Integrative and Comparative Biology Advance Access originally published online on September 28, 2006
Integrative and Comparative Biology 2006 46(6):662-682; doi:10.1093/icb/icl043
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Interspecific variation in metamorphic competence in marine invertebrates: the significance for comparative investigations into the timing of metamorphosis
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* Kewalo Marine Laboratories, 41 Ahui St. Honolulu HI 96813 USA
Friday Harbor Laboratories University of Washington 620 University Road, Friday Harbor, WA 98250 USA
Whitney Laboratory for Marine Biosciences, University of Florida 9505 Ocean Shore Blvd, FL 32080 USA
¶ Hopkins Marine Station, Stanford University, Oceanview Boulevard Pacific Grove, CA, 93950 USA;
** Department of Molecular Biology and Biochemistry, Simon Fraser University Burnaby, BC V5A 1S6, Canada
Correspondence: 1E-mail: cbishop{at}hawaii.edu
Metamorphosis in marine invertebrate larvae is a dynamic, environmentally dependent process that integrates ontogeny with habitat selection. The capacity of many marine invertebrate larvae to survive and maintain metamorphic competence in the absence of environmental cues has been hypothesized to be an adaptive convergence (Hadfield and others 2001). A survey of the literature reveals that a single generalized hypothesis about metamorphic competence as an adaptive convergence is not sufficient to account for interspecific variation in this character. In an attempt to capture this variation, we discuss the "desperate larva hypothesis" and propose two additional hypotheses called the "variable retention hypothesis" and the "death before dishonor hypothesis." To validate these additional hypotheses we collected data on taxa from the published literature and performed a contingency analysis to detect correlations between spontaneous metamorphosis, habitat specificity and/or larval life-history mode, three characters relevant to environmentally induced settlement and metamorphosis. In order to account for phylogenetic bias in these correlations, we also constructed a phylogeny of these taxa and again performed a character-correlation analysis. Both these tests suggest that juvenile habitat specificity is correlated to the capacity of individuals to retain the competent larval state in the absence of substrate cues and therefore validate the existence of more than one hypothesis about metamorphic competence. We provide new data from the sea urchin Lytechinus pictus that suggest that nitric oxide (NO) and thyroxine hormone signaling interact to determine the probability of settlement in response to a settlement cue. Similarly, we provide evidence that thyroxine signaling in the sand dollar Dendraster excentricus increases spontaneous metamorphosis in the absence of cues from adult conspecifics in a manner that is independent of larval age.
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