Comparison Between Modern and Historical Distribution and Diversity of Cutthroat Trout in Colorado

Cutthroat trout were widely and abundantly stocked throughout the state of Colorado from the late 1800's through today. The taxon and  numbers of fish stocked varied over time and place. Because different recognized subspecies of cutthroat trout readily hybridize, one effect of stocking was obfuscation of native diversity and distribution. We used mitochindrial DNA isolated from museum specimens to infer the historical biogeography of cutthroat trout in Colorado. We estimated that there were originally six divergent lineages native to Colorado, each one inhabiting a geographically different major drainage basin. Genes from five of the six lineages have been detected in contemporary populations. The most widely distributed subspecies are O. c. pleuriticus, native to the Yampa and Green River basins, and O. c. n. ssp., native to the Gunnison and Colorado River basins. The widespread distribution of these two subspecies in the state presumably reflects the fact that these two subspecies were used for intensive stocking efforts. We detected one relict population of putatively unadmixed O. c. stomias (the Greenback cutthroat trout) in a single, small stream outside its native range. Our results underscore the tremendous influence of human-mediated movement of cutthroat trout on current estimates of diversity and distribution.