| asymmetric reproductive output by the monogenean pseudodiplorchis americanus. | pseudodiplorchis americanus accumulates its entire reproductive output in utero during hibernation of its host, scaphiopus couchii. infective larvae are released only during the toads' brief entry into water for breeding. in one host population studied prior to transmission, in s.e. arizona, adult worms contained 0-326 infective stages; 19% of 178 worms produced 51% of the total larvae. reproductive output was positively correlated with body length which was considered to reflect worm age; first ... | 1991 | 1852489 |
| the relationship between pseudodiplorchis americanus (monogenea) density and host resources under controlled environmental conditions. | a previous study has shown that, under natural conditions, energy reserves of the desert toad, scaphiopus couchii, are negatively related to the density of infection by pseudodiplorchis americanus. however, this was based predominantly on collections of active animals from breeding congregations and inevitably selected toads which were in good condition. the parasite, a blood-feeding monogenean, occurs in burdens of up to 30 worms/host (mean intensity 6 worms/host) and represents a significant d ... | 1994 | 8159463 |
| survival of pseudodiplorchis americanus (monogenea) under controlled environmental conditions. | populations of pseudodiplorchis americanus infecting the desert toad, scaphiopus couchii, have previously been shown to be remarkably stable from year to year, despite wide variation in conditions promoting invasion. the present study aimed to document the survival of both first-year and pre-existing adults under controlled laboratory temperatures. first-year worm survival in experimentally infected toads was shown to be very high for the first 5 months after migration to the definitive site, an ... | 1994 | 8159464 |
| parasitic disease in amphibians: control by the regulation of worm burdens. | this review considers three case studies based on macroparasites of anurans: (a) natural infections in the permanently-aquatic xenopus laevis which represent the worm burdens acquired, and the implications for pathology, when hosts are exposed to continuous, year-round, transmission; (b) the desert toad, scaphiopus couchii, which experiences invasion very briefly each year and provides a simplified system involving only a single significant infection (pseudodiplorchis americanus); (c) the mesic ... | 1995 | 8632921 |
| gene expression during estivation in spadefoot toads, scaphiopus couchii: upregulation of riboflavin binding protein in liver. | a cdna library constructed from liver of 2-month estivating female spadefoot toads, scaphiopus couchii, was differentially screened to reveal genes that were induced or upregulated during estivation. after two rounds of screening a clone was isolated that showed 60% higher expression in liver of estivating, versus control, toads. the clone possessed a 1.0 kb insert which annealed to a single 0.7 kb band on northern blots. sequencing revealed a 1053 nucleotide full-length cdna; the largest potent ... | 1999 | 10404124 |
| effect of predator-prey phylogenetic similarity on the fitness consequences of predation: a trade-off between nutrition and disease? | a largely neglected aspect of foraging behavior is whether the costs and benefits of predation vary as a function of phylogenetic (i.e., genetic) similarity between predator and prey. prey of varying phylogenetic similarities to predators might differ in value because both the risk of pathogen transmission and the nutritional quality of prey typically decline with decreasing phylogenetic similarity between predator and prey. i experimentally evaluated this hypothesis by feeding omnivorous spadef ... | 2000 | 10718730 |
| parasite adaptation to extreme conditions in a desert environment. | deserts represent universally recognized extreme environments for animal life. this paper documents the highly specialized adaptations of pseudodiplorchis americanus, a monogenean parasite of the desert toad, scaphiopus couchii. building on a long-term record of parasite population ecology (continuing since the early 1980s), field studies focus on the effects of severe drought in the sonoran desert, arizona, in the mid 1990s. this provides a test of the ability of the host-parasite system to tol ... | 1999 | 11254147 |
| host factors limiting monogenean infections: a case study. | comprehensive field data on polystomatid monogeneans record low prevalence and intensity of infection and suggest that worm burdens in this group are strongly regulated: thus, in the majority of polystoma species infecting anuran amphibians mean abundance is typically less than one parasite/host. there is circumstantial evidence that the dominant control is attributable to host factors which over-ride variations in transmission success. this review provides a brief summary of information on pseu ... | 2002 | 11835975 |
| pathological effects of pseudodiplorchis americanus (monogenea: polystomatidae) on the lung epithelium of its host, scaphiopus couchii. | infection of the desert toad, scaphiopus couchii, by the monogenean pseudodiplorchis americanus involves 2 principal sites: post-invasion juveniles reside in the respiratory tract for 1 month before migrating to the urinary bladder where they reach sexual maturity and may live up to 4 years. while previous work has demonstrated the long-term impact on host condition of the blood-feeding adults, this study assesses pathological effects of the short-term pulmonary infection. lung ultrastructure wa ... | 2002 | 12211607 |
| distortion product otoacoustic emissions in frogs: correlation with middle and inner ear properties. | four frog species, rana pipiens, scaphiopus couchii, xenopus laevis and bombina orientalis, were examined for distortion product otoacoustic emissions (dpoae). these species were chosen for their diverse otic morphologies. rana has a well-developed caudal extension of the amphibian papilla within the inner ear; scaphiopus, xenopus and bombina do not. rana and scaphiopus have a tympanic middle ear, xenopus has a subcutaneous tympanic disk and bombina has only an operculum. dpoaes were present in ... | 2002 | 12372639 |
| urea and kcl have differential effects on enzyme activities in liver and muscle of estivating versus nonestivating species. | the effects of 300 mm urea or 300 mm kcl on the maximal activities of 25 enzymes of intermediary metabolism were assessed in extracts of liver and muscle from spadefoot toads (scaphiopus couchii), leopard frogs (rana pipiens), and rats to assess their sensitivity to these osmolytes. during estivation, toads can lose -50% of total body water, and urea, which is known for its action as a protein denaturant, accumulates to 200-300 mm. the data show that the maximal activities of toad liver enzymes ... | 2002 | 12555807 |
| higher thyroid hormone receptor expression correlates with short larval periods in spadefoot toads and increases metamorphic rate. | spadefoot toad species display extreme variation in larval period duration, due in part to evolution of thyroid hormone (th) physiology. specifically, desert species with short larval periods have higher tail tissue content of th and exhibit increased responsiveness to th. to address the molecular basis of larval period differences, we examined th receptor (tr) expression across species. based on the dual function model for the role of tr in development, we hypothesized that desert spadefoot spe ... | 2011 | 21651912 |
| variation in the effects of antidiuretic hormone on the isolated skin of the toad, scaphiopus couchi. | the rate of active sodium transport as measured by short-circuit current across the isolated skin of the toad, scaphiopus couchi, was elevated following vasopressin (0.2 units/ml) or arginine vasotocin (0.1 units/ml) treatment of skins from active animals at all times of the year tested. skins from dormant animals showed no such elevation at any time of the year. the rate of active sodium transport was elevated following treatment with dibutyryl cyclic amp (2.5mm) plus theophylline (10 mm) in al ... | 1996 | 177715 |
| larval hannemania sp. infestations of spea spp. in the southern high plains, texas, usa. | we describe a case history of larval hannemania sp. (acari: trombiculidae) infestations in two spadefoot toads (spea spp. anura: pelobatidae) captured from playa wetlands in the southern high plains, texas. hannemania sp. larvae were superficially attached to the skin, not encysted, and dermal changes were not observed. gross field examinations revealed a presumed occurrence of hannemania sp. in spea spp. at four of 24 wetlands in 2003 and 2004. although other species of amphibians were present ... | 2007 | 17984273 |
| ancestral variation and the potential for genetic accommodation in larval amphibians: implications for the evolution of novel feeding strategies. | few studies provide empirical evidence for phenotypic plasticity's role in the evolution of novel traits. one way to do so is to test whether latent plasticity is present in an ancestor that can be refined, enhanced, or diminished by selection in derived taxa (through "genetic accommodation"), thereby producing novel traits. here, we evaluated whether gut plasticity preceded and promoted the evolution of a novel feeding strategy in spadefoot toad tadpoles. we studied scaphiopus couchii, whose ta ... | 2016 | 18460093 |
| urea and salt effects on enzymes from estivating and non-estivating amphibians. | the effects of urea, cations (k+,nh4,na+,cs+,li+), and trimethylamines on the maximal activities and kinetic properties of pyruvate kinase (pk) and phosphofructokinase (pfk) from skeletal muscle were analyzed in two anuran amphibians, an estivating species, the spadefoot toad scaphiopus couchii, and a semi-aquatic species, the leopard frog rana pipiens. urea, which accumulates naturally to levels of 200-300 mm during estivation in toads, had only minor effects on the vmax, kinetic constants and ... | 1994 | 8047069 |
| plasma and brain angiotensin concentrations associated with water response behavior in the desert anuran, scaphiopus couchii under natural conditions in the field. | terrestrial amphibians obtain water by absorption across a specialized region of the ventral skin and exhibit a behavior, the water absorption response (wr) to place that region in contact with moist surfaces. spadefoot toads (scaphiopus couchii) spend dry months of the year in burrows, then emerge during brief periods of summer rainfall and seek water sources for rehydration and reproduction. we tested the hypothesis that these toads have changes in plasma and/or central angiotensin concentrati ... | 2010 | 20708705 |
| effects of density and predation on scaphiopus couchi tadpoles in desert ponds. | the effects of density on growth and development of scaphiopus couchi tadpoles in desert ponds were investigated, and sources of mortality over a three-year period were documented. in 16 of the 82 ponds monitored, predation was the principal cause of death, demonstrating that tadpoles in desert ponds may be exposed to high levels of predation, although the overall importance of predation is less here than in more mesic areas. desiccation was the primary cause of mortality in 49 ponds. growth and ... | 1987 | 28312260 |
| population differentiation of temperate amphibians in unpredictable environments. | amphibians are a globally distributed and diverse lineage, but much of our current understanding of their population genetic structure comes from studies in mesic temperate habitats. we characterize the population genetic structure of two sympatric explosive breeding amphibians in the southwestern deserts of the united states: the great plains toad (anaxyrus cognatus) and couch's spadefoot toad (scaphiopus couchii). for both species, we find limited genetic differentiation even between populatio ... | 2009 | 19573030 |
| angiotensin ii induces water absorption behavior in two species of desert anurans. | the octapeptide, angiotensin ii (a-ii), induces drinking behavior in several vertebrate species; however, relatively little is understood about a-ii-induced thirst in amphibians. scaphiopus couchii and bufo cognatus were dehydrated to 90% of their ad libitum weight. this level of dehydration was sufficient to induce water absorption response (wr) behavior in both species. fully hydrated toads injected intraperitoneally with a-ii exhibited a significant amount of wr behavior. the minimum effectiv ... | 1994 | 8034281 |
| dna replication in the amphibia. | autoradiographic techniques were used to measure rate of replication and length of the replication unit in cultured cells of scaphiopus couchi, bufo cognatus, rana clamitans, and triturus viridescens, having nuclear dna amounts in the ratio 1:4:7:39 respectively. the autoradiographic experiments were designed to show whether the larger amounts of nuclear dna are correlated with more rapid rates of synthesis and/or with longer replication units. -- the dna replication rate was 2.5 mu/minute (corr ... | 1975 | 125187 |
| osmotic tolerance of the muscles of two desert-inhabiting toads, bufo cognatus and scaphiopus couchi. | | 1964 | 14206962 |
| competition, predation, and the distributions of four desert anurans. | several studies have shown that larval competition and susceptibility to predation affect distributions of amphibian assemblages across ephemeral and perennial habitats. however, few studies have examined mechanisms affecting distribution patterns and site use of anurans adapted to highly ephemeral habitats. this study examines hypotheses about competition and predation as mechanisms creating non-overlapping patterns of site use in four anurans that breed in highly ephemeral habitats: scaphiopus ... | 2001 | 28547198 |
| freeze-induced expression of a novel gene, fr47, in the liver of the freeze-tolerant wood frog, rana sylvatica. | the ability to endure the freezing of body fluids is well developed as an adaptation for winter survival in several species of woodland frogs. recently, the mechanisms supporting natural freeze tolerance have been shown to include the expression of novel genes. one such novel gene, fr47, codes for a 390-amino acid protein present in the livers of freeze-tolerant anurans (rana sylvatica, pseudacris crucifer, hyla versicolor) but not in freeze-intolerant species (rana pipiens, scaphiopus couchii). ... | 2003 | 12531477 |
| genetic accommodation via modified endocrine signalling explains phenotypic divergence among spadefoot toad species. | phenotypic differences among species may evolve through genetic accommodation, but mechanisms accounting for this process are poorly understood. here we compare hormonal variation underlying differences in the timing of metamorphosis among three spadefoot toads with different larval periods and responsiveness to pond drying. we find that, in response to pond drying, pelobates cultripes and spea multiplicata accelerate metamorphosis, increase standard metabolic rate (smr), and elevate whole-body ... | 2017 | 29051478 |
| behavioral, molecular and integrative mechanisms of amphibian osmoregulation. | amphibian water balance has been studied at many levels of biological order. terrestrial species must react to environmental cues that relate to water availability while some arboreal species have cutaneous skin secretions that can reduce evaporative water loss. the indian tree frog. polypedates maculatus, uses cutaneous secretions and wiping behavior to lower evaporation but also relies on moist microclimates to endure prolonged survival away from water. the related species, p. leucomystax, inh ... | 1999 | 10222590 |
| comparative dna renaturation kinetics in amphibians. | amphibian haploid genome sizes vary from 9 x 10(8) to 8 x 10(10) nucleotide pairs. the rate of reassociation of dna from amphibians of different genome sizes has been employed to eliminate one of the theoretical models of chromosome structure. scaphiopus couchi, bufo marinus, and rana clamitans, whose haploid genome sizes are in the ratio 2:7:10, all contain sequences of dna represented once in the haploid genome. this indicates that their chromosomes are not composed of identical lateral strand ... | 1971 | 5279521 |
| the effects of in vivo and in vitro hyperosmolality on skeletal muscle performance in the amphibians rana pipiens and scaphiopus couchii. | 1. the effect of in vivo and in vitro hyperosmolality on skeletal muscle function was investigated in two species of anuarans scaphiopus couchii and rana pipiens. 2. muscle contractile performance, measured as peak tetanic tension declined to greater degree when tissue dehydration occurred in vitro rather than in vivo, even though tissue water contents were greater in vivo. 3. the muscles from s. couchii, a more dehydration tolerant species than r. pipiens, maintained tension at lower tissue wat ... | 1982 | 6130873 |
| antipredator behavior promotes diversification of feeding strategies. | animals often facultatively engage in less risky behavior when predators are present. few studies, however, have investigated whether, or how, such predator-mediated behavior promotes diversification. here, we ask whether tadpoles of the spadefoot toad scaphiopus couchii have a diminished ability to utilize a potentially valuable resource--anostracan fairy shrimp--because of behavioral responses to predation risk imposed by carnivorous tadpoles of the genus spea. observations of a congener of sc ... | 2012 | 22596058 |
| diet and hormonal manipulation reveal cryptic genetic variation: implications for the evolution of novel feeding strategies. | when experiencing resource competition or abrupt environmental change, animals often must transition rapidly from an ancestral diet to a novel, derived diet. yet, little is known about the proximate mechanisms that mediate such rapid evolutionary transitions. here, we investigated the role of diet-induced, cryptic genetic variation in facilitating the evolution of novel resource-use traits that are associated with a new feeding strategy--carnivory--in tadpoles of spadefoot toads (genus spea). we ... | 2010 | 20573627 |
| life in the slow lane: molecular mechanisms of estivation. | estivation is a state of aerobic hypometabolism used by organisms to endure seasonally arid conditions, often in desert environments. estivating species are often active for only a few weeks each year to feed and breed and then retreat to estivate in sheltered sites, often underground. in general, estivation includes a strong reduction in metabolic rate, a primary reliance on lipid oxidation to fuel metabolism, and methods of water retention, both physical (e.g. cocoons) and metabolic (e.g. urea ... | 2002 | 12443930 |
| tyrosine kinases and phosphatases in the estivating spadefoot toad. | to endure seasonally arid conditions, spadefoot toads (scaphiopus couchii) spend 9-10 months underground each year in a hypometabolic state, termed estivation. protein tyrosine kinases (ptks) and phosphatases (ptps) were evaluated in organs of control and estivating toads to assess their possible role in signal transduction during estivation. total ptk activity decreased by 27-52 % in liver, lung and skeletal muscle during estivation but rose by 66% in heart. total ptp activity changed only in l ... | 2001 | 11410711 |
| the muscle fatty acid binding protein of spadefoot toad (scaphiopus couchii). | fatty acid binding protein was purified from skeletal muscle of the spadefoot toad (scaphiopus couchii), an estivating species. while estivating, this animal relies on the fatty acid oxidation for energy. hence we were interested in the behaviour of fatty acid binding protein under conditions of elevated urea (up to 200 mm) and potassium chloride such as exist during estivation. also we examined whether there were interactions between glycolytic intermediates and the binding ability of the prote ... | 2000 | 10818268 |
| effects of dehydration on plasma osmolality, thirst-related behavior, and plasma and brain angiotensin concentrations in couch's spadefoot toad, scaphiopus couchii. | under dehydrating conditions, many terrestrial vertebrates species exhibit increases in plasma osmolality and their drinking behavior. under some circumstances, this behavioral change is accompanied by changes in plasma and central angiotensin concentrations, and it has been proposed that these changes in angiotensin levels induce the thirst-related behaviors. in response to dehydration, the spadefoot toad, scaphiopus couchii, exhibits thirst-related behavior in the form of cutaneous drinking. t ... | 2000 | 10766966 |
| intra- and extracellular dehydration has no effect on plasma levels of angiotensin ii in an amphibian. | previous studies have demonstrated that both dehydration (intra and extracellular) and treatment with angiotensin ii (a-ii) induce changes in thirst-related behavior in the spadefoot toad, scaphiopus couchii. one of the steps in determining a causal relationship between a hormone and a behavior is to determine that there is association between an animal's performance of the behavior and changes in endogenous hormonal concentrations. the hypothesis tested that plasma levels of the peptide hormone ... | 2000 | 10684557 |
| reversible phosphorylation control of skeletal muscle pyruvate kinase and phosphofructokinase during estivation in the spadefoot toad, scaphiopus couchii. | both pyruvate kinase (pk) and phosphofructokinase (pfk) occur in two different forms, separable by isoelectric focusing (ief), in skeletal muscle of the spadefoot toad scaphiopus couchii. during estivation (aerobic dormancy) the proportions of the two forms changed compared with controls; in both cases the amount of enzyme in peak i (pi = 5.3-5.4) decreased whereas activity in peak ii (isoelectric point = 6.2-6.4) increased. in vitro incubation of crude muscle extracts with 32p-atp under conditi ... | 1999 | 10395081 |
| intra- and extracellular dehydration-induced thirst-related behavior in an amphibian. | the behavioral response to dehydration is critical to an animal's survival. because of their permeable skin, amphibians are particularly sensitive to dehydrating conditions. we tested the hypothesis that different forms of dehydration induce water absorption response (wr) behavior in the desert spadefoot toad, scaphiopus couchii. first, we determined the behavioral response to intracellular dehydration by treating fully hydrated toads with increasing concentrations of hypertonic solutions of nac ... | 2017 | 10073473 |
| ecological constraints on amphibian metamorphosis: interactions of temperature and larval density with responses to changing food level. | phenotypic plasticity is adaptive for an organism inhabiting a variable environment if the optimal phenotype of a trait that affects fitness varies with environmental conditions, and if the organism can perceive environmental conditions and respond appropriately. wilbur and collins have proposed that amphibian larvae might respond adaptively to changes in their resource environment. if conditions for growth in the aquatic environment deteriorate, then a tadpole should metamorphose earlier and sm ... | 1998 | 28308472 |
| antioxidant defenses and lipid peroxidation damage in estivating toads, scaphiopus couchii. | tissue-specific changes in antioxidant defenses and lipid peroxidation damage were analyzed in spadefoot toads, scaphiopus couchii, to determine how these responded during estivation, a state of suppressed oxygen consumption. maximal activities of glutathione-s-transferase, glutathione reductase, glutathione peroxidase, superoxide dismutase and catalase were measured in six organs from 2-month-estivated toads and compared with activities in animals awakened for 10 days after estivation. activiti ... | 1998 | 9542148 |
| effects of androgens on male sexual behavior and secondary sex characters in the explosively breeding spadefoot toad, scaphiopus couchii. | in male scaphiopus couchii, plasma elevations in androgens are associated with the seasonal expression of sexual behavior. to test the hypothesis that androgens are necessary for the expression of one aspect of sexual behavior, amplexus, and for the development of secondary sex characteristics in male s. couchii, the effects of testosterone (t) and dihydrotestosterone (dht) on clasping behavior and thumb pad growth were investigated. forty toads were divided into five treatment groups as follows ... | 1997 | 9109602 |
| reproductive endocrinology of the explosively breeding desert spadefoot toad, scaphiopus couchii. | the spadefoot toad, scaphiopus couchii, is an explosively breeding, desert dwelling amphibian that shows two characteristics hypothesized to select for a dissociated breeding pattern: it lives in a harsh environment and it has a very short, but predictable breeding period. we tested the hypothesis that these factors select for a dissociated breeding cycle by measuring plasma steroid hormones and the gametogenic cycles in a free-living population of s. couchii. blood and tissue samples were obtai ... | 1997 | 9000472 |
| central angiotensin ii induces thirst-related responses in an amphibian. | angiotensin ii (a-ii), a potent inducer of thirst-related behavior in many vertebrate species, was injected into the third ventricle of the brain of the spadefoot toad, scaphiopus couchii. following injection of 10 ng a-ii the animals demonstrated a significant increase in water absorption response (wr) behavior, in which toads press their ventral skin to a moist surface and absorb water by osmosis. this increase in the frequency of wr behavior was positively correlated with an increase in water ... | 1995 | 7782064 |
| genetic variation for phenotypic plasticity in the larval life history of spadefoot toads (scaphiopus couchii). | phenotypic plasticity in life-history traits is common. the relationship between phenotype and environment, or reaction norm, associated with life-history plasticity can evolve by natural selection if there is genetic variation within a population for the reaction norm and if the traits involved affect fitness. as with other traits, selection on plasticity in a particular trait or in response to a particular environmental factor may be constrained by trade-offs with other traits that affect fitn ... | 1994 | 28565166 |
| genetic variation for larval anuran (scaphiopus couchii) development time in an uncertain environment. | couch's spadefoot toads (scaphiopus couchii) breed in ponds of uncertain duration. in natural ponds, larvae exhibit considerable variation in growth, size at metamorphosis, and development time. phenotypic differences in development time may dramatically affect survivorship in these ponds. a quantitative-genetic analysis of larval traits was undertaken to determine the potential evolutionary relevance of phenotypic variation observed in the field. additive genetic variance was detected for devel ... | 1988 | 28563872 |
| adaptive plasticity in development of scaphiopus couchii tadpoles in desert ponds. | couch's spadefoot toads (scaphiopus couchii) breed in ephemeral desert ponds that are highly variable in duration. rapid development is expected to be advantageous in short-duration ponds, but slower development, allowing more time for growth, may be advantageous in ponds of longer duration. previous experiments have revealed both genetic variation in development time and phenotypic plasticity in response to pond drying. in this paper, i examine the norms of reaction of five sibships of tadpoles ... | 1988 | 28563867 |
| paternal effects on offspring traits in scaphiopus couchi (anura: pelobatidae). | maternal half-siblings sired by large male scaphiopus couchi had higher probabilities of surviving than maternal half-sibs sired by smaller males. half-sibs sired by large and small males did not differ in tadpole body weight, duration of larval period, number of toadlets produced, or toadlet body weight. these results suggest that which male a female mates with may influence important components of her offspring's fitness. | 1987 | 28311985 |
| the beta adrenergic receptor and cyclic 3',5'-adenosine monophosphate: possible roles in the regulation of melanophore responses of the spadefoot toad, scaphiopus couchi. | | 1969 | 4389916 |
| cocoon surrounding desert-dwelling frogs. | a cocoon formed from a single cell layer of shed stratum corneum may reduce water loss from the skin of desert-dwelling frogs while these aestivate in soil-filled burrows. in several australian examples, the cocoon is a single layer of cells, and thus differs from the multilayered structure obtained from an american species, scaphiopus couchi. | 1967 | 6026672 |