Inbreeding Depression Reduces Fitness in Colorado's Remaining Greenback Cutthroat Trout

Recent molecular studies on trout of the southern Rocky Mountains have revealed the existence of a unique lineage native to the South Platte basin thought to be the true Greenback Cutthroat Trout (GBCT), Colorado’s state fish.  Ironically, the same widespread stocking efforts that jeopardized so many native trout populations across the West preserved this South Platte native outside its aboriginal range in a fishless stream above a natural barrier for 130 years.  As such, this population displays very little genetic diversity.  As sole heir to the GBCT title however, managers are anxious to replicate this population elsewhere across its former range to help ensure its long-term security.  Large repatriation projects are planned, but culturing a developing broodstock to facilitate those efforts has been challenging, suggesting that inbreeding depression may be complicating those efforts.  A formal evaluation of several fitness measures in a blind common garden type experiment using pure GBCT, a genetically diverse population from a sister clade, and their hybrids, revealed that at least growth (0.014 g/g/d) and survival (20.8%) among pure GBCT was less than half that of the other groups.  These results suggest that ambitious recovery goals for this taxon may need to be reevaluated.