Graduation Date

Fall 2022

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Karen Kiemnec-Tyburczy

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Catalina Cuellar-Gempeler

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Amy Sprowles

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

John Reiss

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories



The American Bullfrog (Rana catesbeiana) is a highly invasive species that has successfully colonized habitats around the world. The genetic variability of immune genes within invasive populations, like that of bullfrogs, may contribute to how resistant a population is to pathogens. The objective of this project was to characterize the genetic diversity of an immune gene in invasive bullfrog populations in California to better understand how persistent these populations might be over time. To characterize immune gene variability, I isolated exon 2 of the Major Histocompatibility Complex (MHC) Class II Beta chain gene and a neutral mitochondrial marker, cytochrome b (cyt b), from five bullfrog populations. I used standard population genetic metrics to compare the genetic diversity between these two loci across populations. I found high diversity in MHC II exon relative to cyt b, however these populations harbored differing levels of diversity at both loci. I also reconstructed a phylogeny of the isolated alleles with those from other ranids and found that the majority of my MHC alleles clustered with other R. catesbeiana alleles instead of with those of other ranids, except two alleles may exhibit transspecies polymorphism. The majority of the selection tests detected significant positive selection acting on MHC alleles, while there was little evidence on cyt b. Overall, these non-native populations have similar genetic diversity to other native amphibian populations. I conclude that they likely have sufficient genetic diversity to persist in the face of novel pathogens they may encounter in non-native habitats.

Citation Style