EFFECTS OF LARVAL DENSITY ON POSTMETAMORPHIC SPADEFOOT TOADS (SPEA HAMMONDII)

Abstract

To evaluate the effects of larval environment on postmetamorphic performance in the spadefoot toad, Spea hammondii, larvae were reared at one of two densities, creating groups of small and large terrestrial juveniles. These terrestrial juveniles were reared, either individually in the laboratory or in groups in outdoor tanks, at high and low food levels until they were 1 yr old. Larger terrestrial juveniles had higher probabilities of survival to 1 yr of age than smaller juveniles. Larval density did not strongly affect the maximum postmetamorphic growth rate of metamorphs. Body mass differences resulting from larval environment were maintained or slightly increased over the first year of terrestrial growth. The only exception occurred among males receiving high food after metamorphosis in both the laboratory and outdoor tanks; here the size differences disappeared. Larval environment did not influence the proportion of males reaching maturity in their first year. No females matured in their first year; this difference in the rate of maturation in males and females is consistent with published field studies. In outdoor tanks, males from the high-density larval treatment were active on the surface more often than those from the low-density larval treatment. These results are in general agreement with previous studies that have suggested that small size at metamorphosis is associated with lower adult fitness, in this case through lower survival and smaller body sizes. However, the results of this study suggest that the extent to which larval environment can influence subsequent terrestrial characteristics, such as growth and behavior, may vary with sex and terrestrial food availability.