Ecological developmental biology (eco‐devo) explores the mechanistic relationships between the processes of individual development and environmental factors. Recent studies imply that some of these relationships have deep evolutionary origins, and may even pre‐date the divergences of the simplest extant animals, including cnidarians and sponges. Development of these early diverging metazoans is often sensitive to environmental factors, and these interactions occur in the context of conserved signaling pathways and mechanisms of tissue homeostasis whose detailed molecular logic remain elusive. Efficient methods for (...) transgenesis in cnidarians together with the ease of experimental manipulation in cnidarians and sponges make them ideal models for understanding causal relationships between environmental factors and developmental mechanisms. Here, we identify major questions at the interface between animal evolution and development and outline a road map for research aimed at identifying the mechanisms that link environmental factors to developmental mechanisms in early diverging metazoans.Also watch the Video Abstract. (shrink)

The diploblastic Cnidaria form one of the most ancient metazoan phyla and thus provide a useful outgroup for comparative studies of the molecular control of development in the more complex, and more often studied, triploblasts. Among cnidarians, the reef building coral Acropora is a particularly appropriate choice for study. Acropora belongs to the Anthozoa, which several lines of evidence now indicate is the basal class within the phylum Cnidaria, and has the practical advantages that its reproduction is predictable, external and (...) accessible and that the base content of its genome is not strongly biased. The Acropora system has already provided insights into ancestral linkages of homeobox genes and the evolution of the Pax genes, and has the potential to provide further new perspectives on the age, role in development, and evolution of these and other gene families. BioEssays 22:291–296, 2000. © 2000 John Wiley & Sons, Inc. (shrink)

Although Caenorhabditis and Drosophila proved invaluable in unraveling the molecular mechanisms of apoptosis, it is now clear that these animals are of limited value for understanding the evolution of apoptotic systems. Whereas data from these invertebrates led to the assumption that the extrinsic apoptotic pathway is restricted to vertebrates, recent data from cnidarians and sponges indicate that this pathway predates bilaterian origins. Here we review the phylogenetic distribution of caspase‐8, the initiator caspase of the extrinsic apoptotic pathway, its paralogs and (...) other components of the network. The ancestral caspase‐8 gave rise to four paralogs early in vertebrate evolution, and these have been maintained in many tetrapods. However, eutherians have lost caspase‐18 and myomorph rodents have lost caspase‐10, these losses suggesting functional redundancy amongst caspase‐8 paralogs. The apoptotic network of the eumetazoan ancestor appears to have been complex and vertebrate like, and is only now being revealed by studying simple animals. (shrink)