We examined range-wide patterns of genetic variation among Campostoma populations to infer the progression of events that may have shaped species distributions and freshwater diversity across the SMO and adjacent areas. The recovered gene genealogies indicate that: (1) a widespread ancestral form inhabiting an ancient Rio Grande system diverged into two evolutionary lineages following isolation of southern drainages, possibly due to the combined influence of tectonic events and increasing regional aridity (Hubbs & Miller, 1948; Smith, 1981; Miller & Smith, 1986; Metcalfe et al., 2002); (2) divergence into two evolutionary lineages was followed by range expansion from Atlantic to Pacific drainages due to drainage evolution and river capture events; and (3) further inter-basin exchange has occurred via more recent headwater capture events, hydrological connections, and possible anthropogenic introductions. As a consequence, the geographic distribution of genetic variation does not necessarily correspond to drainage boundaries, where geographically close but hydrologically disjunctive populations from independent drainages may be more closely related than geographically distant populations from the same river drainage.

This study was funded by NSF grant (DEB 0817027) to R.L.M., by BBVA-Foundation support to the project ‘Studies for the conservation of cyprinids in arid/semiarid environments of the Iberian Peninsula and North America’ to A.P. (ref. 060501070030), the US Environmental Protection Agency and Tulane University.

Peer reviewed