Undergraduate Honors Theses

Thesis Defended

Spring 2011

Document Type

Thesis

Department

Ecology and Evolutionary Biology

First Advisor

Dr. Alexander Cruz

Abstract

The cichlid fish (Perciformes: Teleostei) of the Rift Valley lakes of Africa are commonly viewed as non-human model evolutionary organisms that offer lessons about evolution that can be applied to many other organisms, due to the fact that new cichlid species evolve in the Rift Valley lakes at an accelerated rate when compared to other locales. In order to use them as such, however, the mechanisms by which the cichlids evolve into new species must be understood. Visual sexual selection by females has been implicated in numerous studies as a driving force in these radiations. Recently, the ability of females to discriminate in this fashion has come under threat in Lake Victoria, where water clarity has declined due to anthropogenic factors such as increased agricultural cultivation and deforestation. As a result, an increase in mating and hybridization among multiple cichlid species has been seen in the portions of the lake that are most affected by this reduction in water clarity. Comparatively little research has been done on the possible effects of reduced water clarity on the other two major lakes of the region, Lake Tanganyika and Lake Malawi. Utilizing video playback technology, it was found that reducing the amount of light transmitted (using opaque filters) between female Metriaclima estherae (a Malawian cichlid) and videos of a male of the same species and a male of a different species significantly reduces the relative amount of time the female spends with the male of the same species versus the male of a different species. The use of opaque filters is intended to simulate the effects of real-world reductions in water clarity in Lake Malawi that may occur in the future. The result found here indicates that, similar to Lake Victoria, cichlids in Lake Malawi may be more prone to choose mates of a different species when living in areas with reduced water clarity. Management plans for the lake, then, should take robust action to prevent reductions in water clarity.

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