Diversity of brain morphology in teleosts: brain and ecological niche.

Modern teleosts have more copies of developmental regulatory genes than other vertebrates, probably due to a whole genome duplication that occurred specifically at the base of the lineage of ray-finned fishes. The genome duplication generates duplicated genes (including their regulatory regions), and one of the duplicates might become redundant and free from selective pressures. These redundant genes might be more easily mutated during evolution. Brain morphogenesis is a process that is dependent on a large genetic program in which a subprogram for the regionalization of the brain is coupled with that for cell-proliferation control. If beneficial mutations took place in key genes within the genetic program for brain morphogenesis, it might result in the enhancement of region-specific cell proliferation and cell survival in the corresponding brain subdivisions. This mechanism might account for the appearance of various forms of teleost brains, which have been preserved under selection pressure in diverse environments. It is conceivable that variously modified brains might evolve under the conditions of natural selection so that the brains help fit the teleost species for diverse ecological niches. Copyright 2007 S. Karger AG, Basel.