Adaptation in the African egg‐eating snake: a comparative approach to a classic study in evolutionary functional morphology

Abstract

AbstractA key component to any adaptive hypothesis is that the adaptive trait in question must confer a performance advantage and, in turn, an increase in fitness, relative to those animals displaying the phylogenetically antecedent condition. Among the most striking purported adaptations in vertebrates are those found in the African snake genus Dasypeltis. These snakes are unique in that they eat bird eggs to the exclusion of all other prey. Detailed functional morphological analysis dating back 50 years has highlighted a suite of morphological features in the head and trunk region hypothesized to assist these animals in eating bird eggs, and yet no comparative performance studies of egg‐eating ability have ever been conducted in this group of snakes. The purpose of this study was twofold: first, we wanted to compare egg‐eating performance in Dasypeltis with a facultative egg eater, the common king snake Lampropeltis getula. Second, we wanted to test the hypothesis that a selective regime exists in Africa conducive to the selection and subsequent fixation of the hypothesized egg‐eating morphological adaptations. Our results show that a strong advantage exists in egg‐eating ability for Dasypeltis. The difference is so large (only large Lampropeltis can eat small eggs) that analysis by analysis of covariance becomes difficult due to problems with collinearity. Our results examining potential selective regimes show that more birds lay eggs of a readily ingestible size in Africa than in a representative region in the United States. Additionally, the largest radiation of African ground‐nesting birds existed in Africa before the colubrid explosion during the Miocene, which gave rise to Dasypeltis, giving further support to previous adaptive hypotheses regarding the unique morphology of these snakes.