Pathways linking female personality with reproductive success are trait- and year-specific

Personality (i.e., among-individual variation in average behavior) often covaries with fitness, but how such personality–fitness relationships come about is poorly understood. Here, we explore potential mechanisms by which two female personality traits (female–female aggression and female nest defense as manifested by hissing behavior) were linked with annual reproductive success in a population of great tits (Parus major), a socially monogamous species with biparental care. We hypothesized that personality-related differences in reproductive success result from variation in reproductive decision (lay date, brood size) and/or parental provisioning rates. Relative support for these mechanisms was evaluated using path analysis on data collected in two successive years. We reveal that larger broods were provisioned at a higher rate by both parents and that female, but not male, provisioning rate was involved in the trade-off between offspring number (brood size) and fledgling mass. Among-individual variation in female aggression, via its association with female provisioning rate, was negatively linked to fledgling mass (i.e., indirect effect), yet only in one of the study years. Male provisioning rate did not influence these relationships. In contrast, among-individual variation in hissing behavior was directly and negatively linked with fledgling mass in both years, via an underlying mechanism that remains to be identified (i.e., direct effect). Together, our findings emphasize that personality–fitness relationships may come about via different mechanisms across personality traits and/or years, thereby illustrating additional complexity in how selection might act on and maintain among-individual variation in behavioral phenotypes in the wild.

Nestling telomere shortening, but not telomere length, reflects developmental stress and predicts survival in wild birds

Developmental stressors often have long-term fitness consequences, but linking offspring traits to fitness prospects has remained a challenge. Telomere length predicts mortality in adult birds, and may provide a link between developmental conditions and fitness prospects. Here, we examine the effects of manipulated brood size on growth, telomere dynamics and post-fledging survival in free-living jackdaws. Nestlings in enlarged broods achieved lower mass and lost 21% more telomere repeats relative to nestlings in reduced broods, showing that developmental stress accelerates telomere shortening. Adult telomere length was positively correlated with their telomere length as nestling ( r = 0.83). Thus, an advantage of long telomeres in nestlings is carried through to adulthood. Nestling telomere shortening predicted post-fledging survival and recruitment independent of manipulation and fledgling mass. This effect was strong, with a threefold difference in recruitment probability over the telomere shortening range. By contrast, absolute telomere length was neither affected by brood size manipulation nor related to survival. We conclude that telomere loss, but not absolute telomere length, links developmental conditions to subsequent survival and suggest that telomere shortening may provide a key to unravelling the physiological causes of developmental effects on fitness.

Female Hematozoan Infection Reduces Hatching Success but not Fledging Success in Pied Flycatchers Ficedula hypoleuca

We report association between female blood parasite prevalence (percentage of infected birds) just after egg laying and reproductive success in two successive breeding seasons, in a breeding population of Pied Flycatcher Ficedula hypoleuca in central Spain. Females infected with Trypanosoma spp. had a higher probability of deserting their clutches during the incubation period than noninfected females. Females infected with Haemoproteus balmorali hatched proportionally fewer eggs than noninfected females. Female infected with H. balmorali during the incubation period may have a decreased ability to thermoregulate which may affect their incubation capacity. Fledging success, breeding success, fledgling mass, and tarsus length were not associated with infection of the mother by blood parasites during the incubation period, suggesting that females and their mates may compensate during the nestling period for the negative effect of blood parasites during the incubation period.