Oxygen consumption of gestating Aspic vipers, Vipera aspis (L.), was strongly dependent on body temperature and mass. Temperature-controlled, mass-independent oxygen consumption did not differ between pregnant and nonpregnant females. Maternal metabolism was not influenced during early gestation by the number of embryos carried but was weakly influenced during late gestation. These results differ from previous investigations that show an increase in mass-independent oxygen consumption in reproductive females relative to nonreproductive females and a positive relationship between metabolism and litter size. These data also conflict with published field data on V. aspis that show a strong metabolic cost associated with reproduction. We propose that, under controlled conditions (i.e., females exposed to precise ambient temperatures), following the mobilisation of resources to create follicles (i.e., vitellogenesis), early gestation per se may not be an energetically expensive period in reproduction. However, under natural conditions, the metabolic rate of reproductive females is strongly increased by a shift in thermal ecology (higher body temperature and longer basking periods), enabling pregnant females to accelerate the process of gestation. Combining both laboratory and field investigation in a viviparous snake, we suggest that reproduction entails discrete changes in the thermal ecology of females to provide optimal temperatures to the embryos, whatever their number. This results in the counterintuitive notion that metabolism may well be largely independent of fecundity during gestation, at least in an ectothermic reptile.

No abstract

Most animals that possess potent venom display a wide variety of warning messages to discourage predators. Tiger snakes are large and highly venomous elapids that exhibit these anti-predator behaviours. We compared the antipredator behaviours of two neighbouring and genetically indistinguishable populations in Western Australia (Herdsman Lake, HL and Carnac Island, CI). CI is free from human, native and feral predation. All of these factors represent a continual threat on HL situated on the mainland. Neither body size, nor sex influenced defensive behaviours. However, we observed a marked interpopulation difference among adults in the degree to which anti-predator behaviours were displayed when snakes were continually aggravated: HL snakes exhibited a typical warning signal (flat-neck) and bite, while CI snakes remained very docile. In stark contrast, neonates of both populations exhibited marked anti-predator behaviours and both populations were indistinguishable in terms of the intensity of display. Neonates reared in captivity, hence regularly confronted by human predators, became more defensive in comparison with neonates exposed to natural conditions on CI; similarly several adult CI snakes kept in captivity became more defensive. Our results highlight the extreme behavioural plasticity of snakes. We also hypothesize that CI snakes may become more placid over time as they grow up in an environment free from predation.

Animals resident on small islands provide excellent opportunities to carry out detailed mark-recapture studies. Populations are closed and ecosystems are often simpler than those of mainland sites. These factors enable the study of cryptic species that have otherwise been neglected. Snakes are notable for their secretive nature and, as a result, few natural populations have been accurately described through long-term mark-recapture monitoring. A population of tiger snakes ( Notechis scutatus ) was studied on Carnac Island, a small limestone island (16 ha) off the coast of Western Australia. Population estimates show that snake density is very high, with more than 20 adult snakes per ha. This equates to a biomass of more than 100 kg of a top predator concentrated in a very small area. Such a high predator density can be explained because adult snakes feed mainly on chicks of nesting birds that breed in large colonies on Carnac but forage elsewhere. Substantial annual growth rates in body size in most individuals suggest that food availability is high on Carnac. Growth rates decreased more sharply in adult females than in males, whereas annual changes in body mass were similar in both sexes, probably because of the high energetic costs of reproduction experienced by females. Surprisingly, the sex ratio was highly biased, with males largely outnumbering females.