The "good genes" hypothesis predicts that mating preferences enable females to select mates of superior genetic quality. The genetic consequences of the preference shown by female gray tree frogs for long-duration calls were evaluated by comparing the performance of maternal half-siblings sired by males with different call durations. Offspring of male gray tree frogs that produced long calls showed better performance during larval and juvenile stages than did offspring of males that produced short calls. These data suggest that call duration can function as a reliable indicator of heritable genetic quality.

Good genes'' models of sexual selection predict that male courtship displays can advertise genetic quality and that, by mating with males with extreme displays, females can obtain genetic benefits for their offspring. However, because the relative performance of different genotypes can vary across environments, these genetic benefits may depend on the environmental context; in which case, static mating preferences may not be adaptive. To better understand how selection acts on the preference that female gray tree frogs (Hyla versicolor) express for long advertisement calls, I tested for genetic benefits in two realistic natural environments, by comparing the performance of half-sibling offspring sired by males with long versus short calls. Tadpoles from twelve such maternal half-sibships were raised in enclosures in their natal pond at two densities. In the low-density treatment, offspring of long-call males were larger at metamorphosis than were offspring of short-call males, whereas in the high-density treatment, offspring of males with long calls tended to metamorphose later than offspring of males with short calls. Thus, although the genes indicated by long calls were advantageous under low-density conditions, they were not beneficial under all conditions, suggesting that a static preference for long calls may not be adaptive in all environments. Such a genotype-by-environment interaction in the genetic consequences of mate choice predicts that when the environment is variable, selection may favor plasticity in female preferences or female selectivity among environments to control the conditions experienced by the offspring.

One of the major unanswered questions in the study of global amphibian declines is why only some species or populations suffer declines. A possible explanation is that species and populations vary in the genetic basis of their tolerance to environmental stress such as chemical contamination. The presence of genetic variation in tolerance to chemicals and in fitness traits of amphibians is essential for persistence of species populations through survival and successful reproduction in contaminated environments. We tested for the presence of genetic variation in the tolerance of amphibian larvae to the insecticide carbaryl using gray treefrog tadpoles (Hyla versicolor). We also assessed whether tolerance of tadpoles is negatively associated with larval performance traits directly related to adult fitness, thereby providing a test of the "cost of tolerance" hypothesis. Our results demonstrate significant variation in tolerance of tadpoles to the insecticide carbaryl within a single population of the gray treefrog, Hyla versicolor. Our half-sibship design indicates that variation among sires explains a significant amount of the variation in chemical tolerance thereby suggesting a heritability genetic basis. Our results also indicate the presence of a fitness tradeoff with tolerance to the chemical carbaryl being negatively correlated, or traded off, with survival of tadpoles reared in the field in the absence of the chemical. Knowledge of genetic tradeoffs with chemical tolerance under realistic environmental conditions will be important for predicting the rate of adaptation and potential for persistence of species. Finally, the partitioning of environmental and genetic variation in tolerance to chemicals is critical to identifying which species are most susceptible, the amount of genetic variance present, the potential for adaptation to contaminants, and the presence of fitness tradeoffs. Such information is necessary to clearly understand the persistence of populations, and ultimately, the processes leading to species declines.

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