Gender-related behaviors: evidence for a trade-off between sexual functions in a hermaphrodite

According to sex allocation theory, hermaphrodites are expected to allocate most of their reproductive resources to the female function when there is a low level of mate competition and to shift them to the male function when mate competition increases: sex allocation theory assumes that there is a trade-off between sexual functions. Although several studies highlight some adjustments of sex allocation according to mating opportunities, empirical support for the trade-off between sexual functions is surprisingly scarce. Here we argue that this lack of support for a trade-off might partially depend on the fact that sex allocation studies often overlook gender-related traits other than gamete production. We investigated whether parental care (a putative female behavior) and motility (a proxy for mate searching, and a putative male behavior) varied plastically according to mating opportunities in the hermaphroditic polychaete worm Ophryotrocha diadema. We found that parental care was highe...