Date of Award


Degree Type


Degree Name

Master of Science - Biology



First Advisor

Dr. Jennifer Gumm

Second Advisor

Dr. Matthew Kwiatkowski

Third Advisor

Dr. Vance Imhoff

Fourth Advisor

Dr. Josephine Taylor


Invasive species are detrimental to native species and when hybridization is involved a decrease in biodiversity may result. Cyprinodon variegatus is an invasive species that has caused devastation to several Cyprinodon species through rapid hybridization and genetic introgression. Cyprinodon rubrofluviatilis is native to the Brazos, Wichita and Red Rivers but fish collected between 2006-2012 from the Brazos River expressed intermediate morphological traits suggesting hybridization had occurred. My objective was to investigate if C. variegatus and C. rubrofluviatilis had hybridized in the Brazos River and if so, to determine the extent of introgression. Molecular analysis of specimens collected between 2013-2017 identified low levels of introgression in 2013-2015 but no signs of hybridization in 2017. Morphological analysis showed significant differences between species, genetic grouping, river, and most drainages with little evidence of intermediate phenotypes. Although hybridization and introgression between C. variegatus and C. rubrofluviatilis is not widespread, it remains a threat to native Cyprinodon in this region.



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