Australian Journal of Ecology (1996) 21, 355-362 Decreased food intake in reproducing lizards: A fecundity- dependent cost of reproduction? LIN SCHWARZKOPF* Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada Abstract Reproduction has been shown to be costly in viviparous skinks, both in terms of survival and in terms of growth and future reproductive output. One possible source of such costs could be a reduction in food intake, with an associated reduction in energy available for maintenance and future reproduction. Therefore, I compared food intake in male and female southern water skinks {Eulamprus tympanum), to determine whether food intake was reduced during reproduction in either sex. In addition, I measured the relationship between reduction in food intake and the total volume of offspring or testis, A reduction in food intake proportional to the volume of offspring suggests that costs associated with reduced energy intake may be fecundity dependent. Food intake was estimated using the total volume of stomach contents of individuals. Females ate significantly less (mean volume of stomach contents = 0,13mL) than males (mean = 0,36 mL) just before parturition in January, when embryos were largest. After parturition, females ate significantly more than males. Otherwise, there were no significant differences between the food intake of males and females. Females reduced food intake by eating smaller food items. Females with relatively large numbers of ova or embryos ate relatively less, and therefore decreased food intake in females may be a fecundity-dependent cost of reproduction in these lizards. Males did not reduce food intake during periods when testes were enlarged and mating occurred. Decreased food intake during reproduction is probably an important source of reproductive costs to females of these viviparous lizards, but does not appear to be important in males. Key words: cost of reproduction, Eulamprus tympamtm, fecundity-dependence, food intake, growth, lizard, reproduction, Scincidae, skink. INTRODUCTION Sexual differences in diet and food intake have been observed in various taxonomic groups of organisms, and have been attributed to body size differences, differential habitat use and/or differences in reproductive strategies (Selander 1966; Schoener 1967; Shine 1986), Differences in diet and food intake between the sexes may, in tum, have important demographic implications for males and females, resulting in differential growth rates, and differ- ential survival probabilities related to foraging risk (Shine 1980; Madsen 1987), Also, differences in diet may be an important selective force affecting morphology of males and females (Shine 1988), Due to the increased energy requirements associated with reproducing, food intake increases during repro- duction in many animals (Moustgaard 1969), There are, however, numerous examples of species that reduce • Presen t address: Department of Zoology and Tropical Ecology, James Cook University, Townsville, QLD 4811, Australia, Accepted for publication November 1995, feeding at this time (various birds and mammals: Mrosovsky & Sherry 1980; reptiles: Shine 1980; inver- tebrates: Baird et al 1986; amphibians: Ryser 1989; fish: Svensson 1988), A reduction in food intake due to reproduction may be an important source of costs of reproduction, because low energy intake may deplete energy stores available for maintenance, thereby reducing survival or causing a decrease in future reproductive output in iteroparous organisms. In males, decreased growth rate caused by reduced food intake may cause decreased opportunities for mating due to social factors, because male-male competition or female choice may favour large males (e,g, Carothers 1981; Cooper & Vitt 1993), In species with a significant, positive relationship between body size and fecundity, females suffer a reduction in future reproductive output if decreased feeding causes reduced growth rate, and therefore reduced lifetime fecundity. In addition, ifthe degree of reduction in food intake depends on the number of offspring in a litter or clutch, reduced food intake may constitute a fecundity-dependent cost of reproduction. This may occur when space for food inside the body cavity is