Published papers

Under phosphorus (P) deficiency, Lupinus albus develops cluster roots that allow efficient P acquisition, while L. angustifolius without cluster roots also grows well. Both species are non‐mycorrhizal. We quantitatively examined the carbon budgets to investigate the different strategies of these species. Biomass allocation, respiratory rates, protein amounts and carboxylate exudation rates were examined in hydroponically‐grown plants treated with low (1 μM; P1) or high (100 μM; P100) P. At P1, L. albus formed cluster roots, and L. angustifolius increased biomass allocation to the roots. The respiratory rates of the roots were faster in L. albus than in L. angustifolius. The protein amounts of the non‐phosphorylating alternative oxidase and uncoupling protein were greater in the cluster roots of L. albus at P1 than in the roots at P100, but similar between the P treatments in L. angustifolius roots. At P1, L. albus exuded carboxylates at a faster rate than L. angustifolius. The carbon budgets at P1 were surprisingly similar between the two species, which is attributed to the contrasting root growth and development strategies. L. albus developed cluster roots with rapid respiratory and carboxylate exudation rates, while L. angustifolius developed a larger root system with slow respiratory and exudation rates. Under phosphorus deficiency, Lupinus albus developed cluster roots with fast respiratory and carboxylate exudation rates, while L. angustifolius developed a large root system with slow respiratory and exudation rates. These contrasting traits resulted in similar whole‐plant carbon budgets.

Global temperature increases are predicted to have pronounced negative effects on the metabolic performance of both terrestrial and aquatic organisms. These metabolic effects may be even more pronounced in intertidal organisms that are subject to multiple, abruptly changing abiotic stressors in the land-sea transition zone. Of the available studies targeting the intertidal environment, emphasis has largely been on water-breathing model organisms and this selective focus resulted in limited reliable forecasts on the impact of global warming on primarily air-breathing intertidal species. We investigated the thermal sensitivity of six phylogenetically related fiddler crab species that occupy different microhabitats on intertidal shores from south America and east Asia to test how bimodal-breathing intertidal ectotherms cope with thermal stress. We examined the metabolic physiology and thermal limits of the crabs by measuring their cardiac function and oxygen consumption along a thermal gradient. Their specific thermal microhabitat was also appraised. We found that subtropical fiddler crab species inhabiting vegetated microhabitats have lower upper lethal temperatures and therefore greater thermal sensitivity in comparison to their tropical counterparts. Additionally, females exhibited higher oxygen consumption and lower lethal temperatures in comparison to males. Our results contradict previous predictions that species from higher latitudes that experience greater temperature variability have broader latitudinal distributions, greater phenotypic plasticity and lower thermal sensitivity. Furthermore, the higher thermal sensitivity demonstrated by female fiddler crabs with respect to males strongly suggests a role of both gametogenesis and physiological dimorphism on the thermal performance of tropical and subtropical intertidal organisms. These observations ultimately, advocates for further studies on sex-biased and development-biased thermal sensitivity before drawing any generalizations based on a single sex or life stage.

Air-breathing fish risk losing aerially sourced oxygen to ambient hypoxic water since oxygenated blood from the air-breathing organ returns through the heart to the branchial basket before distribution. This loss is thought to help drive the evolutionary reduction in gill size with the advent of air-breathing. In many teleost fish, gill size is known to be highly plastic by modulation of their anatomic diffusion factor (ADF) with inter-lamellar cell mass (ILCM). In the anoxia-tolerant crucian carp, ILCM recedes with hypoxia but regrows in anoxia. The air-breathing teleost Chitala ornata has been shown to increase gill ADF from normoxic to mildly hypoxic water by reducing ILCM. Here, we test the hypothesis that ADF is modulated to minimize oxygen loss in severe aquatic hypoxia by measuring ADF, gas-exchange, and by using computed tomography scans to reveal possible trans-branchial shunt vessels. Contrary to our hypothesis, ADF does not modulate to prevent oxygen loss and despite no evident trans-branchial shunting, C. ornata loses only 3% of its aerially sourced O 2 while still excreting 79% of its CO 2 production to the severely hypoxic water. We propose this is achieved by ventilatory control and by compensating the minor oxygen loss by extra aerial O 2 uptake.

Predictions of individual responses to climate change are often based on the assumption that temperature affects the metabolism of individuals independently of their body mass. However, empirical evidence indicates that interactive effects exist. Here, we investigated the response of individual standard metabolic rate (SMR) to annual temperature range and forecasted temperature rises of 0.6–1.2°C above the current maxima, under the conservative climate change scenario IPCC RCP2.6. As a model organism, we used the amphipod Gammarus insensibilis, collected across latitudes along the western coast of the Adriatic Sea down to the southernmost limit of the species' distributional range, with individuals varying in body mass (0.4–13.57 mg). Overall, we found that the effect of temperature on SMR is mass dependent. Within the annual temperature range, the mass-specific SMR of small/young individuals increased with temperature at a greater rate (activation energy: E=0.48 eV) than large/old individuals (E=0.29 eV), with a higher metabolic level for high-latitude than low-latitude populations. However, under the forecasted climate conditions, the mass-specific SMR of large individuals responded differently across latitudes. Unlike the higher-latitude population, whose mass-specific SMR increased in response to the forecasted climate change across all size classes, in the lower-latitude populations, this increase was not seen in large individuals. The larger/older conspecifics at lower latitudes could therefore be the first to experience the negative impacts of warming on metabolism-related processes. Although the ecological collapse of such a basic trophic level (aquatic amphipods) owing to climate change would have profound consequences for population ecology, the risk is significantly mitigated by phenotypic and genotypic adaptation.

Central retinal artery occlusion (CRAO) is an obstruction of the retinal artery carrying oxygen to the cells in the inner retinal layers. This lack of oxygen may result in irreversible loss of sight if not treated within 24−36 h. We propose a dextran-based oxygen nanobubble (DONB) platform for intravitreal delivery of oxygen to rescue the inner retina from such ischemic damage. The size distribution of DONBs was 119.6 ± 44.9 nm and the zeta (ζ)-potential was −35.54 ± 10.54 mV. The DONBs were found to be stable in amber vials at 5 ± 3 °C for over 4 months and the formulation was not cytotoxic. The therapeutic efficacy of DONBs was first evaluated in retinal precursor cell lines which showed excellent recovery and then in a hypoxia/reperfusion rat eye model. Oxygen distribution measurements and histology indicated excellent recovery of the ganglion and inner retinal cell layers. Electroretinography exhibited normal retinal function. Our unique approach suggests a promising pathway to treat CRAO, a blinding condition for which no effective treatment exists.

Oxygen availability is key in determining habitat suitability for marine fish. As a result of climate change, low oxygen conditions are predicted to occur more frequently and over a greater geographic extent. Studies assessing the long-term chronic effects and impacts for commercially important fish are rare. To assess the potential effects of climate-induced low oxygen on fisheries, physiological data, such as critical thresholds, derived from laboratory experiments on 5 commercial fish species were integrated with hindcast and future oxygen projections from the hydrodynamic-biogeochemical model GETM-ERSEM. By using this approach, changes in habitat suitability from the 1970s to 2100 were identified. In the North Sea, the current extent of areas with the lowest oxygen levels is smaller than during the 1970s, with improved oxygen conditions having less impact on species’ critical thresholds. Oxygen levels are expected to decrease again in the coming century due to climate change, although not to the minima of previous decades. In affected areas and years, intermediate oxygen levels could have temporary impacts in late summer on swimming, growth, ingestion and metabolic scope of adult fish. These results demonstrate that although physical model oxygen projections help to provide insight, they are insufficient by themselves to predict the full potential impacts of climate change on fish distribution and fisheries. Such modelling requires underpinning through experimentation, particularly of the physiological effects of climate change on different life stages so that effects on reproduction, growth and commercial catches can be determined and tailored, and robust management measures put in place.

Quantifying a species thermal tolerance is critical to assessing biological impacts of anticipated increases in temperature (e.g., climate change). Although many studies have documented the critical thermal maximum (CT max ) of fish, there is a paucity of research on thermal biology of sturgeon. The shortnose sturgeon (Acipenser brevirostrum LeSueur, 1818) is a threatened species that exists along the eastern coast of North America. They can be exposed to temperatures ranging from freezing to above 25 °C. Using a heating rate of 6 °C/h, CT max and the associated hematological responses of shortnose sturgeon acclimated to 10, 15, and 20 °C were determined. There was a significant positive relationship between CT max and body mass, and CT max increased significantly with increases in acclimation temperature (T a ). In general, hematology of thermally stressed fish was modified relative to control (nonstressed) fish. Hematocrit, plasma lactate, and plasma Na + and Cl – of fish were all significantly influenced by thermal stress and T a. Glucose and K + were only significantly influenced by thermal stress. Future studies should address the importance of other stressors, such as salinity and toxicants, on thermal relationships of sturgeon.