Author Date

2020

Degree Name

Department

Biology

College

Life Sciences

Defense Date

2020-03-03

Publication Date

2020-03-10

First Faculty Advisor

Jerald B Johnson

First Faculty Reader

Byron J Adams

Honors Coordinator

Steven L Peck

Keywords

poeciliidae, variation, morphology, lateralization

Abstract

How genetic variation is maintained in the face of strong natural selection is an important problem in evolutionary biology. Selection should erode genetic diversity, leading to more and more homogeneous populations. Yet in nature, we commonly see high degrees of genetic variation, even for traits that are important to fitness. Negative frequency-dependent selection, a balancing selective force that favors traits when they are rare but not when they are common, is a mechanism proposed to maintain polymorphisms in a population. However, there is little empirical data to demonstrate how negative frequency-dependent selection sustains variation. Xenophallus umbratilis is a bilaterally symmetrical species of livebearing fish that exhibits asymmetry in the male gonopodium, the male intromittent organ which terminates with a sinistral or dextral twist. I test the hypothesis that in species such as Xenophallus umbratilis, where such asymmetrical morphologies exist, negative frequency-dependent selection maintains variation in the gonopodium within populations.