Shape and size variation in elapid snake fangs, and the effects of phylogeny and diet

Abstract

Recent studies have found correlations between the shape of snake teeth/fangs and diet. These studies were done at a very broad phylogenetic scale, making it desirable to test if correlations are still detectable at a narrower evolutionary scale, specifically within the family Elapidae. To this end, we studied fang shape in a dense selection of elapids representing most genera worldwide (74%). We used three-dimensional geometric morphometrics to analyse fang diversity and evaluate possible correlations between fang shape, fang size, and diet. We detected only weak phylogenetic signal in our dataset for both shape and size, and no significant evolutionary allometry when correcting for phylogeny. Overall, the distribution of elapid fangs in morphospace was found to be surprisingly conservative, with only a few outliers. The only two dietary categories that were found to have a significant effect on fang shape are fish and snakes, while mammals have a significant effect on absolute but not relative fang size. Our results show that there are disparate patterns in fang-diet relationships at different evolutionary scales. Across all venomous snakes, previous work found that fangs are strongly influenced by diet, but within elapids our study shows these same associations are weaker and often non-significant. This could result from limitations in these types of studies, or could reflect the fact that elapids are a relatively young clade, where recent extensive divergences in diet have yet to be mirrored in fang shape, suggesting a lag between changes in ecology and dental morphology.