Under the radar: genetic assessment of Rio Grande Shiner (Notropis jemezanus) and Speckled Chub (Macrhybopsis aestivalis), two Rio Grande basin endemic cyprinids that have experienced recent range contractions

The Rio Grande drainage of the southwestern United States and Mexico has
undergone intense anthropogenic alteration by water diversions, extraction
and associated habitat changes. These alterations have disproportionately
impacted the pelagic broadcast spawning guild of minnows (pelagophils).
Several Rio Grande endemic pelagophils, including the co-occurring Rio
Grande Shiner (Notropis jemezanus) and Speckled Chub (Macrhybopsis
aestivalis), have experienced dramatic recent range-wide declines yet have
slipped under the radar of conservation efforts. The status of N.
jemezanus and M. aestivalis in the Rio Grande and Pecos River was
evaluated and standing genetic variation were characterized. Genetic
evidence indicates that populations of both species found in the Rio
Grande and Pecos River are genetically distinct. Additionally, 159 outlier
loci were identified in M. aestivalis suggesting possible local adaptation
in the Rio Grande and Pecos River populations. Though range-wide genetic
data are limited, N. jemezanus populations in both rivers harbor
considerable genetic diversity. Mitochondrial data from both taxa are
consistent with a history of secondary contact between formerly isolated
populations with deeply divergent haplotypes found within the Rio Grande
and Pecos River populations of N. jemezanus and within the Rio Grande
population of M. aestivalis. Extensive survey efforts in the lower Rio
Grande and its tributaries in Texas document significant range contraction
and near extirpation of N. jemezanus from this part of the basin;
highlighting the need for immediate action to protect the
species.