Abstract
Pelage luminance has been found in many mammalian systems to follow patterns predicted by Gloger’s rule where darker colored animals are associated with environments that are warmer and more moist. Sciurids have one of the greatest diversities of color patterns and hues among mammalian families. We have used comparative methods to investigate whether the luminance of dorsal pelage in 137 species across Sciuridae conform to prediction of Gloger’s rule and other background matching expectations. We found using phylogenetic multiple regression, as well as univariate regression, that Sciurids generally conform to expectations of Gloger’s rule. Darker species are associated with environments with higher primary productivity, higher temperature, higher humidity, and lower solar radiation. Moreover, in support of the predictions of background matching, darker squirrel species were associated with environments with greater soil carbon content and higher fire frequency. Our macroevolutionary study sheds some light on selective pressures that are driving the evolution of coloration in Sciurids, but more comparative research is needed to fully understand other selective pressures that have led to the wide diversity of color patterns and hues.
Highlights
Gloger’s rule is an ecogeographic rule describing the tendency of animals living in warm and wet environments to be darker (Gloger, 1833; Rensch, 1929)
We hypothesized that pelage luminance will be significantly associated with other environmental variables that are more directly associated with background matching
Model Selection for Comparative Phylogenetic Analysis. Both runs of the Markov Chain Monte Carlo (MCMC) converged as evidenced by the stationarity of the trace plots
Summary
Gloger’s rule is an ecogeographic rule describing the tendency of animals living in warm and wet environments to be darker (Gloger, 1833; Rensch, 1929). Biologists that study Gloger’s rule often investigate how well multiple environmental variables (i.e., temperature, environmental moisture, primary productivity, solar radiation, and their surrogates) predict the brightness of animal color. Another possible mechanism is selection for pelage color to match that of the background substrate (Nachman et al, 2003; Vignieri et al, 2010), the color of which may be predicted by the variables mentioned above. The rodent family Sciuridae is a fascinating group to study color-pattern evolution because, unlike most other rodent families, squirrels have evolved extremely diverse pelages that include many types of patterns (e.g., stripes, spots, and patches) and hues (e.g., red, brown, tan, and black), and a range of luminances from black to very light (Figure 1) (Thorington et al, 2012). We hypothesized that pelage luminance will be significantly associated with other environmental variables that are more directly associated with background matching (soil carbon content, soil density, and frequency of wildfires)
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