Abstracts (first author)
Extending sex role research to hermaphroditism: post-copulatory alteration of male and female functions via seminal fluid in a freshwater snail
There are generally two sex roles that can be expressed separately (males and females) or simultaneously (hermaphrodites). Several fundamental differences in reproduction between these two sexual systems invoke interesting questions for generalization of sex role research. For instance, in contrast to separate sexes, a hermaphrodite theoretically has the unique possibility to alter its mating partner’s male as well as female functions to its own benefit. Here, we present the first study of such mate influencing in the great pond snail Lymnaea stagnalis. Previous work has shown that proteins in the seminal fluid delay egg mass production in sperm recipients, something that also becomes apparent from multiple mating experiments. We now report that this seems to be beneficial for sperm donors, as delayed egg mass production leads to more investment per egg. In addition, we found that recently-inseminated sperm donors transfer half the amount of sperm to mating partners, which is also caused by male accessory gland products. Crucially, we reveal that, as a consequence, these donors obtain less paternity success. This decrease, which reduces the male function of recipients, would be beneficial for donors if recipients invest more in their female reproductive output in response. In other words, they seem to invest less in their ejaculate and more in their eggs. These two functions of seminal fluid in a hermaphrodite suggest their unique post-copulatory opportunities, in contrast to gonochorists. It would be interesting for future research to test if these post-copulatory effects of seminal fluid proteins alter evolutionary trajectories under various sexual selection scenarios.