Graduation Year


Document Type

Open Access Senior Thesis

Degree Name

Bachelor of Arts


W.M. Keck Science Department

Second Department

Environmental Analysis

Reader 1

Diane Thomson

Reader 2

Bryan Thines

Terms of Use & License Information

Terms of Use for work posted in Scholarship@Claremont.

Rights Information

© 2016 Elizabeth Medford


Hybridization, the process of interbreeding between individuals of different species, is one method by which plants and animals adapt to a changing environment. One example of such adaptation through hybridization may be occurring on the California Channel Islands with two species of Castilleja. While United State Geological Survey (USGS) researchers have been studying the populations of Castilleja affinis and Castilleja mollis to determine if hybridization is occurring on Santa Rosa Island since the early 1990s, up until this point primarily overt phenotypic characteristics have been used to differentiate between the two species. Genetic methods of differentiation were adopted to confirm that hybridization is in fact occurring on the island, possibly in response to climate change. Hybrids may be expanding into areas once occupied by pure C. mollis, because they might carry some of C. affinis’ traits like an ability to survive warmer, drier climates as parts of the island are starting to become warmer and drier. In this study, I have developed a cleaved amplified polymorphic sequences (CAPS) marker based on internal transcribed spacer (ITS) regions to differentiate between the two species and hybrids and have applied these CAPS markers to genotype DNA samples isolated from 132 individuals. This protocol was used to determine the extent of hybridization on Santa Rosa Island in conjunction with ongoing surveys conducted by the USGS. Work focused on genotyping previously collected samples from two main sites on the island, which allowed confirmation that patterns observed based on phenotype in the field are supported by genetic data. In the future, findings will link genetic type with survivorship and growth data, to test whether hybrids perform differently than pure C. mollis. Broadly, this will determine if the two species are in fact hybridizing as a method for adapting to climate change, the most severe threat to Channel Island biodiversity.