Data from: Effects of ovarian fluid on sperm traits and its implications for cryptic female choice in zebrafish

In polyandrous mating systems, females maintain the opportunity to bias
male fertilization success after mating in a process known as cryptic
female choice. Mechanisms of cryptic female choice have been described
both in internal and external fertilizers, and may affect fertilization
processes at different stages before, during and after fertilization.
While in internal fertilizers, females have substantial control over sperm
storage and fertilization, in external fertilizers, female control is
limited. A key factor proposed to mediate cryptic female choice is the
fluid surrounding the eggs, the ovarian fluid, as it may directly affect
sperm performance. Here, we studied the role of ovarian fluid in
post-mating sexual selection using the zebrafish, Danio rerio. Firstly, we
assessed how ovarian fluid affects sperm swimming performance compared to
freshwater. We focussed on sperm motility, velocity, swimming trajectory
and longevity, all traits associated with competitive fertilization
success in externally fertilizing fish. In a second step, we used a North
Carolina II design to explore female, male, and female x male effects by
testing sperm motility of two males in the ovarian fluid of two females in
a total of eleven blocks. Our results suggest that the ovarian fluid
affects sperm performance differently from freshwater. Specifically, sperm
velocity, motility and longevity were higher in the ovarian fluid than in
freshwater, whereas sperm linearity and beat cross frequency showed the
opposite pattern. Moreover, these effects varied according to male and
female identities, supporting the potential for cryptic female choice
mediated by ovarian fluid in this species.