Income breeding and temperature-induced plasticity in reproductive traits in lizards.

We used the northern grass lizard Takydromus septentrionalis as a model animal to examine the energy allocation strategy and whether body temperature can affect maternal reproductive traits in lizards. We maintained adult females collected from the field soon after winter dormancy under three thermal conditions (24.0+/-1.0 degrees C, 28.0+/-1.0 degrees C and 32.0+/-1.0 degrees C) throughout the subsequent reproductive season, and then recorded their energy intake, digestive efficiency, body size and mass changes, and reproductive parameters. Manipulation of body temperature in reproducing females affected energy intake and several maternal reproductive characteristics. Females allocated energy to reproduction following the fulfillment of energetic requirements for metabolism and growth. The reduced energy availability for reproduction constrained females at low or high body temperatures to produce fewer and smaller eggs per season but had no role in influencing the number of eggs produced in single reproductive bouts. Females used currently acquired energy to fuel reproduction, and this strategy did not shift seasonally from the first to subsequent clutches. Our study supports the idea that the use of currently acquired energy for reproduction may be more widespread in ectotherms than thought before, and shows for the first time that egg size is thermally plastic in T. septentrionalis, where eggs produced in single reproductive bouts are believed to be well optimized for size.