Interactive effects of temperature and hypoxia on diffusive water flux and oxygen uptake rate in the tidepool sculpin, Oligocottus maculosus

Osmo-respiratory compromise in the mosshead sculpin (Clinocottus globiceps): effects of temperature, hypoxia, and re-oxygenation on rates of diffusive water flux and oxygen uptake

In nature, mosshead sculpins (Clinocottus globiceps) are challenged by fluctuations in temperature and oxygen levels in their environment. However, it is unclear how mosshead sculpins modulate the permeability of their branchial epithelia to water and O2 in response to temperature or hypoxia stress. Acute decrease in temperature from 13 to 6 oC reduced diffusive water flux rate by 22% and ṀO2 by 51%, whereas acute increase in temperature from 13 to 25 oC increased diffusive water flux rate by 217% and ṀO2 by 140%, yielding overall Q10 values of 2.08 and 2.47 respectively. Acute reductions in oxygen tension from >95% to 20% or 10% air saturation did not impact diffusive water flux rates, however, ṀO2 was reduced significantly by 36% and 65% respectively. During 1-h or 3-h recovery periods diffusive water flux rates were depressed while ṀO2 exhibited overshoots beyond the normoxic control level. Many responses differed from those seen in our parallel earlier study on the tidepool sculpin, a cottid with similar hypoxia tolerance but much smaller gill area that occupies a similar environment. Overall, our data suggest that during temperature stress, diffusive water flux rates and ṀO2 follow the traditional osmo-respiratory compromise pattern, but during hypoxia and re-oxygenation stress, diffusive water flux rates are decoupled from ṀO2.

The interplay between prior selection, mild intermittent exposure, and acute severe exposure in phenotypic and transcriptional response to hypoxia

Hypoxia has profound and diverse effects on aerobic organisms, disrupting oxidative phosphorylation and activating several protective pathways. Predictions have been made that exposure to mild intermittent hypoxia may be protective against more severe exposure and may extend lifespan. Here we report the lifespan effects of chronic, mild, intermittent hypoxia, and short‐term survival in acute severe hypoxia in four clones of Daphnia magna originating from either permanent or intermittent habitats. We test the hypothesis that acclimation to chronic mild intermittent hypoxia can extend lifespan through activation of antioxidant and stress‐tolerance pathways and increase survival in acute severe hypoxia through activation of oxygen transport and storage proteins and adjustment to carbohydrate metabolism. Unexpectedly, we show that chronic hypoxia extended the lifespan in the two clones originating from intermittent habitats but had the opposite effect in the two clones from permanent habitats, which also showed lower tolerance to acute hypoxia. Exposure to chronic hypoxia did not protect against acute hypoxia; to the contrary, Daphnia from the chronic hypoxia treatment had lower acute hypoxia tolerance than normoxic controls. Few transcripts changed their abundance in response to the chronic hypoxia treatment in any of the clones. After 12 h of acute hypoxia treatment, the transcriptional response was more pronounced, with numerous protein‐coding genes with functionality in oxygen transport, mitochondrial and respiratory metabolism, and gluconeogenesis, showing upregulation. While clones from intermittent habitats showed somewhat stronger differential expression in response to acute hypoxia than those from permanent habitats, contrary to predictions, there were no significant hypoxia‐by‐habitat of origin or chronic‐by‐acute treatment interactions. GO enrichment analysis revealed a possible hypoxia tolerance role by accelerating the molting cycle and regulating neuron survival through upregulation of cuticular proteins and neurotrophins, respectively.

Hypoxia and High Temperature as Interacting Stressors: Will Plasticity Promote Resilience of Fishes in a Changing World?

AbstractDetermining the resilience of a species or population to climate change stressors is an important but difficult task because resilience can be affected both by genetically based variation and by various types of phenotypic plasticity. In addition, most of what is known about organismal responses is for single stressors in isolation, but environmental change involves multiple environmental factors acting in combination. Here, our goal is to summarize what is known about phenotypic plasticity in fishes in response to high temperature and low oxygen (hypoxia) in combination across multiple timescales, to ask how much resilience plasticity may provide in the face of climate change. There are relatively few studies investigating plasticity in response to these environmental stressors in combination; but the available data suggest that although fish have some capacity to adjust their phenotype and compensate for the negative effects of acute exposure to high temperature and hypoxia through acclimation or developmental plasticity, compensation is generally only partial. There is very little known about intergenerational and transgenerational effects, although studies on each stressor in isolation suggest that both positive and negative impacts may occur. Overall, the capacity for phenotypic plasticity in response to these two stressors is highly variable among species and extremely dependent on the specific context of the experiment, including the extent and timing of stressor exposure. This variability in the nature and extent of plasticity suggests that existing phenotypic plasticity is unlikely to adequately buffer fishes against the combined stressors of high temperature and hypoxia as our climate warms.

Effects of Microplastics on Immune Responses of the Yellow Catfish Pelteobagrus fulvidraco Under Hypoxia

Compared with marine organisms, research on microplastics (MPs) in freshwater organisms is still less although MPs have been widely found in the freshwater ecosystem. Hypoxia is a ubiquitous issue in freshwater aquaculture, and under such scenarios, the toxic effects of MPs on typical aquaculture fish need to be clarified. In this study, we studied the effects of MPs (polystyrene) on specific growth rate (SGR), hypoxia-inducible factor-1α (HIF-1α), tumor necrosis factor-α (TNF-α), interleukin-8 (IL-8), and interferon (IFN) in the yellow catfish (Pelteobagrus fulvidraco) under hypoxic conditions. After 15 days of exposure, the SGR was not affected by MPs or hypoxia. MPs significantly increased the expressions of HIF-1α and TNF-α but inhibited the expression of IFN at high concentration MPs under normoxia. However, hypoxia significantly inhibited the expression of IL-8 and TNF-α under high MP concentration and low MP concentration, respectively. In addition, MPs had significant concentration-dependent inhibitory effects on IFN under hypoxia. Surprisingly, a positive correction between HIF-1α and TNF-α was found in fish. Although hypoxia might alleviate the effects of MPs with low concentrations, the interaction of hypoxia and MPs aggravated the negative effects of MPs on immune factors at high concentration MPs. This study provided new insight into the complex effects of hypoxia and MPs on aquatic organisms, and future studies should focus on the cellular pathways of immune cells in fish. Given that MPs could induce the immune response in fish, considerations should be paid to the impacts of MPs on freshwater aquaculture, and hypoxia should be taken into consideration when evaluating the effects of MPs.