Brain anatomy of a clonal fish, the Amazon molly (Poecilia formosa): Effects of early-life environment

Abstract

Abstract During ontogeny, environmental factors can impact the development of manifold traits that often aid in survival. This may include differential investment in brain regions in response to cognitive challenges. Especially the brain anatomy of fishes seems to respond readily to biotic and abiotic factors. However, we currently lack sufficient data to determine the extent to which such changes are consistent across species. To extend the phylogenetic breadth in this endeavour we studied how brain anatomy of Amazon mollies (Poecilia formosa) responds to the presence or absence of physical enrichment and/or social companions. The Amazon molly is a clonal species and genetically highly uniform, so that differences in brain anatomy of individuals from the same clonal lineage are most likely due to the environmental conditions provided, not to inherent genetic differences. We quantified brain anatomy by determining the volumes of six main brain regions (olfactory bulb; telencephalon; optic tectum; cerebellum; dorsal medulla; hypothalamus) and overall brain size. While brain anatomy was overall unaffected by the visual presence of a conspecific, we found that the cerebellum was larger in animals reared in an environmentally complex habitat. Our results corroborate the idea that usage of certain cognitive domains fosters enlargement in the region governing those.