Male inbreeding reduces fertility, but does not accelerate in vivo sperm senescence: an experimental approach in a polyandrous bird.

Inbreeding can decrease male fertility, despite sperm cells being haploid. However, to date, the role of post-meiotic sperm senescence within the female in reducing fertilization probability of sperm from inbred males is unknown. In this study, we experimentally created inbred and outbred male Japanese quail (Coturnix japonica) and let them copulate once with a female. We subsequently monitored the fertility of their eggs until the fertilization probability reached zero, after 11 days. Fertilization probability was lower for inbred males, but the decline over time did not differ from that of outbred males. Independent of inbreeding, the decline in fertilization probability accelerated over time. Hence, we provide evidence for senescence in the functionality of sperm occurring within the female, but no evidence for inbreeding effects on this functionality decline.