Lizards Combine Stored Energy and Recently Acquired Nutrients Flexibly to Fuel Reproduction

1. Energy allocation strategies for reproduction are viewed typically as a continuum between reliance on 'income' (recently acquired energy) vs. 'capital' (stored reserves) for fuelling reproduction. Because ectothermy facilitates long-term energy storage and often involves low feeding rates, traditional views suggest that many ectotherms rely heavily on stored reserves for egg production. 2. We explored the temporal relationship between energy intake and expenditure in a multi-clutching lizard (Amphibolurus muricatus) by evaluating the effect of maternal nutrition on reproductive output and by contrasting δⁱ³C measurements of the maternal diet and endogenous energy stores with that of the eggs produced. 3. Our experiment revealed that females utilize both endogenous energy stores and recently acquired food to fuel reproduction; this pattern did not shift seasonally from first to second clutches produced. Importantly, however, egg lipid was derived primarily from capital, whereas egg protein was derived about equally from both income and capital. 4. Overall, these results suggest that the energy allocation strategy used for reproduction differs among egg components, and that the use of recently acquired energy for reproduction may be more widespread in ectotherms than thought previously.