Conservation Physiology最新文献

Human impacts on ecosystems have intensified variation in water variability for terrestrial life, thus challenging the maintenance of water balance, or hydroregulation. The accelerated development and accessibility of technologies and computational models over the past decade have enabled researchers to predict changes in animal hydroregulation and environmental water with greater spatial and temporal precision. Focusing on reptiles and amphibians, we discuss current methods, limitations and advances for quantifying ecologically relevant metrics of environmental water stressors and organismal responses to both acute and long-term water stress that are applicable for conservation and management. We also highlight approaches that integrate environmental water data with an organism's water balance and physiological, behavioural and life history traits to predict the limits of species' responses and assess their vulnerability to climate change. Finally, we outline promising future directions and opportunities in hydroregulation studies with a conservation focus, including broader inferences about acclimation responses, linking gene expression to functional changes, and exploring inter- and transgenerational plasticity and adaptive evolution. Advances in these fields will facilitate more accurate assessments of species' capacities and the limits of hydroregulation in response to a more variable and unpredictable future climate.

White sturgeon (Acipenser transmontanus) are in decline globally, and populations in the Sacramento-San Joaquin River Basin are particularly vulnerable due to habitat impacts, variable recruitment and altered food availability, all of which are exacerbated by climate change. The minimal metabolic expenditure required to maintain homeostasis, termed standard metabolic rate (SMR), is thought to have broad ecological relevance because it correlates with other important measures of metabolic demand and a range of fitness-related behavioural traits. SMR is variable among individuals and this variation may also underlie variation in behaviour. Additionally, SMR has been shown to be phenotypically flexible in the presence of changing food availability. The objective of this study was to assess how nutritional status may affect the relationship between SMR and locomotor activity in juvenile white sturgeon. We reared white sturgeon at 15°C under an optimal feed rate (OFR, 5.3% bodyweight/day) and low feed rate (LFR, 2.6% bodyweight/day) for 6 weeks, measuring SMR and locomotor activity at the 3- and 6-week timepoints. OFR fish were significantly larger than LFR fish at both timepoints, but mass-specific SMR was not significantly different across treatment or time. We found that only fish under the greatest nutritional stress (6 weeks at LFR) showed a significant relationship between SMR and locomotor activity. This is evidence that observable correlations between physiological and behavioural traits may only become apparent under the influence of environmental stressors. As changing climate is projected to impact food web dynamics and food availability, understanding how nutritional state affects physiological and behavioural traits may help to predict how animals respond to future shifts.

Amphibians face global declines linked to anthropogenic environmental change, including modifications to freshwater habitats. Human impacts on water chemistry, including acid rain and run-off of road salt into wetlands, may affect the physiology of amphibians with aquatic life stages. Specifically, water pH varies among freshwater habitats and affects amphibian development, behaviour, and physiology. For example, changes in skin pH affect the activity of enzymes on the skin, including those involved in antimicrobial functions. In this study, we explored the ability of free-ranging amphibians to maintain homeostasis across a range of naturally occurring water pH and salinity. We sampled two species of frogs at 19 wetlands around Peterborough, Ontario, measuring water pH, water salinity, and the skin pH of northern leopard frogs (Lithobates pipiens; n = 141) and green frogs (Lithobates clamitans; n = 329). We found that water pH increased with salinity, and was weakly related to the proportion of built-up habitat around wetlands. Frog skin pH was significantly associated with water pH, but both species showed a strong ability to buffer their skin pH across a range of conditions. On average, the ventral skin pH of L. pipiens increased by 0.37 units for each 1 unit increase in water pH, while skin pH of L. clamitans increased by 0.12. Specific responses to water chemistry differed between the two species: skin pH of L. pipiens varied with demographic group and body size, but skin pH of L. clamitans did not. As human effects on wetland habitats increase, these amphibians' ability to buffer skin pH may provide some protection against anthropogenic changes in wetland water chemistry.

Serological surveillance enhances our understanding of influenza A virus (IAV) exposure and dynamics in wild bird populations. Traditional serum-based testing, while effective, poses logistical challenges for large-scale surveillance, particularly in remote regions, for small-bodied species or in scenarios such as hunter-harvested samples where serum collection can be impractical. This study evaluates the use of whole blood collected on high-quality cellulose filter strips as an alternative to serum for detecting antibodies against IAV nucleoprotein (NP) and hemagglutinin (HA) H5 and H7 targets. We tested paired serum and whole blood on filter strips collected from wild birds using the commercially available IDEXX AI MultiS Screen Ab test and in-house competitive enzyme-linked immunosorbent assays (ELISAs) developed at the National Centre for Foreign Animal Disease (NCFAD) of the Canadian Food Inspection Agency. Strong correlations (ρ = 0.77) were observed between serum and whole blood on filter strips for NP detection with the IDEXX ELISA, while moderate correlations were noted for NCFAD's NP (ρ = 0.58) and H5 (ρ = 0.65) assays. Correlation between serum and whole blood on filter strips for NCFAD's H7 assay was poor, although interpretation is limited due to the small sample size of H7 positives. Threshold optimization using the Youden index improved diagnostic performance, with optimized cutoffs identified for NP (sample-to-negative < 0.7708 for IDEXX and percentage inhibition [PI] > 39.56 for NCFAD) and H5 (PI > 20.37). Storage conditions impacted performance, with frozen whole blood on filter strips achieving higher sensitivity compared to those stored at room temperature. These findings support the use of filter strips to collect whole blood as an informative alternative for IAV serological surveillance in wild birds when serum is unavailable, provided optimal storage conditions and threshold adjustments are implemented, although serum remains the superior sample type.

Increasingly frequent and intense heatwaves are expected to elevate the risks of heat-related mortality among birds. Most studies have focused on arid-zone avifaunas and the extent to which risks will increase in other habitats, particularly humid lowlands, remains unclear. We tested the prediction that increasing air temperature and corresponding increases in humidity, and hence wet-bulb temperature (T _W; lowest temperature achievable via adiabatic evaporation), will increase exposure to conditions associated with lethal hyperthermia. We empirically determined maximum T _W (T _W-max) for an Afrotropical forest frugivore, the trumpeter hornbill (Bycanistes bucinator) as T _W-max = 31.7 ± 1.0°C. We then modelled current and future exposure to conditions associated with T _W > T _W-max across this species' range. Under a business-as-usual emissions scenario and assuming no vegetation buffering of air temperature (T _air), trumpeter hornbills will experience T _W > T _W-max for at least 1 day year^-1 over 46% of their current range, compared to 30% at present. However, the frequency of exposure will increase substantially and reach ~100 days year^-1 in parts of the southern Democratic Republic of Congo. When we incorporated the thermal buffering effect of vegetation, end-century exposure to T _W > T _W-max decreased by 0.3-66.7%, emphasizing the role of cool microsites provided by vegetation. Our analyses reveal the exposure of birds inhabiting humid environments at low latitudes to conditions associated with a risk of lethal hyperthermia under resting conditions will increase substantially in coming decades, putting a large fraction of global avian biodiversity at risk of population declines and local extinctions.

In fish, polyunsaturated fatty acids (PUFAs) are essential structural elements in cellular membranes, participate in pathway regulation and act as important energy storage sources for optimum growth performance. However, they are also highly susceptible to peroxidation and thus potential oxidative damage. Omega-3 fatty acid content can vary among individuals and populations of fish and can therefore modulate their health status or resistance to oxidative stress. Our objective was to modulate [Formula: see text] omega-3 content in fish through different diets and estimate its impact on growth performance, overall fatty acid composition, oxidative stress parameters and antioxidant activity. We conducted experiments on juveniles (1⁺) of four salmonid groups: Arctic charr (Salvelinus alpinus), brook charr (Salvelinus fontinalis) and their reciprocal hybrids. We found that growth performance in the four groups was negatively affected by high dietary fatty acid content. The content of thiobarbituric acid reactive substances (TBARS, a marker of lipids peroxidation) significantly rose in Arctic charr when fed the omega-3-rich diet. It was also observed that individuals with high docosahexaenoic acid and low [Formula: see text] omega-6 content had lower TBARS content. Consequently, high omega-3/omega-6 ratios were accompanied by lower oxidative stress levels. This supports the utilization of omega-3/omega-6 ratios as a marker of the ability of fish to modulate oxidative stress both in the wild and in an aquaculture context. This will further help to predict responses to environmental or nutritional modifications.

Phenotypic plasticity is thought to be critical in allowing organisms to cope with environmental change, but the factors that limit this plasticity are poorly understood, which hampers predictions of species resilience to anthropogenic climate change. Here, we ask if limited plasticity in key traits constrains performance at high temperatures, using two California hatchery strains of rainbow trout (Oncorhynchus mykiss). Aerobic and anaerobic metabolic performance declined at a high but ecologically relevant acclimation temperature (24°C), suggesting performance cannot be maintained at this temperature, despite acclimation. Similarly, while both whole-organism thermal tolerance and hypoxia tolerance improved with acclimation to moderately elevated temperatures, compensation was limited at the highest acclimation temperature. These limits at the whole-organism level were aligned with limits at lower levels of biological organization. At the organ level, absolute scope to increase heart rate with acute warming (Δƒ_Hmax) did not increase between the upper two acclimation temperatures, and the safety margin for cardiac performance decreased at the highest acclimation temperature. At the cellular level, at 24°C, there were transcriptomic changes in the heart consistent with a cellular stress response. These limits across multiple levels of biological organization were observed under conditions that are ecologically relevant at the southern end of the species range, which suggests that thermal plasticity is likely insufficient to buffer rainbow trout against even modest anthropogenic warming in these regions.

[This corrects the article DOI: 10.1093/conphys/coaf005.].

Warming ocean temperatures can increase the metabolic rates of fishes, potentially contributing to changes in their growth and survival to recruitment age. During prolonged marine heatwave conditions in the Gulf of Alaska between 2014 and 2019, Pacific Cod (Gadus macrocephalus) metabolic rates may have increased, but little is known about the relationship between metabolism and temperature for immature individuals of this species. We examined the effect of prolonged temperature exposure (~1 year) on the performance (standard, routine, and maximum metabolic rates; critical swimming speed; and aerobic scope) and swimming efficiency (cost of transport and optimal swimming speed) of age-1 Pacific Cod during two laboratory experiments across a range of temperatures (Expt. 1: 2°C, 4°C, 6°C and 8°C; Expt. 2: 6°C, 10°C and 14°C). We also explored relationships between performance and additional body state variables (e.g. condition and growth) and environmental variables (e.g. photoperiod and salinity). Temperature did not influence baseline metabolic performance (standard and routine metabolic rates) in either experiment. However, we observed significantly higher baseline metabolic rates in Expt. 2 compared to Expt. 1, even at the same temperatures. In contrast, maximum performance metrics (e.g. maximum metabolic rate and critical swimming speed) were significantly influenced by temperature. These patterns in performance were generally explained by differing costs of transport and rates of oxygen consumption during swimming trials between the two experiments. Further, body state variables and environmental variables were poorly correlated with performance, even when combined in a multivariate framework. Together, these findings suggest that other factors, such as season, oceanographic conditions early in life, year-class effects, or epigenetic effects, may influence Pacific Cod metabolism more than temperature or measured body state variables and environmental variables following prolonged thermal acclimation.

Salmonid fishes are a focal point of conservation physiology due to their high value to humans and ecosystems, and their susceptibility to decline from climate change. A significant challenge in conserving these fishes is that populations of the same species can be locally adapted to vastly different habitats within their wild ranges and can therefore have unique tolerance or vulnerability to environmental stressors within those habitats. Within the state of Oregon, USA, summer steelhead (Oncorhynchus mykiss) inhabit both cool, coastal waters most typically associated with Pacific salmonids and arid, inland environments where temperatures are more extreme. Here, we utilized streamside physiological experiments paired with habitat temperature monitoring to assess the thermal tolerance and vulnerability of four populations of summer steelhead from distinct thermal habitats. All populations had unique responses of critical thermal maximum, aerobic scope and exercise recovery to temperature. Despite populations from warm habitats exhibiting higher thermal tolerance than populations from cooler habitats, summer steelhead from warm habitats appear to be more vulnerable to the physiological consequences of warming based on the extreme temperatures they already experience during the summer. These results demonstrate an example of thermal physiology varying between populations within the same portion of their latitudinal range and highlight the need for habitat-specific conservation strategies for this species.