Rapid Evolutionary Radiation of Marine Zooplankton in Peripheral Environments
Rapid evolutionary radiation of marine zooplankton in peripheral environments Michael N Dawson†‡§ and William M. Hamner¶ †Biological, Earth, and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia; ‡Coral Reef Research Foundation, P.O. Box 1765, Koror, PW 96940, Palau; and ¶Department of Ecology and Evolutionary Biology, P.O. Box 951606, University of California, Los Angeles, CA 90095 Communicated by Robert T. Paine, University of Washington, Seattle, WA, May 2, 2005 (received for review January 28, 2005) Populations of jellyfish, Mastigias sp., landlocked in tropical marine southeast Australia taxa are consistent with subdivision of lakes during the Holocene, show extreme genetic isolation (0.74 < species ranges during Pleistocene low stands (16). Marine fossil ST < 1.00), founder effects (genetic diversity: 0.000 < < 0.001), faunas of North and Central America show pulse extinction and rapid morphological evolution, and behavioral adaptation. These speciation events Ϸ2 million years ago (17). Thus, much modern results demonstrate incipient speciation in what we propose may marine diversity appears to have originated during the relatively be modern analogues of Plio-Pleistocene populations isolated in short periods of glacially lowered sea levels that predominated ocean basins by glacially lowered sea level and counterparts to during the late Pliocene and Pleistocene ‘‘icehouse’’ climate modern marine populations isolated on archipelagos and other (2, 18, 19). distant shores. Geographic isolation in novel environments, even if The details of such events are difficult to study in many marine geologically brief, may contribute much to marine biodiversity taxa; they are impossible to study in gelatinous marine zooplank- because evolutionary rates in marine plankton can rival the most ton, an ecologically important and phyletically diverse group rapid speciation seen for limnetic species, such as cichlids and including ctenophores, salps, pteropods, cubozoan, hydrozoan, sticklebacks.
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