Data from: 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
higher under low mating opportunities while motility increased under high
mating opportunities, and that the two behaviors were negatively
correlated with each other – i.e. there was a trade-off between them. We
also observed the behavior of a separate-sex species closely-related to O.
diadema – Ophryotrocha labronica. We found that males moved more than
females in the separate-sex species and that mothers performed more
parental care than fathers in both Ophryotrocha species. Our results
provide convincing evidence in support of a trade-off between sexual
functions and highlight the importance of investigating sex-allocation
adjustments in reproductive traits others than gametes.