Abstract
Evolutionary conflicts of interest can give rise to traits advantageous for one sex but harmful to the other. This may lead to a co-evolutionary arms race where harmful traits and corresponding counter-adaptations arise. Darwin believed that such sexual conflicts, could not occur in hermaphrodites, mainly because the sexes are joined within one individual. Contrary to Darwin's conviction, recent theoretical work suggests that sexual selection can cause sexual conflict in simultaneous hermaphrodites, but there is as of yet no direct evidence that this is indeed the case. The proposed research aims at identifying the occurrence of sexual conflicts in the simultaneously hermaphroditic pond snail Lymnaea stagnalis. Furthermore, the physiological basis of sexual conflict will be investigated. Preliminary experiments suggest that both at the level of sperm survival and of resource allocation there exist conficts between the male and the female function of Lymnaea. The conflict over sperm survival is caused by sperm digestion (which is common in hermaphrodites). Therefore, it is clearly advantageous from the male point of view to prevent the digestion of donated sperm. We will investigate the occurrence of two ways in which this may be brought about: 1) increasing the amount of ejaculate without increasing the amount of sperm and 2) transferring chemicals to the female that prevent sperm digestion. The conflict over resource allocation stems from the fact that early copulation as a female causes accelerated female maturation, but retards body growth. Again this strategy is advantageous from the male point of view. However, the combination of these effects on female copulants causes a net loss of their reproductive success. We intend to study these fitness consequences by determining the effects of experimental manipulations on paternity and overall numbers of offspring. The physiological mechanisms underlying the sexual conflicts will be studied using both biochemical and electrophysiological methods. In conclusion, our aim is to provide the first direct evidence for the existence of sexual conflict in simultaneous hermaphrodites. Demonstrating sexual conflict in hermaphrodites will have important implications for the understanding of speciation, biodiversity and the evolution of bizarre hermaphroditic mating behaviours.
Netherlands