Reproductive behaviour and sex trait allocations in an external fertilizer – the Charr (Salvelinus alpinus)

Abstract

This thesis illuminates several aspects of mate choice and sexual selection in a species with external fertilization and no parental care. At a general level we have contributed to the basic framework within evolutionary biology and ecology and at a more specific level, as the proximate mechanisms controlling the associations between immune response, parasite intensities and traits indicative of sperm quality are not straightforward, we examined the effect of increased immunological activity on sperm traits. Our results have established the significance of male social status, and in the two inter-disciplinary studies, showed that parasitized and infected males seem to invest more in sperm quality, less in ornamental development and adapt to sperm competition (i.e., subordinate mating tactic). Thus, as reproductive decisions in charr seem to be strongly influenced by parasites and antigens, host parasite co-evolution may have been a significant mechanism in the maintenance and evolution of both male sexual behaviour and ornamentation.