Conservation Physiology最新文献

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.

Techniques for using natural anti-predator cues to guide the movements of animals and reduce human-wildlife conflict are highly desired. With continuous use, sensory adaptation, habituation and adaptive behavioural changes often reduce the efficacy of sensory deterrents. Theory suggests responses can be maintained with application practices that modulate the stimulus in time (on/off) or by continuously varying stimulus intensity. In aquatic environments, damage-released alarm cues from injured conspecifics are a reliable source of information regarding predation risk that can be used to guide the movements of invasive fishes. We used sea lampreys, Petromyzon marinus, drawn from an invasive population, to investigate whether modulating alarm cue exposure (on/off) or varying cue concentration during continuous exposure (low/high) would forestall predicted declinations in swim activity and spatial avoidance. We found that continuous exposure to alarm cue at a fixed concentration resulted in the predicted decline in swim activity. Modulating odour exposure timing (on/off) partially prevented response declination in swim activity, whereas varying odour concentration (low/high) fully prevented the reduction. We did not observe the previously reported habituation of the spatial avoidance response, likely due to the use of a small high-throughput assay system. Our results suggest modulating alarm cue exposure by varying odour concentration to prevent response declination holds promise as a management practice. Moreover, test systems for developing management practices should be carefully matched to the scale of the behavioural response being investigated.

Plant conservation programs strive to integrate information from various life-history stages of focal species when developing holistic recovery strategies. Therefore, in-depth knowledge of the seed-to-seedling transition, a crucial phase that begins with the germination process, provides key perspectives that support recovery. Analyses of seed functions (e.g. germination timing) and related traits (e.g. germination rate, temperature requirements, stress tolerance) in response to selective pressures (e.g. temperature) can fill key knowledge gaps for the seeds of most at-risk plants. Here, we investigated the germination ecology of Harperocallis flava, a rare, globally imperilled, federally and state endangered (government protected) species from Florida, USA. We tested the germination of fresh seeds from three habitats collected over 3 years following exposure to simulated seasonal temperatures of winter (day/night temperatures of 20/10°C), early spring/late fall (25/15°C), early fall/late spring (30/20°C), or summer (35/25°C). We quantified the germination response of H. flava seeds to habitat of origin, seasonal temperature and collection year to determine how these factors influence germination dynamics and to inform seed-based conservation of this and other rare species. Considerable variation in germination responses was observed among the temperature treatments, seed collection years and habitats. Germination tended to be lower at simulated summer temperatures and higher at winter and late fall/early spring temperatures, which suggests that germination in the wild likely occurs in the period following natural shedding while temperatures are below 30°C (i.e. late fall through early spring). Moreover, the spatiotemporal variation of the germination responses highlights the value of basing conservation recommendations on multi-year, multi-population seed biology research when possible.

Given the imminent threat of global warming and rising water temperatures in Austria, this study investigated the effects of elevated temperature on gene expression, energy reserves, and cellular energy status in brown trout (Salmo trutta), a species particularly sensitive to increasing water temperature. A total of 250 fish were placed in four stream channels under flow-through conditions. Two channels were maintained at 9 °C as controls, while the other two had their temperature gradually increased to 20 °C over seven days and then maintained at 20 °C for 21 days. Sampling was conducted on day 1, after the temperature reached 20 °C, and the last day of high-temperature exposure on day 21. At each sampling point growth, hepatosomatic index and the fat content of the viscera were measured and/or calculated, and liver samples were taken for gene expression and metabolite analyses. Elevated temperature significantly increased the expression of genes related to cellular stress response (hsp70, hsp90 aa1, cat, and casp8) compared to controls. However, there was no significant difference in the expression of genes associated with lipid and carbohydrate metabolism (d5fad and pfkfb4). Furthermore, there was a decrease in energy storage indicated by a decrease in the hepatosomatic index, glycogen, triglycerides and ATP in the liver as well as the fat content of the viscera. Cellular energy status also significantly decreased, as indicated by the calculated adenylate energy charge. Physiologically, this culminated in suppression of growth in the treatment group after 21 days. This study shows that elevated temperature leads to significant trade-offs in brown trout, which may lead to ecological consequences over the long run. These findings offer critical insights into the physiological impacts of elevated temperature that help evaluate the species' acclimation to rising water temperature and inform the development of effective conservation strategies in a warming world.

Noninvasive faecal hormone analyses can provide valuable information on the physiological state of wild animals and how they respond to ecological changes or anthropogenic disturbances. However, preservation techniques to prevent hormone alteration can be problematic, and not all are field friendly. We compared five processing methodologies to preserve samples for faecal glucocorticoid, progestagen and thyroid hormone metabolites. Samples were collected from adult zoo Africa savanna elephants (Loxodonta africana) (one male, four females) immediately after defecation. Subsamples were then subjected to five preservation methods: lyophilisation (LYO) (considered the gold standard), dehydration, solid-phase extraction (SPE) and two ethanol extraction methods-with and without being immediately dried down. Faecal glucocorticoid, progestagen and thyroid hormone metabolites were quantified by validated enzyme immunoassays. After 7 days at room temperature (to emulate shipping conditions), faecal glucocorticoid metabolite concentrations were lower for all methods compared to LYO. For thyroid hormone metabolite concentrations, the dehydration process resulted in higher concentrations compared to LYO, whereas with SPE, concentrations were lower. For faecal progestagen metabolite concentrations, there were no discernible differences across methods. Based on these results, we recommend ethanol extraction followed by immediate sample desiccation, a method that combines technical simplicity with the advantage of ambient temperature sample storage and transportation. Nevertheless, each investigator should consider the best method for the research question, field conditions, budget, equipment accessibility and shipping requirements, especially as results can vary by species and assay used. With growing interest in assessing animal welfare, validating field methods for noninvasive hormone monitoring is essential.

The Gulf of Mexico represents the largest ecological barrier between breeding and non-breeding grounds for long-distance migratory songbirds in the Nearctic-Neotropical system. Despite the prominence of the Gulf of Mexico, there are still gaps on fundamental physiological aspects of stopover of migrants in this region, including the role and relative importance of fat and lean mass depletion and deposition. We examined the arrival body condition of Nearctic-Neotropical migrants at a coastal stopover site on St. George Island, FL, in the northern Gulf of Mexico during pre-breeding migration in the spring of 2016-2018. We precisely determined lean body and fat masses on individual birds after a trans-Gulf migratory flight via quantitative magnetic resonance (QMR) technology. We hypothesized that birds with non-breeding ranges in South America would arrive with lower fat and lean masses than birds with non-breeding ranges in the Caribbean or Central America. We also hypothesized that songbirds would increase lean mass at a greater rate than fat mass, as they rebuilt muscle and organ masses. We also compared QMR lean and fat measurements to visual measures of fat and muscle scores. A total of 44 Nearctic-Neotropical migratory bird species occur on St. George Island during spring stopover. Non-breeding range did not influence the arrival fat mass or arrival lean mass in 10 focal transient species, meaning those that have no breeding or non-breeding populations on the site. Our results from recaptured individuals indicated that body mass increase during stopover derives from both lean and fat mass accumulation. Our results provide a robust quantitative assessment of songbird arrival body condition on the northern Gulf of Mexico and contribute to the understanding of the physiology of migratory songbirds after a long-distance flight, which will help inform management decisions for stopover sites located around ecological barriers.

Marine heatwaves occurring against the backdrop of rising global sea surface temperatures have triggered mass coral bleaching and mortality. Irradiance is critical to coral growth but is also an implicating factor in photodamage, leading to the expulsion of symbiotic algae under increased temperatures. Numerical modelling is a valuable tool that can provide insight into the state of the symbiont photochemistry during coral bleaching events. However, very few numerical physiological models combine the influence of light and temperature for simulating coral bleaching. The coral bleaching model used was derived from the coral bleaching representation in the eReefs configuration of the CSIRO Environmental Modelling Suite, with the most significant change being the equation for the rate of detoxification of reactive oxygen species. Simulated physiological bleaching outcomes from the model were compared to photochemical bleaching proxies measured during an ex situ moderate degree-heating week (up to 4.4) experiment. The bleaching response of Acropora divaricata was assessed in an unshaded and 30% shade treatment. The model-simulated timing for the onset of bleaching under elevated temperatures closely corresponded with an initial photochemical decline as observed in the experiment. Increased bleaching severity under elevated temperature and unshaded light was also simulated by the model, an outcome confirmed in the experiment. This is the first experimental validation of a temperature-mediated, light-driven model of coral bleaching from the perspective of the symbiont. When forced by realistic environmental conditions, process-based mechanistic modelling could improve accuracy in predicting heterogeneous bleaching outcomes during contemporary marine heatwave events and future climate change scenarios. Mechanistic modelling will be invaluable in evaluating management interventions for deployment in coral reef environments.