Pre- and post-mating selection on male capelin

Abstract

All animals, as sexual eukaryotes, undergo a biphasic lifecycle characterized by alternation between haploid and diploid phases, wherein selection occurs in both pre- and post-mating stages. The first research chapter investigated male capelin reproductive potential through semen assessment during the spawning season, aiming to test the hypothesis that male-biased body size dimorphism results from endurance rivalry, which is a form of pre-mating selection. Findings revealed that a majority of capelin exhibited abundant semen during the spawning season. Capelin demonstrated the ability to regenerate semen within two days and did not show a decline in gamete ability for fertilization during six days of captivity. This continuous readiness for mating by maintaining semen supports the hypothesis of male-biased sexual dimorphism attributed to endurance rivalry. The second research chapter examined the effects of postejaculation pre-fertilization sperm experiences (environmental conditions) on embryo development and, if adaptive, its potential underlying mechanisms. Capelin sperm and embryos are sensitive to salinity and represent a good system for investigating this phenomenon. Contrary to prior research findings in other fish species, this study found that post-ejaculation semen salinity experiences had no effect on embryo development. Further investigations are warranted to elucidate the mechanisms and factors influencing the mating readiness and reproductive resilience of male capelin, as well as to determine whether capelin sperm experiences beyond salinity exposure exert an influence on offspring development.