Physaria thamnophila microsatellite dataset

Taxonomy, genetics and biogeography each make key contributions to
biological conservation. However, integrating these disciplines to obtain
a coherent account of the status of a taxon of concern is not always
straightforward. This is the case for the cross-border endemic
plant Physaria thamnophila (Brassicaceae). This US
federally-listed endangered species is restricted to a set of unique
geological sites just north of the Rio Grande (Rio Bravo del Norte) river
in south Texas, USA. A single highly-disjunct occurrence of this species
is found on a geologically and ecologically distinct site 260 km to the
south, in Tamaulipas, Mexico. In this work, we quantify the genetic
differentiation between the U.S. and Mexican populations using four
microsatellite markers and sequences from three nuclear genes. In both
sets of data, we find a high level of genetic divergence consistent with
geographic isolation on a time scale of 1–2.5 million years. Further, we
provide a hypothesis for the geological basis of this geographic
isolation. Integrating our data with ecological, taxonomic and
conservation considerations, we propose the sub-specific designation of
Physaria thamnophila subsp. loretensis for the Mexican population. The
evolutionary and conservation implications of this designation are
presented.