Gravitational stress and the evolution of relative tail‐length in arboreal snakes (1100.10)

Abstract

Gravity imposes potentially important constraints on blood circulation in elongate animals during upright posture or climbing. We test the hypothesis that arboreal snakes have longer tails than non‐scansorial species and interpret the results in context of adaptation to gravity stress. Length data for 226 species in 15 snake families were divided among three gravitational habitats (G‐habitats: stenotopically arboreal, eurytopically arboreal/terrestrial, and non‐scansorial) to categorize climbing habits. We analyzed data using conventional statistics and phylogenetically independent contrasts by constructing a composite tree. Mean relative tail length (RTL) increased and mean relative snout‐vent length decreased with increasing arboreality among the three G‐habitats, independent of phylogeny. Mean total body length (TL) was not different between the two arboreal G‐habitats. Snakes with longer RTLs have a larger percentage of elongate blood vessels contained within relatively tight integument of the tail, which theoretically mitigates postural blood pooling. TL may be constrained in adult female arboreal snakes, and this could be driving an evolutionary tradeoff between longer RTL and lower female fecundity. Our results complement previous studies and suggest that elongated RTLs of arboreal snakes function, at least in part, as an adaptive response to gravity stress.Grant Funding Source: Supported by the U.S. National Science Foundation grant IOS–0926802 to HBL