Assortative mating for telomere length and antioxidant capacity in barn swallows (Hirundo rustica)

The composition of breeding pairs can deviate from random, resulting in a positive association between homologous traits between mates. Assortative mating can arise either as a by-product of constraints imposed on random pairing by variation in individual life histories or because of mutual sex preferences. Because individuals that prefer high-quality mates gain fitness advantages, mate choice should result in positive assortative mating for traits that are associated with individual quality. Telomeres are nucleoprotein complexes that function to maintain chromosome integrity. Telomeres shorten at each cell division, but the rate of shortening depends on exogenous and endogenous effects, including antioxidant defense mechanisms that reduce the negative impact of pro-oxidants on telomere length. Once a critical length is attained, cells enter either senescence or apoptosis, causing a decline in tissue renewal and ultimately in individual performance. Assortative mating is therefore expected both for telomere length and for antioxidant defense because both males and females may accrue benefits from choosing a mate with long telomeres and efficient antioxidant defense. Consistent with this prediction, in the barn swallow (Hirundo rustica), we found a positive correlation between telomere length (RTL) and total antioxidant capacity (TAC) of social mates which was not the spurious result of age or breeding date. Because parents with relatively long telomeres produce offspring which also have relatively long telomeres, assortative mating seems to be adaptive. The evidence of assortative mating for telomere length and antioxidant capacity suggests that epigamic signals exist that reliably reflect these traits and may mediate mutual mating preferences. Significance statement: Telomeres protect chromosome integrity but shorten at each cell division, impairing organismal functions. Because individuals vary in telomere length and rate of shortening, as well as in antioxidant defenses reducing the negative impact of pro-oxidants on telomeres, adaptive mate choice should result in assortative mating for telomere length and antioxidants. Consistent with this prediction, in barn swallows, telomere length and antioxidant capacity were positively correlated between social mates.