Meeting Abstract

87.5  Monday, Jan. 6 11:15  How many times might complex brains have evolved? MOROZ, LL; Univ. of Florida moroz@whitney.ufl.edu

The origin of complex centralized brains and elementary cognitive functions are two major evolutionary transitions in the history of our planet. We integrate a large-scale comparative neuronal transcriptome (>200 species) and genomic sequencing data (from several new sequenced genomes including ctenophores, Aplysia, cephalopods and related lophotrochozoans) with modern phylogenomics to reconstruct parallel evolution of neuronal centralization. In contrast to the widely accepted monophyletic scenario (i.e. the presence of a centralized nervous system in urbilateria), our analysis suggests that complex brains may have independently evolved at least 9 to 11 times within Metazoa. Even within Mollusca, the cephalization events might have occurred at least five times. It is now possible to employ single-cell RNA-seq protocols to follow up the evolution of homologous, even ancestral, neuronal lineages at significant speciation distances. Thus, using examples from ctenophores, molluscs and basal deuterostomes, we start to decipher changes in the genomic organization of neurogenic tissues underlying the formation of ganglionic structures or even their fusion into a centralized brain. In summary, the modular organization of neurogenic pathways and memory-forming circuits is a common feature. However, these pathways and circuits have very complex ancestry and, frequently, very different molecular makeup with an independent recruitment of both shared and numerous lineage-specific gene products.