The impact of helping experience on helper life-history and fitness in a cooperatively breeding bird.

Cooperative breeding occurs when helpers provide alloparental care to the offspring of a breeding pair. One hypothesis of why helping occurs is that helpers gain valuable skills that may increase their own future reproductive success. However, research typically focuses on the effect of helping on short-term measures of reproductive success. Fewer studies have considered how helping affects long-term fitness measures. Here, we analyze how helping experience affects key breeding and fitness-related parameters in the Seychelles warbler (Acrocephalus sechellensis). Importantly, we control for females that have cobred (reproduced as a subordinate by laying an egg within a territory in which they are not a dominant breeder), as they already have experience with direct reproduction. Helping experience had no significant association with any of the metrics considered, except that helpers had an older age at first dominance. Accounting for helping experience, females that had cobred produced more adult offspring (≥1 year) after acquiring dominance and had a higher lifetime reproductive success (LRS) than females that had never cobred. Our results suggest that, in the Seychelles warbler, helping experience alone does not increase the fitness of helpers in any of the metrics considered, and highlights the importance of separating the effects of helping from cobreeding. Our findings also emphasize the importance of analyzing the effect of helping at various life-history stages, as higher short-term fitness may not translate to an overall increase in LRS.

The long-lasting legacy of reproduction: lifetime reproductive success shapes expected genetic contributions of humans after 10 generations.

An individual's lifetime reproductive success (LRS) measures its realized genetic contributions to the next generation, but how well does it predict this over longer periods? Here we use human genealogical data to estimate expected individual genetic contributions (IGC) and quantify the degree to which LRS, relative to other fitness proxies, predicts IGC over longer periods. This allows an identification of the life-history stages that are most important in shaping variation in IGC. We use historical genealogical data from two non-isolated local populations in Switzerland to estimate the stabilized IGC for 2230 individuals approximately 10 generations after they were born. We find that LRS explains 30% less variation in IGC than the best predictor of IGC, the number of grandoffspring. However, albeit less precise than the number of grandoffspring, we show that LRS does provide an unbiased prediction of IGC. Furthermore, it predicts IGC better than lifespan, and accounting for offspring survival to adulthood does not improve the explanatory power. Overall, our findings demonstrate the value of human genealogical data to evolutionary biology and suggest that reproduction-more than lifespan or offspring survival-impacts the long-term genetic contributions of historic humans, even in a population with appreciable migration.