Ovarian cyclicity and fecundity in boreal common frogs Rana temporaria L. along a climatic gradient

Hypotheses that the patterns of energy storage, ovarian development and fecundity change along a climatic gradient were tested. Data from adult female common frogs Rana temporaria L. were collected in three study areas from mixed boreal lowland forest to alpine heath. There were no consistent altitudinal trends in body length or weight. Age, however, increased with altitude. During the feeding season, the rate of primary deposition of energy in the fat bodies was higher in mid-altitude than in lowland females. Relative ovary weight increased faster in alpine heath and mid-altitude frogs than in lowland frogs. There were no indications of an ovarian resting period. Rather, with increased altitude the oocytes for next year's reproduction tended to have entered the vitellogenic growth phase even before oviposition; possibly this was an adaptation to a short feeding season. Body length and fecundity were exponentially related in the lowland and the mid-altitude study areas. The relationship between body weight and fecundity appeared to be linear in at least the lowland population. Fecundity per gram body mass increased with age. Although differences between study areas were found, there was no consistent altitudinal trend in either absolute or size-relative fecundity. Fecundity varied between years as well as between populations. A negative correlation between relative liver weight and fecundity indicated a high cost to reproduction. Nevertheless, skipping years of reproduction, a phenomenon suggested to occur primarily in resource-poor environments, was rare.