Mutations in the male germ-line are common and in highly monogamous species males may benefit from selecting against own, mutated sperm. This will, in turn, reduce a male’s chance of fertilizing, but, on the other hand, prevent loss of DNA order down the family line. The importance of sperm selection by the male will be related to the intensity of sperm competition. That is, in species with high levels of sperm competition male selection against own sperm will impose high fitness costs and therefore be se lected against. Consequently, a lowered control of mutated sperm could explain the increased mutations rates - originating from the male germ-line - documented to co-occur with increased sperm competition. Identification of mutated sperm cells are most li kely conducted by the immune system, which also surveys other somatic cells, and antibody coating of sperm cells are commonly observed in male vertebrates. This project will examine the extent of immunoglobulin coating of sperm cells from males in dominan t and subordinate reproductive roles – roles experiencing different intensity of sperm competition.