The population biology of Hyla calypsa, a stream-breeding treefrog from lower Central America

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)



First Committee Member

Jay M. Savage - Committee Chair


I describe Hyla calypsa as a species distinct from Hyla lancasteri based on adult and larval morphology, oviposition site, egg and clutch characteristics and vocalizations. I studied the population biology of Hyla calypsa in the Cordillera de Talamanca of south-central Costa Rica from 1991-1994. Territorial males are present throughout the year although females may arrive along the stream three times per season to deposit clutches of 10-36 eggs on vegetation overhanging the stream. Both males and females may live over 750 d and return to the same areas of the stream during this time. The extended rainy season at this site (Apr.-Dec.) allows for a prolonged breeding season. The asynchronous arrival of females at the breeding site combined with the prolonged breeding season results in male-biased nightly sex ratios and the opportunity for female mate choice. The uneven dispersion of males and clutches along the transect suggests that females preferentially choose either particular resident males or areas of the stream.Reproductive success was unevenly distributed among the males in the population, with a few males siring the majority of clutches and tadpoles. A multivariate analysis of the distribution of reproductive success with regard to male morphology (SVL, mass), behavior (site tenure, nightly frequency of calling), and territory quality indicates that positive directional selection operates on breeding site tenure. This directional selection for increased site tenure and the high but variable clutch mortality due to drosophilid fly parasitism may be maintaining the extended breeding season, despite low hatching success late in the year. There was no evidence for stabilizing, disruptive, or correlational selection.


Biology, Ecology; Biology, Zoology

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