An analysis of continent-wide patterns of sexual selection in a passerine bird.

Laboratoire de Parasitologie Evolutive, CNRS UMR 7103, Universitè Pierre et Marie Curie, Bât. A, 7eme etage, 7 quai St. Bernard, Case 237, F-75252 Paris Cedex 05, France.
Evolution (Impact Factor: 4.66). 05/2006; 60(4):856-68. DOI: 10.1554/05-665.1
Source: PubMed

ABSTRACT Patterns of selection are widely believed to differ geographically, causing adaptation to local environmental conditions. However, few studies have investigated patterns of phenotypic selection across large spatial scales. We quantified the intensity of selection on morphology in a monogamous passerine bird, the barn swallow Hirundo rustica, using 6495 adults from 22 populations distributed across Europe and North Africa. According to the classical Darwin-Fisher mechanism of sexual selection in monogamous species, two important components of fitness due to sexual selection are the advantages that the most attractive males acquire by starting to breed early and their high annual fecundity. We estimated directional selection differentials on tail length (a secondary sexual character) and directional selection gradients after controlling for correlated selection on wing length and tarsus length with respect to these two fitness components. Phenotype and fitness components differed significantly among populations for which estimates were available for more than a single year. Likewise, selection differentials and selection gradients differed significantly among populations for tail length, but not for the other two characters. Sexual selection differentials differed significantly from zero across populations for tail length, particularly in males. Controlling statistically for the effects of age reduced the intensity of selection by 60 to 81%, although corrected and uncorrected estimates were strongly positively correlated. Selection differentials and gradients for tail length were positively correlated between the sexes among populations for selection acting on breeding date, but not for fecundity selection. The intensity of selection with respect to breeding date and fecundity were significantly correlated for tail length across populations. Sexual size dimorphism in tail length was significantly correlated with selection differentials with respect to breeding date for tail length in male barn swallows across populations. These findings suggest that patterns of sexual selection are consistent across large geographical scales, but also that they vary among populations. In addition, geographical patterns of phenotypic selection predict current patterns of phenotypic variation among populations, suggesting that consistent patterns of selection have been present for considerable amounts of time.


Available from: Piotr Matyjasiak, May 12, 2015
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    ABSTRACT: Plumage color is a composite trait and each component can provide information regarding individual quality. Melanin-based color is one of the most common plumage coloration in birds. This color comprises two types of melanin pigments: eumelanin (black pigment) and pheomelanin (yellow-reddish pigment), and it is affected by several post-molting processes such as UV damage, staining, and preen oils. In some birds, pheomelanin-based plumage color is related to several measures of sexual selection; however, pheomelanin is almost always expressed together with eumelanin and affected by post-molting processes. Therefore, it is still unclear whether (and to what extent) pheomelanin can explain the observed relationship between plumage color and the measure of sexual selection. Here we examined the melanin (both eumelanin and pheomelanin) concentration in relation to breeding onset, as a fitness component associated with sexual selection in male Barn Swallows (Hirundo rustica gutturalis). We found that throat feathers in males contained more pheomelanin than those in females. The amount of pheomelanin, but not eumelanin, declined throughout the sampling period, indicating that pheomelanin pigmentation conveys different information than eumelanin. Even after correcting for depigmentation of melanin, males with more pheomelanin bred earlier than the others. Together with the results from previous studies, these findings indicate that pheomelanin-based coloration may have evolved via sexual selection for pheomelanin pigmentation in Barn Swallows. Zusammenfassung Phäomelanin Pigmentierung bei männlichen Rauchschwalben ( Hirundo rustica gutturalis ) und Brutbeginn Gefiederfärbung ist eine vielteilige Eigenschaft, und jede Komponente kann Informationen liefern über die Qualität eines Individuums. Melanin-Färbung ist eine der häufigsten Gefiederfärbungen bei Vögeln. Diese Farbe besteht aus zwei Typen des Melanin-Pigments: Eumelanin (schwarz) und Phäomelanin (gelb-rötlich), und unterliegt verschiedenen weiteren Veränderungen nach der Mauser, wie Schädigung durch UV-Strahlung, Schmutz und Bürzeldrüsenfett. Bei manchen Vögeln hängt eine Phäomelanin-Färbung zusammen mit verschiedenen Maßen der sexuellen Auslese; allerdings wird Phäomelanin fast immer zusammen mit Eumelanin gebildet und ist von Einwirkungen nach der Mauser betroffen. Daher ist es noch immer unklar, ob und inwieweit Phäomelanin die beobachteten Zusammenhänge zwischen Gefiederfärbung und den Maßen der sexuellen Auslese erklären kann. Hier untersuchten wir die Melaninkonzentration im Vergleich zum Brutbeginn als Fitness-Merkmal im Zusammenhang mit sexueller Auslese bei männlichen Rauchschwalben (Hirundo rustica gutturalis). Wir fanden, dass Kehlfedern bei Männchen mehr Phäomelanin enthielten als bei Weibchen. Die Menge an Phäomelanin, aber nicht Eumelanin, nahm über den Zeitraum der Untersuchung ab, was darauf hindeutet, dass die Phäomelanin-Färbung andere Informationen vermittelt als die Eumelanin-Färbung. Selbst nach einer Korrektur für die Entfärbung des Melanin, begannen Männchen mit mehr Phäomelanin früher mit dem Brüten. Zusammen mit Ergebnissen aus früheren Untersuchungen, deuten diese Erkenntnisse darauf hin, dass Phäomelanin-Färbung bei Rauchschwalben sich über sexuelle Selektion entwickelt haben könnten.
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