Cerebral lateralization and its relationship to phylogeny and aggression in anabantoid fishes.

We examined the relationship between aggression and cerebral lateralization, as expressed by eye-use preference in a mirror-response paradigm, in six species of anabantoid fishes in the teleost family Belontiidae. Our objective was to test the hypothesis that frequency-dependent selection should decrease lateralization at the population level in more aggressive species. The mean laterality index did not differ significantly among the six species, nor did any of the species differ from zero, which suggests that populations of these fishes are neither left- nor right-eye biased. In spite of species differences in aggressive behavior, there was no relationship between population-level laterality and aggression as we had originally predicted. The degree of individual lateralization did differ significantly among some species. A phylogenetic generalized least squares (PGLS) analysis showed that these species differences were not due to phylogenetic distance. Individual laterality was also unrelated to aggression. Fishes in the genus Betta were the most individually lateralized, but varied in the intensity of aggressive behavior they displayed toward the mirrors. Taxa such as paradise fish (Macropodus opercularis and Pseudosphromenus dayi) were intermediate in eye-use preferences and gourami (Trichogaster trichopterus) displayed little cerebral lateralization. We also used the PGLS method to reconstruct ancestral values for individual lateralization in this group of fishes, from which we conclude that the ancestral condition was one of low variance in eye-use preference.