Data from: Chronological and biological age predict seasonal reproductive timing: an investigation of clutch initiation and telomeres in birds of known age

Female vertebrates that breed earlier in the season generally have greater reproductive success. However, evidence suggests that breeding early may be costly, thus leading to the prediction that females with fewer future reproductive events will breed earlier in the season. While chronological age is a good indicator of remaining lifespan, telomere lengths may also be good biomarkers of longevity as they potentially reflect lifetime 'wear and tear' (i.e. "biological age"). We examined whether variation in the timing of the first seasonal clutch was related to age and telomere length in female dark-eyed juncos (Junco hyemalis), predicting that older females and those with shorter telomeres would breed earlier. Both predictions held true and were independent of each other, as telomere length did not significantly vary with age. These results suggest that females may adjust their reproductive effort based on both chronological and biological age.繁殖季提早繁殖的雌性脊椎动物通常具有更高的繁殖成功率。然而，已有研究表明提早繁殖可能需要付出相应代价，据此可提出预测：未来繁殖事件更少的雌性个体，会在繁殖季更早开展繁殖活动。尽管实际年龄（chronological age）是剩余寿命的良好指示指标，但端粒长度（telomere length）也可作为衡量长寿的有效生物标志物，因其能够潜在反映机体一生的“累积磨损”（即“生物学年龄”）。本研究以雌性暗眼灯草鹀（Junco hyemalis）为研究对象，探究其首次季节性产卵的时间差异是否与年龄及端粒长度相关，并预测年龄更大的雌性以及端粒更短的个体将会更早繁殖。两项预测均得到验证，且二者彼此独立——端粒长度并未随实际年龄发生显著变化。上述结果表明，雌性个体或许会同时依据实际年龄与生物学年龄来调整自身的繁殖投入。