Western blot can distinguish natural and acquired antibodies to Mycoplasma agassizii in the desert tortoise (Gopherus agassizii)

Mycoplasma agassizi has been identified as a cause of upper respiratory tract disease (URTD) in the threatened Mojave population of the desert tortoise (Gopherus agassizii), and anti-M. agassizii antibodies have been found by ELISA in as many as 15% of these animals across their geographic range. Here we report that a cohort of 16 egg-reared desert tortoises never exposed to M. agassizii had ELISA antibody titers to this organism that overlapped with titers obtained from some M. agassizii-infected tortoises. These natural antibodies were predominantly of the IgM class. Western blots of plasma from these non-infected tortoises produced a characteristic banding pattern against M. agassizii antigens. A group of 38 wild-caught desert tortoises was tested by ELISA, and although some of these tortoises had antibody titers significantly higher than the non-infected tortoises, there was considerable overlap at the lower titer levels. However, Western blot analysis revealed distinct banding patterns that could readily distinguish between the non-infected tortoises and tortoises with acquired antibodies, regardless of ELISA antibody titers. We conclude that desert tortoises have natural antibodies to M. agassizii that can compromise the determination of infection status by ELISA. However, the Western blot technique can distinguish between natural and acquired antibody patterns and can be used to confirm the diagnosis of M. agassizii infections in the desert tortoise.     

PCR primers for microsatellite loci in the desert tortoise (Gopherus agassizii,Testudinidae)

The desert tortoise, Gopherus agassizii, is a threatened species native to the North American desert southwest and is recognized as having distinct Mojave and Sonoran populations. We identified six polymorphic microsatellite loci in the desert tortoise. All six loci were polymorphic in Sonoran samples. Five of the loci were variable in Mojave samples with varying degrees of amplification success. Two of the loci exhibited low allelic variation (2–3 alleles) while four were highly variable (8–27 alleles).     

Flow cytometric method for quantifying viable Mycoplasma agassizii,an agent of upper respiratory tract disease in the desert tortoise (Gopherus agassizii)

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.     

Polymorphic microsatellite markers for the Mojave desert tortoise, Gopherus agassizii

We describe primers and polymerase chain reaction (PCR) conditions to amplify 14 tri- and tetranucleotide microsatellite loci for the Mojave desert tortoise (Gopherus agassizii). Across three populations (87 individuals) located in the Mojave Desert, USA, the markers yielded a range of four to 33 alleles and an average observed heterozygosity of 0.733 (range 0.433 to 0.933). We neither detected linkage disequilibrium between any pair of loci nor did we find a consistent pattern of deviation from Hardy-Weinberg equilibrium. These microsatellites are designed for PCR multiplexing, and provide higher throughput capacity to aid in conservation genetics studies for this threatened species.     

Histomorphometric studies of dermal bone in the desert tortoise, Gopherus agassizii.

Dermal bone biopsies were collected from the periphery of the carapaces of adult desert tortoises (Gopherus agassizii) from grazed and ungrazed habitats near the Arizona/Utah border (USA). Quantitative bone histomorphometry was performed on these biopsies as well as on dermal bone biopsies collected from captive juvenile desert tortoises. Except for mild osteomalacia, carapaces of adult desert tortoises from the grazed habitat were relatively normal. No signs of osteopenia were observed. Based on the low numbers of osteoblasts and osteoclasts in dermal bone of both populations of adult desert tortoises, it appears that the peripheral carapace is relatively inert with very low levels of dermal bone turnover. Bone cells and osteoid were more common in dermal bone biopsies from the carapace and plastron of captive juvenile desert tortoises than in adult desert tortoises. However, the great variability in the incidence of bone cells among individuals and the difficulty in collecting juvenile desert tortoises in the field limit the usefulness of dermal bone biopsies from animals of this age group. Based on these results, we propose that dermal bone of the peripheral carapace is a poor sample site for evaluating the effects of dietary or environmental conditions on calcified tissues in desert tortoises.     

Using motion-sensor camera technology to infer seasonal activity and thermal niche of the desert tortoise (Gopherus agassizii)

Understanding the relationships between environmental variables and wildlife activity is an important part of effective management. The desert tortoise (Gopherus agassizii), an imperiled species of arid environments in the southwest US, may have increasingly restricted windows for activity due to current warming trends. In summer 2013, we deployed 48 motion sensor cameras at the entrances of tortoise burrows to investigate the effects of temperature, sex, and day of the year on the activity of desert tortoises. Using generalized estimating equations, we found that the relative probability of activity was associated with temperature (linear and quadratic), sex, and day of the year. Sex effects showed that male tortoises are generally more active than female tortoises. Temperature had a quadratic effect, indicating that tortoise activity was heightened at a range of temperatures. In addition, we found significant support for interactions between sex and day of the year, and sex and temperature as predictors of the probability of activity. Using our models, we were able to estimate air temperatures and times (days and hours) that were associated with maximum activity during the study. Because tortoise activity is constrained by environmental conditions such as temperature, it is increasingly vital to conduct studies on how tortoises vary their activity throughout the Sonoran Desert to better understand the effects of a changing climate.     

Quantitative PCR method for detection of mycoplasma spp. DNA in nasal lavage samples from the desert tortoise (Gopherus agassizii)

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.     

Digesta passage and functional anatomy of the digestive tract in the desert tortoise (Xerobates agassizii)

The herbivorous tortoise Xerobates agassizii contents with large fluctuations in the quality and abundance of desert pastures. Responses to grass (Schismus barbatus), herbage (Sphaeralcea ambigua) and pelleted diets were studied in captive animals. Digestive anatomy was investigated in wild tortoises. Cornified esophageal epithelia and numerous mucus glands along the digestive tract indicated a resistance to abrasive diets. Gastric contents were acidic whereas hindgut digesta were near neutral pH. The colon was the primary site of fermentation with short-chain fatty acids mainly comprised of acetate (69–84%), propionate (10–15%) and n-butyrate (1–12%). Fibre digestion was extensive and equivalent to 22–64% of digestible energy intakes. Large particles of grass (25 mm Crmordants) were excreted as a pulse but retained longer than either fluids (Co-EDTA) or fine particles (2 mm; Yb). Patterns of marker excretion suggested irregular mixing of only the fluid and fine particulate digesta in the stomach and the colon. Mean retention times of Crmordants were 14.2–14.8 days on the grass and highfibre pellets. Intakes of grass were low and accompanied by smaller estimates of digesta fill than for the high-fibre pellets. Digestive capacity was large and estimated at 11–21% of body mass on these diets. The capacious but simple digestive anatomy of the tortoise may provide the greatest flexibility in utilizing a variety of forages in its unreliable habitat.Abbreviations bm body mass - DM drymatter - EDTA ethylene-diamine tetra-acetic acid - MRT mean retention time - NDF neutral detergent fibre - SCFA short-chain fatty acid(s) - T _max time to maximum marker concentration     

Neuroendocrine peptides (insulin, pancreatic polypeptide, neuropeptide Y, galanin, somatostatin, substance P, and neuropeptide gamma) from the desert tortoise, Gopherus agassizii.

The traditional view that Testudines (tortoises and turtles) should be regarded as the surviving clade of the anapsid reptiles rather than classified with the diapsid reptiles (snakes, lizards, and crocodiles) has recently been challenged. Neuropeptide Y, neuropeptide gamma, and somatostatin-14 were isolated from an extract of the brain, substance P and galanin from an extract of the intestine, and insulin and pancreatic polypeptide from an extract of the pancreas of the desert tortoise, Gopherus agassizii. Despite that crocodilians did not appear until the late Triassic, the amino acid sequences of the tortoise peptides resemble those of the American alligator quite closely. The primary structures of neuropeptide Y, somatostatin-14, and neuropeptide gamma are the same in tortoise and alligator. The primary structures of substance P, insulin, galanin, and pancreatic polypeptide in the two species differ by 1, 3, 5, and 8 amino acid residues, respectively. Although fewer neurohormonal peptides from squamates (lizards and snakes) have been characterized, the primary structures of neuropeptide gamma, insulin, and pancreatic polypeptide from the Burmese python and the desert tortoise differ by 3, 8, and 18 residues, respectively. The data suggest, therefore, a closer phylogenetic relationship between Testudines and Crocodilians than that derived from 'classical' analyses based on morphological criteria and the fossil record.     

Sex differences in plasma corticosterone in desert tortoises, Gopherus agassizii, during the reproductive cycle

Blood samples from 30 female and 20 male adult desert tortoises, Gopherus agassizii, were collected at monthly intervals during the annual reproductive cycle (April to October). Plasma corticosterone and the sex steroids in each of the samples were analyzed by radioimmunoassay. Mean corticosterone levels in males were significantly higher than in females (P < 0.001) in every month. Male tortoises showed a marked seasonal pattern in plasma corticosterone with a highly significant peak in July, August, September, and October that corresponded with a similar peak in plasma testosterone. Testosterone and corticosterone in the male showed a highly significant correlation (P < 0.0001). The pattern of corticosterone in the female was less marked, with a significant peak in May during the mating and nesting season, but no association with the peak in estradiol in late summer was apparent. The highest levels of corticosterone in the males were associated with the peak in spermatogenesis and intense male-male combat. These results support similar data from other reptiles that suggest increased glucocorticoid secretion during periods of increased activity and metabolism.     

Variation in plasma lipids during the reproductive cycle of male and female desert tortoises,Gopherus agassizii

Plasma triacylglycerol, phospholipid, cholesterol, cholesterol esters, fatty acids, and total lipids were measured in 30 female and 20 male desert tortoises (Gopherus agassizii) during the annual reproductive cycle in the eastern Mojave desert, Nevada. Blood samples were collected at monthly intervals from April to October. All lipid fractions, with the exception of free fatty acids, were significantly higher in female plasma than in male plasma in all months of the year. In contrast, free fatty acids were higher in male plasma than in female plasma in all months. The seasonal pattern in estradiol secretion mirrored that of triacylglycerol, phospholipid, cholesterol, and total lipid, all of which showed a significant correlation with the hormone. Estradiol and the vitellogenesis-associated lipids were all significantly higher in August, September, October, and April than in June. The seasonal variation in cholesterol ester levels in females did not correlate with any of the reproductive events and did not appear to be involved in yolk precursor formation. Total lipid in males showed a negative correlation with testosterone and spermatogenesis. Individual fatty acids in the June and August samples (at the highest and lowest estradiol levels) were compared in male and female plasma. The percent of C18:3n3, C18:2n6, C18:1n9, C20:5n3, and C22:5 were significantly higher in the June female plasma sample than in the August sample. Docosahexanoic (C22:6n3) acid was barely detectable in female plasma in either month.     

Serologic and molecular evidence for Testudinid herpesvirus 2 infection in wild Agassiz's desert tortoises, Gopherus agassizii

Following field observations of wild Agassiz's desert tortoises (Gopherus agassizii) with oral lesions similar to those seen in captive tortoises with herpesvirus infection, we measured the prevalence of antibodies to Testudinid herpesvirus (TeHV) 3 in wild populations of desert tortoises in California. The survey revealed 30.9% antibody prevalence. In 2009 and 2010, two wild adult male desert tortoises, with gross lesions consistent with trauma and puncture wounds, respectively, were necropsied. Tortoise 1 was from the central Mojave Desert and tortoise 2 was from the northeastern Mojave Desert. We extracted DNA from the tongue of tortoise 1 and from the tongue and nasal mucosa of tortoise 2. Sequencing of polymerase chain reaction products of the herpesviral DNA-dependent DNA polymerase gene and the UL39 gene respectively showed 100% nucleotide identity with TeHV2, which was previously detected in an ill captive desert tortoise in California. Although several cases of herpesvirus infection have been described in captive desert tortoises, our findings represent the first conclusive molecular evidence of TeHV2 infection in wild desert tortoises. The serologic findings support cross-reactivity between TeHV2 and TeHV3. Further studies to determine the ecology, prevalence, and clinical significance of this virus in tortoise populations are needed.     

Implications of Anthropogenic Landscape Change on Inter-Population Movements of the Desert Tortoise (Gopherus agassizii)

In the Sonoran Desert of North America, populations of the desert tortoise (Gopherus agassizii) occur in rocky foothills throughout southwestern Arizona and northwestern Mexico. Although tortoise populations appear to be isolated from each other by low desert valleys, individuals occasionally move long distances between populations. Increasingly, these movements are hindered by habitat fragmentation due to anthropogenic landscape changes. We used molecular techniques and radiotelemetry to examine movement patterns of desert tortoises in southern Arizona. We collected blood samples from 170 individuals in nine mountain ranges and analyzed variability in seven microsatellite loci to determine genetic differentiation among populations. Gene flow estimates between populations indicate that populations exchanged individuals historically at a rate greater than one migrant per generation, and positive correlation between genetic and geographic distance of population pairs suggests that the limiting factor for gene flow among populations is isolation by distance. Life history traits of the desert tortoise, a long-lived species with delayed sexual maturity, may severely constrain the ability of small populations to respond to disturbances that increase adult mortality. Historic gene flow estimates among populations suggests that recovery of declining populations may rely heavily on the immigration of new individuals from adjacent mountain ranges. Management strategies compatible with the evolutionary history of gene flow among disjunct populations will help ensure the long-term persistence of Sonoran desert tortoise populations.     

The dazed and confused identity of Agassiz's land tortoise, Gopherus agassizii (Testudines, Testudinidae) with the description of a new species, and its consequences for conservation

We investigate a cornucopia of problems associated with the identity of the desert tortoise, Gopherus agassizii (Cooper). The date of publication is found to be 1861, rather than 1863. Only one of the three original cotypes exists, and it is designated as the lectotype of the species. Another cotype is found to have been destroyed in the 1906 San Francisco earthquake and subsequent fire. The third is lost. The lectotype is genetically confirmed to be from California, and not Arizona, USA as sometimes reported. Maternally, the holotype of Gopherus lepidocephalus (Ottley & Velázques Solis. 1989) from the Cape Region of Baja California Sur, Mexico is also from the Mojavian population of the desert tortoise, and not from Tiburon Island, Sonora, Mexico as previously proposed. A suite of characters serve to diagnose tortoises west and north of the Colorado River, the Mojavian population, from those east and south of the river in Arizona, USA, and Sonora and Sinaloa, Mexico, the Sonoran population. Species recognition is warranted and because Gopherus lepidocephalus is from the Mojavian population, no names are available for the Sonoran species. Thus, a new species, Gopherus morafkaisp. n., is named and this action reduces the distribution of Gopherus agassizii to only 30% of its former range. This reduction has important implications for the conservation and protection of Gopherus agassizii, which may deserve a higher level of protection.