EVOLUTIONARY AND DEVELOPMENTAL MECHANISMS OF MAMMALIAN SKIN ADAPTATIONS

Abstract

Uncovering the genomic and developmental basis of evolved or adaptive morphological variation is a long-standing goal in biology. It is well understood that variation arises as a product of evolutionary changes to developmental programs, less understood however is how these changes generate the novel morphologies. Many recent studies have focused on organisms which have lost traits or structures; these studies provide support for the hypothesis that has implicated the regulation of developmental genes by cis-regulatory elements as important and the more likely cause for a large portion of variation between species. However, the mechanisms by which novel traits originate remain unknown.Here, integrating approaches from comparative genomics to functional genetics across different mammalian systems, I have investigated how genomes have changed to give rise to novel traits. I show that evolution can act on conserved developmental pathways by targeting cis-regulatory elements which control expression of key regulators. By shifting the expression of developmental pathways, through either prolonging existing expression patterns, creating new expression domains, or creating/eliminating/altering connections between developmental genes, changes to the developmental and molecular pathways of structures and traits becomes possible. I also show evidence that convergent gain of traits across both closely related, and distantly related organisms is driven by deploying similar existing gene regulatory networks rather than by evolving new genes or new regulatory networks. These findings offer a more holistic dissection of trait gain, further our understanding of how adaptive traits can arise, and how evolutionary pressures drive changes to genomes.