Publications

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toxicity of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (hmx) in three vertebrate species.the explosive, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine or high-melting explosive (hmx), has been found in soils in areas used for testing and training by the military. many of these areas contain habitat for valued wildlife species. in an effort to better understand the environmental consequences from exposure, a reptilian (western fence lizard [sceloporus occidentalis]), an amphibian (red-backed salamander [plethodon cinereus]), and a mammalian species (rabbit [oryctolagus cuniculus]) ...201020012743
effects of an invasive forest pathogen on abundance of ticks and their vertebrate hosts in a california lyme disease focus.invasive species, including pathogens, can have important effects on local ecosystems, including indirect consequences on native species. this study focuses on the effects of an invasive plant pathogen on a vertebrate community and ixodes pacificus, the vector of the lyme disease pathogen (borrelia burgdorferi) in california. phytophthora ramorum, the causative agent of sudden oak death, is a non-native pathogen killing trees in california and oregon. we conducted a multi-year study using a grad ...201020941513
impact of the experimental removal of lizards on lyme disease risk.the distribution of vector meals in the host community is an important element of understanding and predicting vector-borne disease risk. lizards (such as the western fence lizard; sceloporus occidentalis) play a unique role in lyme disease ecology in the far-western united states. lizards rather than mammals serve as the blood meal hosts for a large fraction of larval and nymphal western black-legged ticks (ixodes pacificus-the vector for lyme disease in that region) but are not competent reser ...201121325326
relative clonal proportions over time in mixed-genotype infections of the lizard malaria parasite plasmodium mexicanum.vertebrate hosts of malaria parasites (plasmodium) often harbour two or more genetically distinct clones of a single species, and interaction among these co-existing clones can play an important role in plasmodium biology. however, how relative clonal proportions vary over time in a host is still poorly known. experimental mixed-clone infections of the lizard malaria parasite, plasmodium mexicanum, were followed in its natural host, the western fence lizard using microsatellite markers to determ ...201121396372
geographic variation in the effects of heat exposure on maximum sprint speed and hsp70 expression in the western fence lizard sceloporus occidentalis.we examined whether western fence lizards sceloporus occidentalis occurring in thermally divergent environments display differential responses to high temperature in locomotor performance and heat-shock protein (hsp) expression. we measured maximum sprint speed in s. occidentalis from four populations at paired latitudes and elevations before and after exposure to an experimental heat treatment and then quantified hind-limb muscle hsp70 expression. lizards collected from northern or high-elevati ...201122030850
toxic effects of oral 2-amino-4,6-dinitrotoluene in the western fence lizard (sceloporus occidentalis).the compound 2-amino-4,6-dinitrotoluene (2a-dnt) was evaluated under laboratory conditions in the western fence lizard (sceloporus occidentalis) to assess the potential for reptile toxicity. oral ld(50) values were 1406 and 1867 mg/kg for male and female lizards, respectively. based on responses from a 14-day subacute study, a 60-day subchronic experiment followed where lizards were orally dosed at 0, 5, 15, 20, 25, 30 mg/kg-d. at day 60, number of days and survivors, food consumption, and chang ...201121067851
the effect of exogenous testosterone on ectoparasite loads in free-ranging western fence lizards.numerous factors impact the dynamics of host-parasite relationships, such as host sex, hormonal state, reproductive condition, host health, and behavior. in particular, males from a variety of taxa frequently carry heavier parasite burdens than females, particularly during breeding season when testosterone concentrations are elevated. using western fence lizards (sceloporus occidentalis), we tested the hypothesis that high circulating testosterone concentrations in male lizards induce high tick ...201222689269
in vitro maintenance of a pure-cone retina.the retina of the lizard, sceloporus occidentalis, appears to have only cone photoreceptors. eyecups from this animal were incubated in media containing earle's balanced salts, supplemented with amino acids and vitamins, and gassed with 5% co2/95% o2. under these conditions, good morphology, protein synthesis, and normal cyclic amp and cyclic gmp levels were maintained for 1-2 days. this in vitro preparation is likely to be useful for pharmacological studies of cone photoreceptors.20123516917
how do host sex and reproductive state affect host preference and feeding duration of ticks?parasitism is one of the most notable forms of symbiosis in the biological world, with nearly all organisms hosting parasites. in many vertebrates, males have higher ectoparasite burdens than females, especially when testosterone concentrations are elevated. furthermore, reproductive females may have higher ectoparasite burdens than non-reproductive females. it is possible that testosterone-stimulated behaviors in males and offspring investment by females incur energetic costs that inhibit immun ...201222526292
multiple environmental stressors elicit complex interactive effects in the western fence lizard (sceloporus occidentalis).evaluation of multiple-stressor effects stemming from habitat degradation, climate change, and exposure to chemical contaminants is crucial for addressing challenges to ecological and environmental health. to assess the effects of multiple stressors in an understudied taxon, the western fence lizard (sceloporus occidentalis) was used to characterize the individual and combined effects of food limitation, exposure to the munitions constituent 2,4,6-trinitrotoluene (tnt), and plasmodium mexicanum ...201222975894
impacts of an introduced forest pathogen on the risk of lyme disease in california.global changes such as deforestation, climate change, and invasive species have the potential to greatly alter zoonotic disease systems through impacts on biodiversity. this study examined the impact of the invasive pathogen that causes sudden oak death (sod) on the ecology of lyme disease in california. the lyme disease bacterium, borrelia burgdorferi, is maintained in the far western united states by a suite of animal reservoirs including the dusky-footed woodrat (neotoma fuscipes) and deer mo ...201222607076
eco-epidemiological factors contributing to the low risk of human exposure to ixodid tick-borne borreliae in southern california, usa.little is known about the eco-epidemiology of lyme disease in southern california, a region where the incidence is much lower than it is in northern california. here, we sought to discover the previously unknown microhabitats of nymphs of the primary vector, the western black-legged tick (ixodes pacificus), in 3 moderately to heavily-utilized state parks in the santa monica mountains in los angeles county; to elucidate the seasonal distribution and abundance of adults of i. pacificus and another ...201323643357
effect of host lizard anemia on host choice and feeding rate of larval western black-legged ticks (ixodes pacificus).although ticks are known to exhibit preferences among host species, there is little evidence that ticks select hosts within a species based on physiological condition. it may be beneficial for ticks to choose hosts that are easier to feed upon if the ticks can perceive indicative chemical or other signals from the host. for example, if ticks can detect host hematocrit they may choose hosts with high hematocrit, facilitating a faster blood meal. it may similarly be adaptive for ticks to avoid ane ...201323760685
permeability of roads to movement of scrubland lizards and small mammals.a primary objective of road ecology is to understand and predict how roads affect connectivity of wildlife populations. road avoidance behavior can fragment populations, whereas lack of road avoidance can result in high mortality due to wildlife-vehicle collisions. many small animal species focus their activities to particular microhabitats within their larger habitat. we sought to assess how different types of roads affect the movement of small vertebrates and to explore whether responses to ro ...201323772966
unraveling the relative importance of oral and dermal contaminant exposure in reptiles: insights from studies using the western fence lizard (sceloporus occidentalis).despite widespread recognition of significant data deficiencies, reptiles remain a relatively understudied taxon in ecotoxicology. to conduct ecological risk assessments on reptiles frequently requires using surrogate taxa such as birds, but recent research suggests that reptiles have significantly different exposure profiles and toxicant sensitivity. we exposed western fence lizards, sceloporus occidentalis, to the same quantities of three model chemicals via oral (gavage) and dermal (ventral s ...201424941063
leukocyte profiles for western fence lizards, sceloporus occidentalis, naturally infected by the malaria parasite plasmodium mexicanum.plasmodium mexicanum is a malaria parasite that naturally infects the western fence lizard, sceloporus occidentalis , in northern california. we set out to determine whether lizards naturally infected with this malaria parasite have different leukocyte profiles, indicating an immune response to infection. we used 29 naturally infected western fence lizards paired with uninfected lizards based on sex, snout-to-vent length, tail status, and the presence-absence of ectoparasites such as ticks and m ...201424945903
entrainment of the circadian activity rhythm of a lizard to melatonin injections.the circadian activity rhythms of lizards (sceloporus occidentalis) can be entrained (synchronized) to a period of 24 hr by melatonin injections given every other day at the same time of day, but not by saline injections. the activity onsets of the entrained lizards exhibited two preferred phase-relationships (approximately 165 degrees and approximately 30 degrees) with the time of melatonin injections with the 30 degree phase only rarely observed. these results suggest that endogenous rhythms o ...20144070395
effects of temperature on feeding duration, success, and efficiency of larval western black-legged ticks (acari: ixodidae) on western fence lizards.the western black-legged tick (ixodes pacificus) is a common tick species throughout the western usa and is the major vector for borrelia burgdorferi, the lyme disease causing bacterium. western fence lizards (sceloporus occidentalis) are a major host for juvenile i. pacificus, but are incompetent hosts for b. burgdorferi, which makes this host-parasite relationship of particular interest. in order to shed further light on this complex host-parasite relationship, we investigated the effects of t ...201526188858
improving reptile ecological risk assessment: oral and dermal toxicity of pesticides to a common lizard species (sceloporus occidentalis).reptiles have been understudied in ecotoxicology, which limits consideration in ecological risk assessments. the goals of the present study were 3-fold: to improve oral and dermal dosing methodologies for reptiles, to generate reptile toxicity data for pesticides, and to correlate reptile and avian toxicity. the authors first assessed the toxicity of different dosing vehicles: 100 μl of water, propylene glycol, and acetone were not toxic. the authors then assessed the oral and dermal toxicity of ...201525760295
populations of the lizard, sceloporus occidentalis, that differ in melanization have different rates of wound healing.mechanisms underlying production of animal coloration can affect key traits besides coloration. melanin, and molecules regulating melanin, can directly and indirectly affect other phenotypic traits, such as immune function. we asked whether melanization and a whole-organism measure of immune function are associated with wound healing. working with two populations of adult male western fence lizards, sceloporus occidentalis, we compared one high-elevation and one low-elevation population in calif ...201627597293
oxygen concentration affects upper thermal tolerance in a terrestrial vertebrate.we tested the oxygen limitation hypothesis, which states that animals decline in performance and reach the upper limits of their thermal tolerance when the metabolic demand for oxygen at high temperatures exceeds the circulatory system's ability to supply adequate oxygen, in air-breathing lizards exposed to air with different oxygen concentrations. lizards exposed to hypoxic air (6% o2) gaped, panted, and lost their righting response at significantly lower temperatures than lizards exposed to no ...201627264957
phenotypic correlates of melanization in two sceloporus occidentalis (phrynosomatidae) populations: behavior, androgens, stress reactivity, and ectoparasites.mechanisms underlying production of animal coloration can affect key traits besides coloration. melanin, and molecules regulating melanin, can directly and indirectly affect other phenotypic traits including aggression, stress-reactivity, and immune function. we studied correlation of melanization with these other traits, comparing within- and between-population differences of adult male western fence lizards, sceloporus occidentalis. we compared one high- and one low-elevation population in cal ...201627137079
direct and indirect effects of petroleum production activities on the western fence lizard (sceloporus occidentalis) as a surrogate for the dunes sagebrush lizard (sceloporus arenicolus).the dunes sagebrush lizard (sceloporus arenicolus) is a habitat specialist of conservation concern limited to shin oak sand dune systems of new mexico and texas (usa). because much of the dunes sagebrush lizard's habitat occurs in areas of high oil and gas production, there may be direct and indirect effects of these activities. the congeneric western fence lizard (sceloporus occidentalis) was used as a surrogate species to determine direct effects of 2 contaminants associated with oil and gas d ...201626456391
lowering metabolic rate mitigates muscle atrophy in western fence lizards.extended periods of skeletal muscle disuse can cause a significant loss of contractile proteins, which compromises the ability to generate force, mechanical work or power, thus compromising locomotor performance. several hibernating organisms can resist muscle atrophy despite months of inactivity. this resistance has been attributed to a reduction in body temperature and metabolic rate and activation of physiological pathways that counteract pathways of protein degradation. however, in these sys ...201728507191
tick microbiome and pathogen acquisition altered by host blood meal.lyme disease, a zoonotic disease, is the most prevalent vector-borne disease in the northern hemisphere. diversity of the vector (tick) microbiome can impact pathogen transmission, yet the biotic and abiotic factors that drive microbiome diversity are largely unresolved, especially under natural, field conditions. we describe the microbiome of ixodes pacificus ticks, the vector for lyme disease in the western united states, and show a strong impact of host blood meal identity on tick microbiome ...201727858931
fear no colors? observer clothing color influences lizard escape behavior.animals often view humans as predators, leading to alterations in their behavior. even nuanced aspects of human activity like clothing color affect animal behavior, but we lack an understanding of when and where such effects will occur. the species confidence hypothesis posits that birds are attracted to colors found on their bodies and repelled by non-body colors. here, we extend this hypothesis taxonomically and conceptually to test whether this pattern is applicable in a non-avian reptile and ...201728792983
phylogenetic analyses reveal that schellackia parasites (apicomplexa) detected in american lizards are closely related to the genus lankesterella: is the range of schellackia restricted to the old world?species of schellackia reichenow, 1919 have been described from the blood of reptiles distributed worldwide. recently, schellackia spp. detected in european and asian lizards have been molecularly characterised. however, parasites detected in american lizard hosts remain uncharacterised. thus, phylogenetic affinities between the old and new world parasite species are unknown.201729017602
correlates of melanization in multiple high- and low-elevation populations of the lizard, sceloporus occidentalis: behavior, hormones, and parasites.hormones mediate the expression of suites of correlated traits and hence may act either to facilitate or constrain adaptive evolution. selection on one trait within a hormone-mediated suite of traits may lead to a change in the strength of the hormone signal, causing changes in correlated traits. growing evidence suggests that melanization, which is in part regulated by hormonal signals, is tightly linked to other traits, such as aggression and stress physiology. here, we examine six populations ...201729356435
multiple color patches and parasites in sceloporus occidentalis: differential relationships by sex and infection.parasites generally have a negative influence on the color expression of their hosts. sexual selection theory predicts resistant high-quality individuals should show intense coloration, whereas susceptible low-quality individuals would show poor coloration. however, intensely colored males of different species of old and new world lizards were more often infected by hemoparasites. these results suggest that high-quality males, with intense coloration, would suffer higher susceptibility to hemopa ...201830538729
multiple environmental stressors induce complex transcriptomic responses indicative of phenotypic outcomes in western fence lizard.the health and resilience of species in natural environments is increasingly challenged by complex anthropogenic stressor combinations including climate change, habitat encroachment, and chemical contamination. to better understand impacts of these stressors we examined the individual- and combined-stressor impacts of malaria infection, food limitation, and 2,4,6-trinitrotoluene (tnt) exposures on gene expression in livers of western fence lizards (wfl, sceloporus occidentalis) using custom wfl ...201830518325
lead bioaccumulation in texas harvester ants (pogonomyrmex barbatus) and toxicological implications for texas horned lizard (phrynosoma cornutum) populations of bexar county, texas.uptake of lead from soil was examined in order to establish a site-specific ecological protective concentration level for the texas horned lizard (phrynosoma cornutum) at the former humble refinery in san antonio, texas. soils, harvester ants, and rinse water from the ants were analyzed at 11 texas harvester ant (pogonomyrmex barbatus) mounds. soil concentrations at the harvester ant mounds ranged from 13 to 7474 mg/kg of lead dry weight. ant tissue sample concentrations ranged from < 0.82 to 21 ...201829305803
parallel behavioral and morphological divergence in fence lizards on two college campuses.the spread of urban development has dramatically altered natural habitats, modifying community relationships, abiotic factors, and structural features. animal populations living in these areas must perish, emigrate, or find ways to adjust to a suite of new selective pressures. those that successfully inhabit the urban environment may make behavioral, physiological, and/or morphological adjustments that represent either evolutionary change and/or phenotypic plasticity. we tested for effects of ur ...201829444102
downsizing for downtown: limb lengths, toe lengths, and scale counts decrease with urbanization in western fence lizards (sceloporus occidentalis).urbanization induced habitat loss and alteration causes significant challenges for the survival of many species. identifying how species respond to urbanization can yield insights for the conservation of wildlife, but research on reptiles has been narrowly-focused. we compared morphology among four populations of western fence lizards (sceloporus occidentalis) to determine whether a common native species affected by urbanization exhibits morphological differences consistent with habitat use. we ...201932774080
the lizard gut microbiome changes with temperature and is associated with heat tolerance.vertebrates harbor trillions of microorganisms in the gut, collectively termed the gut microbiota, which affect a wide range of host functions. recent experiments in lab-reared vertebrates have shown that changes in environmental temperature can induce shifts in the gut microbiota, and in some cases these shifts have been shown to affect host thermal physiology. however, there is a lack of information about the effects of temperature on the gut microbiota of wild-caught vertebrates. moreover, in ...202032591376
establishment of brown anoles (anolis sagrei) across a southern california county and potential interactions with a native lizard species.the brown anole, anolis sagrei, is a native species to the caribbean; however, a. sagrei has invaded multiple parts of the usa, including florida, louisiana, hawai'i and more recently california. the biological impacts of a. sagrei invading california are currently unknown. evidence from the invasion in taiwan shows that they spread quickly and when immediate action is not taken eradication stops being a viable option. in orange county, california, five urban sites, each less than 100 ha, were s ...202032296613
melanization, α-melanocyte stimulating hormone and steroid hormones in male western fence lizards from nine populations.hormones can mediate suites of correlated traits. melanocortins regulate melanin synthesis and elements of the melanocortin system can directly, and indirectly, affect a number of other traits, such as stress reactivity. trait correlations within the melanocortin system have been studied mainly in birds and mammals but less so in reptiles. we examined adult male western fence lizards (sceloporus occidentalis) and if melanization was correlated with plasma levels of three hormones, including pept ...202031563645
body size impacts critical thermal maximum measurements in lizards.understanding the mechanisms behind critical thermal maxima (ctmax; the high body temperature at which neuromuscular coordination is lost) of organisms is central to understanding ectotherm thermal tolerance. body size is an often overlooked variable that may affect interpretation of ctmax, and consequently, how ctmax is used to evaluate mechanistic hypotheses of thermal tolerance. we tested the hypothesis that body size affects ctmax and its interpretation in two experimental contexts. first, i ...202032851814
to cool or not to cool? intestinal coccidians disrupt the behavioral hypothermia of lizards in response to tick infestation.it is generally accepted that parasites exert negative effects on their hosts and that natural selection favors specific host responses that mitigate this impact. it is also known that some components of the host immune system often co-evolve with parasite antigens resulting in a host-parasite arms race. in addition to immunological components of the anti-parasitic response, host behavioral responses are also important in this arms race and natural selection may favor avoidance strategies that p ...202031540802
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