Editorial [ Mini Hot Topic Genomic Platforms for "evo-devo" Guest Editor: Ralf J. Sommer ]

Much of the knowledge in modern biology is based on studies of a handful of model organisms, such as the mouse Mus musculus, the fruit fly Drosophila melanogaster, the worm Caenorhabditis elegans and the weed Arabidopsis thaliana [1]. In the last 10 years genomic resources have revolutionized research in these organisms and provided precise knowledge of the molecular mechanisms governing fundamental biological processes: The genome sequence, expression profiling, large-scale RNA interference and yeast-two hybrid screens moved biology into the "-omics"-era. However, these fascinating developments have to be placed into an evolutionary perspective: All established model organisms represent just one of many species in a given taxa. For example, D. melanogaster is one of more than 1000 Drosophila species and one of more than one million insects [2]. Similarly, C. elegans is a nematode, but there are an estimated 1-10 million of these mostly very tiny and inconspicuous organisms [3]. Also, these organisms do not represent the tree of life in a comprehensive way. Molecular phylogeny suggests that insects and nematodes, i.e. D. melanogaster and C. elegans, represent closely related taxa and belong to a group called Ecdysozoa [4]. At the same time, the other major branch of the invertebrates, the so-called Lophotrochozoans including the molluscs and annelids, is not represented by any model organism at all. A closer look at the phylogeny reveals yet another problem. Within their groups, model organisms often belong to highly derived taxa. For example, Drosophila is a dipteran fly, C. elegans a rhabditid nematode and both do not represent all of the typical ancestral characters of insects and nematodes, respectively. Many interesting questions result from these evolutionary and phylogenetic considerations: How representative are the selected model organisms? Is what we find in D. melanogaster true for all other Drosophila species, or even for all insects? Can we use our knowledge about the model organisms to reconstruct the evolutionary history of insects, nematodes or mammals? And finally, what can we learn about humans when we study vertebrate or even invertebrate models? In the late 80th and early 90th, evolutionary developmental biology was born as a new discipline in developmental biology. "Evo-devo", as it is often called, tries to provide answers to these questions and aims for a developmental understanding of the evolution of form, morphology and biological diversity. The idea is simple: Turn away from the well-known model organisms and study organisms that look similar, but nonetheless different. With the wealth of Drosophila knowledge at hand, look into beetles and butterflies. Compare developmental patterning as known in C. elegans with other nematode species. Compare the mouse with other mammals, Xenopus with other frogs and the zebrafish with Medaka. Take the Arabidopsis data and look into other weeds, trees and non-flowering plants. Although there was a lot of skepticism initially, evolutionary developmental biology has passed the test of time and many exciting research projects are under way [5]. The idea is simple, that's true. However, the practical realization proves rather complicated, as there are many technical challenges to be faced. In many model organisms, modern research is based on genetic analysis (Drosophila, C. elegans) or gene knockout approaches (mouse), tools that are simply not available in most nonmodel organisms. Stable DNA-mediated transformation is standard in Drosophila, C. elegans, Arabidopsis and the mouse, but is still a problem in most non-model organisms. And finally, there is no genome sequence and there are no genome-dependent "-omics" approaches available in non-model species.