Recent natural selection causes adaptive evolution of an avian polygenic trait

We used extensive data from a long-term study of great tits (Parus major) in the United Kingdom and Netherlands to better understand how genetic signatures of selection translate into variation in fitness and phenotypes. We found that genomic regions under differential selection contained candidate genes for bill morphology and used genetic architecture analyses to confirm that these genes, especially the collagen gene COL4A5, explained variation in bill length. COL4A5 variation was associated with reproductive success, which, combined with spatiotemporal patterns of bill length, suggested ongoing selection for longer bills in the United Kingdom. Last, bill length and COL4A5 variation were associated with usage of feeders, suggesting that longer bills may have evolved in the United Kingdom as a response to supplementary feeding

Avian eggshell coloration: New perspectives on adaptive explanations

Recent work suggests that the evolution of egg coloration may have been constrained in three important ways that have not yet been critically synthesized in any review. First, on account of birds being able to see in the ultraviolet spectrum, the interaction between the properties of avian vision and the light environment of nests imply different perceptions of egg coloration from those experienced by humans. Second, a new hypothesis to explain blue-green egg coloration interprets it as a sexually selected signal to males of the laying female's genetic quality. Third, evidence from taxa as divergent as sparrowhawks and great tits indicates that protoporphyrin pigments responsible for maculation (spotting patterns) have a structural function in compensating for eggshell thinning, as caused by calcium stress, and, more recently, dichlorodiphenyltrichloroethane. We consider this to be the most convincing explanation for the primary function of spotting, although an important secondary function might arise through the fact that individual patterns of maculation may allow birds to identify their own eggs, effectively serving as signatures in the face of inter- or intra-specific brood parasitism. These constraints or hypotheses are not mutually exclusive, and should not be taken to imply that one, but not other, agents of selection might apply to any one species. However, the sexually-selected eggshell coloration hypothesis is least plausible for hole-nesting birds because of the poor light quality available, although such species have been the focus of research in this area, and only a single experimental study has shown a link between egg coloration and male provisioning. Furthermore, the observed relationships between female phenotypic quality and egg traits do not necessarily imply that they have signalling functions. © 2010 The Linnean Society of London.Revie

Effects of the doubly labelled water procedure on great tits Parus major feeding young

Capsule. Female Great Tit Parus major feeding rate behaviour was highly variable between individuals, but no effect of the doubly labelled water (DLW) procedure on female visit rate was detected, whereas visit rates by males, which were neither trapped or manipulated, increased following trapping and manipulation of their partners. Aims. To test the assumption that the subject’s behaviour is normal during the measurement period when using DLW to measure energy expenditure. Methods. Visits to the nest box by parents feeding young were counted separately for females and males on the day before and the day after the female only was trapped to measure her energy expenditure using DLW. Visit rates were also counted for control pairs. Results. Female visit rates did not differ before and after manipulation, or between experimental and control pairs, but bird behaviour was highly variable between individuals. In contrast, the visit rates of both experimental and control males, which were not trapped, increased on the second day. Conclusion. The results for female behaviour supported the assumption of normality, but a small subset of particular individuals may be prone to adverse reactions. The response of the males may have been a reaction to disturbance at the nest