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European Arachnology 2000 (S. Toft & N. Scharff eds.), pp. 145-156. © Aarhus University Press, Aarhus, 2002. ISBN 87 7934 001 6 (Proceedings of the 19th European Colloquium of Arachnology, Århus 17-22 July 2000)

Female genital morphology and sperm priority patterns in (Araneae)

GABRIELE UHL University of Bonn, Institute of Zoology, Department of Ethology, Kirschallee 1, D- 53115 Bonn, Germany ([email protected])

Abstract For spiders, gross female spermathecal morphology has been widely used as the major predictor of sperm priority pattern depending either upon taxonomic classification or on the number of ducts that connect with the spermathecae. In order to establish whether, or to what degree, the female reproductive tract follows a cul-de-sac (one duct connects to the spermatheca) or a conduit design (two ducts connect to the spermatheca at opposite ends) I present information on genital mor- phology of two haplogyne ( phalangioides, ; erythrina, ) and two entelegyne species (Nephila clavipes, Tetragnathidae; Pityohyphantes phrygianus, ). Predictions based on female anatomy and copulatory mechanisms are compared to available data on sperm utilization patterns. Female genital anatomy deviates markedly from the expected pattern in all cases. There are more than the two predicted types of sperm storage sites: sperm can either be stored in the bursa, or in spermathecae connected by two ducts that lie close together, or in multiple sperm stores of different morphology. If males are able to insert their genital structures as far as to the lumen of the female sperm storage organ, male manipulation of sperm masses stored from previ- ous males are possible and changes in sperm priority patterns can be expected. Combined infor- mation on detailed female anatomy and copulatory mechanism do not suffice to make reliable pre- dictions on the pattern of sperm priority. Possible reasons for this discrepancy are briefly outlined.

Key words: Sexual selection, sperm storage, female choice.

INTRODUCTION that depends on the relative number of sperm Female spiders show a propensity to mate with stored from each male. On the other hand, non- more than one male (Austad 1984; Elgar 1998), random utilization of sperm from a particular and maintain sperm for long periods in their male is termed sperm precedence or priority, sperm-storage organs (e.g. Uhl 1993a). More- and is generally seen as a consequence of over, male spiders are unable to monopolize sperm stratification within the sperm storage access to a female for the duration of her repro- organ of the female (Austad 1984; Elgar 1998; ductive life, mainly because life expectancy for see Simmons & Siva-Jothy 1998 for definitions). males is usually shorter than for females (Elgar Sperm from different males may remain strati- 1998). Sperm from one of several males may be fied within the spermathecae either because utilized randomly as sperm mix in the sper- sperm are non-motile, or are transferred or mathecae leading to similar fertilization success stored in distinctive portions, thus leading to a of successive males or to fertilization success positional advantage. Whether the first or the 146 European Arachnology 2000 last male to mate sires most of the offspring may thus purely depend on the position of the sperm mass within the female sperm storage organ. The commonly accepted hypothesis on sperm precedence patterns in spiders relies on the fact that the sperm masses are stratified within the female genital tract (Austad 1984). Austad proposed that spermathecal morphology may represent a phylogenetic con- straint which would lead to a non-adaptive pattern of sperm priority (Fig. 1). The term Fig. 1. The original hypothesis by Austad (1984) proposed a phyletic limitation to sperm precedence ‘non-adaptive’ in this context probably meant patterns in spiders. The ‘taxon independent’ hy- that adaptation was not recent but related back pothesis only assumes a connection between the to an ancestral stage. Spiders (Araneoclada) are number of ducts that connect to the spermathecae classified into two groups, the and and P2 values. the (Coddington & Levi 1991). Formerly, spiders were said to exhibit a funda- female genital morphology determines sperm mental dichotomy in the female spermathecal priority patterns, and sperm stratification oc- morphology that divides along phylogenetic curred, species with one or two ducts that con- lines with the Haplogynae possessing one duct nect with the spermathecae should exhibit dis- and the Entelegynae possessing two ducts that tinctly different sperm priority patterns (Fig. 1). connect with the spermathecae. If this were I will use the terms haplogyne genitalia or hap- consistently so, the hypothesis that the two logyne condition for species with one duct and groups have distinctly different sperm priority entelegyne genitalia or entelegyne condition patterns would be based on a firm morphologi- for species with two ducts, irrespective of taxo- cal basis. However, in a number of genera nomic classification. Thus a spider, classified as within the entelegyne families Uloboridae, Tet- belonging to the Haplogynae can exhibit fe- ragnathidae, and the superfamily male genital morphology of the entelegyne Palpimanoidea reversal to the haplogyne con- condition as in the case of the two Pholcid spe- dition with only a single spermathecal duct cies mentioned earlier. occurred (see Coddington & Levi 1991, and Sperm of haplogyne species passes along even Austad himself 1984). Likewise, within the single duct during copulation and again the haplogyne Pholcidae, there are at least two outward at oviposition (Fig. 2a). Austad (1984) species in which two ducts have evolved inde- termed this design, that is very similar to that pendently (Huber 1996). The idea that Hap- in many (Walker 1980), ‘cul-de- logynae und Entelegynae each have uniform sac’ (dead end). The entelegyne condition, on female genital morphology is thus not sup- the other hand, was termed ‘conduit’ situation ported. As a consequence, inferring distinctly (one-way) and consists of a copulatory duct different sperm precedence patterns for taxa of that leads to the spermatheca and a fertilization the two groups is untenable. duct through which sperm reaches the eggs for To examine the hypothesis that sperm pri- fertilization (Fig. 2b). Predictions about sperm ority patterns depend on the morphology of priority are that species with dead-end sper- female genitalia independent of phylogenetic mathecae should exhibit last male sperm prior- position seems to be a more rewarding task. In ity as the last sperm to enter should lie closest Austad´s paper, this hypothesis is mixed with to the single duct. This would represent a ‘last the previous one on phylogenetic constraints. If in - first out’ system. On the other hand, species Uhl: Spider genitalia and sperm priority 147

gree, it follows a cul-de-sac or conduit design. I therefore present detailed genital morphology for two haplogyne (Pholcus phalangioides (Fuesslin 1775) Pholcidae; (Walckenaer, 1802), Dysderidae) and two entel- egyne species (Nephila edulis (Labillardière, 1799), Tetragnathidae; Pityohyphantes phry- gianus (C.L. Koch, 1836), Linyphiidae). For each species, I further present information on copu- latory mechanisms. Possible access of male genitalia to the sperm storage site inside the female is crucial to the possibility that males physically manipulate sperm priority patterns. I also summarize published studies to check the predictions based on genital morphology and copulatory mechanism against paternity patterns. Fig. 2. Hypothetical sperm stratification inside the Apart from physical male manipulation of spermatheca of (a) spider with haplogyne genitalia stored sperm masses there are numerous other, and (b) spider with entelegyne genitalia and conse- more cryptic possible mechanisms, e.g. chemical quences of sperm priority patterns. S1: sperm from manipulation. Products of the male reproduc- first male, S2: sperm from second male. tive organs that are transferred during copula- tion often induce female resistance to further with one-way spermathecae are predicted to mating, earlier oviposition, and even sperm exhibit first male sperm priority, because the transport (Eberhard 1997). On the other hand, first sperm to enter should be closest to the fer- female behavioural, morphological or physio- tilization duct and be the first to exit (first in - logical mechanisms that occur during or after first out). The priority pattern should have im- copulation were shown to impose a bias on plications for the mating strategy: species of the male reproductive success (Eberhard 1996). Al- haplogyne condition should tend to guard though cryptic processes can be expected to play mates just before egg laying, whereas species of an important role, I will restrict this paper the entelegyne condition should tend to guard mainly to the question of whether female genital penultimate females (see Elgar 1998). morphology and copulatory mechanism allow Sperm utilization by females after multiple predictions on the pattern of sperm priority. copulations is expressed as the proportion of offspring fathered by the last male to mate. In a Pholcus phalangioides typical experimental double-mating trial this is The cellar spider P. phalangioides has only one the proportion of eggs sired by the second male genital opening through which copulation and to mate, P2 (Boormann & Parker 1976). Sperm egg laying are achieved as in typical haplogyne mixing is expected to lead to P2 values around spiders. However, there are no spatially sepa- 50% whereas sperm precedence of the first or rated sperm storage organs of the cul-de-sac second male leads to low or high P2 values. type (Fig. 3a). Sperm is stored in the bursa it- In order to test whether female genital mor- self, and is embedded in a secretion produced phology allows predictions on sperm priority by the female before copulation (Uhl 1994a). patterns, the anatomy of the female reproduc- Complicated glands produce this matrix, and tive tract needs to be examined in detail, possibly also cause sperm activation (Uhl thereby establishing whether, or to what de- 1994b). What was formerly described as sper- 148 European Arachnology 2000

Fig. 3. Schematic presentation a b of female genital anatomy and place of sperm storage in (a) Pholcus phalangioides (Pholcidae), (b) Dysdera erythrina (Dys- SP deridae) (c) Nephila edulis (Tetragnathidae) and (d) Pityohy- phantes phrygianus (Linyphiidae). UE CD: copulatory duct, CF: copu- PD latory fold, FD: fertilization duct, FF: fertilization fold, GO: genital opening, PD: posterior diver- ticulum, SP: spermatheca, UE: GO GO uterus eternus (= bursa). Dot- ted lines indicate the existence of folds instead of ducts. Shaded areas indicate places of sperm storage. c d SP1

SP SP2

FD CF FF CD GO GO mathecae by Wiehle (1933) only rarely contains findings: if female genital morphology played a few sperm. This structure was shown to have the most important role, sperm mixing should a different function: it is a fold connected to occur and P2 should vary around 50%, whereas muscles that serves to open the genital valve sperm displacement via movement before egg laying (Uhl 1994a). Overall, genital would predict a last male advantage. Investiga- morphology in P. phalangioides deviates mark- tions on sperm priority in the cellar spider edly from the expected pattern. showed a mean P2 value of 66% for first broods During copulation, several parts of the male of seven females (Yoward 1998, Tab. 1), despite pedipalp are inserted into the female: the pro- a much shorter copulation duration in second cursus, the embolus, the appendix (a coupling matings compared to first ones (Uhl 1993b; structure) and the uncus (Uhl et al. 1995). The Yoward 1998). The analysis of a larger sample embolus is inserted directly into the female se- size of 47 first broods showed high mean pater- cretion where the sperm are stored and semi- nity value of 78% for second males (Schäfer & thin sections from twice mated females showed Uhl 2002). However, both investigations dem- no obvious stratification of sperm masses (Uhl onstrate highly variable paternity values (Tab. 1994a). The male performs rhythmic twisting 1). The number of pedipalp movements a male movements with the simultaneously inserted performs during copulation is a good predictor during copulation, which result in of his fertilization success (Schäfer & Uhl 2002). extrusion of sperm near the centre of the female Thus, the number of movements very likely genital opening (Uhl et al. 1995). influences the degree of displacement of previ- Two different predictions arise from these ous male´s sperm in second matings. Uhl: Spider genitalia and sperm priority 149

Table 1. Compilation of data available both on sperm priority and genital mechanisms in spiders. a : calculated from Yoward´s data for first broods to allow comparison between species b : note that mean P2 values did not meet assumptions of normality.

P2 in % Genital Male Predictions Source mechanism manipulation possible ? Species (n) Mean Range median known? possible? (sd)(se) Haplogyne genital structure

Bursal storage

Pholcus phalangioides (7) 0.66 a 0.39-1.00 0.66 yes yes yes Yoward 1996; Uhl et (0.22) al. 1995 (47) 0.78 0.00-1.00 0.89 Schäfer & Uhl 2002. (0.25) pluchei (40) 0.74 b 0.09-1.00 ? yes yes yes Kaster & Jakob 1997; (0.04) Huber 1995 Physocyclus globosus (12) 0.38 0.00-1.00 0.44 yes yes no Eberhard et al. 1993; (0.30) Huber & Eberhard 1997 Cul-de-sac

Tetragnatha extensa (7) ~ 0.70 (0.36) ? ~ yes no access yes West & Toft 1999

Entelegyne genital structure „Cul-de-sac“ type

Nephila clavipes (63) 0.18 0.00-1.00 0.02 ~ yes yes no Christenson & Cohn (0.32) 1988 Nephila edulis (8) 0.66 (0.56) 0.83 yes yes yes Schneider et al. 2000; Uhl & Vollrath 1998 Nephila plumipes (33) 0.46 (0.05) 0.42 ~ yes yes no Schneider & Elgar 2001 Latrodectus hasselti (11) 0.56 0.00-1.00 ~ yes yes ~yes Andrade 1996; see text for morphological data on various species

Sperm extrusion was also found for another ent male and female mechanisms that may bias pholcid spider, Physocyclus globosus (Tacza- paternity. Further investigations are needed nowski, 1874) (Huber & Eberhard 1997). Sperm that examine whether and to what extend a masses only emerged in copulations with non- male removes his own sperm relative to his virgin females, they appeared gradually rather rival´s sperm. Also, sperm transfer may not be than in step with male pedipalp movements a time dependent process as is often assumed: and continued to emerge after copulation it may either relate to pedipalp movements or ended. Double mating experiments revealed a to copulation duration. For P. phalangioides pre- mean P2 of 38% (Eberhard et al. 1993; Tab.1). liminary results suggest the former mechanism Copulation durations in virgin versus mated (Uhl, unpublished). In fact, time independent females are not nearly as different as in P. pha- sperm transfer was found in Frontinella commu- langioides (Huber & Eberhard 1997; Uhl 1993b). nis (Hentz, 1850) (Austad 1982, syn. F. In P. phalangioides, sperm extrusion can also pyramitela) and Micrathena gracilis (Walckenaer, occur in copulations with virgin females, extru- 1805) (Bukowski & Christenson 1997). Both sion seems to appear in step with male move- studies investigated sperm release from the ments and does not continue after copulation. male palp by interrupting copulations and Apparently, closely related species with similar counting the remaining number of sperm in the genital morphology have evolved very differ- palp. Other studies that suggest that sperm 150 European Arachnology 2000 transfer were time related actually investigated stored sperm. Multiple organs may further fa- sperm uptake and storage by the female, not cilitate specialization in short-term and long- sperm release. However, these may be dis- term sperm storage as occurs in Drosophila tinctly separate processes that are often con- (Pitnick et al. 1999). To date, there is no infor- founded (Bukowski & Christenson 1997). mation on sperm priority pattern in D. Data on sperm priority and copulatory erythrina. mechanism exists for yet another Pholcid spi- der, (Scopoli, 1763). High Nephila edulis last male sperm precedence in this species Because N. edulis is an entelegyne spider, we (Kaster & Jakob 1997) may also be a result of would expect to find two ducts that connect on male manipulation, as male genitalia reach the opposite sides of the spermathecae to form a place of sperm storage (Huber 1995). one-way system. Female genital morphology in N. edulis does possess two ducts (in and out) Dysdera erythrina connected to each of the two spermatheca, but, Semi-thin sections show that two structures the details of the connections to the spermathe- function as sperm storage organs in D. cae differ from the assumptions made by the erythrina: the so-called posterior diverticulum Austad hypothesis. The ducts are close to- (PD), a large dilatation of the genital cavity gether and the reproductive tract looks more similar to the structure found in Pholcus phalan- like a cul-de-sac than a conduit (Fig. 3c). The gioides, and a bilobed anterior spermatheca spermatheca lacks a septum that would create (Fig. 3b; Cooke 1966; Schult 1980; Uhl 2000). the equivalent of a one-way system inside of Thus, genital morphology deviates strongly the spermathecal lumen. Based on female mor- from the presumed haplogyne pattern. Both phology alone, the sperm from the last male structures are equipped with glandular tissue should be closer to the fertilisation duct, and but the glandular tissue of the two is markedly last male sperm priority should prevail. The different. The glandular tissue of the sper- male pedipalp in N. edulis consists of a compact matheca is composed of complicated glandular genital bulb provided with a long conductor units around cuticular ductules, whereas the that supports the sperm transferring structure, glandular tissue of the posterior diverticulum the embolus (Uhl & Vollrath 1998). The embo- is composed of rather simple gland cells (Uhl lus is rolled up inside the bulb and can be 2000). The products presumably differ, leading pushed out of the tip of the conductor. During to possibly different storage conditions for the copulation, the embolus reaches the lumen of spermatozoa. Encapsulated spermatozoa are the spermathecae (Uhl & Vollrath 1998) which found in each lobe of the spermatheca. Sperm makes stratification unlikely and speaks in seems to be packed much tighter in the sper- favour of sperm mixing. Male manipulation of mathecae than in the posterior diverticulum. previous males’ sperm, also seems possible. The male pedipalp in D. erythrina is a sim- An investigation on sperm priority in N. ple, blunt tipped structure, and thus probably edulis shows a mean P2 value of 66% (median reaches only as far as the posterior diverticu- 83%) based on 8 matings (Schneider et al. 2000) lum (PD). Due to its size, it is highly unlikely (Tab. 1), which tentatively suggests that sperm that it enters the duct to the bilobed sper- manipulation by subsequent males is possible. matheca. Thus, male manipulation is only pos- On the other hand, in N. edulis duration and sible for the PD, not for the spermatheca and it frequency of copulation is a very good predic- is tempting to suggest that the two types of tor of paternity independent of mating order, sperm storage organs have evolved to allow (in which suggests that sperm are utilized accord- the case of the PD) or prevent (in the case of the ing to relative numbers. As mentioned above, spermatheca) males from accessing previously caution has to be applied when assuming grad- Uhl: Spider genitalia and sperm priority 151 ual sperm transfer on the basis of a correlation seems that males adapt their genital size to that between copulation duration and sperm utili- appropriate to the most common female size. zation. In N. clavipes (Linnaeus, 1767) this corre- As a consequence of this finding, it might lation was found although sperm transfer oc- be expected that copulatory mechanisms for curs during the first of many insertion bouts (T. males of different sizes should be similar. How- E. Christenson pers. comm.). In N. clavipes clear ever, the study by Schneider et al. (2000) first male advantage was demonstrated (mean showed that small males had a mating advan- P2 value: 18%) (Christenson & Cohn 1988). Be- tage, they mated for longer and fertilized more sides possible male manipulation an alternative eggs than large males. explanation for the priority pattern would be that significantly different sperm numbers are Pityohyphantes phrygianus taken up by the female depending on the mat- We might expect linyphiids to represent ing order (T.E. Christenson pers. comm.). In- ‘proper’ conduit type spiders, as the linyphiid vestigations on sperm release and uptake by Frontinella communis exhibits clear first male Cohn (1988) point in this direction. In N. sperm priority with little variation in P2 plumipes (Latreille, 1804) equal sperm numbers (Austad 1982). seem to mix in the female spermatheca (mean The epigynum of P. phrygianus has a scape, P2: 46%, Schneider & Elgar 2001, Tab. 1). Al- with an atrium on both sides. There are two though female and male morphology appears spermathecae on each side, one is straight and to be very similar in the three Nephila species, thumb-like (spI) and the other is twisted (spII) transfer, storage and ultization mechanisms and surrounds the straight one half way (Fig. seem to be quite different. Clearly, further in- 3d). Both spermathecae extend from a massive vestigations are needed. U-shaped structure. As in D. erythrina, the com- Due to extreme intraspecific male size vari- position of the associated glands differs be- ability in Nephila (Vollrath 1980), one might tween spermathecae, as only the twisted sper- expect small males to be at a disadvantage if it mathecae exhibit a strip of glandular ductules. comes to copulatory mechanisms and sperm The internal characteristics are quite compli- transfer. Size variability could lead to different cated: a fold rather than a tube functions as a degrees of mating efficiency and fertilization copulatory ‘duct’, leading to the spermathecae success for males of different sizes. However, (Uhl & Gunnarsson 2001). This copulatory fold in N. edulis genital characters show negative is ‘sealed’ after copulation with a homogeneous allometric values when plotted against somatic secretion, probably to impair copulatory suc- characters, which means that small males have cess of subsequent males. At the base of the relatively large genitalia and large males rela- spermathecae there is a valve-like structure tively small genitalia (Uhl & Vollrath 2000). that makes intromission of male genital struc- Although male somatic size has a coefficient of ture unlikely. Surprisingly, a fertilisation duct variation of about 45%, genital variability is does not exist in P. phrygianus (Uhl & Gunnars- only 20% (p < 0.01, Lewontin’s method 1966). son 2001). A fold extends from the base of the Mean values of male and female genitalic char- spermathecae laterally along the ventral wall acters match surprisingly well: embolus length towards the opening of the atrium. From there, minus conductor length in the male has a mean it turns into the epigastric fold leading towards of 1.3 mm while mean copulatory duct length the gonoduct. This fold is the only connection in the female is 1.28 mm (Uhl & Vollrath 2000). between the spermathecae and the oviduct. There seem to be strong selective advantages Such folds have also been found in other Liny- leading towards intermediate, standardized phiids, including Lepthyphantes (Saaristo & sizes of male genitalia as in many other species Tanasevitch 1996) and Batyphantes gracilis of insects and spiders (Eberhard et al. 1998). It (Blackwall, 1841) (M. Saaristo pers. comm.). 152 European Arachnology 2000

Histological sections depicted by Engelhardt first chamber and may thus be able to manipu- (1910) on Linyphia triangularis (Clerck, 1757) late stored sperm. also point in this direction (but see van Hels- In the entelegyne genus Latrodectus dingen 1969). (Theridiidae), genital morphology of both sexes In P. phrygianus, various apical parts of the does not vary considerably between species. male palp (the ‘embolic division’ sensu Merrett The two spermathecae are heavily sclerotized, 1963) probably couple to the knob of the u- dumb-bell shaped structures with anterior and shaped base, an interpretation derived from the posterior lobes. These lobes are connected by position of the mating plug. If this is the case, an intermediate, more slender part. In some males are not expected to be able to physically species like in L. hesperus Chamberlin & Ivie, manipulate stored sperm masses directly. The 1935, the spermathecae are of the functional predicted sperm priority pattern based on female cul-de-sac type with copulatory and fertiliza- genital morphology is last male priority against tion duct close together (Bhatnagar & Rempel which the production of a mating plug evolved. 1962, misidentified as L. curacaviensis), whereas in other species (e.g. L. hystrix Simon, 1890; L. Other species geometricus C.L. Koch, 1841; L. cinctus Black- Investigations on sperm priority patterns are wall, 1865; L. renivulvatus Dahl, 1902: Knoflach generally rare for spiders, and information on & van Harten 2002; L. revivensis: Berendonck & genital morphology and copulatory mechanism Greven 2002) the ducts are further apart. At the for these species is often unavailable. However, end of copulation, the tip of the embolus typi- there is some information on both aspects for cally breaks off and remains either in the nar- Tetragnathidae and Theridiidae. Published row entrance of the spermatheca, as for exam- data on sperm priority are summarized in El- ple in L. dahli Levi, 1959, or is deeply inserted gar (1998) and Uhl & Vollrath (1998). in the lumen of the spermatheca (L. geometricus) The Tetragnathinae is an entelegyne spider (Knoflach & Van Harten 2002). The broken em- subfamily, in which female genitalia of the hap- bolus tips do not necessarily prevent the female logyne condition occur. West & Toft (1999) from remating, but in the case of L. renivulva- found that the last male fertilized about 70% of tus, in which whole emboli may break and plug the eggs in first egg sacs of extensa the copulatory ducts (Knoflach & van Harten (Linnaeus, 1758) (Tab.1). From what is known 2002) successful remating seems impossible. In about male and female genital morphology of L. dahli and L. geometricus Knoflach & van Tetragnatha species it is questionable whether Harten report cases in which two tips were the male pedipalp has access to the spermathe- found in one spermathecal entrance. For the cae (e.g. Wiehle 1963; Uhl et al. 1992), which latter species Müller (1985) detected four tips in would lead to the prediction of last male sperm the spermatheca and one in the bursa. In L. hes- priority as was found for T. extensa. However, perus and L. revivensis, however, only a single in a drawing of genitalia of T. montana Simon, tip was found in each spermathecal entrance, 1900 in functional contact, it seems as if the em- whereas several more could be found in the boli were inserted into the spermathecae bursa (Bhatnagar & Rempel 1962; Berendonck (Huber & Senglet 1997). Unfortunately, female & Greven 2002). The data from L. hesperus, L. genitalia are not fully depicted which reviviensis and L. renivulvatus suggest that suc- copulatory mechanism obscure. The tetrag- cessful intromission of palps is only possible nathid Leucauge mariana (Keyserling, 1881), on once for each spermatheca. If a male is allowed the other hand, possesses a conduit design with to inseminate only one spermatheca but not the three successive sperm storage chambers other, an additional copulation with another (Eberhard & Huber 1998). Moreover, the male male may occur, which will lead to sperm of embolus may reach as far as to the lumen of the different males being stored in different storage Uhl: Spider genitalia and sperm priority 153 organs. The only information on sperm priority CONCLUSION we have to date is from a study on yet another Each of the four spiders investigated deviates species, L. hasselti Thorell, 1870, in which sperm considerably from the assumptions underlying mixing with considerable variation occurs the modified Austad´s hypothesis. Obviously, (Andrade 1996). It remains to be clarified female genital morphology is extremely variable whether mixed paternity in L. hasselti results even within families. Data on morphology and from sperm mixing in a given spermathecae or sperm usage show that sperm precedence pat- from activation of sperm stored in different terns cannot be predicted by the number of spermathecae. The latter situation may explain ducts connected to a spermatheca. Even if spe- why some males have no paternity success cies are classified according to their specific de- whereas others fertilize 100% of the eggs. sign of female genital morphology, independent of their phylogenetic position, and even if Is sperm stratification a plausible assump- knowledge on copulatory mechanisms is in- tion? cluded, predictions on sperm precedence pat- In the testis, male spiders produce encapsu- terns are difficult to make. Unfortunately, there lated spermatozoa. These remain encapsulated is only little information on detailed genital during sperm induction into the male pedipalp morphology, copulatory mechanisms and P2 and are transferred in an encapsulated state to values for single spider species which would the female (Alberti 1990). Whereas in Leucauge help to clarify the matter. Beyond morphology, mariana (Eberhard & Huber 1998) sperm activa- manifold processes of male and female manipu- tion (better: decapsulation) within the female lation, male and female age, remating intervals occurs soon after insemination, sperm are and body size may influence sperm transfer, stored in an inactive state in Pholcus phalan- storage and usage. Adaptation, not constraints gioides, probably until shortly before egg laying seems to play the major role in shaping sperm (Uhl 1994a). Both studies investigated the con- priority patterns. Thus, researchers should re- ditions of sperm in situ, in the female sperm frain from assuming particular precedence pat- storage organ. A study on Nephila clavipes terns solely on the basis of either taxonomic clas- (Brown 1985) demonstrated that decapsulation sification or the number of ducts present. took 7 to 18 days from mating, depending on whether the female had moulted the same day ACKNOWLEDGEMENTS or mated later in adulthood. Brown squeezed I cordially thank Søren Toft and Nikolaj Scharff the spermathecal content onto a slide contain- for inviting me to give this talk at the 19th Euro- ing physiological saline, which may have influ- pean Colloquium of Arachnology in Århus. enced the results as sperm become active when William Eberhard, Jutta Schneider, Tina Beren- transferred to physiological saline. It should be donck, Barbara Knoflach-Thaler, Michael noted that decapsulated sperm do not necessar- Schmitt and an anonymous referee gave valu- ily move in the female genital tract as it may able comments on a previous draft of the require additional stimuli for sperm to become manuscript. I am especially grateful to Bill mobile. These findings show that although Eberhard, whose thorough comments helped to sperm stratification may occur in some taxa it is substantially improve this paper. not a general characteristic of spiders. 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