36142 – Evolution of color patterns in garter snakes

Reporting Year:
Crater Lake NP
Principal Investigator:
Mr Michael Westphal
Mailing Address:
Department of Zoology
Oregon State University
3029 Cordley Hall
Corvallis, OR 97331
United States
Additional investigators or key field assistants (first name, last nbame, office phone, office email):
Stevan J. Arnold
Permit #:
Park-assigned Study Id. #:
Study Title:
Evolution of color patterns in garter snakes
Permit Start Date:
Jul 27, 2005
Permit Expiration Date:
Jul 27, 2006
Study Start Date:
Jul 27, 2005
Study End Date:
Jul 27, 2007
Study Status:
Activity Type:
My research seeks to identify the genetic bases and evolutionary mechanisms underlying the evolution of bright coloration in garter snakes. Such coloration is typically not expected in small animals subject to predation unless a countermanding selective advantage is conferred by the coloration, thereby swamping out the adaptive benefit of crypsis. The existence of color variants (such as melanism) in the wild provides an opportunity to examine “the exception that proves the rule,” i.e., by investigating those factors that allow variants to exist and/or those factors that maintain variants at low frequencies in wild populations, we can learn more about the selective regimes that maintain the wild (=non-mutant) type. Wizard Island melanistic T. sirtalis are an ideal study subject. S. Arnold’s laboratory has conducted research on the same subspecies for the past 20 years at Eagle Lake, California, providing a wealth of ecological and genetic baseline data. Using these data, I hope to gather genetic and ecological data on Wizard Island snakes to determine why these forms are at high frequency on the island and, in turn, identify which factors maintain bright coloration in normal garter snakes.
Findings and Status:
I conducted one visit to Wizard Island on September 18, 2005. On that day I collected a single individual Thamnophis sirtalis. This was a year-old snake with an unusual and unexpected color pattern, in that it cannot be characterized either as “wild-type” or “melanistic.” Rather than exhibiting the wild-type patterns of yellow stripes and red blotches, this snake had pale stripes and blotches of a uniform pinkish white. This morph appears similar to very rare individuals seen in some dens in Manitoba, Canada, which I have called the “salmon morph.” This morph also coincides with the presence of melanistic snakes. I have no explanation for this apparent correlation. Two hypotheses suggest themselves: either this morph is genetically linked to melanism in some way, or else it is maintained by the same selection regime that maintains melanism. More studies are needed to establish the relative frequencies of wild-type, melanistic, and salmon-morph individuals on Wizard Island.
For this study, where one or more specimens collected and removed from the park but not destroyed during analyses?
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Funding provided this reporting year by other sources:
Fill out the following ONLY IF the National Park Service supported this project in this reporting year by providing money to a university or college
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