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1.
Ecohealth ; 16(2): 235-247, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-31346852

RESUMO

An important contribution to infectious disease emergence in wildlife is environmental degradation driven by pollution, habitat fragmentation, and eutrophication. Amphibians are a wildlife group that is particularly sensitive to land use change, infectious diseases, and their interactions. Residential suburban land use is now a dominant, and increasing, form of land cover in the USA and globally, contributing to increased pollutant and nutrient loading in freshwater systems. We examined how suburbanization affects the infection of green frog (Rana clamitans) tadpoles and metamorphs by parasitic flatworms (Echinostoma spp.) through the alteration of landscapes surrounding ponds and concomitant changes in water quality. Using sixteen small ponds along a forest-suburban land use gradient, we assessed how the extent of suburban land use surrounding ponds influenced echinostome infection in both primary snail and secondary frog hosts. Our results show that the degree of suburbanization and concurrent chemical loading are positively associated with the presence and burden of echinostome infection in both host populations. This work contributes to a broader understanding of how land use mediates wildlife parasitism and shows how human activities at the household scale can have similar consequences for wildlife health as seemingly more intensive land uses like agriculture or urbanization.


Assuntos
Echinostoma , Equinostomíase/veterinária , Rana clamitans/parasitologia , Caramujos/parasitologia , População Suburbana/estatística & dados numéricos , Animais , Connecticut , Equinostomíase/epidemiologia , Equinostomíase/etiologia , Larva/parasitologia , Tanques
2.
Dis Aquat Organ ; 133(3): 207-216, 2019 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-31187735

RESUMO

Given that climate change is predicted to alter patterns of temperature variability, it is important to understand how shifting temperatures might influence species interactions, including parasitism. Predicting thermal effects on species interactions is complicated, however, because the temperature-dependence of the interaction depends on the thermal responses of both interacting organisms, which can also be influenced by thermal acclimation, a process by which organisms adjust their physiologies in response to a temperature change. We tested for thermal acclimation effects on Lithobates clamitans tadpole susceptibility to the fungus Batrachochytrium dendrobatidis (Bd) by acclimating tadpoles to 1 of 3 temperatures, moving them to 1 of 5 performance temperatures at which we exposed them to Bd, and measuring Bd loads on tadpoles post-exposure. We predicted that (1) tadpole Bd load would peak at a lower temperature than the temperature for peak Bd growth in culture, and (2) tadpoles acclimated to intermediate temperatures would have overall lower Bd loads across performance temperatures than cold- or warm-acclimated tadpoles, similar to a previously published pattern describing tadpole resistance to trematode metacercariae. Consistent with our first prediction, Bd load on tadpoles decreased with increasing performance temperature. However, we found only weak support for our second prediction, as acclimation temperature had little effect on tadpole Bd load. Our results contribute to a growing body of work investigating thermal responses of hosts and parasites, which will aid in developing methods to predict the temperature-dependence of disease.


Assuntos
Quitridiomicetos , Rana clamitans , Aclimatação , Animais , Larva , Temperatura
3.
Am J Physiol Regul Integr Comp Physiol ; 317(2): R301-R311, 2019 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-31141416

RESUMO

Chytridiomycosis, a lethal skin disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), disrupts skin function of amphibians, interfering with ionic and osmotic regulation. To regulate fungal loads, amphibians increase their rate of skin sloughing. However, sloughing also causes a temporary loss of ionic and osmotic homeostasis due to disruption of the skin, a key osmoregulatory organ. The combined effects of increased sloughing frequency and chytridiomycosis contribute to the high rates of mortality from Bd infections. However, the mechanisms responsible for the loss of cutaneous osmotic regulation remain unknown. We measured the changes in whole animal water uptake rates, in vitro transcutaneous water fluxes across the ventral skin, and the mRNA expression of epithelial water transport proteins (aquaporins, AQPs) and junctional proteins in Bd-infected and uninfected Litoria caerulea skin. We hypothesize that infected frogs would show reduction/inhibition in cutaneous water transporters responsible for regulating water balance, and sloughing would exacerbate cutaneous water fluxes. We found that infected, nonsloughing frogs had an impaired rate of water uptake and showed increased rates of in vitro water efflux across the ventral skin. In uninfected frogs, the expression of AQPs and junction genes increased significantly with sloughing, which may assist in regulating cutaneous water movements and barrier function in the newly exposed skin. In contrast, infected frogs did not show this postsloughing increase in AQP gene expression. The combination of increased sloughing frequency, impaired water uptake rates, and increased rates of water loss likely contributes to the loss of osmotic homeostasis in frogs infected with Bd.


Assuntos
Quitridiomicetos/patogenicidade , Pele/microbiologia , Equilíbrio Hidroeletrolítico/fisiologia , Água/metabolismo , Animais , Homeostase/fisiologia , Micoses/microbiologia , Rana clamitans/microbiologia , Pele/metabolismo
4.
Sci Total Environ ; 682: 282-290, 2019 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-31121353

RESUMO

An important challenge in amphibian ecotoxicology and conservation is that amphibian toxicity tests are usually focused on a single chemical while populations experience multiple, simultaneous stressors. For example, about 14 million tons of road de-icing salts are used each year in North America with NaCl accounting for 98% of total salt use and, hence, elevated chloride is an important environmental stressor to aquatic organisms, including amphibians. As well, higher temperature as a result of climate change is becoming an increasingly important environmental stressor. There are no data on the combined effects of chloride and temperature on amphibians hinders conservation efforts. We conducted field studies to characterize chloride concentrations and water temperatures in known amphibian breeding habitats and performed toxicity tests to explore impacts of these two stressors on a common anuran, the green frog (Lithobates clamitans). A 96-hour acute toxicity test was conducted to first determine a chloride LC50 (2587.5 mg Cl-/L) at a single, neutral temperature, which was used to inform the treatment levels of the sub-chronic test, which also included a temperature range. In the sub-chronic study, green frog larvae were exposed to three temperatures (18, 22, and 25 °C), and four concentrations of chloride (0, 500, 1000, and 2000 mg Cl-/L) for 35 days. At all temperatures, tadpoles exposed to 2000 mg Cl-/L had significantly higher mortality. While there was no significant effect of temperature alone on mortality, survival of tadpoles was significantly lower at 1000 mg Cl-/L at the two higher temperatures suggesting a potentiation of chloride ion toxicity with increasing temperature. Comparing toxicity results to field measurements of chloride and temperature suggests green frog tadpoles and other species with similar sensitivity are likely negatively affected. Data on additional species and populations would further increase our understanding of how salt and temperature may shape aquatic communities.


Assuntos
Cloretos/toxicidade , Aquecimento Global , Temperatura Alta/efeitos adversos , Rana clamitans/metabolismo , Poluentes Químicos da Água/toxicidade , Animais , Mudança Climática , Relação Dose-Resposta a Droga , Larva/efeitos dos fármacos , Larva/crescimento & desenvolvimento , Maryland , Rana clamitans/crescimento & desenvolvimento , Testes de Toxicidade Subcrônica
5.
J Wildl Dis ; 55(1): 262-265, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-30024771

RESUMO

We documented mortality of green frog ( Rana clamitans) tadpoles in Wisconsin, US, attributed to severe Perkinsea infection. Final diagnosis was determined by histopathology. followed by molecular detection of pathogenic Perkinsea clade (PPC) of frogs in the liver. To our knowledge, this represents the first detection of PPC in the midwestern US.


Assuntos
Alveolados , Infecções Protozoárias em Animais/parasitologia , Rana clamitans/parasitologia , Animais , Larva/parasitologia , Infecções Protozoárias em Animais/epidemiologia , Infecções Protozoárias em Animais/mortalidade , Wisconsin/epidemiologia
6.
Ecohealth ; 15(3): 608-618, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-30094775

RESUMO

Amphibian ranaviruses occur globally, but we are only beginning to understand mechanisms for emergence. Ranaviruses are aquatic pathogens which can cause > 90% mortality in larvae of many aquatic-breeding amphibians, making them important focal host taxa. Host susceptibilities and virulence of ranaviruses have been studied extensively in controlled laboratory settings, but research is needed to identify drivers of infection in natural environments. Constructed ponds, essential components of wetland restoration, have been associated with higher ranavirus prevalence than natural ponds, posing a conundrum for conservation efforts, and emphasizing the need to understand potential drivers. In this study, we analyzed 4 years of Frog virus 3 prevalence and associated environmental parameters in populations of wood frogs (Lithobates sylvaticus) and green frogs (Lithobates clamitans) in a constructed pond system. High prevalence was best predicted by low temperature, high host density, low zooplankton concentrations, and Gosner stages approaching metamorphosis. This study identified important variables to measure in assessments of ranaviral infection risk in newly constructed ponds, including effects of zooplankton, which have not been previously quantified in natural settings. Examining factors mediating diseases in natural environments, particularly in managed conservation settings, is important to both validate laboratory findings in situ, and to inform future conservation planning, particularly in the context of adaptive management.


Assuntos
Anfíbios/virologia , Larva/virologia , Tanques/virologia , Rana clamitans/virologia , Ranavirus/isolamento & purificação , Áreas Alagadas , Animais , Infecções por Vírus de DNA/epidemiologia , Suscetibilidade a Doenças , New York
7.
Environ Toxicol Chem ; 37(10): 2699-2704, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-30035389

RESUMO

In areas with heavy pesticide use, it is easy to attribute population declines to environmental contamination. The Blanchard's cricket frogs (Acris blanchardi) is an amphibian experiencing declines and range contractions across its distribution in the Midwest Corn Belt (USA). Experimental studies suggest that cricket frogs are sensitive to pesticides, but there are few studies examining this species' susceptibility to contaminants in realistic environments or comparing relative impacts with other anuran species. I reared 3 summer breeding anurans in outdoor mesocosms posthatching through metamorphosis to examine the effects of 2 insecticides (imidacloprid and carbaryl) and 1 herbicide (glyphosate with polyoxyethylene tallow amine) on larval development and metamorphosis. Cricket frogs were positively affected by insecticide exposure, likely a result of changes in the food web that increased food abundance. However, metamorphosis of green frogs (Lithobates clamitans) and gray tree frogs (Hyla chrysoscelis) appeared unaffected by pesticide exposure. The results of the present study suggest that the impacts of pesticides alone are unlikely to have population-level impacts for the anurans examined. Environ Toxicol Chem 2018;37:2699-2704. © 2018 SETAC.


Assuntos
Anuros/crescimento & desenvolvimento , Ecossistema , Praguicidas/toxicidade , Rana clamitans/crescimento & desenvolvimento , Análise de Variância , Animais , Carbaril/toxicidade , Exposição Ambiental/análise , Glicina/análogos & derivados , Glicina/toxicidade , Herbicidas/toxicidade , Inseticidas/toxicidade , Larva/efeitos dos fármacos , Larva/crescimento & desenvolvimento , Neonicotinoides/toxicidade , Nitrocompostos/toxicidade , Polietilenoglicóis/toxicidade , Especificidade da Espécie , Fatores de Tempo
8.
Sci Total Environ ; 624: 1348-1359, 2018 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-29929247

RESUMO

Pesticide use in agricultural areas requires the application of numerous chemicals to control target organisms, leaving non-target organisms at risk. The present study evaluates the hepatic metabolomic profile of one group of non-target organisms, amphibians, after exposure to a single pesticide and pesticide mixtures. Five common-use pesticide active ingredients were used in this study, three herbicides (atrazine, metolachlor and 2,4-d), one insecticide (malathion) and one fungicide (propiconazole). Juvenile green frogs (Lithobates clamitans) were reared for 60-90days post-metamorphosis then exposed to a single pesticide or a combination of pesticides at the labeled application rate on soil. Amphibian livers were excised for metabolomic analysis and pesticides were quantified for whole body homogenates. Based on the current study, metabolomic profiling of livers support both individual and interactive effects where pesticide exposures altered biochemical processes, potentially indicating a different response between active ingredients in pesticide mixtures, among these non-target species. Amphibian metabolomic response is likely dependent on the pesticides present in each mixture and their ability to perturb biochemical networks, thereby confounding efforts with risk assessment.


Assuntos
Metaboloma/fisiologia , Praguicidas/toxicidade , Rana clamitans/fisiologia , Testes de Toxicidade , Animais , Atrazina/análise , Ecossistema , Herbicidas/análise , Inseticidas/análise , Metamorfose Biológica/efeitos dos fármacos , Praguicidas/análise , Poluentes Químicos da Água
9.
J Vis Exp ; (125)2017 07 08.
Artigo em Inglês | MEDLINE | ID: mdl-28715368

RESUMO

One of the most feasible methods of measuring presynaptic calcium levels in presynaptic nerve terminals is optical recording. It is based on using calcium-sensitive fluorescent dyes that change their emission intensity or wavelength depending on the concentration of free calcium in the cell. There are several methods used to stain cells with calcium dyes. Most common are the processes of loading the dyes through a micropipette or pre-incubating with the acetoxymethyl ester forms of the dyes. However, these methods are not quite applicable to neuromuscular junctions (NMJs) due to methodological issues that arise. In this article, we present a method for loading a calcium-sensitive dye through the frog nerve stump of the frog nerve into the nerve endings. Since entry of external calcium into nerve terminals and the subsequent binding to the calcium dye occur within the millisecond time-scale, it is necessary to use a fast imaging system to record these interactions. Here, we describe a protocol for recording the calcium transient with a fast CCD camera.


Assuntos
Cálcio/metabolismo , Terminações Nervosas/metabolismo , Junção Neuromuscular/fisiologia , Animais , Rana clamitans
10.
Artigo em Inglês | MEDLINE | ID: mdl-28748486

RESUMO

Diverse animals communicate using multicomponent signals. How a receiver's central nervous system integrates multiple signal components remains largely unknown. We investigated how female green treefrogs (Hyla cinerea) integrate the multiple spectral components present in male advertisement calls. Typical calls have a bimodal spectrum consisting of formant-like low-frequency (~0.9 kHz) and high-frequency (~2.7 kHz) components that are transduced by different sensory organs in the inner ear. In behavioral experiments, only bimodal calls reliably elicited phonotaxis in no-choice tests, and they were selectively chosen over unimodal calls in two-alternative choice tests. Single neurons in the inferior colliculus of awake, passively listening subjects were classified as combination-insensitive units (27.9%) or combination-sensitive units (72.1%) based on patterns of relative responses to the same bimodal and unimodal calls. Combination-insensitive units responded similarly to the bimodal call and one or both unimodal calls. In contrast, combination-sensitive units exhibited both linear responses (i.e., linear summation) and, more commonly, nonlinear responses (e.g., facilitation, compressive summation, or suppression) to the spectral combination in the bimodal call. These results are consistent with the hypothesis that nonlinearities play potentially critical roles in spectral integration and in the neural processing of multicomponent communication signals.


Assuntos
Colículos Inferiores/citologia , Neurônios/fisiologia , Dinâmica não Linear , Rana clamitans/fisiologia , Vocalização Animal/fisiologia , Estimulação Acústica , Potenciais de Ação/fisiologia , Animais , Anuros/fisiologia , Vias Auditivas/fisiologia , Percepção Auditiva , Feminino , Modelos Neurológicos , Comportamento Sexual Animal
11.
Environ Toxicol Chem ; 36(10): 2855-2867, 2017 10.
Artigo em Inglês | MEDLINE | ID: mdl-28474750

RESUMO

Heavy metal contamination may have adverse effects on wetland biota, particularly on amphibians. Severe immunotoxic effects elicited in Euphlyctis hexadactylus (Indian green frog) because of metal exposure (Cd, Cr, Cu, Pb, and Zn) in the Bellanwila-Attidiya Sanctuary, a polluted urban wetland in Sri Lanka, provided the rationale for the present study. We evaluated the biochemical and histopathological effects of this metal contamination with a reference E. hexadactylus population and a laboratory exposure group that was subjected to 28 d of exposure to a mixture of Cd, Cr, Cu, Pb, and Zn (5 ppm in each mixture). A histopathological scoring for the semiquantification of tissue damage was established. Results of the biochemical and histopathological markers were remarkably consistent between the 2 exposure scenarios, providing validation for the heavy metal exposure hypothesis. Damage to liver, kidney, lung, and skin of metal-exposed E. hexadactylus quantified multiple impairments absent in the reference frogs. Liver injuries complemented significantly elevated aspartate transaminase (AST), alanine transaminase (ALT), γ-glutamyl transferase (γ-GT), and alkaline phosphatases in frog liver homogenate, indicating hepatocellular leakage and loss of functional and structural integrity of the hepatocyte membrane in both field- and laboratory-exposed frogs. Significant elevation of Kupffer cell hypertrophy, pigmentation, inflammatory cell infiltrates and hepatic inflammation, extramedullary hematopoiesis, karyocytomegaly of hepatocytes (p < 0.05) of the liver, and degeneration of epithelia and necrosis of the lung, manifested as impairments in both metal exposure scenarios. Significantly reduced serum total protein and albumin and significantly elevated urea and creatinine in metal-exposed frogs were indicative of hepatic and renal dysfunction, respectively. The present study affirms histopathology-related biochemical alterations as potential biomarkers for heavy metal toxicity in amphibians. Environ Toxicol Chem 2017;36:2855-2867. © 2017 SETAC.


Assuntos
Fígado/efeitos dos fármacos , Metais Pesados/toxicidade , Rana clamitans/metabolismo , Poluentes Químicos da Água/toxicidade , Alanina Transaminase/sangue , Animais , Aspartato Aminotransferases/sangue , Biomarcadores/sangue , Creatinina/sangue , Rim/efeitos dos fármacos , Rim/patologia , Fígado/enzimologia , Fígado/patologia , Pulmão/efeitos dos fármacos , Pulmão/patologia , Metais Pesados/química , Pele/efeitos dos fármacos , Pele/patologia , Sri Lanka , Regulação para Cima/efeitos dos fármacos , Ureia/sangue , Poluentes Químicos da Água/química , Áreas Alagadas , gama-Glutamiltransferase/sangue
12.
BMC Genomics ; 17(1): 844, 2016 10 28.
Artigo em Inglês | MEDLINE | ID: mdl-27793086

RESUMO

BACKGROUND: The extent to which sex reversal is associated with transitions in sex determining systems (XX-XY, ZZ-ZW, etc.) or abnormal sexual differentiation is predominantly unexplored in amphibians. This is in large part because most amphibian taxa have homomorphic sex chromosomes, which has traditionally made it challenging to identify discordance between phenotypic and genetic sex in amphibians, despite all amphibians having a genetic component to sex determination. Recent advances in molecular techniques such as genome complexity reduction and high throughput sequencing present a valuable avenue for furthering our understanding of sex determination in amphibians and other taxa with homomorphic sex chromosomes like many fish and reptiles. RESULTS: We use DArTseq as a novel approach to identify sex-linked markers in the North American green frog (Rana clamitans melanota) using lab-reared tadpoles as well as wild-caught adults from seven ponds either in undeveloped, forested habitats or suburban ponds known to be subject to contamination by anthropogenic chemicals. The DArTseq methodology identified 13 sex-linked SNP loci and eight presence-absence loci associated with males, indicating an XX-XY system. Both alleles from a single locus show partial high sequence homology to Dmrt1, a gene linked to sex determination and differentiation throughout Metazoa. Two other loci have sequence similarities to regions of the chimpanzee and human X-chromosome as well as the chicken Z-chromosome. Several loci also show geographic variation in sex-linkage, possibly indicating sex chromosome recombination. While all loci are statistically sex-linked, they show varying degrees of female heterozygosity and male homozygosity, providing further evidence that some markers are on regions of the sex chromosomes undergoing higher rates of recombination and therefore further apart from the putative sex determining locus. CONCLUSION: The ease of the DArTseq platform provides a useful avenue for future research on sex reversal and sex chromosome evolution in vertebrates, particularly for non-model species with homomorphic or cryptic or nascent sex chromosomes.


Assuntos
Evolução Molecular , Marcadores Genéticos , Rana clamitans/genética , Cromossomos Sexuais , Processos de Determinação Sexual/genética , Animais , Análise por Conglomerados , Feminino , Ligação Genética , Sequenciamento de Nucleotídeos em Larga Escala , Masculino
13.
Dis Aquat Organ ; 121(2): 97-104, 2016 09 26.
Artigo em Inglês | MEDLINE | ID: mdl-27667807

RESUMO

Few studies have documented seasonal variation of Batrachochytrium dendrobatidis (Bd) infection rates in larval amphibians. We identified 4 natural populations of northern green frogs Lithobates clamitans melanota in Pennsylvania (USA) that contained Bd-infected tadpoles during post-wintering collections in May and June, after hibernating tadpoles had overwintered in wetlands. However, we failed to detect infected tadpoles at those wetlands when pre-wintering collections were made in late July through early September. We observed 2 cohorts of tadpoles that appeared to lack Bd-infected individuals in pre-wintering collections, yet contained Bd-infected individuals the following spring. We also observed 4 cohorts of pre-wintering tadpoles that were Bd-free, even though post-wintering tadpoles collected earlier in the year were infected with Bd. Our results suggest that tadpoles either reduce Bd infections during the summer months, and/or infections proliferate sometime prior to (or shortly after) tadpoles emerge from hibernation. It is unlikely that pre-wintering tadpoles were too small to detect Bd zoospores because (1) there was no correlation between Bd zoospore levels and tadpole size or stage, and (2) size was not a significant predictor of infection status. These results suggest that, while sampling larvae can be an effective means of collecting large sample sizes, investigators in our Mid-Atlantic region should conduct sampling by early summer to maximize the chances of detecting Bd. Further research is warranted to determine whether wetland topography and warm, shallow microhabitats within wetlands contribute to a population's ability to drastically reduce Bd prevalence prior to overwintering at ponds.


Assuntos
Quitridiomicetos , Micoses/veterinária , Rana clamitans/microbiologia , Estações do Ano , Animais , Larva/microbiologia , Micoses/microbiologia , Prevalência
14.
J Exp Zool A Ecol Genet Physiol ; 325(5): 285-93, 2016 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-27194039

RESUMO

Seasonal acclimatization permits organisms to maintain function in the face of environmental change. Tadpoles of the green frog (Lithobates clamitans) overwinter as tadpoles in much of their range. Because they are active in winter, we hypothesized that green frog tadpoles would display acclimatization of metabolic and locomotor function. We collected tadpoles in Sewanee, Tennessee (35.2°N) in winter and summer. Tadpoles collected during each season were tested at both winter (8°C) and summer (26°C) temperatures. Winter tadpoles were able to maintain swimming performance at both temperatures, whereas swimming performance decreased at cold temperatures in summer tadpoles. There was no evidence for seasonal acclimatization of whole-animal metabolic rate. Although whole-animal metabolic acclimatization was not observed, the activities of cytochrome c oxidase, citrate synthase, and lactate dehydrogenase measured in skeletal muscle homogenates showed higher activity in winter-acclimatized tadpoles indicating compensation for temperature. Further, the composition of muscle membranes of winter tadpoles had less saturated and more monounsaturated fatty acids and a higher ω-3 balance, unsaturation index, and peroxidation index than summer tadpoles. These data indicate that reversible phenotypic plasticity of thermal physiology occurs in larval green frog tadpoles. They appear to compensate for colder temperatures to maintain burst-swimming velocity and the ability to escape predators without the cost of maintaining a constant, higher standard metabolic rate in the winter.


Assuntos
Aclimatação/fisiologia , Rana clamitans/fisiologia , Estações do Ano , Temperatura , Animais , Larva/crescimento & desenvolvimento , Larva/fisiologia , Rana clamitans/crescimento & desenvolvimento
15.
Ecology ; 97(4): 834-41, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-27220200

RESUMO

Predators play a key role in shaping natural ecosystems, and understanding the factors that influence a predator's kill rate is central to predicting predator-prey dynamics. While prey density has a well-established effect on predation, it is increasingly apparent that predator density also can critically influence predator kill rates. The effects of both prey and predator density on the functional response will, however, be determined in part by their distribution on the landscape. To examine this complex relationship we experimentally manipulated prey density, predator density, and prey distribution using a tadpole (prey)-dragonfly nymph (predator) system. Predation was strongly ratio-dependent irrespective of prey distribution, but the shape of the functional response changed from hyperbolic to sigmoidal when prey were clumped in space. This sigmoidal functional response reflected a relatively strong negative effect of predator interference on kill rates at low prey: predator ratios when prey were clumped. Prey aggregation also appeared to promote stabilizing density-dependent intraguild predation in our system. We conclude that systems with highly antagonistic predators and patchily distributed prey are more likely to experience stable dynamics, and that our understanding of the functional response will be improved by research that examines directly the mechanisms generating interference.


Assuntos
Odonatos/fisiologia , Comportamento Predatório/fisiologia , Rana clamitans/fisiologia , Animais , Modelos Biológicos , Ninfa/fisiologia
16.
J Genet Genomics ; 43(4): 199-207, 2016 04 20.
Artigo em Inglês | MEDLINE | ID: mdl-27157807

RESUMO

In this study, we constructed dual-transgene vectors (pDT1, pDT7, and pDT7G) that simultaneously co-expressed two genes in plants. ACTIN2 and UBQ10 promoters were used to control the expression of these two genes. The 4×Myc, 3×HA, and 3×Flag reporter genes allowed for the convenient identification of a tunable co-expression system in plants, whereas the dexamethasone (Dex) inducible reporter gene C-terminus of the glucocorticoid receptor (cGR) provided Dex-dependent translocation of the fusion gene between the nucleus and cytoplasm. The function of pDT vectors was validated using four pairwise genes in Nicotiana benthamiana or Arabidopsis thaliana. The co-expression efficiency of two genes from the pDT1 and pDT7G vectors was 35% and 42%, respectively, which ensured the generation of sufficient transgenic materials. These pDT vectors are simple, reliable, efficient, and time-saving tools for the co-expression of two genes through a single transformation event and can be used in the study of protein-protein interactions or multi-component complexes.


Assuntos
Arabidopsis/genética , Engenharia Genética/métodos , Vetores Genéticos/genética , Transformação Genética , Transgenes/genética , Animais , Plantas Geneticamente Modificadas , Regiões Promotoras Genéticas/genética , Rana clamitans/genética
17.
J Anim Ecol ; 85(4): 1014-24, 2016 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-27040618

RESUMO

Global climate change is expected to alter patterns of temperature variability, which could influence species interactions including parasitism. Species interactions can be difficult to predict in variable-temperature environments because of thermal acclimation responses, i.e. physiological changes that allow organisms to adjust to a new temperature following a temperature shift. The goal of this study was to determine how thermal acclimation influences host resistance to infection and to test for parasite acclimation responses, which might differ from host responses in important ways. We tested predictions of three, non-mutually exclusive hypotheses regarding thermal acclimation effects on infection of green frog tadpoles (Lithobates clamitans) by the trematode parasite Ribeiroia ondatrae with fully replicated controlled-temperature experiments. Trematodes or tadpoles were independently acclimated to a range of 'acclimation temperatures' prior to shifting them to new 'performance temperatures' for experimental infections. Trematodes that were acclimated to intermediate temperatures (19-22 °C) had greater encystment success across temperatures than either cold- or warm-acclimated trematodes. However, host acclimation responses varied depending on the stage of infection (encystment vs. clearance): warm- (22-28 °C) and cold-acclimated (13-19 °C) tadpoles had fewer parasites encyst at warm and cold performance temperatures, respectively, whereas intermediate-acclimated tadpoles (19-25 °C) cleared the greatest proportion of parasites in the week following exposure. These results suggest that tadpoles use different immune mechanisms to resist different stages of trematode infection, and that each set of mechanisms has unique responses to temperature variability. Our results highlight the importance of considering thermal responses of both parasites and hosts when predicting disease patterns in variable-temperature environments.


Assuntos
Aclimatação , Rana clamitans , Trematódeos/fisiologia , Infecções por Trematódeos/veterinária , Animais , Mudança Climática , Interações Hospedeiro-Parasita , Larva/crescimento & desenvolvimento , Rana clamitans/crescimento & desenvolvimento , Temperatura , Infecções por Trematódeos/imunologia , Infecções por Trematódeos/parasitologia
18.
Appl Environ Microbiol ; 82(8): 2457-2466, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26873311

RESUMO

Amphibian populations worldwide are being threatened by the disease chytridiomycosis, which is caused by Batrachochytrium dendrobatidis To mitigate the effects of B. dendrobatidis, bioaugmentation of antifungal bacteria has been shown to be a promising strategy. One way to implement bioaugmentation is through indirect horizontal transmission, defined as the transfer of bacteria from a host to the environment and to another host. In addition, direct horizontal transmission among individuals can facilitate the spread of a probiotic in a population. In this study, we tested whether the antifungal bacterium Janthinobacterium lividum could be horizontally transferred, directly or indirectly, in a laboratory experiment using Lithobates clamitans tadpoles. We evaluated the ability of J. lividumto colonize the tadpoles' skin and to persist through time using culture-dependent and culture-independent techniques. We also tested whether the addition of J. lividum affected the skin community in L. clamitans tadpoles. We found that transmission occurred rapidly by direct and indirect horizontal transmission, but indirect transmission that included a potential substrate was more effective. Even though J. lividum colonized the skin, its relative abundance on the tadpole skin decreased over time. The inoculation of J. lividum did not significantly alter the skin bacterial diversity of L. clamitans tadpoles, which was dominated by Pseudomonas Our results show that indirect horizontal transmission can be an effective bioaugmentation method. Future research is needed to determine the best conditions, including the presence of substrates, under which a probiotic can persist on the skin so that bioaugmentation becomes a successful strategy to mitigate chytridiomycosis.


Assuntos
Larva/microbiologia , Oxalobacteraceae/isolamento & purificação , Probióticos , Rana clamitans/microbiologia , Animais , Pele/microbiologia
19.
Dis Aquat Organ ; 118(2): 113-27, 2016 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-26912042

RESUMO

Long-term monitoring of amphibians is needed to clarify population-level effects of ranaviruses (Rv) and the fungal pathogen Batrachochytrium dendrobatidis (Bd). We investigated disease dynamics of co-occurring amphibian species and potential demographic consequences of Rv and Bd infections at a montane site in the Southern Appalachians, Georgia, USA. Our 3-yr study was unique in combining disease surveillance with intensive population monitoring at a site where both pathogens are present. We detected sub-clinical Bd infections in larval and adult red-spotted newts Notophthalmus viridescens viridescens, but found no effect of Bd on body condition of adult newts. Bd infections also occurred in larvae of 5 anuran species that bred in our fishless study pond, and we detected co-infections with Bd and Rv in adult newts and larval green frogs Lithobates clamitans. However, all mortality and clinical signs in adult newts and larval anurans were most consistent with ranaviral disease, including a die-off of larval wood frogs Lithobates sylvaticus in small fish ponds located near our main study pond. During 2 yr of drift fence monitoring, we documented high juvenile production in newts, green frogs and American bullfrogs L. catesbeianus, but saw no evidence of juvenile recruitment in wood frogs. Larvae of this susceptible species may have suffered high mortality in the presence of both Rv and predators. Our findings were generally consistent with results of Rv-exposure experiments and support the purported role of red-spotted newts, green frogs, and American bullfrogs as common reservoirs for Bd and/or Rv in permanent and semi-permanent wetlands.


Assuntos
Notophthalmus/microbiologia , Notophthalmus/virologia , Tanques , Comportamento Predatório , Rana clamitans/microbiologia , Rana clamitans/virologia , Animais , Quitridiomicetos/imunologia , Infecções por Vírus de DNA/epidemiologia , Infecções por Vírus de DNA/veterinária , Infecções por Vírus de DNA/virologia , Georgia , Larva/microbiologia , Larva/virologia , Micoses/microbiologia , Micoses/transmissão , Micoses/veterinária , Rana clamitans/fisiologia , Ranavirus/isolamento & purificação , Estações do Ano , Fatores de Tempo
20.
Physiol Biochem Zool ; 88(5): 576-85, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26658253

RESUMO

Stable isotope analysis is an increasingly useful ecological tool, but its accuracy depends on quantifying the tissue-specific trophic discrimination factors (TDFs) and isotopic incorporation rates for focal taxa. Despite the technique's ubiquity, most laboratory experiments determining TDFs and incorporation rates have focused on birds, mammals, and fish; we know little about terrestrial ectotherms, and amphibians in particular are understudied. In this study we used two controlled feeding experiments to determine carbon (δ(13)C) and nitrogen (δ(15)N) isotope TDFs for skin, whole blood, and bone collagen and incorporation rates for skin and whole blood in adult green frogs, Lithobates clamitans. The mean (±SD) TDFs for δ(13)C were 0.1‰ (±0.4‰) for skin, 0.5‰ (±0.5‰) for whole blood, and 1.6‰ (0.6‰) for bone collagen. The mean (±SD) TDFs for δ(15)N were 2.3‰ (±0.5‰) for skin, 2.3‰ (±0.4‰) for whole blood, and 3.1‰ (±0.6‰) for bone collagen. A combination of different isotopic incorporation models was best supported by our data. Carbon in skin was the only tissue in which incorporation was best explained by two compartments, which had half-lives of 89 and 8 d. The half-life of carbon in whole blood was 69 d. Half-lives for nitrogen were 75 d for skin and 71 d for whole blood. Our results help fill a taxonomic gap in our knowledge of stable isotope dynamics and provide ecologists with a method to measure anuran diets.


Assuntos
Carbono/metabolismo , Nitrogênio/metabolismo , Rana clamitans/metabolismo , Animais , Osso e Ossos/química , Isótopos de Carbono , Colágeno/química , Isótopos de Nitrogênio/metabolismo , Pele/química , Fatores de Tempo
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