Kenkel, C. | bioRxiv Science

bioRxiv2018

Transgenerational inheritance of shuffled symbiont communities in the coral Montipora digitata

Adult organisms may \"prime\" their offspring for environmental change through a number of genetic and non-genetic mechanisms, termed parental effects. Some coral species can alter their thermal tolerance by shuffling the proportions of Symbiodinium types within their endosymbiotic communities, but it is unclear if this plasticity can be transferred to offspring in corals that have maternal symbiont transmission. We evaluated symbiont community composition in tagged colonies of Montipora digitata from Orpheus Island, Australia, over two successive annual spawning seasons, the second of which overlapped with the 2016 mass coral bleaching event on the Great Barrier Reef. We applied amplicon sequencing of the ITS2 locus to samples of four families (parent colonies and 10-12 eggs per family) to characterize their potential for symbiont shuffling and to determine if shuffled abundances were preserved in gametes. Symbiont cell densities and photochemical efficiencies of the symbionts photosystem II differed significantly among adults in 2016, suggesting differential responses to increased temperatures. Although abundances of the dominant symbiont haplotype, a representative of clade C15, did not differ among families or over time, low-abundance (\"background\") ITS2 types differed more among years (2015 vs. 2016) than between life stages (parent vs. offspring). Results indicate that background symbiont shuffling can occur in a canonically stable symbiosis, and that such plastic changes to the symbiont community are heritable. To our knowledge, this is the first evidence that shuffled Symbiodinium communities can be inherited by early life-history stages and supports the hypothesis that plastic changes in microbial communities may serve as a mechanism of rapid coral acclimation to changing environmental conditions.

microbiology↗

bioRxiv2017

Functional genomic analysis of corals from natural CO2-seeps reveal core molecular responses involved in acclimatization to ocean acidification

Little is known about the potential for acclimatization or adaptation of corals to ocean acidification and even less about the molecular mechanisms underpinning these processes. Here we examine global gene expression patterns in corals and their intracellular algal symbionts from two replicate population pairs in Papua New Guinea that have undergone long-term acclimatization to natural variation in pCO2. In the coral host, only 61 genes were differentially expressed in response to pCO2 environment, but the pattern of change was highly consistent between replicate populations, likely reflecting the core expression homeostasis response to ocean acidification. Functional annotations highlight lipid metabolism and a change in the stress response capacity of corals as a key part of this process. Specifically, constitutive downregulation of molecular chaperones was observed, which may impact response to combined climate-change related stressors. Elevated CO2 has been hypothesized to benefit photosynthetic organisms but expression changes of in hospite Symbiodinium in response to acidification were greater and less consistent among reef populations. This population-specific response suggests hosts may need to adapt not only to an acidified environment, but also to changes in their Symbiodinium populations that may not be consistent among environments. This process adds another challenging dimension to the physiological process of coping with climate change.

genomics↗