Convergent evolution of brain morphology and communication modalities in lizards

Abstract

Abstract Animals communicate information within their environments via visual, chemical, auditory, and/or tactile modalities. The use of each modalityis generally linked to particular brain regions, but it is not yet known whether the cellular morphology of neurons in these regions has evolved in association with the relative use of a modality.We investigated relationships between the behavioral use of communication modalities and neural morphologies in six lizard species. Two of these species (Anolis carolinensis and Leiocephalus carinatus) primarily use visual signals to communicate with conspecifics and detect potential prey, and two (Aspidoscelis gularis and Scincella lateralis) communicate and forage primarily using chemical signals. Two other species (Hemidactylus turcicus and Sceloporus olivaceus) use both visual and chemical signals. For each species, we performed behavioral observations and quantified rates of visual and chemical behaviors. We then cryosectioned brain tissues from 9–10 males of each species and measured the soma size and density of neurons in two brain regions associated with visual behaviors (the lateral geniculate nucleus and the nucleus rotundus) and one region associated with chemical behaviors (the nucleus sphericus). With analyses conducted in a phylogenetic context, we found that species that performed higher rates of visual displays had a denser lateral geniculate nucleus, and species that used a higher proportion of chemical displays had larger somas in the nucleus sphericus. These relationships suggest that neural morphologies in the brain have evolved convergently in species with similar communication behaviors.