Longer telomeres during early life predict higher lifetime fitness in females but not males

The mechanisms that contribute to variation in lifetime reproductive success are not well understood. One possibility is that telomeres, conserved DNA sequences at chromosome ends that often shorten with age and stress exposures, may reflect differences in vital processes or themselves influence fitness. Telomere length often predicts longevity, but longevity is only one component of fitness and little is known about how longevity and lifetime reproductive success relate to telomere dynamics in wild populations. We examined the relationships between telomere length beginning in early life, telomere loss into adulthood, and lifetime reproductive success in free-living house sparrows (Passer domesticus). We found that females, but not males, with longer telomeres during early life had higher lifetime reproductive success, due to associations with longevity and not reproduction per year or attempt. Telomeres decreased with age in both sexes, but telomere loss was not associated with lifetime fitness. Sparrow telomeres may reflect differences in quality or condition rather than in pace of life, but only in females. Sexually discordant selection on telomeres is expected to influence the stability and maintenance of within population variation in telomere dynamics and suggests that any role telomeres play in mediating life-history trade-offs may be sex specific.

Methods
The samples we used came from a long-term study of a free-living population of house sparrows (Passer domesticus) breeding in artificial nest boxes located at the University of Kentucky’s Agricultural Experiment Station North Farm complex in Lexington, KY. Blood samples were collected from birds in the nest at 10 days of age and then at least once post-independence. To measure relative telomere length, DNA was extracted from whole blood samples and relative telomere length was measured using quantitative PCR (qPCR). Measures of longevity and reproductive success were collected by frequent census of breeding sites (nest-boxes) to identify color-marked individuals and to document clutch size and survival of offspring to 10 days of age. The data have been organized into 4 datsets, described in the MS and the Supplement.