Phylogenetic Analysis of Algal Symbionts Associated with Four North American Amphibian Egg Masses

Egg masses of the yellow-spotted salamander Ambystoma maculatum form an association with the green alga “Oophila amblystomatis” (Lambert ex Wille), which, in addition to growing within individual egg capsules, has recently been reported to invade embryonic tissues and cells. The binomial O. amblystomatis refers to the algae that occur in A. maculatum egg capsules, but it is unknown whether this population of symbionts constitutes one or several different algal taxa. Moreover, it is unknown whether egg masses across the geographic range of A. maculatum, or other amphibians, associate with one or multiple algal taxa. To address these questions, we conducted a phylogeographic study of algae sampled from egg capsules of A. maculatum, its allopatric congener A. gracile, and two frogs: Lithobates sylvatica and L. aurora. All of these North American amphibians form associations with algae in their egg capsules. We sampled algae from egg capsules of these four amphibians from localities across North America, established representative algal cultures, and amplified and sequenced a region of 18S rDNA for phylogenetic analysis. Our combined analysis shows that symbiotic algae found in egg masses of four North American amphibians are closely related to each other, and form a well-supported clade that also contains three strains of free-living chlamydomonads. We designate this group as the ‘Oophila’ clade, within which the symbiotic algae are further divided into four distinct subclades. Phylogenies of the host amphibians and their algal symbionts are only partially congruent, suggesting that host-switching and co-speciation both play roles in their associations. We also established conditions for isolating and rearing algal symbionts from amphibian egg capsules, which should facilitate further study of these egg mass specialist algae

Gene expression of endangered coral (Orbicella spp.) in flower garden banks National Marine Sanctuary after Hurricane Harvey

About 190 km south of the Texas–Louisiana border, the East and West Flower Garden Banks (FGB) have maintained > 50% coral cover with infrequent and minor incidents of disease or bleaching since monitoring began in the 1970s. However, a mortality event, affecting 5.6 ha (2.6% of the area) of the East FGB, occurred in late July 2016 and coincided with storm-generated freshwater runoff extending offshore and over the reef system. To capture the immediate effects of storm-driven freshwater runoff on coral and symbiont physiology, we leveraged the heavy rainfall associated with Hurricane Harvey in late August 2017 by sampling FGB corals at two time points: September 2017, when surface water salinity was reduced (∼34 ppt); and 1 month later when salinity had returned to typical levels (∼36 ppt in October 2017). Tissue samples (N = 47) collected midday were immediately preserved for gene expression profiling from two congeneric coral species (Orbicella faveolata and Orbicella franksi) from the East and West FGB to determine the physiological consequences of storm-derived runoff. In the coral, differences between host species and sampling time points accounted for the majority of differentially expressed genes. Gene ontology enrichment for genes differentially expressed immediately after Hurricane Harvey indicated increases in cellular oxidative stress responses. Although tissue loss was not observed on FGB reefs following Hurricane Harvey, our results suggest that poor water quality following this storm caused FGB corals to experience sub-lethal stress. We also found dramatic expression differences across sampling time points in the coral’s algal symbiont, Breviolum minutum. Some of these differentially expressed genes may be involved in the symbionts’ response to changing environments, including a group of differentially expressed post-transcriptional RNA modification genes. In this study, we cannot disentangle the effects of reduced salinity from the collection time point, so these expression patterns could also be related to seasonality. These findings highlight the urgent need for continued monitoring of these reef systems to establish a baseline for gene expression of healthy corals in the FGB system across seasons, as well as the need for integrated solutions to manage stormwater runoff in the Gulf of Mexico.https://www.frontiersin.org/articles/10.3389/fmars.2019.00672/fullPublished versionPublished versio

Ancient DNA from coral-hosted Symbiodinium reveal a static mutualism over the last 172 years.

Ancient DNA (aDNA) provides powerful evidence for detecting the genetic basis for adaptation to environmental change in many taxa. Among the greatest of changes in our biosphere within the last century is rapid anthropogenic ocean warming. This phenomenon threatens corals with extinction, evidenced by the increasing observation of widespread mortality following mass bleaching events. There is some evidence and conjecture that coral-dinoflagellate symbioses change partnerships in response to changing external conditions over ecological and evolutionary timescales. Until now, we have been unable to ascertain the genetic identity of Symbiodinium hosted by corals prior to the rapid global change of the last century. Here, we show that Symbiodinium cells recovered from dry, century old specimens of 6 host species of octocorals contain sufficient DNA for amplification of the ITS2 subregion of the nuclear ribosomal DNA, commonly used for genotyping within this genus. Through comparisons with modern specimens sampled from similar locales we show that symbiotic associations among several species have been static over the last century, thereby suggesting that adaptive shifts to novel symbiont types is not common among these gorgonians, and perhaps, symbiotic corals in general

Varied effects of algal symbionts on transcription factor NF-κB in a sea anemone and a coral: possible roles in symbiosis and thermotolerance

Many cnidarians, including the reef-building corals, undergo symbiotic mutualisms with photosynthetic dinoflagellate algae of the family Symbiodiniaceae. These partnerships are sensitive to temperature extremes, which cause symbiont loss and increased coral mortality. Previous studies have implicated host immunity and specifically immunity transcription factor NF-κB as having a role in the maintenance of the cnidarian-algal symbiosis. Here we have further investigated a possible role for NF-κB in establishment and loss of symbiosis in various strains of the anemone Exaiptasia (Aiptasia) and in the coral Pocillopora damicornis. Our results show that NF-κB expression is reduced in Aiptasia larvae and adults that host certain algae strains. Treatment of Aiptasia larvae with a known symbiosis-promoting cytokine, transforming growth factor β, also led to decreased NF-κB expression. We also show that aposymbiotic Aiptasia (with high NF-κB expression) have increased survival following infection with the pathogenic bacterium Serratia marcescens as compared to symbiotic Aiptasia (low NF-κB expression). Furthermore, a P. damicornis coral colony hosting Durusdinium spp. (formerly clade D) symbionts had higher basal NF-κB expression and decreased heat-induced bleaching as compared to two individuals hosting Cladocopium spp. (formerly clade C) symbionts. Lastly, genome-wide gene expression profiling and genomic promoter analysis identified putative NF-κB target genes that may be involved in thermal bleaching, symbiont maintenance, and/or immune protection in P. damicornis. Our results provide further support for the hypothesis that modulation of NF-κB and immunity plays a role in some, but perhaps not all, cnidarian-Symbiodiniaceae partnerships as well as in resistance to pathogens and bleaching.Accepted manuscrip

Algae Living in Salamanders, Friend or Foe?

Roughly speaking, our bodies use energy from the sun, but we can\u27t use sunlight directly. Instead, plants and algae collect sunlight and store it as chemical energy through the process of photosynthesis. We can access that fuel directly when we eat plants, or indirectly when we eat other animals that eat plants. However, in some invertebrate animals (those without a backbone) the relationships to algae are more intimate. Tiny single-celled algal symbionts can actually live inside the cells of living corals and small animals like hydra that live in water. The algae live in a safe environment inside animal cells and are provided with building block materials to function. They use sunlight to convert the building block materials into larger molecules to store energy and build cellular structures. At the same time some of that stored solar energy is directly transferred to the host animal, allowing it to live in otherwise nutrient poor environments. Thus the algae and their hosts depend on one another to live and thrive. These mutually beneficial relationships are called photosymbioses. [excerpt

Screening by coral green fluorescent protein (GFP)-like chromoproteins supports a role in photoprotection of zooxanthellae

Green fluorescent protein (GFP)-like pigments are responsible for the vivid colouration of many reef-building corals and have been proposed to act as photoprotectants. Their role remains controversial because the functional mechanism has not been elucidated. We provide direct evidence to support a photoprotective role of the non-fluorescent chromoproteins (CPs) that form a biochemically and photophysically distinct group of GFP-like proteins. Based on observations of Acropora nobilis from the Great Barrier Reef, we explored the photoprotective role of CPs by analysing five coral species under controlled conditions. In vitro and in hospite analyses of chlorophyll excitation demonstrate that screening by CPs leads to a reduction in chlorophyll excitation corresponding to the spectral properties of the specific CPs present in the coral tissues. Between 562 and 586 nm, the CPs maximal absorption range, there was an up to 50 % reduction of chlorophyll excitation. The screening was consistent for established and regenerating tissue and amongst symbiont clades A, C and D. Moreover, among two differently pigmented morphs of Acropora valida grown under identical light conditions and hosting subclade type C3 symbionts, high CP expression correlated with reduced photodamage under acute light stress

Nutrient availability and metabolism Affect the stability of coral–Symbiodiniaceae symbioses

Coral reefs rely upon the highly optimized coral–Symbiodiniaceae symbiosis, making them sensitive to environmental change and susceptible to anthropogenic stress. Coral bleaching is predominantly attributed to photo-oxidative stress, yet nutrient availability and metabolism underpin the stability of symbioses. Recent studies link symbiont proliferation under nutrient enrichment to bleaching; however, the interactions between nutrients and symbiotic stability are nuanced. Here, we demonstrate how bleaching is regulated by the forms and ratios of available nutrients and their impacts on autotrophic carbon metabolism, rather than algal symbiont growth. By extension, historical nutrient conditions mediate host–symbiont compatibility and bleaching tolerance over proximate and evolutionary timescales. Renewed investigations into the coral nutrient metabolism will be required to truly elucidate the cellular mechanisms leading to coral bleaching

Improving the Heat Tolerance of Vulnerable Corals through their Algal Symbionts

Tropical coral reefs are one of the most impressive and diverse ecosystems on the face of the earth. Found in warm, tropical waters around the globe, these reefs are major supporters of the immense biodiversity of the area. The health of coral reefs is highly influential on the overall health of the entire ecosystem. In recent years, intensifying climate change has resulted in an accelerated rise in seawater temperatures and the frequency and severity of coral bleaching. Coral bleaching occurs in response to harsh environmental conditions that cause corals to enter a period of extreme stress. During this time, corals expel their algal symbionts – ending the symbiotic relationship with the zooxanthellae. Corals are especially vulnerable to permanent damage in this bleached state. As major supporters of the success of marine ecosystems and coastal communities alike, it is imperative that ecosystems are rehabilitated and protected from future harm. Coral polyps have long generation times, making them unable to keep up with the rate at which the climate is currently changing. Without human intervention, coral reefs will not survive the next century. Studies have indicated that the introduction of thermotolerant strains of Symbiodinium, the algal symbiont associated with corals, improves the heat tolerance of corals. This review examines the use of thermotolerant algal symbionts as a potential long-term rehabilitation and mitigation strategy. The thermal tolerance of zooxanthellae has been shown to transfer to coral species, making these species of corals more resilient to the increasing ocean temperatures and harsher conditions associated with climate change. Experimentally implanting thermotolerant strains of Symbiodinium may serve as a viable solution to the problem of corals’ slow adaptation times. Additional mitigation strategies may be required during the conservation of coral reefs to ensure the overall health of the reef for years to come. Climate change has shown no indication of slowing down in future years. It is critical that mitigation efforts are implemented immediately to identify feasible, long-term solutions to assist vulnerable corals in beating the heat

Bleaching in foraminifera with algal symbionts: implications for reef monitoring and risk asessment

Reef-dwelling larger foraminifers share key characteristics with reefbuilding corals: they are prolific producers of calcium carbonate, they are physiologically dependent upon algal endosymbionts, and representatives of both groups have suffered bleaching episodes in recent decades. Since 1991, bleaching has been observed in populations of Amphistegina in all subtropical oceans, with peak bleaching in 1992 and secondary peaks in 1998 and 2005. Amphistegina populations exhibiting chronic, intermediate-intensity bleaching characteristically show anomalously high incidences of shell breakage, shell deformities, evidence of predation, and microbial infestation. Asexual reproduction is profoundly affected; broods from partly bleached parents typically have fewer individuals, many of which are anomalous in shape and size. Key differences between bleaching in corals and Amphistegina are that corals typically bleach by expelling their symbionts, while Amphistegina bleach when damaged symbionts are digested, and that mass coral bleaching requires high light but correlates most consistently with elevated temperatures, while bleaching in Amphistegina is induced by light. Amphistegina are particularly sensitive to the shorter (300-490 nm) wavelengths of solar radiation, which have increased in intensity relative to longer visible wavelengths (>;490-700 nm) in clear reef waters over the past 30 years as a consequence of stratospheric ozone depletion. Abundances and visual assessments of Amphistegina populations can be used as a low-cost risk-assessment tool. These protists are sensitive to environmental conditions over days to weeks, and provide a method to quickly distinguish between water quality (local) and photo-oxidative (global) stresses. Risk assessments based on the combined use of in situ measurements and low-cost indicators can provide resource managers with essential information to decide when more costly chemical or molecular procedures are needed to determine local sources of stress

Identifying algal symbionts in lichen symbioses

Lichens are a ubiquitous terrestrial symbiosis of fungi with photoautotrophic microorganisms. The identification of the hosted photoautotrophs is notoriously difficult. Molecular data to clarify evolutionary relationships on the involved algal and cyanobacterial lineages are accumulating, but the assignment to species is challenging for various reasons. One of the challenges is the limited knowledge on the alpha diversity of photoautotrophs. New lineages are being discovered with increasing amounts of sequencing. Identification tools could incorporate these aspects, by routinely updating the assignment process. We propose the establishment of a classification tool using algal sequence data from public databases