Quantifying cryptic Symbiodinium diversity within Orbicella faveolata and Orbicella franksi at the Flower Garden Banks, Gulf of Mexico.

Elizabeth A Green,Mikhail V Matz,Sarah W Davies,Mónica Medina

doi:10.7717/peerj.386

Elizabeth A Green, Mikhail V Matz + Show 2 more

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https://doi.org/10.7717/peerj.386

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Abstract

The genetic composition of the resident Symbiodinium endosymbionts can strongly modulate the physiological performance of reef-building corals. Here, we used quantitative metabarcoding to investigate Symbiodinium genetic diversity in two species of mountainous star corals, Orbicella franksi and Orbicella faveolata, from two reefs separated by 19 km of deep water. We aimed to determine if the frequency of different symbiont genotypes varied with respect to coral host species or geographic location. Our results demonstrate that across the two reefs both coral species contained seven haplotypes of Symbiodinium, all identifiable as clade B and most closely related to type B1. Five of these haplotypes have not been previously described and may be endemic to the Flower Garden Banks. No significant differences in symbiont composition were detected between the two coral species. However, significant quantitative differences were detected between the east and west banks for three background haplotypes comprising 0.1%–10% of the total. The quantitative metabarcoding approach described here can help to sensitively characterize cryptic genetic diversity of Symbiodinium and potentially contribute to the understanding of physiological variations among coral populations.

Highlights

The symbiotic relationship between scleractinian corals and dinoflagellate algae in the genus Symbiodinium is well known, but there is still much to understand about the establishment and plasticity of this complex symbiosis
But significant FST (p < 0.02) between banks (Table 1), which was reflected on the STRUCTURE plot (Fig. 2)
Five of the seven quantifiable haplotypes did not have an exact match in the NCBI sequence database and were potentially novel. It remains to be seen whether these haplotypes are endemic to the Flower Garden Banks (FGB), since this metabarcoding approach has not yet been widely applied across the Caribbean. Another alternative is that the detected rare haplotypes represent artifacts of amplification, sequencing or bioinformatics analysis, which is probable in cases such as ours when OTUs are expected to be of low sequence diversity, necessitating the use of high sequence identity thresholds (97%) during OTU inference

Summary

Introduction

The symbiotic relationship between scleractinian corals and dinoflagellate algae in the genus Symbiodinium is well known, but there is still much to understand about the establishment and plasticity of this complex symbiosis. Knowledge of Symbiodinium taxonomic diversity has increased over the last two decades with advancing molecular genotyping techniques detecting novel genotypes within each of the nine recognized clades (Coffroth & Santos, 2005; Pochon & Gates, 2010). Some of these genotypes may impart different physiological benefits and evidence suggests that the genetic composition of. Understanding the flexibility of symbiosis between corals capable of housing a mixed infection (Douglas, 1998; LaJeunesse et al, 2003) versus corals with supposedly strict specificity for one symbiont type (Diekmann et al, 2002; Sampayo et al, 2007) will lead to a better understanding of the ability of corals to survive environmental stressors

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