Summary:

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.

Summary:

Climate change often triggers the question if species response to a changing environment will enable them to persist. However, species and especially tightly co-evolved ones, do not exist alone and are largely dependent on interactions with others within communities. Here, we use a mechanistic approach to test the general hypothesis that interspecific differences in the response to short-term thermal changes can change the outcome of host-parasitoid behavioural interactions. We measured the effect of temperature (15, 20 and 25°C) on resting metabolic rates (RMR) of the main pest of cereal crops in Western Europe, the grain aphid host pest Sitobion avenae and its main specialist parasitic wasp, Aphidius rhopalosiphi. Also, thermal behavioural responses of host and parasitoid were measured independently and in interaction, since behavioural strategies of both species largely determine parasitism success. At high temperature parasitoids had lower oviposition efficiency and aphids expressed more defensive behaviours. This alteration in behaviour is likely due to the higher RMR of hosts than parasitoids at high temperature, suggesting RMR is a valuable proxy for predicting the direction of change in the outcome of species interactions. We proposed temperature-induced alteration of species interactions to be a mechanism through which climate change affects ecological communities. Since our findings show that relatively modest thermal changes with non-lethal effects can alter interactions in co-evolved species, ecosystem services such as biological control of pest populations, could be drastically affected.