Journal of Animal Ecology 2008, 77, 1242–1249 doi: 10.1111/j.1365-2656.2008.01442.x © 2008 The Authors. Journal compilation © 2008 British Ecological Society Blackwell Publishing Ltd Lizards combine stored energy and recently acquired nutrients flexibly to fuel reproduction Daniel A. Warner 1 *, Xavier Bonnet 2 , Keith A. Hobson 3 and Richard Shine 1 1 School of Biological Sciences, University of Sydney, New South Wales 2006, Australia; 2 Centre d’Etudes Biologiques de Chizé, CNRS, F-79360 Villiers en Bois, France; and 3 Environment Canada, 11 Innovation Boulevard, Saskatoon, Saskatchewan, Canada, S7N 3H5 Summary 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 δ 13 C 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. Key-words: Amphibolurus muricatus, capital breeding, carbon-13, income breeding, stable isotopes Journal of Animal Ecology(2007) doi: 10.1111/j.1365-2656.2007.0@@@@.x Introduction The temporal relationship between the acquisition of energy and its expenditure for reproduction is an important axis of life history variation. Although energy acquisition and allocation tactics cover a continuum, they can be viewed usefully in terms of two end-points: reliance on ‘capital’ vs. ‘income’ to fuel reproductive expenditure (Bonnet, Bradshaw & Shine 1998; Meijer & Drent 1999). ‘Income’ breeders expend energy for reproduction soon after that energy is acquired, whereas ‘capital’ breeders gather energy over long periods prior to utilizing these stored reserves for reproduction (reviewed by Jönsson 1997). These two strategies of energy allocation can influence selection on life-history attributes (e.g. the number and quality of offspring produced, or the frequency of reproduction: Jönsson 1997; Bonnet et al. 2001; Brown & Shine 2002; Lourdais et al. 2002), as well as the sensitivity of reproductive output to local conditions. For example, local resource availability should influence immediate reproductive output strongly in income breeders, but not in capital breeders (due to the temporal separation of energy acquisition and expenditure in the latter group). Clearly, both types of energy allocation strategies have associated costs and benefits; long-term energy storage may allow capital breeders to cope with unpredictable environments or low food availability (Calow 1979; Santos & Llorente 2004), whereas income breeders can increase their reproductive output more rapidly in response to an increase in local food supply (Jönsson 1997). Most research on these issues has focused upon avian and mammalian species (Drent & Daan 1980; Festa-Bianchet, Gaillard & Jorgenson 1998; Kunkele 2000; Veloso & Bozinovic 2000; Voigt 2003), and detailed studies have revealed that these high-energy systems rely on income breeding to fuel some aspect of reproductive expenditure (Bronson & Manning 1991; Klaassen et al. 2001; Gauthier, Bêty & Hobson 2003; Wheatley et al. 2008). On the other hand, features associated with ectothermy may facilitate long-term energy storage, such that capital breeding may be more energetically efficient than income breeding in ectotherms (Bonnet et al. 1998). Consistent with this idea, stored energy reserves (i.e. fat bodies) are used to fuel reproduction in many ectothermic animals (Schultz, Clifton & Warner 1991; *Correspondence author and present address: Daniel A. Warner, Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, Iowa 50011, USA. E-mail: dwarner@iastate.edu