Samuel Dupont

Impact of near-future ocean acidification on echinoderms

As a consequence of increasing atmospheric CO2, the world’s oceans are warming and slowly becoming more acidic (ocean acidification, OA) and profound changes in marine ecosystems are certain. Calcification is one of the primary targets for studies of the impact of CO2-driven climate change in the oceans and one of the key marine groups most likely to be impacted by predicted climate change events are the echinoderms. Echinoderms are a vital component of the marine environment with representatives in virtually every ecosystem, where they are often keystone ecosystem engineers. This paper reviews and analyses what is known about the impact of near-future ocean acidification on echinoderms. A global analysis of the literature reveals that echinoderms are surprisingly robust to OA and that important differences in sensitivity to OA are observed between populations and species. However, this is modulated by parameters such as (1) exposure time with rare longer term experiments revealing negative impacts that are hidden in short or midterm ones; (2) bottlenecks in physiological processes and life-cycle such as stage-specific developmental phenomena that may drive the whole species responses; (3) ecological feedback transforming small scale sub lethal effects into important negative effects on fitness. We hypothesize that populations/species naturally exposed to variable environmental pH conditions may be pre-adapted to future OA highlighting the importance to understand and monitor environmental variations in order to be able to to predict sensitivity to future climate changes. More stress ecology research is needed at the frontier between ecotoxicology and ecology, going beyond standardized tests using model species in order to address multiple water quality factors (e.g. pH, temperature, toxicants) and organism health. However, available data allow us to conclude that near-future OA will have negative impact on echinoderm taxa with likely significant consequences at the ecosystem level.

Aerobic scope fails to explain the detrimental effects on growth resulting from warming and elevated CO2 in Atlantic halibut

As a consequence of increasing atmospheric CO2, the worlds oceans are becoming warmer and more acidic. Whilst the ecological effects of these changes are poorly understood, it has been suggested that fish performance including growth will be reduced mainly as a result of limitations in oxygen transport capacity. Contrary to the predictions given by the oxygen- and capacity-limited thermal tolerance hypothesis, we show that aerobic scope and cardiac performance of Atlantic halibut (Hippoglossus hippoglossus) increase following 14–16 weeks exposure to elevated temperatures and even more so in combination with CO2-acidified seawater. However, the increase does not translate into improved growth, demonstrating that oxygen uptake is not the limiting factor for growth performance at high temperatures. Instead, long-term exposure to CO2-acidified seawater reduces growth at temperatures that are frequently encountered by this species in nature, indicating that elevated atmospheric CO2 levels may have serious implications on fish populations in the future.

Induced cell proliferation in putative haematopoietic tissues of the sea star, Asterias rubens (L.)

SUMMARY The coelomic fluid of the echinoderm Asterias rubens possesses large populations of circulating coelomocytes. This study aimed to expand the knowledge about the haematopoietic sources of these cells. Injection of the immune-stimulating molecules lipopolysaccharide (LPS) and concanavalin A (ConA) resulted in an increase in coelomocytes. To investigate if these molecules induce cell proliferation in putative haematopoietic tissues (HPTs), short-term exposure of the substitute nucleotide 5-bromo-2′-deoxyuridine (BrdU) was conducted. Immunohistochemical analysis, using fluorescein-labelled antibodies to trace BrdU, showed pronounced cell division in the coelomic epithelium and axial organ. In the pyloric caeca, not considered as an HPT, proliferation was not detected. BrdU labelling of monolayers of cells obtained by collagenase treatment of coelomic epithelium, axial organ and Tiedemann body revealed induced cell proliferation in response to both LPS and ConA while proliferation of pyloric caeca and circulating coelomocytes remained sparse. By using confocal microscopy it was observed that both the morphology and functional behaviour of cells released from explants of coelomic epithelium showed high similarity to those of circulating phagocytes. It was concluded that the increased coelomocyte numbers observed in response to LPS and ConA were reflected in an induced cell proliferation in coelomic epithelium, axial organ and Tiedemann body, which reinforces the idea that these organs are HPTs and the sources of coelomocyte renewal.

Growth or differentiation? Adaptive regeneration in the brittlestar Amphiura filiformis.

SUMMARY Amphiura filiformis is a burrowing brittlestar, which extends arms in the water column when suspension feeding. In previous studies, unexpectedly high variability was observed in regeneration rate between individuals even when experiments were performed under identical conditions. The aims of this work were to understand this variability and interpret the observed variability in terms of adaptation to sublethal predation. Our experiments on the dynamics of arm regeneration in A. filiformis revealed that the developmental program during regeneration is well adapted to its burrowing life style. We demonstrate that there is a trade-off between regeneration in length and functional recovery for feeding (differentiation index). The amount of tissue lost (length lost), which represents the quantity of tissue needed to completely regenerate an intact arm with no previous history of regeneration, determines whether the arm will invest more energy in growth and/or in differentiation, which must be a reflection of the ability to differentially regulate developmental programs during regeneration. We show that combining regeneration rate with differentiation index provides an ideal tool for the definition of a standard temporal framework for both field and laboratory studies of regeneration.

Response to ‘How and how not to investigate the oxygen and capacity limitation of thermal tolerance (OCLTT) and aerobic scope – remarks on the article by Gräns et al.’

We appreciate the on-going discussion and healthy evaluation of the hypothesis of oxygen and capacity limitation of thermal tolerance (OCLTT). However, we think it is unfortunate that Portner (Portner, 2104) sees little value in our study ([Grans et al., 2014][1]), which currently represents the

Nerve cells of Xenoturbella bocki (phylum uncertain) and Harrimania kupfferi (enteropneusta) are positively immunoreactive to antibodies raised against echinoderm neuropeptides

The phylogenetic position of Xenoturbella spp. has been uncertain since their discovery in 1949. It has been recently suggested that they could be related to Ambulacraria within Deuterostomia. Ambulacraria is a taxon that has been suggested to consist of Hemichordata and Echinodermata. The hypothesis that X. bocki was related to Ambulacraria as well as the hypothesis of a monophyletic Ambulacraria is primarily based on the analysis of DNA sequence data. We tested both phylogenetic hypotheses using antibodies raised against SALMFamide 1 and 2 (S1, S2), neuropeptides isolated from echinoderms, on X. bocki and the enteropneust Harrimania kupfferi. Both species showed distinct positive immunoreactivity against S1 and S2. This finding supports the Ambulacraria-hypothesis and suggests a close phylogenetic relationship of X. bocki to Ambulacraria. In particular, the presence of immunoreactivity against S2 can be interpreted as a synapomorphy of Enteropneusta, Echinodermata, and Xenoturbella spp

Serotonin and nitric oxide interaction in the control of bioluminescence in northern krill, Meganyctiphanes norvegica (M. Sars)

SUMMARY The role of nitric oxide (NO) in the control of bioluminescence (light production) in the crustacean Meganyctiphanes norvegica (krill) was investigated using pharmacological and immunohistochemical methods. All nitrergic drugs tested failed to induce bioluminescence per se but modulated light production stimulated by 5-hydroxytryptamine (5-HT). NO donors [sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP)] injected in live specimens significantly reduced light production stimulated by 5-HT, whereas inhibition of the enzyme NO synthase (NOS) with l-NAME (NG-nitro-l-arginine methyl ester) resulted in an enhancement of the 5-HT response. The effects of NO do not seem to be mediated via production of cGMP as injections of a cGMP analogue (8-Bromoguanosine 3′,5′-cyclic monophosphate) gave inconclusive effects on the 5-HT-stimulated light response. Inhibition of cGMP production with ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) did not affect the light response. Moreover, a few individuals showed a considerably higher response to 5-HT in April and June compared with specimens collected in the autumn and winter. Furthermore, both NOS-like and 5-HT-like materials were detected by immunohistochemistry inside the light organs. NOS-like immunoreactivity was primarily observed in structures associated with vessels inside the light organs, whereas 5-HT-like material was abundant in nerve fibres throughout the whole light organ. The results suggest that NO has a modulatory role at several levels in the control of light production in M. norvegica and that NO and 5-HT interact in this regulation.

Bridging the regeneration gap: insights from echinoderm models

NATURE REVIEWS | GENETICS www.nature.com/reviews/genetics Bridging the regeneration gap: insights from echinoderm models In their Review1, Sánchez Alvarado and Tsonis present an interesting discussion of “...the model systems that are currently used to dissect the molecular and cellular bases of regeneration, with a focus on in vivo models”. Surprisingly, echinoderms received little attention. Regeneration potential is expressed to a maximum extent in echinoderms2. Larval and adult echinoderms from each of the five classes exhibit natural, rapid regeneration of entire lost parts following predation or other traumatic events (FIG. 1). As adults, echinoderms can regenerate many organs, including limbs, disc, gut, spines and podia and, in some species, regeneration is used for asexual reproduction2,3. Moreover, the process has been studied extensively at molecular, cellular, tissue and ecological levels (for example, REFS 2–7). All the regenerative strategies that are currently described in animals are represented in echinoderms. Arm regeneration in ophiuroids and crinoids is an epimorphic blastemal process, by which new tissues arise from active proliferation of migratory undifferentiated cells (amoebocytes and coelomocytes), which accumulate at the end of the nerve cord as a blastema. In sea stars and sea urchins, morphallaxis is the main regenerative process, involving cells derived from existing tissues by differentiation, transdifferentiation or migration2,3. Importantly, echinoderms are deuterostomes and an average of 70% of echinoderm genes have human homologues8. Therefore, the processes involved in echinoderm regeneration are more likely to be extended to mammals than those observed in other classical models such as Hydra or planarians, which are more distantly related to chordates.