Richard Tracy

• Doctor of Philosophy
• University of Nevada, Reno

Comparative studies, especially of related species that span across ecoregions, have the potential to increase our understanding of different ecological or evolutionary pressures that may drive host–pathogen dynamics. We quantified differences in immune investment, via differential leukocyte counts and bacteria‐killing assays, across four closely r...

Mojave desert tortoises (Gopherus agassizii), a threatened species under the US Endangered Species Act, are long-lived reptiles that experience a chronic respiratory disease. The virulence of primary etiologic agent, Mycoplasma agassizii, remains poorly understood, but it exhibits temporal and geographic variability in causing disease outbreaks in...

We assessed the potential for microbial interactions influencing a well-documented host-pathogen system. Mycoplasma agassizii is the known etiological agent of upper respiratory tract disease in Mojave desert tortoises (Gopherus agassizii), but disease in wild animals is extremely heterogeneous. For example, a much larger proportion of animals harb...

Research on water exchange in frogs has historically assumed that blood osmotic potential drives water exchange between a frog and its environment, but here we show that the "seat patch" (the primary site of water exchange in many anurans), or other sites of cutaneous water uptake, act as an anatomic "compartment" with a water potential controlled...

The northeastern extreme of the Mojave desert tortoise (Gopherus agassizii) distribution near Zion National Park in Utah is contested as a natural range limit because of its suboptimal habitat and known anthropogenic movements of tortoises. In this study, we added microsatellite data from nine tortoises from the Zion area to a previously published...

RANA FORRERI (Forrer's Grass Frog). MEXICO: MEXICO: Municipio de Ixtapan de la Sal: San Alejo (18°50'13"N, 99°43'30"W) 1650 m. 20 November 1994. R. Cruz. Coleccion Herpetologica del Instituto de Biologia, Universidad Nacional Autonoma de Mexico (IBH 11131). Municipio de Santo Tomas de los Platanos: "El Llano" (19°10'54"N, 100°14'19"W) 1200 m. 28 Au...

Mycoplasma agassizii is a common cause of upper respiratory tract disease in Mojave desert tortoises (Gopherus agassizii). So far, only two strains of this bacterium have been sequenced, and very little is known about its patterns of genetic diversity. Understanding genetic variability of this pathogen is essential to implement conservation program...

We describe two new cryptic species of Bufo within the subgenus Anaxyrus discovered in Central Nevada of the western United States. Our analyses revealed that these two localized endemic toads are genetically divergent and morphologically distinct, yet were concealed under the range of the broadly distributed western toad (Bufo boreas), which occur...

We challenged the common practice of using a single mean absorptance based on unfiltered skylight spectra to model operative temperature for reptiles in filtered light habitats by examining the effects of plant canopies on light transmittance. To assess differences in light filtration over a range of microhabitats, spectra were recorded under canop...

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 respiratory tract, pertinent to this species’ susceptibility to upper respiratory tract disease. We quantified bacteria-killing activity of blood plasma and diffe...

Mycoplasma testudineum is one of the pathogens that can cause upper respiratory tract disease in desert tortoises, Gopherus agassizii. We sequenced the genome of M. testudineum BH29T (ATCC 700618T = MCCM 03231T), isolated from the upper respiratory tract of a Mojave desert tortoise with upper respiratory tract disease. The sequenced draft genome, o...

Mycoplasma agassizii is one of the known causative agents of upper respiratory tract disease (URTD) in Mojave desert tortoises (Gopherus agassizii) and in gopher tortoises (Gopherus polyphemus). We sequenced the genomes of M. agassizii strains PS6T (ATCC 700616) and 723 (ATCC 700617) isolated from the upper respiratory tract of a Mojave desert tort...

Attributing biological explanations to observed ecogeographical and ecological patterns requires eliminating potential statistical and sampling artifacts as alternative explanations of the observed patterns. Here, we assess the role of sample size, statistical power, and geographic inclusivity on the general validity and statistical significance of...

Diverse bacterial communities are found on every surface of macro-organisms, and they play important roles in maintaining normal physiological functions in their hosts. While the study of microbiomes has expanded with the influx of data enabled by recent technological advances, microbiome research in reptiles lags behind other organisms. We sequenc...

We quantified the severity of upper respiratory tract disease (URTD) and immunological metrics (differential white blood cell counts and bacteria‐killing ability of blood plasma) in relation to climatic variables in 20 populations of Mojave desert tortoise (Gopherus agassizii). Prevalence and infection intensity of Mycoplasma agassizii, an etiologi...

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 grou...

In disease ecology, the host immune system interacts with environmental conditions and pathogen properties to affect the impact of disease on the host. Within the host, pathogens may interact to facilitate or inhibit each other’s growth, and pathogens interact with different hosts differently. We investigated co-infection of two Mycoplasma and the...

In an attempt to improve estimates of evaporative water loss (EWL) as a component of species distribution models, Riddell et al. (2017) compared the traditional method for empirically measuring skin resistance (ri ) to that determined by a mathematical model based in physics. They argued that the resulting differences between these two approaches h...

We describe a new species of toad from the Great Basin region of northern Nevada belonging to the Bufo (Anaxyrus) boreas species complex. This cryptic species was detected through genetic analyses of toad populations sampled throughout the Great Basin and the morphological evidence was quantified through extensive sampling of live toads within the...

Upper respiratory tract disease (URTD), caused by Mycoplasma agassizii, has been deemed a threat to populations of Mojave Desert Tortoises, Gopherus agassizii. Previous work on URTD has focused on serology and visual health examinations to determine the extent of this disease in some natural tortoise populations. Here, we present the first range-wi...

Pathogens that cause subclinical diseases or exhibit low infection intensities are difficult to quantify in wild populations. Mojave desert tortoises ( Gopherus agassizii ) have been the focus of much research aimed at measuring the presence of upper respiratory disease (URTD) and URTD-associated pathogens, and techniques used to quantify disease i...

As long-lived reptiles, Mojave Desert Tortoises (Gopherus agassizii (Cooper, 1861)) are expected to make substantial energetic investments in immune defense. This species also has many adaptations to living in an arid environment characterized by seasonal extremes in temperature and resource availability. By housing G. agassizii at a controlled, co...

We report on a survey of the small mammal communities of Anaho Island and the mainland surrounding Pyramid Lake in the Great Basin of western Nevada. Ten rodent species were detected on the mainland, but only the deer mouse (Peromyscus maniculatus) was detected on Anaho Island. Although the mean abundance of deer mice on the Pyramid Lake mainland w...

Background/Question/Methods Of the five Gopherus tortoise species, all but the Texas tortoise are federally listed in some capacity by the U.S. Fish and Wildlife Service. An upper respiratory tract disease (URTD) has been implicated as a cause of population declines in both the gopher tortoise (G. polyphemus) and Mojave desert tortoise (G. agassi...

Field metabolic rates (FMR) and water influx rates (WIR) were measured in Gila Monsters (Heloderma suspectum) in the Mojave Desert of southern Nevada. Gila Monsters had rates of energy use that were less than half of those expected for lizards of their size, including species that live in arid habitats. Free-living Gila Monsters also had comparativ...

We propose a new heuristic model that incorporates metabolic rate and pace of life to predict a vertebrate species' investment in adaptive immune function. Using reptiles as an example, we hypothesize that animals with low metabolic rates will invest more in innate immunity compared with adaptive immunity. High metabolic rates and body temperatures...

Abstract We have previously shown that ecological habit (e.g., arboreal, terrestrial, amphibious) correlates with thermoregulatory behaviors and water balance physiology among species of hylid frogs in northern Australia. We hypothesized that these frogs would be different with respect to their field hydration states because of the challenges assoc...

Patterns of body size evolution on islands provide compelling cases of rapid and dramatic phenotypic evolution in terrestrial vertebrates, yet debate remains over the relative roles of predation and resource availability in driving such evolution. We compared the morphology of five reptile species (four lizards, one snake) from Anaho Island, a dese...

Mitoura thornei , Thorne's hairstreak butterfly, is endemic to a single mountain in southwestern North America. The small geographic range of this species coupled with threats to its host plant, Hesperocyparis forbesii , motivated a study of habitat association and mapping of both butterfly and host distributions. Specifically, the following questi...

Background/Question/Methods Ecology originated from scholarship in the philosophy of science and in the study of natural history. These areas gave birth to zoology and botany, and to natural questions about why plants and animals existed where they do. Biology emerged as a uniting influence between the zoology and botany, and helped us understand...

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 f...

Wildlife translocation is increasingly used to mitigate disturbances to animals or habitat due to human activities, yet little is known about the extent to which translocating animals causes stress. To understand the relationship between physiological stress and translocation, we conducted a multiyear study (2007–2009) using a population of desert...

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 poly...

Vertebrate immune systems are understood to be complex and dynamic, with trade-offs among different physiological components (e.g., innate and adaptive immunity) within individuals and among taxonomic lineages. Desert tortoises (Gopherus agassizii) immunised with ovalbumin (OVA) showed a clear trade-off between levels of natural antibodies (NAbs; i...

We translocated 120 Agassiz's desert tortoises to 5 sites in Nevada and Utah to evaluate the effects of translocation on tortoise survivorship, reproduction, and habitat use. Translocation sites included several elevations, and extended to sites with vegetation assemblages not typically associated with desert tortoises in order to explore the possi...

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...

We evaluated the performance of airborne HyperSpecTIR (HST) images for detecting and classifying the invasive riparian vegetation saltcedar along the Muddy River in Clark County, Nevada. HyperSpecTIR image reflectance spectra (227 bands, 450–2450 nm) were acquired for the following four vegetation covers: invasive saltcedar, native honey mesquite,...

The desert tortoise is a charismatic flagship species throughout the deserts of the southwestern United States. We used tools from the field of population genetics to identify where populations occur in the listed portion of the species' range and to recommend revisions to the existing recovery units that are critical to managing the desert tortois...

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 evalua...

A Mojave Desert shrub community was experimentally burned to understand changes in seed bank of desert annual plant species in response to wildfire. Seed mortality ranged from 55 to 80%, and fire caused significant losses of native and alien annual seeds. Schismus arabicus, Schismus barbatus, Bromus madritensis, Bromus tectorum, Erodium cicutarium...

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 g...

Post-fire changes in desert vegetation patterns are known, but the mechanisms are poorly understood. Theory suggests that pulse dynamics of resource availability confer advantages to invasive annual species, and that pulse timing can influence survival and competition among species. Precipitation patterns in the American Southwest are predicted to...

Background/Question/Methods Operative temperature (Te) is a useful tool for asking ecological questions concerning the energetic interactions between organisms and their environments. The operative temperature of an animal can be calculated either mathematically or estimated by using a physical model. Both methods integrate measurements of energy...

We used simulations from a biophysical model that integrates interlinked exchanges of energy and water between frogs and their environments to address questions about the limits to thermoregulation and about adaptations for arboreality. Body size and cutaneous resistance (Rc) both significantly affected body temperature (Tb) and the time to desicca...

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...

We present a new, plaster model for measuring operative environmental temperature (Te) and water loss of amphibians with little or no cutaneous resistance to water loss. These models are made from molds of live animals, cast in plaster of Paris, and can be fitted with water reservoirs that allow them to be used for extended periods. Plaster models...

The technique of counting growth rings to estimate age of turtles is widespread in the scientific literature. Review articles to date have provided primarily lists of authors who have found the technique useful or not, but these reviews have failed to evaluate properly how well the technique actually works. In an attempt to examine how well the pub...

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...

1. Traits strongly related to fitness, such as offspring number, are expected to show intraspecific variation among individuals. However, offspring number is invariant in several reptiles, birds, and mammals. Most shorebirds (210+ species), for example, have an invariant clutch size of four eggs, which is unexpected in such an ecologically, behavio...

Assessing the recovery of the federally listed Mojave population of desert tortoises Gopherus agassizii requires detecting subtle changes in population size over a period of many years. The methods that have been employed by the US Fish and Wildlife Service to estimate population density of desert tortoises are inadequate for detecting modest trend...

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....

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...

Although the skin of most amphibians measured to date offers no resistance to evaporative water loss (EWL), some species, primarily arboreal frogs, produce skin secretions that increase resistance to EWL. At high air temperatures, it may be advantageous for amphibians to increase EWL as a means to decrease body temperature. In Australian hylid frog...

1. Patterns of daily and seasonal activity for seven species of tenebrionid beetles, genus Eleodes, were investigated in the shortgrass prairie of northeastern Colorado. The relationship between time of activity, body temperatures, and rates of water loss of the beetles was examined in the field and in laboratory experiments. 2. Common species were...

We examined burrow microclimate and cocoon formation of the burrowing frog, Cyclorana australis, from northern Australia, during the dormancy season by monitoring frogs in burrows in the field. At the beginning of the dry season, while the soils were still quite moist, frogs dug shallow burrows, with 2–8 cm of soil above the top of the burrow chamb...

1. How body mass and body temperature influence metabolic rate has been of interest for decades. Today that interest can be seen in the form of debates over the proper scaling coefficients, and the mechanistic underpinnings of allometric models for metabolic rate in relation to body mass and body temperature. We tested explicit assumptions built in...

This research examined the onset, duration, and termination of hibernation in Desert Tortoises (Gophents agassizii) over several years at multiple sites in the northeastern part of their geographic range, and recorded the temperatures experienced by tortoises during winter hibernation. The timing of hibernation by Desert Tortoises differed among si...

Translocation could be used as a tool in conservation of the threatened Mojave Desert Tortoise (Gopherus agassizii) by moving individuals from harm’s way and into areas where they could contribute to conservation of the species. Numerous factors may affect the success of translocations, including the conditions experienced by tortoises in holding f...

The federally listed desert tortoise (Gopherus agassizii) is currently monitored using distance sampling to estimate population densities. Distance sampling, as with many other techniques for estimating population density, assumes that it is possible to quantify the proportion of animals available to be counted in any census. Because desert tortois...

Diet quality and body size affected passage time of 2 diets (higher and lower in fiber) in hatchling and juvenile desert tortoises (Gopherus agassizii). Mean retention time of the liquid fraction of each diet was significantly shorter than that of the solid fraction, and hatchlings had shorter passage times than Juveniles. Habitat disturbances that...

Many of the threats to the persistence of populations of sensitive species have physiological or pathological mechanisms, and those mechanisms are best understood through the inherently integrative discipline of physiological ecology. The desert tortoise was listed under the Endangered Species Act largely due to a newly recognized upper respiratory...

Established indexes of thermoregulation in ectotherms compare body temperatures of real animals with a null distribution of operative temperatures from a physical or mathematical model with the same size, shape, and color as the actual animal but without mass. These indexes, however, do not account for thermal inertia or the effects of inertia when...

The invasive weed yellow starthistle (Centaurea solstitialis) has infested between 4 and 6 million hectares in California. It often forms dense infestations and rapidly depletes soil moisture, preventing the establishment of other species. Precise assessment of its canopy cover, especially low-density abundance in the earlier growing season, is the...

The four species that comprise the Bufo boreas group of toads are critically imperiled in all or portions of their geographical ranges. We present data from 16 microsatellite loci isolated from B. boreas that cross-amplify in these four species. These markers have proven useful in the analyses of population structure and conservation genetics, and...