Document Type

Honors Capstone Project

Date of Submission

Spring 5-1-2009

Capstone Advisor

Dr. R. Craig Albertson

Honors Reader

Dr. William Starmer

Capstone Major

Biology

Capstone College

Arts and Science

Audio/Visual Component

no

Capstone Prize Winner

no

Won Capstone Funding

no

Honors Categories

Sciences and Engineering

Subject Categories

Biology

Abstract

An animal’s skeletal and muscular structures form a biological machine capable of interacting with its environment. When anatomical form changes the resulting modification in biomechanical function can allow it to occupy a new ecological niche. The cichlid fishes of the major East African Rift Lakes have been frequently regarded as one of the best know examples of adaptive radiations that have produced a large variety of skull shapes in an unusually short span of evolutionary time that has permitted the use of an extremely wide variety of feeding niches. I studied the anatomical diversity of this incredible lineage by dissecting and photographing the skulls and jaws of 219 specimens (which accounted for more than 85% of the genera found in the three largest East African Rift Lakes) and my data include at least one species from 44 of the Tanganyika cichlid genera (>86% of the genera found in the lake), 50 of the Malawi genera (>86%), and 14 Lake Victoria species from 8 genera (>72%). I examined anatomical landmarks that are of biomechanical importance for fish feeding using geometric morphometric analyses, which are coordinate based mathematical analyses of anatomical form. The results confirmed that the levels of anatomical diversity among the head and jaw morphologies among the cichlids ofLake Tanganyika,MalawiandVictoriaare significantly different. The two major lineages of the Lake Malawi cichlids, the "rock dwellers (mbuna) and the "sand dwellers" show large areas of overlap in morphological diversity and despite having both evolved skull shapes that are not possessed by the other, their skull shape disparity levels are not significantly different. Skull elongation represents the single largest component of total head shape variation in all three lakes and my results support the hypothesis that it may be the first and simplest shape transformation to occur. Some of the most interesting results of my research indicate that there may be a linear relationship between the age of a rift lake and the magnitude of anatomical diversity present among its cichlids. These results provide a nearly comprehensive measurement of the anatomical diversity of the rift lake cichlid skulls and provide a quantitative description of a classic example of an adaptive radiation. These morphological data are being used to select specimens for studying genetic and developmental shifts that have contributed to this explosive cranial anatomy diversification. These are preliminary data that serve as a foundation for future studies of the genetic controls of vertebrate skull shape.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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