The fate of received sperm in the reproductive tract of a hermaphroditic snail and its implications for fertilisation

Abstract

Multiple mating, sperm storage and internal fertilisation enhance sperm competition. The great pond snail can use stored sperm for over three months, and frequently mates with different partners. This hermaphrodite, Lymnaea stagnalis, can also selffertilise and often produces egg masses containing both selfed and outcrossed eggs. Hence, a sperm recipient may exert considerable control over paternity. Using microsatellite markers, we show that when allosperm are present, all genotyped eggs are cross-fertilised. We also find that sperm have the opportunity to compete, because double matings lead on average to equal paternity for each sperm donor. This indicates that received sperm are randomly mixed in storage. To gain further insight into the mechanisms underlying the process of sperm storage, digestion and utilisation, we investigated the fate of donated sperm at different times after copulation. We find that within 3 h after transfer most sperm have been transported into the sperm-digesting organ. Fluorescent labelling of sperm in histological sections further reveals that allosperm are not stored in the fertilisation pouch, but upstream in either the hermaphroditic duct, seminal vesicles, or ovotestis. Besides contributing to the understanding of the mechanisms underlying sperm competition and/or cryptic sperm choice, this study shows that mixed mating cannot be treated as a separate issue in hermaphroditic animals.

Social snails: the effect of social isolation on cognition is dependent on environmental context

“…The response to crowding in this species, found when individuals are exposed to live snails, but not dead shells or water containing cues from crowded animals, supports the theory that snails are socially aware of direct contact with conspecifics independent of waterborne cues (De Caigny and Lukowiak, 2008). It may be that this period of isolation, in a hermaphrodite that can store sperm from previous mating partners (Koene et al, 2009), is insufficient to alter cognitive function when calcium is not limited.…”

Sperm as a paternal investment: a model of sex allocation in sperm-digesting hermaphrodites

“…For example, sperm donors who mate with a recipient share roughly equal paternity in a snail (Koene et al 2009), as our models assume. The comparative study about the effect of usage of sperm on sexual traits is required.…”

“…Some hermaphroditic animals with internal fertilization, such as snails (e.g., Dillen et al 2009;Koene et al 2009) and flatworms (e.g., Vreys et al 1997), digest a fraction of sperm received from other individuals (Michiels 1998). A mathematical model by Greeff and Michiels (1999) suggests the counterintuitive conclusion that sperm digestion results in increased male allocation.…”

Evidence for age-dependent mating strategies in the simultaneous hermaphrodite snail,Lymnaea stagnalis(L.)

“…Lymnaea can produce offspring via self-fertilization and crossfertilization but once allosperm has been received outcrossing is favoured (Cain, 1956;Knott et al, 2003;Koene et al, 2008). Once sperm has been received most of the ejaculate is digested and only a small proportion of the sperm is stored (Geraerts and Joosse, 1984;Koene et al, 2008).…”

“…Once sperm has been received most of the ejaculate is digested and only a small proportion of the sperm is stored (Geraerts and Joosse, 1984;Koene et al, 2008). De Visser et al (De Visser et al, 1994) showed in young middle-aged Lymnaea, that half of the reproductive resources that are available are invested in the male function (copulation).…”