Data from: Cryptic choice of conspecific sperm controlled by the impact of ovarian fluid on sperm swimming behaviour

Despite evidence that variation in male-female reproductive compatibility exists in many fertilization systems, identifying mechanisms of cryptic female choice at the gamete level has been a challenge. Here, under risks of genetic incompatibility through hybridization, we show how salmon and trout eggs promote fertilization by conspecific sperm. Using in vitro fertilization experiments that replicate the gametic micro-environment, we find complete inter-fertility between both species. However, if either species' ova were presented with equivalent numbers of both sperm types, conspecific sperm gained fertilization precedence. Surprisingly, the species' identity of the eggs did not explain this cryptic female choice, which instead was primarily controlled by conspecific ovarian fluid, a semi-viscous, protein-rich solution which bathes the eggs and is released at spawning. Video-analyses revealed that ovarian fluid doubled sperm motile lifespan, and straightened swimming trajectory, behaviours allowing chemoattraction up a concentration gradient. To confirm chemoattraction, cell migration tests through membranes containing pores that approximated to the egg micropyle showed that conspecific ovarian fluid attracted many more spermatozoa though the membrane, compared with heterospecific fluid or water. These combined findings together identify how cryptic female choice can evolve at the gamete level and promote reproductive isolation, mediated by a specific chemoattractive influence of ovarian fluid on sperm swimming behaviour.SALMON TROUT HYBRIDISATIONS SPERM SATURATED FINAL yeates et al 2013 Figure 1Data on fertilization success rates for means in first half of Figure 1Sperm competition data Figure 1 Yeates et al 2013Sperm competition success data for second half of Figure 1FERTILIZATION RATE DATA YEATES ET AL 2013 FIG 2Data for fertilization rate means in Figure 2salmon and trout male OF competition success YEATES ET AL 2013 FIG 3Sperm competition success data for Figure 3HYBRID EGG DEVELOPMENT AND EMBRYO VIABILITY RATE CHECK DATA Yeates et al 2013Embryo development data to check hybrid viability does not confound sperm competition success resultssperm trait means gage et al 2013Sperm trait data for Figure 4TRANSWELL_DATA MEANS yeates et al 2013Transwell sperm migration data raw counts Figure