Naturally and sexually selected constraints on morphology, behavior, and coloration in the African cichlid genus Labeotropheus
The haplochromine cichlid fishes of Lake Malawi, Africa, have formed an immense species
flock that represents the greatest monophyletic assemblage of vertebrate animals in the
world. The causes of this evolutionary explosion have been attributed to the effects of
both natural and sexual selection. In this dissertation project, I explore four mechanisms
by which natural and/or sexual selection may have achieved this incredible diversity using
the two species of the widespread Malawian genus Labeotropheus. In Chapter 1, I
examine naturally- and sexually-selected constraints on male nuptial coloration and find
that both depth and geography constrain this coloration; red-colored individuals of both
species are found most prevalently at shallower depths and in the northwestern portion of
Lake Malawi. Furthermore, there is an effect of the presence of Labeotropheus
fuelleborni on the nuptial coloration of L. trewavasae. When found allopatrically
from L. fuelleborni, L. trewavasae tends to be blue, while in sympatry it tends to be
red. This suggests a possible role for nuptial coloration as a reproductive isolation/mate
recognition signal. Chapter 2 is a description of my investigation of inter- and intraspecific
morphological divergence in the Labeotropheus using geometric morphometric methods.
The results further confirm the well-established morphological distinctions between these
species, and go on to demonstrate morphological differences among populations within species.
In Chapter 3, I examine whether or not males of L. fuelleborni can distinguish between
sympatric and allopatric conspecific opponents in agonistic encounters. While the results
suggest that they cannot, there may be extraneous factors that my experiment did not consider
or examine. Finally, in Chapter 4, I present the first empirical evidence demonstrating that
male nuptial coloration is indeed a sexually-selected characteristic in haplochromine cichlids.
My experiments investigating the effects of differences in both chroma and within-pattern
color contrast show that females do prefer males with more saturated colors, which demonstrates
directional selection on an aspect of nuptial color in the Labeotropheus.