Meeting Abstract
Convergent evolution results in shared, analogous phenotypes along independent lineages. Palaeognathae, a clade containing flightless ratites and volant tinamous, offers a unique opportunity to study the processes underlying convergent evolution: recent phylogenies support at least three losses of flight within the clade. Despite independent transitions to flightlessness, there are notable phenotypic similarities among ratites; for example, all ratites have reduced forelimbs and lack a sternal keel. To determine if convergent genomic changes govern convergent phenotypic changes, we have generated ten new high-quality genomes (three tinamous and seven ratites), and produced a phylogenetically based whole-genome alignment containing an additional 32 birds and non-avian reptiles. Our comparative genomic analysis uncovered many conserved non-exonic elements (CNEEs) that exhibit repeated acceleration along flightless ratite lineages, while remaining conserved in volant palaeognaths and neognaths. Since CNEEs often contain enhancers and other regulatory elements, these results suggest a strong role for regulatory evolution during these convergent losses of flight. ATAC-seq is now being carried out on the limbs of chicken (Gallus gallus), alongside the flightless emu (Dromaius novaehollandiae), and greater rhea (Rhea americana) to determine if candidate CNEEs: (1) exist in regions of accessible chromatin, and (2) display epigenomic differences between volant and flightless species. Putative enhancers are also being tested within a reporter construct in the developing chicken limb. This integrative approach will allow us to examine the functional developmental basis of a convergent phenotype.
