Selection on multiple sexual signals in two Central and Eastern European populations of the barn swallow

Abstract

Variation in intensity and targets of sexual selection on multiple traits has been suggested to play a major role in promoting phenotypic differentiation between populations, although the divergence in selection may depend on year, local conditions or age. In this study, we quantified sexual selection for two putative sexual signals across two Central and East European barn swallow (Hirundo rustica rustica) populations from Czech Republic and Romania over multiple years. We then related these differences in selection to variation in sexual characters among barn swallow populations. Our results show that tail length and ventral coloration vary between populations, sexes, and age classes (first‐time breeders vs. experienced birds). We found that selection on tail length was stronger in first‐time breeders than in experienced birds and in males than in females in the Romanian population, while these differences between age groups and sexes were weak in Czech birds. We suggest that the populational difference in selection on tail length might be related to the differences in breeding conditions. Our results show that ventral coloration is darker (i.e., has lower brightness) in the Romanian than in the Czech population, and in experienced birds and males compared with first‐time breeders and females, respectively. The sexual difference in ventral coloration may suggest sexual selection on this trait, which is supported by the significant directional selection of ventral coloration in first‐time breeding males on laying date. However, after controlling for the confounding effect of wing length and tarsus length, the partial directional selection gradient on this trait turned nonsignificant, suggesting that the advantage of dark ventral coloration in early breeding birds is determined by the correlated traits of body size. These findings show that ventral coloration may be advantageous over the breeding season, but the underlying mechanism of this relationship is not clarified.

Pangenomics provides insights into the role of synanthropy in barn swallow evolution

“…The barn swallow is a well-studied (17–22) migratory passerine bird with six recognised subspecies in Europe, Asia, Africa and the Americas (23). While still poorly understood, recent studies have started to shed light on its genetics (18,24–29). The barn swallow demographic history reconstructed from genomic data suggests that the current barn swallow distribution derives from a relatively recent expansion, probably driven by the spread of human settlements providing more nesting opportunities (28,30).…”

“…Because of its strong association with humans, the barn swallow (Hirundo rustica) is a well-suited model to investigate the evolution and genetic bases of behaviours correlated to synanthropy. The barn swallow is a well-studied (17)(18)(19)(20)(21)(22) migratory passerine bird with six recognised subspecies in Europe, Asia, Africa and the Americas (23). While still poorly understood, recent studies have started to shed light on its genetics (18,(24)(25)(26)(27)(28)(29).…”

“…The barn swallow is a well-studied (17)(18)(19)(20)(21)(22) migratory passerine bird with six recognised subspecies in Europe, Asia, Africa and the Americas (23). While still poorly understood, recent studies have started to shed light on its genetics (18,(24)(25)(26)(27)(28)(29).…”

Analysis of female song provides insight into the evolution of sex differences in a widely studied songbird

“…Numerous studies have identified male plumage traits associated with strong female preferences and increased fitness (Byers et al, 2010; Møller, 1988; Rodríguez et al, 2006; Ryan et al, 2019; Searcy & Andersson, 1986). In contrast, relatively few studies have found relationships between female visual signals and fitness proxies, but see: (Amundsen et al, 1997; Bulluck et al, 2017; Cain & Ketterson, 2011; Jawor et al, 2004; Pap et al, 2019). Likewise, many studies have examined the fitness correlates of male song (Catchpole & Slater, 2003; Gil & Gahr, 2002), but only a handful have looked at how female song impacts fitness (Brunton et al, 2016; Cain et al, 2015; Kleindorfer et al, 2016b; Krieg & Getty, 2016a).…”

Analysis of female song provides insight into the evolution of sex differences in a widely studied songbird

“…Numerous studies have identified male plumage traits associated with strong female preferences and increased fitness (Byers et al, 2010;Møller, 1988;Rodríguez et al, 2006;Ryan et al, 2019;Searcy & Andersson, 1986). In contrast, relatively few studies have looked for or uncovered relationships between female visual signals and fitness proxies, but see: (Amundsen et al, 1997;Bulluck et al, 2017;Cain & Ketterson, 2011;Jawor et al, 2004;Pap et al, 2019). Likewise, many studies have examined the fitness correlates of male song (Catchpole & Slater, 2003;Gil & Gahr, 2002), but only a handful have looked at how female song impacts fitness (Brunton et al, 2016;Cain et al, 2015;Kleindorfer et al, 2016;Krieg & Getty, 2016).…”