Journal of Comparative Physiology B-Biochemical Systems and Environmental Physiology最新文献

Lowering heart rate while diving helps marine mammals regulate blood pressure while redistributing blood flow and conserving oxygen during extended dives. However, the classic characterization of this dive response-as a pronounced and abrupt reduction in heart rate observed during forced dives in laboratory settings-contrasts with the higher minimum heart rates and oscillatory patterns observed in freely diving marine mammals in the wild. To assess this apparent discrepancy in cardiovascular control, we measured the heart rates of three Steller sea lions (Eumetopias jubatus) using subcutaneous cardiac monitors during trained stationary dives (3-4 m) in an aquarium pool. During 12 of the longest dives (76-161 s), heart rates decreased from an average of 95 to 34 bpm within the first 26 s of submergence. However, while mean HR at depth eventually averaged around 31 bpm, it also oscillated between 27 and 39 bpm every ~ 5-6 s (0.2 Hz) for much of the dive, before rising prior to surfacing. The observed relatively slow drops in heart rates were similar to those seen in other marine mammals, suggesting an optimal rate of decline that reflects the anticipated conditions of voluntary dives. We further hypothesize that the oscillating minimum heart rates of freely diving marine mammals reflect time delays in the baroreceptor reflex due to the prolongation of circulation time. Our findings suggest these delays shape the rate and pattern of heart rate decline, ultimately influencing cardiovascular control, gas management, and breath-hold duration in diving mammals.

Parasites interact with their host in variable environments that are often subject to water scarcity and dehydration. Drosophilid fruit flies and associated ectoparasitic mites interact across a range of microhabitats, typically in decaying organic matter, such as fallen fruit and cactus tissue, that dries out and deteriorates over periods ranging from days to months. Here, we report that mite parasitism of Drosophila increases with exposure to increasingly dry conditions for two fly-mite systems (D. nigrospiracula-Macrocheles and D. melanogaster-Gamasodes). In D. melanogaster, artificial selection for increasing behavioral resistance did not eliminate this effect, as previously selected lines remained relatively more resistant than non-selected controls even under dry conditions. Water balance assays confirmed that mites became dehydrated when held under dry conditions, which was also associated with increased mite activity. Exposure of D. melanogaster to mites dehydrated by exposure to low relative humidity increased parasitism, further supporting that prevalence of infestation intensifies under dry conditions. The results indicate that ectoparasitism in this system is affected by the water content of the mites. The increased motivation of mites to parasitize flies under dry conditions may serve to replenish mite water stores and facilitate dispersal to more favorable microhabitats.

Ageing is a multifactorial process characterised by the progressive dysregulation of redox homeostasis in different organs. Although various endogenous and exogenous factors influencing ageing have been identified, limited evidence exists regarding the effects of chronic cold exposure on aged rats. To address this, we investigated interscapular brown (iBAT) and retroperitoneal white (rWAT) adipose tissue, skeletal muscle, and liver in rats (3-, 6- and 24-month-old) at 22 ± 1 °C, alongside a cohort of 24-month-old rats kept at 4 ± 1 °C from 6 to 24 months of age. We measured antioxidant defence (AD) components: the activity of copper zinc (CuZnSOD) and manganese (MnSOD) superoxide dismutase, catalase, glutathione peroxidase (GSH-Px), glutathione reductase (GR), thioredoxin reductase (TR), glutathione S-transferase (GST), and total glutathione (GSH) content. With chronological ageing, enzyme activity decreased in rWAT (catalase, GSH-Px, GR, TR, GST) and iBAT (GSH-Px). Conversely, aged rats exposed to 4 ± 1 °C showed an upregulation of AD components in rWAT (catalase, GSH-Px, GR, TR, GST; GSH), iBAT (catalase, GSH-Px, TR; GSH), and muscle (GSH-Px, GR, TR, GST), compared to age-matched group. However, CuZnSOD and MnSOD activities remained unchanged across all experimental groups and tissues. In addition, none of the measured AD components in the liver changed significantly across groups. Collectively, these results reveal a distinct modulation of the AD profiles in different organs, both during chronological ageing and after long-term exposure to cold, underscoring an integrated systemic responsiveness. This is most evident in the preserved AD response to prolonged cold exposure in the key thermogenic tissue, iBAT, of aged rats.

Elevated heat and low phytoplankton abundance are physiologically and ecologically challenging marine organisms of the northeast Pacific, including the mussel Mytilus californianus. During low tide, mussels are exposed to warm air and undergo anaerobic metabolism. Tidal variation coincides with daily fluctuations in food availability requiring flexible response systems (e.g., changes in digestive enzyme activity) to maintain homeostasis. In this study we allowed mussels to acclimate in tidal mesocosms with or without aerial heat across high and low levels of food abundance, after which we measured amylase (carbohydrase) activity and gene expression. Remarkably, enzyme activity was unpredictably elevated during low tide in fasted or moderate heat-stress (+ 8 °C; 23 °C) conditions, thereby potentially mitigating energy losses posed by environmental stress. Heat stress combined with fasting (multistressor) presented a marked challenge for mussels as evidenced by lower amylase activity compared to other treatments. A subsequent acute aerial heat-shock (+ 17 °C; 32 °C) negatively impacted amylase activity across all acclimation groups. Gene expression of amylase was anticorrelated with activity suggestive that mussels' sense environmental fluctuations and respond by regulating digestive enzyme activity. Although mussels can employ these strategies to dampen short-term stress, the heatwaves predicted to persist in their ecosystems in the future may curtail their effectiveness.