Phylogenetic patterns in learning and decision making in pit vipers (Viperidae: Crotalinae)

Learning is a key behavioural adaptation allowing animals to respond to complex and changing environments. Although the field of animal behaviour has seen an increase in the taxonomic breadth of learning studies in recent decades, investigations within an explicit, broad phylogenetic framework are rare, curtailing our understanding of the evolution of learning and advanced cognition. Pit vipers (Viperidae: Crotalinae) represent a particularly interesting taxon in which to study patterns in learning as they are widely studied, have had learning documented in many species, occupy a range of ecological niches and possess vast and varied natural history traits. We investigated the latency to decision in a laboratory thermal maze in 13 species of pit viper (7 species of rattlesnakes and 6 species of nonrattlesnake pit viper) and one true viper species (the puff adder, Bitis arietans (Viperidae: Viperinae), as an outgroup comparison). Relative to the other pit vipers, rattlesnakes uniformly and quickly (after only one trial) decreased their latency to respond to thermal stress; their latency remained low and uniform across the remaining 11 trials. All other pit viper species failed to modify their behaviour across trials and maintained a consistent latency across all 12 trials, as did the puff adder. This pattern could reflect differential learning abilities between rattlesnake and nonrattlesnake pit vipers. Our results underscore the advantages of incorporating a broad phylogenetic perspective when investigating learning and comparative cognition.