The genetic makeup of populations in a particular geographic area should conform, in part, to environmental structure. Three polymorphic enzyme loci in the amphipod Gammarus minus are geographically differentiated in gene frequencies in the mid-Appalachian Mountains of the eastern United States, and genetic breaks usually coincide with topographical features and stream divides. Areas with well integrated drainage systems have a high degree of genetic uniformity.
Hetrick, Steven W. and James L. Gooch.
Genetic differentiation in populations of the freshwater amphipod Gammarus minus Say in a karst area.
International Journal of Speleology,
Available at: http://scholarcommons.usf.edu/ijs/vol11/iss1/2