Aggression in closely related Malawi cichlids varies inversely with habitat complexity |
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Authors: | Patrick D Danley |
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Institution: | (1) Department of Biology, Baylor University, One Bear Place #97388, Waco, TX 76798, USA |
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Abstract: | Within the past 2 million years, the cichlids of Lake Malawi have diversified into well over 500 species resulting in one
of the worlds largest lacustrine fish radiations. As a result, many of the habitats within the lake support a high diversity
of species. In these highly species rich communities, male cichlids must acquire and defend a territory to successfully reproduce.
Within the rock-dwelling cichlids of Lake Malawi (mbuna), this has resulted in the formation of polyspecific leks on the heterogeneous
rocky benthos. Aggression is fairly common in these leks and has been tied not only to individual reproduction but to the
larger phenomenon of community assembly and the maintenance of biological diversity. In this study, I examined the patterns
of aggressive acts of four species within the mbuna genus Maylandia at two locations in the southern Lake Malawi. The number of aggressive acts of two sympatric species was examined at each
location. At each site, one species defends territories over bedrock and the other over cobble. The number of aggressive acts
across the four species was compared. The influence of habitat type on male aggression was examined and the targets of male
aggression were identified to evaluate several hypotheses concerning the evolution of male aggression. The results show that
aggression quantitatively varied among species, was largely directed towards heterospecifics, and was strongly influenced
by habitat type. The aggressive behavior of one sympatric species pair, Maylandia benetos and Maylandia zebra, was observed under controlled laboratory conditions. Laboratory results support field observations: the bedrock associated
species performed more aggressive acts and aggressive acts were directed equally at con- and heterospecifics. The results
of this study suggest that habitat complexity plays a larger role in shaping aggressive behavior than other suggested factors
such as competition for resources. |
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