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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. [ABSTRACT FROM AUTHOR]

Courtship sounds made by three sympatric cichlid species,Pseudotropheus zebra,P. callainosand an undescribed species known asP.‘zebra gold’ were recorded and compared to investigate the potential role of acoustic signals in mate choice. Sounds were emitted during‘quiver’ and‘circle’ components of the male courtship display and consisted of rapidly repeated pulse units. Some sound variables differed significantly among species withP. callainosgenerally being separated from the other two species. This species produced sounds with higher peak frequency(for a given length) and lower number of pulses thanP.‘zebra gold’ and higher pulse durations thanP. zebra. In addition, standard length was inversely related to peak frequency in bothP.‘zebra gold’ andP. callainos(this relation was not tested inP. zebradue to the small sample size). These differences might indicate different regimes of intraspecific sexual selection among the three species. [ABSTRACT FROM AUTHOR]