Conservation Physiology最新文献

Assessing how at-risk species respond to co-occurring stressors is critical for predicting climate change vulnerability. In this study, we characterized how young-of-the-year White Sturgeon (Acipenser transmontanus) cope with warming and low oxygen (hypoxia) and investigated whether prior exposure to one stressor may improve the tolerance to a subsequent stressor through "cross-tolerance". Fish were acclimated to five temperatures within their natural range (14-22°C) for one month prior to assessment of thermal tolerance (critical thermal maxima, CTmax) and hypoxia tolerance (incipient lethal oxygen saturation, ILOS; tested at 20°C). White Sturgeon showed a high capacity for thermal acclimation, linearly increasing thermal tolerance with increasing acclimation temperature (slope = 0.55, adjusted R² = 0.79), and an overall acclimation response ratio (ARR) of 0.58, from 14°C (CTmax = 29.4 ± 0.2°C, mean ± S.E.M.) to 22°C (CTmax = 34.1 ± 0.2°C). Acute warming most negatively impacted hypoxia tolerance in 14°C-acclimated fish (ILOS = 15.79 ± 0.74% air saturation), but prior acclimation to 20°C conferred the greatest hypoxia tolerance at this temperature (ILOS = 2.60 ± 1.74% air saturation). Interestingly, individuals that had been previously tested for thermal tolerance had lower hypoxia tolerance than naïve fish that had no prior testing. This was particularly apparent for hypoxia-tolerant 20°C-acclimated fish, whereas naïve fish persisted the entire 15-h duration of the hypoxia trial and did not lose equilibrium at air saturation levels below 20%. Warm-acclimated fish demonstrated significantly smaller relative ventricular mass, indicating potential changes to tissue oxygen delivery, but no other changes to red blood cell characteristics and somatic indices. These data suggest young-of-the-year White Sturgeon are resilient to warming and hypoxia, but the order in which these stressors are experienced and whether exposures are acute or chronic may have important effects on phenotype.

Freshwater fishes are increasingly facing extinction. Some species will require conservation intervention such as habitat restoration and/or population supplementation through mass-release of hatchery fish. In California, USA, a number of conservation strategies are underway to increase abundance of the endangered Delta Smelt (Hypomesus transpacificus); however, it is unclear how different estuarine conditions influence hatchery fish. The goal of this study was to evaluate a year of Delta Smelt field deployments to inform species conservation strategies of suitable conditions for smelt physiology. Hatchery-reared Delta Smelt was deployed in experimental cages (seven deployments) throughout the Estuary in the winter, summer and fall of 2019. Effects of season and location of cage deployments on fish health (condition factor and histological condition of liver and gill), growth, thermal tolerance and survival were evaluated. The results indicate both seasonal and location differences, with high survival in the winter (100%) and fall (88-92%) compared to lower survival in summer (67%). In the summer, one of the study sites had no surviving fish following high temperature exposure, which peaked ~26°C. After 29 days in the cages, surviving Delta Smelt in summer and fall showed signs of nutritional stress that may be related to biofouling of the cages limiting passive food inputs, restriction of natural foraging behaviour by containment in the cages, and water temperatures that were too high given the chronically low pelagic productivity in the Estuary overall. Field measurements of upper thermal tolerance (CTmax) following caging exposures suggest that laboratory measures of CTmax may overestimate the realized tolerance in a more stochastic field environment. This study demonstrates the utility of using cages as an experimental tool to better understand aspects of Delta Smelt physiological responses to environmental changes across estuarine habitats in a more natural-field setting, while also highlighting potential limitations of using cages.

The physiological performance of ectotherms is influenced by temperature, raising concerns about the impact of global warming on ectotherms. Understanding the relationship between ecologically relevant temperatures and the physiological performance of ectotherms provides a basis for assessing their resilience to changing environments. Absolute aerobic scope (AAS) is a functional metric of the thermal performance of aquatic ectotherms. The thermal profile of chum salmon (Oncorhynchus keta) returning to the Kitakami River, Japan, in early October has already been explored in a previous study; however, the ecological aspects of their upriver migration (e.g. spawning site, migratory duration and experienced temperature) and their connection to AAS thermal profiles are not fully understood. To address this gap, we released 53 marked chum salmon throughout the spawning season (October-November), of which 48 were tracked using radio telemetry. Over 3 years, 18 were successfully tracked to their spawning sites, and 13 were tracked partway. The longest track was 93 km. The spawning sites of Kitakami River chum salmon depended on migration timing, with earlier run salmon tending towards upriver sites. Chum salmon returning in October spawned in the middle basin, typically requiring >5 days to reach the spawning sites, whereas those returning in November spawned in the lower sections in 1-3 days. Comparing the estimated thermal occupancy of migrating salmon with the published AAS profile, we found that Kitakami River chum salmon in early October spent almost all of their time within the optimal temperature window for AAS and tended to be below the peak temperature of AAS. Our findings provide a basis for the ecological features of migrating chum salmon in rivers and shed light on their aerobic thermal performance in the natural environment.

Monitoring physiological indicators including heart rate (HR) is crucial for managing animal welfare across diverse settings, from precision livestock farming to wildlife conservation. HR is a reliable indicator of energy expenditure and stress, yet the invasive nature of HR loggers limits their application in wild and free-ranging species. This study explores whether overall dynamic body acceleration (ODBA), measured with an external accelerometer, can serve as a less invasive proxy for HR. Using free-ranging cattle as a model species in Norway, we examined the relationship between ODBA and HR to assess how external accelerometry might indirectly reflect physiological states in settings that resemble wild conditions. Cattle provide an ideal model because they share some characteristics with wild herbivores, including exposure to diverse terrain and potential predation, whilst offering advantages for handling and sensor retrieval. Our findings showed that low ODBA values corresponded to static behaviours (e.g. standing, ruminating), where small movements caused HR spikes, whilst higher ODBA reflected dynamic activities (e.g. walking, foraging), with HR plateauing. This relationship suggests that ODBA can be used to approximate HR in environments where direct HR measurement is challenging. By using accelerometry to infer HR changes in free-ranging cattle, this study offers insights that could extend to wild species, offering a tool for conservationists to monitor and manage animal health and well-being less invasively.

Environmental factors play an important role in phenotypic development of fishes, which has implications for hatchery-reared fishes that are released into the wild where natural cues are present. There is interest in examining how early exposure to dietary odourants can affect development of olfaction. The aim of our study was to use behavioural, molecular and electro-physiological techniques to evaluate how introduction of the amino acid L-alanine to the rearing environment might influence the development of olfactory perception of dietary cues, growth and survival in lake sturgeon (Acipenser fulvescens), a species of conservation concern. We hypothesized that exposure to amino acids would influence the onset of feeding during dietary transitions from endogenous to exogenous feeding and predicted that the introduction of L-alanine during early development would promote growth and survival of age-0 lake sturgeon. Additionally, we hypothesized that olfaction in lake sturgeon is a developmentally plastic trait, predicting that the addition of L-alanine prior to exogenous feeding would influence mRNA transcript abundance of genes associated with detection of dietary cues. Our approach was to add L-alanine daily from 17 to 20 days post-fertilization (DPF) before the onset of exogenous feeding. We sampled individuals at 17, 21, 26, 31, 50, 65 and 80 DPF. Additionally, olfactory sensitivity to L-alanine was tested at ~1 year via electro-olfactogram (EOG). We observed no significant differences in mortality or EOG response between L-alanine and control treatments; however, significant differences were observed in morphometrics, behaviour and mRNA transcript abundance of all genes throughout development. Our results indicated the olfactory system exhibited developmental plasticity in response to L-alanine treatment until 50-65 DPF, suggesting that environmental odourants may influence early development of key olfactory processes. Our data could inform practises at conservation hatcheries that are used as part of enhancement programmes for lake sturgeon.

Coastal estuaries globally, including the San Francisco Estuary (SFE), are experiencing significant degradation, often resulting in fisheries collapses. The SFE has undergone profound modifications due to population growth, industrialization, urbanization and increasing water exports for human use. These changes have significantly altered the aquatic ecosystem, favouring invasive species and becoming less hospitable to native species such as the longfin smelt (Spirinchus thaleichthys). With longfin smelt abundance declining to <1% of historical numbers, there is a pressing need for laboratory-based experiments aimed at investigating the effects of varying environmental conditions on their stress response and physiology. This study explored the impact of temperature (11 and 14°C) and turbidity maintained with algae (1, 4 and 11 nephelometric turbidity units (NTU)) on the physiological condition of juvenile longfin smelt. Fish were sampled after 2 and 4 weeks in experimental conditions and analysed for whole-body cortisol, glucose, lactate and protein. Condition factor was calculated using length and weight measurements. Critical thermal maximum trials were conducted to assess how prior rearing conditions affected upper thermal tolerance. Cortisol levels were significantly higher in fish held in low-turbidity conditions, whilst glucose levels were significantly greater at lower temperatures and higher turbidities. Protein-to-mass ratios were significantly greater in higher turbidity conditions, with a significant interaction between temperature and turbidity further influencing these ratios. Moreover, 14°C led to diminished condition factors but increased upper thermal tolerances (26.3 ± 0.05 vs 24.6 ± 0.18) compared to longfin smelt at 11°C, highlighting a potential trade-off between the induction of defense mechanisms and subsequent reductions in energy and growth. Data suggest that cooler temperatures (11°C) and elevated turbidities (11 NTU) can benefit juvenile longfin smelt by reducing stress and enhancing growth and energy. These findings hold significant implications for informing and optimizing future endeavours in the culturing and conservation of this species.

Leatherback turtles (Dermochelys coriacea) are endangered by anthropogenic threats. Characterizing the physiologic response of leatherback turtles under various stressors may inform conservation strategies. In this study, a commercially available enzyme immunoassay for aldosterone was validated for leatherback turtle plasma, and it was used with previously validated assays for corticosterone and free thyroxine (fT4) to evaluate the physiologic status of leatherback turtles that were entangled in fishing gear, stranded on shore, nesting or intentionally captured at sea during ecologic studies. Mean aldosterone concentrations were significantly higher in entangled turtles (156 ± 102 pg/ml), stranded turtles (274 ± 165 pg/ml) and intentionally captured turtles (457 ± 464 pg/ml) than in nesting females (23 ± 16 pg/ml). In contrast, nesting females had higher fT4 (2.9 ± 0.6 pg/ml) compared to entangled turtles (0.8 ± 0.9 pg/ml), stranded turtles (0.7 ± 0.8 pg/ml) and intentionally captured turtles (0.3 ± 0.2 pg/ml). Corticosterone concentrations were significantly higher in stranded individuals (10.9 ± 6.6 ng/ml) compared with nesting (3.8 ± 2.0 ng/ml) and intentionally captured turtles (3.6 ± 2.5 ng/ml), with intermediate levels in entangled turtles (5.1 ± 2.8 ng/ml). This study provides additional insight into the variable physiologic status of leatherback turtles under the influence of different anthropogenic and natural stressors, and it provides an additional tool to evaluate the role of aldosterone in the acute stress response and health of endangered sea turtle species.

Modern production-oriented farming has led to a decline in agricultural biodiversity. In Europe, one example of concern is the common hamster Cricetus cricetus, a hibernating rodent once largely distributed in farmlands and now listed as Critically Endangered. The decline of this species is tied to a significant decrease in hamsters' body mass at emergence from hibernation and in reproduction rate. Previous work has shown that monocultures of maize and wheat, which induce severe nutrient deficiencies, are a major cause of this phenomenon. To prevent such deficiencies, we tested in controlled conditions the effect of eight nutritive diets on hamsters' hibernation and reproduction. Diets were selected for their nutritional content and based on farmers' consultation. We tested three lipid-rich associations ('oat-sunflower', 'potato-sunflower' and 'buckwheat-sunflower'), two protein-rich associations ('maize-bean' and 'maize-pea') and an intermediate association ('wheat-soybean'), as well as 'sprouted wheat' and 'sugar beet'. Hamsters fed the lipid-rich diets showed a better body condition at the end of hibernation. However, a low reproductive success was recorded in all groups, with only 17% of reproductive trials leading to birth. Nonetheless, the amount of protein ingested by the mothers before reproduction increased birth probability whilst pups' survival to weaning was positively correlated to mothers' body condition. Overall, our results show that hamsters need a balanced diet to ensure their ability to reproduce. Indeed, low-protein diets led to lower birth rates and low-lipid diets led to reduced body condition and subsequently low pups' survival. The 'wheat-soybean' association best fulfilled hamsters' nutritional needs. Overall, these results highlight the need to improve current farming practices to provide a more fulfilling nutritional environment for common hamsters and the farmland fauna.