Secondary sex traits,parasites, immunity and ejaculate quality in the Arctic charr

Ejaculate quality may limit male reproductive success. Sperm cells are immunologically perceived as non-self in the male reproductive tract and may therefore be attacked by the immune system. Males may consequently have to suppress their immune system in order to produce high-quality ejaculates. This suppression may be influenced by the current level of parasite infections, suggesting that only parasite-resistant males are able to produce high-quality ejaculates. In a study of naturally infected male Arctic charr sampled during their spawning period, we found that the density of circulating granulocytes, spleen mass and the intensity of infection by one nematode species located outside the testes were negatively associated with ejaculate quality. This suggests that a male''s extra-testicular immune environment may affect the production of high-quality ejaculates and that parasite infections located in the extra-testicular soma may influence ejaculate quality, a trait most likely under directional selection. Moreover, male fertilization potential was negatively correlated with their red spawning coloration. In conclusion, these results emphasize the importance of parasites and immunity as factors generating variability in sperm quality, suggesting that parasite resistance may be of importance for maintaining variance in reproductive success even after copulation.