Aim To examine the effects of historical climate change and drainage isolation on the distribution of mitochondrial DNA cytochrome b genetic variation within the rainbow darter, Etheostoma caeruleum (Percidae: Etheostomatinae).Location Eastern North American streams including tributaries to the Mississippi River, Great Lakes, Potomac River and Hudson Bay drainages.Methods Parsimony analyses, Bayesian analyses and haplotype networks of mitochondrial DNA sequences.Results Four major clades were recovered from sampled populations of E. caeruleum. Three of four clades are distributed in the western portion of the species' range (primarily west of the Mississippi River). Samples from this region do not form a monophyletic group, and sequences often vary greatly between samples from adjacent stream systems (up to 7.2% divergence). A basal clade includes samples from the White River system in the Ozark Highlands. The northern Ozarks-upper Midwest clade includes samples from Missouri River tributaries and the upper Midwest (Hudson Bay, upper Mississippi River, and western Lake Michigan drainage). The eastern clade is composed of individuals from the Ohio River, Great Lakes and Potomac River. The Mississippi River corridor clade includes samples from middle and lower Mississippi River tributaries. Main conclusionsThe four major clades of E. caeruleum are deep allopatric lineages with well-defined boundaries and have additional phylogeographical structure within each clade. The Ozark Highlands have the greatest levels of diversity relative to distributional area, with marked cytochrome b subdivisions between adjacent stream systems. Samples from previously glaciated areas do not have a subset of the cytochrome b diversity found in unglaciated areas, but four separate source areas are identified based on phylogenetic analyses. Dispersal into previously glaciated areas followed several known glacial outlets and, based on sequence divergence between populations, may have occurred during different glacial or interglacial stages. The disjunct distribution and cytochrome b pattern of E. caeruleum in the Mississippi River corridor clade is consistent with late Pleistocene and Recent changes in the course and characteristics of the middle and lower Mississippi River. Phylogeographical boundaries between clades of E. caeruleum correspond to independent sources of biogeographical information and provide insight into historical stream drainage relationships, post-glacial colonization and drainage isolation patterns.

Incongruence between recognized taxonomy and phylogenetic relationships between two species from a diverse clade (Percidae: Etheostomatinae) of stream fishes was found in a mitochondrial (mt) DNA gene tree. Two darters in subgenus Oligocephalus, Etheostoma uniporum current darter and Etheostoma caeruleum rainbow darter were sampled throughout their sympatric distribution in the Ozark Highlands of the central United States. Sequences from cytochrome (cyt) b and the first intron of the nuclear marker S7 were analysed separately using maximum parsimony and Bayesian methods. Cyt b recovered both species as polyphyletic; E. uniporum haplotypes were interspersed within E. caeruleum. However, both species were monophyletic and non-sister taxa based on S7. The cyt b gene tree pattern is caused by introgressive hybridization resulting in the mtDNA replacement of E. uniporum haplotypes by those of E. caeruleum. Some E. uniporum haplotypes are shared with geographically proximate E. caeruleum, and this is consistent with recent hybridization, while other E. uniporum haplotypes indicate historical sorting of introgressed lineages. The mechanism of introgression is likely asymmetric sneaking behaviour by male E. uniporum, a mating tactic observed in related species. MtDNA replacement may have occurred in E. uniporum due to drift fixation in a historically small female effective population. Additional evidence for darter hybridization will likely be discovered in future molecular genetic surveys of the nearly 200 species in eastern North America.

The sturgeon subfamily Scaphirhynchinae contains two genera of obligate freshwater sturgeon: Scaphirhynchus and Pseudoscaphirhynchus, from North America and Central Asia, respectively. Both genera contain morphologically variable species. A novel data set containing multiple individuals representing four diagnosable morphological variants for two species of Pseudoscaphirhynchus, P. hermanni and P. kaufmanni, was generated. These data were used to test taxonomic hypotheses of monophyly for the subfamily Scaphirhynchinae, monophyly of both Scaphirhynchus and Pseudoscaphirhynchus, monophyly of P. hermanni and P. kaufmanni, and monophyly of the recognized morphological variants. Monophyly of the subfamily Scaphirhynchinae is consistently rejected by all phylogenetic reconstruction methodologies with the molecular character set while monophyly of both river sturgeon genera is robustly supported. The molecular data set also rejects hypotheses of monophyly for sampled species of Pseudoscaphirhynchus as well as monophyly for the recognized intraspecific morphological variants. Interestingly both Scaphirhynchus and Pseudoscaphirhynchus demonstrate the same general pattern in reconstructed topologies; a lack of phylogenetic structure in the clade with respect to recognized diversity. Despite rejection of monophyly for the subfamily Scaphirhynchinae with molecular data, reconstructed hypotheses from morphological character sets consistently support monophyly for this subfamily. Disparities among the data sets, as well as reasons for rejection of monophyly for Scaphirhynchinae and species of Scaphirhynchus and Pseudoscaphirhynchus with molecular characters are examined and a decreased rate of molecular evolution is found to be most consistent with the data.

Microsatellite variation from 13 disomic loci is reported for a total of 208 individuals of the genus Scaphirhynchus. This includes 105 individuals of the pallid sturgeon (Scaphirhynchus albus) from the lower Mississippi River, 11 pallid sturgeon from the Upper Mississippi and Missouri rivers, 65 shovelnose sturgeon (S. platorynchus) from the lower Mississippi River, six Alabama sturgeon (S. suttkusi), and 21 individuals of sturgeon identified as intermediate between S. albus and S. platorynchus. Results indicate that all five of the above population/species units are significantly differentiated from one another based on pairwise F ST estimates. Locus Spl-7 was diagnostic for the Alabama sturgeon and serves to further differentiate this allopatric species from other Scaphirhynchus. Classification of genotypes with and without a priori designations failed to clearly delineate the species and intermediates in the latter case but was successful for the species but not in the intermediates in the former case. The presence of six unique alleles in five of the 21 morphologically ÔintermediateÕ sturgeon examined requires additional evaluation but suggests that these individuals are possibly not the result of hybridization. We hope that raising these important issues will bring all stakeholders to the table to establish a concerted effort needed for both morphological and molecular analyses to adequately address the question of hybridization and the origin of the morphological variation in these fishes.

The capture of a crystal darter Crystallaria asprella, a state endangered species in Missouri, from the main stem of Big River (Meramec River drainage) in August 2009 represented the first documentation of the species in nearly 50 years from Big River, Jefferson County, and only the second record ever reported from this river.