Post-prandial chemosensory searching in black rat snakes

Abstract

In a laboratory experiment, black rat snakes, Elaphe o. obsoleta, increased rates of tongue flicking following ingestion of prey. This post-prandial tongue-flick increase, in combination with searching behaviour, represented post-prandial chemosensory searching (PPCS). Such chemosensory searching enabled rat snakes to locate subsequent prey more quickly than initial prey, which may prove beneficial in the wild. Single snakes of five other colubrid species also showed post-prandial tongue flick increases in similar experiments. Field observations are described that support inferences drawn from experimental results. Strike-induced chemosensory searching (SICS) is well known in venomous snakes, and was thought to have evolved as an adaptation for chemically trailing envenomated prey after voluntary release. This study adds to a growing list of non-venomous squamates that appear to show SICS, suggesting that the trait may instead be widespread and ancestral. The data are consistent with the view that SICS arose in a snake–lizard ancestor and may now serve different functions in different lineages. The emerging scenario for the evolution of chemosensory searching is a complex mix of adaptation and exaptation, underscoring the need to distinguish historical origin from current utility in the study of behavioural traits.