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: 4.61). 05/2006; 60(4):856-68. DOI: 10.1554/05-665.1
Source: PubMed


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.

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    • "The length of the outermost rectrices (hereafter, tail length) of males is under directional sexual selection in several barn swallow populations, including the population we studied here, as long-tailed males enjoy larger success in mating and sperm competition (Møller , 1994; Saino et al., 1997; Turner, 2006). However, sexual and natural selection on tail length has been shown to vary in time in another European population (Møller & Sz ep, 2005), as well as in space, at continental scale (Møller et al., 2006). Long-tailed males have higher viability (Møller, 1994; Saino et al., 2011). "
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    ABSTRACT: Parents should differentially invest in sons or daughters depending on the sex-specific fitness returns from male and female offspring. In species with sexually selected heritable male characters, highly ornamented fathers should overproduce sons, which will be more sexually attractive than sons of less ornamented fathers. Because of genetic correlations between the sexes, females that express traits which are under selection in males should also overproduce sons. However, sex allocation strategies may consist in reaction norms leading to spatio-temporal variation in the association between offspring sex ratio (SR) and parental phenotype. We analyzed offspring SR in barn swallows (Hirundo rustica) over 8 years in relation to two sexually dimorphic traits: tail length and melanin-based ventral plumage coloration. The proportion of sons increased with maternal darkness and paternal tail length, consistently with sexual dimorphism in these traits. The size of the effect of these parental traits on sex ratio was large compared to other studies of offspring SR in birds. Barn swallows thus manipulate offspring SR to overproduce 'sexy sons' and potentially to mitigate the costs of intra-locus sexually antagonistic selection. Inter-annual variation in the relationships between offspring SR and parental traits was observed which may suggest phenotypic plasticity in sex allocation and provides a proximate explanation for inconsistent results of studies of sex allocation in relation to sexual ornamentation in birds. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Full-text · Article · Apr 2015 · Journal of Evolutionary Biology
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    • "Studies investigating spatial variation in phenotypic selection across large geographical scales are still scarce, and the understanding of patterns of selection and of the selective agents behind phenotypic patterns remains poor. Such studies have been conducted in relation to behavioural traits (Soler et al., 1999, 2001), morphology (Blanckenhorn et al., 1999; Svensson & Sinervo, 2004; Møller et al., 2006; Gosden & Svensson, 2008) and other phenotypic traits, including animal coloration (Calsbeek, Bonvini & Cox, 2010; Weese et al., 2010; Svensson & Waller, 2013). However, few studies have assessed geographical variation in contemporary selection on sexually selected colour ornaments. "
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    ABSTRACT: Local environmental and ecological conditions are commonly expected to result in local adaptation, although there are few examples of variation in phenotypic selection across continent-wide spatial scales. We collected standardized data on selection with respect to the highly variable plumage coloration of pied flycatcher (Ficedula hypoleuca Pall.) males from 17 populations across the species' breeding range. The observed selection on multiple male coloration traits via the annual number of fledged young was generally relatively weak. The main aim of the present study, however, was to examine whether the current directional selection estimates are associated with distance to the sympatric area with the collared flycatcher (Ficedula albicollis Temminck), a sister species with which the pied flycatcher is showing character displacement. This pattern was expected because plumage traits in male pied flycatchers are changing with the distance to these areas of sympatry. However, we did not find such a pattern in current selection on coloration. There were no associations between current directional selection on ornamentation and latitude or longitude either. Interestingly, current selection on coloration traits was not associated with the observed mean plumage traits of the populations. Thus, there do not appear to be geographical gradients in current directional fecundity selection on male plumage ornamentation. The results of the present study do not support the idea that constant patterns in directional fecundity selection would play a major role in the maintenance of coloration among populations in this species. By contrast, the tendency for relatively weak mosaic-like variation in selection among populations could reflect just a snapshot of temporally variable, potentially environment-dependent, selection, as suggested by other studies in this system. Such fine-grained variable selection coupled with gene flow could maintain extensive phenotypic variation across populations. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●●, ●●–●●.
    Full-text · Article · Jan 2015 · Biological Journal of the Linnean Society
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    • "As we have discussed in this review, decades of work on the different sexually selected traits in this species show that the relative roles of streamer length, coloration, and possibly song in mate choice and male-male competition vary among subspecies . Even among European populations there is variation the strength of selection on tail length, although it remains consistently positive among populations (Møller et al. 2006). Likewise, the information conveyed by these traits varies geographically, with some evidence suggesting that long tail streamers in Europe advertise indirect benefits (Møller 1994a; Møller et al. 1998a); but see (Bro-Jørgensen et al. 2007) for alternative explanations), whereas coloration has been suggested to advertise direct and indirect benefits in Japan(Kojima et al. 2009; Hasegawa et al. 2012), and could relate to both direct and indirect benefits in North America (Safran and McGraw 2004; Safran et al. 2005). "
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    ABSTRACT: Barn Swallows (Hirundo rustica), a group of passerine birds comprised of six closely related subspecies, are well known throughout their nearly worldwide distribution, in part because of their close association with human settlements. A tractable species for both individual-based and population-level studies, Barn Swallows are a prominent model system in evolutionary, ecological, and behavioral research. Here we review work on sexual selection and population divergence in this species complex, focusing on comparative studies among populations and subspecies. We summarize variation in the targets of mate choice and in the information conveyed by sexually selected traits, and conclude that the benefits advertised by different traits may vary geographically. Finally, we consider the role of sexual selection as a driver of population divergence in this widespread and phenotypically variable species complex.
    Full-text · Article · Dec 2014
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