Abstract
During the course of migration and dispersal, new populations of a species may be founded by a small number of initial colonists. The genetic material of such a population will be limited to those alleles introduced by these few founders and may not be representative of the species as a whole. The evolutionary significance of such a genetic bottleneck, termed by Mayr (1942) the founder principle, has been extensively investigated. Powell and Richmond (1974) and Jones and Yamazaki (1974) have suggested that in populations of Drosophila founded by very small numbers of individuals or small numbers of homozygous lines, erratic changes in allozyme frequencies may occur due to linkage disequilibria. These disturbances in the genetic material of a population, similar to the genetic revolution envisioned by Mayr (1954), may lead to novel outcomes in population phenotypes (Palenzona et al., 1974; Mertz et al., 1976) and the reorganization of genomes (Mayr, 1954). For example, the speciation of Drosophila heteroneura and D. silvestris in the Hawaiian Islands is attributed to single gravid females colonizing newly formed open habitats (Carson, 1970, 1971), and similar speciation processes have been observed experimentally (Powell, 1978) as well as in a recently founded population of D. pseudoobscura (Prakash et al., 1969; Prakash, 1972). Studies of chromosomal polymorphisms in Drosophila species suggest an important role for genetic bottleneck not only during speciation but also in microevolutionary processes (Da Cunha et al., 1959; Dobzhansky, 1963). These studies have
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