Stabilizing natural selection on the early expression of a secondary sexual trait in a passerine bird.

Natural selection is a central tenet of evolutionary theory, yet the estimation of the direction and intensity of selection remains problematic. Here, we assess the strength of selection on the early expression of a secondary sexual ornament, bill colour, in male European blackbirds (Turdus merula) using 5 years of capture-mark-recapture (CMR) data. The best-fitting model consisted of a quadratic relationship between survival rate and bill colour, indicating stabilizing natural selection on the early expression of a secondary sexual trait. There was no evidence for sexual selection acting on bill colour in the first year. We suggest that the consideration of early selection and the adoption of refined statistical methods may reveal patterns of selection in the wild that have, as yet, remained undetected.

Does beak coloration of male blackbirds play a role in intra and/or intersexual selection?

In many bird species, males may show brightly coloured traits and variance in male mating success may be explained by female preference and/or competition between males favouring the most coloured males. Male beak coloration has been suggested to play an important role in the pairing pattern of European blackbirds. Here, we investigate female preference and male-male interactions in relation to male beak coloration in this species. We used a field experiment to measure female and male responses toward stuffed decoys showing either of two beak coloration representing the extremes of the natural variation from yellow to orange. Decoys were situated on the centre of plots and behaviours of males and females approaching the decoy were recorded. The total number of males and females approaching the decoy did not differ between the two model treatments. Similarly, there was no difference in the mean time that males and females spent near the decoy. The number of males displaying aggressive postures did not differ between treatments and no female adopted a sexual posture. We discuss the relevance of our results and potential limitations associated with the experimental procedure.

Pair-bonding in birds and the active role of females: a critical review of the empirical evidence.

Over the recent years the role of females in maintaining or breaking the pair-bond in socially monogamous birds has received growing attention. Here, we review the overall evidence for a direct and predominant role of female behaviour in initiating or preventing divorce and its relevance for the understanding of both interspecific and intraspecific variation in divorce rate in monogamous bird species. The evidence is so far limited to a few species. We discuss the relevance of some alternative explanations and confounding factors. We conclude that the possible predominance of females in both initiating divorce or limiting its occurrence deserves further consideration. Future studies should favour experimental approaches, such as mate-removal experiments.

[Role of (serum and secretory) IgA deficiency in chronic respiratory disorders. A proposal 21 cases]. / Place des déficits en IgA (sériques et sécrétoires) dans les affections respiratoires chroniques A propos de 21 observations

The current possibility of measuring at one and the same time serum IgA and sputum SIgA, has led to precision in knowledge of IgA deficits in respiratory pathology. The authors report 21 cases detected in a group of 1000 patients (adults, adolescents and children), suffering from various chronic respiratory disorders and who had either total deficits in serum and sputum IgA (6 cases) or partial deficits (15 cases - mixed [5], serum IgA [5i1, sputum IgA [5]. In 9 cases the assoicated respiratory disorder was bronchiectasis, in 7 recurrent rhino-tracheo-bronchitis and in 5 asthma. In no cases were any extra-respiratory manifestations noted, in particular digestive disturbance or auto-immune disease. In some cases there was an associated deficit in IgE and, much less commonly, in IgG or M. Cellular immunity was not altered. The authors then discuss the place of IgA and SIgA deficitis in the pathogenesis of chronic respiratory pathology as well as their substitutive treatment using natural human immunoglobulins and the results thereof.