Silver spoons and snake body sizes: prey availability early in life influences long-term growth rates of free-ranging pythons

1. A 13-year study of free-ranging water pythons (Liasis fuscus) and their main prey (dusky rats, Rattus colletti) in tropical Australia provided extensive data on the relationship between python growth rates and prey availability. 2. Python growth rates exhibited considerable variation among individuals. Growth rates of siblings were not correlated, suggesting that environmental rather than genetic factors cause this wide variation. 3. The availability of prey varied considerably among years, due to annual variation in rainfall patterns. Pythons grew more rapidly ill years with high rat abundance than in years when rats were scarce. Also, python cohorts that hatched in years when prey were abundant exhibited faster growth rates than those that hatched when prey were scarce. 4. The snakes showed strong ontogenetic consistency in relative growth rates: that is, an individual with faster-than-average growth in its first year of life continued to grow rapidly throughout the study period. Thus, these pythons displayed a strong 'silver spoon' effect, whereby favourable conditions (high prey abundance) in the first year of life exerted a long-term effect on growth trajectories and thus, adult body sizes. This effect was strongest in the faster-growing sex (females). 5. Hence, the current body size composition of the python population reflects stochastic rainfall-induced annual variation in prey availability over the preceding decades.