Host–symbiont recombination versus natural selection in the response of coral–dinoflagellate symbioses to environmental disturbance

Abstract

Mutualisms between reef-building corals and endosymbiotic dinoflagellates are particularly sensitive to environmental stress, yet the ecosystems they construct have endured major oscillations in global climate. During the winter of 2008, an extreme cold-water event occurred in the Gulf of California that bleached corals in the genus Pocillopora harbouring a thermally ‘sensitive’ symbiont, designated Symbiodinium C1b-c , while colonies possessing Symbiodinium D1 were mostly unaffected. Certain bleached colonies recovered quickly while others suffered partial or complete mortality. In most colonies, no appreciable change was observed in the identity of the original symbiont, indicating that these partnerships are stable. During the initial phases of recovery, a third species of symbiont B1 Aiptasia , genetically identical to that harboured by the invasive anemone, Aiptasia sp., grew opportunistically and was visible as light-yellow patches on the branch tips of several colonies. However, this symbiont did not persist and was displaced in all cases by C1b-c several months later. Colonies with D1 were abundant at inshore habitats along the continental eastern Pacific, where seasonal turbidity is high relative to offshore islands. Environmental conditions of the central and southern coasts of Mexico were not sufficient to explain the exclusivity of D1 Pocillopora in these regions. It is possible that mass mortalities associated with major thermal disturbances during the 1997–1998 El Niño Southern Oscillation eliminated C1b-c holobionts from these locations. The differential loss of Pocillopora holobionts in response to thermal stress suggests that natural selection on existing variation can cause rapid and significant shifts in the frequency of particular coral–algal partnerships. However, coral populations may take decades to recover following episodes of severe selection, thereby raising considerable uncertainty about the long-term viability of these communities.

Lipid biomarkers in Symbiodinium dinoflagellates: new indicators of thermal stress

“…Ecological and environmental parameters such as the history of thermal exposure and Symbiodinium-coral association (Baker 2003;Cooper et al 2011;Jones et al 2008;LaJeunesse et al 2010) may additionally impact the overall thermal stress response.…”

“…Batch cultures of types C1 (S. goreauii strain CCMP 2466, originally isolated from the anemone Discosoma sancti-thomae; hereafter "type C1") and D1 (CCMP 2556, originally isolated from the coral Montastraea faveolata; hereafter "type D1") were employed. Type C1 is an ecologically and geographically abundant type (e.g., LaJeunesse et al 2003) reported to be relatively sensitive to heat stress (e.g., LaJeunesse et al 2010).…”

Novel algal symbiont (Symbiodinium spp.) diversity in reef corals of Western Australia

“…A growing body of evidence indicates that some symbionts in clade D can (1) increase the thermotolerance of some host taxa (Rowan 2004, Berkelmans & van Oppen 2006, but see Abrego et al 2008), and (2) become more abundant in coral populations after episodes of severe bleaching and mortality (Baker et al 2004, Jones et al 2008, 2010b. Hosting these symbionts, however, likely represents a trade-off in terms of growth rate and/or reduced carbon uptake in juveniles (Little et al 2004, Cantin et al 2009 Higher abundance of D1a may have resulted from (1) changes in symbiont communities as a result of severe physiological stress resulting in bleaching (e.g.…”

“…Baker et al 2004, Jones et al 2008), (2) differential survival and/or reproduction (e.g. LaJeunesse et al 2010b), or (3) both mechanisms. However, since individual colonies were not monitored through time during the present study, and non-bleached colonies were selectively sampled from Dampier, the mechanism(s) that contributed to the observed distribution patterns of ITS-2 type D1a cannot be teased out from the effects of chronically higher temperatures in the Dampier region compared to Ningaloo or the Abrolhos Islands.…”

“…LaJeunesse 2002). Studies have shown that functional traits can differ among symbiont types both in hospite and in culture, particularly with respect to their temperature optima (Iglesias-Prieto et al 1992, Warner et al 1999Thornhill et al 2008, Hennige et al 2009), response to thermal stress, and influence on the relative bleaching susceptibility/ resistance of their scleractinian hosts , Glynn et al 2001, Rowan 2004, Goulet et al 2005, Berkelmans & van Oppen 2006, Jones et al 2008, LaJeunesse et al 2010b.…”