Biology subjects

Mark, F. C.

Publications and source records attributed to Mark, F. C..

4 recordsLinked to original sources

bioRxiv2023

Low Pcrit but no hypoxia tolerance? Hypoxia compensation in the Arctic keystone species Boreogadus saida.

Global warming has already caused a loss of almost 50% Arctic sea-ice coverage since the 1980s. Sea-ice loss strengthens summer stratification of the oceans water column and, consequently, hypoxic zones in the deep-water layers may form. The present study investigated the response of an Arctic keystone species, the Polar cod, Boreogadus saida, to hypoxia and warming. We measured the respiratory capacity (standard, routine and maximum metabolic rates, SMR, RMR, MMR, aerobic scope, critical oxygen saturation (Pcrit)) and swimming performance of Polar cod under progressive hypoxia at 2.4 {degrees}C and after warm acclimation to close to the species thermal limit (10.0 {degrees}C) via flow-through and swim tunnel respirometry. We observed clear and stable patterns that were similar in both thermal regimes: Polar cod displayed oxygen-regulating behaviour under progressive hypoxia, with SMR never below aerobic baseline metabolism and a very stable AS. Our study revealed that Polar cod can handle exceptionally low oxygen saturations down to a Pcrit of 5.9 % air saturation at typical habitat temperatures. Closer to critical temperatures (10.0 {degrees}C), Pcrit rose to 21.6 % air saturation. However, the pertinent question remains whether the observed behaviour can be summarized under classic hypoxia tolerance, as we a) did not observe any metabolic downregulation and b) no anaerobic component of the hypoxia response in Polar cod, which are usually put forward in the definition of hypoxia tolerance. Therefore, we describe the observed metabolic response to hypoxia rather as metabolic hypoxia compensation than hypoxia tolerance as the mechanisms involved here actively seek to improve oxygen supply instead of (anaerobically) tolerating hypoxia through metabolic depression.

physiology↗

bioRxiv2023

Genomic evidence for West Antarctic Ice Sheet collapse during the Last Interglacial Period

The marine-based West Antarctic Ice Sheet (WAIS) is considered vulnerable to irreversible collapse under future climate trajectories and its tipping point may even lie within the mitigated warming scenarios of 1.5-2 {degrees}C of the United Nations Paris Agreement. Knowledge of ice loss during similarly warm past climates, including the Last Interglacial, when global sea levels were 5-10 m higher than today, and global average temperatures of 0.5-1.5 {degrees}C warmer than preindustrial levels, could resolve this uncertainty. Here we show, using a panel of genome-wide, single nucleotide polymorphisms of a circum-Antarctic octopus, persistent, historic signals of gene flow only possible with complete WAIS collapse. Our results provide the first empirical evidence that the tipping point of WAIS loss could be reached even under stringent climate mitigation scenarios. One-Sentence SummaryHistorical gene flow in marine animals indicate the West Antarctic Ice Sheet collapsed during the Last Interglacial.

evolutionary biology↗

bioRxiv2021

Transgenerational effects decrease larval resilience to ocean acidification and warming but juvenile European sea bass could benefit from higher temperatures in the NE Atlantic

1.The aim of this study was to investigate the effect of ocean acidification (OA) and warming (OW) as well as the transgenerational effect of OA on larval and juvenile growth and metabolism of a large economically important fish species with a long generation time. Therefore we incubated European sea bass from Brittany (France) for two generations (>5 years in total) under current and predicted OA conditions (PCO2: 650 and 1700 {micro}atm). In the F1 generation both OA condition were crossed with OW (temperature: 15-18{degrees}C and 20-23{degrees}C). We found that OA alone did not affect larval or juvenile growth and OW increased developmental time and growth rates, but OAW decreased larval size at metamorphosis. Larval routine metabolic rate (RMR) and juvenile standard metabolic rate (SMR) were significantly lower in cold compared to warm conditioned fish and also lower in F0 compared to F1 fish. We did not find any effect of OA on RMR or SMR. Juvenile PO2crit was not affected by OA, OW or OAW in both generations. We discuss the potential underlying mechanisms resulting in beneficial effects of OW on F1 larval growth and RMR and in resilience of F0 and F1 larvae and juveniles to OA, but on the other hand resulting in vulnerability of F1, but not F0 larvae to OAW.. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures. Summary statementWe found that OA did not affect developmental time, growth, RMR and SMR, while OW increased these traits. OAW decreased larval size at metamorphosis. We discuss underlying mechanisms and the ecological perspective resulting from these results and conclude that recruitment to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures in Atlantic waters.

physiology↗

bioRxiv2019

Future ocean warming may prove beneficial for the northern population of European seabass, but ocean acidification does not

1.The worlds oceans are acidifying and warming due to increasing amounts of atmospheric CO2. Thermal tolerance of fish much depends on the cardiovascular ability to supply the tissues with oxygen. The heart itself is highly dependent on oxygen and heart mitochondria thus might play a key role in shaping an organisms tolerance to temperature. The present study aimed to investigate the effects of acute and chronic warming on respiratory capacities of European sea bass (Dicentrarchus labrax L.) heart mitochondria. We hypothesized that acute warming would impair mitochondrial respiratory capacities, but be compensated after long-term. Increasing PCO2 may cause intracellular changes, likely further constricting cellular energy metabolism.\n\nWe found increased leak respiration rates in acutely warmed heart mitochondria of cold-conditioned fish in comparison to measurements at their rearing temperature, suggesting a lower aerobic capacity to synthesize ATP. However, thermal acclimation led to increased mitochondrial functionality, e.g. higher RCRo in heart mitochondria of warm-conditioned compared to cold-conditioned fish. Exposure to high PCO2 synergistically amplified the effects of acute and long-term warming, but did not result in changes by itself. We explained the high ability to maintain mitochondrial function under OA with the fact that seabass are moving between various environmental conditions. Improved mitochondrial capacities after warm conditioning could be due to the origin of this species in the warm waters of the Mediterranean. Our results also indicate that seabass are not yet fully adapted to the colder temperatures in their northern distribution range and might benefit from warmer temperatures.\n\nSummary statementMitochondria of juvenile European sea bass hearts are impaired by acute warming, but seem to benefit from acclimation to warmer temperatures, they are only marginally impacted by ocean acidification.

physiology↗