Up to the mountain: venom evolution in montane pitvipers (Cerrophidion)

Rosales Garcia, Ramses A.

ramsesr@g.clemson.edu

Parkinson, Chris

Department of Biological Sciences

Clemson University

Clemson, South Carolina USA

Snake venom is an adaptive trait shaped by selection. However, genetic drift might be more important in determining venom phenotypic variation than previously thought. Drift is particularly important in species with isolated, small populations, such as pitvipers inhabiting high elevation mountains. The montane pitvipers of the genus Cerrophidion inhabit the mountainous regions of Middle America. Here, we use this group as a model to explore the roles of selection and drift in venom evolution. Montane pitviper venom is mainly known from studies of the Costa Rican endemic C. sasai, yet the venom composition of the other species has not been studied. Therefore, we describe the venom gland transcriptome of C. petlalcalensis, C. tzotzilorum, and C. godmani from Mexico, and a C. sasai from Costa Rica. Additionally, for C. godmani, we test for a signal of selection on toxin genes. We found that Cerrophidion venom transcriptomes are mainly composed of SVMPs, PLA2s, and SVSPs; however, the expression of these toxin families and individual toxins varies considerably among and within species. Toxins within C. godmani are not under strong selection pressures and are instead evolving via mutation-drift equilibrium. Additionally, we determined the PLA2s composition of each species and found variation in paralog composition among taxa and compositional variation within C. godmani. Our results indicate that C. godmani has a phenotypically diverse venom that varies among populations.