Posts Tagged 'echinoderms'

Sensitivity of sea urchin fertilization to pH varies across a natural pH mosaic

In the coastal ocean, temporal fluctuations in pH vary dramatically across biogeographic ranges. How such spatial differences in pH variability regimes might shape ocean acidification resistance in marine species remains unknown. We assessed the pH sensitivity of the sea urchin Strongylocentrotus purpuratus in the context of ocean pH variability. Using unique male–female pairs, originating from three sites with similar mean pH but different variability and frequency of low pH (pHT ≤ 7.8) exposures, fertilization was tested across a range of pH (pHT 7.61–8.03) and sperm concentrations. High fertilization success was maintained at low pH via a slight right shift in the fertilization function across sperm concentration. This pH effect differed by site. Urchins from the site with the narrowest pH variability regime exhibited the greatest pH sensitivity. At this site, mechanistic fertilization dynamics models support a decrease in sperm–egg interaction rate with decreasing pH. The site differences in pH sensitivity build upon recent evidence of local pH adaptation in S. purpuratus and highlight the need to incorporate environmental variability in the study of global change biology.

Continue reading ‘Sensitivity of sea urchin fertilization to pH varies across a natural pH mosaic’

Spatio-temporal environmental variation mediates geographical differences in phenotypic responses to ocean acidification

Phenotypic plasticity is expected to play a major adaptive role in the response of species to ocean acidification (OA), by providing broader tolerances to changes in pCO2 conditions. However, tolerances and sensitivities to future OA may differ among populations within a species because of their particular environmental context and genetic backgrounds. Here, using the climatic variability hypothesis (CVH), we explored this conceptual framework in populations of the sea urchin Loxechinus albus across natural fluctuating pCO2/pH environments. Although elevated pCO2 affected the morphology, physiology, development and survival of sea urchin larvae, the magnitude of these effects differed among populations. These differences were consistent with the predictions of the CVH showing greater tolerance to OA in populations experiencing greater local variation in seawater pCO2/pH. Considering geographical differences in plasticity, tolerances and sensitivities to increased pCO2 will provide more accurate predictions for species responses to future OA.

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Risk and resilience: variations in magnesium in echinoid skeletal calcite

Echinoids have high-magnesium (Mg) calcite endoskeletons that may be vulnerable to CO2-driven ocean acidification. Amalgamated data for echinoid species from a range of environments and life-history stages allowed characterization of the factors controlling Mg content in their skeletons. Published measurements of Mg in calcite (N = 261), supplemented by new X-ray diffractometry data (N = 382), produced a database including 8 orders, 23 families and 73 species (~7% of the ~1000 known extant species), spanning latitudes 77°S to 72°N, and including 9 skeletal elements or life stages. Mean (± SD) skeletal carbonate mineralogy in the Echinoidea is 7.5 ± 3.23 wt% MgCO3 in calcite (range: 1.5-16.4 wt%, N = 643). Variation in Mg within individuals was small (SD = 0.4-0.9 wt% MgCO3). We found significant differences among skeletal elements: jaw demi-pyramids were the highest in Mg, whereas tests, teeth and spines were intermediate in Mg, but generally higher than larvae. Higher taxa have consistent mineralogical patterns, with orders in particular showing Mg related to first appearance in the fossil record. Latitude was a good proxy for sea-surface temperature (SST), although incorporating SST where available produced a slightly better model. Mg content varied with latitude; higher Mg content in warmer waters may reflect increased metabolic and growth rates. Although the skeletons of some adult urchins may be partially resistant to ocean acidification, larvae and some species may prove to be vulnerable to lowered pH, resulting in ecosystem changes in coastal marine environments.

Continue reading ‘Risk and resilience: variations in magnesium in echinoid skeletal calcite’

pH regulation and excretion in echinoderms

As osmoconformers with low metabolic rates, echinoderms are generally regarded as rather weak acid–base regulators. Accordingly, little attention has been placed on whether echinoderms have evolved mechanisms to regulate ionic homeostasis. In the last century, only few studies examined the acid–base physiology of echinoderms, mostly sea urchins. These studies were conducted in an environmental context as some species inhabit rock pools and experience periodic emersion from their marine environment that can cause a metabolic acidosis. Lately, acid–base physiology in marine invertebrates, especially calcifying species, has received considerable attention as these animals were considered as particularly vulnerable in the context of CO2-induced ocean acidification. A substantial extracellular pH regulatory ability has been hypothesized to determine the degree of sensitivity in marine taxa. The emerging field of ocean acidification research in the last decade also shed new light on the acid–base physiology in echinoderms. Therefore, most of the available literature on echinoderm acid–base physiology describes the effects of CO2-induced seawater acidification on the extracellular acid–base homeostasis of echinoderm adults and larvae. This book chapter will summarize the most recent advances of acid–base physiology and nitrogen excretion in echinoderms in the face of ocean acidification. It will cover adult pH regulation as far as mechanistic data is available and also echinoderm larval physiology in respect to intracellular and extracellular acid–base regulation. Finally, it will make a short excursion into the ocean acidification research field, since most of the conducted research started because of this.

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Transcriptomic responses to seawater acidification among sea urchin populations inhabiting a natural pH mosaic

Increasing awareness of spatial and temporal variation in ocean pH suggests some marine populations may be adapted to local pH regimes and will therefore respond differently to present-day pH variation and to long-term ocean acidification. In the Northeast Pacific Ocean, differences in the strength of coastal upwelling cause latitudinal variation in prevailing pH regimes that are hypothesized to promote local adaptation and unequal pH tolerance among resident populations. In this study, responses to experimental seawater acidification were compared among six populations of purple sea urchins (Strongylocentrotus purpuratus) inhabiting areas that differ in their frequency of low pH exposure and that prior research suggests are locally adapted to seawater pH. Transcriptomic analyses demonstrate urchin populations most frequently exposed to low pH seawater responded to experimental acidification by expressing genes within major ATP producing pathways at greater levels than populations encountering low pH less often. Multiple genes within the tricarboxylic acid cycle, electron transport chain, and fatty acid beta oxidation pathways were up-regulated in urchin populations experiencing low pH conditions most frequently. These same metabolic pathways were significantly over-represented among genes both expressed in a population-specific manner and putatively under selection to enhance low pH tolerance. Collectively, these data suggest natural selection is acting on metabolic gene networks in order to redirect ATP toward acid-base regulatory processes and enhance tolerance of seawater acidification. As a trade-off, marine populations more tolerant of low pH may have less energy to put toward other aspects of fitness and to respond to additional ocean change.

Continue reading ‘Transcriptomic responses to seawater acidification among sea urchin populations inhabiting a natural pH mosaic’

Effects of ocean warming and acidification on the early benthic ontogeny of an ecologically and economically important echinoderm

The sea urchin Loxechinus albus is a benthic shallow water coastal herbivore and an exploited natural resource. This study evaluated the consequences of projected near-future ocean acidification (OA) and warming (OW) for small juveniles of this species. Individuals were exposed for 7 mo to contrasting pCO2 (~400 and 1200 µatm) and temperature (~16 and 19°C) levels. We compared grazing rates during the first 2 mo of rearing. After an additional period (2 to 7 mo), we compared body size change (in terms of diameter, and wet and buoyant weight), self-righting, dislodgement resistance, foraging speeds, test dissolution rate, oxygen consumption and strength of structural integrity. Regardless of the temperature, urchins reared under present-day pCO2 grazed preferentially on algae also reared under present-day pCO2 conditions. However, urchins reared under elevated pCO2 at both temperatures exhibited no grazing preference. Other traits such as growth rate in terms of diameter, vertical foraging speed and tenacity were not affected significantly by pCO2, temperature and the interaction between them. However, growth rate in terms of wet weight, metabolism and dissolution rate of empty urchin tests was significantly affected by temperature and pCO2 but not by the interaction between them. At 16°C, self-righting was faster for individuals reared at elevated pCO2 but no differences were found at 19°C. We conclude that OA and OW may disrupt some early benthic ontogenetic traits of this species and thus have negative ecological and economic consequences. However, most traits will be not threated by the 2 investigated stressors.

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Genomic characterization of the evolutionary potential of the sea urchin Strongylocentrotus droebachiensis facing ocean acidification

Ocean acidification (OA) is increasing due to anthropogenic CO2 emissions, and poses a threat to marine species and communities worldwide. To better project the effects of acidification on organisms’ health and persistence an understanding is needed of (1) the mechanisms underlying developmental and physiological tolerance, and (2) the potential populations have for rapid evolutionary adaptation. This is especially challenging in non-model species where targeted assays of metabolism and stress physiology may not be available or economical for large-scale assessments of genetic constraints. We used mRNA sequencing and a quantitative genetics breeding design to study mechanisms underlying genetic variability and tolerance to decreased seawater pH (-0.4 pH units) in larvae of the sea urchin Strongylocentrotus droebachiensis. We used a gene ontology-based approach to integrate expression profiles into indirect measures of cellular and biochemical traits underlying variation in larval performance (i.e., growth rates). Molecular responses to OA were complex, involving changes to several functions such as growth rates, cell division, metabolism, and immune activities. Surprisingly, the magnitude of pH effects on molecular traits tended to be small relative to variation attributable to segregating functional genetic variation in this species. We discuss how the application of transcriptomics and quantitative genetics approaches across diverse species can enrich our understanding of the biological impacts of climate change.

Continue reading ‘Genomic characterization of the evolutionary potential of the sea urchin Strongylocentrotus droebachiensis facing ocean acidification’

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Ocean acidification in the IPCC AR5 WG II

OUP book