Schmidt, B. R., Hotz, H., Anholt, B. R., Guex, G.-D. and Semlitsch, R. D. 1998. Factors contributing to the maintenance of the genetic polymorphism at the locus LDH-B in the pool frog, Rana lessonae. Canadian Journal of Zoology, in press.


Abstract -- We tested for environmental factors that may lead to balancing selection and to the maintenance of a genetic polymorphism at the enzyme locus lactate dehydrogenase B (LDH-B) in the pool frog, Rana lessonae. We raised tadpoles individually in a factorial experiment where we manipulated temperature, food level, and food quality. The only statistically significant difference among LDH-B genotypes was for growth rate with the heterozygote performing best. Although the difference was not significant, heterozygotes also tended to perform best for size at metamorphosis. However, heterozygotes did not perform best for other traits (age at metamorphosis, survival and rate of metamorphosis) where differences among LDH-B genotypes were not significant as well. The size of the effect of LDH-B genotype depended on the environment, suggesting that the locus may be selectively neutral in some environments. There were no genotype-environment interactions in the sense that reaction norms along environmental gradients did not cross. When we raised tadpoles in groups, e/e homozygotes had a significantly higher mass and developed at the significantly highest rate. In addition, there may be a trade off between larval and adult performance: adult frogs show a different ranking in performance of LDH-B genotypes than tadpoles do. These results suggest that the genetic polymorphism is maintained through heterozygote advantage, possibly in conjunction with antagonistic pleiotropy.


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Peter Beerli (beerli@scs.fsu.edu)