Functional diversity of photobiological traits within the genus Symbiodinium appears to be governed by the interaction of cell size with cladal designation

Abstract

SummaryDinoflagellates of the genus Symbiodinium express broad diversity in both genetic identity (phylogeny) and photosynthetic function to presumably optimize ecological success across extreme light environments; however, whether differences in the primary photobiological characteristics that govern photosynthetic optimization are ultimately a function of phylogeny is entirely unresolved.We applied a novel fast repetition rate fluorometry approach to screen genetically distinct Symbiodinium types (n = 18) spanning five clades (A-D, F) for potential phylogenetic trends in factors modulating light absorption (effective cross-section, reaction center content) and utilization (photochemical vs dynamic nonphotochemical quenching;The variability of PSII light absorption was independent of phylogenetic designation, but closely correlated with cell size across types, whereas PSII light utilization intriguingly followed one of three characteristic patterns: (1) Our functional trait-based approach shows, for the first time, how Symbiodinium photosynthetic function is governed by the interplay between phylogenetically dependent and independent traits, and is potentially a means to reconcile complex biogeographic patterns of Symbiodinium phylogenetic diversity in nature.

Use of Open Source Hardware and Software Platforms to Quantify Spectrally Dependent Differences in Photochemical Efficiency and Functional Absorption Cross Section within the Dinoflagellate Symbiodinium spp.

“…Spectrally dependent differences in algal photochemistry can not only provide more detail of photochemical differences within a single symbiosis, and also may potentially be a powerful tool for resolving genetically (and functionally) different Symbiodinium populations across diverse cnidarian hosts, including reef building corals. These results, while limited in scope, are similar to those of a more extensive study by Suggett et al (2015) that examined 18 genetically distinct cultured Symbiodinium isolates with a single waveband excitation (peak excitation, 450 nm) fast repetition rate fluorometer. Specifically, that work noted that different phylotypes of Symbiodinium could be grouped into particular clusters based on the balance of how symbionts used the fraction of open PSII reaction centers (i.e., photochemical quenching or…”

“…Algal cell density and volume was assessed by replicate hemocytometer counts (n = 6) under 100x magnification. Samples were photographed using a Nikon microphot-FXA epifluorescent microscope and then analyzed by computer using Image J software (NIH) using methods similar to Suggett et al (2015). For photopigment quantification, pelleted cells were lysed in 90% methanol with a bead beater (BioSpec) for 60 s, incubated at −20 • C for 2 h and then centrifuged for 5 min at 5,000 rpm to remove remaining debris.…”

“…Such phenotypic assessment (Phenomics) is gaining momentum within other photobiological fields where comprehension of genetic variability has far outpaced phenotypic descriptions (Furbank and Tester, 2011). Phenotypic structure across different symbiont types grown in culture has been documented using photophysiological metrics as measured using active chlorophyll fluorometric measurements (Suggett et al, 2015). However, environmental variables such as light intensity and the spectral characteristics inherent to the coral host in which the symbiont resides can also influence photobiological behavior (Iglesias-Prieto and Trench, 1997b;Iglesias-Prieto et al, 2004;Wangpraseurt et al, 2012Wangpraseurt et al, , 2014.…”

Environmental Drivers of Variation in Bleaching Severity of Acropora Species during an Extreme Thermal Anomaly

“…This result suggests that it is the presence of a specific heat-tolerant symbiont, rather than the ability to host multiple symbiont types, that confers thermal tolerance. We note, however, that while there is an increasing research emphasis on the functional differences between Symbiodinium clades (e.g., Suggett et al, 2015Suggett et al, , 2017, the coral species coverage of these data remains relatively sparse and this constrained our analyses. We limited our analysis to the level of Symbiodinium clades, but differences in thermal tolerance exist among Symbiodinium belonging to the same clade (Tchernov et al, 2004;Sampayo et al, 2008;Correa and Baker, 2009;LaJeunesse et al, 2014).…”

Molecular signatures of host specificity linked to habitat specialization in Exaiptasia sea anemones

“…S. minutum may therefore be favored in thermally stable, intermediate light environments, with Symbiodinium clade A predominating if exposure to high light and temperature is likely. This pattern of distribution is consistent with previously reported photophysiological characteristics of representatives of these Symbiodinium lineages (Goulet et al., 2005; Suggett et al., 2015). Similar variation in symbiont type according to abiotic environment is well documented in natural populations of corals (Keshavmurthy et al., 2012; Rowan, Knowlton, Baker, & Jara, 1997).…”