Hyla Chrysoscelis Research Articles

Sound source segregation in grey treefrogs: spatial release from masking by the sound of a chorus

Animals that communicate acoustically in noisy social environments face the problem of perceptually segregating behaviourally relevant signals from background noise. Studies of humans indicate improvements in speech perception tasks when target speech and a masking noise with the frequency spectrum of speech come from different locations. Thus for humans, spatial release from masking is an important mechanism of sound source segregation that functions in acoustic communication in noisy, real-world environments. Little previous work has investigated the mechanisms of sound source segregation in nonhuman animals that rely on acoustic signalling. I investigated spatial release from masking in the grey treefrog, Hyla chrysoscelis . Grey treefrogs form large breeding aggregations in which males produce loud advertisement calls that are necessary and sufficient for species recognition, source localization and selective mate choice by females. I tested the hypothesis that females would experience a release from masking when a synthetic advertisement call (target signal) and an artificial noise with the spectrum of a grey treefrog chorus (masker) were spatially separated. Using a phonotaxis paradigm, I assessed females' responses to the target signal at four signal-to-noise ratios (SNR) and two angular separations. Female responsiveness to the target signal increased as the SNR increased from −12 dB to +6 dB. More important, phonotaxis responses were faster at a 90° angle of signal–masker separation compared to one of just 7.5°. These results support the hypothesis that spatial release from masking is a potentially important mechanism for sound source segregation in animal acoustic communication.

Pesticide alters oviposition site selection in gray treefrogs

Understanding the impacts of pesticides on non-target organisms is an important issue for conservation biology. Research into the environmental consequences of pesticides has largely focused on pesticide toxicity. We have less understanding of the nonlethal effects of pesticides, and the consequences of nonlethal effects for species and communities. For example, we know very little about whether pesticides alter habitat selection behavior. Understanding whether pesticides alter habitat selection is important because pesticide-induced shifts in habitat selection could either magnify or reduce the toxic effects of contaminants by funneling organisms into or directing them away from contaminated sites. Here we present four field experiments that examine the effect of the commercial pesticide Sevin and its active ingredient, carbaryl, on oviposition site selection by the gray treefrog (Hyla chrysoscelis). Our results show that uncontaminated pools consistently received 2-3 times more eggs than contaminated pools; that treefrogs appeared to respond to Sevin directly, not indirectly via its effects on the aquatic food web, and that this preference persisted across a range of temporal and spatial scales. Both Sevin and carbaryl per se reduced oviposition, while other volatile chemicals (e.g., our solvent control, acetone) had no effect. These findings suggest that in order to understanding the consequences of contaminants in aquatic systems we will need to consider not only toxicity, but also how contaminant effects on habitat selection alter the way organisms distribute themselves in the environment.

Excretion and conservation of glycerol, and expression of aquaporins and glyceroporins, during cold acclimation in Cope's gray tree frogHyla chrysoscelis

Cope's gray tree frog Hyla chrysoscelis accumulates glycerol during cold acclimation. We hypothesized that, during this process, gray tree frogs adjust renal filtration and/or reabsorption rates to retain accumulated glycerol. During cold acclimation, plasma concentrations of glycerol rose >200-fold, to 51 mmol/l. Although fractional water reabsorption decreased, glomerular filtration rate (GFR) and, consequently, urine flow were <5% of warm levels, and fractional glycerol reabsorption increased. In contrast, dehydrated frogs increased fractional water reabsorption, decreased GFR, and did not accumulate glycerol. We hypothesized that expression of proteins from the aquaporin (AQP)/glyceroporin (GLP) family was associated with changing patterns of water and glycerol movement. We cloned the cDNA for three such proteins, quantified mRNA expression in nine tissues using real-time quantitative PCR, and functionally characterized them using a Xenopus oocyte expression system. HC-1, an AQP1-like water channel conferring low glycerol permeability, is expressed ubiquitously in warm- and cold-acclimated tissues. HC-2, a water channel most similar to AQP2, is primarily expressed in organs of osmoregulation. HC-3, which is most similar to AQP3, is functionally characterized as a GLP, with low permeability to water but high permeability to glycerol. Aspects of expression levels and functional characteristics varied between cold and warm conditions for each of the three AQPs, suggesting a complex pattern of involvement in osmoregulation related to thermal acclimation.

A NEW SPECIES OF MYXIDIUM (MYXOSPOREA: MYXIDIIDAE), FROM THE WESTERN CHORUS FROG, PSEUDACRIS TRISERIATA TRISERIATA, AND BLANCHARD'S CRICKET FROG, ACRIS CREPITANS BLANCHARDI (HYLIDAE), FROM EASTERN NEBRASKA: MORPHOLOGY, PHYLOGENY, AND CRITICAL COMMENTS ON AMPHIBIAN MYXIDIUM TAXONOMY

During March 2001-April 2004, 164 adult anurans of 6 species (47 Rana blairi, 35 Rana catesbeiana, 31 Hyla chrysoscelis, 31 Pseudacris triseriata triseriata, 11 Bufo woodhousii, and 9 Acris crepitans blanchardi) from Pawnee Lake, Lancaster County, Nebraska, were surveyed for myxozoan parasites. Of these, 20 of 31 (65%) P. triseriata triseriata and 1 of 9 (11%) A. crepitans blanchardi were infected with a new species of Myxidium. Myxidium melleni n. sp. (Myxosporea) is described from the gallbladder of the western chorus frog, P. triseriata triseriata (Hylidae). This is the second species of Myxidium described from North American amphibians. Mature plasmodia are disc-shaped or elliptical 691 (400-1,375) x 499 (230-1,200) x 23 (16-35) microm, polysporic, producing many disporic pansporoblasts. The mature spores, 12.3 (12.0-13.5) x 7.6 (7.0-9.0) x 6.6 (6.0-8.0) microm, containing a single binucleated sporoplasm, are broadly elliptical, with 2-5 transverse grooves on each valve, and contain 2 equal polar capsules 5.2 (4.8-5.5) x 4.2 (3.8-4.5) microm positioned at opposite ends of the spore. Myxidium melleni n. sp. is morphologically consistent with other members of Myxidium. However, M. melleni n. sp. was phylogenetically distinct from other Myxidium species for which DNA sequences are available. Only with improved morphological analyses, accompanied by molecular data, and the deposit of type specimens, can the ambiguous nature of Myxidium be resolved. Guidelines for descriptions of new species of Myxidium are provided.

Signal timing by the gray treefrog, Hyla chrysoscelis: Responses to conspecific and heterospecific advertisement calls

Breeding choruses often consist of multiple species sharing the same communication channel. Whether and how a signaler adjusts the timing of its signals, an often important predictor of receiver response, may therefore depend on the species identity of its neighbor. How males of the gray treefrog, Hyla chrysoscelis, adjusted advertisement call timing towards the calls of conspecifics and those of the closely related, syntopic species, H. versicolor, was examined. During interactions between calling males, calls were timed such that there was little signal overlap regardless of whether the neighbor was conspecific or heterospecific. In response to playbacks of conspecific and heterospecific advertisement calls, males generally avoided producing calls during either stimulus type, and instead produced them during the silent gaps between stimuli. There were, however, significant differences in the latencies of response to conspecific and heterospecific signals. Males produced calls with shorter latencies after the heterospecific calls, which resulted in their often rapid placement within the silent intervals between stimuli. In contrast, calls produced after conspecific stimuli almost always had a distinct gap after the stimulus ended. These results are discussed in light of hypotheses for the function of adjustments in the timing of acoustic sexual signals.

NOVEL FEATURES OF AN INDUCIBLE DEFENSE SYSTEM IN LARVAL TREE FROGS (HYLA CHRYSOSCELIS)

Organisms in aquatic ecosystems must often tolerate variable environmental conditions, including an uncertain risk of predation. Individuals that can maintain plastic defenses against predation will increase their survival when predators are present, but will not incur the costs of these defenses when the risk of predation is low and the defense is not induced. Larvae of the pond-breeding anuran Hyla chrysoscelis develop a conspicuous phenotype in the presence of predators consisting of a brightly colored tail and a deeper tail fin. In this study, I attempted to identify the source of the chemical signal that induces this defensive morphology in this species. I tested whether metabolites alone, originating from the prey but passing through the predator, were able to induce the same morphological response as the combination of alarm signals released directly by attacked conspecifics, and metabolites. I used morphometric and tail conspicuousness data to assess tadpole response to the perceived risk of predation by larval odonate predators (Anax junius). I also tested whether this inducing cue could be recognized across species by measuring the morphological response of H. chrysoscelis tadpoles exposed to cues emitted when tadpoles of a closely related genus (Pseudacris crucifer) were consumed. Tadpoles exhibited a clean graded response of both overall shape and tail morphology in response to all cues, corresponding to their relative reliability as indicators of a risk of predation. H. chrysoscelis tadpoles were also able to respond to cues emitted when tadpoles of a closely related genus were consumed by predators. These results illustrate that tadpoles of this species are able to respond to metabolites alone without alarm signals, and that interspecific chemical communication is a primary mechanism for predator avoidance in this inducible defense system.

Glycerol permeability in erythrocytes from an amphibian that accumulates glycerol in the cold

During cold acclimation, gray treefrogs Hyla chrysoscelis accumulate >50 mM glycerol in the extracellular fluid. That glycerol likely is synthesized in the liver and then delivered to other tissues, where it acts as an intracellular cryoprotectant and osmotic agent. We hypothesized that the permeability of cells to glycerol would be enhanced in cold acclimation. We tested this hypothesis on erythrocytes using two protocols, a lysis assay in which glycerol uptake induces osmotic lysis, and uptake of radio-labeled glycerol. We addressed four questions: a) What is the effect of temperature on glycerol permeability? (Permeability was markedly reduced in cells tested at lower temperatures.) b) What is the effect of cold acclimation on permeability properties? (We were unable to detect a change in permeability induced by cold-acclimation.) c) Is there geographic variation in these parameters? (Frogs from southern populations had similar properties as those from Ohio.) d) Are aquaporins involved in the uptake of glycerol? (Both lysis induced by glycerol uptake and influx of labeled glycerol were essentially abolished by mercurial compounds that inhibit aquaporins. We detected one prominently expressed aquaporin in erythrocytes, identified using primers designed from an ortholog likely to be in the glyceroporin family.) Thus, we suggest that treefrog red blood cells have glyceroporins that are constitutively expressed, and that allow intracellular accumulation of glycerol during cold acclimation.

Acoustic spectral preferences in two cryptic species of grey treefrogs: implications for mate choice and sensory mechanisms

Females are expected to use spectral properties of acoustic signals for mate choice because dominant frequency often provides reliable information about male size. The advertisement calls of grey treefrogs ( Hyla chrysoscelis and H. versicolor ) have two main frequency bands: the amplitude of the dominant, high-frequency band averages 7–10 dB greater than that of the low-frequency band. The frequencies of these peaks were negatively correlated with male body size in both species. I used two-speaker playbacks of synthetic calls to generate preference functions for both species based on simultaneous variation in the frequencies of the two bands and, for H. versicolor , on variation in single-component calls; frequencies of most of these stimuli fell within the range of the dominant, high-frequency band. When two-component sounds were used, preference functions were bimodal and broad, with peaks close to ( H. versicolor ) or slightly higher than ( H. chrysoscelis ) mean frequencies in conspecific calls. Because preferences were not strong, I predict that females exert only weak stabilizing or directional selection on male call frequencies. When single-component calls were used in tests of H. versicolor , the preference-function peak was shifted to a lower-than-average frequency within the high-frequency range. I hypothesize that such a frequency may better stimulate both of the inner ear organs, whose tuning roughly matches frequencies in the two bands in conspecific calls, than a single component of average or much lower-than-average frequency. Females of both species preferred calls with both spectral peaks to calls with a single, high-frequency peak, even when the low-frequency peak was attenuated by 24–30 dB. This result serves to emphasize that typically subdominant frequency components can have seemingly disproportionate effects on signal attractiveness.

ADVERTISEMENT-CALL PREFERENCES IN DIPLOID-TETRAPLOID TREEFROGS (HYLA CHRYSOSCELIS AND HYLA VERSICOLOR): IMPLICATIONS FOR MATE CHOICE AND THE EVOLUTION OF COMMUNICATION SYSTEMS

Signals used for mate choice and receiver preferences are often assumed to coevolve in a lock-step fashion. However, sender-receiver coevolution can also be nonparallel: even if species differences in signals are mainly quantitative, females of some closely related species have qualitatively different preferences and underlying mechanisms. Two-alternative playback experiments using synthetic calls that differed in fine-scale temporal properties identified the receiver criteria in females of the treefrog Hyla chrysoscelis for comparison with female criteria in a cryptic tetraploid species (H. versicolor); detailed preference functions were also generated for both species based on natural patterns of variation in temporal properties. The species were similar in three respects: (1) pulses of constant frequency were as attractive as the frequency-modulated pulses typical of conspecific calls; (2) changes in preferences with temperature paralleled temperature-dependent changes in male calls; and (3) preference functions were unimodal, with weakly defined peaks estimated at values slightly higher than the estimated means in conspecific calls. There were also species differences: (1) preference function slopes were steeper in H. chrysoscelis than in H. versicolor; (2) preferences were more intensity independent in H. chrysoscelis than in H. versicolor; (3) a synergistic effect of differences in pulse rate and shape on preference strength occurred in H. versicolor but not in H. chrysoscelis; and (4) a preference for the pulse shape typical of conspecific calls was expressed at the species-typical pulse duration in H. versicolor but not in H. chrysoscelis. However, females of H. chrysoscelis did express a preference based on pulse shape when tested with longer-than-average pulses, suggesting a hypothesis that could account for some examples of nonparallel coevolution. Namely, preferences can be hidden or revealed depending on the direction of quantitative change in a signal property relative to the threshold for resolving differences in that property. The results of the experiments reported here also predict patterns of mate choice within and between contemporary populations. First, intraspecific mate choice in both species is expected to be strongly influenced by variation in temperature among calling males. Second, simultaneous differences in pulse rate and pulse shape are required for effective species discrimination by females of H. versicolor but not by females of H. chrysoscelis. Third, there is greater potential for sexual selection within populations and for discrimination against calls produced by males in other geographically remote populations in H. chrysoscelis than in H. versicolor.

ADVERTISEMENT-CALL PREFERENCES IN DIPLOID-TETRAPLOID TREEFROGS (HYLA CHRYSOSCELIS AND HYLA VERSICOLOR): IMPLICATIONS FOR MATE CHOICE AND THE EVOLUTION OF COMMUNICATION SYSTEMS

Signals used for mate choice and receiver preferences are often assumed to coevolve in a lock-step fashion. However, sender-receiver coevolution can also be nonparallel: even if species differences in signals are mainly quantitative, females of some closely related species have qualitatively different preferences and underlying mechanisms. Two-alternative playback experiments using synthetic calls that differed in fine-scale temporal properties identified the receiver criteria in females of the treefrog Hyla chrysoscelis for comparison with female criteria in a cryptic tetraploid species (H. versicolor); detailed preference functions were also generated for both species based on natural patterns of variation in temporal properties. The species were similar in three respects: (1) pulses of constant frequency were as attractive as the frequency-modulated pulses typical of conspecific calls; (2) changes in preferences with temperature paralleled temperature-dependent changes in male calls; and (3) preference functions were unimodal, with weakly defined peaks estimated at values slightly higher than the estimated means in conspecific calls. There were also species differences: (1) preference function slopes were steeper in H. chrysoscelis than in H. versicolor; (2) preferences were more intensity independent in H. chrysoscelis than in H. versicolor; (3) a synergistic effect of differences in pulse rate and shape on preference strength occurred in H. versicolor but not in H. chrysoscelis; and (4) a preference for the pulse shape typical of conspecific calls was expressed at the species-typical pulse duration in H. versicolor but not in H. chrysoscelis. However, females of H. chrysoscelis did express a preference based on pulse shape when tested with longer-than-average pulses, suggesting a hypothesis that could account for some examples of nonparallel coevolution. Namely, preferences can be hidden or revealed depending on the direction of quantitative change in a signal property relative to the threshold for resolving differences in that property. The results of the experiments reported here also predict patterns of mate choice within and between contemporary populations. First, intraspecific mate choice in both species is expected to be strongly influenced by variation in temperature among calling males. Second, simultaneous differences in pulse rate and pulse shape are required for effective species discrimination by females of H. versicolor but not by females of H. chrysoscelis. Third, there is greater potential for sexual selection within populations and for discrimination against calls produced by males in other geographically remote populations in H. chrysoscelis than in H. versicolor.

FUNGAL PATHOGEN CAUSES COMPETITIVE AND DEVELOPMENTAL STRESS IN LARVAL AMPHIBIAN COMMUNITIES

Ecologists increasingly recognize pathogens as playing significant roles in community dynamics, yet few experimental studies have documented patterns of disease impacts on natural systems. We studied the effects of a pathogenic fungus (Batrachochytrium dendrobatidis) on community interactions between two sympatric North American anurans: Fowler's toad, Bufo fowleri, and the gray treefrog, Hyla chrysoscelis. Recent studies have identified chytridiomycosis as an emerging infectious disease, whose widespread occurrence poses a significant risk for amphibian populations. We manipulated the presence of B. dendrobatidis in replicated experimental tanks and examined if exposure to this fungus during development could influence recruitment and competitive interactions between larval Bufo and Hyla. Tanks were followed throughout larval development, and we recorded survival, time to metamorphosis, and body mass at metamorphosis. We also tested the effects of competitive and pathogen-mediated stress on developmental stability by measuring fluctuating asymmetry (FA) of surviving metamorphs. B. dendrobatidis had no significant effect on larval survival, but the pathogen reduced metamorphic body mass and increased larval-period length. B. dendrobatidis had different effects on larval growth depending on the community structure; in the presence of the pathogen, both Bufo and Hyla metamorphosed at smaller body masses when reared together compared to when reared separately. Bufo also had strong negative effects on Hyla development, but only in the presence of B. dendrobatidis. FA of hind-limb length was significantly higher for metamorphs from pathogen tanks, but was not associated with density or competitive environment. Our results suggest that chytridiomycosis may impact Bufo and Hyla directly by reducing life-history performance and increasing developmental instability, and indirectly by inducing interspecific competitive effects in mixed-species environments.

Chytridiomycosis impacts predator-prey interactions in larval amphibian communities

Despite ecologists increasingly recognizing pathogens as playing significant roles in community dynamics, few experimental studies have quantified patterns of disease impacts on natural systems. Amphibians are experiencing population declines, and a fungal pathogen ( Batrachochytrium dendrobatidis; Chytridiomycota) is a suspected causal agent in many declines. We studied the effects of a pathogenic fungus on community interactions between the gray treefrog, Hyla chrysoscelis, and eastern newts, Notophthalmus viridescens. Recent studies have characterized chytridiomycosis as an emerging infectious disease, whose suspected rapid range expansion and widespread occurrence pose a significant risk for amphibian populations worldwide. We reared larvae in outdoor polyethylene experimental tanks and tested the effects of initial larval density, predator presence, and fungal exposure on Hyla recruitment and predator-prey interactions between Hyla and Notophthalmus. Newts reduced treefrog survival, and high intraspecific density decreased metamorphic body mass independent of B. dendrobatidis. The presence of fungi reduced treefrog body mass at metamorphosis by 34%, but had no significant main effect on survival or larval period length. B. dendrobatidis differentially affected larval development in the presence of predators; Hyla developed slower when reared with the pathogen, but only when newts were present. This significant predator-by-pathogen interaction suggests that the impact of chytridiomycosis on larval amphibians may be exacerbated in complex communities. Our data suggest that B. dendrobatidis effects on host life history may be complex and indirect. Direct measurements of the community-level effects of pathogens offer an important opportunity to understand a significant threat to global biodiversity-declining amphibian populations.

Interactive Effects of a Heavy Metal and Chytridiomycosis on Gray Treefrog Larvae (Hyla chrysoscelis)

Abstract We studied the effects of a pathogenic fungus (Batrachochytrium dendrobatidis; Chytridiomycota) on larval fitness in the Gray Treefrog (Hyla chrysoscelis). Recent studies have identified chytridiomycosis as an emerging infectious disease that poses a significant risk for amphibian populations worldwide. We also tested the effects of the heavy metal copper, a common environmental contaminant in aquatic environments, on larval fitness. We reared larvae in laboratory containers and tested whether exposure to copper and B. dendrobatidis affected Hyla survival, growth, and development. Neither exposure to B. dendrobatidis nor copper significantly affected survival to metamorphosis. Metamorphic body mass was significantly reduced in the presence of B. dendrobatidis, but copper did not significantly affect larval growth. Both copper and B. dendrobatidis exposure significantly increased larval period length, but copper differentially affected development in the presence of B. dendrobatidis. Hyla develope...

Functional equivalence of non‐lethal effects: generalized fish avoidance determines distribution of gray treefrog, Hyla chrysoscelis, larvae

How patterns of prey abundance are generated determines how predation influences population and community level dynamics. We investigated how a natural population of ovipositing treefrogs, Hyla chrysoscelis, partitioned their eggs amongst experimental ponds differing in the non‐lethal presence of five fish predators, each representing a distinct family. Four fish predators were functionally equivalent in terms of the behavioral response they induced in H. chrysoscelis females and hence the distribution of larval H. chrysoscelis. Mean number of H. chrysoscelis eggs deposited was significantly decreased by the mere presence of these predators relative to controls, with three species eliciting a complete avoidance (e.g. no eggs deposited). One fish predator, Aphredoderus sayanus, was statistically indistinguishable from the control treatment. These data mimic patterns of species distribution observed in nature in response to the presence of fish, but suggest an alternative mechanism for generating patterns of prey abundance amongst habitats differing in their predator composition. Furthermore, our results expand the importance of predator induced non‐lethal effects as a process that could dramatically affect population and community level dynamics.

Observations on the life history and descriptions of coccidia (Apicomplexa) from the western chorus frog, Pseudacris triseriata triseriata, from eastern Nebraska.

Two hundred and twenty-four anurans of 6 species (47 adults and 16 tadpoles of Rana blairi, 35 R. catesbeiana, 31 Hyla chrysoscelis, 30 adults and 46 tadpoles of Pseudacris triseriata triseriata, 11 Bufo woodhousii, and 8 Acris crepitans) from Pawnee Lake, Lancaster County, Nebraska, were surveyed for coccidian parasites during March 2001 to May 2002. Of these, 23 of 30 (77%) adults and 4 of 46 (9%) tadpoles of P. t. triseriata shed oocysts of Isospora cogginsi n. sp. Oocysts of I. cogginsi were ovoid, 19.3 x 15.1 (18-23 x 11-20) microm, with a thin, smooth, colorless, single-layered wall, with no micropyle or oocyst residuum. Sporocysts were ovoid, 13.3 x 9.9 (11-15 x 9-13) microm, with a thin, colorless, smooth wall, and Stieda body absent. Sporocyst residuum was present, 5.5 x 5.3 (4-7 x 4-7) microm, consisting of numerous granules. Histological examination of frogs and tadpoles infected with the new species revealed endogenous stages including mature meronts, developing microgamonts, mature microgametes, mature macrogamonts, and young unsporulated oocysts located in the cytoplasm of the epithelial cells of the small intestine. Concurrently, 2 adult P. t. triseriata shed oocysts of Eimeria streckeri. Oocysts of E. streckeri were spherical, 15.7 x 15.4 (14-17 x 14-19) microm, with a thin, smooth, single-layered, colorless wall with an oocyst residuum composed of numerous granules surrounding a large vacuolated area, with a previously undescribed globularlike body present within the vacuole, and no micropyle. Sporocysts were ovoid, 9.1 x 6.1 (7-10 x 5-7) microm, with a thin, colorless, smooth wall with a Stieda body and sporocyst residuum. Our results are the first to document infection of adult and tadpole stages of frogs of the same species with the same species of coccidian, indicating that adult frogs may contaminate breeding ponds with oocysts during their breeding season and infect tadpoles directly by the ingestion of sporulated oocysts.

Season and testosterone affect contractile properties of fast calling muscles in the gray tree frog Hyla chrysoscelis.

In anurans, circulating levels of androgens influence certain secondary sexual characteristics that are expressed only during the breeding season. We studied the contractile properties of external oblique muscles (used to power sound production) in a species of North American gray tree frog, Hyla chrysoscelis, during the breeding season and also in testosterone-treated captive males and females after the breeding season. Compared with the muscles of breeding-season males, the trunk muscles of postbreeding-season males have 50% less mass, 60% longer twitches, and 40% slower shortening velocities. Testosterone levels similar to those found in breeding-season male hylid frogs restore the contractile speed and mass of male trunk muscles and also convert the small slow trunk muscles of females into larger fast-contracting muscles. We conclude that androgens likely play a key role in altering the contractile properties of these muscles in males during the annual cycle, allowing them to operate in the breeding season at the frequencies required to produce the characteristic rapidly pulsed calls of this species. Females as well as nonbreeding-season males do not produce advertising calls, and therefore the slower muscles found in these animals may allow more economic operation of these muscles. The effects of testosterone on female trunk muscles indicate the potential of this hormone in contributing to the sexual dimorphism in size and contractile properties of these muscles, but this dimorphism is likely due to the interaction of more than one hormone.

Nonparallel coevolution of sender and receiver in the acoustic communication system of treefrogs

Advertisement calls of closely related species often differ in quantitative features such as the repetition rate of signal units. These differences are important in species recognition. Current models of signal/receiver co-evolution predict two possible patterns in the evolution of the mechanism used by receivers to recognize the call. (1) Classical sexual selection models (Fisher-Process, good-genes/indirect benefits, direct benefits models) predict that close relatives use qualitatively similar signal recognition mechanisms tuned to different values of a call parameter. (2) Receiver bias models (hidden preference, pre-existing bias models) predict that if different signal recognition mechanisms are used by sibling species, evidence of an ancestral mechanism will persist in the derived species, and evidence of a pre-existing bias will be detectable in the ancestral species. We describe qualitatively different call recognition mechanisms in sibling species of treefrogs. Whereas Hyla chrysoscelis uses pulse rate to recognize male calls, H. versicolor uses absolute measurements of pulse duration and interval duration. We found no evidence of either hidden preferences or pre-existing biases. The results are compared with similar data from katydids (Tettigonia sp.). The data are discussed with regard to current models of signal/receiver co-evolution.

Developmental Effects of Ambient UV-B Light and Landfill Leachate in Rana blairi and Hyla chrysoscelis

This study assessed the effects of ambient UV light on the development of two native species of anurans, Rana blairi and Hyla chrysoscelis, during their normal breeding season in Oklahoma. Additionally, the effects of ambient UV light and water contaminated with landfill leachate in Rana blairi were examined. Embryos were collected from the field and distributed equally among replicates of four filter treatments of ambient UV light in experimental tubs filled with either FETAX solution or landfill leachate diluted to 25, 10, and 5%concentrations. Three endpoints (mortality, teratogenesis, and growth) were compared between filter treatments. By itself, UV-B caused no significant effects. Leachate at 10 and 25% concentrations caused 100% mortality across all filter treatments. There was a significant interaction between filter treatment and water toxicity at leachate concentrations of 5% for both malformation and growth. Increased UV-B exposure decreased the malformation rate and increased growth in the leachate treatments.

Antibiotic resistance in coagulase-negative staphylococci isolated from Cope's gray treefrogs (Hyla chrysoscelis).

Organisms belonging to the genus Staphylococcus were isolated on mannitol salt agar from the feces of wild caught Cope's gray treefrogs (Hyla chrysoscelis) from east-central Kansas. All 222 presumptive isolates were confirmed as coagulase-negative staphylococci with Staphylococcus sciuri and Staphylococcus xylosus being most prevalent. Antibiotic susceptibility patterns to five different antibiotics were determined and the results indicated 99% of all isolates were resistant to penicillin G and 59% of the isolates were resistant to oxacillin, a clinical substitute for methicillin. Due to the significance of methicillin resistance in the genus Staphylococcus, 10 randomly chosen oxacillin resistant organisms were analyzed for the presence of the mecA gene, which is known to code for methicillin resistance. The gene was detected in four of the 10 organisms examined. These data indicate that gray treefrogs are harboring inordinately large numbers of methicillin resistant staphylococci as part of their normal flora and that the mechanism of methicillin resistance may be independent of mecA.

Antibiotic resistance in coagulase-negative staphylococci isolated from Cope’s gray treefrogs ( Hyla chrysoscelis)

Organisms belonging to the genus Staphylococcus were isolated on mannitol salt agar from the feces of wild caught Cope’s gray treefrogs ( Hyla chrysoscelis) from east-central Kansas. All 222 presumptive isolates were confirmed as coagulase-negative staphylococci with Staphylococcus sciuri and Staphylococcus xylosus being most prevalent. Antibiotic susceptibility patterns to five different antibiotics were determined and the results indicated 99% of all isolates were resistant to penicillin G and 59% of the isolates were resistant to oxacillin, a clinical substitute for methicillin. Due to the significance of methicillin resistance in the genus Staphylococcus, 10 randomly chosen oxacillin resistant organisms were analyzed for the presence of the mecA gene, which is known to code for methicillin resistance. The gene was detected in four of the 10 organisms examined. These data indicate that gray treefrogs are harboring inordinately large numbers of methicillin resistant staphylococci as part of their normal flora and that the mechanism of methicillin resistance may be independent of mecA.