2021 journal article
Assessing the P-crit in relation to temperature and the expression of hypoxia associated genes in the mayfly, Neocloeon triangulifer
SCIENCE OF THE TOTAL ENVIRONMENT, 808.
Hypoxia is a growing concern in aquatic ecosystems. Historically, scientists have used the P crit (the dissolved oxygen level below which an animal can no longer oxyregulate) to infer hypoxia tolerance across species. Here, we tested the hypothesis that the P crit is positively correlated with temperature in the mayfly, Neocloeon triangulifer. Cross-temperature comparisons showed a modest (r = 0.47), but significant (p < 0.0001) association between temperature and P crit despite relatively large interindividual variability (Coefficient of Variance (CV) = 39.9% at 18 °C). We used the expression of hypoxia-responsive genes EGL-9 (an oxygen sensing gene and modulator of HIF-1a activity) and LDH (a hypoxia indicator) to test whether oxygen partial pressure near the P crit stimulates expression of hypoxia-responsive genes. Neither gene was upregulated at oxygen levels above the estimated P crit , however, at or below the P crit estimates, expression of both genes was stimulated (~20- and ~3-fold change for EGL-9 and LDH, respectively). Finally, we evaluated the influence of hypoxic exposure time and pretreatment conditions on the mRNA expression levels of hypoxia-responsive genes. When larvae were exposed to a gradual reduction of DO, hypoxic gene expression was more robust than during instantaneous exposure to hypoxia. Our data provide modest support for traditional interpretation of the P crit as a physiologically meaningful shift from aerobic to anaerobic metabolism in N. triangulifer. However, we also discuss limitations of the P crit as a proxy measure of hypoxia tolerance at the species level.