Document Type

Thesis

Date of Degree Completion

Spring 2025

Degree Name

Master of Science (MS)

Department

Biology

Committee Chair

Lixing Sun

Second Committee Member

Ian Quitadamo

Third Committee Member

Alison Scoville

Abstract

Dominance hierarchies are a central feature of social species, influencing access to resources, reproductive opportunities, and survival. In many animals, body size is a primary determinant of social rank, but other morphological traits may also contribute. This study investigates how physiological traits—including body size, pigmentation, lachrymal striping, and egg spots—relate to social dominance in Astatotilapia burtoni, a socially dynamic African cichlid.

Side-profile photographs were used to measure body size, red, green, and blue pigmentation intensity, lachrymal stripe area, and egg spot count. Behavioral interactions were recorded and analyzed using the Elo rating system to generate a continuous measure of social rank. Partial Least Squares Regression and Linear Mixed Models were used to assess which traits best predicted Elo rating.

Both analyses identified body size as the most consistent and statistically supported predictor of social rank. Red pigmentation showed a secondary association with rank in the multivariate PLSR model, but did not significantly improve model fit in the LMM. Other traits, including lachrymal striping, egg spots, and green or blue pigmentation, were not supported as predictors in either analysis.

These results support the conclusion that body size is the most reliable morphological indicator of dominance in A. burtoni under laboratory conditions. The application of the Elo rating system provided a robust framework for quantifying hierarchical dynamics and linking them to individual traits.

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