Constraints, allometry, and adaptation: food habits and reproductive biology of Australian brownsnakes (Pseudonaja: Elapidae)

Phylogenetic conservatism, allometry, and proximate environmental effects may be as important as adaptation in determining interspecific variance in diets and life-histories, especially within rather than among lineages. This view is supported by data from dissection of 2152 preserved specimens of 10 species of Australian "brownsnakes" (Pseudonaja), and by observations of captive snakes. All species except P. modesta grow to >1 m in length. The extent of sexual size dimorphism is similar in all taxa but is influenced by allometry; males are slightly larger, relative to females, in larger species. Most of the larger taxa (affinis, textilis, and "nuchalis") eat a wide range of terrestrial vertebrates, especially small mammals. Smaller species of Pseudonaja tend to eat lizards and frogs, as do juveniles of the larger species. Pseudonaja inframacula is unusual in its restriction to forested areas and the scarcity of mammals in its diet. The diets of most species of Pseudonaja are phylogenetically conservative, with intrageneric variance mainly due to differing body sizes (probably because of gape-limitation). Reproductive biology of this genus is also conservative and dependent upon body size. Maternal body size correlates with clutch size intraspecifically, and with both mean fecundity and mean offspring size interspecifically. Adaptation may have been important primarily during divergence of the ancestral taxon from other elapids. For example, compared to most other Australian elapids, all Pseudonaja produce large clutches of small eggs. Individuals of Pseudonaja are unusual also in their ability to thrive in disturbed habitats and their utilization of introduced mammals (especially Mus) as a significant food source.