Genomic and phenotypic divergence informs translocation strategies for an endangered freshwater fish

Translocation, the movement of organisms for conservation purposes, can result in unintended introgression if genetic material flows between populations in new ways. The Bluemask Darter Etheostoma akatulo is a federally endangered species of freshwater fish inhabiting the Caney Fork River system and three of its tributaries (Collins River, Rocky River, and Cane Creek) in Tennessee. The current conservation strategy for Bluemask Darters involves translocating the progeny of broodstock from the Collins River (in the west) to the Calfkiller River (in the east) where the species had been extirpated. In this study, we use ddRAD sequence data from across the extant range to assess this translocation strategy in light of population structure, phylogeny, and demography. We also include museum specimen data to assess morphological variation among extant and extirpated populations. Our analyses reveal substantial genetic and phenotypic disparities between a western population in the Collins River and an eastern population encompassing the Rocky River, Cane Creek, and upper Caney Fork, the two of which shared common ancestry more than 100,000 years ago. Furthermore, morphological analyses classify 12 of 13 Calfkiller River specimens with phenotypes consistent with the eastern population. These results suggest that current translocations perturb the evolutionary boundaries between two delimited populations. Instead, we suggest that repopulating the Calfkiller River using juveniles from the Rocky River could balance conflicting signatures of demography, diversity, and divergence. Beyond conservation, the microgeographic structure of Bluemask Darter populations adds another puzzle to the phylogeography of the hyperdiverse freshwater fishes in eastern North America.

The evolution of male nuptial colour in a sexually dimorphic group of fishes (Percidae: Etheostomatinae)

To test hypotheses explaining variation in elaborate male colouration across closely related species groups, ancestral-state reconstructions and tests of phylogenetic signal and correlated evolution were used to examine the evolution of male body and fin colouration in a group of sexually dichromatic stream fishes known as darters (Percidae: Etheostomatinae). The presence or absence of red-orange and blue-green male colour traits were scored across six body regions in 99 darter species using a recently estimated amplified fragment length polymorphism (AFLP) phylogeny for comparative analyses. Ancestral-state reconstructions infer the most recent common ancestor of darters to lack red-orange colour and possess blue-green colour on different body regions, suggesting variation between species is due to independent gains of red-orange and losses of blue-green. Colour traits exhibit substantial phylogenetic signal and are highly correlated across body regions. Comparative analyses were repeated using an alternative phylogenetic hypothesis based on one mitochondrial and two nuclear genes, yielding similar results to analyses based on the AFLP phylogeny. Red-orange colouration in darters appears to be derived; whereas, blue-green appears to be ancestral, which suggests that different selection mechanisms may be acting on these two colour classes in darters.

Association between parasite load and orange, but not blue, male nuptial colouration in Etheostoma caeruleum

The hypothesis that males possessing more vivid nuptial colouration are of better quality with regard to individual measures of health such as parasite infection was investigated by taking spectral measurements of orange and blue bars in the nuptial males of a sexually dichromatic stream fish rainbow darter Etheostoma caeruleum to determine if male colouration in this species varied with parasite load in the form of black spot disease. The yellow chroma of orange bars, i.e. the relative contribution of wavelengths in the range of 550-625 nm to total brightness, was the only spectral measurement significantly associated with parasite counts. These results are discussed in the context of sexual selection and the potential of orange bars in E. caeruleum to serve as honest indicators of quality to potential mates.