Data for collected samples and mating experiment of Acilius Japonicus

Previous studies have predicted that antagonistic intraspecific evolution
of sexually dimorphic characters causing rapid speciation can be driven by
demographic history and environmental variations. However, researchers
have rarely examined this issue in the wild. Here, we examined
intraspecific evolution of sexually dimorphic characters and its driving
force by using a diving beetle, Acilius japonicus, which has very marked
sexually dimorphic characters. Males with wider big suction cups could
copulate with females with a higher success rate, whereas the mating
durations of females with more hairs on their pronota were shorter.
Females in a region with greater interpopulation genetic differentiation
had more pronotal hairs. Considering that a previous study showed that
less continuity among populations leads to a higher female cost of mating,
this result suggests a greater female cost of mating in this region.
Females at warmer sites also had more pronotal hairs. In light of the
increase in O2 consumption in warmer water, our result suggests that more
pronotal hairs in females at warmer sites have been maintained to prevent
prolonged underwater mating at higher O2 demand. These findings suggest
that demographic history and temperature can direct the evolution of
sexually dimorphic characters related to sexual conflict in females.