Genetic Diversity within and between Sibling-Species of Salt-marsh Horseflies (Diptera: Tabanidae)

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Abstract
A population genetic study of the sibling-species pair of greenhead horseflies, Tabanus nigrovittatus and T. conterminus, was conducted along the Atlantic coast of North America. Four gene loci of twelve surveyed were found to serve as species diagnostic markers. Sympatric populations of the two species were identified from Massachusetts to Virginia; no hybrids were observed anywhere in this range. The coefficient of genetic distance between the two species was 0.453, which coincides with other reported values among sibling-species of Diptera. For each species, genetic diversity was divided into, within and between subpopulation components. For both species, only a small proportion of the total genetic diversity was contained in the differences between local subpopulations. T. nigrovittatus displayed strong latitudinal clines in allelic frequencies at two gene loci, but the patterns of variation at other polymorphic loci were substantially less heterogeneous throughout its range.