Data from: The effects of parasitism on sex allocation of a hermaphroditic acorn barnacle

Sex allocation theory predicts the adaptive allocation of resources to
male versus female reproduction in simultaneous hermaphrodites in response
to individual characteristics or environmental factors. Because parasites
uptake resources from their hosts, their presence could affect the sex
allocation of the hosts. We investigated the effects of infestation status
and infestation intensity by the rhizocephalan barnacle Boschmaella
japonica on reproduction, including sex allocation, of the host intertidal
barnacle Chthamalus challengeri. Feeding activity was also examined as a
factor related to resource intake. Both male and female reproductive
investment decreased with increasing parasite infestation, and the sex
allocation of large-infested hosts was more male-biased than that of large
uninfested hosts. Moreover, in contrast to the model prediction that male
investment does not change under resource limitation, male investment
decreased in infested hosts whose resources were taken by parasites. This
reduction in male investment could be explained by changes in mating group
size since infested hosts have shorter penises and consequently can access
fewer mating partners.