Determinants of reproductive output in female water pythons (Liasis fuscus: Pythonidae)

Female water pythons from a population in tropical Australia were captured shortly before oviposition and their eggs were incubated under constant conditions. We obtained data on 1605 eggs and 1285 hatchlings from 111 females to evaluate factors influencing reproductive output. Most reproductive traits varied only slightly between the 2 yr of the study. Successive clutches by the same female were consistent in mean egg and offspring sizes, hatching success, and oviposition date. Whether or not an adult-size female python reproduced in a given year was a function of her body size and her condition. The proportion of reproductive animals was highest at intermediate body sizes, apparently because the largest females could not gather enough energy for reproduction as well as maintenance costs. Clutch sizes and egg sizes were directly affected by maternal body length and maternal condition, but these effects were obscured by a strong indirect effect: a tradeoff between egg size and clutch size. Date of hatching depended primarily on date of oviposition (which in turn differed among subpopulations within our study area, apparently due to thermal factors), but incubation periods also differed between years. Maternal body condition after oviposition was influenced by pre-oviposition condition and relative clutch mass. Path analysis revealed a series of strong effects, both direct and indirect, in the relationships among reproductive variables.