Disentangling natural dispersal versus human-mediated introduction of the Longfin Dace across the trans-continental divide

Authors: Alex Cameron, David Camak, Megan Osborne, Tyler Pilger, David Propst, Thomas Turner

Year: 2019

Abstract

A long-standing objective of biogeography is to relate patterns of genetic diversity to historical and contemporary processes that influence the distribution of populations across a landscape. For some taxa, the role of human-mediated dispersal can confound the signal from natural processes and obscure our understanding of a species’ evolutionary history. The Longfin Dace, Agosia chrysogaster, is a small-bodied minnow native to the Upper Gila River basin in New Mexico. Accounts as early as the 1950’s proposed that the Longfin Dace was recently introduced into tributaries of the Mimbres River and the Rio Grande. Human-mediated dispersal was hypothesized as a mechanism for crossing the trans-continental divide, but recent molecular evidence suggests that headwater capture events may have mediated the east to west movement of other fish taxa (e.g., Pantosteus plebeius). Therefore, it is plausible that populations of the Longfin Dace found east of the trans- continental divide were established via a similar headwater capture event as P. plebeius as opposed to human-mediated dispersal. We sequenced a mitochondrial locus for 294 individuals collected across Arizona and New Mexico to examine range-wide patterns of historic population structure. Additionally, we assayed a panel of 9 microsatellite loci for 165 individuals collected in New Mexico to infer the mechanism of colonization across the trans-continental divide.