Comparative analysis of corrected tiger genome provides clues to their neuronal evolution

Abstract

The availability of completed and draft genome assemblies of tiger, leopard, and other felids provides an opportunity to gain comparative insights on their unique evolutionary adaptations. However, genome-wide comparative analyses are very sensitive to errors in genome sequences and thus require accurate genomic assemblies for reliable evolutionary insights. In this study, while analyzing the tiger genome, we found almost one million erroneous substitutions in the coding and non-coding region of the genome affecting 4,472 genes, hence, biasing the current understanding of tiger evolution. Moreover, these errors produced several misleading observations in previous studies. Thus, to gain insights into the tiger evolution, we corrected the erroneous bases in the genome assembly and gene set of tiger, which was also validated by resequencing of a Bengal tiger genome and transcriptome. A comprehensive evolutionary analysis was performed using 10,920 orthologs from nine mammalian species including the corrected gene sets of tiger and leopard, and using five different methods at three hierarchical levels i.e. felids, Panthera, and tiger. The unique genetic changes in tiger revealed that the genes showing the signatures of adaptation in tiger were enriched in development and neuronal functioning. Specifically, the genes belonging to Notch signalling pathway, which is among the most conserved pathways involved in embryonic and neuronal development, were found to be significantly diverged in tiger in comparison to the other mammals. Our findings suggest the role of adaptive evolution in neuronal functions and development processes, which correlates well with the presence of exceptional traits such as sensory perception, strong neuro-muscular coordination, and hypercarnivorous behavior in tiger.