Abstract

Adaptive phenotypic plasticity can be viewed as an evolutionary strategy that enables organisms to match their phenotypes to local conditions. I studied two neighbouring populations of amphibious fresh-water tiger snakes, Notechis ater occidentalis, from Western Australia. One mainland population occurs around a lake, feeds primarily on frogs, and is under strong predation pressure, whereas the second population inhabits a small offshore island with no standing water and no known predators, and feeds primarily on chicks. The availability of water and its use as a habitat differ considerably between the two populations. I compared experimentally the locomotor capacities and behaviour of individuals from both populations in water, treating neonates and adults separately. Sex did not significantly influence any trait in both populations, in either adults or neonates. At birth, the two populations exhibited very little difference in swimming speed, stamina, apnoea capacities or behaviour. However, adult mainland snakes had greater apnoea capacities and faster burst swimming speed than island snakes. Mainland adult snakes also spontaneously swam underwater for longer, and a higher proportion filled their lungs while surface swimming compared with island specimens. This study suggests strong behavioural flexibility in tiger snakes depending on habitats.