Life-History Variation in a Population of the Australian Frog Ranidella signifera: Seasonal Changes in Clutch Parameters

Abstract

Clutch parameters of the Australian frog Ranidella signifera were studied over 3.5 yr in a population in the Adelaide Hills, South Australia. During its prolonged breeding season from March to Nov. peak breeding occurred in July and Aug. There was significant variation in clutch parameters over the breeding season. Egg size was largest in the peak breeding period and smaller earlier and later in the season. Clutch size was smaller late in the season. This seasonal variation in clutch parameters was also related to temperature for the 30-day period prior to egg laying. Only clutch size showed a significant effect of season after adjustment for temperature. The most likely explanation for the observed variation in egg size was that it depended on the environment (particularly temperature) experienced by the female during egg formation. These observations are consistent with other data suggesting that egg size has less impact on fitness than does temperature at development, sibship, and the timing and position of egg laying. A negative correlation between egg size and clutch size, after correction for female size and temperature, suggested a trade-off between size and number of offspring. However, a positive relationship between female size and clutch size indicated that larger females could produce large eggs and still produce more eggs than could smaller females. The data also suggest that different factors may influence the way a late-season clutch is packaged, relative to early and midseason clutches.