title: CORRESPONDENCE BETWEEN COLD TOLERANCE AND TEMPERATE BIOGEOGRAPHY IN A WESTERN ATLANTIC SYMBIODINIUM (DINOPHYTA) LINEAGE(1).
abstract: Many corals form obligate symbioses with photosynthetic dinoflagellates of the genus Symbiodinium Freudenthal (1962). These symbionts vary genotypically, with their geographical distribution and abundance dependent upon host specificity and tolerance to temperature and light variation. Despite the importance of these mutualistic relationships, the physiology and ecology of Symbiodinium spp. remain poorly characterized. Here, we report that rDNA internal transcribed spacer region 2 (ITS2) defined Symbiodinium type B2 associates with the cnidarian hosts Astrangia poculata and Oculina arbuscula from northerly habitats of the western Atlantic. Using pulse-amplitude-modulated (PAM) fluorometry, we compared maximum photochemical efficiency of PSII of type B2 to that of common tropical Symbiodinium lineages (types A3, B1, and C2) under cold-stress conditions. Symbiont cultures were gradually cooled from 26°C to 10°C to simulate seasonal temperature declines. Cold stress decreased the maximum photochemical efficiency of PSII and likely the photosynthetic potential for all Symbiodinium clades tested. Cultures were then maintained at 10°C for a 2-week period and gradually returned to initial conditions. Subsequent to low temperature stress, only type B2 displayed rapid and full recovery of PSII photochemical efficiency, whereas other symbiont phylotypes remained nonfunctional. These findings indicate that the distribution and abundance of Symbiodinium spp., and by extension their cnidarian hosts, in temperate climates correspond significantly with the photosynthetic cold tolerance of these symbiotic algae.
authors.affiliation: Odum School of Ecology, University of Georgia, Athens, Georgia 30602, USA Department of Biological Sciences, 101 Rouse Life Sciences Building, Auburn University, Auburn, Alabama 36849, USAOdum School of Ecology, University of Georgia, Athens, Georgia 30602, USADepartment of Plant Biology, University of Georgia, Athens, Georgia 30602, USAOdum School of Ecology, University of Georgia, Athens, Georgia 30602, USADepartment of Plant Biology, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Thornhill
authors.affiliation: Odum School of Ecology, University of Georgia, Athens, Georgia 30602, USA Department of Biological Sciences, 101 Rouse Life Sciences Building, Auburn University, Auburn, Alabama 36849, USAOdum School of Ecology, University of Georgia, Athens, Georgia 30602, USADepartment of Plant Biology, University of Georgia, Athens, Georgia 30602, USAOdum School of Ecology, University of Georgia, Athens, Georgia 30602, USADepartment of Plant Biology, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: Dustin W
authors.initials: DW
authors.lastname: Kemp
authors.affiliation: Odum School of Ecology, University of Georgia, Athens, Georgia 30602, USA Department of Biological Sciences, 101 Rouse Life Sciences Building, Auburn University, Auburn, Alabama 36849, USAOdum School of Ecology, University of Georgia, Athens, Georgia 30602, USADepartment of Plant Biology, University of Georgia, Athens, Georgia 30602, USAOdum School of Ecology, University of Georgia, Athens, Georgia 30602, USADepartment of Plant Biology, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: Brigitte U
authors.initials: BU
authors.lastname: Bruns
authors.affiliation: Odum School of Ecology, University of Georgia, Athens, Georgia 30602, USA Department of Biological Sciences, 101 Rouse Life Sciences Building, Auburn University, Auburn, Alabama 36849, USAOdum School of Ecology, University of Georgia, Athens, Georgia 30602, USADepartment of Plant Biology, University of Georgia, Athens, Georgia 30602, USAOdum School of Ecology, University of Georgia, Athens, Georgia 30602, USADepartment of Plant Biology, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: William K
authors.initials: WK
authors.lastname: Fitt
authors.affiliation: Odum School of Ecology, University of Georgia, Athens, Georgia 30602, USA Department of Biological Sciences, 101 Rouse Life Sciences Building, Auburn University, Auburn, Alabama 36849, USAOdum School of Ecology, University of Georgia, Athens, Georgia 30602, USADepartment of Plant Biology, University of Georgia, Athens, Georgia 30602, USAOdum School of Ecology, University of Georgia, Athens, Georgia 30602, USADepartment of Plant Biology, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Schmidt
keywords: Astrangia poculata; Oculina arbuscula; Symbiodinium; biogeography; cold temperature stress; coral; molecular diversity; zooxanthellae