Data from: Early breeding females experience greater telomere loss

Annual reproductive success is often highest in individuals that initiate breeding early, yet relatively few individuals start breeding during this apparently optimal time. This suggests that individuals, particularly females who ultimately dictate when offspring are born, incur costs by initiating reproduction early in the season. We hypothesized that increases in the aging rate of somatic cells may be one such cost. Telomeres, the repetitive DNA sequences on the ends of chromosomes, may be good proxies of biological wear and tear as they shorten with age and in response to stress. Using historical data from a long-term study population of dark-eyed juncos (Junco hyemalis), we found that telomere loss between years was greater in earlier breeding females, regardless of chronological age. There was no relationship between telomere loss and the annual number of eggs laid or chicks that reached independence. However, telomere loss was greater when temperatures were cooler, and cooler temperatures generally occur early in the season. This suggests that environmental conditions could be the primary cause of accelerated telomere loss in early breeders.TelomereCode.R code for analyses conducted in manuscriptDegradation.csv file with data for analysis of telomere degradation over time (ie., number of years sample was stored).FinalNestAge.csv file with all data for analyzing correlations of annual reproductive output, reproductive success, and age with seasonal nest initiation date.FinalTeloCode.csv file with all data for analyzing correlations of seasonal nest initiation, temperature, annual reproductive output, and reproductive success with change in telomere length.Repeatability.csv file with all data for analyzing repeatability of T/S ratio.DataColumnDescriptorsShort description of column titles in each .csv file