Chemical Basis of Prey Recognition in Thamnophiine Snakes: The Unexpected New Roles of Parvalbumins

Detecting and locating prey are key to predatory success within trophic chains. Predators use various signals through specialized visual, olfactory, auditory or tactile sensory systems to pinpoint their prey. Snakes chemically sense their prey through a highly developed auxiliary olfactory sense organ, the vomeronasal organ (VNO). In natricine snakes that are able to feed on land and water, the VNO plays a critical role in predatory behavior by detecting cues, known as vomodors, which are produced by their potential prey. However, the chemical nature of these cues remains unclear. Recently, we demonstrated that specific proteins–parvalbumins–present in the cutaneous mucus of the common frog (Rana temporaria) may be natural chemoattractive proteins for these snakes. Here, we show that parvalbumins and parvalbumin-like proteins, which are mainly intracellular, are physiologically present in the epidermal mucous cells and mucus of several frog and fish genera from both fresh and salt water. These proteins are located in many tissues and function as Ca2+ buffers. In addition, we clarified the intrinsic role of parvalbumins present in the cutaneous mucus of amphibians and fishes. We demonstrate that these Ca2+-binding proteins participate in innate bacterial defense mechanisms by means of calcium chelation. We show that these parvalbumins are chemoattractive for three different thamnophiine snakes, suggesting that these chemicals play a key role in their prey-recognition mechanism. Therefore, we suggest that recognition of parvalbumin-like proteins or other calcium-binding proteins by the VNO could be a generalized prey-recognition process in snakes. Detecting innate prey defense mechanism compounds may have driven the evolution of this predator-prey interaction

Larval growth in polyphenic salamanders: making the best of a bad lot

Polyphenisms are excellent models for studying phenotypic variation, yet few studies have focused on natural populations. Facultative paedomorphosis is a polyphenism in which salamanders either metamorphose or retain their larval morphology and eventually become paedomorphic. Paedomorphosis can result from selection for capitalizing on favorable aquatic habitats (paedomorph advantage), but could also be a default strategy under poor aquatic conditions (best of a bad lot). We tested these alternatives by quantifying how the developmental environment influences the ontogeny of wild Arizona tiger salamanders (Ambystoma tigrinum nebulosum). Most paedomorphs in our study population arose from slow-growing larvae that developed under high density and size-structured conditions (best of a bad lot), although a few faster-growing larvae also became paedomorphic (paedomorph advantage). Males were more likely to become paedomorphs than females and did so under a greater range of body sizes than females, signifying a critical role for gender in this polyphenism. Our results emphasize that the same phenotype can be adaptive under different environmental and genetic contexts and that studies of phenotypic variation should consider multiple mechanisms of morph production