Salinity influences the distribution of marine snakes: implications for evolutionary transitions to marine life

Abstract

Secondary transitions from terrestrial to marine life provide remarkable examples of evolutionary change. Although the maintenance of osmotic balance poses a major challenge to secondarily marine vertebrates, its potential role during evolutionary transitions has not been assessed. In the current study, we investigate the role of oceanic salinity as a proximate physiological challenge for snakes during the phylogenetic transition from the land to the sea. Large‐scale biogeographical analyses using the four extant lineages of marine snakes suggest that salinity constrains their current distribution, especially in groups thought to resemble early transitional forms between the land and the sea. Analyses at the species‐level suggest that a more efficient salt‐secreting gland allows a species to exploit more saline, and hence larger, oceanic areas. Salinity also emerged as the strongest predictor of sea snake richness. Snake species richness was negatively correlated with mean annual salinity, but positively correlated with monthly variation in salinity. We infer that all four independent transitions from terrestrial to marine life in snakes may have occurred in the Indonesian Basin, where salinity is low and seasonally variable. More generally, osmoregulatory challenges may have influenced the evolutionary history and ecological traits of other secondarily marine vertebrates (turtles, birds and mammals) and may affect the impact of climate change on marine vertebrates.

Dehydration and Drinking Behavior of the Marine File SnakeAcrochordus granulatus

“…The coupling of excess salt with lack of freshwater is likely the principal deterrent to the evolutionary transition from terrestrial to marine habitats in secondarily marine vertebrates Dunson and Mazzotti 1989;Heatwole 1999;Brischoux et al 2012). These animals are particularly challenged to obtain water because of the higher salt content of the environment relative to that of their body fluids.…”

Foraging behaviour and energy budgets of sea snakes: insights from implanted data loggers

“…The repeated independent colonization of marine habitats provides exceptional opportunities for comparative studies, to clarify the processes involved in a major phylogenetic transition in habitat types (e.g. Shine & Shetty, ; Brischoux et al ., ).…”

Pelagic sea snakes dehydrate at sea

“…salt glands in birds and non-avian reptiles) [3]. However, the efficacy of such mechanisms has been questioned recently by noting dependence on fresh water that appears to limit the distribution and abundance of marine snakes [1,[4][5][6][7].…”

“…The Earth's oceans teem with life, yet these salty environments are physiologically challenging because of the virtual absence of fresh water. The evolutionary transition of animals from land or fresh water to a marine habitat therefore is difficult because of the osmoregulatory challenges posed by salinity [1,2]. The successful clades of marine vertebrates that have undergone significant radiations in marine environments-bony fishes, cetaceans, pinnipeds, sea turtles, sea snakes and some birds-are thought to live independently of fresh water and to have overcome the osmoregulatory challenges by evolving anatomical and physiological specializations that maintain water balance (e.g.…”