How Weird is The Worm? Evolution of the Developmental Gene Toolkit in .

Comparative developmental biology and comparative genomics are the cornerstones of evolutionary developmental biology. Decades of fruitful research using nematodes have produced detailed accounts of the developmental and genomic variation in the nematode phylum. Evolutionary developmental biologists are now utilising these data as a tool with which to interrogate the evolutionary basis for the similarities and differences observed in Nematoda. Nematodes have often seemed atypical compared to the rest of the animal kingdom-from their totally lineage-dependent mode of embryogenesis to their abandonment of key toolkit genes usually deployed by bilaterians for proper development-worms are notorious rule breakers of the bilaterian handbook. However, exploring the nature of these deviations is providing answers to some of the biggest questions about the evolution of animal development. For example, why is the evolvability of each embryonic stage not the same? Why can evolution sometimes tolerate the loss of genes involved in key developmental events? Lastly, why does natural selection act to radically diverge toolkit genes in number and sequence in certain taxa? In answering these questions, insight is not only being provided about the evolution of nematodes, but of all metazoans.