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Western Fence Lizard (western + fence_lizard)

Distribution by Scientific Domains
Life Sciences100%

Selected Abstracts

Dose-related effects following oral exposure of 2,4-dinitrotoluene on the western fence lizard, Sceloporus occidentalis

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2008
Jamie G. Suski
Abstract 2,4-dintitrotoluene (2,4-DNT) is an explosive frequently found in the soil of military installations. Because reptiles can be common on these sites, ecological risk assessments for compounds such as 2,4-DNT could be improved with toxicity data specific to reptiles. Western fence lizards, Sceloporus occidentalis, were used to develop a laboratory toxicity model for reptiles. A hierarchical approach was used; acute to subchronic studies were conducted to provide toxicity data relevant to short- and long-term exposures. First, a modified median lethal dose (LD50) study was conducted on male and female lizards using a stage-wise probit model. The LD50 was 577 mg/kg for female and 380 mg/kg for male lizards. Subsequently, a subacute experiment was conducted to further assess 2,4-DNT toxicity to male lizards and to define exposure levels for a longer term, subchronic study. The subchronic study was conducted for 60 consecutive days; male lizards were exposed to 0, 9, 15, 25, 42, 70 mg/kg/d. Dose-dependent mortality was observed in the three highest dose groups (25, 42, and 70 mg/kg/d); all other animals survived the study duration. Benchmark dose model calculations based on mortality indicated a 5% effect level of 15.8 mg/kg/d. At study termination, a gross necropsy was performed, organ weights were taken, and blood was collected for clinical and hematological analysis. Body weight, kidney weight, food consumption, postdose observations, and blood chemistries all were found to be significantly different from controls at doses above 9 mg/kg/d. Also, preliminary results suggest behavioral observations, and reduced food consumption may be a sensitive indicator of toxicity. The present study indicates Sceloporus occidentalis is suitable for evaluating toxicity of compounds to reptilian species. [source]

Toxicity of oral exposure to 2,4,6-trinitrotoluene in the western fence lizard (Sceloporus occidentalis),

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2008
Craig A. McFarland
Abstract Contamination of the soil with the explosive 2,4,6-trinitrotoluene (TNT) has been found at military sites, many of which are habitats used by reptiles. To provide data useful in assessing ecological risk for reptilian species, acute, subacute, and subchronic oral toxicity studies were conducted with the western fence lizard (Sceloporus occidentalis). Oral median lethal dose (LD50) values for TNT in corn oil were 1,038 and 1,579 mg/kg of body weight for male and female lizards, respectively. Overt signs of toxicity included chromaturia, abdominal enlargement, and tremors. A 14-d subacute study followed in which male lizards were orally dosed with TNT (corn oil) at 0, 33, 66, 132, 263, 525, and 1,050 mg/kg of body weight each day. Clinical signs of toxicity, while similar to the LD50 study, were more subtle and noted in lizards receiving TNT amounts of at least 66 mg/kg/d. Chromaturia was an early consistent sign, often preceding the onset of adverse effects. Male lizards in the 60-d subchronic study were dosed at 0, 3, 15, 25, 35, and 45 mg/kg/d with nearly complete survival (>90%) for lizards in all treatments. Changes in food consumption and body weight were observed at 35 and 45 mg/kg/d. Alterations in hematological end points; blood chemistries (albumin, total protein, alkaline phosphatase, calcium); kidney, spleen, and liver weights; and adverse histopathology were observed in lizards exposed at 25 to 45 mg/kg/d. Testosterone concentration, sperm count, and motility were variable between treatments. Although not significant, incidences of hypospermia and testicular atrophy were observed in some individuals. Together, these data suggest a lowest-observed-adverse effect level of 25 mg/kg/d and a no-observed-adverse effect level of 15 mg/kg/d in S. occidentalis. [source]

Dose-related effects following oral exposure of 2,4-dinitrotoluene on the western fence lizard, Sceloporus occidentalis

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2008
Jamie G. Suski
Abstract 2,4-dintitrotoluene (2,4-DNT) is an explosive frequently found in the soil of military installations. Because reptiles can be common on these sites, ecological risk assessments for compounds such as 2,4-DNT could be improved with toxicity data specific to reptiles. Western fence lizards, Sceloporus occidentalis, were used to develop a laboratory toxicity model for reptiles. A hierarchical approach was used; acute to subchronic studies were conducted to provide toxicity data relevant to short- and long-term exposures. First, a modified median lethal dose (LD50) study was conducted on male and female lizards using a stage-wise probit model. The LD50 was 577 mg/kg for female and 380 mg/kg for male lizards. Subsequently, a subacute experiment was conducted to further assess 2,4-DNT toxicity to male lizards and to define exposure levels for a longer term, subchronic study. The subchronic study was conducted for 60 consecutive days; male lizards were exposed to 0, 9, 15, 25, 42, 70 mg/kg/d. Dose-dependent mortality was observed in the three highest dose groups (25, 42, and 70 mg/kg/d); all other animals survived the study duration. Benchmark dose model calculations based on mortality indicated a 5% effect level of 15.8 mg/kg/d. At study termination, a gross necropsy was performed, organ weights were taken, and blood was collected for clinical and hematological analysis. Body weight, kidney weight, food consumption, postdose observations, and blood chemistries all were found to be significantly different from controls at doses above 9 mg/kg/d. Also, preliminary results suggest behavioral observations, and reduced food consumption may be a sensitive indicator of toxicity. The present study indicates Sceloporus occidentalis is suitable for evaluating toxicity of compounds to reptilian species. [source]

Phenotypic evolution in high-elevation populations of western fence lizards (Sceloporus occidentalis) in the Sierra Nevada Mountains

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2010
ADAM D. LEACHÉ
Adaptive divergence in response to variable habitats, climates, and altitude is often accentuated along elevation gradients. We investigate phenotypic evolution in body size and coloration in the western fence lizard (Sceloporus occidentalis Baird & Girard, 1852) across elevation gradients in Yosemite National Park, California, situated in the Sierra Nevada mountains of Western North America. High-elevation populations occurring above 2100 m a.s.l. are recognized as a separate subspecies (Sceloporus occidentalis taylori Camp, 1916), with a distinctive phenotype characterized by a large body size and extensive blue ventral pigmentation. We sampled S. occidentalis from across elevation gradients in Yosemite National Park, California, and collected phenotypic data (body size and ventral coloration measurements; 410 specimens) and mitochondrial DNA sequence data (complete NADH1 gene; 969 bp, 181 specimens) to infer phylogenetic relationships, and examine the genetic and phenotypic diversity among populations. Populations of S. occidentalis in Yosemite National Park follow Bergmann's rule and exhibit larger body sizes in colder, high-elevation environments. The high-elevation subspecies S. o. taylori is not monophyletic, and the mitochondrial DNA genealogy supports a model of convergent phenotypic evolution among high-elevation populations belonging to different river drainages. The hypothesis that separate populations of S. occidentalis expanded up river drainages after the recession of glaciers is supported by population demographic analyses, and suggest that Bergmann's clines can evolve rapidly along elevation gradients. The distinctive high-elevation phenotype that is attributable to S. o. taylori has evolved independently several times, and includes adaptive phenotypic changes associated with increases in body size and ventral coloration. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 630,641. [source]

Dose,response and time course relationships for vitellogenin induction in male western fence lizards (Sceloporus occidentalis) exposed to ethinylestradiol

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2002
Sandra M. Brasfield
Abstract The long-term goal of this research is to develop and validate an in vivo reptile model for endocrine-mediated toxicity using fence lizards (Sceloporus spp.). One of the best defined estrogenic responses in oviparous vertebrates is induction of the yolk precursor protein, vitellogenin (Vtg). In this study, dose,response and time course relationships for Vtg induction were determined in male western fence lizards (Sceloporus occidentalis) given intraperitoneal injections of 17,-ethinylestradiol (EE2). Plasma Vtg was quantified directly with an antibody-capture enzyme-linked immunosorbent assay (ELISA) and indirectly using plasma alkalinelabile phosphate (ALP) in order to compare these two methods. Both ELISA and ALP predicted similar median effective dose (ED50 [dose causing a 50% maximal response]) values for plasma Vtg induction (0.167 mg/kg for ELISA and 0.095 mg/kg for ALP). In addition, both ELISA and ALP detected significant Vtg induction at a dose of 0.0003 mg/kg of EE2, which was the lowest dose used in our study. A decrease in body weight at the highest dose (10 mg/kg) and an increase in hepatosomatic index at the four highest doses were observed. Serial dilutions of plasma from an EE2 -exposed male revealed a high correlation between plasma Vtg and ALP determinations in this species. In conclusion, our data show that plasma ALP may be a suitable alternative for measuring plasma Vtg compared with developing a Vtg ELISA in fence lizards exposed to estrogenic compounds. [source]

Phenotypic evolution in high-elevation populations of western fence lizards (Sceloporus occidentalis) in the Sierra Nevada Mountains

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2010
ADAM D. LEACHÉ
Adaptive divergence in response to variable habitats, climates, and altitude is often accentuated along elevation gradients. We investigate phenotypic evolution in body size and coloration in the western fence lizard (Sceloporus occidentalis Baird & Girard, 1852) across elevation gradients in Yosemite National Park, California, situated in the Sierra Nevada mountains of Western North America. High-elevation populations occurring above 2100 m a.s.l. are recognized as a separate subspecies (Sceloporus occidentalis taylori Camp, 1916), with a distinctive phenotype characterized by a large body size and extensive blue ventral pigmentation. We sampled S. occidentalis from across elevation gradients in Yosemite National Park, California, and collected phenotypic data (body size and ventral coloration measurements; 410 specimens) and mitochondrial DNA sequence data (complete NADH1 gene; 969 bp, 181 specimens) to infer phylogenetic relationships, and examine the genetic and phenotypic diversity among populations. Populations of S. occidentalis in Yosemite National Park follow Bergmann's rule and exhibit larger body sizes in colder, high-elevation environments. The high-elevation subspecies S. o. taylori is not monophyletic, and the mitochondrial DNA genealogy supports a model of convergent phenotypic evolution among high-elevation populations belonging to different river drainages. The hypothesis that separate populations of S. occidentalis expanded up river drainages after the recession of glaciers is supported by population demographic analyses, and suggest that Bergmann's clines can evolve rapidly along elevation gradients. The distinctive high-elevation phenotype that is attributable to S. o. taylori has evolved independently several times, and includes adaptive phenotypic changes associated with increases in body size and ventral coloration. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 630,641. [source]