Water Resources Research Act Program

Details for Project ID 2015MT298B

Student Fellowship: Environmental DNA to evaluate individual variation in rainbow trout spawning date

Institute: Montana
Year Established: 2015 Start Date: 2015-03-01 End Date: 2016-02-28
Total Federal Funds: $909 Total Non-Federal Funds: $400

Principal Investigators: Taylor Wilcox

Project Summary: Rainbow trout (Oncorhynchus mykiss; RBT) have been introduced across the Intermountain West, including into streams and rivers with westslope cutthroat trout (Oncorhyncus clarki lewisi; WCT). Where RBT have been introduced, they produce fertile hybrids with native WCT, and these hybrids interbreed with both parental species types1. Over time, continued back-crossing can create a hybrid swarm where there is no reproductive barrier between RBT and WCT. This type of hybridization with RBT, called “introgressive hybridization”, is a serious threat to WCT persistence1. Introgressive hybridization is not uniform across the introduced range of RBT, and in some streams WCT and RBT both persist with limited introgression. A possible mechanism for limiting introgression between cutthroat trout and RBT is segregation in timing2 or location3 of spawning. Partial temporal segregation of spawning date between WCT, RBT, and their hybrids has been shown in some Montana streams using radio-telemetry4 and trapping of migrating spawners5 at a dispersal barrier. However, neither method can determine precise spawning date, both methods are expensive and labor- intensive, and animal trapping at dispersal barriers is infeasible for most streams. Some research suggests that this introgression is primarily mediated by just a few highly fit individuals6. These individuals must not only have high fitness, but also must overlap spatially and temporally with the opposite species during spawning. To better understand this dynamic, it would be useful to not only understand the mean spawning date of WCT and RBT in streams, but also variation in spawning date among individuals. I am conducting a study to test a novel method to determine fish spawning date. Environmental DNA (eDNA) is a new technology that samples water, soil, or the air for free DNA and cell debris to detect organisms7. Based on preliminary work with brook trout (Salvelinus fontalis) in 2013, I hypothesize that eDNA shedding rates from fish in streams increases during spawning due to increased fish metabolism and activity such as digging out redds for egg deposition. I would like to also ask if interspecific variable eDNA markers that detect genetic variation between individuals within the same species can be used to help understand variation in spawning date between WCT and RBT, and among individuals of both species, both of which could affect rates of introgression.