Date of Award

8-2025

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

School

Biological, Environmental, and Earth Sciences

Committee Chair

Dr. Jake Schaefer

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Dr. Brian Kreiser

Committee Member 2 School

Biological, Environmental, and Earth Sciences

Committee Member 3

Dr. Kaitlin Baudier

Committee Member 3 School

Biological, Environmental, and Earth Sciences

Abstract

Understanding how reproductive isolation arises between closely related species is central to evolutionary research. Hybridization is widespread across taxa and shaped by interactions among environmental factors, evolutionary history, genetic compatibility, and behavior. These forces often operate nonlinearly across space and time, yet mate choice is frequently assessed under artificial conditions that may not reflect natural behavior. To address this limitation, female mate preference was investigated within the Fundulus notatus species complex, where F. notatus and F. olivaceus hybridize at varying rates across replicate contact zones. Using a free-choice design, behavioral trials were conducted with individuals from populations characterized by high and low hybridization rates, along with F. notatus crosses produced from the divergent populations. During six-hour trials, fish interacted freely in semi-natural arenas while movements were tracked using AI video monitoring. Female association time with conspecific versus heterospecific males was used as a proxy for mate preference. Additionally, male standard length and spot density were measured to assess the influence of morphology on female behavior. Results revealed significant clade-level variation in female association behavior. Preferences for conspecific versus heterospecific males varied predictably with population-level hybridization rates: females from low-hybridizing populations exhibited stronger conspecific preferences, while those from high-hybridizing populations showed weaker discrimination. Clade-cross females displayed intermediate behavior, supporting a genetic basis for variation in mate preference. Furthermore, body size and spot count influenced female association across populations. These findings highlight the role of behavioral isolation in maintaining species boundaries.

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