REPRODUCTIVE ENERGY ALLOCATION AND LONG-TERM ENERGY STORES IN A VIVIPAROUS LIZARD (EULAMPRUS-TYMPANUM)

When animals reproduce, does energy for the brood come from stored res erves (from food eaten months or years before), or from food eaten dur ing the current reproductive season? Variation in the duration of ener gy storage prior to reproduction is an important, but little-studied, axis of life history variation. We experimentally manipulated the avai lability of resources to females of a long-lived viviparous lizard (Eu lamprus tympanum, Scincidae) in the first year of a two-year study to assess the relative importance of current food intake vs, stored reser ves as sources of energy for breeding. Females given greater access to high temperatures (and hence, to resources) in the laboratory amassed larger caudal energy stores than did females with lesser opportunitie s. Energy intake during gestation slightly influenced offspring size, but the magnitude of energy stores prior to ovulation had a more drama tic effect: females with larger caudal energy stores produced much lar ger litters in the following year. Growth rates of females were unaffe cted by basking treatments or by reproduction in either year, but fema les that reproduced in the second year showed a large concomitant decr ease in caudal energy stores compared to females that did not reproduc e, indicating a large energetic cost of reproduction. Hence, reproduct ive output within this species can be influenced by resource availabil ity over 12 months prior to reproduction, and simple comparisons of re productive output with current resource availability may fail to detec t the ways in which phenotypically plastic life history traits are inf luenced by environmental features. In addition to an appropriate tempo ral framework, models of resource allocation should also incorporate t he possible roles of physiological and morphological constraints (e.g. , maternal inability, in some species, to modify post ovulation reprod uctive expenditure) and trade-offs with other life history currencies (e.g., decrements in maternal survival due to high relative clutch mas ses). The time lag between resource acquisition and expenditure may ha ve significant consequences for a population's demographic response to shifts in resource availability or predation pressure (via tail autot omy). Finally, this study illustrates the way in which thermal aspects of the environment can influence life history phenotypes in ectotherm ic vertebrates with long-term energy stores.