Effects of Pb exposure on sperm quality and reproductive output of red-legged partridge

Abstract

Lead (Pb) poisoning by the ingestion of shot pellets, bullet fragments or fishing weights is a frequent cause of death in wild birds, but also have a wide range of sublethal effects. Here we report on the effects that a sublethal Pb exposure during the prelaying period have on the breeding performance of red-legged partridges (Alectoris rufa). We studied separately the effects of exposing males or females on egg properties, laying performance, reproductive success, levels of dietary antioxidants and carotenoid-based coloration. We also studied the effects of male exposure on sperm quality and the relationship between sperm quality, carotenoid-based ornaments and antioxidant levels. We show that the prelaying Pb exposure induced the production of heavier and larger eggs, heavier chicks and reduced hatching success when females, but not males, were exposed. Fecundation rate and other laying performance parameters were unaffected. In males, Pb exposure decreased acrosomal integrity and sperm motility, and increased sperm vigour, but did not affect sperm viability, concentration or overall progress. Moreover, clutch size was increased in pairs in which the male had been exposed to Pb in comparison to unexposed pairs. Pb exposure increased levels of circulating antioxidants in males, whereas the percentage of eye-ring area pigmented by carotenoids decreased in exposed females. Overall, the sublethal Pb doses used here did not induce spermatozoon death or infertility in males, but rather caused an increase in reproductive investment. Pb exposed females also exhibited increased investment in reproduction, laying larger and heavier eggs and chicks, but had reduced carotenoid-based coloration and hatching rate. Several sperm parameters showed positive relationships with carotenoid-based coloration and levels of antioxidants that were influenced by Pb exposure, suggesting that redder males may be more capable to preserve sperm from oxidative stress.