Genetic changes coinciding with the colonization of California by the walnut husk fly, Rhagoletis completa.

In order to examine the genetic effects of a population bottleneck, the agricultural pest Rhagoletis completa (Diptera: Tephritidae) was analyzed using electrophoretic data in its native and introduced ranges. The fly was accidentally introduced into southern California in the 1920s, and in the 1950s expanded its range into N California, Oregon, and Washington. Three genetic differences between 8 natural and 8 introduced populations were observed. 1) greater allele frequency variance in introduced than natural populations; 2) larger negative values of the inbreeding coefficient in the introduced than the native population; and 3) larger amounts of linkage disequilibrium between the sex-linked genes and sex chromosomes in the introduced than native populations. These effects are partially interrelated, with an especially strong relation between the inbreeding coefficient and linkage disequilibrium. These effects are most simply explained as drift, although segregation distortion and natural selection may also be involved.-Author