The Experts below are selected from a list of 1464 Experts worldwide ranked by ideXlab platform
K. W. Hunter - One of the best experts on this subject based on the ideXlab platform.
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chronic disease in the mojave Desert Tortoise host physiology and recrudescence obscure patterns of pathogen transmission
Ecology and Evolution, 2017Co-Authors: Franziska C Sandmeier, S. A. Dupre', Hossein Ali Mohammadpour, Richard C Tracy, Ron Marlow, Nichole Maloney, David Hyde, K. W. HunterAbstract:A seminatural, factorial-design experiment was used to quantify dynamics of the pathogen Mycoplasma agassizii and upper respiratory tract disease in the Mojave Desert Tortoise (Gopherus agassizii) over 2 years. Groups of initially healthy animals were separated into serologically positive (seropositive), seronegative, and artificially infected groups and paired into 23 pens. We found no evidence of long-term immune protection to M. agassizii or of immunological memory. Initially seronegative, healthy Tortoises experienced an equal amount of disease when paired with other seronegative groups as when paired with seropositive and artificially infected groups—suggesting that recrudescence is as significant as transmission in introducing disease in individuals in this host–pathogen system. Artificially infected groups of Tortoises showed reduced levels of morbidity when paired with initially seronegative animals—suggesting either a dilution effect or a strong effect of pathogen load in this system. Physiological dynamics within the host appear to be instrumental in producing morbidity, recrudescence, and infectiousness, and thus of population-level dynamics. We suggest new avenues for studying diseases in long-lived ectothermic vertebrates and a shift in modeling such diseases.
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mycoplasmal upper respiratory tract disease across the range of the threatened mojave Desert Tortoise associations with thermal regime and natural antibodies
Ecohealth, 2013Co-Authors: Franziska C Sandmeier, S. A. Dupre', Hossein Ali Mohammadpour, Bridgette E Hagerty, Richard C Tracy, K. W. HunterAbstract:Most research of upper respiratory tract disease (mycoplasmal URTD) in the threatened Mojave Desert Tortoise (Gopherus agassizii) has worked under the hypothesis that the pathogen, Mycoplasma agassizii, has a relatively consistent and predictable effect on Tortoise populations across their natural range. In contrast, we hypothesized that multiple factors influence the prevalence of disease and analyzed biological and environmental variables that vary significantly across the Mojave Desert. We used multiple regression models to analyze associations between mycoplasmal URTD and the genetic structure of 24 Tortoise populations, levels of natural antibody (NAb) to M. agassizii in Tortoises (one component of the innate immune system), precipitation, and colder thermal regimes. We detected a significant, positive association between mean levels of NAb and seroprevalence to M. agassizii. We hypothesized that NAbs may provide tolerance to mycoplasmal infections and that more tolerant populations may act as host reservoirs of disease. We also detected significant associations between colder winters and mycoplasmal URTD, suggesting that colder winters may depress Tortoise immune resistance against M. agassizii or enhance conditions for the growth of M. agassizii.
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A quantitative PCR method for assessing the presence of Pasteurella testudinis DNA in nasal lavage samples from the Desert Tortoise (Gopherus agassizii)
Journal of Microbiological Methods, 2012Co-Authors: S. A. Dupre', Franziska C Sandmeier, C R Tracy, K. W. HunterAbstract:Abstract Pasteurella testudinis has been associated with upper respiratory tract disease (URTD) in the threatened Desert Tortoise ( Gopherus agassizii ). Our goal was to develop a sensitive and specific qPCR method for detecting DNA from P. testudinis in nasal lavage fluid collected from Desert Tortoises in the field. Probes for 16S ribosomal RNA and RNA polymerase β-subunit (rpoB) genes were designed. A standard curve generated with DNA extracted from known numbers of bacterial cells determined by flow cytometry revealed a lower detection limit of 50 fg /ml (10 bacteria/ml). The nasal lavage fluid contained no interfering substances, and the qPCR method did not recognize normal flora DNA. The nasal lavage samples from 20 Desert Tortoises captured in Clark County, Nevada, USA in 2007 and housed at the Desert Tortoise Conservation Center, were all positive for P. testudinis DNA by qPCR. Another set of 19 lavage samples collected in 2010 from wild Desert Tortoises in the Mojave Desert were tested and 84% were positive for P. testudinis DNA. Fully validated, this qPCR method will provide a means of determining colonization rate. When used in conjunction with serological methods and clinical evaluations, both infection rate and disease rate can be determined for this potential URTD pathogen. This new assay provides an important tool for managing the threatened populations of the Mojave Desert Tortoise.
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quantitative pcr method for detection of mycoplasma spp dna in nasal lavage samples from the Desert Tortoise gopherus agassizii
Journal of Microbiological Methods, 2011Co-Authors: S. A. Dupre', C R Tracy, K. W. HunterAbstract:Abstract Mycoplasma agassizii and M. testudineum have been associated with upper respiratory tract disease (URTD) in the threatened Desert Tortoise ( Gopherus agassizii ). Because microbiological culture methods have proven difficult to employ in wild Desert Tortoises, our goal was to develop a sensitive and specific qPCR method for detecting and quantifying mycoplasma DNA in nasal lavage fluid collected in the field. Primers for 16S ribosomal RNA gene sequences specific for M. agassizii and M. testudineum were designed, together with primers that recognize conserved sequences of both microorganisms. Standard curves generated with DNA extracted from known numbers of mycoplasma cells revealed a lower detection limit of approximately 5 fg. The qPCR method did not recognize normal flora DNA, and nasal lavage fluid contained no interfering substances. Nasal lavage samples collected from 20 captive Desert Tortoises housed at the Desert Tortoise Conservation Center (Clark County, Nevada, USA) revealed the presence of M. agassizii DNA in 100% of the Tortoises. Concentrations ranged from a low of 6 pg ml − 1 to a high of 72,962 pg ml − 1 . Only one of the Tortoises was positive for M. testudineum . Interestingly, not all of the qPCR positive Tortoises showed evidence of seroconversion, suggesting that they were colonized but not infected. This new quantitative method will provide a critical tool for managing threatened populations of the Desert Tortoise.
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flow cytometric method for quantifying viable mycoplasma agassizii an agent of upper respiratory tract disease in the Desert Tortoise gopherus agassizii
Letters in Applied Microbiology, 2010Co-Authors: Hossein Ali Mohammadpour, S. A. Dupre', D. Redelman, C R Tracy, K. W. HunterAbstract:Aims: Mycoplasma agassizii can cause upper respiratory tract disease in the threatened Desert Tortoise of the Southwestern United States. Two technical challenges have impeded critical microbiological studies of this microorganism: (i) its small size limits the use of light microscopy for cell counting and (ii) its extremely slow growth in broth and agar cultures impedes colony counting. Our aim was to develop a rapid and sensitive flow cytometric method using a vital fluorescent dye to enumerate viable M. agassizii cells. Methods and Results: Here, we demonstrate that the nonfluorescent molecule 5-carboxyfluorescein (5-CF) diacetate acetoxymethyl ester penetrates M. agassizii cell membranes and it is converted in the cytoplasm to the fluorescent molecule 5-CF by the action of intracellular esterases. Labelled mycoplasma cells can be easily detected by flow cytometry, and cultures with as few as 100 viable mycoplasma cells ml−1 can be labelled and counted in less than 1 h. Experiments using temperature-induced cell death demonstrated that only viable M. agassizii cells are labelled with this procedure. Conclusions: A rapid and sensitive flow cytometric technique has been developed for enumerating viable M. agassizii cells. Significance and Impact of the Study: This technique should facilitate basic immunological, biochemical and pharmacological studies of this important pathogen which may lead to new diagnostic and therapeutic methods.
S. A. Dupre' - One of the best experts on this subject based on the ideXlab platform.
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chronic disease in the mojave Desert Tortoise host physiology and recrudescence obscure patterns of pathogen transmission
Ecology and Evolution, 2017Co-Authors: Franziska C Sandmeier, S. A. Dupre', Hossein Ali Mohammadpour, Richard C Tracy, Ron Marlow, Nichole Maloney, David Hyde, K. W. HunterAbstract:A seminatural, factorial-design experiment was used to quantify dynamics of the pathogen Mycoplasma agassizii and upper respiratory tract disease in the Mojave Desert Tortoise (Gopherus agassizii) over 2 years. Groups of initially healthy animals were separated into serologically positive (seropositive), seronegative, and artificially infected groups and paired into 23 pens. We found no evidence of long-term immune protection to M. agassizii or of immunological memory. Initially seronegative, healthy Tortoises experienced an equal amount of disease when paired with other seronegative groups as when paired with seropositive and artificially infected groups—suggesting that recrudescence is as significant as transmission in introducing disease in individuals in this host–pathogen system. Artificially infected groups of Tortoises showed reduced levels of morbidity when paired with initially seronegative animals—suggesting either a dilution effect or a strong effect of pathogen load in this system. Physiological dynamics within the host appear to be instrumental in producing morbidity, recrudescence, and infectiousness, and thus of population-level dynamics. We suggest new avenues for studying diseases in long-lived ectothermic vertebrates and a shift in modeling such diseases.
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mycoplasmal upper respiratory tract disease across the range of the threatened mojave Desert Tortoise associations with thermal regime and natural antibodies
Ecohealth, 2013Co-Authors: Franziska C Sandmeier, S. A. Dupre', Hossein Ali Mohammadpour, Bridgette E Hagerty, Richard C Tracy, K. W. HunterAbstract:Most research of upper respiratory tract disease (mycoplasmal URTD) in the threatened Mojave Desert Tortoise (Gopherus agassizii) has worked under the hypothesis that the pathogen, Mycoplasma agassizii, has a relatively consistent and predictable effect on Tortoise populations across their natural range. In contrast, we hypothesized that multiple factors influence the prevalence of disease and analyzed biological and environmental variables that vary significantly across the Mojave Desert. We used multiple regression models to analyze associations between mycoplasmal URTD and the genetic structure of 24 Tortoise populations, levels of natural antibody (NAb) to M. agassizii in Tortoises (one component of the innate immune system), precipitation, and colder thermal regimes. We detected a significant, positive association between mean levels of NAb and seroprevalence to M. agassizii. We hypothesized that NAbs may provide tolerance to mycoplasmal infections and that more tolerant populations may act as host reservoirs of disease. We also detected significant associations between colder winters and mycoplasmal URTD, suggesting that colder winters may depress Tortoise immune resistance against M. agassizii or enhance conditions for the growth of M. agassizii.
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A quantitative PCR method for assessing the presence of Pasteurella testudinis DNA in nasal lavage samples from the Desert Tortoise (Gopherus agassizii)
Journal of Microbiological Methods, 2012Co-Authors: S. A. Dupre', Franziska C Sandmeier, C R Tracy, K. W. HunterAbstract:Abstract Pasteurella testudinis has been associated with upper respiratory tract disease (URTD) in the threatened Desert Tortoise ( Gopherus agassizii ). Our goal was to develop a sensitive and specific qPCR method for detecting DNA from P. testudinis in nasal lavage fluid collected from Desert Tortoises in the field. Probes for 16S ribosomal RNA and RNA polymerase β-subunit (rpoB) genes were designed. A standard curve generated with DNA extracted from known numbers of bacterial cells determined by flow cytometry revealed a lower detection limit of 50 fg /ml (10 bacteria/ml). The nasal lavage fluid contained no interfering substances, and the qPCR method did not recognize normal flora DNA. The nasal lavage samples from 20 Desert Tortoises captured in Clark County, Nevada, USA in 2007 and housed at the Desert Tortoise Conservation Center, were all positive for P. testudinis DNA by qPCR. Another set of 19 lavage samples collected in 2010 from wild Desert Tortoises in the Mojave Desert were tested and 84% were positive for P. testudinis DNA. Fully validated, this qPCR method will provide a means of determining colonization rate. When used in conjunction with serological methods and clinical evaluations, both infection rate and disease rate can be determined for this potential URTD pathogen. This new assay provides an important tool for managing the threatened populations of the Mojave Desert Tortoise.
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quantitative pcr method for detection of mycoplasma spp dna in nasal lavage samples from the Desert Tortoise gopherus agassizii
Journal of Microbiological Methods, 2011Co-Authors: S. A. Dupre', C R Tracy, K. W. HunterAbstract:Abstract Mycoplasma agassizii and M. testudineum have been associated with upper respiratory tract disease (URTD) in the threatened Desert Tortoise ( Gopherus agassizii ). Because microbiological culture methods have proven difficult to employ in wild Desert Tortoises, our goal was to develop a sensitive and specific qPCR method for detecting and quantifying mycoplasma DNA in nasal lavage fluid collected in the field. Primers for 16S ribosomal RNA gene sequences specific for M. agassizii and M. testudineum were designed, together with primers that recognize conserved sequences of both microorganisms. Standard curves generated with DNA extracted from known numbers of mycoplasma cells revealed a lower detection limit of approximately 5 fg. The qPCR method did not recognize normal flora DNA, and nasal lavage fluid contained no interfering substances. Nasal lavage samples collected from 20 captive Desert Tortoises housed at the Desert Tortoise Conservation Center (Clark County, Nevada, USA) revealed the presence of M. agassizii DNA in 100% of the Tortoises. Concentrations ranged from a low of 6 pg ml − 1 to a high of 72,962 pg ml − 1 . Only one of the Tortoises was positive for M. testudineum . Interestingly, not all of the qPCR positive Tortoises showed evidence of seroconversion, suggesting that they were colonized but not infected. This new quantitative method will provide a critical tool for managing threatened populations of the Desert Tortoise.
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flow cytometric method for quantifying viable mycoplasma agassizii an agent of upper respiratory tract disease in the Desert Tortoise gopherus agassizii
Letters in Applied Microbiology, 2010Co-Authors: Hossein Ali Mohammadpour, S. A. Dupre', D. Redelman, C R Tracy, K. W. HunterAbstract:Aims: Mycoplasma agassizii can cause upper respiratory tract disease in the threatened Desert Tortoise of the Southwestern United States. Two technical challenges have impeded critical microbiological studies of this microorganism: (i) its small size limits the use of light microscopy for cell counting and (ii) its extremely slow growth in broth and agar cultures impedes colony counting. Our aim was to develop a rapid and sensitive flow cytometric method using a vital fluorescent dye to enumerate viable M. agassizii cells. Methods and Results: Here, we demonstrate that the nonfluorescent molecule 5-carboxyfluorescein (5-CF) diacetate acetoxymethyl ester penetrates M. agassizii cell membranes and it is converted in the cytoplasm to the fluorescent molecule 5-CF by the action of intracellular esterases. Labelled mycoplasma cells can be easily detected by flow cytometry, and cultures with as few as 100 viable mycoplasma cells ml−1 can be labelled and counted in less than 1 h. Experiments using temperature-induced cell death demonstrated that only viable M. agassizii cells are labelled with this procedure. Conclusions: A rapid and sensitive flow cytometric technique has been developed for enumerating viable M. agassizii cells. Significance and Impact of the Study: This technique should facilitate basic immunological, biochemical and pharmacological studies of this important pathogen which may lead to new diagnostic and therapeutic methods.
Kenneth E Nussear - One of the best experts on this subject based on the ideXlab platform.
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Desert Tortoise Use of Burned Habitat in the
2020Co-Authors: K. Kristina Drake, Todd C Esque, Kenneth E Nussear, Lesley A. Defalco, Sara J. Scoles-sciulla, Andrew T. Modlin, Philip A MedicaAbstract:Wildfires burned 24,254ha of critical habitat designated for the recovery of the threatened Mojave Desert Tortoise (Gopherus agassizii) in southern Nevada during 2005. The proliferation of non-native annual grasses has increased wildfire frequency and extent in recent decades and continues to accelerate the conversion of Tortoise habitat across the Mojave Desert. Immediate changes to vegetation are expected to reduce quality of critical habitat, yet whether Tortoises will use burned and recovering habitat differently from intact unburned habitat is unknown. We compared movement patterns, home-range size, behavior, microhabitat use, reproduction, and survival for adult Desert Tortoises located in, and adjacent to, burned habitat to understand how Tortoises respond to recovering burned habitat. Approximately 45% of home ranges in the post-fire environment contained burned habitat, and numerous observations (n ¼12,223) corroborated Tortoise use of both habitat types (52% unburned, 48% burned). Tortoises moved progressively deeper into burned habitat during the first 5 years following the fire, frequently foraging in burned habitats that had abundant annual plants, and returning to adjacent unburned habitat for cover provided by intact perennial vegetation. However, by years 6 and 7, the live cover of the short-lived herbaceous perennial Desert globemallow (Sphaeralcea ambigua) that typically re-colonizes burned areas declined, resulting in a contraction of Tortoise movements from the burned areas. Health and egg production were similar between burned and unburned areas indicating that Tortoises were able to acquire necessary resources using both areas. This study documents that adult Mojave Desert Tortoises continue to use habitat burned once by wildfire. Thus, continued management of this burned habitat may contribute toward the recovery of the species in the face of many sources of habitat loss. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
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local niche differences predict genotype associations in sister taxa of Desert Tortoise
Diversity and Distributions, 2019Co-Authors: Taylor Edwards, Todd C Esque, Rich Inman, Stewart A Fotheringham, Janet Franklin, Kenneth E NussearAbstract:AIMS: To investigate spatial congruence between ecological niches and genotype in two allopatric species of Desert Tortoise that are species of conservation concern. LOCATION: Mojave and Sonoran Desert ecoregions; California, Nevada, Arizona, Utah, USA. METHODS: We compare ecological niches of Gopherus agassizii and Gopherus morafkai using species distribution modelling (SDM) and then calibrate a pooled‐taxa distribution model to explore local differences in species–environment relationships based on the spatial residuals of the pooled‐taxa model. We use multiscale geographically weighted regression (MGWR) applied to those residuals to estimate local species–environment relationships that can vary across the landscape. We identify multivariate clusters in these local species–environment relationships and compare them against models of (a) a geographically based taxonomic designation for two sister species and (b) an environmental ecoregion designation, with respect to their ability to predict a genotype association index for these two species. RESULTS: We find non‐identical niches for these species, with differences that span physiographic and vegetation niche dimensions. We find evidence for two distinct clusters of local species–environment relationships that when mapped, predict an index of genotype association for the two sister taxa better than did either the geographically based taxonomic designation or an environmental ecoregion designation. MAIN CONCLUSIONS: Exploring local species–environment relationships by coupling SDM and MGWR can benefit studies of biogeography and conservation. We find that niche separation in habitat selection conforms to genotypic differences between sister taxa of Tortoise in a recent secondary contact zone. This result may inform decision making by agencies with regulatory or land management authority for the two sister taxa addressed here.
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tools to understand seasonality in health quantification of microbe loads and analyses of compositional ecoimmunological data reveal complex patterns in mojave Desert Tortoise gopherus agassizii populations
Canadian Journal of Zoology, 2019Co-Authors: Franziska C Sandmeier, Kenneth E Nussear, C R Tracy, Kristina K Drake, K L Leonard, T E Esque, Jennifer M GermanoAbstract:Using data from six wild Mojave Desert Tortoise (Gopherus agassizii (Cooper, 1861)) populations, we quantified seasonal differences in immune system measurements and microbial load in the respirato...
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inferring social structure and its drivers from refuge use in the Desert Tortoise a relatively solitary species
Behavioral Ecology and Sociobiology, 2016Co-Authors: Kenneth E Nussear, Todd C Esque, Christina M Aiello, Peter J Hudson, Shweta BansalAbstract:For several species, refuges (such as burrows, dens, roosts, nests) are an essential resource for protection from predators and extreme environmental conditions. Refuges also serve as focal sites for social interactions, including mating, courtship, and aggression. Knowledge of refuge use patterns can therefore provide information about social structure, mating, and foraging success, as well as the robustness and health of wildlife populations, especially for species considered to be relatively solitary. In this study, we construct networks of burrow use to infer social associations in a threatened wildlife species typically considered solitary—the Desert Tortoise. We show that Tortoise social networks are significantly different than null networks of random associations, and have moderate spatial constraints. We next use statistical models to identify major mechanisms behind individual-level variation in Tortoise burrow use, popularity of burrows in Desert Tortoise habitat, and test for stressor-driven changes in refuge use patterns. We show that seasonal variation has a strong impact on Tortoise burrow switching behavior. On the other hand, burrow age and topographical condition influence the number of Tortoises visiting a burrow in Desert Tortoise habitat. Of three major population stressors affecting this species (translocation, drought, disease), translocation alters Tortoise burrow switching behavior, with translocated animals visiting fewer unique burrows than residents. In a species that is not social, our study highlights the importance of leveraging refuge use behavior to study the presence of and mechanisms behind non-random social structure and individual-level variation. Our analysis of the impact of stressors on refuge-based social structure further emphasizes the potential of this method to detect environmental or anthropogenic disturbances. Adaptive and social behavior that affects fitness is now being increasingly incorporated in the conservation and management of wildlife species. However, direct observations of social interactions in species considered to be solitary are difficult, and therefore integration of behavior in conservation and management decisions in such species has been infrequent. For such species, we propose quantifying refuge use behavior as it can provide insights towards their (hidden) social structure, establish relevant contact patterns of infectious disease spread, and provide early warning signals of population stressors. Our study highlights this approach in a long-lived and threatened species, the Desert Tortoise. We provide evidence toward the presence of and identify mechanisms behind the social structure in Desert Tortoises formed by their burrow use preferences. We also show how individuals burrow use behavior responds to the presence of population stressors.
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inferring social structure and its drivers from refuge use in the Desert Tortoise a relatively solitary species
bioRxiv, 2016Co-Authors: Kenneth E Nussear, Todd C Esque, Christina M Aiello, Peter J Hudson, Shweta BansalAbstract:For several species, refuges (such as burrows, dens, roosts, nests) are an essential resource for protection from predators and extreme environmental conditions. Refuges also serve as focal sites for social interactions including mating, courtship and aggression. Knowledge of refuge use patterns can therefore provide information about social structure, mating and foraging success, as well as the robustness and health of wildlife populations, especially for species considered to be relatively solitary. In this study, we construct networks of burrow use to infer social associations in a threatened wildlife species typically considered solitary - the Desert Tortoise. We show that Tortoise social networks are significantly different than null networks of random associations, and have moderate spatial constraints. We next use statistical models to identify major mechanisms behind individual-level variation in Tortoise burrow use, popularity of burrows in Desert Tortoise habitat and test for stressor-driven changes in refuge use patterns. We show that seasonal variation has a strong impact on Tortoise burrow switching behavior. On the other hand, burrow age and topographical condition influence the number of Tortoises visiting a burrow in Desert Tortoise habitat. Of three major population stressors affecting this species (translocation, drought, disease), translocation alters Tortoise burrow switching behavior, with translocated animals visiting fewer unique burrows than residents. In a species that is not social, our study highlights the importance of leveraging refuge use behavior to study the presence of and mechanisms behind non-random social structure and individual-level variation. Our analysis of the impact of stressors on refuge-based social structure further emphasizes the potential of this method to detect environmental or anthropogenic disturbances.
Todd C Esque - One of the best experts on this subject based on the ideXlab platform.
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Desert Tortoise Use of Burned Habitat in the
2020Co-Authors: K. Kristina Drake, Todd C Esque, Kenneth E Nussear, Lesley A. Defalco, Sara J. Scoles-sciulla, Andrew T. Modlin, Philip A MedicaAbstract:Wildfires burned 24,254ha of critical habitat designated for the recovery of the threatened Mojave Desert Tortoise (Gopherus agassizii) in southern Nevada during 2005. The proliferation of non-native annual grasses has increased wildfire frequency and extent in recent decades and continues to accelerate the conversion of Tortoise habitat across the Mojave Desert. Immediate changes to vegetation are expected to reduce quality of critical habitat, yet whether Tortoises will use burned and recovering habitat differently from intact unburned habitat is unknown. We compared movement patterns, home-range size, behavior, microhabitat use, reproduction, and survival for adult Desert Tortoises located in, and adjacent to, burned habitat to understand how Tortoises respond to recovering burned habitat. Approximately 45% of home ranges in the post-fire environment contained burned habitat, and numerous observations (n ¼12,223) corroborated Tortoise use of both habitat types (52% unburned, 48% burned). Tortoises moved progressively deeper into burned habitat during the first 5 years following the fire, frequently foraging in burned habitats that had abundant annual plants, and returning to adjacent unburned habitat for cover provided by intact perennial vegetation. However, by years 6 and 7, the live cover of the short-lived herbaceous perennial Desert globemallow (Sphaeralcea ambigua) that typically re-colonizes burned areas declined, resulting in a contraction of Tortoise movements from the burned areas. Health and egg production were similar between burned and unburned areas indicating that Tortoises were able to acquire necessary resources using both areas. This study documents that adult Mojave Desert Tortoises continue to use habitat burned once by wildfire. Thus, continued management of this burned habitat may contribute toward the recovery of the species in the face of many sources of habitat loss. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
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genes in space what mojave Desert Tortoise genetics can tell us about landscape connectivity
Conservation Genetics, 2020Co-Authors: Kirsten E Dutcher, Anna Mitelberg, Amy G Vandergast, Todd C Esque, Jill S Heaton, Marjorie D Matocq, Ken E NussearAbstract:Habitat loss and fragmentation in the Mojave Desert have been increasing, which can create barriers to movement and gene flow in populations of native species. Disturbance and degradation of Mojave Desert Tortoise habitat includes linear features (e.g. highways, railways, a network of dirt roads), urbanized areas, mining activities, and most recently, utility-scale solar facilities. To evaluate the spatial genetic structure of Tortoises in an area experiencing rapid habitat loss, we genotyped 299 Tortoises at 20 microsatellite loci from the Ivanpah valley region along the California/Nevada border. We used a Bayesian clustering analysis to quantify population genetic structure across valley and mountain pass habitats. A spatial principal components analysis was used to further investigate patterns with isolation-by-distance. To explicitly consider landscape features (e.g. habitat and anthropogenic linear barriers), we used maximum likelihood population effects analyses. We quantified recent gene flow through relatedness using a maximum likelihood pedigree approach. We detected three genetic clusters that generally corresponded to valleys separated by mountains, with one genetically distinguishable population in a mountain pass. Pedigree analyses showed second order relationships up to 60 km apart suggesting a greater range of interactions and inter-relatedness than previously suspected. Our results support historical gene flow with isolation-by-resistance and reveal reduced genetic connectivity across two parallel linear features bisecting our study area (a railway and a highway). Our work demonstrates the potential for Tortoises to use a range of habitats, spanning valleys to mountain passes, but also indicates habitat fragmentation limits connectivity with relatively rapid genetic consequences.
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development of a genotyping protocol for mojave Desert Tortoise scat
Chelonian Conservation and Biology, 2019Co-Authors: Anna Mitelberg, Amy G Vandergast, Ken E Nussear, Kirsten E Dutcher, Todd C EsqueAbstract:Abstract Noninvasive fecal genotyping can be a useful tool for population monitoring of elusive species. We tested extraction protocols on scat samples from the threatened Mojave Desert Tortoise, G...
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local niche differences predict genotype associations in sister taxa of Desert Tortoise
Diversity and Distributions, 2019Co-Authors: Taylor Edwards, Todd C Esque, Rich Inman, Stewart A Fotheringham, Janet Franklin, Kenneth E NussearAbstract:AIMS: To investigate spatial congruence between ecological niches and genotype in two allopatric species of Desert Tortoise that are species of conservation concern. LOCATION: Mojave and Sonoran Desert ecoregions; California, Nevada, Arizona, Utah, USA. METHODS: We compare ecological niches of Gopherus agassizii and Gopherus morafkai using species distribution modelling (SDM) and then calibrate a pooled‐taxa distribution model to explore local differences in species–environment relationships based on the spatial residuals of the pooled‐taxa model. We use multiscale geographically weighted regression (MGWR) applied to those residuals to estimate local species–environment relationships that can vary across the landscape. We identify multivariate clusters in these local species–environment relationships and compare them against models of (a) a geographically based taxonomic designation for two sister species and (b) an environmental ecoregion designation, with respect to their ability to predict a genotype association index for these two species. RESULTS: We find non‐identical niches for these species, with differences that span physiographic and vegetation niche dimensions. We find evidence for two distinct clusters of local species–environment relationships that when mapped, predict an index of genotype association for the two sister taxa better than did either the geographically based taxonomic designation or an environmental ecoregion designation. MAIN CONCLUSIONS: Exploring local species–environment relationships by coupling SDM and MGWR can benefit studies of biogeography and conservation. We find that niche separation in habitat selection conforms to genotypic differences between sister taxa of Tortoise in a recent secondary contact zone. This result may inform decision making by agencies with regulatory or land management authority for the two sister taxa addressed here.
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inferring social structure and its drivers from refuge use in the Desert Tortoise a relatively solitary species
Behavioral Ecology and Sociobiology, 2016Co-Authors: Kenneth E Nussear, Todd C Esque, Christina M Aiello, Peter J Hudson, Shweta BansalAbstract:For several species, refuges (such as burrows, dens, roosts, nests) are an essential resource for protection from predators and extreme environmental conditions. Refuges also serve as focal sites for social interactions, including mating, courtship, and aggression. Knowledge of refuge use patterns can therefore provide information about social structure, mating, and foraging success, as well as the robustness and health of wildlife populations, especially for species considered to be relatively solitary. In this study, we construct networks of burrow use to infer social associations in a threatened wildlife species typically considered solitary—the Desert Tortoise. We show that Tortoise social networks are significantly different than null networks of random associations, and have moderate spatial constraints. We next use statistical models to identify major mechanisms behind individual-level variation in Tortoise burrow use, popularity of burrows in Desert Tortoise habitat, and test for stressor-driven changes in refuge use patterns. We show that seasonal variation has a strong impact on Tortoise burrow switching behavior. On the other hand, burrow age and topographical condition influence the number of Tortoises visiting a burrow in Desert Tortoise habitat. Of three major population stressors affecting this species (translocation, drought, disease), translocation alters Tortoise burrow switching behavior, with translocated animals visiting fewer unique burrows than residents. In a species that is not social, our study highlights the importance of leveraging refuge use behavior to study the presence of and mechanisms behind non-random social structure and individual-level variation. Our analysis of the impact of stressors on refuge-based social structure further emphasizes the potential of this method to detect environmental or anthropogenic disturbances. Adaptive and social behavior that affects fitness is now being increasingly incorporated in the conservation and management of wildlife species. However, direct observations of social interactions in species considered to be solitary are difficult, and therefore integration of behavior in conservation and management decisions in such species has been infrequent. For such species, we propose quantifying refuge use behavior as it can provide insights towards their (hidden) social structure, establish relevant contact patterns of infectious disease spread, and provide early warning signals of population stressors. Our study highlights this approach in a long-lived and threatened species, the Desert Tortoise. We provide evidence toward the presence of and identify mechanisms behind the social structure in Desert Tortoises formed by their burrow use preferences. We also show how individuals burrow use behavior responds to the presence of population stressors.
Richard C Tracy - One of the best experts on this subject based on the ideXlab platform.
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chronic disease in the mojave Desert Tortoise host physiology and recrudescence obscure patterns of pathogen transmission
Ecology and Evolution, 2017Co-Authors: Franziska C Sandmeier, S. A. Dupre', Hossein Ali Mohammadpour, Richard C Tracy, Ron Marlow, Nichole Maloney, David Hyde, K. W. HunterAbstract:A seminatural, factorial-design experiment was used to quantify dynamics of the pathogen Mycoplasma agassizii and upper respiratory tract disease in the Mojave Desert Tortoise (Gopherus agassizii) over 2 years. Groups of initially healthy animals were separated into serologically positive (seropositive), seronegative, and artificially infected groups and paired into 23 pens. We found no evidence of long-term immune protection to M. agassizii or of immunological memory. Initially seronegative, healthy Tortoises experienced an equal amount of disease when paired with other seronegative groups as when paired with seropositive and artificially infected groups—suggesting that recrudescence is as significant as transmission in introducing disease in individuals in this host–pathogen system. Artificially infected groups of Tortoises showed reduced levels of morbidity when paired with initially seronegative animals—suggesting either a dilution effect or a strong effect of pathogen load in this system. Physiological dynamics within the host appear to be instrumental in producing morbidity, recrudescence, and infectiousness, and thus of population-level dynamics. We suggest new avenues for studying diseases in long-lived ectothermic vertebrates and a shift in modeling such diseases.
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mycoplasmal upper respiratory tract disease across the range of the threatened mojave Desert Tortoise associations with thermal regime and natural antibodies
Ecohealth, 2013Co-Authors: Franziska C Sandmeier, S. A. Dupre', Hossein Ali Mohammadpour, Bridgette E Hagerty, Richard C Tracy, K. W. HunterAbstract:Most research of upper respiratory tract disease (mycoplasmal URTD) in the threatened Mojave Desert Tortoise (Gopherus agassizii) has worked under the hypothesis that the pathogen, Mycoplasma agassizii, has a relatively consistent and predictable effect on Tortoise populations across their natural range. In contrast, we hypothesized that multiple factors influence the prevalence of disease and analyzed biological and environmental variables that vary significantly across the Mojave Desert. We used multiple regression models to analyze associations between mycoplasmal URTD and the genetic structure of 24 Tortoise populations, levels of natural antibody (NAb) to M. agassizii in Tortoises (one component of the innate immune system), precipitation, and colder thermal regimes. We detected a significant, positive association between mean levels of NAb and seroprevalence to M. agassizii. We hypothesized that NAbs may provide tolerance to mycoplasmal infections and that more tolerant populations may act as host reservoirs of disease. We also detected significant associations between colder winters and mycoplasmal URTD, suggesting that colder winters may depress Tortoise immune resistance against M. agassizii or enhance conditions for the growth of M. agassizii.
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making molehills out of mountains landscape genetics of the mojave Desert Tortoise
Landscape Ecology, 2011Co-Authors: Bridgette E Hagerty, Todd C Esque, Kenneth E Nussear, Richard C TracyAbstract:Heterogeneity in habitat often influences how organisms traverse the landscape matrix that connects populations. Understanding landscape connectivity is important to determine the ecological processes that influence those movements, which lead to evolutionary change due to gene flow. Here, we used landscape genetics and statistical models to evaluate hypotheses that could explain isolation among locations of the threatened Mojave Desert Tortoise (Gopherus agassizii). Within a causal modeling framework, we investigated three factors that can influence landscape connectivity: geographic distance, barriers to dispersal, and landscape friction. A statistical model of habitat suitability for the Mojave Desert Tortoise, based on topography, vegetation, and climate variables, was used as a proxy for landscape friction and barriers to dispersal. We quantified landscape friction with least-cost distances and with resistance distances among sampling locations. A set of diagnostic partial Mantel tests statistically separated the hypotheses of potential causes of genetic isolation. The best-supported model varied depending upon how landscape friction was quantified. Patterns of genetic structure were related to a combination of geographic distance and barriers as defined by least-cost distances, suggesting that mountain ranges and extremely low-elevation valleys influence connectivity at the regional scale beyond the Tortoises’ ability to disperse. However, geographic distance was the only influence detected using resistance distances, which we attributed to fundamental differences between the two ways of quantifying friction. Landscape friction, as we measured it, did not influence the observed patterns of genetic distances using either quantification. Barriers and distance may be more valuable predictors of observed population structure for species like the Desert Tortoise, which has high dispersal capability and a long generation time.
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defining population structure for the mojave Desert Tortoise
Conservation Genetics, 2010Co-Authors: Bridgette E Hagerty, Richard C TracyAbstract:We used highly variable microsatellite markers to identify population structure, movement, and biological boundaries for populations of the Desert Tortoise, Gopherus agassizii, in the Mojave and Colorado Deserts of the southwestern United States. The Mojave Desert Tortoise (listed as “threatened” by the U.S. Fish and Wildlife Service) has a large geographic range, long generation time, low population densities, and little above-ground activity. Additionally, the dispersal patterns of individual Tortoises are virtually unknown, making indirect methods to assess movement among populations valuable. Using Bayesian assignment tests, we detected hierarchical structuring within the Mojave Desert Tortoise. Three basal groups were identified, and these corresponded to the mitochondrial DNA haplotypes reported in 1989. Additional population structure was evident within each basal unit, and this structure corresponds with major geographic barriers. Our analyses suggest that gene flow among populations was historically high because levels of population differentiation were low across the range. Geographic distance explained a large proportion of variation in genetic distance (68%), which pinpoints that dispersal is limited only on a regional scale. In light of these new analyses of the genetic population structure of the Mojave Desert Tortoise, we make new recommendations for the number and locations of recovery units for conservation of this species.
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upper respiratory tract disease urtd as a threat to Desert Tortoise populations a reevaluation
Biological Conservation, 2009Co-Authors: Franziska C Sandmeier, S. A. Dupre', Richard C Tracy, K. W. HunterAbstract:The relationships between Mycoplasma agassizii, a causative agent of upper respiratory disease (URTD), and Desert Tortoise (Gopherus agassizii), generally illustrate the complexities of disease dynamics in wild vertebrate populations. In this review, we summarize current understanding of URTD in Mojave Desert Tortoise populations, we illustrate how inadequate knowledge of Tortoise immune systems may obfuscate assessment of disease, and we suggest approaches to future management of URTD in Desert Tortoise populations. We challenge the view that M. agassizii causes consistent levels of morbidity and/or mortality across the Mojave Desert. Instead, URTD may be described more accurately as a context-dependent disease. In addition, new evidence for relatively high levels of natural antibodies to M. agassizii in Desert Tortoises suggests possible problems in conventional diagnostic tests of disease in Tortoises as well as a possible Tortoise immune mechanism to protect against M. agassizii. Partly because of the problems in diagnostic testing, we recommend abandoning policies to euthanize Tortoises that test positive for an immune response to M. agassizii. Based on this review, we question management strategies aimed solely at reducing Mycoplasma spp. in Desert Tortoise populations, and advocate a more careful consideration of extrinsic factors as a cause of symptomatic disease.