Genetic and landscape level threat assessments and status review of the Candy Darter (Etheostoma osburni)
Dates
Start Date
2016-10-01
End Date
2018-09-30
Summary
The Candy Darter, an endemic fish of the New River drainage in VA and WV, has been petitioned as a potential candidate for listing under the Endangered Species Act (Barb Douglas, USFWS, Elkins, WV, personal communication). Historically, the Candy Darter occurred over a wide range within the lower New River drainage, but many populations have been extirpated (Daniel A. Cincotta, personal communication). In West Virginia, the species has been extirpated from the lower Greenbrier River system, the Indian Creek drainage, and the Bluestone River drainage. Extant populations are restricted to the upper Greenbrier system and the Gauley river drainage in West Virginia. In Virginia, the species is restricted to the Valley and Ridge physiographic [...]
Summary
The Candy Darter, an endemic fish of the New River drainage in VA and WV, has been petitioned as a potential candidate for listing under the Endangered Species Act (Barb Douglas, USFWS, Elkins, WV, personal communication). Historically, the Candy Darter occurred over a wide range within the lower New River drainage, but many populations have been extirpated (Daniel A. Cincotta, personal communication). In West Virginia, the species has been extirpated from the lower Greenbrier River system, the Indian Creek drainage, and the Bluestone River drainage. Extant populations are restricted to the upper Greenbrier system and the Gauley river drainage in West Virginia. In Virginia, the species is restricted to the Valley and Ridge physiographic province, and is known historically from less than 10 New River tributaries, but has experienced range reduction (Jenkins and Burkhead 1993).
In addition to range reduction, the most pressing concern in WV populations is introgressive hybridization with the introduced Variegate Darter, which was first documented by Switzer (2004). A hybrid zone including introgressive hybridization was later documented in Anthony Creek of the Greenbrier River drainage (Switzer et al. 2007, 2008). The introgressive hybridization issue is primarily occurring in the Greenbrier River population, which is likely the largest extant population of the Candy Darter. More recently, Isaac Gibson (current graduate student advised by Dr. Amy Welsh, WVU) has determined that the hybrid zone has expanded farther upstream in the Greenbrier River drainage, as well as evidence of introgression extending above Summersville dam in the Gauley River drainage.
Currently, there is an immediate need to further address the introgressive hybridization issue. Expansion of the hybrid zone and genetic swamping has the potential to eliminate pure Candy Darters in the Greenbrier and Gauley river drainages, thus extirpating the remaining populations in West Virginia. The Bluestone Dam on the New River appears to be blocking the upstream spread of Variegate Darters into Virginia. However, our recent data suggest that Summersville Dam did not prevent Variegate Darter access to the upper Gauley River drainage, an introduction event that may have resulted from bait-bucket transfer. Our research has documented Variegate Darters to be relatively common downstream of Bluestone Dam. Given introduction upstream of Summersville Dam, it is likely just a matter of time before bait-bucket transfer introduces Variegate Darters upstream of Bluestone Dam, allowing access to the New River in Virginia.
There is also a need to understand overall genetic diversity and population structure in the remaining Candy Darter populations. By using an expanded suite of genetic markers, populations connected through migration can be identified, which can also facilitate the delineation of potential future invasion routes for the Variegate Darter. If populations are isolated from each other, they may have experienced a loss of genetic diversity, contributing further to the threat of extinction for the Candy Darter.
Our results will have direct management and conservation implications for the Candy Darter. Results from the proposed study will provide (1) current data on the introgressive hybridization issue, (2) data on genetic diversity and population genetic structure, (3) a review and compilation of published and unpublished literature on the ecology of the species, and on range reduction based on historic and recent data, and (4) a landscape level threat assessment for the historic and current range of the Candy Darter using GIS-based methods. An understanding of Candy Darter genetics and landscape level impacts will also be useful toward consideration of potential translocations of the species into previously inhabited streams. Results from the proposed research will provide valuable data to inform the candidate listing review process.
Objecties:
The objectives of the proposed research are to (1) conduct genetic analyses on introgressive hybridization between the Candy Darter and introduced Variegate Darter, including comparison with existing genetic data, (2) assess genetic diversity and population structure of remaining Candy Darter populations, (3) provide a review and compilation of published and unpublished literature on the ecology of the species, and on range reduction based on historic and recent data, and (4) produce a landscape level threat assessment for the historic and current range of the Candy Darter using GIS-based methods.
