Predicting developmental processes from evolutionary patterns: a molecular phylogeny of the zebrafish (Danio rerio) and its relatives

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Abstract
Central to most evolutionary research is the desire to understand the proximate and ultimate factors leading to increased biological diversity. Developmental and evolutionary biology are intimately linked since one factor that limits evolutionary diversification is ontogenetic feasibility to diversify morphology. The connection between these two biological disciplines, although historically recognized, remained long unappreciated. Most work in developmental biology is exclusively concerned with elucidating developmental processes in a small number of model systems, which are then assumed to be representative of a much larger number of species. Typically in this work developmental mutants are induced through mutagens and subsequently mutated genes are identified that are responsible for the altered (loss of function) and wildtype developmental phenotypes. Recently, the zebrafish,Danio rerio, has become one of the most popular model systems in vertebrate developmental biology. We present a DNA-based phylogeny for the zebrafish and 20 of its close relatives. The molecular phylogeny is based on homologous regions of the large (16S) and small (12S) mitochondrial ribosomal RNA genes. We argue that these closely related species of zebrafish, if viewed in an explicitly phylogenetic context, can be treated asnatural mutantsthat lend themselves well to comparative developmental work. Such comparisons might include the study of the developmental mechanisms of somatogenesis in various species of danios that differ in segment numbers (through hybridization, transgenic or other experimental embryological techniques). Based on the extensive zebrafish phylogeny we explore the connection between ontogeny and phylogeny and argue that evolutionary biology cannot only test plausible historical scenarios, but might also be able to predict and help characterize which differences in developmental processes are responsible for differences between species and more general evolutionary trends.