Conservation Physiology最新文献

The thermally dynamic nearshore Beaufort Sea, Alaska, is experiencing climate change-driven temperature increases. Measuring thermal tolerance of broad whitefish (Coregonus nasus) and saffron cod (Eleginus gracilis), both important species in the Arctic ecosystem, will enhance understanding of species-specific thermal tolerances. The objectives of this study were to determine the extent that acclimating broad whitefish and saffron cod to 5°C and 15°C changed their critical thermal maximum (CT_max) and HSP70 protein and mRNA expression in brain, muscle and liver tissues. After acclimation to 5°C and 15°C, the species were exposed to a thermal ramping rate of 3.4°C · h^-1 before quantifying the CT_max and HSP70 protein and transcript concentrations. Broad whitefish and saffron cod acclimated to 15°C had a significantly higher mean CT_max (27.3°C and 25.9°C, respectively) than 5°C-acclimated fish (23.7°C and 23.2°C, respectively), which is consistent with trends in CT_max between higher and lower acclimation temperatures. There were species-specific differences in thermal tolerance with 15°C-acclimated broad whitefish having higher CT_max and HSP70 protein concentrations in liver and muscle tissues than saffron cod at both acclimation temperatures. Tissue-specific differences were quantified, with brain and muscle tissues having the highest and lowest HSP70 protein concentrations, respectively, for both species and acclimation temperatures. The differences in broad whitefish CT_max between the two acclimation temperatures could be explained with brain and liver tissues from 15°C acclimation having higher HSP70a-201 and HSP70b-201 transcript concentrations than control fish that remained in lab-acclimation conditions of 8°C. The shift in CT_max and HSP70 protein and paralogous transcripts demonstrate the physiological plasticity that both species possess in responding to two different acclimation temperatures. This response is imperative to understand as aquatic temperatures continue to elevate.

Upper thermal limits in many fish species are limited, in part, by the heart's ability to meet increased oxygen demand during high temperatures. Cardiac plasticity induced by developmental temperatures can therefore influence thermal tolerance. Here, we determined how incubation temperatures during the embryonic stage influence cardiac performance across temperatures during the sensitive larval stage of the imperiled longfin smelt. We transposed a cardiac assay for larger fish to newly hatched larvae that were incubated at 9°C, 12°C or 15°C. We measured heart rate over increases in temperature to identify the Arrhenius breakpoint temperature (T_AB), a proxy for thermal optimum and two upper thermal limit metrics: temperature when heart rate is maximized (T_peak) and when cardiac arrhythmia occurs (T_Arr). Higher incubation temperatures increased T_AB, T_peak and T_Arr, but high individual variation in all three metrics resulted in great overlap of individuals at T_AB, T_peak and T_Arr across temperatures. We found that the temperatures at which 10% of individuals reached T_peak or T_Arr and temperatures at which number of individuals at T_AB relative to T_peak (ΔN(T_AB,T_peak)) was maximal, correlated more closely with upper thermal limits and thermal optima inferred from previous studies, compared to the mean values of the three cardiac metrics of the present study. Higher incubation temperatures increased the 10% T_peak and T_Arr thresholds but maximum ΔN(T_AB,T_peak) largely remained the same, suggesting that incubation temperatures modulate upper thermal limits but not T_opt for a group of larvae. Overall, by measuring cardiac performance across temperatures, we defined upper thermal limits (10% thresholds; T_peak, 14.4-17.5°C; T_Arr, 16.9-20.2°C) and optima (ΔN(T_AB,T_peak), 12.4-14.4°C) that can guide conservation strategies for longfin smelt and demonstrated the potential of this cardiac assay for informing conservation plans for the early life stages of fish.

Obtaining endocrinological profiles using non-invasive methodologies by the measurement of hormone fecal metabolites is a widely used method to monitor ovarian activity and pregnancy in wild species. These tools allow the obtention of physiological information without causing capture-related stress on the individuals. In this research, we aimed to 1) biologically validate a non-invasive method to assess fecal progestagens and estrogens fluctuations during gestation in guanacos (Lama guanicoe) and 2) apply this technique to assess pregnancy in a wild free-ranging population. Fecal samples were collected through the gestation period (~12 months) of female guanacos in a 6.5-ha paddock. An increase in fecal metabolites of both hormones was detected. Progestagens increased gradually, in contrast to estrogens, which remained at basal values for most of the gestation period and peaked only a few days before calving. To assess pregnancy in wild free-ranging animals, fecal samples were collected from a population of La Payunia provincial reserve (Mendoza, Argentina) during the beginning of gestation and at the end of gestation. Through the first months of possible gestation, pregnant females represented between 40 and 80% of the population; at the end of gestation, only 20-40% of the females had confirmed pregnancies. Our results demonstrated that the polyclonal antisera and sexual hormone metabolite assays used here detect variations in the metabolites excreted through feces in guanacos and provide the possibility of non-invasive hormone monitoring of female reproductive status. Also, the findings in wild conditions suggest that natural abortions could have occurred during the first months of gestation. Although some abortions may be natural, the harsh environmental conditions that challenge the support of such a long gestational process may be another relevant factor to consider. The results obtained here enhance our understanding of the reproductive physiology of one of the most emblematic ungulates in South America.

Climate changes pose risks for bumblebee populations, which have declined relative to the growing frequency and severity of warmer temperature extremes. Bumblebees might mitigate the effects of such extreme weather through colonial behaviours. In particular, fanning behaviour to dissipate heat is an important mechanism that could reduce exposure of thermally sensitive offspring to detrimental nest temperatures (T_n). The allocation of workers towards fanning over prolonged periods could impact foraging activity that is essential for colony-sustaining resource gathering. Colony maintenance and growth could suffer as a result of nutritional and high ambient temperature (T_a) thermal stress. It remains uncertain whether a compromise occurs between thermoregulation and foraging under chronic, sublethal heat events and how colony success is impacted as a result. This study held colonies of Bombus impatiens at constant high T_a (25°C, 30°C or 35°C) for 2 weeks while quantifying the percentage of foragers, fanning incidence, nest temperature (T_n) and other metrics of colony success such as the percentage of adult emergence and offspring production. We found that foraging and adult emergence were not significantly affected by T_a, but that thermoregulation was unsuccessful at maintaining T_n despite increased fanning at 35°C. Furthermore, 35°C resulted in workers abandoning the colony and fewer offspring being produced. Our findings imply that heatwave events that exceed 30°C can negatively impact colony success through failed thermoregulation and reduced workforce production.

The Pace-of-Life syndrome proposes that behavioural, physiological and immune characteristics vary along a slow-fast gradient. Urbanization poses several physiological challenges to organisms. However, little is known about how the health status of frogs is affected by urbanization in the Tropics, which have a faster and more recent urbanization than the northern hemisphere. Here, we analysed a suite of physiological variables that reflect whole organism health, reproduction, metabolic and circulatory physiology and leukocyte responses in Leptodactylus podicipinus. Specifically, we tested how leukocyte profile, erythrocyte morphometrics and germ cell density, as well as somatic indices and erythrocyte nuclear abnormalities differ throughout the adult life span between urban and rural populations. We used Phenotypic Trajectory Analysis to test the effect of age and site on each of the multivariate data sets; and a Generalised Linear Model to test the effect of site and age on nuclear abnormalities. Somatic indices, erythrocyte nuclear abnormalities, erythrocyte morphometrics and leukocyte profile differed between populations, but less so for germ cell density. We found a large effect of site on nuclear abnormalities, with urban frogs having twice as many abnormalities as rural frogs. Our results suggest that urban frogs have a faster pace of life, but the response of phenotypic compartments is not fully concerted.

We evaluated the Precision Xtra™ ketometer as part of a larger study categorizing fasting status of free-ranging Steller sea lion (Eumetopias jubatus; SSL) pups which necessitated the identification of plasma β-hydroxybutyrate concentrations ([β-HBA]) around a threshold of <0.3 and ≥0.3 mmol/l. Whole blood samples mixed with sodium heparin (NaHep) or ethylenediaminetetraacetic acid liquid anticoagulants were tested <10 minutes after collection (n = 14; triplicate technical replicates). Plasma (stored at -80°C, NaHep, Thaw1) measured via our laboratory's Reference Assay (Sigma Aldrich, St. Louis, MO, Kit #MAK041) served as the standard [β-HBA] for ketometer comparisons. Our observed β-HBA range (0.0-1.6 mmol/l), consistent with published [β-HBA] of free-ranging Otariid pups, represented the lower 20% of the ketometer's range (0.0-8.0 mmol/l). The maximal coefficient of variation (%CV) of ketometer technical replicates was 9.1% (NaHep, whole blood). The majority of ketometer technical replicate sets (84%, including all matrices, anticoagulants and thawings) were identical (CV = 0%). We found linear relationships and agreement of ketometer [β-HBA] between whole blood preserved with different anticoagulants and between whole blood and plasma (Thaw1) measurements. The ketometer produced results with linearity to the Reference Assay for both whole blood and plasma (Thaw1). We identified a non-linear relationship between plasma at Thaw1 and Thaw2 (tested four months apart, NaHep), as only samples with higher SSL [β-HBA] decreased in concentration, and all others remained the same. With respect to categorizing SSL pup fasting in our larger study, the ketometer's %Accuracy, %Sensitivity and %Specificity for samples with Reference Assay β-HBA <0.2 and >0.4 mmol/l were 100%. We adopted a modified procedure: plasma samples with mean ketometer concentrations ±0.1 mmol/l of 0.3 mmol/l β-HBA were re-evaluated using the Reference Assay, improving measurement precision from tenths (ketometer) to thousandths (assay) mmol/l. The Precision Xtra™ ketometer was valuable to our application over the range of [β-HBA] observed in SSL pup plasma and whole blood samples.

Monitoring the health of wildlife populations is essential in the face of increased agricultural expansion and forest fragmentation. Loss of habitat and habitat degradation can negatively affect an animal's physiological state, possibly resulting in immunosuppression and increased morbidity or mortality. We sought to determine how land conversion may differentially impact cellular immunity and infection risk in Neotropical bats species regularly infected with bloodborne pathogens, and to evaluate how effects may vary over time and by dietary habit. We studied common vampire bats (Desmodus rotundus), northern yellow-shouldered bats (Sturnira parvidens) and Mesoamerican mustached bats (Pteronotus mesoamericanus), representing the dietary habits of sanguivory, frugivory and insectivory respectively, in northern Belize. We compared estimated total white blood cell count, leukocyte differentials, neutrophil to lymphocyte ratio and infection status with two bloodborne bacterial pathogens (Bartonella spp. and hemoplasmas) of 118 bats captured in a broadleaf, secondary forest over three years (2017-2019). During this period, tree cover decreased by 14.5% while rangeland expanded by 14.3%, indicating increasing habitat loss and fragmentation. We found evidence for bat species-specific responses of cellular immunity between years, with neutrophil counts significantly decreasing in S. parvidens from 2017 to 2018, but marginally increasing in D. rotundus. However, the odds of infection with Bartonella spp. and hemoplasmas between 2017 and 2019 did not differ between bat species, contrary to our prediction that pathogen prevalence may increase with land conversion. We conclude that each bat species invested differently in cellular immunity in ways that changed over years of increasing habitat loss and fragmentation. We recommend further research on the interactions between land conversion, immunity and infection across dietary habits of Neotropical bats for informed management and conservation.