Conservation Physiology最新文献

Climate change has resulted in increased incidence and variability of warming episodes in cold-water streams that support salmonids. The capacity to acclimate to warm temperatures may allow cold-water fish to persist in spite of changing thermal regimes, but accurately predicting fish performance under fluctuating stream temperatures also requires understanding re-acclimation to cool water, which is less well understood. We tested how thermal acclimation to warm temperatures and re-acclimation to cool water affected thermal tolerance and physiological endpoints in juvenile brook trout (Salvelinus fontinalis). We show that an initial thermal exposure (22°C, ΔT = 7°C) of 3, 7 and 14 days (but not 1 day) improved critical thermal maximum (CT_max) after a 14-day re-acclimation to cooler temperatures (15°C). Fish growth during the re-acclimation period decreased with increasing duration of initial thermal exposure (22°C). Physiological parameters associated with thermal acclimation (cortisol, glucose, haematocrit and haemoglobin) were lower at 15°C re-acclimation temperature than at the initial thermal treatment (22°C) and in some cases, lower than the 15°C control. Muscle HSP70 protein increased early (1 day) as part of the warm acclimation process and remained elevated at lower levels for up to 14 days. During re-acclimation to 15°C, HSP70 decreased relative to initial measures at 22°C. Fish exposed to the longest thermal treatment (22°C for 14 days) maintained elevated CT_max after 30 days of re-acclimation to 15°C without observed differences in the measured physiological endpoints but returned to control levels after 42 days at 15°C. This work shows that high-temperature acclimation effects in brook trout are retained for up to 30 days following re-acclimation to cool temperatures, and that isolated warming events may be expected to temporarily enhance thermal tolerance in subsequent thermal challenges.

Warming in high-latitude marine ecosystems is leading to the borealization of Arctic communities. Species-specific responses to temperature provide insight into potential co-occurrence or competitive advantage between Arctic and boreal species. Ocean acidification may also lead to unique species-specific responses. At the Pacific-Arctic interface, larval distributions of the boreal Pacific cod (Gadus macrocephalus) are increasingly overlapping with those of Arctic cod (Boreogadus saida). We assessed larval metabolic capacities by measuring metabolic enzyme activities of citrate synthase (CS; aerobic metabolism), lactate dehydrogenase (LDH; anaerobic metabolism), and β-hydroxyacyl CoA dehydrogenase (HOAD; fatty acid metabolism). Throughout early development, Pacific cod enzyme activities, including glycolytic capacity, were higher, and fatty acid metabolism lower than Arctic cod enzyme activities. These responses may reflect a more active larval lifestyle of Pacific cod. Separately, larvae were reared in multiple temperatures (Pacific cod: 3, 6, 10°C; Arctic cod 1.8, 5, 7.3°C) and pCO₂ levels (ambient = ~350 μatm; high = ~1500 μatm). At the cold temperature, Pacific cod enzyme activities were higher than at the control temperature, indicating they were acclimating but less cold adapted than Arctic cod. Arctic cod HOAD activity and LDH:CS ratio were elevated under warmer temperatures suggesting increased energy demand. Elevated pCO₂ levels only affected larvae at their control temperature and resulted in decreased Pacific cod HOAD activity and increased Arctic cod CS and HOAD activities. This indicates differing sensitivities to ocean acidification between the species. Overall, Pacific cod may continue to be constrained in their northern habitat by cold temperatures, but under slight warming to optimal growing temperatures, Pacific cod will have competitive advantage over Arctic cod.

Sea trout (Salmo trutta) migrate to the seawater (SW) for increased food availability. However, heavy infestations with salmon louse (Lepeophtheirus salmonis) can make them return to freshwater (FW). The aim of the present study was to map if and how reinfection with salmon louse and repeated FW exposure affects survival, growth rate, hepatosomatic index (HSI), acid base regulation (plasma pH, strong ion difference), osmoregulation (plasma ions, osmolality) and semen quality (fertilization rate, embryo/fry survival) in sea trout. Individually tagged sea trout (~100 g) were infected with louse copepodids in SW and then switched to FW at the louse pre-adult stage. Twelve days thereafter, FW was replaced with SW, and a second similar louse infection and salinity change were performed. Treatment groups were (i) uninfected control, and infected during the first (ii), second (iii) or both (iv) infection periods. The study ended after a final three-month follow-up in FW involving egg fertilization with sperm of previously infected and uninfected control mature male trout. Lice infection did not affect fish mortality or semen quality, but elevated HSI. In SW, lice-infected fish had lower specific growth rate in weight, higher plasma pH, Na⁺, Cl^- and osmolality, and lower plasma strong ionic difference and Na⁺/Cl^- ratio compared to uninfected fish. After 48 h in FW, lice-infected fish still had higher plasma pH, while plasma Na⁺, Cl^- and osmolality were lower and plasma Na⁺/Cl^- ratio higher in infected than uninfected fish. Louse reinfection did not affect any end points compared to single infection. The results demonstrate that salmon louse disturbs sea trout's Cl^- more than Na⁺ regulation, resulting in reduced hypo-osmotic and hyper-osmotic abilities in SW and FW, respectively. Further, a strong effect of lice on acid-base regulation is evident, shown by elevated plasma pH in both SW and FW.

Rivers are under intense anthropogenic pressure, leading to increases in water temperature and changes in physicochemical properties, which threaten aquatic biota. Understanding how these environmental changes affect heat tolerance in freshwater organisms is critical for assessing the status of wild populations and predicting their vulnerability under global warming scenarios. Here, we studied how body mass and heat tolerance, measured by thermal death time (TDTs) curves under normoxic and hypoxic conditions, vary among populations of the Chilean pencil catfish Trichomycterus areolatus inhabiting a Mediterranean river in central Chile. We detected significant differences in fork length, body mass and Fulton's condition factor among populations, with fish from reference sites being significantly larger and in better condition. Although heat tolerance did not differ among populations, we found a strong effect of body mass under both normoxic and hypoxic experimental conditions. Simulations combining laboratory-derived TDTs with field-recorded water temperatures suggest that the window of vulnerability occurs at lower temperatures but over longer exposures, indicating that heat stress has chronic effects on T. areolatus. Accordingly, the cumulative survival simulation using the warmer season records is predicted to be lower in river sections with reduced levels of dissolved oxygen. While our results did not show population level differences in thermal tolerance per se, the significant effect of individual body mass may translate into varying vulnerability among populations, given their marked differences in body mass distribution. These findings highlight how the interplay between water quality, body condition and heat tolerance shapes the vulnerability of T. areolatus populations to warming. Thus, an integrated perspective is essential to properly assess the impact of global warming on wild freshwater populations.

Anthropogenically induced environmental change has contributed to population declines of important estuarine species, such as oysters. Some restoration programs focused on severely depleted oyster populations in estuarine environments are using hatchery-sourced animals to supplement low wild recruitment. However, carry-over effects, when early life experiences affect later life responses, are known to affect the success of cultured individuals in the wild. The objective of this study was to investigate carry-over effects on eastern oyster (Crassostrea virginica) larvae cultured under a range of salinities-an important environmental stressor on natural populations. Eastern oyster larvae were grown and settled across a range of salinities until large enough to transplant onto two field sites with different average salinities. Larval culture salinity significantly affected post-metamorphosed oyster growth rates until 45 days post-set, where oysters from suboptimal low salinity cultures grew faster immediately post-metamorphosed. Later, larval culture salinity significantly affected oxygen consumption rates and condition index of oysters from the field, and field site significantly interacted with larval culture salinity on physiological metrics. High larval salinity cultures produced oysters with lower energetic expenditures and higher condition index values, on average. Long-term physiological performance of animals depended on both the early culture environment and the subsequent field conditions, and because of the interaction of culture conditions and transplant site, care should be taken to select culture conditions that match those at target relocation sites.

As part of its mission to advance the field of wildlife endocrinology, the International Society of Wildlife Endocrinology aims to develop cost-effective antibodies and enzyme immunoassay kits that support research across a diverse range of species and sample matrices. To provide additional options for the quantification of faecal glucocorticoid metabolites (fGCMs), an antibody against 11-oxoetiocholanolone-17-carboxymethyl oxime (CMO) was generated in rabbits, and an enzyme immunoassay incorporating a horseradish peroxidase-conjugated label and 11-oxoetiocholanolone standard has been developed, designed for use with anti-rabbit IgG secondary antibody coated plates. This mini-kit was used to quantify glucocorticoid metabolites with a 5β-3α-ol-11-one structure in faecal extracts from 23 species: African and Asian elephants, Alpine chamois, American bison, Bengal tiger, blue wildebeest, blue-and-yellow macaw, brushtail possum, cape buffalo, fat-tailed dunnart, Florida manatee, ghost bat, giraffe, golden langur, Gould's wattled bat, hippopotamus, Leadbeater's possum, mandrill, okapi, roan antelope, samango monkey, short-beaked echidna, and western lowland gorilla. Pharmacological (adrenocorticotropic hormone challenge) and biological (inter-zoo translocation, wild capture, social disruption, illness/injury and veterinary intervention) challenges resulted in expected increases in fGCM concentrations, and in a subset of species, closely paralleled results from a previously established immunoassay against 11-oxoetiocholanolone-17-CMO. Two additional species tested, Krefft's glider, which showed contradictory results on this assay compared to a previously validated enzyme immunoassay (EIA) and Ankole cow, where the magnitude increase post-event did not quite reach the 2-fold change criteria, highlight that differences in excreted faecal metabolites across species mean that no EIA will be suitable for all species. This assay provides a valuable new option for assessing adrenal activity across taxa using a group-specific antibody. Future studies should put similar emphasis on validation to determine optimal assay choice for measuring fGCMs in a variety of species.

Manually obtaining the length and other morphometric features of an animal can be time-consuming, and consistent measurements are challenging with large datasets. By leveraging high-throughput computing power and machine learning-based computer vision, such phenotypic data can be rapidly collected with high accuracy. Here we present HusMorph, a novel application with a simple and intuitive graphical user interface (GUI), based on the same machine learning method used in other pipelines such as ML-morph. It consists of an all-in-one package with the goal of making machine learning easy to use for non-experts. The user starts by setting any number of landmarks on a set of photos captured with a standardized setup. From this set, a machine learning model is generated by automatically and randomly searching for the best performing parameters. Next, the user can apply the model to predict landmarks on new standardized photos and visually confirm and export the results of the predictions. For measuring length between landmarks, an additional feature allows for detecting a scale bar for each photo to convert the length from pixels to a metric unit. Our application has been validated and applied to extract standard length from 1935 photos of zebrafish and performs with ~99.5% accuracy compared to manual measurements.

Estuarine environments are characterized by fluctuating abiotic conditions, such as salinity and oxygen partial pressure, which challenge the physiological systems of resident species. Organisms inhabiting these systems have evolved physiological plasticity to cope with this variability, particularly in relation to oxygen availability. Estuarine species tend to exhibit greater hypoxia tolerance compared to coastal marine species, likely due to periodic low oxygen exposure. However, the effects of salinity fluctuations on oxygen transport remains unclear. This study investigated the effects of different salinity levels on the oxygen supply capacity of the Atlantic stingray (Hypanus sabinus), a euryhaline elasmobranch in the temperate west Atlantic and Gulf of Mexico. Maximum metabolic rates and oxygen supply capacity were measured at high, medium and low salinities (32, 16 and 6 psu, respectively). Critical oxygen pressure (P _cMax), where maximum metabolism and aerobic scope become oxygen limited, was also calculated. Results showed a significant 20% increase in oxygen supply capacity and a 30% decrease in P _cMax under low salinity compared to high salinity. These findings suggest that Atlantic stingrays improve their oxygen supply capacity and are more hypoxia tolerant in hyposaline conditions. Enhanced oxygen supply capacity may represent an adaptive strategy, enabling Atlantic stingrays to maintain metabolic performance in low oxygen environments. This study provides novel insight into the adaptive capacity of euryhaline elasmobranchs to balance oxygen transport and metabolic function across salinity gradients. It highlights the importance of physiological plasticity in estuarine species' responses to climate-driven changes in salinity and oxygen availability. These findings can inform management strategies by identifying species with greater resilience to hypoxia and salinity shifts, supporting more effective conservation efforts under future climate scenarios.

For aerial insectivorous birds, whose populations have declined significantly in North America, long-chain polyunsaturated fatty acids (LC-PUFA) that are more abundant in aquatic-emergent insects than terrestrial insects, are important for the development, somatic growth, and health of young birds. Some bird species, however, can convert shorter chain PUFA that occur abundantly in terrestrial insects into LC-PUFA. Our study aimed to evaluate the ability of two aerial insectivore species to synthesize their own LC-PUFA. We hypothesized that terrestrially associated aerial insectivores rely on higher fatty acid conversion rates compared to those associated with wetlands and riparian habitats. We fed wild barn swallow (Hirundo rustica) and purple martin (Progne subis) nestlings ¹³C-labelled essential omega-3 (α-linolenic acid; ALA) or omega-6 (linoleic acid; LA) fatty acids to trace internal fatty acid conversion from these dietary precursors. Using compound-specific stable isotope measurements of livers, we estimated conversion efficiency to LC-PUFA. Barn swallow nestlings converted 76% of the omega-3 ALA and 46% of the omega-6 LA precursors to LC-PUFA. Purple martin nestlings converted 88% of the ALA and 44% of the LA. Both species converted five times more ALA to DHA than previously reported in tree swallows (Tachycineta bicolor) and may be more adapted to fluctuations in diet quality and habitat types. Our research highlights the variability in conversion efficiency within the guild of aerial insectivores and the need to better understand which species may be less resilient to sudden changes in nutritional landscapes.