2014-05-05_REVISION - C1996083 - Laserfiche WebLink

Home Browse Search

HISTORICAL DNA REVEALS EXTINCTIONS AND INVASIONS 11 revision. Because these lineages are represented by museum samples collected after the onset of intensive fish stocking activities (1885) and they are the only lineages not restricted to single drainages, their native distribution and taxonomy remain uncertain. However, we argue that the blue lineage is probably O. c. pleuriti- cus. In both the historical and modern samples, the Yampa River basin appears inhabited by cutthroat trout of the blue lineage (Fig. 4B and Table S5). Importantly, no green lineage cutthroat trout were detected in modern Yampa River samples, a pattern also supported by nuclear data previously generated for 59 Yampa River populations (Rogers 2010). Thus, we infer that the geographical range of the blue lineage was probably restricted to the Yampa and Green River basins and was not widely distributed historically across all major drainages of the west slope. The type specimens of O. c. pleuriticus were collected in the Green River drain- age basin, which encompasses the Yampa River. Therefore, these specimens probably harbour blue line- age haplotypes, although this needs to be confirmed with additional sampling of museum specimens. Because O. c. pleuriticus was the only described subspe- cies from the western slope, the green lineage may represent an undescribed distinct taxon. This lineage appears native to the Colorado and Gunnison rivers, and potentially the Arkansas River basin. Although considered separate basins, the Colorado and Gunnison rivers converge well upstream of the warm desert con- fluence with the Green River and its major tributary the Yampa River. Cold water temperatures would have allowed cutthroat trout to move between the Colorado and Gunnison Rivers, giving rise to a monophyletic group in those two basins. Given the significant barrier between the east and western slopes of the Continental Divide, we believe it is unlikely that the green lineage was native to the Arkansas River drainage. Instead, we believe that by the time the samples were collected in 1889, early stocking activities may have established this lineage in the headwaters of the Arkansas River drain- age. The Twin Lakes fishery, from which the samples were collected, had already seen considerable fish stocking activity by 1889 (Wiltzius 1985). Twin Lakes lie near the first federal fish hatchery in Colorado, and just a dozen miles south of the bustling city of Leadville, the second most populous city in the state at the time. Bringing back O. c. stomias We believe the descendants of fish that were stocked into Bear Creek are the last remaining representatives of O. c. stomias, the greenback cutthroat trout currently recognized as a threatened under the Endangered Species Act. This fish was declared extinct in the 1930s © 2012 Blackwell Publishing Ltd (Green 1937); however, in 1953, a collection of fish from a small stream in the South Platte drainage were identi- fied as O. c. stomias (although not without uncertainty), marking the 'rediscovery' of the greenback cutthroat trout that would eventually launch an intensive recovery effort. Conservation efforts aimed at restoring O. c. stomias in the South Platte and Arkansas River basins were based on taxonomic assessments that were compromised by the extensive mixing of trout among drainages that began in the late 1870s, however. Of the streams and lakes in the South Platte and Arkansas River basins that were subjected to trout removal and restocking with what the best available science sug- gested was O. c. stomias, all appear to harbour lineages native to the western slope of the Continental Divide. Currently, O. c. stomias appears to persist as a single self- sustaining population in a locality outside the native range of the subspecies. The population harbours little genetic variation for loci that are typically variable in cutthroat trout populations (Metcalf et al. 2007) probably the result of few founding fish used in the initial stocking effort or a subsequent population bottle- neck. Low genetic diversity may compromise rehabilita- tion of the taxon, making it essential that planned propagation efforts attempt to maximize genetic diver- sity and assess subsequent fitness. It is encouraging, nonetheless, that the taxon has persisted within a relatively short stretch of a small stream for more than a century, suggesting it is likely to survive and perhaps thrive in other places. Conclusion Regional diversity and distribution of many taxa in North America have changed, sometimes dramatically over the last 150 years (Rahel 2000). For trout native to the Southern Rocky Mountains, anthropogenically driven changes resulted in the extinction of some lineages, and significant declines, range expansions or range shifts of others. Our work comparing historical records of trout propagation and movement with the phylogenetic diversity of historical and modern samples increased our understanding of the status of described taxa and resulted in the rediscovery of a taxon, O. c. stomias, that was at one time declared extinct. Other threatened and endangered species may be subject to similar uncertainty regarding their native diversity and distribution (e.g. Boessenkool et al. 2009; Athrey et al. 2011; Hekkala et al. 2011). In many cases, historical specimens exist in museums that are available for inferring native diversity and taxonomy. With specimens collected up to 150 years ago, our study pushes back the age for recovering DNA from ethanol - preserved specimens for population -level studies by