Comparative Genomics of Color Morphs In the Coral Montastraea cavernosa

Jessica K Jarett,Michael P Lesser,Matthew D Macmanes,M Sabrina Pankey,Kathleen M Morrow

doi:10.1038/s41598-017-16371-9

Jessica K Jarett, Michael P Lesser + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-16371-9

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Abstract

Montastraea cavernosa is a common coral in the Caribbean basin found in several color morphs. To investigate the causes for brown and orange morphs we undertook a genomics approach on corals collected at the same time and depth in the Bahamas. The coral holobiont includes the host, symbiotic dinoflagellates (Symbiodinium spp.), and a diverse microbiome. While the coral host showed significant genetic differentiation between color morphs both the composition of the Symbiodinium spp. communities and the prokaryotic communities did not. Both targeted and global gene expression differences in the transcriptome of the host show no difference in fluorescent proteins while the metatranscriptome of the microbiome shows that pigments such as phycoerythrin and orange carotenoid protein of cyanobacterial origin are significantly greater in orange morphs, which is also consistent with the significantly greater number of cyanobacteria quantified by 16S rRNA reads and flow cytometry. The microbiome of orange color morphs expressed significantly more nitrogenase (nifH) transcripts consistent with their known ability to fix nitrogen. Both coral and Symbiodinium spp. transcriptomes from orange morphs had significantly increased expression of genes related to immune response and apoptosis, which may potentially be involved in maintaining and regulating the unique symbiont population in orange morphs.

Highlights

The worldwide decline of coral reefs has been attributed to a variety of natural and anthropogenic stressors[1,2,3] whose effects appear to be long-term, and potentially irreversible[3,4,5]
Rarefaction curves of observed operational taxonomic units (OTUs) approached an asymptote for all coral samples, which were rarefied at a common depth of 2,200 reads for statistical analysis
Seawater samples were dominated by the phyla Proteobacteria, Cyanobacteria, Bacteroidetes, and Actinobacteria, while communities in coral samples were more diverse than seawater samples and exhibited more variability between replicate samples of the same color morph, especially the brown morph (Fig. 1A)

Summary

Introduction

The worldwide decline of coral reefs has been attributed to a variety of natural and anthropogenic stressors[1,2,3] whose effects appear to be long-term, and potentially irreversible[3,4,5]. In the Caribbean, the great star coral Montastraea cavernosa Linnaeus is abundant on Caribbean and Eastern Atlantic coral reefs and has an extremely wide depth range from shallow through mesophotic depths (3–100 m)[15] It is commonly found in three color morphs, cyan, orange and brown[16,17] and based on multiple lines of molecular and biophysical evidence, the orange morphs contain significant populations of symbiotic cyanobacteria expressing phycoerythrin in their microbiome[18,19,20]. For M. cavernosa the orange and brown color morphs occur side by side in the same environment, which creates a natural comparative experiment to investigate multiple aspects of the biology of host and microbiome in this species of coral. We ask two specific questions: (1) do the molecular and microbial profiles of the two primary color morphs of M. cavernosa differ as it relates to the expression of genes potentially responsible for their color, and (2) are there differences in global gene expression patterns for the coral host, symbiotic dinoflagellates (i.e., Symbiodinium spp.) and microbiome of the holobiont between the color morphs?

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