The influence of nest temperatures and maternal brooding on hatchling phenotypes in water pythons

Previous work on phenotypic plasticity in hatchling reptiles has dealt almost exclusively with lizards and turtles from temperate zone habitats, in taxa where the only maternal control over incubation regimes is exerted via nest site selection. In contrast, water pythons (Liasis fuscus) in northern Australia are tropical snakes that show facultative maternal brooding, with shivering thermogenesis to warm the clutch. Thus, incubation temperatures of this species are influenced both by nest site selection and by maternal care. We experimentally simulated three thermal regimes typical of different types of natural nests in our study population. These were (1) hot, stable temperatures typical of nests laid in the burrows of varanid lizards (constant 32°C); (2) lower and more variable temperatures typical of nests laid inside tree root boles, either with maternal attendance (diel range 27.1°-32.9°C); or (3) in root boles but without maternal attendance (24.3°-32.9°C). We incubated 187 eggs from 15 clutches obtained from field-caught gravid pythons, using a split-clutch design to quantify influences on morphology (offspring size and shape), locomotor performance (swimming ability), and behavior (escape tactics, propensity to strike, willingness to feed in captivity). The thermal regime during incubation strongly affected incubation periods, body sizes, body shapes (mass and tail length relative to snout-vent length), initial growth rates, escape behavior, and willingness to feed. We also detected strong maternal effects on all of these traits, and interactions between maternal effects and incubation regimes. Thus, a female python's 'decisions' as to where she lays her eggs and whether she remains and broods them through development have major consequences for the phenotypes of her offspring.