Using Microsatellites to Characterize the Population Structure of Redline and Greenside Darters in the Upper Tennessee River Basin

Microsatellite markers are powerful genetic tools that have been used to answer questions concerning population structure, population demography, and influences of landscape features on populations. Because microsatellites have become widely available and relatively affordable only recently, they have so far seen little use in non-game stream fishes. As a preliminary assessment of the utility of microsatellites for understanding the population genetic structure of such species, we (1) screened a suite of 18 microsatellite markers developed for various darter species for applicability in redline and greenside darters, two locally abundant fishes of the upper Tennessee River basin (UTRB), and (2) used a set of 5 and 7 applicable markers, respectively, to characterize population genetic patterns of the two species at 16 sites spread throughout the UTRB. For both species, overall gene diversity (HE = 0.71-0.80) and allele richness (A = 7.7-8.7) were high, whereas genetic differentiation (FST = 0.06-0.08) among sites was low. Moreover, differentiation appeared to be driven more by genetic drift than by mutation. This indicates generally weak population structuring across the UTRB. Genetic differentiation among sites was unrelated to the fluvial or aerial distance separating them, but was strongly related to the presence or absence of large dams between them. Because of their high variability and ability to indicate recent alterations of population dynamics (e.g., due to anthropogenic barriers), we expect microsatellites to prove useful in future large-scaled studies of population structure in darters and other fishes.