Swimming and pregnancy in Tiger snakes, Notechis scutatus

Reduced locomotor ability may increase susceptibility to predation and hence may represent a proximate mechanism by which “costs” of reproduction are expressed (Shine, 1980). In squamate reptiles, many examples of such effects have been documented, where non-gravid females and/or males showed higher survival rates than gravid females (Shine, 1980; Andren, 1982, 1985; Madsen, 1987). For instance, pregnancy may entail a reduction in locomotor performances in lizards and snakes (Shine, 1980; Shine, 2003; Bauwens and Thoen, 1981; Garland and Else, 1987; Seigel et al., 1987), including decreased burst speed by 12 to 30%, and endurance by 52 to 55%. Because fleeing from predators or foraging ability depends on speed and/or stamina, reduced locomotor performance resulting from carrying offspring may result in increased risk of predation and/or decreased energy intake compared to non-gravid females. However, less clear is the effect of pregnancy on aquatic locomotion. Many snakes inhabit aquatic environments such as rivers, lakes, swamps, mangroves, or oceans (Voris and Jayne, 1979; Voris and Karns, 1996; Jayne et al., 1988; Shine and Shetty, 2001) and may rely on water for feeding, and/or as an escape route from predators (such as sharks for sea kraits; Weatherhead and Robertson, 1992;