Uncorrelated evolution between vocal and plumage coloration traits in the trogons: a comparative study

Abstract

The costs of bird song incurred in a diversity of ways may result in trade‐offs in the production and maintenance of elaborate plumage ornaments. In this paper, we examine evolutionary trade‐offs between acoustic and visual signalling in trogon birds (Trogonidae). Using multiple regressions with phylogenetically independent contrasts, we found that interspecific variation in male plumage coloration was not significantly predicted by song traits (reduced by PCA) or altitude. Although plumage coloration is expected to decrease with increases in song elaboration, both groups of variables were not related. Given that song and plumage coloration traits are likely targets of sexual selection, we also examined their relationships with sexual plumage dimorphism. We found that male carotenoid‐derived coloration was positively related to sexual plumage dimorphism, suggesting that sexual selection on male carotenoid‐derived coloration may be stronger than on melanin‐ or structurally based coloration, or than on acoustic traits. Comparative studies on other bird families accounting for the effects of phylogeny as well as environmental covariates are required to test the generality of our findings in trogons.

Elaborate visual and acoustic signals evolve independently in a large, phenotypically diverse radiation of songbirds

“…Similar to the rationale provided by Ornelas et al [11], the observed lack of an evolutionary trade-off between song and plumage elaboration in tanagers is consistent with multiple, nonexclusive interpretations. One underlying assumption of the transfer hypothesis is that song and plumage investment both rely on individual condition [4].…”

“…This heterogeneity may be unsurprising given that negatively correlated [9], positively correlated [12] and uncorrelated [11] evolution between secondary sexual signals have all been documented in birds. We found the strongest correlations appeared in relatively species-poor subfamilies of tanagers, such as Dacninae (n ¼ 9) and Nemosiinae (n ¼ 4).…”

Sexual selection: when to expect trade-offs

“…However, among species, negative binomial distributions may be more common, leading to positive associations instead of trade-offs. Two empirical studies reanalysed here that tested for trade-offs [8,9] found limited evidence of them, whereas Badyaev et al [5] found more substantive evidence, but these different outcomes did not correspond to easily perceived differences in the distributions of investments (figure 2). Reasons for the different conclusions largely stem from the use of PCA rather than univariate analyses that were used in the original papers.…”

“…A first PCA was run on song variables (highest frequency, lowest frequency, note length, inter-note interval, number of notes, song length), a second PCA was run on plumage variables (carotenoid-and melaninbased dichromatism), and PC1 scores from the plumage and song PCAs were entered in a third PCA to create scores of total investment. Finally, for Ornelas et al [8], a first PCA included song variables 77-94 (from their supplementary material, table S5). A second PCA included the plumage variables sexual dimorphism, plumage colour-dimorphism, proportion of male plumage that was carotenoid-based and proportion of male plumage that was melanin-based.…”

Macrogeographical variation in the song of a widely distributed African warbler

“…Our song analyses found no evidence that sexual selection has promoted dialects or has led to gradients in song complexity over the species' range (Irwin 2000;Podos & Warren 2007). Subspecies boundaries, which reflect differences in colour and size, do not align with vocal traits, suggesting that different evolutionary pressures may be operating on different phenotypic traits (Ornelas et al 2009). Observers have long recognized that C. erythrops songs differ geographically, but no one has previously characterized the subtle and relatively continuous nature of this change across a 6500 km geographical range (Lynes 1930).…”