Previous studies indicate that (1) defensive displays are associated with habitat use in snakes, (2) visual defenses correlate better with habitat than with phylogeny, and (3) arboreal snakes are more exposed to predators than terrestrial species. We hypothesize that similar patterns exist for diurnal versus nocturnal snakes, and test these hypotheses against the occurrence of 13 defense types directed to visually oriented predators in 92 colubrids from two Neotropical assemblages, one from central Amazonia (26 genera, 41 species) and another from the Atlantic Forest (23 genera, 62 species). Arboreal species and genera displayed more visual defensive tactics than terrestrial ones. Frontal display, gaping, gular inflation, head elevation, neck S-coil, and, apparently, head triangulation, tended to be more frequent in arboreal species, whereas dorsoventral body depression and, apparently, polymorphism, were more frequent in terrestrial ones. Peculiarities of the arboreal microhabitat, such as the prevalence of a green background, a likely higher exposition to predators, and the variety of directions from which a predator would approach may have led to the evolution of peculiar visual defensive tactics in arboreal species. With regard to time of activity, the number of visual defensive tactics was not different between diurnal and nocturnal species or genera. However, frontal display, gaping, gular inflation, and crypsis were prevalent in diurnal snakes, whereas mimicry and, apparently, head triangulation were more frequent in nocturnal forms. Furthermore, green was significantly more frequent in diurnal species, whereas contrasting color patterns were more frequent in nocturnal species. A cluster analysis based on the occurrence of visual defenses resulted mostly in heterogeneous groups of genera regarding phylogenetic position (clade), preferred microhabitat and time of activity. In general, our analyses indicate that the way Neotropical snakes defend themselves from predators results from a complex interaction between ecological factors and phylogenetic constraints.
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Vol. 3 • No. 1