Effects of Hybridization between Nonnative Rainbow Trout and Native Westslope Cutthroat Trout on Fitness-Related Traits

Abstract

Hybridization between introduced and native fauna is a risk to native species and may threaten the long-term persistence of numerous taxa. Rainbow Trout Oncorhynchus mykiss has been one of the most widely introduced species around the globe and often hybridizes with native Cutthroat Trout O. clarkii in the Rocky Mountains. Previous work has shown that hybridization negatively affects reproductive success, but identification of the traits contributing to that reduction has been elusive. In this study, we used a combination of field and laboratory techniques to assess how hybridization with Rainbow Trout affects seven traits during several stages of Westslope Cutthroat Trout development: embryonic survival, ova size, ova energy concentration, sperm motility, juvenile weight, juvenile survival, and burst swimming endurance. Rainbow Trout admixture was correlated with an increase in embryonic survival and ova energy concentration but with a decrease in juvenile weight and burst swimming endurance. These correlations differed from previously observed patterns of reproductive success and likely do not explain the declines in reproductive success associated with admixture. Future investigation of additional, unstudied traits and the use of different environments may shed light on the traits responsible for reproductive success in admixed Cutthroat Trout.

Received January 18, 2015; accepted June 16, 2015

ACKNOWLEDGMENTS

The U.S. Geological Survey and U.S. Fish and Wildlife Service provided funding through the Science Supported Partnership Program. We thank Aaron Nistler, Cal Fraser, Jason Ilgen, Matt Toner, Robert Muth, Taylor Wilcox, Luke Holmquist, Vincent D'Angelo, Brady Miller, Carter Fredenberg, Durae Belcer-Daniels, Rick Hunt, Steve Glutting, and Ninh Vu for help with field and laboratory work. We thank Kotaro Ono, Jake Ferguson, David Beauchamp, and James Kenagy for help with data analysis and interpretation. We thank two anonymous reviewers and Charles Waters for their reviews of earlier versions of this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.