UC Riverside

Changes in dental morphology have profound consequences on the ecology of species and the niches they are adapted to. Here, changes in teeth, specifically in the main components of enamel and dentin, were investigated. Genes encoding the proteins that produce these structures were examined for mutations and utilized in selection analyses to determine the rates of nonsynonymous versus synonymous substitutions via dN/dS ratios. These values were then used to calculate the timing of inactivation of those genes and by proxy their phenotypes to determine if these phenotypes were linked or decoupled in the evolutionary history of toothless baleen whales (Mysticeti) and pangolins (Pholidota). In addition, the enamel genes for toothed whales (Odontoceti) were investigated for mutations and selection patterns given their degenerative enamel. In chapter 1, mysticetes were discovered to possess numerous inactivating mutations in enamel and dentin/tooth-specific genes, many of which were shared among major clades. The elevated dN/dS values suggest that these genes may have been relaxed in the common ancestor of Mysticeti. Inactivation times estimated that enamel was lost before dentin/teeth, the latter of which was lost at most two times, independently in the common ancestor of Balaenidae and Plicogulae. The results from Chapter 2 reveal numerous mutations and elevated dN/dS values among enamel genes in many odontocetes. More mutations and increased relaxed/positive selection correlated to taxa with less complex enamel, with a strong correlation of decreasing dN/dS values associated with increasing enamel complexity. Chapter 3 described inactivating mutations among the tooth genes in three living species pangolins, with many of the genes containing shared mutations in all three taxa. Selection intensity was observed to be elevated and relaxed compared to outgroups. Calculations for the inactivation of genes and phenotypes reveal that enamel was lost around 62 million years ago, but unable to retrieve an inactivation date for dentin/teeth. Overall, these chapters have demonstrated the underlying genetic components necessary for enamel and dentin/tooth production have become pseudogenized molecular relics riddled with mutations in edentulous taxa and have started to build up in taxa with degenerative enamel.