Fang Length Evolution in Vipers is Predicted by Furred and Feathered Diets

Holding, Matthew

Department of Biological Science

Florida State University

Tallahassee, Florida, USA

Trevine, Vivian C.

Instituto Butantan

São Paulo, Brazil

Zinenko, Oleksandr

Museum of Nature

V. N. Karazin Kharkiv National University

Kharkiv, Ukraine

Strickland, Jason L. Rautsaw, Rhett M.

Mason, Andrew J.

Hofmann, Erich P.

Parkinson, Christopher L. Department of Biological Sciences

Clemson University

Clemson, South Carolina, USA

Grazziotin, Felipe G.

Instituto Butantan

São Paulo, Brazil

Summers, Adam P. Department of Biology and School of Aquatic and Fisheries Sciences University of Washington

Friday Harbor, Washington, USA

Santana, Sharlene E. Department of Biology

University of Washington

Seattle, Washington, USA

Davis, Mark A.

Illinois Natural History Survey Champaign, Illinois, USA

Rokyta, Darin R.

Department of Biological Science

Florida State University Tallahassee, Florida, USA

Fangs, stingers, spines, and harpoons are used by diverse animal taxa to inject venom into their prey. Strong selection on venom composition has been repeatedly documented, and we might expect the venom injection apparatus to be under similarly strong selection to meet specific functional demands. Snakes in the family Viperidae (true vipers and pitvipers) consist of ~320 species widely studied by both ecologists and evolutionary biologists. Vipers provide an opportunity to determine how the venom injections systems evolve in response to functional demands of prey killing. Utilizing museum collections, we obtained measurements of fang length in >2000 individual specimens representing 200 viper species. We document the mode and tempo of fang length evolution across this diverse family, and test for relationships between ecology and the rate of fang length evolution across clades. We then leverage data collected from over 100 published diet studies to test the hypothesis that longer fangs evolved in response to demands associated with feeding on prey with coverings of fur or feathers. We find support for this hypothesis, where the percentage of mammals and birds in viper diets is positively correlated with relative fang length. Finally, when controlling for head size, the Gaboon Viper is dethroned as the snake species with the longest fangs, and overtaken instead by the Speckled Forest Pitviper of South America. Venom and the venom delivery system merit further work to determine if they are part of a broader functional and evolutionary module that facilitates feeding in venomous animals.

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