Habitat determines convergent evolution of cephalic horns in vipers

Phenotypic convergence of traits in similar environments can provide insights into the evolutionary processes shaping trait evolution. Among squamate reptiles, horn-like cephalic appendages have evolved under various selective pressures, including selection for defence, crypsis or sexual selection. Yet, among snakes, particularly vipers, the functional and evolutionary significance of horns are unknown. We used a comparative phylogenetic approach with habitat and diet data on 263 viper taxa to shed light on the selective pressures underlying horn evolution in vipers. We detected significant correlations with habitat but not diet. The relative positions of horns are ecologically divergent in that supranasal horns are positively correlated with terrestrial forest habitats while supraocular horns are negatively correlated with terrestrial forest habitats and associated with arboreal or sparsely vegetated habitats. Multiple independent origins of supranasal or supraocular horns in similar habitats provide evidence of adaptive convergence. Comparisons with other snake lineages suggest that cephalic appendages may have evolved under selection for crypsis in ambush foraging snakes.

Brief insight into the behavior, activity, and interspecific interactions of urban Trimeresurus (Cryptelytrops) albolabris (Reptilia: Squamata: Viperidae) vipers in Bangkok, Thailand

Green Pit Vipers are a widely distributed, diverse group of snakes which occur across a variety of habitats. Little is known about their natural history in anthropogenically modified environments, and no ecological work has investigated their persistence in cities. We non-invasively photo-monitored White-lipped Green Pit Vipers Trimeresurus (Cryptelytrops) albolabris in the metropolis of Bangkok, Thailand (n = 4 individuals, mean = 2,658 minutes per individual). Subsequently, we preliminarily characterize urban green pit vipers as nocturnal predators, displaying ambush-foraging at night, sheltering during the day, and having limited movement in between temporal periods. We recorded two predation events of vipers capturing and ingesting anuran prey. Vipers infrequently displayed tail undulations (239 minutes total), with one event occurring immediately before a predation event. We also document chemosensory, probing, and mouth-gaping behaviors having occurred exclusively at night. Other vertebrates including birds, frogs, geckos, small mammals, and a cobra were photographed interacting with focal vipers or their immediate surroundings (315 minutes total). Knowledge of organisms in tropical urban environments is scarce, and the persistence of venomous snakes in these unique and challenging habitats requires further study.

Does foraging mode affect metabolic responses to feeding? A study of pygopodid lizards

Foraging mode (ambush vs. active) profoundly affects many aspects of organismal biology, including metabolic rates and their relationship with food intake. Previous studies on snakes suggest that ambushers tend to have lower standard metabolic rates (SMR) and higher energetic costs of digestion and assimilation of prey (specific dynamic action, or SDA) than do active foragers. However, phylogenetic considerations may be at least partly responsible for such patterns, as foraging mode is strongly conserved evolutionarily and most SDA studies have focused on species from only two lineages of ambush foragers (pythonid and viperid snakes) and one lineage of active foragers (colubrid snakes). We sought to deconfound the effects of phylogeny and foraging mode, investigating SMR and SDA in two closely related pygopodid lizards, the common scaly-foot Pygopus lepidopodus (active forager) and Burton’s legless lizard Lialis burtonis (ambush forager). Consistent with the pattern seen in snakes, L. burtonis exhibits a significantly lower SMR and a higher SDA than does P. lepidopodus. The magnitude of SDA in L. burtonis is comparable to that of some pythons and vipers, providing yet more evidence for the remarkable convergence between this species and ambush-foraging snakes.

Ground squirrel tail-flag displays alter both predatory strike and ambush site selection behaviours of rattlesnakes

Many species approach, inspect and signal towards their predators. These behaviours are often interpreted as predator-deterrent signals—honest signals that indicate to a predator that continued hunting is likely to be futile. However, many of these putative predator-deterrent signals are given when no predator is present, and it remains unclear if and why such signals deter predators. We examined the effects of one such signal, the tail-flag display of California ground squirrels, which is frequently given both during and outside direct encounters with northern Pacific rattlesnakes. We video-recorded and quantified the ambush foraging responses of rattlesnakes to tail-flagging displays from ground squirrels. We found that tail-flagging deterred snakes from striking squirrels, most likely by advertising squirrel vigilance (i.e. readiness to dodge a snake strike). We also found that tail-flagging by adult squirrels increased the likelihood that snakes would leave their ambush site, apparently by elevating the vigilance of nearby squirrels which reduces the profitability of the ambush site. Our results provide some of the first empirical evidence of the mechanisms by which a prey display, although frequently given in the absence of a predator, may still deter predators during encounters.