Why do Viper Snake Horns Exist? The Evolutionary Biology that links these Traits with the Environment

New study discovers a strong correlation between the evolution of a horn type and the snake’s habitat.

A new study by New York University (NYU) Abu Dhabi PhD student Theo Busschau and Principal Investigator at the Evolutionary Genomics Lab at NYU Abu Dhabi Stephane Boissinot provide explanations to the existence and evolution of horns on snakes. 

A key element in the study of evolutionary biology is understanding the adaptive significance of phenotypic variation, plainly, why certain phenotypes exist in a population. The researchers present insights about the evolution of nasal and ocular horns in vipers.

Specifically, Busschau and Boissinot have discovered a correlation between the evolution of specific horn types and viper habitats. This is the first time that a study has provided insights about the evolution of horns in snakes.

“Through the rigorous study of hundreds of species of vipers, we provided key insights about the adaptive significance of horns in vipers. It is our hope that this work will inspire further studies on the function of ocular and nasal horns in different habitat types,” said Boissinot. “The continued study of these incredible reptiles can help the scientific community to understand the complexities of evolution as it continues to happen before our very eyes.”

In the paper titled Habitat determines convergent evolution of cephalic horns in vipers recently published in the journal Biological Journal of the Linnean Society, the researchers analyzed 263 viper species, representative of 68 percent of all known vipers, and created a database of their traits alongside categories of habitats and diets. Within these taxa, the researchers detected significant correlations between horn types and selected habitats. 

For instance, nasal horns showed a clear association with terrestrial forest habitats, while taxa with ocular horns were associated with living in trees or sparsely vegetated habitats. The results also showed that horns were gained and lost often throughout the evolutionary history of vipers, and evolved gradually. There was no significant correlation detected between horn type and diet.

The function and evolutionary history of horns in snakes has long been a mystery to evolutionary biologists. This study is the first to examine the correlation between this adaptive trait and snake ecology. The study fills a gap in an important area of evolutionary science, and leads the way for future studies to explore the function of the horns of vipers and other mysterious adaptive traits.