Dissertations / Theses: 'Desert tortoise'

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Edwards, Taylor. "Desert tortoise conservation genetics." Thesis, The University of Arizona, 2003. http://hdl.handle.net/10150/291566.

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Managing for the long-term survival of a species requires an understanding of its population genetics. The desert tortoise, Gopherus agassizii, inhabits the Mojave and Sonoran deserts of North America. Desert tortoises face many threats to their continued survival, including habitat loss and fragmentation. I used mitochondrial and microsatellite DNA markers to examine genetic structure within and among populations of desert tortoises. I found that both the Mojave and Sonoran populations of desert tortoise exhibit similar patterns of population genetic structure. Gene flow among localities within each region is part of the evolutionary history of the desert tortoise and dispersal events probably play an important role in the long-term maintenance of populations. Movement barriers caused by anthropogenic landscape changes have the potential to effect desert tortoise population viability. Understanding the historical connectivity between and within the Mojave and Sonoran populations of desert tortoises will help facilitate the conservation of this species.

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Gundlach, David L. "Analysis of patch shape and area in desert tortoise habitat." abstract and full text PDF (free order & download UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1456426.

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Kingdon, Lorraine B. "The Search for the Desert Tortoise." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 1992. http://hdl.handle.net/10150/622392.

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Hagerty, Bridgette E. "Ecological genetics of the Mojave desert tortoise." abstract and full text PDF (UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3339179.

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McLuckie, Ann Marie 1965. "Genetics, morphology, and ecology of the desert tortoise (Gopherus agassizii) in the Black Mountains, Mohave County, Arizona." Thesis, The University of Arizona, 1995. http://hdl.handle.net/10150/278528.

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Desert tortoises (Gopherus agassizii) occurring east and south of the Colorado River form the "Sonoran population," a regulatory designation of the U.S. Fish and Wildlife Service, whereas tortoises west and north of the river constitute the "Mojave population." This distinction is based on significant genetic, morphometric and ecological differences. However, mitochondrial DNA, morphometric, and ecological data from the eastern bajada of the Black Mountains (about 40 km east of the Colorado River) identify the evolutionary affinities of those tortoises as Mojavean: ten of eleven Black Mountain tortoises possessed the Mojave genotype, twenty-four of thirty-seven tortoises predominantly expressed the Mojave phenotype, and all tortoises were similar to Mojave populations in macrohabitat selection. Some ecological and behavioral attributes such as home range size and hibernaculum selection did not differ among Mojave, Sonoran, and Black Mountain tortoises. Several hypotheses on how the Mojave trait became established in the Black Mountains are discussed.

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Eliker, Michelle Lee. "The use of spatial reference cues and primary cue strategies for maze running by the desert tortoise, Gopherus Agassizii." CSUSB ScholarWorks, 1997. https://scholarworks.lib.csusb.edu/etd-project/1438.

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Sandmeier, Franziska C. "Immunology and disease in the Mojave Desert tortoise (Gopherus agassizii)." abstract and full text PDF (UNR users only), 2009. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3387823.

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Martin, Brent Errol 1952. "Ecology of the desert tortoise (Gopherus agassizii) in a desert-grassland community in southern Arizona." Thesis, The University of Arizona, 1995. http://hdl.handle.net/10150/278515.

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After 6-10 years of mark-recapture observations, I studied seven desert tortoises by radio-telemetry during 1990-1992 in a desert-grassland community in Pinal County, Arizona. Six estimated home-range areas averaged 14.7 ha. Winter-spring (Nov-Jun) use areas (overline x=0.7 ha) were significantly smaller (P = 0.002) than summer-fall (Jul-Oct) use areas (overline x=10.7 ha). A correction formula inflated 1-2 summer-fall use areas of five tortoises 4-41% larger than their corrected home-range areas. Extended movements by females were significantly more frequent (P = 0.0001) than those of males during Mar-Jul, significantly less frequent (P = 0.0057) than males during Aug-Oct, and most frequent by both sexes in September. Use of two slopes and terraces was not season-dependent (P = 0.9159). Tortoises variably used four shelter types (rock, soil burrow, wood rat nest, vegetation), significantly with south-facing entrance aspects (P 0.0005). Hibernaculum structure and location varied. Hibernation ranged from 88-315 days. Radio-equipped tortoises included reuse of mark-recapture locations.

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Curtin, Amanda Jane Spotila James R. "Bone growth strategies and skeletochronological age estimates of desert tortoise (Gopherus agassizii) populations /." Philadelphia, Pa. : Drexel University, 2006. http://dspace.library.drexel.edu/handle/1860%20/838.

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Jones, Cristina Ann. "MYCOPLASMA AGASSIZII IN THE SONORAN POPULATION OF THE DESERT TORTOISE IN ARIZONA." Thesis, The University of Arizona, 2008. http://hdl.handle.net/10150/193431.

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Upper Respiratory Tract Disease (URTD), caused by the pathogens Mycoplasma agassizii and M. testudineum, has been documented in the desert tortoise (Gopherus agassizii). Although URTD was identified as a putative agent that led to federal listing of the Mojave population of the desert tortoise, little is known about this disease in the Sonoran population of the desert tortoise. The purpose of this study was to determine: 1) the prevalence of URTD across an urban gradient in Greater Tucson, Arizona, 2) the relationship between URTD and captive and free-ranging tortoises in Mohave, Maricopa, and Pima counties in Arizona, and 3) the effects of URTD on desert tortoise home range size and winter temperature selection.

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Inman, Richard D. "How elusive behavior and climate influence the precision of density estimates and desert tortoise populations." abstract and full text PDF (free order & download UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1453581.

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12

Murray, Roy Charles 1968. "Mark-recapture methods for monitoring Sonoran populations of the desert tortoise (Gopherus agassizii)." Thesis, The University of Arizona, 1993. http://hdl.handle.net/10150/278380.

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I determined reliable methods for monitoring Sonoran populations of the desert tortoise. Tortoises were significantly clumped (p < 0.001) on three 1-mi² plots in Arizona, but were not significantly different from random (p > 0.05) on a 1-km² plot, supporting the use of smaller plots in mark-recapture population studies. Simulations showed that Program CAPTURE's Jackknife and Darroch estimators are robust to variations in capturability, which confound most commonly used estimators (e.g., Lincoln-Petersen). Mean capturability determines which estimator is most appropriate for a given population. These methods were applied to data from several tortoise populations. CAPTURE's Jackknife method estimated 70 tortoises/km² in a Mazatzal Mountain, Arizona, population surveyed during 1992. Density was corrected with the mean maximum distance moved method. Regression of CAPTURE estimates indicated two separate populations were stable or increasing from 1990 to 1992, while a third declined. Program JOLLY estimated high survivorship for these three populations (87-100%), but recruitment was lowest for the decreasing population (0-17 tortoises/year).

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Zylstra, Erin R. "Evaluating Monitoring Strategies and Habitat for Tortoises in the Sonoran Desert." Thesis, The University of Arizona, 2008. http://hdl.handle.net/10150/193429.

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Effective conservation requires efficient population monitoring, which can be challenging for rare species like the desert tortoise (Gopherus agassizii). We compared two alternative survey methods that can be used to monitor tortoise populations: distance sampling and site occupancy estimation. In 2005 and 2006 combined, we surveyed 120 1-km transects to estimate density and 40 3-ha plots with five presence-“absence” surveys to estimate occupancy of Sonoran desert tortoises in two mountain ranges in southern Arizona. We found that monitoring programs based on an occupancy framework were more efficient and had greater power to detect linear trends. We also found that habitat use by Sonoran desert tortoises was influenced most by slope and aspect, contrasting with patterns observed in the Mojave Desert. Given its efficiency, power, and ability to gauge changes in distribution while accounting for variation in detectability, occupancy offers a promising alternative for long-term monitoring of Sonoran desert tortoise populations.

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Crossley, Dane Alan. "Development of Cardiovascular Regulation in Embryos of the Domestic Fowl (Gallus Gallus), with a Partial Comparison to Embryos of the Desert Tortoise (Gopherus Agassizii)." Thesis, University of North Texas, 1999. https://digital.library.unt.edu/ark:/67531/metadc2223/.

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In adult vertebrates, cardiovascular regulation is accomplished by numerous systems with neural, hormonal and local components responsible for the majority of regulation. These regulatory components work in concert to maintain the essential function of blood perfusion to adult tissues. Given the essential nature of this function it is therefore surprising that the development of cardiovascular regulation during gestation is poorly understood. The majority of what is known is based on a single vertebrate model, the fetal lamb. The fetal lamb has been used in multiple studies due to the clear clinical applications and has been pivotal in understanding the onset of regulation in developing vertebrates. However, study on the fetal lamb is limited to the latter 40% of gestation and has the added complication of an in-utero developmental strategy. Therefore the primary focus of this dissertation was to characterize basic cardiovascular regulation in the chicken embryo to provided the needed information for it's use an alternative to the fetal lamb. Developing chicken embryos rely on both alpha and beta adrenergic tones to maintain normal heart rate and arterial blood pressure during incubation. However, on day 21, just prior to hatch, these animals lose both tones on arterial pressure suggesting the onset of adult regulation. Cholinergic tone, however, was absent throughout chicken development indicating that it must mature during the neonatal life. Adult cardiovascular reflexes become apparent late in chicken development with a clear baroreflex specifically operating initially on day. However, an adult response to changes in ambient gas tension was absent during incubation suggesting embryos possess unique regulatory systems that are absent in adult chickens. This mechanism is comprised entirely of adrenergic systems with no cholinergic action during change in ambient gas tension. Similar developmental patterns were determined in embryos of the desert tortoise suggesting fundamental differences between in-utero and ex-utero developing vertebrates.

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Tollis, Marc, Dale F. DeNardo, John A. Cornelius, Greer A. Dolby, Taylor Edwards, Brian T. Henen, Alice E. Karl, Robert W. Murphy, and Kenro Kusumi. "The Agassiz’s desert tortoise genome provides a resource for the conservation of a threatened species." PUBLIC LIBRARY SCIENCE, 2017. http://hdl.handle.net/10150/624695.

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Agassiz's desert tortoise (Gopherus agassizii) is a long-lived species native to the Mojave Desert and is listed as threatened under the US Endangered Species Act. To aid conservation efforts for preserving the genetic diversity of this species, we generated a whole genome reference sequence with an annotation based on deep transcriptome sequences of adult skeletal muscle, lung, brain, and blood. The draft genome assembly for G. agassizii has a scaffold N50 length of 252 kbp and a total length of 2.4 Gbp. Genome annotation reveals 20,172 protein-coding genes in the G. agassizii assembly, and that gene structure is more similar to chicken than other turtles. We provide a series of comparative analyses demonstrating (1) that turtles are among the slowest-evolving genome-enabled reptiles, (2) amino acid changes in genes controlling desert tortoise traits such as shell development, longevity and osmoregulation, and (3) fixed variants across the Gopherus species complex in genes related to desert adaptations, including circadian rhythm and innate immune response. This G. agassizii genome reference and annotation is the first such resource for any tortoise, and will serve as a foundation for future analysis of the genetic basis of adaptations to the desert environment, allow for investigation into genomic factors affecting tortoise health, disease and longevity, and serve as a valuable resource for additional studies in this species complex.

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Bailey, Scott Jay 1965. "Hibernacula use and home range of the desert tortoise (Gopherus agassizii) in the San Pedro Valley, Arizona." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278229.

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I quantified several aspects of hibernacula use and estimated home ranges of desert tortoises (Gopherus agassizii) in the San Pedro Valley, Arizona. Tortoises hibernated primarily on steep southerly slopes. Hibernacula included burrows in silt, silt with loose gravel, diatomite and/or diatomaceous marl, and beneath an ash layer, often in conjunction with live vegetation, dead and downed vegetation, and packrat (Neotoma albigula) nests. Male tortoises used longer hibernacula than females (p < 0.02). Female maximum hibernacula temperatures were consistently higher than male maximum hibernacula temperatures, but the difference was not significant (0.05 < p < 0.10). Female minimum hibernacula temperatures were significantly lower than males (p < 0.001) and female hibernacula temperatures fluctuated over a significantly wider temperature range than males (p < 0.01). Hibernacula used by males provided greater thermal buffering than those used by females. Duration of hibernation was positively correlated with shelter length. Home-range estimates did not differ significantly between males and females.

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Agha, Mirza Mickey. "A LONG-TERM INVESTIGATION OF THE FEDERALLY THREATENED DESERT TORTOISE (GOPHERUS AGASSIZII) AT A WIND ENERGY FACILITY IN SOUTHERN CALIFORNIA." UKnowledge, 2015. http://uknowledge.uky.edu/forestry_etds/21.

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With the recent increase in utility-scale wind energy development and current climate variation in the desert southwest US, researchers have become increasingly concerned with the reaction of wildlife and critical habitat. Understanding the relationships among monitoring efforts, climate, industrial landscapes and wildlife is critical to effective management. Given the need for information available on how these potential stressors affect terrestrial wildlife, my objective was to determine how climate variation, wind energy facilities (WEF) and monitoring efforts by researchers influence behavior and survivorship in a population of the federally threatened desert tortoise (Gopherus agassizii). Data were collected via surveys, motion-sensor camera trapping and radio-telemetry during the span of two decades at a WEF in California. Using capture-mark-recapture survivorship analysis and generalized linear mixed-effects models, I acquired long-term estimates of survivorship, activity, and levels of stress response to researchers and climate. From this study I found that researchers as well as abiotic effects influence the probability of voiding, a possible stress induced behavior in desert tortoises. Additionally, we found that tortoise activity and survival is constrained by winter precipitation and habitat types. Further research is needed on proximate mechanisms of wind turbines (noise and vibration) and their effects on desert tortoise behavior.

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Edwards, Taylor Artemus. "A Biogeographic Perspective of Speciation Among Desert Tortoises in the Genus Gopherus." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/556486.

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One of the important contributions genetic studies have made to conservation is the ability to resolve taxonomy and define relationships among populations. However, this can be complicated when species exhibit hybridization. Hybridization can be an important part of the evolutionary process and a critical component in a species ability to adapt to a changing environment. Most hybrid zones are observed at ecotones between two distinct habitats and this may be important in defining the role of hybrid zones in the evolutionary process. I examined hybridization among the three distinct lineages of desert tortoises in the genus Gopherus. An important aspect of this study system is the presence of areas of overlap between divergent lineages of desert tortoise which allowed me to test hypotheses about which forces influence these taxonomic boundaries. Specifically, I tested hypotheses about the contribution of physical vs. ecological segregation and the relative importance of isolation and gene flow in the formation of these disparate desert tortoise lineages. I used mtDNA sequence data and 25 microsatellite loci to perform Bayesian clustering, clinal analyses and habitat suitability modeling to infer population structure and influence of landscape features at each contact zone. In both instances, I observed ecological niche partitioning and limited hybridization at ecotones. I then used mtDNA and four nDNA loci to perform a multi-locus phylogenetic analysis to estimate the species tree among desert tortoise lineages and tested for ancestral admixture with RNA-seq data using demographic inference employed in the software package ∂a∂i. My results validate taxonomic distinction among all three lineages without evidence of ancestral introgression. These data suggest that despite the presence of contemporary hybridization and incomplete reproductive isolation, divergence among these lineages is consistent with species-level differentiation. By clarifying the evolutionary processes that influence the distribution of desert tortoise lineages, this study will directly inform efforts to preserve the evolutionary potential of these threatened species. Ultimately, understanding the evolutionary history of desert tortoises not only clarifies the forces that have driven speciation in this group, but it also contributes to our knowledge of the biogeographic history of the southwestern deserts and how diversity is maintained within them.

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Edwards, Taylor, Kristin H. Berry, Richard D. Inman, Todd C. Esque, Kenneth E. Nussear, Cristina A. Jones, and Melanie Culver. "Testing Taxon Tenacity of Tortoises: evidence for a geographical selection gradient at a secondary contact zone." Wiley, 2015. http://hdl.handle.net/10150/621245.

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UA Open Access Publishing Fund
We examined a secondary contact zone between two species of desert tortoise, Gopherus agassizii and G. morafkai. The taxa were isolated from a common ancestor during the formation of the Colorado River (4–8 mya) and are a classic example of allopatric speciation. However, an anomalous population of G. agassizii comes into secondary contact with G. morafkai east of the Colorado River in the Black Mountains of Arizona and provides an opportunity to examine reinforcement of species’ boundaries under natural conditions. We sampled 234 tortoises representing G. agassizii in California (n = 103), G. morafkai in Arizona (n = 78), and 53 individuals of undetermined assignment in the contact zone including and surrounding the Black Mountains. We genotyped individuals for 25 STR loci and determined maternal lineage using mtDNA sequence data. We performed multilocus genetic clustering analyses and used multiple statistical methods to detect levels of hybridization. We tested hypotheses about habitat use between G. agassizii and G. morafkai in the region where they co-occur using habitat suitability models. Gopherus agassizii and G. morafkai maintain independent taxonomic identities likely due to ecological niche partitioning, and the maintenance of the hybrid zone is best described by a geographical selection gradient model.

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20

Nguyen, Linh Thu. "A spatial model for studying population dynamics of the California Mojave Desert tortoise /." 1999. http://hdl.handle.net/1957/9862.

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21

"Ecological genetics of the Mojave Desert tortoise." UNIVERSITY OF NEVADA, RENO, 2009. http://pqdtopen.proquest.com/#viewpdf?dispub=3339179.

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22

"Sonoran Desert Tortoise (Gopherus morafkai) Growth and Juvenile Habitat Selection at a Long-term Study Site in Central Arizona, USA." Master's thesis, 2012. http://hdl.handle.net/2286/R.I.15900.

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abstract: Biological diversity is threatened by increasing anthropogenic modification of natural environments and increasing demands on natural resources. Sonoran desert tortoises (Gopherus morafkai) currently have Candidate status under the Endangered Species Act (ESA) based on health and habitat threats. To ensure this animal persists in the midst of multiple threats requires an understanding of the life history and ecology of each population. I looked at one physiological and one behavioral aspect of a population of tortoises at the Sugarloaf Mountain (SL) study site in central Arizona, USA. I used 21 years of capture-recapture records to estimate growth parameters of the entire population. I investigated habitat selection of juvenile tortoises by selecting 117 locations of 11 tortoises that had been tracked by radio-telemetry one to three times weekly for two years, selecting locations from both summer active season and during winter hibernation. I compared 22 microhabitat variables of tortoise locations to random SL locations to determine habitat use and availability. Male tortoises at SL reach a greater asymptotic length than females, and males and females appear to grow at the same rate. Juvenile tortoises at the SL site use steep rocky hillsides with high proportions of sand and annual vegetation, few succulents, and enclosed shelters in summer. They use enclosed shelters on steep slopes for winter hibernation. An understanding of these features can allow managers to quantify Sonoran desert tortoise habitat needs and life history characteristics and to understand the impact of land use policies.
Dissertation/Thesis
M.S. Applied Biological Sciences 2012

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23

Bulova, Susan Jan. "Patterns of burrow use by desert tortoises influence of microclimate and chemical cues /." 1994. http://catalog.hathitrust.org/api/volumes/oclc/32405935.html.

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Dissertations / Theses on the topic 'Desert tortoise'

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