Gene flow in North Fork Flathead River
Lesson by Lillard, D. (2014). Using genetics in ecology. Glacier High School, Kalispell, Montana.
Data from:
Boyer, M. C., Muhlfeld, C. C., & Allendorf, F. W. (2008). Rainbow trout (Oncorhynchus mykiss) invasion
and the spread of hybridization with native westslope cutthroat trout (Oncorhynchus clarkia
lewisi). Canadian Journal of Fisheries and Aquatic Sciences, 65(4), 658-669.
Objective: students will analyze genetic data from stream and lake surveys in order to create a model to
describe hybridization patterns in the North Fork Flathead River drainage.
Day 1: Background research
Students use the following links to gain background knowledge of Rainbow and Westslope Cutthroat
trout.
Rainbow resources
http://fieldguide.mt.gov/detail_AFCHA02090.aspx
Cutthroat resources
http://fieldguide.mt.gov/detail_AFCHA02088.aspx
http://www.montanaafs.org/science/species-of-concern/species-status/westslope-cutthroat-trout/
1. Describe or draw a picture of the native range of rainbow trout in Montana.
2. Describe or draw a picture of the current range of rainbow trout in Montana.
3. Describe the food of rainbow trout.
4. Describe the habitat of rainbow trout.
5. Describe spawning behavior of rainbow trout.
6. What are phenotypic markers of a rainbow trout?
7. Draw a picture of the native range of cutthroat trout in Montana.
8. Describe or draw a picture of the current range of westslope cutthroat trout in Montana.
9. Describe the food of westslope cutthroat trout.
10. Describe the habitat of westslope cutthroat trout.
11. Describe spawning behavior of westslope cutthroat trout.
12. What are phenotypic markers of a cutthroat trout?
13. Draw or explain any phenotypic markers that could help someone distinguish a rainbow trout from a
cutthroat trout.
Hybridization
Hybridization occurs between species that are close enough genetically to beget offspring. Sometimes
the offspring are infertile. For instance, a female horse and a male donkey make a mule. Horses and
donkeys share enough genetic material to produce one generation, although mules are infertile because
they have one more horse chromosome than mule chromosomes. Other hybrids may be more closely
related in their genes and produce hybrids that are fertile. Rainbow trout and westslope cutthroat trout
are similar enough to create fertile hybrids that can mate with another hybrid, a rainbow or a cutthroat.
Look at the following map of the North Fork Flathead River. Answer the following questions.
1. What fish is native in this river?
2. Which trout currently occupy this river?
3. Develop a hypothesis for how hybridization will change as we go upriver. Where will we
find the most rainbows, where will we find the most cutthroats, and where will we find the
most hybrids. Explain your reasoning
Day 2
Teacher will summarize findings from previous day (Lecture)
Students: with seat partner, design an experiment to test hypothesis on hybridization.
Observe cutthroat and rainbow specimens
Day 3
Review possible experiments.
Teacher will summarize Boyer experiment. Electrofishing tributaries and North Fork and collecting
genetic data.
Hand out one set of data per student.
Explain Loci of non-coding base pairs.
Student instructions:
Each student should indicate the species for each allele by circling or shading WCT alleles as orange, and
RBT as purple.
Calculate the hybridization for individual fish using the formula: # rainbow alleles/2(diagnostic loci). For
instance, a pure rainbow would be 14/2(7) = 1 or 100%. Indicate hybridization value
Indicate any hybrids by boxing them out.
Calculate total hybridization in the population by dividing total rainbow alleles by number of loci and
number of individuals. # rainbow alleles in population/2(# of individual x # of loci). For instance,
448/2(35 x 7) = .916 or 91.6 %
Day 4
Compile hybridization data.
What sort of trends does the data reveal?
How does the data support or discount your hypothesis?
Day 5
These three CEAL paragraphs are an opportunity to demonstrate your understanding of this last
semester’s topics. Short answers will not be passing grades. Your goal is to display as much of your
knowledge of genetics, evolution, and ecology that you can. Paragraphs will be graded holistically on
the included rubric.
Please print out the rubric and staple it to your paragraphs.
3 CEAL paragraphs
How does genetics provide a valuable tool for biologists studying trout?
Is this population of trout in the North Fork evolving?
What should Wildlife Management do about hybridization in the North Fork? How does ecology
provide evidence for your conclusion?
Abbot Cr
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Ivy Creek
Rabe Creek
Third Creek
Langford
Anaconda Cr
Dutch Creek
Skookoleel Cr
Nicola Cr
Meadow Cr
Cyclone
Trout lake
Moran Cr
Hay Cr. Lower
Deadhorse Cr.
So. Fk. Coal Creek
Red Meadow Lower
So. Fk. Red Meadow Creek
Tepee Creek
Red Meadow Cr. Upper
Moose Cr.
Colts Cr.
Burnham
Parker