Evolution of Miniaturization and Paedomorphism in Fishes of the Order Cypriniformes

Abstract

The order Cypriniformes (carps, minnows and their allies) is a morphologically diverse freshwater fish clade numbering over 4000 species. One species is the model organism zebrafish, Danio rerio. Cypriniform fishes have repeatedly undergone extreme reductions in body size, or miniaturization. Some miniatures are particularly small, and are also paedomorphic, retaining larval characteristics into adulthood. The primary goal of this dissertation research is to study the evolution of miniaturization ane paedomorphism in the order Cypriniformes. The dissertation opens with a brief introduction into the motivation for this research, and an outline for the remaining dissertation. The following chapters of the dissertation present various approaches to study this phenomenon from multiple perspectives: patterns of body size evolution, evolutionary relationships of miniature fishes, and functional genomics underlying miniaturization. Chapter 2 presents an empirical study of the dynamics of body size evolution and its relationship to miniaturization in the Danionidae, a clade including the majority of miniature cypriniform species. Not all miniatures are created equal: some of the smallest vertebrates are paedomorphic Cypriniformes (retaining larval characteristics into adulthood). Prior phylogenetic studies conflicted on the relationships between multiple paedomorphic genera – Paedocypris, Sundadanio, and Danionella – with implications for the number of times paedomorphism evolved. Chapter 3 presents a study utilizing phylogenomics to robustly resolve the relationships of these taxa among Cypriniformes. Finally, chapter 4 presents a study to gain insight into the genetic basis of convergent evolution of paedomorphism using comparative transcriptomics.