Date of Award

Spring 5-2017

Degree Type

Honors College Thesis


Biological Sciences

First Advisor

Jacob Schaefer

Advisor Department

Biological Sciences


Hybrid zones are locations where two interbreeding species coexist and hybridize. The spatial distribution of ecologically similar species is of primary interest in understanding the formation and stability of hybrid zones. These hybrid zones are of significance as they allow for insight into how speciation occurs naturally within the environment. A variety of factors may play a role in determining the spatial distributions of species within hybrid zones. Examples of these factors include variations in temperature gradients, substrate composition, and changes in canopy cover. Fundulus olivaceus and Fundulus notatus are generally found within upstream and downstream habitats respectfully. These habitats change in predictable ways in accordance to the river continuum concept. The purpose of this experiment was to test whether these environmental gradients influence distribution and the structure of hybrid zones. For this study, roughly 40 specimens of each sex and species were collected for a total of 160 fishes. Each specimen was marked with an elastomer tag that coded for species and sex. Three mesocosm treatments were created; a control, heterogeneous and temperature only. The control had no change in habitat variables throughout the treatment while the heterogeneous treatment was arranged to mimic a stream habitat in accordance to the river continuum concept. This includes a shallower, faster moving, colder upstream and a deeper, slower moving, warmer downstream. The homogeneous treatment was arranged identical to the control with only a temperature gradient present. Ten fish of both sex and species, 40 total, were placed in each treatment. It was found that both species exhibited habitat preference when presented with changes in habitat structure. Of the two species, F. notatus, males in particular, exhibited the highest mean index of upstream vs downstream bias.