Abstract
Reproductive isolation of populations may eventually lead to genetic differentiation as gene pools are altered by localized selective factors and drift. The spatial structuring of genetic differentiation depends on the spatial dimensionality of gene flow, which is a reflection of dispersal behavior (e.g., Selander 1970). Edmunds and Alstad (1978) proposed that the sedentary nature of black pineleaf scale Nuculaspis californica Coleman (Homoptera: Diaspididae) promoted the formation of demes that were adapted to the unique genotype of individual pine host plants. This specialization to the genotype of one host could reduce fitness on conspecific hosts that differ in genotype, thereby limiting the spread of scale populations among trees and generating a patchy distribution (Edmunds and Alstad 1978). Support for the demic adaptation hypothesis comes from the patchy distribution common to many species of scale insects, whereby heavily infested trees stand among others that appear free of scale (Miller and Kosztarab 1979). However, attempts to document demic adaptation in natural populations of scale insects have yielded conflicting results (Wainhouse and Howell 1983; Unruh and Luck 1987; Cobb and Whitham 1993; Hanks and Denno 1994).
Published Version
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