Reproductive trade-offs and bet-hedging in Hyla calypsa, a Neotropical treefrog.

I studied spatial and temporal variation in reproductive activity of Hyla calypsa along a montane stream in south-central Costa Rica between 1991 and 1996. Maggots of drosophilid flies killed the greatest number of frog eggs, while mortality from other sources was random and unpredictable. Late-season increases in fly predation may select for high, early reproductive effort by the frogs. Female frogs in this population show intra-clutch and seasonal variation in egg diameter and seasonal variation in clutch size. There were no correlations between female size and egg or clutch parameters. Egg diameter varied more within a clutch than among clutches, suggesting that individual females were allowing for unpredictable environmental conditions or that the larval environment may be selecting for variation in propagule size. This species uses both bet-hedging and trade-offs between offspring size and number to maximize the chance of producing tadpoles. Future studies should determine the advantages of small and large hatchlings and whether these relate to environmental variation in the stream.