Molecular Systematics of the Least Darter (Percidae: Etheostoma microperca): Historical Biogeography and Conservation Implications
A repeated pattern in North American fishes is species having geographic ranges consisting of two disjunct, widely separated areas of distribution, one in previously glaciated northern areas and one in the unglaciated Ozarks. We used phylogenetic analyses of mitochondrial DNA (ND2 and cyt b) and a nuclear DNA sequence (S7 intron 1) to examine the historical biogeography of one such species, the Least Darter, Etheostoma microperca. Uniquely for Ozark fishes, populations in western Ozark tributaries of the Arkansas River represent most of the evolutionary legacy of the species, with three markedly divergent cyt b clades. Populations in the Illinois River (Arkansas) and Shoal Creek (Missouri) appear to have been isolated for about 5 and 2 my, respectively, and potentially represent undescribed species. A wide-ranging northern clade (Hudson Bay, Great Lakes, and Ohio and upper Mississippi river systems) was sister to a clade comprising haplotypes from Blue River and all Ozark haplotypes exclusive of the Illinois River and Shoal Creek clades. The northern clade appears to have survived Illinoian and Wisconsin glaciations in one or more northern refuges and exhibits molecular genetic signals of population expansion during the Sangamon interglacial. The Blue River and western Ozark populations are especially susceptible to local extirpation with little opportunity for replacement. Persistence of these populations will require maintenance of springflows via regional groundwater management.
Distribution of collection localities. (A) All localities; dark lines illustrate present distribution of the species (Burr, 1978; Lee et al., 1980), lower = Blue River (site 1) and Ozark locations; upper = northern portion of the range (extends east to southern Ontario). Dotted line separates eastern and western Upper Midwest haplotype groups. (B) Area inside rectangle in A: 1 = Blue River; 2–4 = three upper Illinois River localities; 5 = Flint Creek; 6 = Spring Creek; 7 = Five Mile Creek; 8 = Shoal Creek; 9 = Spring River; 10 = Little Sac River; 11 = Hahatonka Spring (Niangua River); 12–14 = Lamine River; 15–18 = Gasconade River.
Bayesian tree for the mtDNA haplotypes detected in E. microperca. Outgroups not shown. Haplotype labels (capital letters) are followed in parentheses by number of haplotypes detected; no asterisk = ND2 only; asterisks = ND2 and cyt b concatenated. For the following labels, two haplotypes for one gene were concatenated with the same haplotype (parentheses) for the other: A and C (cyt b A), L and N (cyt b L), Z and ZZ (cyt b Z), MMM and NNN (cyt b MMM), L and LLL (ND2 L). Brackets show locality numbers (Fig. 1). Dots above internal nodes = Bayesian support > 0.95, below = maximum parsimony bootstrap support for values >50%.
Bayesian tree for the S7 intron 1 alleles detected in E. microperca. Outgroups not shown. Haplotype labels (capital letters) are followed by the number detected; NO = Northern Ozarks (Missouri River drainage), WO = Western Ozarks (Arkansas River drainage); brackets = locality numbers (Fig. 1). Asterisks above internal nodes = Bayesian support; below = MP bootstrap support; with one exception (Illinois River clade), only support values greater than 0.95 (Bayesian) and 50% (MP) are shown.
Chronogram for estimated ages of major cyt b clades in E. microperca and its sister group. Po = Pliocene, Ps = Pleistocene. Values at internal nodes = means and 95% highest probability densities.
Contributor Notes
Associate Editor: W. L. Smith.