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

Ejaculate quality may limit male reproductive success. Sperm cells are immu nologically perceived as non-self in the male reproductive tract and may th erefore be attacked by the immune system. Males may consequently have to su ppress their immune system in order to produce high-quality ejaculates. Thi s suppression may be influenced by the current level of parasite infections , suggesting that only parasite-resistant males are able to produce high-qu ality ejaculates. In a study of naturally infected male Arctic charr sample d during their spawning period, we found that the density of circulating gr anulocytes, spleen mass and the intensity of infection by one nematode spec ies located outside the testes were negatively associated with ejaculate qu ality. This suggests that a male's extra-testicular immune environment may affect the production of high-quality ejaculates and that parasite infectio ns located in the extratesticular soma may influence ejaculate quality, a t rait 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 immunit y as factors generating variability in sperm quality, suggesting that paras ite resistance may be of importance for maintaining variance in reproductiv e success even after copulation.