The effect of mating on female reproduction across hermaphroditic freshwater snails

Abstract

Sexual conflicts often arise between mating partners because each sex tries to maximize its own reproductive success. One major male strategy to influence a partner's resource allocation is the transfer of accessory gland proteins. This has been shown to occur in simultaneous hermaphrodites as well as in organisms with separate sexes. Although accessory gland proteins affect the investment of resources in both male and female function, we here specifically focus on female investment. In the great pond snail, Lymnaea stagnalis, previous studies found that the accessory gland protein ovipostatin reduced female fecundity by suppressing egg laying in the partner in the short term (days). To investigate whether this reduction in egg laying is a commonly found effect of mating in freshwater snails, we compared egg output for evidence of suppression in isolated and paired snails of eight pulmonate species. Furthermore, we determined whether the suppression of egg laying caused a shift in resource allocation to the eggs. We found that in five of the eight species egg laying was suppressed, with fewer and lighter egg masses being laid when they had access to a mating partner. In mated pairs of L. stagnalis and Biomphalaria alexandrina, allocation of resources to the eggs was altered in opposite ways: individuals of L. stagnalis laid fewer but larger and heavier eggs; individuals of B. alexandrina laid smaller and lighter eggs, with no change in egg numbers. Such changes in the female function are most likely the result of combined effects of receiving accessory gland proteins, and the cost of mating in both male and female roles. Thus, effects of the maternal environment, including the receipt of accessory gland proteins, on offspring investment are not restricted to species with separate sexes.

Divergence of seminal fluid gene expression and function among natural snail populations

“…Furthermore, the snails injected with seminal fluid from DE and F2 laid smaller eggs (Table 1, Figure 3b). In this assay, we did not detect an increase in egg size of the focal snails injected with seminal fluid from the laboratory strain, although this was expected based on indirect evidence from a previous study (Figure 3b, Swart et al., 2020). The R 2 value indicated that the fixed factor Population explained most variance in egg number, and also explained an approximately equal amount of variance in egg size, as did the random factor, Family (Table 1).…”

“…We next conducted a bioassay to characterize variation in SFP functions among field populations. In brief, we intravaginally injected seminal fluids of selected families into standardized focal snails, and then assessed the reproductive performance of focals, in terms of both egg production and sperm transfer in subsequent matings, as reported in previous studies (Koene et al., 2010; Nakadera et al., 2014; Swart et al., 2020).…”

“…Based on the counts from 5 µl subsamples taken four times per replicate on an Improved Neubauer counting chamber, we estimated the number of sperm in the original solution. To quantify egg production, we digitally scanned egg masses of focal snails deposited two and four days after artificial injection (Van Iersel et al., 2014; Swart et al., 2020). Briefly, we scanned the egg masses using a flatbed scanner (CanoScan LiDE 700F Scanner), and based on these images, we manually counted the number of eggs and measured egg sizes using ImageJ.…”

“…Second, it has been documented that SFPs in L. stagnalis have important functions in reproduction, affecting both egg production and subsequent sperm transfer of mating partners: receiving the SFP LyAcp10 is known to delay egg laying (Koene et al., 2010), whereas two other SFPs, LyAcp5 and LyAcp8b, mediate a reduction in sperm transfer by recipient snails in their subsequent mating in the male role (Nakadera et al., 2014). Receiving seminal fluid is also suggested to increase egg size (Swart et al., 2020). Thirdly, we have an established SFP bioassay based on intravaginally injecting seminal fluid in L. stagnalis (Koene, Hoffer, & Brouwer, 2009; Koene et al., 2010; Nakadera et al., 2014).…”

Estado atual de conhecimento das principais características dos Moluscos / Current state of knowledge of the main characteristics of mollusks

“…O tamanho varia de 5 mm (Physidae) a 33,5cm de comprimento na espécie Triplofusus giganteus (Kiener, 1840) (TAYLOR, 2003;LYONS;LEE, 2018). A reprodução da classe é diversificada, mas normalmente são dioicos, ocorrendo hermafroditas (CASPERS, 1980;SCHÄRER;ARNQVIST, 2012;SWART et al, 2020).…”