The dark side of coloration: Ecogeographical evidence supports Gloger's rule in American marsupials

Abstract

Geographical distribution of color phenotypes and associations with ecological predictors remains poorly understood. An important geographic pattern concerning this topic is Gloger's rule, which predicts the increase of pigmentation in endothermic animals from cold and dry to warm and wet environments. Didelphid marsupials exhibit a variety of color patterns, ranging from light and dark uniform to more complex colorations. However, surprisingly little is known about the adaptive significance of dark coloration in this singular group of mammals. Using a phylogenetic comparative approach, we investigated whether coloration in different body regions of didelphids (i.e., dorsum and face) is associated with variables representing heat and humidity of the environment, as predicted by Gloger's rule. We demonstrated that Gloger's rule explains the interspecific color variation in American marsupials, especially when considering the facial region. Thus, dark coloration was more frequent among didelphid species occupying warm and wet environments than cold and dry environments. We also discuss the selective forces that can potentially explain coat color variation in didelphid marsupials, including camouflage, pathogen resistance, and pleiotropy hypotheses.

Evolution of Pelage Luminance in Squirrels (Sciuridae)

“…Our univariate regression analyses further supported these relationships. These findings are consistent with most predictions of Gloger's rule that have been observed in mammals, including carnivores (da Silva et al, 2016;Caro et al, 2017), artiodactyls (Stoner et al, 2003b), Palearctic shrews (Stanchak and Santana, 2019), primates (Kamilar and Bradley, 2011;Santana et al, 2012), rodents (Lai et al, 2008), and marsupials (Nigenda-Morales et al, 2018;Cerezer et al, 2020). These empirical studies have commonly used temperature, precipitation, latitude, and vegetation to explain patterns of color variation that are associated with climatic factors or surrogates of those factors.…”

Colour scales with climate in North American ratsnakes: a test of the thermal melanism hypothesis using community science images

“…One ecogeographic pattern to explain this trend in P. obsoletus is Gloger's rule, which predicts that darker coloured animals are favoured in warm, wet environments [31]. There are multiple working hypotheses to explain the pattern of Gloger's rule, including increased camouflage, protection from solar radiation and/or parasites, or pleiotropic effects [31,32]. However, studies that more carefully control for joint effects of temperature and precipitation often demonstrate that darker coloured individuals are more likely found in colder areas (i.e.…”

Using computer vision to understand the global biogeography of ant color

“…Gloger's rule (Delhey 2017a) states that more heavily pigmented (darker) organisms are more likely to occur in warmer and more humid environments. This rule is focused on endotherms and finds support among various species and populations of mammals (Kamilar and Bradley 2011, Cerezer et al 2020), birds (Burtt Jr and Ichida 2004, Roulin and Randin 2015) and even plants (Koski and Ashman 2015). While the mechanisms underlying Gloger's rule vary, in insects, a version of the rule called the photoprotection hypothesis (PPH) has been used to explain the presence of darker ants in high UV‐B environments.…”

“…For example, datasets capturing intraspecific variation are often focused on single species (Romano et al 2019) or small geographic regions (Marshall et al 2015). By contrast, datasets that explore variation across many species within a given evolutionary radiation (Delhey et al 2019, Cerezer et al 2020), or which cover large parts of the globe (Zeuss et al 2014, Bishop et al 2016), usually fail to capture intraspecific variability. This trade‐off in data collection strategy has long been necessary because researchers have limited resources.…”