analysis of range expansion in two species undergoing character displacement: why might invaders generally 'win' during character displacement?ecological character displacement occurs when interacting species diverge in resource use and associated traits in response to selection to minimize resource competition between them. yet, when resource quality is asymmetric, the species that monopolizes the more profitable resource following character displacement may have higher fitness and therefore be deemed the 'winner'. here, we ask: does the winner tend to be the resident species (i.e. the earlier inhabitant of the geographic region where ...200818341542
surface water mitigates the anti-metamorphic effects of perchlorate in new mexico spadefoot toads (spea multiplicata) and african clawed frogs (xenopus laevis).spea multiplicata (new mexico spadefoot toad) larvae were exposed to 60, 110, and 1000 microg l(-1) perchlorate dissolved in natural surface water to determine risks associated with perchlorate exposure in desert-adapted anurans. hind- and forelimb development and tail resorption were measured to identify effects of perchlorate exposure. no perchlorate-related effects on snout-vent length, hindlimb length, and proportion metamorphosed were observed in the highest treatment group (positive contro ...201019913875
development and characterization of nine polymorphic microsatellite markers for mexican spadefoot toads (spea multiplicata) with cross-amplification in plains spadefoot toads (s. bombifrons).we developed nine polymorphic microsatellite markers for the mexican spadefoot toad, spea multiplicata. allele numbers range from five to 12, with observed heterozygosities from 0.48 to 0.87. because two loci are in linkage disequilibrium, these nine loci provide eight independent markers. three loci exhibit departure from hardy-weinberg equilibrium, possibly resulting from null alleles or population admixture. these markers will be useful for assessing population structure and relatedness in s. ...200821586053
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 ...201121651912
chiggers recently infesting spea spp. in texas, usa, were eutrombicula alfreddugesi, not hannemania sp.upon re-examination of preserved larval chiggers collected from spadefoot toads (spea bombifrons and spea multiplicata) in the southern high plains of texas, usa, and identified previously as hannemania sp., we found them to be eutrombicula alfreddugesi. a review of previous reports of eutrombicula spp. chiggers on amphibian hosts provides context for current findings. all members of the genus hannemania are specialized larval parasites of amphibians, whereas larval e. alfreddugesi are generalis ...201121719825
effects of chlorothalonil on development and growth of amphibian embryos and larvae.chlorothalonil is a broad spectrum fungicide widely used in agricultural and urban environments, yet little is known regarding its effects on amphibians. we examined effects of chlorothalonil on growth, malformations, and mortality in embryos and larvae of xenopus laevis and spea multiplicata, and assessed variation in sensitivity among aquatic organisms using a species sensitivity distribution (ssd). chlorothalonil induced gut malformations in x. laevis embryos and inhibited growth. tail degene ...201323866729
social signals increase monoamine levels in the tegmentum of juvenile mexican spadefoot toads (spea multiplicata).monoamines are important neuromodulators that respond to social cues and that can, in turn, modify social responses. yet we know very little about the ontogeny of monoaminergic systems and whether they contribute to the development of social behavior. anurans are an excellent model for studying the development of social behavior because one of its primary components, phonotaxis, is expressed early in life. to examine the effect of social signals on monoamines early in ontogeny, we presented juve ...201323681220
widespread disruptive selection in the wild is associated with intense resource competition.disruptive selection has been documented in a growing number of natural populations. yet, its prevalence within individual systems remains unclear. furthermore, few studies have sought to identify the ecological factors that promote disruptive selection in the wild. to address these issues, we surveyed 15 populations of mexican spadefoot toad tadpoles, spea multiplicata, and measured the prevalence of disruptive selection acting on resource-use phenotypes. we also evaluated the relationship betw ...201222857143
an inducible offense: carnivore morph tadpoles induced by tadpole carnivory.phenotypic plasticity is commonplace, and plasticity theory predicts that organisms should often evolve mechanisms to detect and respond to environmental cues that accurately predict future environmental conditions. here, we test this prediction in tadpoles of spadefoot toads, spea multiplicata. these tadpoles develop into either an omnivore ecomorph, which is a dietary generalist, or a carnivore ecomorph, which specializes on anostracan shrimp and other tadpoles. we investigated a novel proxima ...201525897380
choosy cannibals preferentially consume siblings with relatively low fitness prospects.when an individual can selfishly cannibalize a relative or altruistically set it free, the benefits of altruism will be positively associated with the relative's fitness prospects (the benefits it receives from altruism). we tested the prediction that altruism should be preferentially directed toward high-quality relatives using larvae of the new mexican spadefoot toad (spea multiplicata), a species in which tadpoles plastically express omnivore and carnivore ecomorphs. in a no-choice design, we ...201627322127
effects of water loss on new mexico spadefoot toad (spea multiplicata) development, spleen cellularity, and corticosterone levels.amphibian metamorphosis is complex and larval morphology and physiology are completely restructured during this time. amphibians that live in unpredictable environments are often exposed to stressors that can directly and indirectly alter physiological systems during development, with subsequent consequences (carryover effects) later in life. in this study, we investigated the effects of water level reduction on development rate, spleen size and cellularity, and examined the role of corticostero ...201627714986
surface water mitigates the anti-metamorphic effects of elevated perchlorate concentrations in new mexico spadefoot toad larvae (spea multiplicata).perchlorate (clo4-) has potential to negatively impact amphibian populations by inhibiting thyroid hormone production, and thus metamorphosis in developing larvae. however, variability exists in species sensitivity, and there is evidence suggesting that natural surface waters can mitigate the anti-metamorphic potential of perchlorate. new mexico spadefoot toad tadpoles, spea multiplicata, were exposed to natural surface waters spiked with nominal concentrations of 0, 1000, 1350, 1710, 3000, 5110 ...201728608158
kin-mediated morphogenesis in facultatively cannibalistic tadpoles.inclusive fitness theory predicts that organisms can increase their fitness by helping or not harming relatives, and many animals modify their behavior toward kin in a manner consistent with this prediction. morphogenesis also may be sensitive to kinship environment, particularly in species where certain individuals facultatively develop structures that can be used against conspecifics as weaponry. we tested this hypothesis by examining whether and how consanguinity affected the probability that ...199728565095
a suite of molecular markers for identifying species, detecting introgression and describing population structure in spadefoot toads (spea spp.).two congeneric species of spadefoot toad, spea multiplicata and spea bombifrons, have been the focus of hybridization studies since the 1970s. because complex hybrids are not readily distinguished phenotypically, genetic markers are needed to identify introgressed individuals. we therefore developed a set of molecular markers (amplified fragment length polymorphism, polymerase chain reaction-restriction fragment length polymorphism and single nucleotide polymorphism) for identifying pure-species ...201222564443
hybrid female mate choice as a species isolating mechanism: environment matters.a fundamental goal of biology is to understand how new species arise and are maintained. female mate choice is potentially critical to the speciation process: mate choice can prevent hybridization and thereby generate reproductive isolation between potentially interbreeding groups. yet, in systems where hybridization occurs, mate choice by hybrid females might also play a key role in reproductive isolation by affecting hybrid fitness and contributing to patterns of gene flow between species. we ...201626717048
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 ...19979000472
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 ...201710073473
does character displacement initiate speciation? evidence of reduced gene flow between populations experiencing divergent selection.character displacement - trait evolution stemming from selection to lessen resource competition or reproductive interactions between species - has long been regarded as important in finalizing speciation. by contrast, its role in initiating speciation has received less attention. yet because selection for character displacement should act only where species co-occur, individuals in sympatry will experience a different pattern of selection than conspecifics in allopatry. such divergent selection ...201020210828
evolution of character displacement in spadefoot toads: different proximate mechanisms in different species.character displacement occurs when two species compete, and those individuals most dissimilar from the average resource-use phenotypes of the other species are selectively favored. few studies have explored the sequence of events by which such divergence comes about. we addressed this issue by studying two species of spadefoot toads that have undergone ecological character displacement with each other. previous research revealed that phenotypic shifts between sympatric and allopatric populations ...201020394671
acute and chronic toxicity of roundup weathermax and ignite 280 sl to larval spea multiplicata and s. bombifrons from the southern high plains, usa.pesticides have been implicated in widespread amphibian declines. we assessed acute and chronic toxicity of two widely used herbicides to larval new mexico (spea multiplicata) and plains (s. bombifrons) spadefoots from cropland and native grassland playas. roundup weathermax (wm) toxicity estimates (48- and 216-h lc(50); 48-h lc(1)) for both species were similar to environmental concentrations expected from accidental overspray. chronic (30-day) exposure to wm at predicted environmental concentr ...201020541298
reassessment of the environmental model of developmental polyphenism in spadefoot toad tadpoles.polyphenism is the expression of multiple, discrete phenotypes from one genotype, and understanding the environmental factors that trigger development of alternative phenotypes is a critical step toward understanding the evolution of polyphenism and its developmental control. while much is known about the ecology of the well-known carnivore/omnivore polyphenism in spadefoot toad tadpoles, the environmental cues for the development of the specialized carnivore phenotype are not completely clear. ...201120842381
evaluating the targets of selection during character displacement.ecological character displacement occurs when competition imposes divergent selection on interacting species, causing divergence in traits associated with resource use. generally, divergence is assumed to occur when selection acts on the same, continuously varying trait in both species. however, selection might target multiple traits, and even closely related heterospecifics involved in character displacement might differ in selective targets. we investigated the targets of selection in a specie ...201121967434
why do species co-occur? a test of alternative hypotheses describing abiotic differences in sympatry versus allopatry using spadefoot toads.areas of co-occurrence between two species (sympatry) are often thought to arise in regions where abiotic conditions are conducive to both species and are therefore intermediate between regions where either species occurs alone (allopatry). depending on historical factors or interactions between species, however, sympatry might not differ from allopatry, or, alternatively, sympatry might actually be more extreme in abiotic conditions relative to allopatry. here, we evaluate these three hypothesi ...201222479337
maternal investment influences expression of resource polymorphism in amphibians: implications for the evolution of novel resource-use phenotypes.maternal effects--where an individual's phenotype is influenced by the phenotype or environment of its mother--are taxonomically and ecologically widespread. yet, their role in the origin of novel, complex traits remains unclear. here we investigate the role of maternal effects in influencing the induction of a novel resource-use phenotype. spadefoot toad tadpoles, spea multiplicata, often deviate from their normal development and produce a morphologically distinctive carnivore-morph phenotype, ...201020161745
parallel evolution and ecological selection: replicated character displacement in spadefoot toads.ecological character displacement--trait evolution stemming from selection to lessen resource competition between species--is most often inferred from a pattern in which species differ in resource-use traits in sympatry but not in allopatry, and in which sympatric populations within each species differ from conspecific allopatric populations. yet, without information on population history, the presence of a divergent phenotype in multiple sympatric populations does not necessarily imply that the ...200919726477
disruptive selection in natural populations: the roles of ecological specialization and resource competition.disruptive selection is potentially critical in maintaining variation and initiating speciation. yet there are few convincing examples of disruptive selection from nature. moreover, relatively little is known about the causes of disruptive selection. here, we document disruptive selection and its causes in natural populations of spadefoot toad tadpoles (spea multiplicata), which are highly variable in trophic phenotype and resource use. using a mark-recapture experiment in a natural pond, we sho ...200919527118
spadefoot-tadpole polyphenism: histological analysis of differential muscle growth in carnivores and omnivores.understanding the evolution of phenotypic plasticities and the connections among the environment, genotype, and phenotype requires detailed understanding of the proximate mechanisms regulating morphological differences between phenotypes. spea multiplicata tadpoles can develop into two different phenotypes, i.e. carnivores and omnivores, which differ in many morphological and behavioral traits. one of the major differences is enlargement of the jaw and tail musculature in carnivores relative to ...200919459191
a maternal effect mediates rapid population divergence and character displacement in spadefoot toads.despite long-standing interest in character displacement, little is known of its underlying proximate causes. here, we explore the role of maternal effects in character displacement. we specifically investigated whether differences in maternal body condition mediate divergence in the expression of resource-use traits between populations of spadefoot toads (spea multiplicata) that occur in sympatry with a heterospecific competitor and those that occur in allopatry. in sympatry, s. multiplicata is ...200919154374
temporally dissociated, trait-specific modifications underlie phenotypic polyphenism in spea multiplicata tadpoles, which suggests modularity.many organisms that develop in a variable environment show correlated patterns of phenotypic plasticity in several traits. any individual trait modification can be beneficial, neutral, or deleterious in any particular environment; the organism's total fitness, which determines if the plasticity is adaptive, is the sum of these changes. although much is known about how plastic traits contribute to fitness, less is known about the extent to which the various trait changes involved in the plastic r ...200717619754
toxicity of a glufosinate- and several glyphosate-based herbicides to juvenile amphibians from the southern high plains, usa.pesticide toxicity is often proposed as a contributing factor to the world-wide decline of amphibian populations. we assessed acute toxicity (48 h) of a glufosinate-based herbicide (ignite 280 sl) and several glyphosate-based herbicide formulations (roundup weathermax, roundup weed and grass killer super concentrate, roundup weed and grass killer ready-to-use plus on two species of amphibians housed on soil or moist paper towels. survival of juvenile great plains toads (bufo cognatus) and new me ...200919000631
metacercariae of clinostomum attenuatum in ambystoma tigrinum mavortium, bufo cognatus and spea multiplicata from west texas.tissues from barred tiger salamanders (ambystoma tigrinum mavortium), great plains toads (bufo cognatus) and new mexico spadefoots (spea multiplicata) collected from 16 playa wetlands in texas during 1999 and 2000 were examined by light microscopy. digenean cysts were primarily distributed subcutaneously throughout the specimens and occasionally coelomic invasion was noted. the parasites within the cysts were 1.5-2 mm in diameter, with a thin (c. 10 microm wide) eosinophilic-staining tegument, t ...200415575998
differential selection to avoid hybridization in two toad species.the fitness consequences of hybridization critically affect the speciation process. when hybridization is costly, selection favors the evolution of prezygotic isolating mechanisms (e.g., mating behaviors) that reduce heterospecific matings and, consequently, enhance reproductive isolation between species (a process termed reinforcement). if, however, selection to avoid hybridization differs between species, reinforcement may be impeded. here, we examined both the frequency and fitness effects of ...200212389729
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 ...201618460093
four independent electrophoretic markers in spadefoot toads.four enzyme-encoding genes (idh-1, idh-2, ldh-1, and mdh-1), with alleles diagnostic for the spadefoot toads scaphiopus multiplicatus and scaphiopus bombifrons, were investigated in order to characterize their inheritance and linkage relationships. electrophoretic phenotypes in the offspring of natural crosses exhibit mendelian segregation, behaving as genotypes produced by alternative alleles at four independently assorting loci. these phenotypes are useful markers of genetic identity and the d ...20123559167
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 ...200010718730
distribution of neuronal melanocortins in the spadefoot toad spea multiplicata and effects of stress.we examined the effects of an acute stressor on regional alpha-melanocyte-stimulating hormone (alphamsh) content in the new mexican spadefoot toad, spea multiplicata. we first used immunocytochemistry along with radioimmunoassay (ria) to examine the distribution of pro-opiomelanocortin (pomc) neurons in the brain of spea. neurons immunoreactive for alphamsh, beta-endorphin, and corticotropin were observed in the preoptic nucleus and ventral infundibulum of the hypothalamus. ascending immunoreact ...200111509823
mechanism of tongue protraction during prey capture in the spadefoot toad spea multiplicata (anura: pelobatidae).recent studies have used muscle denervation experiments to examine the function of muscles during feeding in frogs. by comparing the results of denervation experiments among taxa, it is possible to identify evolutionary changes in muscle function. the purpose of this study was to examine the function of jaw and tongue muscles during prey capture in spea multiplicata, a representative of the superorder mesobatrachia. all members of this group possess a disjunct hyoid apparatus. we predicted that ...19958530912
polyphenism in spadefoot toad tadpoles as a locally adjusted evolutionarily stable strategy.i examined the evolutionary factors maintaining two environmentally induced morphs in ponds of variable duration. larvae of new mexico spadefoot toads (scaphiopus multiplicatus) often occur in the same pond as a large, rapidly developing carnivorous morph and as a smaller, more slowly developing omnivorous morph. previous studies revealed that carnivores can be induced by feeding tadpoles live fairy shrimp and that morph determination is reversible. field and laboratory experiments indicated tha ...199228568981
the adaptive significance of an environmentally-cued developmental switch in an anuran tadpole.this study investigated the proximate basis of bimodally-distributed, environmentally-induced variation that occurs in natural populations of spade-foot toad tadpoles (scaphiopus multiplicatus). most individuals in most populations occur as a small, slowly-developing omnivore morph. in some of these same populations, a varying number of individuals occur as a large, rapidly-developing carnivore morph (pfennig 1989). censuses of 37 different natural ponds revealed that the frequency of the faster ...199028310961
"kin recognition" among spadefoot toad tadpoles: a side-effect of habitat selection?many animals modify their behavior toward unfamiliar conspecifics as a function of their genetic relatedness. a fundamental problem of any kin recognition study is determining what is being recognized and why. for anuran tadpoles, the predominant view is that associating with relatives is kin-selected because these relatives may thereby accrue benefits through increased growth or predation avoidance. an alternative view is that kin associations are simply a side-effect of habitat selection and t ...199028569036
predatory capture of toads by fly larvae.a natural occurrence of predation upon toads (scaphiopus multiplicatus) by fly larvae (tabanus punctifer) is described. the larvae lie buried in mud, seize the toads with hooked mandibles, pull them partly into the mud, and kill them by feeding on their body fluids. the larvae may ordinarily subsist mostly on invertebrates and take amphibia only opportunistically.198317746204
tadpole competition in a desert anuran community.five interspecific competition experiments performed in artificial ponds under temporary pond-like conditions established that temporary and permanent pond tadpoles interact. temporary pond species typically lowered survivorship and reduced progress towards metamorphosis of permanent pond tadpoles. these results suggest that competitive interactions may partially determine the local distribution of tadpoles in the chihuahuan desert by preventing some permanent pond anurans from using temporary p ...198228310999
skeletal development of the mexican spadefoot, spea multiplicata (anura: pelobatidae).the larval chondrocranium of spea multiplicata is described, as is the development and adult morphology of the skeleton. there are major modifications to the larval chondrocranium throughout development, including the presence of embryonic trabeculae in young tadpoles and significant reorganization of cartilaginous structures at metamorphosis. the first bone to ossify is the parasphenoid (stage 35), followed by the presacral neural arches, ilium, and femur (stage 36). by stage 39, most of the po ...200616572407
reassessment of the environmental mechanisms controlling developmental polyphenism in spadefoot toad tadpoles.identifying the environmental mechanism(s) controlling developmental polyphenism is the first step in gaining a mechanistic and evolutionary understanding of the factors responsible for its expression and evolution. tadpoles of the spadefoot toad spea multiplicata can display either a "typical" omnivorous or a carnivorous phenotype. exogenous thyroxine and feeding on conspecific tadpoles have been accepted as triggers for development of the carnivorous phenotype on the basis of a series of studi ...200415300488
a test of alternative hypotheses for the evolution of reproductive isolation between spadefoot toads: support for the reinforcement do species that interbreed become reproductively isolated? if hybrids are less fit than parental types, natural selection should promote reproductive isolation by favoring the evolution of premating mechanisms that prevent hybridization (a process termed reinforcement). although reinforcement should generate a decline in hybridization over time, countervailing forces of gene flow and recombination are thought to preclude natural selection from enhancing and finalizing reproductive isolation. ...200314761062
asymmetric reproductive character displacement in male aggregation behaviour.reproductive character displacement-the evolution of traits that minimize reproductive interactions between species-can promote striking divergence in male signals or female mate preferences between populations that do and do not occur with heterospecifics. however, reproductive character displacement can affect other aspects of mating behaviour. indeed, avoidance of heterospecific interactions might contribute to spatial (or temporal) aggregation of conspecifics. we examined this possibility in ...201021177683
ecological strategies predict associations between aquatic and genetic connectivity for dryland amphibians.the study of how population genetic structure is shaped by attributes of the environment is a central scientific pursuit in ecology and conservation. but limited resources may prohibit landscape genetics studies for many threatened species, particularly given the pace of current environmental change. understanding the extent to which species' ecological strategies--their life histories, biology, and behavior-predict patterns and drivers of population connectivity is a critical step in evaluating ...201526236850
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 ...201729051478
pre-mining trace element and radiation exposure to biota from a breccia pipe uranium mine in the grand canyon (arizona, usa) watershed.the risks to wildlife and humans from uranium (u) mining in the grand canyon watershed are largely unknown. in addition to u, other co-occurring ore constituents contribute to risks to biological receptors depending on their toxicological profiles. this study characterizes the pre-mining concentrations of total arsenic (as), cadmium (cd), copper (cu), lead (pb), mercury (hg), nickel (ni), selenium (se), thallium (tl), u, and zinc (zn); radiation levels; and histopathology in biota (vegetation, i ...201728091884
influence of sprint speed and body size on predator avoidance in new mexican spadefoot toads (spea multiplicata).predator-prey interactions play an important role in community dynamics and may be important for promoting genetic diversification. diversification may be especially important when prey species have multiple anti-predator strategies available, but these strategies conflict with each other. for example, rapid sprint speed and large size are both thought to decrease vulnerability to many predators. a physiological trade-off between swimming speed and growth rate has been documented in many aquatic ...200918987891
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