Date of Award

Spring 2026

Degree Type

Honors College Thesis

Academic Program

Theatre BFA

Department

Theatre

First Advisor

Jake Schaefer

Advisor Department

Biological Sciences

Abstract

Hybridization between two related species has been widely observed and offers a lens into complex evolutionary processes. Endogenous and exogenous factors affect hybrid fitness and diversification, and pre-zygotic and post-zygotic barriers affect species’ ability to hybridize. Female mate choice is a pre-zygotic isolation mechanism which is known to be more significant than male mate choice in many species, a trend which is linked to females often investing more energy into offspring. Detailing the ways in which these mechanisms operate is integral to understanding hybridization on a larger scale. The species examined here, Fundulus notatus and Fundulus olivaceous, are closely related species of topminnow that coexist in naturally replicated hybrid zones across their overlapping distributions in stream systems across the Southeast United States. Different clades have different rates of hybridization, and a population from each clade (Ouachita River and the Pascagoula River of the Mississippi Basin) were selected for this study because of their respective low and high hybridization rates (FIS of 0.33 and 0.99). F. notatus were selected for this study. We hypothesized that hybridization in this system is nonrandom and controlled by endogenous factors. Individuals from each population were crossed to produce an F2 generation which would not be heterozygous for all inherited traits because of the genetic randomization that occurred during the second cross. The genetic variation would be expressed as varied hybridization rates among F2 F. notatus females if the mechanism for reproductive isolation is endogenous. Eggs collected from mate choice trials conducted with one F2 F. notatus female, one F. notatus male, and one F. olivaceous male were genotyped and identified as hybrid or nonhybrid. Hybridization rates among females were varied and ranged from 0.0 to 1.0. The null hypothesis was strongly rejected with a p-value of < 0.001, meaning that hybridization was nonrandom. The best supported model included both female choice and male interactions (AIC = 125.4), meaning that female mate choice played a role as well as male competition. Hybrid eggs hatched almost as frequently as nonhybrid eggs, and there is potential for hybrid vigor. The F2 F. notatus females will be genotyped, and further research should seek to link genetic markers to trends in hybridization rate.

Download

Share

COinS