Theses and Dissertations from DePaul University

Date of Award

Fall 2025

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Science

College

College of Science and Health

First Advisor

Andrew Conith

Abstract

Cichlid fishes have undergone multiple adaptive radiations in the rift lakes of East Africa pairing rapid taxonomic and morphological diversification. Lake Malawi’s rock-dwelling cichlids (mbuna) have diversified into hundreds of species that partition their habitat by depth and diet resulting in high morphological and behavioral diversity. We characterized morphological differences and performed behavioral assays among four cichlid genera from Lake Malawi focused on understanding form-function relationships in the neurocranium and oral feeding apparatus. We characterized neurocranial shape using 3D geometric morphometrics across a large taxonomic sample of mbuna cichlids, focusing primarily on the Tropheops species complex. Alongside broad changes in neurocranial length, width and depth, we also identified the shape of the vomer, a bone that develops at the most anterior point of the neurocranium, as a major axis of shape variation. Phylogenetic comparative methods revealed vomer angle was associated with habitat depth, suggesting vomer angle is shaped by differences in diet. Given the proximity of the vomer to the upper oral jaws, we assessed if vomer angle and the length of the ascending arm of the premaxilla could be predictive of feeding behavior. We used high-speed videography to record suction and scraping feeding strikes in four mbuna taxa that were also included in the initial morphological study. Vomer angle significantly predicted jaw protrusion angle across both feeding modes. However, ascending arm length showed context-dependent functionality as it was a predictor of jaw protrusion during suction feeding but showed no relationship during scraping. These findings indicate that neurocranial morphology, particularly vomer angle, may represent an important axis of trophic diversification and that cichlids modulate their feeding behavior based on their environment.

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