Submitted to: BMC Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/21/2009
Publication Date: 5/21/2009
Publication URL: www.biomedcentral.com/1471-2148/9/113
Citation: Huestis, D.L., Oppert, B.S., Marshall, J.L. 2009. Geographic Distributions of Idh-1 Alleles in a Cricket are Linked to Differential Enzyme Kinetic Performance Across Thermal Environments. BMC Ecology 9: 113. doi:10.1186/1471-2148-9-113 Interpretive Summary: Crickets are a problem in many urban areas. Even though they may be the same species, crickets found in different areas may adapt genetically to changes in their environment, such as temperature, rainfall, and light. In one cricket species, we compared differences in metabolism enzyme activity over a range of temperatures in individuals found in different parts of the country. We found a strong association between a gene encoding a metabolism enzyme and local temperature. Therefore, these crickets have adapted to living in different temperatures, which may have implications for cricket survival in new areas as climates change due to global warming.
Technical Abstract: Geographic clines within species are often interpreted as evidence of adaptation to varying environmental conditions. However, clines can also result from genetic drift, and these competing hypotheses must therefore be tested empirically. The striped ground cricket, Allonemobius socius, is widely-distributed in the eastern United States, and clines have been documented in both life-history traits and genetic alleles. One clinally-distributed locus, isocitrate dehydrogenase (Idh-1), has been shown previously to exhibit significant correlations between allele frequencies and environmental conditions (temperature and rainfall). Further, an empirical study revealed a significant genotype-by-environmental interaction (GxE) between Idh-1 genotype and temperature which affected fitness. Here, we use enzyme kinetics to further explore GxE between Idh-1 genotype and temperature, and test the predictions of kinetic activity expected under drift or selection. Results We found significant GxE between temperature and three enzyme kinetic parameters, providing further evidence that the natural distributions of Idh-1 allele frequencies in A. socius are maintained by natural selection. Differences in enzyme kinetic activity across temperatures also mirror many of the geographic patterns observed in allele frequencies. Conclusions This study further supports the hypothesis that the natural distribution of Idh-1 alleles in A. socius is driven by natural selection on differential enzymatic performance. This example is one of several which clearly document a functional basis for both the maintenance of common alleles and observed clines in allele frequencies, and provides further evidence for the non-neutrality of some allozyme alleles.