Sperm competition experiment with lake char (Lake Geneva 2017/18)

Male and female wild lake char (Salvelinus umbla) were sampled from Lake Geneva in December 2017 and December 2018. Male size and colouration (all samples, N = 34) were compared to milt characteristics. For the 2017 samples, milt characteristics were also determined after sperm activation in diluted ovarian fluid or water only, and the gametes were used in sperm competition trials: Equal numbers of sperm competed for fertilization in the presence or absence of ovarian fluids. The resulting embryos were raised singly in an environment that supports symbiotic microbes (sublethal stress) or in a clean environment, and microsatellite markers were used to assign in total 1,464 embryos (from 70 experimental trials) to their fathers. Overall, the sperm of more colourful males were faster and reached higher fertilization success than the sperm of pale males. These differences were enhanced by the presence of ovarian fluids. The primary sex ratio did not differ among families and was about 1:1. Female embryos hatched on average later and showed lower stress tolerance than male embryos. There were significant parental effects on offspring growth and mortality, but the sex differences in embryo performance were not family-specific. Offspring of yellow males seemed less stress-tolerant than those of pale males, and embryo development was slowed down with increasing genetic similarity between the parents.