Molecular markers support specific status of Gila robusta and G. nigra in Fossil Creek, AZ

Authors: Thomas E Dowling, Paul C Marsh, Robert W Clarkson

Year: 2016 (xlviii)

Abstract

There has been considerable debate over the specific status of chubs (genus Gila) in the Gila River basin of AZ-NM, especially headwater chub (Gila nigra) and roundtail chub (G. robusta). These two taxa have been difficult to discriminate with morphology and also show high levels of genetic divergence among local populations but not species. These species are rarely geographic proximate, with one example being Fossil Creek, a spring-fed tributary of the Verde River that was managed extensively for hydropower generation beginning in the early 20th century. The creek was chemically treated in 2005 to eradicate non-native fishes and native fishes salvaged. A barrier was installed in the lower reach of the stream, flows were restored, and native fishes repatriated. Here we report results of designed to examine genetic consequences of these management activities on G. robusta and G. nigra. This was achieved by comparing patterns of microsatellite and mtDNA variation from a temporal and longitudinal series of post-project samples collected from above and below barrier falls. Our data demonstrate that G. robusta has become more common downstream of the falls over time, with G. nigra becoming rare; however, G. nigra is able to persist upstream of the barrier in the absence of G. robusta. Results are consistent with continued recognition of Gila robusta and G. nigra as distinct species, with specific implications for the conservation and management of these forms.