Associations between ovarian fluid and sperm swimming trajectories in marine and freshwater teleosts: a meta-analysis

Marine and freshwater spawning environments present fish sperm with unique challenges, but for both, gametes often signal prior to contact via biochemical interactions through maternally-derived compounds (i.e. eggs and ovarian fluid; OF). For example, when OF is incorporated into the fertilization environment, sperm have been observed to exhibit changes in swimming trajectories (e.g. motility and velocity), yet it remains unclear whether the presence of this OF consistently improves sperm performance. The objectives of this study were to determine the overall effect of OF on sperm performance using meta-analysis. Published literature was searched for studies comparing sperm motility and/or velocity in the presence and absence of OF. For each study, the log response ratios (lnRR) was calculated, in which positive values indicate improved performance in the presence of OF. For motility, the overall effect size was non-significant (lnRR = 0.09, CL = −0.06, 0.24), whereas velocity was positively affected by OF (lnRR = 0.10; CL = 0.04, 0.17). When segregated by environment, for freshwater species there was a significant positive effect of the OF on velocity (lnRR = 0.18, CL = 0.07, 0.29), which translated to an increase in velocity of 20%. In contrast, no effect was detected for velocity in marine species (lnRR = −0.01, CL = −0.02, 0.01). Overall, there is evidence that OF improves sperm performance, although spawning environment and/or taxonomic factors are likely to moderate these sperm-OF interactions. Together, these results further our understanding of natural reproductive processes governing sperm performance, mating systems, and fertilization dynamics