Can all snakes swim? A review of the evidence and testing species across phylogeny and morphological diversity

Alternative hypotheses suggest that the reptiles at the origin of snakes were primarily either burrowing, terrestrial or marine. It is possible that the ability to swim varies between the major snake lineages and lifestyles; for example, the highly fossorial blind snakes (Scolecophidia), a lineage that emerged early in snake evolution over 100 My ago, may not be able to swim. However, it is sometimes stated that all snakes can swim suggesting that swimming ability may not be discriminatory. To find out whether this is true, we used a systematic search (PRISMA), including personal communications and information on websites. Of the 3951 species considered, no information was found for 89 % of all snakes. Of the 454 species for which information was found, 382 species were aquatic, only 62 were terrestrial, 6 were arboreal, and only 4 were burrowing. Moreover, almost all belonged to the speciose Colubroides (e.g. 58 % Colubridae, 20 % Elapidae). No reliable information was available for important early diverging lineages (e.g. Scolocophidia, Aniliidae). Faced with this lack of information, we filled in important phylogenetic gaps by testing the swimming capacity of 103 diverse snake species and 13 species of diverse limbed and limbless ectothermic tetrapod vertebrates (Amphisbaenia, Lacertilia, Gymnophiona). All tests were positive. The results show that, 1) all snakes for which information is available (525 species) appear to be able to swim, 2) this is a trait shared by many land vertebrates that undulate laterally. As swimming ability is non-discriminatory, we need to collect detailed measurements on the performance, kinematics and energetic efficiency of swimming snakes. It is also necessary to finely describe the ecology and morphology of the species studied to better understand form∼function relationships and the occupation of ecological niches in snakes.