LAUSR

Female mate choice has strong experimental support as a diversifying force in the speciation of the haplochromine cichlid fishes of Lake MalaŴi, Africa. Somewhat less understood is the role that male-male aggression might have played in the evolution of new species of these fishes. In the rock-dwelling haplochromines of Lake MalaŴi, it is primarily territory-holding males that successfully court females; by determining which males gain territories, male-male aggression could support speciation by excluding less fit males from the breeding population. In order to test the hypothesis that males should direct more aggression towards conspecific rivals, we compared the aggression directed towards conspecific and heterospecific opponents in a sympatric pair of cichlids of the genus Labeotropheus Ahl 1927 (L. fuelleborni Ahl 1927 and L. trewavasae Fryer 1956). We found that, when presented with a pair of rivals, males of both species did direct more aggression towards the conspecific opponent, and the amount of aggression was increased when the conspecific opponent was larger than the heterospecific opponent. Additionally, we found a difference in the behavioural repertoire of the species: L. fuelleborni tends to rely on displays to intimidate opponents, while L. trewavasae employs more physical attacks to drive away opponents. Males of both species can thus recognize conspecifics and assess an opponent's relative threat to their ability to successfully reproduce, and use species-specific strategies to intimidate opponents. This article is protected by copyright. All rights reserved.