Honors College Theses

Publication Date



Biology (B.S.B.)

Document Type and Release Option

Thesis (open access)

Faculty Mentor

Dr. Jamie Roberts


Individual populations of a species will morphologically adapt to their surrounding environment. It has been noted in the past that when species are placed under similar environmental conditions, they will evolve similar morphological structures and shape variation to overcome those obstacles. Redbreast sunfish (Lepomis auritus) were sampled from three different ecoregions (mountainous, Piedmont, and coastal plain) of 4 different isolated river basins in the southeastern North America. It was hypothesized that across basins, populations would show convergent morphological adaptations to mountain, piedmont, and coastal plain condition. I indexed using site elevation as an independent variable, serving as a proxy for ecoregion. I measured 9 morphological variables on 146 preserved redbreast specimens from 32 sites spanning all basins and ecoregions. I used a principal components analysis to visualize the variation among basins and ecoregions and generalized linear mixed models to test hypothesized relationships between each morphological variable and elevation. It was found that mountainous redbreast have smaller eyes, shorter caudal peduncles, and a rounder head shape. This may be due to the clearer waters of mountain streams and the behavior of waiting in the littoral zone as opposed to the turbulent center. However, several traits did not consistently vary with ecoregion in the hypothesized way, suggesting that basin effect cannot be ignored on redbreast morphology.

Thesis Summary

This paper looked at the morphological variation of redbreast sunfish populations from four different river basins across differing ecoregions.