried out. Shells of experimental snails FIG. 4. Outline tracings of typical shells ofa. were dried thoroughly with filter paper Potamopyrgus estuarinus (from the type locality) and placed in open, 9 cm diameter petri and b, P. pupoides. dishes which were kept in a desiccator containing calcium chloride as desiccant. The apparatus was maintained at further into their shells, until in many 20-22°C cases the operculum could no longer be Fifty specimens of Potamopyrgus estua­ seen. A snail was considered dead when rinus and P. antipodarum, and 20 of no withdrawal reaction was elicited upon P. pupoides were used in each experiment. prodding the operculum firmly with a Five individuals of each species were needle, or when signs of putrefying tissue removed from the desiccator every hour were visible around the aperture of for the first 3 hours, and then at 6 hour strongly withdrawn individuals. intervals until all were dead. A snail was considered dead if it showed no sign Results of movement within an hour of being placed in a shallow container of Shell water. Shells of the New Zealand species of (2) A permanently saturated atmos­ Potamopyrgus are small and plain (apart phere was produced in 9 cm covered from periostracal ornamentation), and petri dishes, by placing 6 thicknesses of offer few useful taxonomic characters. water-soaked filter paper on the floor of Shells of P. antipodarum are illustrated each dish. As the petri dish lids were in Figs. 2 and 3. and ofP. estuarinus loose fitting, they permitted adequate andP. pupoides in Fig. 4. gaseous exchange with the outside atmos­ phere. Dishes were kept at 20-25°C. Size and shape In each experiment 40 individuals of each Shell size, shape and variability within species were employed. Snails were exa­ and between populations were examined mined daily to determine whether they biometrically by measuring shell height, were dead or alive, until all had died, or shell width, aperture height and whorl for 56 days in the case of Potamopyrgus number. It was reasoned that by com­ estuarinus, and then after 70 days. Death paring these parameters from a large was not easy to determine towards the number of populations, the nature of the end of the experiment, as with an increase shell variation, i.e., whether continuous in time the snails gradually withdrew or discontinuous variation existed, within 292 M. WINTER BOU RN

25- some populations of P. antipodarum are so unlike that they could be considered sub-specifically different (Mayr et al.,

20- 1953), it is clear that continuous variation

* ¿5 in shell shape is found within this species. 3 Q. By comparison, only limited variability is O a exhibited by the shells of P. estuarinus

o andP. pupoides. 1 0 t Numbers of whorls in fully-grown shells from 100 populations of Potamo­ Cc 3 Z pyrgus antipodarum are shown in Table 1. Again there is considerable variation between populations but no clear division into discrete groups is found. As a

shell height mm general rule, the taller the shell, the more whorls developed.

FIG. 5. Maximum height of shells in 100 To summarize, measurement of shell populations ofPotamopyrgus antipodarum. parameters has not provided evidence of clearcut morphological groups existing within the Potamopyrgus antipodarum the Potamopyrgus complex could be complex, but rather has shown the exis­ determined. Any discontinuities thus tence of continuous variation of size and found might be indicative of separate shape within this species. P. pupoides is lower taxonomic units which could be distinguished by its small, pupiform shell, investigated further. but the shell of P. estuarinus is indistin­ Maximum shell height in populations guishable from those of some forms of of Potamopyrgus antipodarum ranged from P. antipodarum. 4-11-5 mm. When the frequency of these heights is plotted (Fig. 5), the dis­ Ornamentation tribution is approximately normal and The presence or absence of spines or possesses a single peak at 6 6-6 mm. keels has been considered important in 72% of the values lying between 5'5 7‘5 the separation and identification of the mm. By contrast, shells of the other 2 New Zealand species of Potamopyrgus species are more uniform in height, those (Suter. 1905). However, field observa­ of P. estuarinus ranging from 5'5 7'5 tions made during the course of this study mm and those of P. pupoides. 2‘5 3 have shown that within theP. antipodarum mm. complex considerable variation in degree Shell ratios (h:aph, h:w) from selected and nature of shell ornamentation is population*, of the 3 species are compared found, even, in many cases, within a in Figs. 6 and 7. The populations are single population (Fig. 10). Ornamenta­ arranged in order of increasing mean tion is purely periostracal. and no calcium h:aph ratios, and little correlation between is found in the spines. aperture height and shell width is appa­ Potamopyrgus antipodarum was reared rent. Mean shell ratios for all popula­ in the laboratory in order that shell form tions of Potamopyrgus antipodarum are and ornamentation of progeny of known plotted in Fig. 8, and the range of varia­ parent snails could be examined. Some tion of these ratios within populations is investigators (Dell, 1953; Hunter, 1961) shown in Fig. 9. Although the shells of have considered that much shell variation NEW ZEALAND POTAMOPYRGUS 293 a 10 b i~É~l 16 c 15 d 14 e a k i L fin. IO

f 16 g 26 h 15

18

j 15 k 19 i 21 m n É n. 16 n 18 o i 16

P j — ~~i— 18 q i ^ 16 r 16 r TT-— i—rr-— i TT- 1-8 2-0 2-2 2-4 2-6 2*8 7^4 7^6 ' OiT” 2-0 ' 2^2 ' h/ap h ratio h / w ratio

F1G. 6. Variation in shell height: shell width (h:w) ratio, and shell height: aperture height (h:aph) ratio in 18 populations ofPotamopyrgus antipodarum, horizontal bar range; open rectangle=l SD; closed rectangle = 1 SE; vertical bar= mean; numbers at right are sample sizes.

is the result of exposure to different en­ smooth-shelled parent snails, 9 produced vironmental conditions, and this was totally smooth young, and 5 both smooth observed inLymnaea tomentosa reared in and spiny young. No smooth parent the laboratory under different conditions produced only spiny progeny. Of 18 (Boray & McMichael, 1961). spiny adult snails, however, only 3 pro­ In this study the experimental situation duced all spiny young, 3 produced both was reversed, and snails taken from smooth and spiny young, and 12 pro­ differing environments were reared in the duced smooth young. In all cases, snails laboratory under identical conditions. from natural populations consisting solely Experimental populations were main­ of smooth-shelled snails bred true in the tained for up to 3 years. laboratory, but this did not always hold In the first series of rearings 711 pro­ for spiny-shelled snails. geny of 32 parthenogenetic snails from As snails from different populations 12 populations were examined. Of 14 were reared under identical laboratory 294 M. WINTER BOU RN

O c 1 0 b

12

d 12

18

f 14

15

h 15

2 ^ 0 1 7 Ï 1 2^4 1 2^6 ' 2^8 ' ï~^6 ' 1^8 T ?Ô ' h/aph ratio h/w ratio

FIG. 7. Variation in shell height: shell width ratio, and shell height: aperture height ratio in populations of Potamopyrgus pupoides (a d) andP. estuarinus (e-h).

50 -

40 -

3 0 -

- 1 40-

2 30-

10 - ö 20-

io

1 0 - 1 2 3 4 •5 shell dimensions mm

17 19 21 23 25 27 mean shell ratios FIG. 9. Range of variation in shell height: shell width ratio, and shell height: aperture height ratio FIG. 8. Mean shell height : shell width ratios, in 95 populations of Potamopyrgus antipodarum. and mean shell height : aperture height ratios in Broken line=h:aph ratio; solid line=h:w ratio. populations ofPotamopyrgus antipodarum. Bro­ A minimum of 10 shells were measured in all ken line— h: aph ratio; solid line = h: w ratio. populations. Erratum

The figure shown for Fig. 9 (p 294) is incorrect. The correct figure is shown below.

40-

i2 30-

o20-

? 10-

L _

shell ratio range

FIG. 9. Range of variation in shell height: shell width ratio, and shell height : aperture height ratio in 95 populations of Potamopyrgus antipodarum. Broken line = h:aph ratio; solid line = h:w ratio. A minimum of 10 shells were measured in all populations.

The figure shown for Fig. 19 (p 315) is incorrect. The correct figure is shown below.

antipodarum pupoides estuarinus continuing^ genetic'''divergence

elimination of males

obligatory parthenogenesis

reduction in numbers of males (facultative parthenogenes is?)

aquatic amphibious sexual reproduction tendencies

development of shell ornamentation and ovovivipary

shell smooth invasion of freshwater oviparous sexual reproduction

invasion of brackish water

ANCESTOR m arine shell smooth oviparous sexual reproduction

FIG. 19. Postulated steps in the evolution of the New Zealand species Potamopyrgus.of

NEW ZEALAND POTAMOPYRGUS 295

TABLE 1. Numbers of whorls in fully-grown shells from 100 populations ofPotamopyrgus antipodarum.

j 1 No. of Whorls ;ii neignt Totals in mm 4 5 6 7 8 •

3-3*9 1 13 1 • • • 14

4-4*9 • • • 23 30 1 ^4

i 5-5*9 1 4 15 22

6-6-9 • • • 1 5 1 7

7-7-9 • • • • • • 1 I • • • 1

8-8-9 • • • • • • • • • • • • 1 1

2 Totals 41 52 4 1 1 100

TABLE 2. Results of rearings from parthenogenetic individuals Potamopyrgus of antipodarum obtained from a pond at Massey University. i F»* F2 F, *

-o P2* I P* Smooth Spiny Smooth Spiny Smooth Spiny

Smooth 4 1 Smooth 35 0 Smooth 0 37 Spiny 2 3 Spiny 0 10 Spiny 0 22 Smooth 43 0 Spiny 4 20 Spiny 0 33 Spiny 0 10 Spiny 0 16

Spiny 21 20 Smooth 43 0 Smooth 12 0 Smooth 5 0 Smooth 6 0 Smooth 20 0

Spiny 56 3

Smoothf 92 0 Smooth 25 0 Smooth 11 0 Smooth 24 0 Smooth 35 0 Smooth 27 0 Smooth 20 0 Smooth 8 0

*P=parent; F=offspring. |4 snails kept together. 296 M. WINTER BOU RN

a

d

g h

i i 0 123455 j k mm NEW ZEALAND POTAMOPYRGUS 297

conditions, it is impossible to inferenviron- mental influences as the only factors deter­ 60- mining shell ornamentation. This must therefore have a genetic basis. 50- A longer term experiment was carried out using parthenogenetic snails taken from a pond at Massey University, Pal­ 40- merston North, in which smooth and spiny shelled snails were present in 30- approximately equal numbers. All gene­ rations were kept under identical experi­ mental conditions but again a consider­ able amount of variation in shell orna­ mentations was found between the pro­

10 - geny of siblings, and between generations (Table 2). A possible genetic basis for shell poly­ 10 ■14 -18 22 •26 30 morphism in Potamopyrgus jenkinsi and sh e ll dimensions mm P. antipodarum is suggested as follows. Ornamentation may be under polygenic FIG. 11. Whorl measurements of 136 embryonic shells from 19 populations of Potamopyrgus control rather than determined by a single antipodarum. Broken line diameter of first pair of alleles, and the expression of whorl; solid line width of tip of apical whorl. different degrees of shell ornamentation could result from interaction between environmental factors and the genomes of shell secreting cells in the mantle. slight, and less than that found in samples Characteristically, only a part of a cell’s of randomly selected adult snails from the genome is manifest at any one time, and original habitats. environmental changes could modify and Embryonic shell direct gene function producing pheno­ » typic differences, e.g., inducing spine The shells of embryos contained in the development, when the correct genes brood pouch of Potamopyrgus antipoda­ were active. Such a mechanism could rum are semi-transparent and possess account for the intra-speciflc variation in no ornamentation, although transverse shell ornamentation which is frequently growth rings are visible (Fig. 12 c-e). found and which cannot be explained in The embryonic shell possesses D5 whorls simple Mendelian terms or as solely when released from the brood pouch, and environmentally controlled changes of the in older snails these whorls cannot be phenotype. differentiated from later developed shell. In contrast to shell ornamentation, the The width of the tip of the apical whorl shell shape, height, whorl convexity and and the diameter of the first whorl of ratios of shell parameters of progeny in 136 embryonic shells from 19 populations all laboratory populations closely resem­ of Potamopyrgus antipodarum are plotted bled those of the parent. Range of shell in Fig. 11. N o indication of the presence variation between daughter snails was of distinct size groups is found.

FIG. IO. Variation in shell shape and ornamentation in 6 populations Potamopyrgus of antipodarum 1, a-c; 2, d f; 3, g-i; 4, j—1 ; 5, m -o; 6, p-s. M. WINTERBOURN

FIG. 12. Externals and radula ofPotamopyrgus antipodarum, a, Radular teeth, b. Operculum (outer side), c e, Embryonic shells from brood pouch, f. Animal extended (ventral), g, Head pigmenta­ tion. c central; I lateral: im inner marginal; om outer marginal; ca calcareous smear; cl=clear area; t tentacle; m mouth lobe; mg mucous groove; ap aperture; g granule; op position of operculum. NEW ZEALAND POTAMOPYRGUS 299

TABLE 3. Variation in whorl dimensions of embryonic shells from 4 populations Potamopyrgus of antipodarum.

Locality No. of shells Width of apical Diameter of 1st measured tip (mm) whorl (mm)

Lake Rotoiti 10 0 1 0 0 1 3 0-21 0-23

Lake Pupuke IO O i l 0 1 6 0-21 0-23

Ml. Wharite IO 0 0 9 0 1 6 0-20 0-27

Lindis Pass 10 013—016 0 -2 5 -0 -3 1

The range of variation in whorl mea­ against a dark background. The oper­ surements found in embryonic shells from culum is of no value in distinguishing the 4 populations is given in Table 3. Clearly New Zealand species ofPotamopyrgus. intrapopulation size variations can be almost as great as variations between Radula populations. The radula ofPotamopyrgus is taenio- glossan. No important differences in Operculum general tooth shape are found between Stimpson (1865) described the oper­ species, and representative teeth are illus­ culum of Potamopyrgus simply as cor­ trated in Fig. 12a. Within populations, neous, and Suter (1913) did not elaborate slight variations may be found in the further. The following more detailed positions of the teeth on the radular description is based on an examination ribbon with respect to one another. of opercula from 30 populations of P. Some individuals have a clear space antipodarum, 3 of P. estuarinus and 3 of between the central and lateral teeth, but P. pupoides. in others, no gap is found. Radular The ovoid operculum (Fig. 12b) is length generally increases with snail size semi-transparent, its colour ranging from (Fig. 13). yellow to brown. The nucleus is sub­ In all 3 species radulae of fully grown central, subspiral growth lines are clearly individuals examined possessed 62 93 visible and there is no distinct marginal rows of teeth. The rows are closer area. The muscle insertion area is indis­ together in Potamopyrgus pupoides than in tinct but a narrow, clear, quasicrescentic P. antipodarum or P. estuarinus (Fig. 14). area extending over half the length of the Cusp formulae for the 3 species are operculum is present close to the inner given below. These are based on an margin. The clarity of this area is some­ examination of snails from 28 populations what variable. A small, irregularly of Potamopyrgus antipodarum, 3 of P. shaped, calcareous smear is usually pre­ pupoides and 3 ofP. estuarinus. sent to the right of the nucleus. The extent and degree of calcification is also P. pupoides variable but is clearly visible when the (4-5)— 1—(4 5) . 9_ n . 21-25: 29 30 operculum is viewed with top lighting (4 5) — (4 5) 300 M. WINTER BOU RN

rows of teeth per mm shell height mm

FIG. 13. Radular length plotted against shell FIG. 14. Numbers of rows of teeth per mm of height in 14 populations of Potamopyrgus. radular ribbon in the 3 species ofPotamopyrgus. p P. pupoides', e P. estuarinus ; other points P. Broken line P. estuarinus; solid line P. antipodarum. antipodarum; solid histogram P. pupoides.

P. estuarinus The minor variations in tooth shape (3-4)— 1—(3-4) : g 9: )4_j9; 21-35 shown in his figures appear to have been 3 — 3 produced by orientation of the radulae for illustration rather than by true struc­ P. antipodarum tural differences and the dimensions he

(3 :5)~ L ~ Q ^ 5) : 7 13: 15 32: 24 48 provided are far too large. Ponder's (3-5) - (3-5) (1967) figure of the radula of “Potamo­ pyrgus antipodum " (actually P. estuarinus', Results of a study of cusp variation in Ponder, pcrs. comm.) is also inaccurate. 3 populations of Potamopyrgus antipoda­ rum are presented in Table 4. Cusp Externals of animal formulae vary considerably and inP. anti­ The external appearance of the 3 species podarum this variation appears to be is identical (Fig. 12 f, g) except for dif­ independent of variations in shell charac­ ferences in size and intensity of head and teristics. P. pupoides can be distinguished mantle pigmentation. The following des­ using radular characters, (smaller, and cription therefore applies to all 3 the rows of teeth are closer together), species. but P. estuarinus and P. antipodarum The tentacles are long and slender, possess sufficient variability in shape, clear, with black pigment distributed as cusp formulae and radula length: shell in Fig. 12g. The eyes have prominent length ratios to prevent specific differences pigment cups and are located in bulges from being defined. at the bases of the tentacles. They arc Hutton's (1882) cusp formulae for 4 not borne on prominent tubercles as New Zealand “ species " cannot be given described by Morrison (1939). Rostr il the diagnostic importance he gave them. pigment is distributed in fine transverse NEW ZEALAND POTAMOPYRGUS 301

TABLE 4. Variation in numbers of cusps, denticles and serrations on the radular teethPotamopyrgus of antipodarum from 3 populations.*

Inner ^ Outer Locality Central Lateral Marginal Marginal

Massey (4-5)-l-(4-5) 9-11 20-25 31 -47 University ( 3—4)—(3-4)

Tiritca 5-1-5 9-11 25-35 32-45 Stream (3—4)—(3—4)

Makara (4—5)— 1 —(4-5) 9-11 21-29 32-42

(3-4) (3 4)

* Examination of 12 snails per population making duplicate counts of cusps, denticles and serrations on at least 3 teeth per row per radula.

bands, is dark and evenly dispersed in consistent differences in pigment distri­ Potamopyrgus pupoides and P. estuarinus, bution have been found between the New but is often lighter and more variable in Zealand species of Potamopyrgus. Also, P. antipodarum. The mouth lobes are no correlation has been found between white and normally have grey, crescentic pigment intensity and shell form inP. markings dorsally. Pigmentation of the antipodarum as has been suggested may head behind the level of the eyes is always occur inP. jenkinsi (Warwick, 1952). dark and the buccal mass is often visible dorsally near the base of the rostrum. Reproduction The broad, grey foot has a stippled Sex ratio appearance, is rounded posteriorly and truncated anteriorly. The anterior margin Morrison (1939) found that the speci­ is nearly straight, and the antcro-lateral mens of “ Amnicola antipodarum ” he angles are somewhat auriculated. The examined possessed sexual reproduction anterior mucus slit is prominent and and were oviparous, and he assumed extends the width of the foot. The that all the New Zealand species of mantle skirt is black, with a well defined, Potamopyrgus reproduced in this way. pale, anterior margin. Large numbers Later writers, however, apparently un­ of shiny white “ granules ” are found in aware of Morrison's study, have assumed the foot and mantle edge, and frequently them all to be viviparous (Marples, 1962: in the mouth lobes and tentacles close to Dell, 1969), and apart from P. pupoides, the eyes. parthenogenetic (Ponder, 1966). Although both Fretter & Graham The present investigation has shown (1962) and Muus(1963) consider that head that none of the New Zealand species pigmentation is distinctive in different consists solely of parthenogenetic females, species of European Hydrobiidae, and that males are relatively common in and a useful aid in identification, no all 3 species. 302 M. WINTERBOURN

cp bc rs

bc ap rs sdu

sg f

FIG. 15. Reproductive system, a, diagramatic representation of male system, b, penis, c, dia­ gramata representation of female system of Potamopyrgus estuarinus and P. pupoides, d, diagramatic representation of female system of P. antipodarum, e, arrangement of ducts in region of the bursa in P. estuarinus, f. Transverse section of empty brood pouch ofP. antipodarum showing position of sperm groove, p penis; pr prostate; t testis; v vas deferens; ag albumen gland; ap = female opening to palliai cavity; be bursa copulatrix; bp brood pouch; cp capsule gland; od oviduct; rs recepta- culum seminis; sd spermathecal duct; sdu sperm duct; sg sperm groove. NEW ZEALAND POTAMOPYRGUS 303

TABLE 5. Dimensions of sperms of New Zealand species ofPotamopyrgus compared with those of 2 species of European Hydrobiidae.

Total length Head length Species (microns) (microns) Reference iI . P. antipodarum 110 3 Present study

P. estuarinus 140 3 Present study

P. pupoides 110-120 3 Present study

P. jenkinsi 40 4-6 Patil (1958)

Hydrobia ulvae 100 ■>• Patil (1958)

An initial investigation into the occur­ thin, muscular wall. It passes through a rence of males was made by examining large prostate gland embedded in the 6-10 individuals from each of 63 popu­ tissues of the visceral mass at the posterior lations of Potamopyrgus antipodarum, 5 of end of the body whorl, and finally runs P. estuarinus and 3 ofP. pupoides. Males forward on the head, close to the skin, were found in all populations of the 2 to the penis, opening at its tip. No latter species and in 24% ofP. antipo­ proximal dilation of the vas deferens, as darum populations. described in P. jenkinsi by Patil, was In a more comprehensive study, 50 200 found. In all 3 species the vas deferens snails were examined from selected popu­ of mature individuals is normally packed lations. Males were found in 9 out of with living sperm throughout its entire 24 populations of Potamopyrgus anti­ length and consequently has a conspicuous podarum, and in 7 of these they constituted white appearance. less than half of the total sample. (In Sperms have slender, conical heads and populations in which males occurred long, lash-like tails, and are all of the one they represented 2 -52%, mean=29%, of kind. Their dimensions (living) are given snails examined.') InP. estuarinus 36-58% in Table 5 in which comparisons are of population samples were males, and made with the sperm of Potamopyrgus in P. pupoides males constituted 10 28% jenkinsi and Hydrobia ulvae. of population numbers. The sperms of the New Zealand species are comparable in length to those of Male reproductive system Hydrobia ulvae but are 2 4 times as long as those described for P. jenkinsi. As The gross anatomy of the male repro­ the sperm of P. jenkinsi was observed in ductive system is identical in all 3 species sectioned material, however, it is possible (Fig. 15a) and closely resembles that of that the dimensions given are not a good Potamopyrgus jenkinsi as described by indication of their length in life. Patil (1958). The testis lies in the upper The penis (Fig. 15b) is situated on the whorls of the shell on the columella side, right side of the head beneath the mantle and from it arises the vas deferens, a edge. It is simple in form, tapering at its narrow, highly convoluted tube with a tip and bears no accessory lobes. In life 304 M. WINTERBOURN it is colourless and semi-translucent, the Both normally function to store sperm vas deferens being visible within. It is (Fretter & Graham, 1962), but must capable of considerable contraction and have lost this function in parthenogenetic expansion, and when contracted the walls individuals. Fretter and Graham have near its base have a telescopic appearance. suggested that the well developed bursa In preserved specimens the shape and copulatrix of Potamopyrgus jenkinsi may orientation of the penis tend to vary act as a waste dump for excess egg capsule considerably, and usually it becomes secretions. Surrounding the posterior somewhat coiled, especially towards the wall of the brood pouch are a prominent tip. albumen gland and a mucus (shell) gland. The penis is of no value as a taxonomic The single opening of the palliai oviduct character for differentiating between New is situated close to its anterior extremity. Zealand species ofPotamopyrgus. The condition found inP. antipodarum agrees well with that described for P. Female reproductive system jenkinsi by Patil (1958), and Fretter & The structure of the female reproduc­ Graham . tive system divides the New Zealand species of Potamopyrgus into 2 distinct (2) Potamopyrgus estuarinus and P. pu­ groups which possess major differences in poides (Fig. 15c) the form of the lower section of the In these 2 species the form of the female oviduct, and its associated glands. system is identical and differs markedly from that of Potamopyrgus antipodarum (1) Potamopyrgus antipodarum (Fig. 15d) in the structure and function of the lower The ovary is situated on the columellar section which is dominated by the strongly side of the digestive gland in the apical developed capsule gland. The ovary, whorls, and reaches almost to the tip of oviduct, bursa copulatrix and recepta­ the spire. It has a white, rather lumpy culum seminis arc similar in size, shape appearance when mature, and contrasts and position to those ofP. antipodarum, strongly in colour with the brownish and in fertilized individuals the recepta­ digestive gland which has a stippled culum seminis has a vivid, white appea­ appearance. The oviduct leading from rance. given to it by masses of sperm it is slender and thin walled, but its walls packed inside. Both the diverticulae com­ become greatly thickened in the region municate with the spermathccal duct, a of the bursa copulatrix and receptaculum straight tube with a muscular wall, which seminis. Anteriorly, the reproductive sys­ opens to the anterior of the mantle cavity tem consists of the palliai oviduct which and is completely separate from the has a prominent, clearly demarcated capsule gland above. This is unlike the groove, the sperm channel, on its ventral condition found inHydrobia , where the surface (Fig. 15f). In immature indi­ capsule gland forms the palliai oviduct, viduals the thin walled lower oviduct is with the spermathccal duct running along circular in cross section but in mature its ventral surface only partially separated snails it becomes greatly enlarged and by longitudinal folds of tissue. Immedi­ distended to form a brood pouch within ately in front of the bursa copulatrix is which over 100 embryos in various stages the albumen gland whose lumen is con­ of development may be found. The tinuous with that of the capsule gland. sperm channel leads directly to the very Although the exact course of the eggs large bursa copulatrix and via the sperm through the system has not been estab­ duct to the smaller receptaculum seminis. lished it seems probable that the capsule Page Unavailable 306 M. WINTER BOU RN

TABLE 6. Material used for shell protein analysis.

Sample Species Locality Shell form

1 P. pupoides Wananaki B* Smooth

2 a P. estuarinus Huia B Smooth

2 b, c P. estuarinus Huia B Smooth

3 P. estuarinus Heathcote B Smooth

4 P. antipodarum Dannevirke Smooth

5 P. antipodarum Lake Pupuke Spiny

6 P. antipodarum Whangarei Smooth & spiny

7 P. antipodarum Lake Tutira Smooth

8 P. antipodarum Lake Tutira Spiny

* B brackish water.

from Huia (Table 7, 2a. 2b. 2c). When and shell ornamentation was apparent. 2 identical runs were made on the This is clearly demonstrated by comparing sample (2b. 2c) the mean variation the extreme shell forms represented by between amino acid values was 0'26% Lake Pupuke and Dannevirke samples. (range 0-01 0-63%). The mean variation In these, with the exception of tyrosine, between the same amino acids from 2 relative proportions of amino acids are of different samples from the same locality a similar order. The presence of increased (2a. 2b) was 0-71% (range 0-11-2-8%). tyrosine in spiny shells is probably of no This variation incorporates differences significance however, as high concentra­ between specimens, and errors introduced tions are also found in the smooth shells by décalcification, chromatography and of P. estuarinus. Clearly, the New Zea­ data handling. land species cannot be distinguished by Marked differences in amino acid con­ comparing the proportions of amino acids centrations were found between Huia and in shell periostracum as a high degree of Heathcote samples of Potamopyrgus estua­ intra-specific variation is found, parallel­ rinus, glycine, proline, tyrosine and pheny­ ing the wide range of variation in macros­ lalanine being greatly reduced in the copic shell morphology. latter, whereas most others showed cor­ The presence of considerable variation responding increases in proportions. in the proportions of amino acids in the Values for P. pupoides corresponded periostracum of Potamopyrgus species closely to those of P. estuarinus from reinforces similar findings obtained in Huia, apart from a lower proportion of other studies. Hare (1963) found that tyrosine. A wide range of variation was periostracum showed more variation in found inP. antipodarum, and no relation­ amino acid composition than any other ship between amino acid concentration structural unit of the shell, and showed NEW ZEALAND POTAMOPYRGUS 307

TABLE 7. Ratios of periostracal amino acids in the 3 species ofPotamopyrgus , expressed as percent total amino acids.

P. estuarinus P. antipodarum P. pupoides Amino acid

1 2a j r O’ 2c 3 4 5 6 7 8

Aspartic acid 121 12-9 11-5 10 9 14 9 13-3 12-7 11-5 11-7 9-9 Threonine 4-4 3-5 3-2 3-2 4-5 4-6 4-4 3-2 4-8 5-5 Serine 5-3 4-4 4-1 4-0 5-3 4-7 4-4 3-5 5-1 6-7 Glutamic acid 7 0 6-8 6-1 6-4 8-6 7-4 7-6 5-2 7-4 8-5 Proline 4-8 4-7 5-4 5-8 2-2 2-4 2-3 3-6 4-5 5-4 Glycine 32-9 35-7 34-2 34-2 26-6 31 -9 28-9 40-1 26-9 20-5 Alanine 7 0 5-7 5-4 5-2 7-7 4-4 7-1 4-1 8-7 11 -0 1/2 Cystine T* T T T T T T T T T Valine 4-5 4-1 4-4 4-0 6-0 5-6 5-0 3-4 4-4 6-2 Methionine 0-7 0-7 0-5 0-5 0-8 0-8 0-6 0-2 0-5 1 -0 lsoleucine 2-5 2-3 2-1 2-1 2-8 2-7 2-8 1 -8 3-0 3-7 Leucine 4-6 4-3 4-0 4-0 5-4 5-8 5-7 4-0 5-5 6-0 Tyrosine 2-4 6-2 6-9 7-1 3-7 4-1 6-4 4-8 3-2 3-2 Phenylalanine 5-5 4-5 4-1 4-7 4-3 5-4 5-1 6-4 5-5 4-6 Lysine 2-7 2 1 4-9 4-3 3-4 3-2 2-9 3-4 4-4 3-7 Histidine 0-4 0-2 0-3 0-2 0-1 0-6 0-2 1-1 0-7 0-3 Arginine 3-2 1 -6 2-7 3-3 3-6 3-1 3-9 3-8 3-5 3-7

* T =trace.

that samples from the growing edge, jenkinsi raised in the laboratory at dif­ around the periphery of a single specimen ferent salinities. In particular they found of Mytilus californianus may vary 10-15% an increase in the ratio of glycine to the in numbers of residues of many amino acidic amino acids with decreasing salinity. acids. Clearlv defined differences in However, no similar relationship was amino acid composition of periostracum evident when the brackish water species between individuals of the brachiopod P. estuarinus and P. pupoides were com ­ Laqueus californianus have also been pared with P. antipodarum from fresh demonstrated by Jope (1967). water. An important source of amino acid Environmental Relationships variation may be protein heterogeneity, i.e., more than 1 protein may contribute Distribution and general ecology to the periostracum as suggested by Hare (1) Potamopyrgus estuarinus. (1963), Degens et al. (1967) and Jope (1967). Ghiselin et al. (1967) found that Potamopyrgus estuarinus has a clearly environmentally controlled variation in circumscribed habitat, and is confined to the amino acid composition of periostra­ brackish water. Commonly it is found cum is sufficient to mask genetic differ­ near the mouths of streams and rivers ences in many cases. Recently, Hare & entering harbours, where the water is of Meenakshi (1968) have reported that fluctuating salinity. Frequently, the snails changes occurred in the proportions of live a semi-terrestrial existence on mud periostracal amino acids ofPotamopyrgus flats or muddy banks adjacent to river 308 M. WINTERBOURN

ditch substrates including sand. mud. the upper 50- -50 and lower surfaces of stones, and clumps of weed. In river estuaries, snails are

0 i r =1------. -0 normally most abundant towards the sea­ ward end. where salinities remain high. stream 50- 50 Many past reports of the finding of Potamopyrgus antipodarum in brackish water undoubtedly refer toP. estuarinus. 0 i 1------l a r— — l -0 (2) Potamopyrgus pupoides. c o river 5 50- -50 Potamopyrgus pupoides is confined to 3 Q. o brackish water, and is frequently found Q. in association with P. estuarinus in river - 0 T 1 r L0 o estuaries, but is less frequently found on

p o n d mud flats where it would be exposed to S loo- -50 (J the air for regular periods of time. P.

d pupoides exhibits no marked substrate a preferences and is found on stones, mud, 0 T 1 i—r T—I L0 and among living and decaying vegetation. Frequently, it is abundant in estuaries on lake 50- -50 a substrate of smooth, clean sand. n (3) Potamopyrgus antipodarum. 0 “ 1 I 1 rn i i ' i - 0 6 10 1 2 3 4 5 shell height mm ornamentation Potamopyrgus antipodarum occurs throughout New Zealand in a wide variety of habitats, including lowland FIG. 16. Relationship between shell size, orna­ mentation and habitat in 97 populations Pota-of rivers, stony streams, creeks, ditches, mopyrgus antipodarum. Key to shell ornamen­ estuaries, ponds, lakes, springs, wells and tation classes: 1—all snails smooth shelled; 2— permanent seepage. One of the few most smooth; 3—half smooth, half spiny; 4— freshwater habitats it seems unable to most spiny; 5—all spiny. colonize is the temporary pond as the snails apparently lack resistant stages channels, or in harbour backwaters and capable of carrying them over long dry salt swamps. In these situations they seasons. may lie exposed to the air for over half Within the Potamopyrgus antipodarum a tide cycle, and for the other half live in complex a number of relationships be­ water of high salinity. The snails are tween particular shell forms and geo­ inactive when exposed on mud flats, and graphical or ecological distribution are may lie on the surface of the mud, be evident, but none of these relationships partially buried, or be grouped grega­ appears to be so well circumscribed, or riously alongside or under stones, wood, clearly defined, as to warrant taxonomic etc. Snail densities of up to 884.000 per recognition of the populations concerned. m2 have been recorded in the Heathcote The main trends found are: estuary. (a) Many snails at high altitudes, and/ Other snails remain immersed through­ or in relatively oligotrophic waters, have a out the tide cycle, and may occupy various much smaller adult size than most low- NEW ZEALAND POTAMOPYRGUS 309

TABLE 8. Salinity ranges at which the 3 species ofPotamopyrgus have been found living.

Salinity o/oo Maximum Species Diurnal Range Maximum Minimum 1

P. antipodarum 26-4 0 17-7

P. pupoides 32 • 3 2-7 M

P. estuarinus 34 • 8 2 7 * *

land populations. These snails are pre­ only P. antipodarum is found in fresh dominantly smooth shelled. water (Table 8). (/>) Snails in many, but not all, popu­ In order to determine the range of lations north of Auckland attain a very salinities tolerated by each species, the large size, their shells sometimes exceed­ responses of snails kept in water at 11 ing 10 mm in height. This size increase different salinities ranging from 0 33-'c is produced by an increase in the number salinity, were examined in the laboratory. of whorls, rather than by an increase in After 24 hours in the experimental size of the whorls. situation all individuals ofPotamopyrgus (c) There is a tendency for the shells estuarinus and P. pupoides exhibited nor­ of spiny shelled snails in many lakes and mal acitivity at all experimental salinities, rivers to be more slender and strongly 0 33-ó» salinity, andP. antipodarum from shouldered in the South Island than in fresh and brackish waters was active at the North. up to 1 7*5 'oo salinity. Some reduced Although laboratory rearing work has movement of P. antipodarum was found indicated that shell form is not a simple at 21 %o salinity but in more saline water phenotypic response to environment, in all snails withdrew completely into their some instances small size may be the result shells, their opercula acting as physical of reduced growth at low temperatures, barriers to exclude the water. After a or under poor food conditions. Conversely, further 24 hours in water of 3-5 °'c salinity, higher temperatures may permit an increase all previously inactivated snails resumed in the rate and amount of growth, normal activity. resulting in the attainment of large size. In the field, the highest salinity at No clear relationship between shell which Potamopyrgus antipodarum has been height or ornamentation, and different found living is 26-4%=, slightly higher than habitat types was found (Fig. 16), although the greatest salinity at which activity many lake populations tend to consist occurred under experimental conditions. predominantly of spiny snails, whereas It is possible that some intraspecific smooth shelled snails are more abundant variation is found inP. antipodarum with in running water. respect to salinity tolerance as was found in P. jenkinsi by Duncan & Klckowski Salinity relations w (1967). Although P. estuarinus and P. All 3 species of Potamopyrgus are pupoides have not been found in fresh found over a wide range of salinities, but water in the field, they were able to exist 310 M. WINTERBOURN in it for several months in the laboratory. antipodarum estuarinus Perhaps they are unable to reproduce or Exp 1 100 - develop in freshwater. The ability to tolerate a wide range of 50- salinities is clearly advantageous to all 3 species, as rapid changes in salinity are regularly encountered in the estuarine Exp 2 1 hr reaches of rivers frequently inhabited by 100 - them.

Amphibious behaviour in Apart from inhabiting waters of dif­ 2hrs c 1 0 0 - ferent salinities. Potamopyrgus antipoda­ cn rum and P. estuarinus arc frequently _ 50- o found in contrasting physical environ­ ments. P. estuarinus is often abundant 0) n on high-tidal mud flats bordering streams E 100- 3 where snails may be exposed to the air 50 for an appreciable period of each tide cycle, whereas P. antipodarum always i remains in the water. Laboratory experi­ 72hrs ments were carried out to compare the 100 - behaviour of the 2 species when a choice 50- of 3 substrata, submerged mud, exposed water saturated mud. and slightly damp mud. was offered to them. Results of experiments are shown in FIG. 17. Selection of submerged and exposed substrata by Potamopyrgus estuarinus and P. Fig. 17. In Experiment 1 snails were antipodarum in laboratory experiments. Expt. distributed evenly throughout the box at I, snails initially distributed throughout box; the start of the experimental period and examined after 17 hours; Expt. 2, all snails a single examination of their subsequent initially submerged. Substrata: a damp, ex­ distribution was made after 17 hours. posed mud; b saturated mud; c submerged mud. In Experiment 2 all snails were placed in the submerged section of the box on commencing the experiment, and their distribution was examined after 1, 2, 24 The relatively large numbers of Pota­ and 72 hours. Similar results were ob­ mopyrgus antipodarum occupying the mid­ tained in both studies. A clear be­ dle zone of water-saturated mud, is havioural difference between the 2 species probably explained by the presence of was apparent, the majority of Potamo­ favourable respiratory conditions at the pyrgus estuarinus finally selecting the air-water interface in this zone. A similar driest substrate, whereas almost all P. situation is regularly found in still w'ater antipodarum remained in the water, or laboratory cultures lacking vegetation, in were buried in the water-saturated mud which the majority of snails move up the of the middle zone. Movement ofP. sides of the containers and settle imme­ estuarinus from the water to the dry diately beneath the surface film. upper zone is clearly shown in Experi­ Although in the experimental situation ment 2 (Fig. 17). most Potamopyrgus estuarinus remained NEW ZEALAND POTAMOPYRGUS 311

TABLE 9. Time survived by snails in a still, dry atmosphere, and on a dry substratum.

All alive First death All dead Species (hours) occurs (hours) (hours)

P. antipodarum 6 12 30 06

P. estuarinus 0 6 6-12 42

P. pupoides 0 6 6-12 24

permanently in the dry zone and exhibited starvation on the 3 species,( a ) in dry air no active movement back to the water, and on a dry substratum, andb ) ( on a in their natural habitat they do not nor­ damp substratum in moisture saturated mally remain exposed to the air for more air. than a few hours at a time, as tidal move­ The time survived by the 3 species in ments ensure they will be covered at a still, dry atmosphere is shown in Table 9. regular intervals. It is essential that the Similar responses were obtained from all habitat should be submerged regularl} as species. snails cannot move about and feed when Survival times of snails in a moisture- the substrate is dry. One consequence saturated atmosphere, and on a damp of this positive movement out of water substrate is shown in Fig. 18. could be to prevent colonization of per­ Direct observations indicated that snail manent river channels, and so effectively tissues did not become rapidly desiccated isolate populations of P. estuarinus and under these conditions, and that at all P. antipodarum in many areas where their times some moisture was maintained ranges overlap. within the shells of the snails. On a damp, but non-submerged substrate, how­ Effect of desiccation and starvation ever, movement, and consequently feed­ ing, cannot occur and therefore death Associated with the colonization of a probably results from starvation com­ non-aquatic habitat is the problem of bined with desiccation. Deaths ofPota­ preventing desiccation. This is likely to mopyrgus antipodarum and P. pupoides be of considerable importance to a pri­ are therefore attributed to the combined marily aquatic species such as Potamo­ effects of desiccation and starvation. pyrgus estuarinus which is periodically However, the situation was very different exposed to the air. P. antipodarum al­ for P. estuarinus which apparently entered though strictly aquatic, sometimes inha­ a state of dormancy or aestivation, and bits bodies of fresh water with fluctuating had a high survival rate over a long water levels, or which can be drained by period. Individuals which remained natural or artificial means. In such dormant up to 50 days resumed situations, if the snails are unable to activity when transferred to a vessel of withstand exposure to air, whole popu­ water. lations may be quickly destroyed. Little is known about aestivation in the Laboratory experiments were designed Prosobranchia although short term aesti­ to examine the effect of desiccation and vation does occur in some Poniatiasidae 312 M. WINTERBOURN

100- estuarinus

80-

cn

~ 60-

antipodarum

2 0 - pupoides

ft 20 30 40 50 60 70 d a y s

FIG. 18. Survival time of snails on a damp substratum at 20 25" C. CirclesPotamopyrgus pupoides-. squares P. antipodarum-, triangles and broken line P. estuarinus. X-10 snails placed in water (all resumed activity).

(Hunter, 1964) and Hydrobiidae (Dundee, New Zealand. Two of these,P. pupoides 1957). Quick (1920) found thatHydrobia andP. estuarinus, are clearly distinguished spp. could withstand long periods of using morphological, reproductive, and exposure and survive in an apparently ecological evidence, butP. antipodarum desiccated state, and Dundee (1957) has contains a heterogeneous assemblage of noted that dormancy occurs in the amphi­ forms embracing all the purely freshwater bious Pomatiopsis lapidaria in very cold populations. It includes a wide range of or hot and dry weather. This evidently morphological variants, as well as differ­ ensues when there is a lack of sufficient ing reproductive forms, and is found available moisture, the snails lying with under diverse environmental conditions. their opcrcula inserted well into the shell In the past, many of the forms included apertures during the inactive period, and in this species have been considered mor­ becoming reactivated with the onset of phologically distinct enough to be recog­ rain. Clearly the ability to withstand nized as separate species, or to have had long periods of exposure out of water is restricted geographical distributions allow­ advantageous to snails such asP. lapidaria ing them subspecific recognition. This andP. estuarinus which possess an amphi­ study has shown that continuous mor­ bious way of life, and may suffer pro­ phological variation exists within the longed periods of exposure. complex, and that discrete geographical distributions of taxonomic subgroups, DISCUSSION consistent with the definition of the sub­ species (Mayr, et ul., 1953) are difficult The species problem to find. A gradation in reproductive As a result of this study, 3 species of forms, through populations with few Potamopyrgus are now recognized in males, to total parthenogenesis is also NEW ZEALAND POTAMOPYRGUS 313 found, and the possession of these dif­ White (1954) and Mayr (1963) have ferent states, apparently unassociated with pointed out that it is illogical to recognize particular morphological forms, or the parthenogenetic and bisexual “ races ” of occupation of particular habitats adds the same species, irrespective of the mor­ further to the difficulty of discriminating phological resemblances between the geno­ distinct taxonomic units within the com­ types, and they considered that such forms plex. were better recognized as sibling species, The possession of a parthenogenetic if they were indistinguishable by ordinary mode of reproduction by a large propor­ taxonomic criteria. On the other hand, tion of the populations ofPotamopyrgus Mayr et aí. , (1953) have agreed that it is antipodarum is perhaps the major factor unjustifiable to give nomenclatural recog­ responsible for so much of the taxonomic nition to forms with temporary or facul­ uncertainty that has occurred in the past, tative parthenogenesis. In P. antipoda­ and it has permitted the formation of rum, sexually reproducing and partheno­ many reproductively isolated clones in genetic forms are connected by inter­ which divergent evolution has been able mediates possessing limited numbers of to occur. Furthermore, Struhsaker (1968) males, and it seems likely that in such in a discussion of shell variation inLitto­ populations both parthenogenesis and rina spp. suggested that species which are sexual reproduction may occur. viviparous could be expected to have In view of this lack of a sharp division more intra-specific variation because of between reproductive types, and the pre­ decreased distribution (dispersal) and re­ sence of continuous morphological varia­ stricted mating. This would result in tion within the complex, it seems most isolated populations, whereas strictly ovi­ sensible to consider the whole range of parous populations with widespread larvae intergrading populations as a single should be least variable. This contention species. is supported by the findings in the present The suitability of an evolutionary spe­ study, the 2 oviparous species,P. estua­ cies concept such as that of Simpson rinus and P. pupoides possessing limited (1961); “ An evolutionary species is a morphological variability compared with lineage evolving separately from others the extreme plasticity of the ovovivi- and with its own unitary evolutionary parous P. antipodarum. role and tendencies ”, which is not ham­ Reproduction by parthenogenesis also pered by the static restrictions of genetical poses nomenclatural problems. The bio­ (biological) definitions, is evident in a logical species definition (e.g. Mayr, 1963, situation of this kind. “ Species are groups of actually or poten­ Parthenogenesis and evolution inPota­ tially interbreeding natural populations mopyrgus which are reproductively isolated from other such groups ”), applies only to Parthenogenesis was first discovered in sexually reproducing organisms, and it is molluscs by Boycott (1919), in Potamo­ generally accepted that the taxonomy of pyrgus jenkinsi, and later in the American obligatory parthenogens therefore must viviparids Campeloma rufum and C. deci­ be arbitrary. In the past it has been sion by van Cleave & Altringer (1937) based primarily on morphological, eco­ and Medcof (1940), and in 4 species of logical and biogeographic evidence. The Melaniidae by Jacob (1957). Partheno­ occurrence of sexual reproduction and genesis in all these species is thelytokous parthenogenesis in thePotamopyrgus anti­ (female diploid parthenogenesis) and of podarum complex poses further problems. the apomictic type, (i.e., it is ameiotic and

Page Unavailable NEW ZEALAND POTAMOPYRGUS 315

ultimately result within many partheno­ 4 0 - V) genetic species, variability which will not C o necessarily be correlated with geographic 3 oa distribution in the same way as in a a sexually reproducing form. This is what S 2 0 is found inPotamopyrgus antipodarum. a> ■o Suomalainen (1961, 1962) has speculated E 2 10 on the ways in which mutations may be expressed in apomictic parthenogenetic animals, and his theoretical mechanism shell ratio range could possibly apply in the present situa­ tion. He argues that increasing heterozy­ FIG. 19. Postulated steps in the evolution of the gosity will occur between more and more New Zealand species ofPotamopyrgus. gene pairs (because elimination of reces­ sive mutations by natural selection is impossible) until the 2 chromosome sets can no longer be considered diploid or The relationship of Potamopyrgus anti­ polyploid in a genetic sense. This will podarum to the European species P. reduce obstacles to the expression of the jenkinsi mutations present in them, and may thus, in part, even allow the formation of mor­ Potamopyrgus jenkinsi made a sudden phologically divergent biotypes. Further, appearance in Europe, first being de­ with a continuous increase in the degree scribed by E. A. Smith in 1889, although of heterozygosity, an apomictically par­ it may have been present as early as 1859. thenogenetic form gets an ever increasing Its origin is uncertain and has been the chance to benefit from heterosis (hybrid subject of considerable speculation which vigour). This may therefore provide the has been reviewed by Adam (1942), basis for the apparently great adaptive­ Bondeson & Kaiser (1949) and Fretter & ness and dispersive ability of many Graham (1962). The subsequent distri­ parthenogenetic forms (e.g., P. antipoda­ bution ofP. jenkinsi through Europe has rum), although it is in direct contrast with also been discussed by these authors and the widely held view that parthenogenesis others, e.g., Hubendick (1950). leads to a lack of adaptability, and long Attempts to explain the sudden appea­ term disadvantage (White, 1954). rance of Potamopyrgus jenkinsi in Europe Probable steps in the evolution of have been made by various authors, and Potamopyrgus are shown in Fig. 19. 2 possible explanations have been sug­ P. estuarinus and P. pupoides possess the gested; (a) that it arose by mutation primitive features, smooth shell, sexual (Steusloff. 1927; Boettger, 1949), and reproduction and oviparity, and are con­ (b ) that it had been introduced from fined to brackish water, whereas in P. elsewhere. Bondeson & Kaiser (1949) antipodarum shell ornamentation, parthe­ have hypothesized a possible Australian nogenesis and ovoviviparity have develop­ origin on account of the close resemblance ed,probably concurrently with the invasion to the Australian species (?) P. pattisoni, of fresh water. Further divergent evolu­ and Boettger (1951) has suggested a New tion has occurred and is occurring within Zealand origin forP. jenkinsi as he con­ isolated parthenogenetic populations of sidered its shell characters identical with P. antipodarum, resulting in a high degree those of P. badia ( = P . antipodarum) from of genetic and phenotypic variability. the South Island of New Zealand. 3 316 M. WINTER BOURN

As a result of the present study on the P. antipodarum in which variable numbers New Zealand species ofPotamopyrgus, it of males occur in some populations, also is possible to make a more critical com­ exists in P. jenkinsi. The anatomy of the parison with P. jenkinsi than has been male reproductive system in the solitary possible in the past. In doing this, infor­ male P. jenkinsi was identical to that of mation contained in the literature has P. antipodarum, apart from one minor been evaluated, and in addition, living difference, the presence of a small swelling and preserved material of P. jenkinsi in the upper vas deferens, described as the from Scotland has been examined. seminal vesicle by Patil. N o such swell­ The shells of Potamopyrgus jenkinsi are ing has been found inP. antipodarum. variable in shape, size and ornamentation, Both species reproduce throughout the although not as variable as those of year, an unusual condition in freshwater P. antipodarum (T. Warwick, pers comm.), Mollusca (Fretter & Graham, 1962), and and cannot be differentiated from those although a maximum of only 35-40 of some P. antipodarum. Ornamentation embryos has been recorded in the brood is purely periostracal, and exists in many pouch of P. jenkinsi, compared with over degrees of strength, from a faint line to 100 in some individuals ofP. antipodarum. a well marked spinous keel (Warwick. this is unlikely to be of systematic signi­ 1944; Fretter & G raham , 1962). Rearing ficance. Rather, it is probably a func­ experiments (Boycott, 1929; Robson, tion of the size of the snail (and therefore 1926; Warwick, 1944), have shown that the brood pouch) as P. jenkinsi rarely as in P. antipodarum shell ornamentation exceeds about 5 mm in shell height, of progeny does not necessarily follow whereas P. antipodarum may attain a that of the parent, but despite consider­ height greater than 10 mm. able speculation the mechanism control­ Considerable variation in ecology is ling shell ornamentation remains unknown also found in the 2 species.Potamopyrgus (Warwick, 1944; 1952; Bondeson & jenkinsi was initially found in brackish Kaiser, 1949). water (1889) and has since colonized The radula of Potamopyrgus jenkinsi inland waters throughout Europe and the has been described by Woodward (1892) British Isles, first having been recorded and Krull (1935), and new material has in fresh water in England in 1893 (Flunter been examined in this study. The shape & Warwick, 1957). P. antipodarum, simi­ of the teeth, cusp formulae, radular larly, is found in fresh and brackish length, and number of rows of teeth lie water, although it is primarily a freshwater within the ranges found inP. antipodarum. species and has certainly been established Potamopyrgus jenkinsi exhibits consi­ in that environment for a much longer derable variability in colour and pigmen­ period than has P. jenkinsi. Salinity tation of the head and mantle (Robson, records and experimental work have 1920), and it cannot be separated from shown that both species possess a high P. antipodarum on this basis, or on the degree of euryhalinity and can tolerate structure of the operculum, or the form considerable and rapid changes in salinity. of the female reproductive system. Both Maximum salinities at which P. jenkinsi species are ovoviviparous, andP. jenkinsi can reproduce, 12 I8%„, (Duncan & is considered to be parthenogenetic like Klekowski, 1967) correspond closely to many populations ofP. antipodarum. A the value of 17'5’'0, obtained in this study single male of P. jenkinsi has been de­ at which normal activity ofP. antipodarum scribed by Patil (1958), and it is possible ceases and the snails withdraw into their that a situation similar to that found in shells. Both species tolerate waters with NEW ZEALAND POTAMOPYRGUS 317

high and low calcium content, and live in nccke Potamopyrgus jenkinsi (Smith), nebst a variety of still, and running water einer Angabe über ihr Auftreten im Medi­ terrangebiet. Arch. Molluskenk., 80: 57-84. habitats, on hard and soft substrates, and BONDESON, P. & KAISER, E. W., 1949, amongst vegetation. Hydrobia (Potamopyrgus) jenkinsi Smith in To conclude, no significant morpho­ Denm ark illustrated by its ecology. Oikos logical or biological differences between I: 252-281. the 2 nominal species have been found to BORAY, J. C. & McMlCHAEL, D. F., 1961, The identity of the Australian lymnaeid snail date, and the evidence available therefore host of Fasciola hepatica and its response to suggests that they are the same. How­ environment. Aust. J. mar. Freshwater Res., ever. the systematics of the Australian 12: 150 163. hydrobiids, some of which are or have BOYCOTT, A. E., 1919, Observations on the been placed inPotamopyrgus and related local variation ofClausilia bidentata. J. Conch., 16: 10-23. genera, are not clear at present and their BOYCOTT, A. E„ 1929, The inheritance of relationship to the New Zealand species ornamentation in var.aculeata of HydrobiaWr and toP. jenkinsi cannot be clarified until jenkinsi Smith. Proc. maiae. Soc. London, after comprehensive morphological and 18: 230-234. biological studies have been carried out DEGENS, E. T., 1967, Evolutionary trends in­ on them. The presence of related genera ferred from the organic tissue variation of mollusc shells. Medd. fra Dansk. Geo!. Foren- and species in Australia (Williams, 1968) ing, K

HARE. P. E. & ABELSÜN. P. H., 1965. Amino MEDCOF, J. C., 1940, On the life cycle and acid composition of some calcified proteins. other aspects of the snail, Campeloma, in the Carnegie Institution Year Book.62: 223-231. Speed River. Canad. J. Res., 18 D : 165-172. HARE. P. E. & MEENAKSHI. V. R.. 1968, MORRISON, J. P. E., 1939, Notes on the genera Organic composition of some molluscan shell Potamopyrgus and Ly rodes. Nautilus, 52: structures including periostracum.Amer. Zool., 87-88. 8: 792. MU US, B., 1963, Some Danish Hydrobiidae HEDLEY, C. & SUTER, H.. 1893, Reference with the description of a new species.Hydrobia list of the land and freshwater Mollusca of neglecta. Proc. maiae. Soc. Lon., 35: 131-138. New Zealand. Proc. Linn. Soc. New S. Wales, PATIL, A. M., 1958, The occurrence of a male (2), 7: 613 665. of the prosob ranch Potamopyrgus jenkinsi HU BEN DICK. B., 1950. The effectiveness of (Smith) var. carinata Marshall, in the Thames passive dispersal in Hydrobia jenkinsi. Zoo!. at Sonning, Berkshire. Ann. Mag. nat. Hist., Bidr., Uppsala, 28: 493 504. (13) /: 232-240. HUBEND1CK. B.. 1952. Note on genus Fluvio- PATTERSON, C. M., 1967, Chromosome num­ pnpa, with description of two new species. bers and systematics in streptoneuran snails. Occ. Pap. Bishop Mus., 20: 16. Malacologia, 5: 111-125. HUNTER. W. R., 1961. Life cycles of four fresh­ PILSBRY, H. A. & BEQUAERT, J., 1927, The water snails in limited populations in Loch aquatic molluscs of the Belgian Congo with a Lomond with a discussion of infraspecific geographical and ecological account of Congo variation. Proc. zool. Soc. London, 137: Malacology. Bull. Am. Mus. nat. Hist., 53: 135-171. 69 602. HUNTER. W. R.. 1964, Physiological aspects of PONDER, VV. F., 1966, On a subterranean snail ecology in nonmarine molluscs.In: Physiology and a tornid from New Zealand.J. maiae . o f Mollusca. 1. WILBUR. K. M. & YONGE, Soc. Aust., 10: 35 40. C. M., Ed. Academic Press. N.Y., p 83-126. PONDER, W. F., 1967, The classification of the HUNTER. W. R. & WARWICK. T., 1957, Rissoidae and Orbitestellidae with descriptions Records of Potamopyrgus jenkinsi (Smith) in of some new taxa. Trans, roy. Soc. N.Z. Zool., Scottish fresh waters over 50 years (1950 56). 9: 193-224. Proc. roy. Soc. Edinb., B.. 66: 360 373. QUIC K, H. E., 1920, Parthenogenesis in Palu­ HUTTON, F. W., 1882, On the New Zealand destrina jenkinsi from brackish water. J. Hydrobiinae. Trans. N .Z . Inst., 14 : 143 146. Conch., 16: 97. JACOB, J., 1957, Cytological studies of Melanii­ ROBERTSON, J. G., 1966, The chromosomes dae (Mollusca) with special reference to par­ of bisexual and parthenogenetic species of thenogenesis and polyploidy. 1. Oogenesis of Calligrapha (Coleoptera: Chrysomelidae) with the parthenogenetic species of Melanoides notes on sex ratio, abundance and egg number. (Prosobranchia-Gastropoda). Trans, roy. Soc. Can. J. Genet. CytoL, 8: 695-732. Edinb., 63: 341-352. ROBSON, G. C., 1920, On the anatomy of JOPE, M., 1967, The protein of brachiopod Paludestrina jenkinsi. Ann. Mag. nat. Hist., shell— 1. Amino acid composition and im­ (9)5: 425-531. plied protein taxonomy. Comp. Biochem. ROBSON, G. C., 1926, Parthenogenesis in the Physio!., 20: 593 600. mollusc Paludestrina jenkinsi. II. The genetical KRULL, H., 1935. Anatomische Untersuchungen behaviour, distribution, etc., of the keeled an einheimischen Prosobranchiern und Bei­ form (“ var. carinata"). J. exp. Biol., 3: trage zur Phylogenie der Gastropoden.Zoo!. 149-159. Jb., Anat. u. Ontog., 60: 400 464. SANDERSON, A. R., 1940, Maturation in the M ARPLES, B. J., 1962, An introduction to fresh­ parthenogenetic snail Potamopyrgus jenkinsi water Ufe in New Zealand. Whitcombe & (Smith) and in the snailPeringia ulvae { Pennant). Tombs, Christchurch. 160 p. Proc. zool. Soc. Lond., A. / 10: 11-15. MATTOX, N. T., 1938, Morphology of Cam- SIMPSON, G. G., 1961, Principles of animal peloma rufum, a parthenogenetic snail. J. taxonomy. Columbia Univ. Press, N.Y., Morph , 62 : 243 261. 247 p. M AYR, E., 1963, Animal species and evolution. STEUSLOFF, U., 1927, Die Bedeutung der Harvard University Press, Boston. 797 p. Paludestrina jenkinsi E. A. Smith für unsere MAYR, E., LINSLEY, E. G. & USINGER, Vorstellungen über Artenstehung und R. L., 1953, Methods and principles of syste­ Artverbreitung. Verh. int. Ver. Limnol., 3: matic zoology. McGraw-Hill, N.Y., 328 p. 454 459. NEW ZEALAND POTAMOPYRGUS 319

STIMPSON, W., 1865, Researches upon the rufum, a freshwater snail. Amer. Nat., 71: Hydrobiinae and allied forms. Smithsonian 167-184. Misc. Colls.. 201: 1-59. VAN DER SCHALIE, H., 1965, Observations STRUHSAKER, J. W., 1968, Selection mechan­ on the sex of Campeloma (Gastropoda: Vivi­ isms associated with intraspecific shell varia­ paridae). Occ. Pap. Mus. Zool., Univ. Mich., tion in Littorina picta (Prosobranchia: Meso­ 641. gastropoda). Evolution , 22: 459-480. VAN DER SCHALIE, H. & GETZ, L. L., 1962, SUOMALA1NEN. E., 1950. Parthenogenesis in Reproductive isolation in the snailsPoma- animals. Adv. Genet., 3: 193-253. tiopsis lapidaria and P. cincinnat¡ensis. Amer. SUOMALA1NEN, E., 1961, On morphological Midi. Nat., 68: 189-191. differences and evolution of different polyploid VAN DER SCHALIE, H. & GETZ, L. L., 1963, parthenogenetic weevil populations.Hereditas, Comparison of temperature and moisture 47: 309-341. responses of the snail generaPomatiopsis and SUOM ALAINEN, E., 1962, Significance of Oncomelania. Ecology, 44: 73-83. parthenogenesis in the evolution of insects. WARWICK, T., 1944, Inheritance of the keel in Ann. Rev. Entorno!. , 7: 349-366. Potamopyrgus jenkinsi (Smith). Nature, Lond., SUTER, H., 1905, Revision of the New Zealand 154: 798-799. species of the genusPotamopyrgus with descrip­ WARWICK, T., 1952, Strains in the mollusc tion of a new species. Trans. N.Z. Inst., Potamopyrgus jenkinsi (Smith). Nature, Lond., 37: 258 -267. 169: 551-552. SUTER, H., 1913, Manual of the New Zealand WHITE, M. J. D., 1954, Animal cytology Mollusca, with (1915) atlas o f plates. Govern­ and evolution. Cambridge University Press, ment Printers, Wellington, 1120 p. 375 p. TAYLOR, D. W., 1966, A remarkable snail fauna WILLIAMS, W. D., 1968, Australian freshwater from Coahuila, Mexico. Veliger, 9: 152-228. life. The invertebrates of Australian inland TOMLINSON, J., 1966, The advantages of waters. Sun Books, Melbourne, 262 p. hermaphroditism and parthenogenesis. J. WOODWARD. B. B., 1892, On the radula of theoret. Biol., II: 54-58. Paludestrina jenkinsi Smith, and that ofP. ven­ VAN CLEAVE, H. J. & ALTRINGER, D. A., trosa Mont. Ann. Mag. nat. Hist., (6) 9: 1937, Studies on the life cycle ofCampe loma 376-378.

RÉSUMÉ

LES ESPÈCES DE POTAMOPYRGUS DE NOUVELLE-ZÉLANDE

(Gastropoda: Hydrobiidae)

M. Winterbourn

Dans sa revision du genre, Suter (1905) reconnaît 6 espèces et 3 sousespèces de Potamopyrgus dans Its deux principales îles de Nouvelle-Zélande, mais l'élude présente a mis en évidence qu'il n'y a seulement que 3 espèces. Ce sont:P. antipodarum (Gray 1843), P. pupoides Hutton 1882 et une espèce précédemment non reconnue P. estuarinus n. sp. Potamopyrgus estuarinus et P. pupoides sont ovipares, possédant des coquilles lisses non ornementées et se confinent aux eaux saumâtres, tandis P. que antipodarum est ovovivipare, a une coquille extrêmement variable par sa taille, sa forme et son ornemen­ tation et habite aussi bien les eaux douces que saumâtres. Les populations de P. antipodarum peuvent comprendre uniquement des femelles parthénogénétiques ou contenir un pourcentage variable de mâles sexuellement fonctionnels. L'élevage de P. antipodarum au laboratoire a montié que les individus ne conservent pas forcément d'une génération à l'autre les caractères ornementaux de la coquille et que la forme et l'ornementation de la coquille ne dépendent pas à l'origine des facteurs du milieu. La coquille de P. estuarinus est indistingable de certaines coquilles deP. antipodarum, mais P. pupoides est facilement reconnaissable par sa petite çoquille pupiforme. 320 M. WINTERBOURN

La radula, l'opercule, la morphologie externe, la pigmentation du corps et l'appareil reproducteur mâle sont semblables dans toutes les espèces et n'apportent pas de caractères taxonomiques utilisables. Chez Potamopyrgus antipodarum la section inférieure de l'appareil reproducteur femelle est modifié pour former une poche incubatrice, sur le plancher de laquelle s'étend le sillon spermatique ouvert. ChezP. estuarinus et P. pupoides la partie inférieure du tractus génital est dominé par la glande nidamentaire fortement développée qui est effectivement séparée du conduit spermatique situé au-dessus.

Le nombre diploïde de chromosomes est de 24 pour les trois espèces.

La Chromatographie des protéines du périostracum de la coquille n'a pas permis de distinguer de différences significatives entre les espèces en ce qui concerne la composition en amino-acides, mais a mis en évidence de considérables variations intraspécifiques.

Potamopyrgus antipodarum est abondant dans les eaux douces permanentes de toutes sortes et a été trouvé dans une eau atteignant 26°'0 de salinité, bien que les expérimenta­ tions montrent qu'il n'est actif que dans une eau de salinité inférieure à I7,5?'0. On n'a pas établi une nette relation entre la morphologie de la coquille et le type d'habitat; P. estuarinus est surtout abondant dans les estuaires de marées où existent d'importantes fluctuations de la salinité et où beaucoup d'individus sont régulièrement exposés à l'émersion entre chaque marée. P. pupoides occupe un habitat semblable, mais nor­ malement demeure toujours immergé. Au laboratoireP. estuarinus et P. pupoides demeurent actifs à toutes les salinités, depuis l'eau douce jusqu'à l'eau de mer, mais ils n'ont pas été trouvés en eau douce dans la rature.

Des expériences de laboratoire ont montré l'existence de différence le comportement entre les espèces, qui sont en relation avec leurs différences d'habitat.Potamopyrgus estuarinus montre des tendances amphibies prononcées qui n'existent pas chezP. anti­ podarum et se révèle capable de survivre dans un état “ dormant " quand il est exposé à l'air pendant 70 jours.

Le complexe Potamopyrgus antipodarum est examiné à la lumière des conceptions actuelles sur la notion d'espèce, et le haut degré de variabilité qu'on a trouvé dans cette espèce est à mettre en relation avec l'existence de l'ovoviviparité et de la parthénogénèse qui permettent à un haut degré d'évolution divergente d'apparaître indépendamment dans des populations individuelles.

Une comparaison entrePotamopyrgus antipodarum et l'espèce européenneP. jenkinsi (Smith) montre que les deux ne peuvent être distinguées sur des bases anatomiques et que de nombreux faits de leur biologie et de leur écologie sont semblables. Il semble par conséquent probable que les deux sont la même espèce, les spécimens éuropéens ayant été introduits de Nouvelle-Zélande (ou d'Australie?) au cours du 19 eme siècle. A. L. MEW ZEALAND POTAMOPYRGUS 321

AECTPAKT

H0B03EJIAHÜCKME BHflBI POTAMOPYRGUS (GASTROPODA: HYDROBIIDAE)

M. BUHTEPBOyPH

B CBoem peBM 3MM pozia Potamopyrgus, Suter (1905) pa3JiMMaji e HeM 6 emziob m 3 no/iBMZia, oöMTaioiUHX Ha ziByx ochobhmx ocTpoBax Hoeom 3eJiaHziMM; oziHaKo b

HacTOflmeM paóoTe yKa3biBaeTCH, m o m Me e t c h jimiub TpM BMZia: P. antipodum (Gray

1843), P. pupoides (Hutton 1882) m paHee HeM3BecTHbiM bmzi-P. estuarinus n . s p .

P. estuarinus m P. pupoides OTKJiazibiBaioT HMUa, hmgíot rjiaziKyio 6e3 y3opoB pa- KOEMHy M CEH3aHbI B CBOÊM OÖMTaHMM C C OJIOHOB aTblMM BOZiaMM, B TO BpeMfl KaK

P. antipodum hbji ne tc h HMueKJiaziyiiie--:*MBopozi nmeM, cmjibho m 3 Me h mmbom no pa3Me- paM, OMepTâHMHM M OpHaMeHTaUMM paKOBMH b! M ‘i^ B eî KaK E npeCHOM BO/ie TaK M

b coJiOHOBaTow. ilonyjiflUMM P. antipodum MoryT coctohtb tojibko M3 napTeHoreHe- THMecKHX c awoK mjim coziepxraTb pa3JiMMHoe kojimMectbo ocoôeM,<î)yHKUMOHMpyKHUMX

xaK caMUbi. Pa3BezieHMe P • a n t i p o d u m b JiaöopaTopHbix ycJiOBMHx noKa3ajio, mto 3TM MOJIJIIOCKM He OÖH3aTeJlbHO ZiaiOT O pH aM e H TH pO B aH H bie paKOEMHbl M MTO (fcopMa

paKOBHHbi m ee opHaMeHT He 3aEMcht ot chaKTopoE cpe/ibi. PaK O BM H a P. e s t u a r i n u s

He OTJIMMMMa OT paKOBMH HeKOTODbîX P. antipodum, OÜHaKO P. pupoides JierKO OT- JiH q ae T C H ot hmx CBoetf Majie h bkoS paKOBMHOM. Paziyjia, KpwuieMKa, HapyxHaa Mop(J)OJio m h , nu TMeHTauHH T e jía m noJioBan cMCTeMa caMuoB cxo/iH bi y Boex bmziob

m He m Me io t TaKcoHOMMHecKoro 3 n a n e H Mh . y P. antipodum hmxhhh M ac T b xeHCKovi nOJlOBOM C M C T e Mbl MOZIHÍMUMpOBaHa B BblBOÆKOByK) Kawepy C OTKpbITbIM ‘iCeJIOÖKOM æjih cnepMbi, npoxoüHmMM no ee ziHy.

y P. estuarinus m P. pupoides hmxchhm penpoziyKTHBHbiM npoTOK m Mee t b m zi cmjibho pa3EMTOM KancyjibHOM seeJie3bi, oTziejieHHOM o t Jie*amero HMxe npoTOKa cnepMaTe-. KM. ZlMnJIOMÆHOe MMCJIO XpOMOCOM y B o e x T p e x BMÄOB paB H O 2 4 . ripM nOMOUlM MOH- Ho-oöMeHHOM xpoMaTorpadJMM öejiKOE M3 nepMocTpaKa paKOBMH bí He öbiJio ycTaHo- BJieHo p a 3 jim mm m b cocTaEe aMMHOKMCJioT y B o e x bmziob , ozi HaKo oTMenena ero BHyTpMBMZlOBâH M3 MeHMMBOCTb .

P. a n t i p o d u m M30ôMJiyeT e nocTOHHHo-npecHbix BO/iax Bcex TMnoE m ôbuiai-izie h h TaK*e npM coJieHocTM 26%, xoth oKcnepMMei'Tbi noKa3biBaKT, mto btm mojijiiockm aKTMBHbl JIM Ui b npM COJieHOCTM HM*e 17, 5%. He ÖblJIO HaMZieHG HMKâKOM H C H O M KOp- peJiHUMM Me:*;ziy MopcfcoJiorMeM paKOBMHbi m xapaKTepow mx Me c t ooôm t aHM h .

P. e s t u a r i n u s HaMÖoJiee oôMJieH b ocTyapMHX jim t opaji bhom 30Hbi, rzie h aó juc/ia-

I0TCH 3 Ha um Te Ji bHbie KOJieôaHMH coJienocTM m r/ie MHome öpioxoHorMe mojijiiockm peryjinpHo nozisep raioTCtf ocymeHMio bo e pe m h npMJiMBHo-OTJiMBHoro UMKJia.

P. pupoides 3 aHM Mae t cxoziHoe MecTooôMTaHMe, ho oômmho Bcerzia HaxoziMTCH

nozi boziom.B JiaóopaTOpñbix ycJiOBMHx P. e s t u a r i n u s m P. p u p o i d e s ocTaiOTCH aKTMB- H bí MM npM pâ3 HOM COJieHOCTM, HâMMHaH OT npeCHOM B 0/1 bí ZIO MOPCKOM, OÜHaKO B npMpozie ohm b npecHbix Eoziax uocmx nop He ECTpeuajiMCb. JlaöopaTopHbie onbiTbi yKa3biEaioT Ha cymecTBOEaHMe pa3 jimmmm b noEe/ieHMM pa3 JIM MHbIX EM/IOB, KOTOpbie CEH3aHbl C pa3JIMMMHMM B yCJlOBMHX MX OÖMTaHMH.

P. e s t u a r i n u s m Me e t hcho Ebipa^ceimyio TeH/ieH um?j k aMclMÓMOH thoc tm (nero He

HaöJiio/iaeTCH y P. a n t i p o d u m ) m MosceT Ebi^MBaTb Ha B03üyxe b "cohhom" coctohhmm b TeqeHMe 70 ü He m.

KoMnJieKc P. a n t i p o d u m Mccjie/iOB aji c h b CBeTe coBpeMeHHbix TeopMM o BM/ie;

BbicoKan cTeneHb m3 Me h mmboc tm d to to BM/ia cb H3 ana c HajiMHMeM y Hero to o t- Kjia/iKM HMU m ^Bopo'ic/ieHMH, to napToreHe3a, KOTopbie conpoBo^ziaioTCH Bbico-

KOM cTeneHbio ü m b e p re hthom obojhoumm m HaôJiio/iaeTCH He3 aBMCMMo y pa3JiMHHbix nonyjiHUMM.

CpaBHeHMe Me:*cziy P. a n t i p o d u m m eßponemckmm bmziom P. j e n k i n s i (Smith) noKa- 3blBaeT, MTO OHM He MOryT ÔbITb OTJIM MMMbI no aH a TO MM Me C KM M npM 3 HaKâM M MTO MHorMe MepTbi mx ÔMOJiorMM m oKOJiorMM cxo/iHbi. ilooTOMy KaxeTCH BnoJiHe Bepo-

HTHblM, MTO OÖa OHM HBJIHIOTCH OÜHMM M TeM X e BHUOM, nOCKOJIbKy esponeMCKMe yJIMTKM Ö bíJIM MH TpO/iy UMpOBaHbl M3 HOBOM 3eJiaH/IMM (mJIM ABCTpaJIMM? ) E XIX C TOJie TMM .

Z.A.F.