Dark pigmentation limits thermal niche position in birds

Abstract

Animal pigmentation has evolved because of several adaptive functions. In the case of pigmentation produced by melanins, the most common pigments in animals, the main function is protection against UV radiation. However, pigmentation also affects animal surface's ability to absorb solar radiation and gain heat, which may represent a thermal constraint for endotherms due to their relatively high and constant body temperatures. As darker colours absorb more radiation than lighter colours, dark‐pigmented endotherm animals may exhibit limited performance under high ambient temperatures and thus be constrained at occupying hot environments. While the influence of pigmentation on the determination of the thermal niches of ectotherms, particularly reptiles, has been the focus of several studies, this remains an unexplored issue for endotherm animals. Here, we made a detailed quantification of the expression of pigmentation phenotypes produced by melanins in 96 species of birds inhabiting the Spanish sector of the Iberian Peninsula and estimated their climate niche position by calculating the effects of ambient temperature, insolation and precipitation on bird occurrence at a fine 10 × 10 km spatial scale. After controlling for the body size and the nocturnal condition of species, and for phylogenetic and spatial effects, we found a positive association between plumage reflectance and the functional response of bird distribution to spring–summer ambient temperature and insolation but not to precipitation. Thus, bird species preferentially occupying the hotter and sunnier areas of Spain exhibit lighter plumage pigmentation. Our findings suggest that darker birds are limited from occupying environments with high temperatures, unveiling a constraint in endotherms imposed by their pigmentation phenotype. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13094/suppinfo is available for this article.

Reconciling ecogeographical rules: rainfall and temperature predict global colour variation in the largest bird radiation

“…Similarly, work on Spanish birds also reported a positive correlation between plumage lightness and temperature, but not with rainfall (Galván et al . ). This variability in climatic effects is reflected by our own analysis because the strength and direction of climatic effects varied across bird families and zoogeographic realms (Figs.…”

“…; Delhey ; Galván et al . ), fungi (Cordero et al . ) and perhaps even in plants (Watson & Hanham ; Burns ; Cuthill ).…”

“…Indeed, recent comparative analyses on birds have revealed patterns that seemingly oppose some aspects of Gloger's rule, namely that species with darker plumage are often found in colder rather than warmer regions (Friedman & Remeš ; Delhey ; Galván et al . ; Medina et al . ).…”

“…For example, the relationship between lightness and temperature could be positive in places such as Australia (Friedman & Remeš ; Delhey ) or Spain (Galván et al . ), where the need for thermoregulation to avoid overheating may play an important role, and negative at higher latitudes, driven by the need for camouflage against snowy surfaces. Thus, heterogeneous patterns of correlations in different biogeographic regions are not unexpected.…”

Climate‐driven convergent evolution of plumage colour in a cosmopolitan bird

“…On the other hand, Bogert's rule, or the "thermal melanism rule", postulates that animals inhabiting colder areas should be darker coloured, because they gain a thermal advantage comparing to paler individuals as a consequence of greater absorption of solar radiation (Bogert, 1949;Trullas, van Wyk & Spotila, 2007). These rules have been verified in a large variety of animals, spanning from insects (Bishop et al, 2016;Mayr, 1963) to birds Delhey, 2017Delhey, , 2018Friedman & Remeš, 2016;Galvan, Rodríguez-Martínez, & Carrascal, 2018;Zink & Remsen, 1986) and mammals (Caro, 2005;Kamilar & Bradley, 2011;Nigenda-Morales, Harrigan, & Wayne, 2018;Stoner, Caro, & Graham, 2003). In birds in particular, geographical variation in plumage colour compatible with these two biogeographical rules has been shown both at the withinspecies level (Roulin & Randin, 2015;Zink & Remsen, 1986) and in comparative studies (Delhey, 2018;Friedman & Remeš, 2016;Passarotto et al, 2018).…”