Senescent males carry premutagenic lesions in sperm

As organisms age, DNA of somatic cells deteriorates, but it is believed that germ cells are protected from DNA-damaging agents. In recent years, this vision has been challenged by studies on humans indicating that genomic instability in germ cells increases with age. However, nothing is known about germ line senescence in wild animals. Here, we examine DNA damage in sperm of a wild vertebrate, the blue-footed booby Sula nebouxii. One of the major types of premutagenic DNA damage generated by oxidative stress (a proximal cause of ageing) is loss of single bases resulting in apurinic/apyrimidinic sites (AP sites). We examined AP sites in the sperm of known-age males sampled during courtship on Isla Isabel, Mexico. We show that damage to the DNA of sperm increases with age of male blue-footed boobies. Moreover, we found that sexual attractiveness (foot colour) declines with age and is correlated with germ line damage of senescent males. By choosing attractive males, females might reduce the probability of their progeny bearing damaged DNA. This study reports the first evidence of senescence in the germ line of a wild vertebrate and future studies should investigate whether this burden of senescence is sidestepped by potential sexual partners.