HR: 1340h
AN: B33B-0258    [Abstracts]
TI: The Macroevolutionary Interplay Between Planktic Larvae and Benthic Predators
AU: * Peterson, K J
EM: kevin.j.peterson@dartmouth.edu
AF: Department of Biological Sciences, Dartmouth College, Hanover, NH 03755 United States
AB: Many marine invertebrates have a complex life cycle whereby the egg, rather than developing directly to the juvenile stage, develops instead into a intermediate larval form which may spend weeks to months feeding in the plankton before it becomes competent to undergo metamorphosis into the benthic juvenile. Because the selective advantages provided to the animal by having a planktotrophic larval stage are largely unknown, the reasons behind their origin and subsequent maintenance over geological time are not well understood. Using both a molecular clock and the fossil record, I show that four primitively non-feeding larval forms evolved sometime between the late Ediacaran and Early Cambrian, and feeding larvae appear to have evolved from non-feeding ancestors sometime between the Late Cambrian and Middle Ordovician in at least five, if not eight, of eight different clades analyzed. Thus, the initial exploitation of the predator-free pelagos by larvae was achieved independently multiple times by the end of the Early Cambrian, most likely driven by benthic predation pressures upon developing eggs and embryos. Then, because the evolution of larval planktotrophy from lecithotrophic ancestors correlates with the dramatic rise in the generic number of benthic suspension feeders in the Early Ordovician, it seems likely that benthic suspension feeding selected for fecundity, and thus indirectly for planktotrophy, in multiple lineages of marine invertebrates by the end of the Middle Ordovician.
DE: 9614 Paleozoic
DE: 4817 Food chains
DE: 4855 Plankton
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting