Distribution of iridescent colours in hummingbird communities results from the interplay between selection for camouflage and communication

Abstract

Identification errors between closely related, co-occurring, species may lead to misdirected social interactions such as costly interbreeding or misdirected aggression. This selects for divergence in traits involved in species identification among co-occurring species, resulting from character displacement. On the other hand, predation may select for crypsis, potentially leading co-occurring species that share the same environment and predators to have a similar appearance. However, few studies have explored how these antagonistic processes influence colour at the community level. Here, we assess colour clustering and overdispersion in 189 hummingbird communities, tallying 112 species, across Ecuador and suggest possible evolutionary mechanisms at stake by controlling for species phylogenetic relatedness. In hummingbirds, most colours are iridescent structural colours, defined as colours that change with the illumination or observation angle. Because small variations in the underlying structures can have dramatic effects on the resulting colours and because iridescent structures can produce virtually any hue and brightness, we expect iridescent colours to respond finely to selective pressures. Moreover, we predict that hue angular dependence -a specific aspect of iridescent colours -may be used as an additional channel for species recognition. In our hummingbird assemblages in Ecuador, we find support for colour overdispersion in ventral and facial patches at the community level even after controlling for the phylogeny, especially on iridescence-related traits, suggesting character displacement among co-occurring species. We also find colour clustering at the community level on dorsal patches, suspected to be involved in camouflage, suggesting that the same cryptic colours are selected among co-occurring species.

Speciation rates are positively correlated with the rate of plumage color evolution in hummingbirds

“…Bright iridescent colors are acquired in males only at sexual maturity but are often absent in females (Pitelka 1942;Wolf and Stiles 1970;Bleiweiss 1992b). Colors from the belly, mantle, and rump are thought to be involved in crypsis due to a correlation with the background color of the habitat (Pitelka 1951;Gruson et al 2019). Additional feather patches, such as cheeks, shoulders, or tails, are sometimes included in aggressive or courtship displays but these are rare instances in most species.…”

“…We investigated the relationship between color evolution and speciation rates in hummingbirds (Trochilidae), a large clade of nonpasserine birds extensively known for their brilliant and iridescent coloration (Osorio and Ham 2002;Eliason et al 2020). This family is indisputably monophyletic, species rich, and represents a classical example of color diversity thought as product of sexual and natural selection (Darwin 1880;Parra 2010;McGuire et al 2014;Gruson et al 2019). Diversification in hummingbirds has been mainly associated with ecological opportunity (Ricklefs 2006;Mahler et al 2010), throughout its dynamic biogeographic history, including the invasion of South America and expansions and contractions along the Andes and the Panamanian Isthmus (McGuire et al 2014;Benham et al 2015).…”

“…2014; Gruson et al. 2019). Diversification in hummingbirds has been mainly associated with ecological opportunity (Ricklefs 2006; Mahler et al.…”

Hummingbird iridescence: an unsuspected structural diversity influences colouration at multiple scales

“…It does however seem that the full range of possible hues is not explored in hummingbirds. This is probably in part due to our non-exhaustive sampling of hummingbird species but also likely reflects evolutionary constraints, either on the structures themselves or on the resulting colour [3].…”

“…S1: directional patches, which are only visible at a very narrow angle range [2] and are often very bright and saturated, and diffuse patches, for which some colour is visible from any angle [2] and that are often not as bright as directional patches. Directional patches are often located on facial or ventral patches and thought to be involved in communication while diffuse patches are often located on dorsal patches and thought to be involved in camouflage [3]. Additionally, although all hummingbird species display some degree of iridescence, striking differences can be noticed between the various species and body patches in terms of brightness (describing how much light is reflected by the object), saturation (describing the colour “purity”) and directionality [4].…”