Population structure of rhagoletis mendax, the blueberry maggot

Rhagoletis mendax, the blueberry maggot, is a member of the R. pomonella species complex, well- known as a possible example of sympatric speciation via host race formation. Using electrophoretic data for 16 loci, I have determined that the population structure of R. mendax differs sharply from that of the well-known apple maggot fly, R. pomonella, as follows: (i) geographical differentiation across eastern North America is very small (F_ST = 0.015 as opposed to F_ST = 0.220 in R. pomonella), (ii) no latitudinal dines in allele frequencies exist, and (iii) consistent differentiation with respect to individual host plant and host plant species was not seen (although such differentiation could not be studied as effectively in R. mendax as in R. pomonella). Fum and Had show strong linkage disequilibrium in two northern populations, and weak but significant disequilibrium across the entire geographical range of R. mendax. The genetic uniformity of R. mendax may be a consequence of its restriction to a single host plant species over most of its range.