Integrative and Comparative Biology Advance Access published online on September 20, 2006
Integrative and Comparative Biology, doi:10.1093/icb/icl038
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Jason Hodin 1 *
* To whom correspondence should be addressed. Synopsis Metamorphosis is a substantial morphological transition between 2 multicellular phases in an organism's life cycle, often marking the passage from a prereproductive to a reproductive life stage. It generally involves major physiological changes and a shift in habitat and feeding mode, and can be subdivided into an extended phase of substantial morphological change and/or remodeling, and a shorter-term phase (for example, marine invertebrate "settlement," insect "adult eclosion," mushroom fruiting body emergence) where the actual habitat shift occurs. Disparate metamorphic taxa differ substantially with respect to when the habitat shift occurs relative to the timing of the major events of morphogenetic change. I will present comparative evidence across a broad taxonomic scope suggesting that longer-term processes (morphogenetic changes) are generally hormonally regulated, whereas nitric oxide (NO) repressive signaling often controls the habitat shift itself. Furthermore, new evidence from echinoids (sea urchins, sand dollars) indicates a direct connection between hormonal and NO signaling during metamorphosis. I incorporate 2 hypotheses for the evolution of metamorphosis--one involving heterochrony, the other involving phenotypic integration and evolutionarily stable configurations (ESCs)--into a network model for metamorphosis in echinoderms (sea urchins, starfish, and their kin). Early indications are that this core regulatory network can be acted upon by natural selection to suit the diverse ecological needs of disparate metamorphic organisms, resulting in evolutionary expansions and contractions in the core network. I briefly speculate on the ways that exposure to xenobiotic pollutants and other compounds might influence successful settlement of juveniles in the wild. Indeed, environmentally regulated life history transitions--such as settlement, metamorphosis, and reproductive maturation--may be developmental periods that are especially sensitive to such pollutants.
Metamorphosis: A Multikingdom Approach
Expanding networks: Signaling components in and a hypothesis for the evolution of metamorphosis
1 Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA
Jason Hodin, E-mail: seastar{at}stanford.edu
Abstract
From the symposium "Metamorphosis: A Multikingdom Approach" presented at the annual meeting of the Society for Integrative and Comparative Biology, January 4-8, 2006, at Orlando, Florida.
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  C. D. Bishop, M. J. Huggett, A. Heyland, J. Hodin, and B. P. Brandhorst Interspecific variation in metamorphic competence in marine invertebrates: the significance for comparative investigations into the timing of metamorphosis Integr. Comp. Biol., December 1, 2006; 46(6): 662 - 682. [Abstract] [Full Text] [PDF]
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