Moving in two worlds: aquatic and terrestrial locomotion in sea snakes (Laticauda colubrina, Laticaudidae)

Yellow-lipped sea kraits (Laticauda colubrina) are amphibious in their habi ts. We measured their locomotor speeds in water and on land to investigate two topics: (1) to what degree have adaptations to increase swimming speed (paddle-like tail etc.) reduced terrestrial locomotor ability in sea kraits ?; and (2) do a sea krait's sex and body size influence its locomotor abili ty in these two habitats, as might be expected from the fact that different age and sex classes of sea kraits use the marine and terrestrial environme nts in different ways? To estimate ancestral states for locomotor performan ce, we measured speeds of three species of Australian terrestrial elapids t hat spend part of their time foraging in water. The evolutionary modificati ons of Laticauda for marine life have enhanced their swimming speeds by abo ut 60%, but decreased their terrestrial locomotor speed by about 80%. Large r snakes moved faster than smaller individuals in absolute terms but were s lower in terms of body lengths travelled per second, especially on land. Ma le sea kraits were faster than females (independent of the body-size effect ), especially on land. Prey items in the gut reduced locomotor speeds both on land and in water. Proteroglyphous snakes may offer exceptional opportun ities to study phylogenetic shifts in locomotor ability, because (1) they d isplay multiple independent evolutionary shifts from terrestrial to aquatic habits, and (2) one proteroglyph lineage (the laticaudids) displays consid erable intraspecific and interspecific diversity in terms of the degree to which they use terrestrial vs. aquatic habitats.