Interspecific Variation in Primate Countershading: Effects of Activity Pattern, Body Mass, and Phylogeny

Abstract

Countershading is defined as an animal displaying a dark dorsal and light ventral surface. This color pattern is found in numerous species, yet there are relatively few quantitative tests that examine its potential adaptive nature. The most frequently employed explanation for countershading is its ability to increase crypsis. I used a comparative approach to test 2 predictions of this hypothesis in primates. First, diurnal species should exhibit stronger countershading versus nocturnal species because light levels are low at night, reducing the benefit of countershading. Second, the degree of countershading should decrease as body mass increases because large animals should have a lower predation risk. I collected data from 171 museum specimens representing 63 primate species. Using digital photography, I quantified the average luminance values on the ventral and dorsal surfaces of each specimen and defined the degree of countershading as the ratio of these values. Nocturnal primates displayed similar levels of countershading compared to diurnal species. Previous studies have shown that some nocturnal primates are more active when moonlight levels are high, suggesting that countershaded pelages may act as an antipredator adaptation. I also found support for a negative relationship between body mass and the degree of countershading using both species values and phylogenetically independent contrasts. There were some exceptions to this pattern, including low levels of countershading for most callitrichine species, which may be due to the vertical positional behavior of many callitrichines, thereby reducing any benefit gained from countershading. In sum, variation in primate countershading is related to body mass and phylogeny, but not to activity pattern.