Posts Tagged 'adaptation'

Using stable isotope analysis to determine the effects of ocean acidification and warming on trophic interactions in a maerl bed community

Ocean acidification and warming are likely to affect the structure and functioning of marine benthic communities. This study experimentally examined the effects of ocean acidification and warming on trophic interactions within a maerl bed community by using stable carbon and nitrogen isotope analysis. Two three‐month experiments were conducted in winter and summer seasons with four different combinations of pCO2 (ambient and elevated pCO2) and temperature (ambient and +3°C). Experimental assemblages were created in tanks held in the laboratory and were composed of calcareous (Lithothamnion corallioides) and fleshy algae (Rhodymenia ardissonei, Solieria chordalis, and Ulva sp.), gastropods (Gibbula magus and Jujubinus exasperatus), and sea urchins (Psammechinus miliaris). Our results showed higher seaweed availability for grazers in summer than winter. Therefore, grazers were able to adapt their diet seasonally. Increased pCO2 and temperature did not modify the trophic structure in winter, while shifts in the contribution of seaweed were found in summer. Combined acidification and warming increased the contribution of biofilm in gastropods diet in summer conditions. Psammechinus miliaris mostly consumed L. corallioides under ambient conditions, while the alga S. chordalis became the dominant food source under high pCO2 in summer. Predicted changes in pCO2 and temperature had complex effects on assemblage trophic structure. Direct effects of acidification and warming on seaweed metabolism may modify their abundance and biomass, affecting their availability for grazers. Climate change may also modify seaweeds’ nutritive value and their palatability for grazers. The grazers we investigated were able to change their diet in response to changes in algal assemblages, an advantage given that warming and acidification alter the composition of algal communities.

Continue reading ‘Using stable isotope analysis to determine the effects of ocean acidification and warming on trophic interactions in a maerl bed community’

The dynamics of rapid adaptation to ocean acidification in the Mediterranean mussel

Global climate change has intensified the need to assess if, and how, natural populations adapt to abrupt shifts in their environment. The tempo of adaptation in natural systems has been the subject of theoretical and empirical investigation for decades. Recent evidence from genome-wide sequencing approaches has indicated that evolution may proceed at a pace previously deemed theoretically impossible. Such studies, however, have largely observed these processes in the context of model systems, and the extent to which these patterns will hold in ecologically-relevant species subject to the dramatic environmental perturbations associated with global change is unclear. Accordingly, this thesis investigates the capacity for, and mechanisms by which, the Mediterranean mussel, Mytilus galloprovincialis, may rapidly adapt to expected declines in global seawater pH. Reductions in seawater pH constitute a global change stressor impacting marine species globally, with anticipated impacts altering the structure and services of numerous ecological communities. Due to its experimental tractability, as well as its ecological and economic importance, M. galloprovincialis has become a model-species for exploring the physiological and morphological impacts of low pH seawater. Yet, the extent to which evolution may offset observed phenotypic consequences is unknown. To address this knowledge gap the present thesis explores the following: (i) the processes shaping and maintaining variation in low pH tolerance across the species’ native range; (ii) the extent to which the standing variation within natural populations of M. galloprovincialis can facilitate the magnitude of evolution necessary for persistence under global change conditions; and (iii) the molecular basis of low pH adaptation in marine bivalves and beyond. My results elucidate how contemporary gradients in pH variability shape distinct patterns of low pH plasticity across natural populations. Furthermore, my findings demonstrate that the standing variation within natural populations is sufficient for rapid adaptation to even extreme reductions in seawater pH. Lastly, I provide mechanistic links between the molecular mechanisms influenced by shifts in the external seawater pH environment and fitness-related abnormalities observed in M. galloprovincialis, a finding that likely explains observed low pH sensitivity across a broad range of marine metazoans. This thesis thus lends to our conceptual understanding regarding the dynamics of rapid adaptation in natural populations, while explicitly informing the management of an ecologically and economically important marine species as global change progresses.

Continue reading ‘The dynamics of rapid adaptation to ocean acidification in the Mediterranean mussel’

Acclimatization drives differences in reef-building coral calcification rates

Coral reefs are susceptible to climate change, anthropogenic influence, and environmental stressors. However, corals in Kāneʻohe Bay, Hawaiʻi have repeatedly shown resilience and acclimatization to anthropogenically-induced rising temperatures and increased frequencies of bleaching events. Variations in coral and algae cover at two sites—just 600 m apart—at Malaukaʻa fringing reef suggest genetic or environmental differences in coral resilience between sites. A reciprocal transplant experiment was conducted to determine if calcification (linear extension and dry skeletal weight) for dominant reef-building species, Montipora capitata and Porites compressa, varied between the two sites and whether or not parent colony or environmental factors were responsible for the differences. Despite the two sites representing distinct environmental conditions with significant differences between temperature, salinity, and aragonite saturation, M. capitata growth rates remained the same between sites and treatments. However, dry skeletal weight increases in P. compressa were significantly different between sites, but not across treatments, with linear mixed effects model results suggesting heterogeneity driven by environmental differences between sites and the parent colonies. These results provide evidence of resilience and acclimatization for M. capitata and P. compressa. Variability of resilience may be driven by local adaptations at a small, reef-level scale for P. compressa in Kāneʻohe Bay.

Continue reading ‘Acclimatization drives differences in reef-building coral calcification rates’

Ervilia castanea (Mollusca, Bivalvia) populations adversely affected at CO2 seeps in the North Atlantic

Highlights

  • The bivalve Ervilia castanea was studied at volcanic CO2 seeps and reference sites.
  • Abundance, size and net-calcification were inversely related to CO2 levels.
  • Large individuals were scarce or absent at high CO2 sites.
  • Recruitment of this bivalve was highest at the CO2 seeps.
  • Abundance and size of E. castanea were positively correlated with Chl-a in sediment.

Abstract

Sites with naturally high CO2 conditions provide unique opportunities to forecast the vulnerability of coastal ecosystems to ocean acidification, by studying the biological responses and potential adaptations to this increased environmental variability. In this study, we investigated the bivalve Ervilia castanea in coastal sandy sediments at reference sites and at volcanic CO2 seeps off the Azores, where the pH of bottom waters ranged from average oceanic levels of 8.2, along gradients, down to 6.81, in carbonated seawater at the seeps. The bivalve population structure changed markedly at the seeps. Large individuals became less abundant as seawater CO2 levels rose and were completely absent from the most acidified sites. In contrast, small bivalves were most abundant at the CO2 seeps. We propose that larvae can settle and initially live in high abundances under elevated CO2 levels, but that high rates of post-settlement dispersal and/or mortality occur. Ervilia castanea were susceptible to elevated CO2 levels and these effects were consistently associated with lower food supplies. This raises concerns about the effects of ocean acidification on the brood stock of this species and other bivalve molluscs with similar life history traits.

Continue reading ‘Ervilia castanea (Mollusca, Bivalvia) populations adversely affected at CO2 seeps in the North Atlantic’

Environmentally-induced parental or developmental conditioning influences coral offspring ecological performance

The persistence of reef building corals is threatened by human-induced environmental change. Maintaining coral reefs into the future requires not only the survival of adults, but also the influx of recruits to promote genetic diversity and retain cover following adult mortality. Few studies examine the linkages among multiple life stages of corals, despite a growing knowledge of carryover effects in other systems. We provide a novel test of coral parental conditioning to ocean acidification (OA) and tracking of offspring for 6 months post-release to better understand parental or developmental priming impacts on the processes of offspring recruitment and growth. Coral planulation was tracked for 3 months following adult exposure to high pCO2 and offspring from the second month were reciprocally exposed to ambient and high pCO2 for an additional 6 months. Offspring of parents exposed to high pCO2 had greater settlement and survivorship immediately following release, retained survivorship benefits during 1 and 6 months of continued exposure, and further displayed growth benefits to at least 1 month post release. Enhanced performance of offspring from parents exposed to high conditions was maintained despite the survivorship in both treatments declining in continued exposure to OA. Conditioning of the adults while they brood their larvae, or developmental acclimation of the larvae inside the adult polyps, may provide a form of hormetic conditioning, or environmental priming that elicits stimulatory effects. Defining mechanisms of positive acclimatization, with potential implications for carry over effects, cross-generational plasticity, and multi-generational plasticity, is critical to better understanding ecological and evolutionary dynamics of corals under regimes of increasing environmental disturbance. Considering environmentally-induced parental or developmental legacies in ecological and evolutionary projections may better account for coral reef response to the chronic stress regimes characteristic of climate change.

Continue reading ‘Environmentally-induced parental or developmental conditioning influences coral offspring ecological performance’

Standing genetic variation fuels rapid adaptation to ocean acidification

Global climate change has intensified the need to assess the capacity for natural populations to adapt to abrupt shifts in the environment. Reductions in seawater pH constitute a conspicuous global change stressor that is affecting marine ecosystems globally. Here, we quantify the phenotypic and genetic modifications associated with rapid adaptation to reduced seawater pH in the Mediterranean mussel, Mytilus galloprovincialis. We reared a genetically diverse larval population in two pH treatments (pHT 8.1 and 7.4) and tracked changes in the shell-size distribution and genetic variation through settlement. Additionally, we identified differences in the signatures of selection on shell growth in each pH environment. Both phenotypic and genetic data show that standing variation can facilitate adaptation to declines in seawater pH. This work provides insight into the processes underpinning rapid evolution, and demonstrates the importance of maintaining variation within natural populations to bolster species’ adaptive capacity as global change progresses.

Continue reading ‘Standing genetic variation fuels rapid adaptation to ocean acidification’

Selectively bred oysters can alter their biomineralization pathways, promoting resilience to environmental acidification

Commercial shellfish aquaculture is vulnerable to the impacts of ocean acidification driven by increasing carbon dioxide (CO2) absorption by the ocean as well as to coastal acidification driven by land run off and rising sea level. These drivers of environmental acidification have deleterious effects on biomineralization. We investigated shell biomineralization of selectively bred and wild‐type families of the Sydney rock oyster Saccostrea glomerata in a study of oysters being farmed in estuaries at aquaculture leases differing in environmental acidification. The contrasting estuarine pH regimes enabled us to determine the mechanisms of shell growth and the vulnerability of this species to contemporary environmental acidification. Determination of the source of carbon, the mechanism of carbon uptake and use of carbon in biomineral formation are key to understanding the vulnerability of shellfish aquaculture to contemporary and future environmental acidification. We, therefore, characterized the crystallography and carbon uptake in the shells of S. glomerata, resident in habitats subjected to coastal acidification, using high‐resolution electron backscatter diffraction and carbon isotope analyses (as δ13C). We show that oyster families selectively bred for fast growth and families selected for disease resistance can alter their mechanisms of calcite crystal biomineralization, promoting resilience to acidification. The responses of S. glomerata to acidification in their estuarine habitat provide key insights into mechanisms of mollusc shell growth under future climate change conditions. Importantly, we show that selective breeding in oysters is likely to be an important global mitigation strategy for sustainable shellfish aquaculture to withstand future climate‐driven change to habitat acidification.

Continue reading ‘Selectively bred oysters can alter their biomineralization pathways, promoting resilience to environmental acidification’

Present and future adaptation of marine species assemblages: DNA-based insights into climate change from studies of physiology, genomics, and evolution

Marine species live in a dynamic physical and biological environment that demands frequent physiological adjustment and can result in strong natural selection or shifts in species ranges. We illustrate the patterns and processes of adaptation to environmental change with genetic-based examples that range from a focus on single proteins to whole genomes to whole communities. This work shows how single amino acid changes adapt proteins to function at different temperatures. It shows how acidification impacts expression of proteins in energy pathways in adults and exerts natural selection on many genes in larvae. Whole genome surveys along coastlines are now possible, and they reveal unexpected patterns of genetic differentiation even in highly dispersive species. Genetic surveys of over 70 species along the North American west coast show high levels of genetic diversity and genetic structure clustered at headlands and capes known to mark species range boundaries. Finally, new surveys of DNA variation in whole communities show promise for rapid monitoring that can augment and complement traditional dive surveys. Overall, dynamics in the physical environment have a strong effect on organism physiology, which results in diverse patterns of population growth and persistence, as well as of species range and evolutionary capacity. The high level of adaptive genetic variation shown here suggests an ability for marine populations to adapt in the face of climate change, but many questions remain about how fast, complete, and effective this evolution will be.

Continue reading ‘Present and future adaptation of marine species assemblages: DNA-based insights into climate change from studies of physiology, genomics, and evolution’

Rare genetic variation and balanced polymorphisms are important for survival in global change conditions

Standing genetic variation is important for population persistence in extreme environmental conditions. While some species may have the capacity to adapt to predicted average future global change conditions, the ability to survive extreme events is largely unknown. We used single-generation selection experiments on hundreds of thousands of Strongylocentrotus purpuratus sea urchin larvae generated from wild-caught adults to identify adaptive genetic variation responsive to moderate (pH 8.0) and extreme (pH 7.5) low-pH conditions. Sequencing genomic DNA from pools of larvae, we identified consistent changes in allele frequencies across replicate cultures for each pH condition and observed increased linkage disequilibrium around selected loci, revealing selection on recombined standing genetic variation. We found that loci responding uniquely to either selection regime were at low starting allele frequencies while variants that responded to both pH conditions (11.6% of selected variants) started at high frequencies. Loci under selection performed functions related to energetics, pH tolerance, cell growth and actin/cytoskeleton dynamics. These results highlight that persistence in future conditions will require two classes of genetic variation: common, pH-responsive variants maintained by balancing selection in a heterogeneous environment, and rare variants, particularly for extreme conditions, that must be maintained by large population sizes.

Continue reading ‘Rare genetic variation and balanced polymorphisms are important for survival in global change conditions’

pH variability exacerbates effects of ocean acidification on a Caribbean crustose coralline alga

Crustose coralline algae (CCA) are among the most sensitive marine taxa to the pH changes predicted with ocean acidification (OA). However, many CCA exist in habitats where diel cycles in pH can surpass near-future OA projections. The prevailing theory that natural variability increases the tolerance of calcifiers to OA has not been widely tested with tropical CCA. Here, we assess the response of the reef-building species Lithophyllum congestum to stable and variable pH treatments, including an ambient control (amb/stable). The amb/variable treatment simulated an ambient diel cycle in pH (7.65–7.95), OA/stable simulated constant low pH reflecting worst-case year 2100 predictions (7.7), and OA/variable combined diel cycling with lower mean pH (7.45–7.75). We monitored the effects of pH on total calcification rate and photophysiology (maximum quantum yield) over 16 weeks. To assess the potential for acclimatization, we also quantified calcification rates during the first (0–8 weeks), and second (8–16 weeks) halves of the experiment. Calcification rates were lower in all pH treatments relative to ambient controls and photophysiology was unaffected. At the end of the 16-week experiment, total calcification rates were similarly low in the amb/variable and OA/stable treatment (27–29%), whereas rates declined by double in the OA/variable treatment (60%). When comparing the first and second halves of the experiment, there was no acclimatization in stable treatments as calcification rates remained unchanged in both the amb/stable and OA/stable treatments. In contrast, calcification rates deteriorated between periods in the variable treatments: from a 16–47% reduction in the amb/variable treatment to a 49–79% reduction in the OA/variable treatment, relative to controls. Our findings provide compelling evidence that pH variability can heighten CCA sensitivity to reductions in pH. Moreover, the decline in calcification rate over time directly contrasts prevailing theory that variability inherently increases organismal tolerances to low pH, and suggests that mechanisms of tolerance may become limited with increasing time of exposure. The significant role of diel pH cycling in CCA responses to OA indicates that organisms in habitats with diel variability could respond more severely to rapid changes in ocean pH associated with OA than predicted by experiments conducted under static conditions.

Continue reading ‘pH variability exacerbates effects of ocean acidification on a Caribbean crustose coralline alga’


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Ocean acidification in the IPCC AR5 WG II

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