A Genetic Analysis of Habitat Selection in the Cactophilic Species, Drosophila mojavensis

Abstract

Past studies of habitat selection in insects have addressed various relationships among variation, heredity and natural selection; three basic factors for the process of evolution. Most research on habitat choice in insects concentrates on the selection of host plants as feeding and oviposition sites because these resources are demonstrably related to fitness (Whitham 1980). Indeed, the concept of host plant races even implies a degree of coevolution of an insect with such resources (Jaenike 1981). Demonstration that two populations or species currently using different host plant species also have different loci or alleles at a single locus that exerts control over habitat choice is a frequent test for past coevolution with the respective host plants (Huettel and Bush 1972). These studies are helpful in comparing the outcome of evolution with theoretical models of population subdivision and their associated speciation patterns (Maynard Smith 1966, Bush 1969). To predict future evolutionary possibilities, however, an investigation of genetic polymorphism for habitat preference behavior within a single population is valuable. Establishing that individual genetic differences in host plant preferences exist allows the prediction of a response to any form of natural selection: directional, stabilizing or disruptive. Quantification of the amount of genetic variation in behavior, which is the trait’s heritability when measured as a precentage of the phenotypic variance, reveals the rate of evolution of behavior when information on the intensity of natural selection is available also (Falconer 1981). The aims of this study are: (1) to learn whether a monophagous insect population has genetic variation for acceptance of an unfamiliar host plant species; and (2) to quantify the amount of such genetic variation in behavior that is available to produce a response to natural selection in future generations.