Intermittent hypoxia elicits a unique physiological coping strategy in Fundulus killifish
Bibliographic record
Abstract
Fish encounter daily cycles of hypoxia in the wild, but the physiological strategies for coping with repeated cycles of normoxia and hypoxia (intermittent hypoxia) are poorly understood. Contrastingly, the physiological strategies for coping with continuous (constant) exposure to hypoxia have been studied extensively in fish. The main objective of this thesis was to understand how Fundulus killifish cope with a diurnal cycle of intermittent hypoxia, an ecologically relevant pattern of aquatic hypoxia in the natural environment. To do this, I characterized the effects of intermittent hypoxia on hypoxia tolerance, oxygen transport, metabolism, and the oxidative stress defense system of killifish, and compared these effects to fish exposed to normoxia, a single cycle of hypoxia-normoxia, and constant hypoxia. Specifically, I studied the following topics: (i) how acclimation to intermittent hypoxia modifies hypoxia tolerance, and the hypoxia acclimation response of Fundulus heteroclitus (Chapter 2), (ii) metabolic adjustments occurring during a hypoxia-reoxygenation cycle (Chapter 3), (iii) how acclimation to intermittent hypoxia alters O2 transport capacity and maximal aerobic metabolic rate (Chapter 4), (iv) the effects of hypoxia and reoxygenation on reactive oxygen species and oxidative stress (Chapter 5), and (v) variation in hypoxia tolerance and in the hypoxia acclimation responses across Fundulus fishes (Chapter 6). Killifish rely on a unique and effective physiological strategy to cope with intermittent hypoxia, and that this strategy is distinct from both the response to a single bout of acute hypoxia-reoxygenation (12 h hypoxia followed by 6 h reoxygenation) and to chronic exposure to constant hypoxia (24 h hypoxia per day for 28 d). Key features of the acclimation response to intermittent hypoxia include (i) maintenance of resting O2 consumption rate in hypoxia followed by a substantial increase in O2 consumption rate during recovery in normoxia, (ii) reversible increases in blood O2 carrying capacity during hypoxia bouts, (iii) minimal recruitment of anaerobic metabolism during hypoxia bouts, and (iv) protection of tissues from oxidative damage despite alterations in the homeostasis of reactive oxygen species and cellular redox status. Of these features, (i) is unique to intermittent hypoxia, (ii) also occurs in fish exposed to acute hypoxia-reoxygenation, and (iii) and (iv) are observed in both fish acclimated to intermittent hypoxia as well as those acclimated to constant hypoxia. This is the most extensive investigation to date on how fish cope with the energetic and oxidative stress challenges of intermittent hypoxia, and how these responses differ from constant hypoxia. This thesis adds substantial insight into the general mechanisms by which animals can respond to an ecologically important but poorly understood feature of the aquatic environment.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".