Meeting Abstract
In female birds, timing of clutch initiation is controlled by both external (e.g. photoperiod, temperature, food availability) and internal (e.g. body condition, endogenous circannual rhythms) factors. Internal factors representative of remaining lifespan may also influence seasonal timing of reproduction in female birds, as individuals that breed earlier in the season generally have greater reproductive success. However, evidence suggests that breeding early may be costly. Therefore, it may be expected that females with fewer future reproductive events are more likely to breed early in the season. While chronological age is a good indicator of remaining lifespan, telomere lengths may be a better biomarker of longevity as they reflect both chronological age and potentially lifetime oxidative stress exposure. We examined whether variation in the timing of first clutch initiation was related to telomere length in female Dark-eyed Juncos (Junco hyemalis). We found that in female juncos with prior reproductive experience, there was a correlation between telomere length and the date on which the first egg was laid such that early breeders had shorter telomeres. These results are consistent with our hypothesis that early breeders have a shorter remaining lifespan, and suggest that birds may adjust their current reproductive effort based on lifetime physiological wear-and-tear. Alternatively, if timing of clutch initiation is repeatable among individuals, shorter telomeres in early breeders may reflect the costs of breeding early the previous season.
