Variable offspring provisioning and fitness: a direct test in the field

Summary 1 Variation in the quality of the offspring environment can lead to the evolution of variable offspring provisioning. For variable offspring provisioning to evolve, the magnitude of provisioning per offspring must have effects on offspring and parental fitness. 2 Females of the quacking frog, Crinia georgiana, produce clutches of eggs in which egg size varies between individuals in the population and also within clutches, independent of female size or condition. A trade-off between egg size and number exists. 3 Using microsatellite markers to trace offspring to parents, and therefore clutch type, we tested the performance of tadpoles from clutches of large, small and variable-sized eggs in ponds in the field. 4 Clutches of large eggs resulted in the highest parental fitness and clutches of small eggs resulted in lower parental fitness values. 5 The parental fitness indicated that conditions in these ponds were harsh. Clutches with variable egg sizes had intermediate parental fitness but may be of benefit as a bet-hedging strategy when the qualities of ponds are unpredictable. 6 This study provides new empirical evidence of important offspring and parental fitness consequences of variable maternal provisioning under natural conditions in the field and demonstrates the importance of moving experimental life-history studies out of the laboratory into the field where realistic selection pressures act on developing offspring.