Reproductive senescence in a polymorphic raptor: phenotypic, sex, and environmental effects

The decline in reproductive performance with age (reproductive senescence) is a well-known process in evolutionary biology. Still, the interactive nature of factors operating at the individual level, such as sex or phenotype, and their effects on the rates of senescence, are understudied. Little is also known about the interaction between certain phenotypic traits and early-life conditions, despite the latter being known to impact fitness and senescence. Species that show genetically determined polymorphisms may aid to disentangle variation in senescence in response to environmental constraints, particularly when distinct physiological and behavioral responses are found across phenotypes. Here, using complete life histories gathered over 13 yr, we evaluated age, environmental and phenotypic effects on annual offspring number and lifetime reproductive success in a color polymorphic raptor, the Eleonora's falcon (<i>Falco eleonorae</i>). In females, we found evidence of within-individual reproductive senescence with differing patterns between color morphs, highlighting the need to further explore the sex-specific effects of overproducing melanin on senescence rates. We also found higher breeding success at older ages in both sexes, indicating population-level effects (selective appearance). Independent of sex and morph, higher lifetime reproductive success was associated with the exposure to a benign developmental environment, suggesting a "silver-spoon" effect of early-life conditions on fitness. However, in short-lived individuals, the negative effects of a harsh developmental environment on reproductive output were less evident. We propose that a breeding strategy that maximizes reproductive effort early in adulthood may be beneficial under unfavorable early-life conditions, at the expense of shorter lifespan.