Costs of Reproduction in a Population of the Frog Crinia signifera (Anura: Myobatrachidae) from Southeastern Australia

Abstract

Common eastern froglets (Crinia signifera) breeding in a pond at Darkes Forest, New South Wales, were studied from June 1987 to May 1989. All frogs entering and leaving the pond were caught by a pit-fall and drift-fence system in order to measure rates of reproduction, loss of body mass due to reproduction and mortality of frogs in the pond area. Clutch mass varied greatly among females, with reproductive frequencies and RCMs (=relative clutch masses) increasing with female body length. Females with high RCMs experienced significantly higher post-reproductive mortality than did other reproducing females. Most male frogs lost body mass during breeding periods in the pond area, spending a mean period of 68 days there. Most males entered the pond area only once per year. Male frogs suffered higher mortality when in the pond area than did females, presumably due to greater exposure to predators as a result of their calling activity. The reproductive strategy of Crinia signifera is characterized by high levels of reproductive expenditure, despite high consequent mortality rates for both sexes. We infer that the low annual survival rates of frogs in this population have favored the evolution of (i) high levels of reproductive effort in both sexes, and (ii) variable clutch sizes and RCMs in females, because of the advantages of reproducing as soon as environmental conditions are suitable. Life-history theory is based on the idea that natural selection tends to maximize lifetime re- productive success of individuals (e.g., Stearns, 1976). In particular, trade-offs between current and future reproductive expenditure are be- lieved to be important determinants of optimal (and hence, perhaps, observed) levels of repro- ductive expenditure in iteroparous organisms (Williams, 1966a). These trade-offs may influ- ence a number of life-history characteristics (e.g.,