Intraspecific and interspecific variation in thermotolerance and photoacclimation in Symbiodinium dinoflagellates

Abstract

Light and temperature are major drivers in the ecology and biogeography of symbiotic dinoflagellates living in corals and other cnidarians. We examined variations in physiology among 11 strains comprising five species of clade A We grew cultures at 26°C (control) and 32°C (high temperature) over a duration of 18 days while measuring growth and photochemical efficiency ( / ). Responses to thermal stress ranged from susceptible to tolerant across species and strains. Most strains exhibited a decrease in cell densities and / when grown at 32°C. Tolerance to high temperature () was calculated for all strains, ranging from 0 (unable to survive at high temperature) to 1 (able survive at high temperature). There was substantial variation in thermotolerance across species and among strains. One strain had a close to 1, indicating that growth was not reduced at 32°C for only this one strain. To evaluate the combined effect of temperature and light on physiological stress, we selected three strains with different levels of thermotolerance (tolerant, intermediate and susceptible) and grew them under five different light intensities (65, 80, 100, 240 and 443 µmol quanta m s) at 26 and 32°C. High irradiance exacerbated the effect of high temperature, particularly in strains from thermally sensitive species. This work further supports the recognition that broad physiological differences exist not only among species within clades, but also among strains within species demonstrating that thermotolerance varies widely between species and among strains within species.

Free‐living and symbiotic lifestyles of a thermotolerant coral endosymbiont display profoundly distinct transcriptomes under both stable and heat stress conditions

“…This brings critical attention to the importance of examining the response of Symbiodiniaceae holistically as the responses in culture may not be representative of in hospite endosymbionts. To date, the vast majority of transcriptomic assessments of Symbiodiniaceae within the context of thermal stress have been performed exclusively on free‐living cultures (Barshis et al, ; Baumgarten et al, ; Díaz‐Almeyda et al, ; Gierz et al, ; Levin et al, ; Levin, Suggett, Nitschke, van Oppen, & Steinberg, ; Liew, Li, Baumgarten, Voolstra, & Aranda, ; Xiang, Nelson, Rodriguez, Tolleter, & Grossman, ), and while they have been insightful, they may present not only a reduced, but also a biased transcriptional picture of the alterations that occur in Symbiodiniaceae in hospite. Only one other investigation directly compared gene expression in hospite to free‐living conditions (Rosic, Pernice, Dunn, Dove, & Hoegh‐Guldberg, ), but it focused on only two heat‐shock protein genes.…”

“…There is an existing body of work demonstrating that the shift of the dominant symbiont (shuffling) or acquisition of new species of symbionts (switching) from the environment enables holobionts, the coral host and its diverse assemblage of symbionts, to better withstand climate‐related increases in seawater temperatures (Baker, ; Berkelmans & Van Oppen, ; Jones, Berkelmans, van Oppen, Mieog, & Sinclair, ; Lewis, Neely, & Rodriguez‐Lanetty, ; Rowan, ; Stat, Carter, & Hoegh‐Guldberg, ). More recently, significant differences in heat tolerance have been reported both within a single Symbiodiniaceae genus (Díaz‐Almeyda et al, ) as well as between genera (Grégoire, Schmacka, Coffroth, & Karsten, ), revealing that different Symbiodiniaceae species have differing thermal optima and tolerances. A well‐studied case is Durusdinium trenchii (previously Symbiodinium trenchii [LaJeunesse et al, ]), an ITS2–D1a subtype within Clade D, that confers an increase in heat tolerance of 1–1.5°C to coral hosts (Berkelmans & Van Oppen, ; Rowan, ).…”

Genetic variation in Breviolum antillogorgium, a coral reef symbiont, in response to temperature and nutrients

“…The family Symbiodiniaceae is taxonomically diverse and is comprised of over seven distinct genera (LaJeunesse et al, 2018) with substantial within-genus variation representing groups of related species (Coffroth & Santos, 2005;LaJeunesse et al, 2018). Though many studies have examined functional trait diversity among and within Symbiodiniaceae genera (Frade, Bongaerts, Winkelhagen, Tonk, & Bak, 2008;Grégoire, Schmacka, Coffroth, & Karsten, 2017;Hennige, Suggett, Warner, McDougall, & Smith, 2009;Iglesias-Prieto & Trench, 1994;Karim, Nakaema, & Hidaka, 2015;Krämer, Caamaño-Ricken, Ricther, & Bischof, 2012;McGinty, Pieczoonka, & Mydlarz, 2012;Oakley, Schmidt, & Hopkinson, 2014;Ramsby, Shirur, Iglesias-Prieto, & Goulet, 2014;Robison & Warner, 2006;Rodríguez-Romän & Iglesias-Prieto, 2005;Suggett et al, 2008;Takahashi, Whitney, & Badger, 2009), fewer studies have examined functional trait diversity among and within closely related species within the Symbiodiniaceae (Diaz-Almeyda et al, 2017;Goyen et al, 2017;Klueter, Trapani, Archer, McIlroy, & Coffroth, 2017;Suggett et al, 2015). Functional trait variation is correlated with phylogenetic relatedness in some cases, but not in others, highlighting the need to examine functional trait variation at lower taxonomic scales (Suggett, Warner, & Leggat, 2017).…”

Two threatened Caribbean coral species have contrasting responses to combined temperature and acidification stress

“…The subtypes of C present were not determined. Although considerable physiological variability exists within and among subtypes within clades (Díaz‐Almeyda et al ), the A‐ and C‐types found in A. cervicornis are generally considered to be thermally sensitive compared to D1a. (Howells et al ; Díaz‐Almeyda et al ).…”