Abstract
The barn swallow, Hirundo rustica, is a model species for studying sexual selection, particularly female mate choice. Although there have already been several reviews of female mate choice and its geographic variation in this species, all of them have focused on secondary sexual characteristics. Here, for better understanding of the general pattern of female mate choice and their influence on male phenotype, I review all of the female mate choice criteria ever reported in the barn swallow, emphasizing the importance of relatively inconspicuous male traits. These include resources defended or provided by males, such as territory and paternal investment. In addition, females prefer a nestling-like vocalization, enticement call, which is particularly noteworthy because females prefer immature calls. This pattern contrasts with female choice based on secondary sexual characteristics, in which more mature, elaborate male traits are almost always favored. Nestling-like male traits are widespread, and thus female avoidance of, rather than preference for, mature forms might be common. In addition to selection on the target trait itself, these resources and nestling-like male traits would also matter in understanding the evolution of the overall male phenotype and its geographic variation, due to the interrelationships among male target traits and those among female mate preferences. Female preferences for inconspicuous traits are highly dependent on ecological factors such as nest predation pressure, and thus overall male phenotype including secondary sexual characteristics might be more predictable than previously thought. Future studies should focus on not only conspicuous secondary sexual characteristics but inconspicuous male traits.
Highlights
Female mate choice is a key issue in evolutionary ecology: it affects the evolution of elaborate male traits and their geographic variation, as well as population growth, extinction, and speciation, at least in theory (Andersson 1994; Coyne and Orr 2004; Brooks and Griffith 2010)
Its understanding is still insufficient, because most studies have focused solely on secondary sexual characteristics, perhaps in part due to the intuitive importance of sexual selection (Andersson 1994) or due to its eye-catching nature (Tazzyman et al 2014)
This circumstance potentially biases our understanding of female mate choice and its evolutionary impact on male phenotype
Summary
Female mate choice is a key issue in evolutionary ecology: it affects the evolution of elaborate male traits and their geographic variation, as well as population growth, extinction, and speciation, at least in theory (Andersson 1994; Coyne and Orr 2004; Brooks and Griffith 2010). Territory quality is often related to male morphological traits (e.g., throat coloration in this species; Hasegawa et al 2014; Wilkins et al 2015), multivariable analysis indicates that territory quality is an important mate choice criteria than male morphology (effect size, Zr = 0.60, 95% CI = 0.14–1.06 for laying date and 0.62, 95% CI = 0.11–1.12 for pairing date, computed from R2 value, is quite high for female preference for territory quality, though sample sizes were small (n = 21, 18, respectively); note that mean overall effect size for plumage ornaments was 0.21; Romano et al 2017a).
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