Linking environmental salinity to respiratory phenotypes and metabolic rate in fishes: a data mining and modelling approach.

The gill is the primary site of ionoregulation and gas exchange in adult teleost fishes. However, those characteristics that benefit diffusive gas exchange (large, thin gills) may also enhance the passive equilibration of ions and water that threaten osmotic homeostasis. Our literature review revealed that gill surface area and thickness were similar in freshwater (FW) and seawater (SW) species; however, the diffusive oxygen (O2) conductance (Gd) of the gill was lower in FW species.

Nitrogen recycling via gut symbionts increases in ground squirrels over the hibernation season.

Hibernation is a mammalian strategy that uses metabolic plasticity to reduce energy demands and enable long-term fasting. Fasting mitigates winter food scarcity but eliminates dietary nitrogen, jeopardizing body protein balance. Here, we reveal gut microbiome-mediated urea nitrogen recycling in hibernating thirteen-lined ground squirrels ().

How the gut and liver hibernate.

For hibernating mammals, the transition from summer active to winter hibernation seasons come with significant remodeling at cellular, organ and whole organism levels. This review summarizes and synthesizes what is known about hibernation-related remodeling in the gastrointestinal tract of the thirteen-lined ground squirrel, including intestinal and hepatic physiology and the gut microbiota. Hibernation alters intestinal epithelial, immune and cell survival pathways in ways that point to a protective phenotype in the face of prolonged fasting and major fluctuations in nutrient and oxygen delivery during torpor-arousal cycles.

Shallow metabolic depression and human spaceflight: a feasible first step.

Synthetic torpor is an induced state of deep metabolic depression (MD) in an organism that does not naturally employ regulated and reversible MD. If applied to spaceflight crewmembers, this metabolic state may theoretically mitigate numerous biological and logistical challenges of human spaceflight. These benefits have been the focus of numerous recent articles where, invariably, they are discussed in the context of hypothetical deep MD states in which the metabolism of crewmembers is profoundly depressed relative to basal rates.

The utility and determination of in fishes.

The critical O tension () is the lowest  at which an animal can maintain some benchmark rate of O uptake ( ). This  has long served as a comparator of hypoxia tolerance in fishes and aquatic invertebrates, but its usefulness in this role, particularly when applied to fishes, has recently been questioned. We believe that remains a useful comparator of hypoxia tolerance provided it is determined using the proper methods and hypoxia tolerance is clearly defined.

Shifts in metabolic fuel use coincide with maximal rates of ventilation and body surface rewarming in an arousing hibernator.

It is well established that hibernating mammals rely predominantly on lipid stores to fuel metabolism throughout the hibernation season. However, it is unclear if other endogenous fuels contribute to the rapid, ~400-fold increase in metabolic rate during the early phase of arousal from torpor. To investigate this issue, we used cavity ring-down spectroscopy, a technique that provides a real-time indication of fuel use by measuring the ratio of C to C in the exhaled CO of arousing 13-lined ground squirrels ().

Can variation among hypoxic environments explain why different fish species use different hypoxic survival strategies?

In aquatic environments, hypoxia is a multi-dimensional stressor that can vary in O level (partial pressure of O in water, w ), rate of induction and duration. Natural hypoxic environments can therefore be very different from one another. For the many fish species that have evolved to cope with these different hypoxic environments, survival requires adjusting energy supply and demand pathways to maintain energy balance.

Synthetic torpor: A method for safely and practically transporting experimental animals aboard spaceflight missions to deep space.

Animal research aboard the Space Shuttle and International Space Station has provided vital information on the physiological, cellular, and molecular effects of spaceflight. The relevance of this information to human spaceflight is enhanced when it is coupled with information gleaned from human-based research. As NASA and other space agencies initiate plans for human exploration missions beyond low Earth orbit (LEO), incorporating animal research into these missions is vitally important to understanding the biological impacts of deep space.

Metabolic depression and the evolution of hypoxia tolerance in threespine stickleback, .

Anthropogenic increases in global temperature and agricultural runoff are increasing the prevalence of aquatic hypoxia throughout the world. We investigated the potential for a relatively rapid evolution of hypoxia tolerance using two isolated (for less than 11 000 years) populations of threespine stickleback: one from a lake that experiences long-term hypoxia (Alta Lake, British Columbia) and one from a lake that does not (Trout Lake, British Columbia). Loss-of-equilibrium (LOE) experiments revealed that the Alta Lake stickleback were significantly more tolerant of hypoxia than the Trout Lake stickleback, and calorimetry experiments revealed that the enhanced tolerance of Alta Lake stickleback may be associated with their ability to depress metabolic rate (as indicated by metabolic heat production) by 33% in hypoxia.

Rates of hypoxia induction alter mechanisms of O uptake and the critical O tension of goldfish.

The rate of hypoxia induction (RHI) is an important but overlooked dimension of environmental hypoxia that may affect an organism's survival. We hypothesized that, compared with rapid RHI, gradual RHI will afford an organism more time to alter plastic phenotypes associated with O uptake and subsequently reduce the critical O tension () of the rate of O uptake ( ). We investigated this by determining values for goldfish exposed to short (∼24 min), typical (∼84 min) and long (∼480 min) duration trials to represent different RHIs.

Calorespirometry reveals that goldfish prioritize aerobic metabolism over metabolic rate depression in all but near-anoxic environments.

Metabolic rate depression (MRD) has long been proposed as the key metabolic strategy of hypoxic survival, but surprisingly, the effects of changes in hypoxic O tensions (w ) on MRD are largely unexplored. We simultaneously measured the O consumption rate ( ) and metabolic heat of goldfish using calorespirometry to test the hypothesis that MRD is employed at hypoxic w  values and initiated just below , the wbelow which  is forced to progressively decline as the fish oxyconforms to decreasing w Specifically, we used closed-chamber and flow-through calorespirometry together with terminal sampling experiments to examine the effects of w  and time on , metabolic heat and anaerobic metabolism (lactate and ethanol production). The closed-chamber and flow-through experiments yielded slightly different results.

Ambient CO2, fish behaviour and altered GABAergic neurotransmission: exploring the mechanism of CO2-altered behaviour by taking a hypercapnia dweller down to low CO2 levels.

Recent studies suggest that projected rises of aquatic CO2 levels cause acid-base regulatory responses in fishes that lead to altered GABAergic neurotransmission and disrupted behaviour, threatening fitness and population survival. It is thought that changes in Cl(-) and HCO3 (-) gradients across neural membranes interfere with the function of GABA-gated anion channels (GABAA receptors). So far, such alterations have been revealed experimentally by exposing species living in low-CO2 environments, like many oceanic habitats, to high levels of CO2 (hypercapnia).

Characterizing the metabolic capacity of the anoxic hagfish heart.

Pacific hagfish, Eptatretus stoutii, can recover from 36 h of anoxia at 10°C. Such anoxia tolerance demands the mobilization of anaerobic fuels and the removal of metabolic wastes--processes that require a functional heart. The purpose of this study was to measure the metabolic response of the excised, cannulated hagfish heart to anoxia using direct calorimetry.

The evolution of Root effect hemoglobins in the absence of intracellular pH protection of the red blood cell: insights from primitive fishes.

The Root effect, a reduction in blood oxygen (O(2)) carrying capacity at low pH, is used by many fish species to maximize O(2) delivery to the eye and swimbladder. It is believed to have evolved in the basal actinopterygian lineage of fishes, species that lack the intracellular pH (pH(i)) protection mechanism of more derived species' red blood cells (i.e.

The transition in hemoglobin proton-binding characteristics within the basal actinopterygian fishes.

Carbon dioxide (CO(2)) transport in the blood of fishes is aided by the proton-binding properties of hemoglobin (Hb) through either a high-intrinsic buffer value and small oxylabile proton binding (Haldane effect), or a low buffer value and large Haldane effect. Primitive species, such as elasmobranchs and sarcopterygians have been shown to rely on the former, while derived species, such as teleosts rely on the latter. Both strategies are effective in the transport of CO(2) in the blood.