Rana Sphenocephala Research Articles

Reproductive Plasticity in the Nematode Gyrinicola batrachiensis: Does an Intermediate Reproductive Strategy Exist in Sexually Reproducing, Didelphic Pinworms?

Phenotypic plasticity is a process in which multiple phenotypes arise from 1 genotype because of environmental selection pressures. Gyrinicola batrachiensis has a heterogeneous reproductive strategy such that females reproduce either via parthogenesis with thick-shelled eggs in a single uterus or sexual reproduction with thick- and thin-shelled eggs in separate uterine horns. No evidence exists that strains of G. batrachiensis are able to switch between parthenogenetic and sexual reproduction. Thin-shelled eggs are autoinfective, and thick-shelled eggs act as transmission agents once shed into the aquatic environment. Our primary goal was to determine whether dioecious, didelphic pinworms that infect Rana sphenocephala, a slow-developing tadpole, and Osteopilus septentrionalis, a quick-developing tadpole, display reproductive plasticity with concern to thick- and thin-egg development. We performed experimental cross-infections in aquatic mesocosms to determine if dioecious, didelphic worms vary (based on tadpole host) in their ability to produce thin-shelled eggs: O. septentrionalis (hylid) egg masses were exposed to infected R. sphenocephala (ranid) tadpoles, ranid egg masses to infected hylid tadpoles, and a fully crossed infection that exposed ranid and hylid egg masses to infected tadpoles of both anuran families. Results indicated that worms reproduced via didelphic haplodiploidy in experimental ranid and hylid hosts, but that worms from hylids produced only thick-shelled eggs, which supports an intermediate reproductive strategy in O. septentrionalis. There was a significant difference in the mean intensities of ranid and hylid hosts, supporting our assertion that females infecting ranids are capable of producing autoinfective, thin-shelled eggs, and females infecting hylids do not produce such thin-shelled, autoinfective eggs because of the host microenvironment.

Habitat predictors of genetic diversity for two sympatric wetland-breeding amphibian species.

Population genetic diversity is widely accepted as important to the conservation and management of wildlife. However, habitat features may differentially affect evolutionary processes that facilitate population genetic diversity among sympatric species. We measured genetic diversity for two pond‐breeding amphibian species (Dwarf salamanders, Eurycea quadridigitata; and Southern Leopard frogs, Lithobates sphenocephalus) to understand how habitat characteristics and spatial scale affect genetic diversity across a landscape. Samples were collected from wetlands on a longleaf pine reserve in Georgia. We genotyped microsatellite loci for both species to assess population structures and determine which habitat features were most closely associated with observed heterozygosity and rarefied allelic richness. Both species exhibited significant population genetic structure; however, structure in Southern Leopard frogs was driven primarily by one outlier site. Dwarf salamander allelic richness was greater at sites with less surrounding road area within 0.5 km and more wetland area within 1.0 and 2.5 km, and heterozygosity was greater at sites with more wetland area within 0.5 km. In contrast, neither measure of Southern Leopard frog genetic diversity was associated with any habitat features at any scale we evaluated. Genetic diversity in the Dwarf salamander was strongly associated with land cover variables up to 2.5 km away from breeding wetlands, and/or results suggest that minimizing roads in wetland buffers may be beneficial to the maintenance of population genetic diversity. This study suggests that patterns of genetic differentiation and genetic diversity have associations with different habitat features across different spatial scales for two syntopic pond‐breeding amphibian species.

Reproduction and growth of the Southern Leopard Frog, Lithobates sphenocephalus utricularius (Harlan, 1825), in Virginia: implications for seasonal shifts in response to global climate change

An examination of 750 museum specimens of the Southern Leopard Frog (Lithobates sphenocephalus) collected during 1938‐1989 from eastern Virginia (USA) provided comparative life‐history data from the northeastern portion of this species geographic range. Individuals were collected in all months except December. Testis size was largest and incidence of gravid females was highest during fall and spring. In both sexes, fat storage was lowest during late‐winter‐spring, which is indicative of increased activity and commencement of breeding. Incidence of food in stomachs was lowest in late winter and relatively high thereafter, especially in males. Geographic trends in five lifehistory traits were corroborated for the Southern Leopard Frog in this study, including breeding season, egg size, mean adult body size, sexual size dimorphism, and larval metamorphosis season. In response to hotter summers and milder winters, as predicted to occur with climate change, the reproductive characteristics for this species in Virginia will likely shift to resemble contemporary reproductive patterns of southern populations.

Detritus Quality Produces Species-Specific Tadpole Growth and Survivorship Responses in Experimental Wetlands

Abstract Although many non-native species negatively influence amphibian populations, non-native aquatic vegetation has been documented to have positive, negative, and neutral effects on anuran larvae. To evaluate the response of anurans to non-native plants, we exposed two frog species, Gray Treefrog (Hyla versicolor-chrysoscelis) and Southern Leopard Frog (Lithobates sphenocephalus), to detritus from either native hardwood trees, non-native purple loosestrife (Lythrum salicaria), or a mixture of both. Experiments were conducted in artificial ponds, and we recorded the survival, growth, and metamorphic size of larvae. Gray Treefrog survival was highest in tanks with native leaf litter. Developmental time did not differ among treatments, but tadpoles in tanks with purple loosestrife were significantly larger than those in tanks with native leaf litter. Southern Leopard Frog survival was lowest in the mixed vegetation treatment. As with Gray Treefrogs, developmental time was not influenced by treatment, bu...

Weather, hydroregime, and breeding effort influence juvenile recruitment of anurans: implications for climate change

AbstractAmphibians that primarily breed in ephemeral wetlands are especially vulnerable to climate change because they rely on rainfall or temperature to initiate breeding and create suitable hydroregimes (water duration, timing, frequency, depth) for reproductive success. Hydroregime effects on reproductive success are likely to differ among species because of differences in reproductive strategies: the length and timing of breeding period, rate of larval development, and timing of metamorphosis. We applied an information‐theoretic approach to 22 consecutive years of continuous amphibian trapping data at eight ephemeral wetlands to test hypotheses regarding environmental (hydroregime, weather) and biological (adult breeding effort) factors affecting juvenile recruitment (JR) by six focal species representing four reproductive strategies. We hypothesized that (1) JR by species with similar reproductive strategies would be influenced by similar variables; (2) JR would be higher for all species when models encompassed the maximum time span of potential tadpole occurrence and development; and (3) JR rates within individual wetlands and breeding cycles would correlate most closely between species with similar breeding strategies. The best model for all focal species (except Scaphiopus holbrookii) encompassed the maximum time span and indicated that ≥1 hydroregime variable, total precipitation, or both were important drivers of reproductive success; average air temperature was not. Continuous hydroperiod through peak juvenile emigration was an important predictor of JR for species with prolonged breeding periods, slow larval development, and a “fixed” late spring start date for juvenile emigration (regardless of when oviposition occurred, or cohort age; Lithobates capito, Lithobates sphenocephalus), but not for species with rapid larval development and continual emigration as cohorts complete metamorphosis (Anaxyrus terrestris, Anaxyrus quercicus, Gastrophryne carolinensis, S. holbrookii). Total rainfall was positively associated with recruitment for most species; depth characteristics affected species differently. Annual JR was positively correlated among species with similar reproductive strategies. Our results indicate that weather and hydroregime characteristics interact with reproductive strategies that differ among amphibian species and influence reproductive plasticity, opportunity, and success. Effects of altered weather patterns associated with climate change on amphibian reproductive success may correspond more closely among species having similar reproductive strategies, with critical implications for population trends and assemblages.

Larval Anuran Stable Isotope Signatures and Stoichiometry Across Multiple Geographically Isolated Wetlands in the Southeastern United States

Abstract Animals live in complex environments that vary spatially and temporally. This heterogeneity strongly influences the availability and quality of food resources and has strong impacts on growth and survival of consumers. Geographically isolated wetlands provide an interesting system to study trophic relationships because they vary spatially and temporally in hydrology and vegetation. Larval anurans play an important role in these wetland systems because they are often the most abundant consumers. Yet, little is known about larval anuran diet. Here we assessed the diet of 3 larval anurans (Acris gryllus [Southern Cricket Frog], Hyla gratiosa [Barking Treefrog], and Lithobates sphenocephalus [Southern Leopard Frog]), across 2 isolated wetland types (marsh and cypress savanna) using a stable isotope mixing model, stable isotope analysis in R (SIAR). Furthermore, we assessed variation in basal resource and anuran tissue stoichiometry (C:N). Our analyses suggested that larvae of these 3 species primaril...

Stable isotopes reveal an invasive plant contributes more than native sources to anuran larvae diets

ABSTRACTForaging theory suggests organisms increase their fitness through dietary and energetic choices. In nature, organisms choose to consume balanced optimal diets but as exotic plants invade ecosystems, new foraging options become available. Often these plants have different traits and can negatively affect fitness of foragers by lowering survival or growth due to toxicity. Wetland habitats are highly susceptible to plant invasions which can have negative effects on nutrient cycling. The purpose of this study was to examine whether invasion of purple loosestrife (Lythrum salicaria) alters tadpole foraging preference thus potentially impacting their survivorship and fitness. We designed a common garden experiment and utilized stable isotopic signatures to investigate the contribution of purple loosestrife and native hardwood detritus to larval wood frog (Rana sylvatica) and southern leopard frog (Rana sphenocephala) diets. Tadpoles derived a higher percentage of resources from purple loosestrife compared to native hardwood detritus when presented with both options, despite its high concentration of toxic secondary compounds. It is unknown if tadpoles can detect competing fitness signals that may be associated with higher nutrient and toxicity levels in purple loosestrife. Discovering the presence or absence of such signals will promote a greater understanding of selective foraging in changing environments.

Joint effects of resources and amphibians on pond ecosystems.

Primary production can be controlled through bottom-up (e.g., resources) or top-down (e.g., predators) constraints. Two key bottom-up resources in small aquatic systems are light and nutrients, and forest canopy cover heavily influences these factors, whereas amphibian and invertebrate colonizers exert top-down pressure as grazers and predators. We designed our experiment to specifically manipulate two different top-down and bottom-up factors. We manipulated resources by altering light (low/high) and nutrient (low/high) availability; omnivores with the presence/absence of southern leopard frog tadpoles (Lithobates sphenocephalus); and predators with the presence/absence of spotted salamander larvae (Ambystoma maculatum) in a full-factorial experiment conducted over 14weeks. We observed that both bottom-up and top-down effects were important in predicting lower trophic level biomass. We found a significant top-down effect of salamanders on Daphnia, but tadpoles had the strongest overall effect on the food web, influencing phytoplankton (+), periphyton (-), and chironomids (-). None of our models were good predictors of phytoplankton biomass, but both shading and nutrient availability relatively equally boosted periphyton biomass. We also found large temporal differences in food-web dynamics. Our results underscore the need for more information into how ecosystem functioning could be altered by land use, amphibian extirpation, and climate change.

Host use and seasonality of Culex (Melanoconion) iolambdis (Diptera: Culicidae) from eastern Florida, USA

Culex (Melanoconion) iolambdis (Dyar, 1918) is a mosquito (Diptera: Culicidae) species found throughout much of tropical America, including southern Florida. Relatively few reports are available regarding the ecology of Cx. iolambdis, despite its widespread distribution and putative involvement in transmission of Venezuelan equine encephalitis virus. To quantify habitat and host utilization, adults of Cx. iolambdis were sampled from resting shelters at a field site in Vero Beach, Florida, over a 12-month period. Culex iolambdis (1109 males, 3072 females) constituted more than half (56.76%) of all mosquitoes sampled (24 species) and was active year-round. Unfed females and gravid females of Cx. iolambdis were significantly more abundant in mangrove habitat, while males and blood-fed females were not. PCR-based bloodmeal analysis of 305 females revealed that Cx. iolambdis has very wide host breadth, feeding on birds (37.0% overall), reptiles (26.6%), amphibians (23.3%) and mammals (13.1%). Green heron (Butorides virescens), Southern leopard frog (Lithobates sphenocephala) and American alligator (Alligator mississippiensis) were the most commonly fed upon hosts. Bloodmeals from different host classes varied significantly with season, suggesting that Cx. iolambdis may play a role in the amplification and epidemic transmission of zoonotic arboviruses affecting human health.

Integrating copper toxicity and climate change to understand extinction risk to two species of pond-breeding anurans.

Chemical contamination is often suggested as an important contributing factor to amphibian population declines, but direct links are rarely reported. Population modeling provides a quantitative method to integrate toxicity data with demographic data to understand the long-term effects of contaminants on population persistence. In this study we use laboratory-derived embryo and larval toxicity data for two anuran species to investigate the potential for toxicity to contribute to population declines. We use the southern toad (Anaxyrus terrestris) and the southern leopard frog (Lithobates sphenocephalus) as model species to investigate copper (Cu) toxicity. We use matrix models to project populations through time and quantify extinction risk (the probability of quasi-extinction in 35yr). Life-history parameters for toads and frogs were obtained from previously published literature or unpublished data from a long-term (>35yr) data set. In addition to Cu toxicity, we investigate the role of climate change on amphibian populations by including the probability of early pond drying that results in catastrophic reproductive failure (CRF, i.e., complete mortality of all larval individuals). Our models indicate that CRF is an important parameter for both species as both were unable to persist when CRF probability was >50% for toads or 40% for frogs. Copper toxicity alone did not result in significant effects on extinction risk unless toxicity was very high (>50% reduction in survival parameters). For toads, Cu toxicity and high probability of CRF both resulted in high extinction risk but no synergistic (or greater than additive) effects between the two stressors occurred. For leopard frogs, in the absence of CRF survival was high even under Cu toxicity, but with CRF Cu toxicity increased extinction risk. Our analyses highlight the importance of considering multiple stressors as well as species differences in response to those stressors. Our models were consistently most sensitive to juvenile and adult survival, further suggesting the importance of terrestrial stages to population persistence. Future models will incorporate multiple wetlands with different combinations of stressors to understand if our results for a single wetland result in a population sink within the landscape.

The Effects of Crayfish Predation and Vegetation Cover on Tadpole Growth, Survival, and Nonlethal Injury

Abstract Predator–prey interactions play an important role in structuring larval anuran communities in ephemeral wetlands. The type of interaction often depends on the predator species and the complexity of the aquatic habitat. We experimentally evaluated the effects of Panhandle Crayfish (Procambarus evermanni) predation on larval Southern Leopard Frogs (Lithobates sphenocephalus) and larval Ornate Chorus Frogs (Pseudacris ornata). We performed separate experiments for each anuran species and used multiple vegetation treatments to examine whether vegetation could provide refugia from crayfish predation. Our results indicate that crayfish are effective predators of anuran larvae regardless of the amount of vegetation present. Encounters between tadpoles and crayfish often resulted in nonlethal tail injury for tadpoles, suggesting that crayfish predation is prominent in ephemeral wetland communities. Leopard frog tadpoles in predator treatments also grew larger than their counterparts in nonpredator treatm...

Specialist and generalist amphibians respond to wetland restoration treatments

ABSTRACTAvailable habitat within a landscape is often more limited for specialist species than for generalists. Therefore, specialists are potentially more vulnerable to extinction. The goal of our study was to better understand the ephemeral wetland habitat associations of specialist and generalist amphibians within a longleaf pine landscape in the southeastern United States. We also sought to determine specialist (e.g., oak toad [Anaxyrus quercicus], Maybee's salamander [Ambystoma maybeei], pine woods treefrog [Hyla femoralis], carpenter frog [Lithobates virgatipes]) and generalist (e.g., spotted salamander [Ambystoma maculatum], Cope's gray treefrog [Hyla chrysoscelis], southern leopard frog [Lithobates sphenocephalus]) species’ responses to specific habitat restoration treatments. From 2005–2010, we examined the relationship between aquatic specialist and generalist amphibian species occupancy and wetland vegetation structure. We measured vegetation and amphibian responses to prescribed fire and vegetation mulching (a fire surrogate), plus a combination of mulching and burning. Untreated controls were wetlands that had not burned for 4–15 years. We combined data from this study and a previous study to elucidate patterns in amphibian assemblages in relation to fire history. Specialist relative species richness was highest when canopy openness was high and leaf litter depth was low, conditions best achieved by mulching plus burning. Some specialist species were not detected in wetlands with >8 years since fire, and some generalist species were not detected in wetlands with <2 years since fire, indicating that as vegetation structure changes with time since fire, there is a corresponding shift in the amphibian assemblage. Important patterns in species distributions can be overlooked if relationships to environment and responses to habitat change are too generalized and do not account for shifts in community composition. For conservation of longleaf pine specialist species, we recommend that uplands continue to be prescribed‐burned on a 1–3‐year return interval. Burning should occur during the early growing season when possible to maximize the probability that wetland basins burn. In cases where species of high conservation value are at imminent risk of extinction, we recommend a combination of mulching and burning to most quickly restore suitable habitat structure. © 2016 The Wildlife Society.

Herpetofaunal Diversity and Seasonality from a Remnant Coastal Chenier Forest in Southwestern Louisiana

Cheniers are ancient beach ridges in southwestern Louisiana that are often characterized by coastal forest surrounded by marshland. Coastal chenier forests (CCFs) are considered an imperiled habitat in Louisiana because many forest remnants are considerably impacted due to human activities and recent hurricanes. Because little is known about the herpetofaunal community of CCFs, I initiated a seasonal herpetofaunal diversity and abundance study on a privately-owned, remnant CCF in eastern Cameron Parish, Louisiana. Utilizing coverboards and drift fence arrays with pitfall and funnel traps, I documented 12 species (4 anuran, 4 snake, 3 lizard, and 1 turtle) comprising CCF obligate and facultative species, as well as one marsh transient species. Species-accumulation curves indicate the sample was representative of the small herpetofaunal community. Three amphibian (Incilius nebulifer [Gulf Coast Toad], Lithobates sphenocephalus utricularius [Coastal Plains Leopard Frog], and Gastrophryne carolinensis [Eastern Narrow-mouthed Toad]) and 2 reptile (Scincella lateralis [Little Brown Skink] and Thamnophis p. proximus [Orangestriped Ribbonsnake]) species comprised 94% of the captures. Diversity was highest during the spring, with 3 months (March–May) of sampling detecting 92% of the total diversity observed. Sampling during single months only yielded 42–75% of the diversity. Amphibian abundance varied by month (highest June to September) and with the presence of rain, whereas reptile abundance only varied by month (highest in March). Funnel traps were more effective and quantified diversity better than pitfall traps or coverboards. The herpetofaunal diversity at the site was low and comprised of mostly generalist species; regional specimen records also exhibit a modest herpetofaunal community. This data will provide baseline information to determine the impacts of future hurricanes on the herpetofaunal community, analyze recolonization dynamics following hurricanes, and make comparisons to other CCF remnants in the region. I also provide recommendations for improving herpetofauna sampling methodology in coastal settings.

Importance of forestry practices relative to microhabitat and microclimate changes for juvenile pond-breeding amphibians

Balancing the goals of forest management and species conservation is a major challenge. Forestry practices could be refined with greater understanding of the importance of large-scale forestry practices versus smaller-scale microhabitat and microclimate variables in driving demographic vital rates for species of conservation concern. We examined the relative importance of forestry practices, microhabitat, and microclimate on juvenile anuran survival and growth. To do so, we examined three different species: wood frogs (Lithobates sylvaticus), American toads (Anaxyrus americanus), and southern leopard frogs (Lithobates sphenocephalus), in three different years using terrestrial enclosures. Terrestrial enclosures were placed in forestry treatment plots with unharvested forest, partial cut forest, early successional forest (ESF; i.e. 4–6year old clearcut) with downed wood removed, and ESF with downed wood retained in central Missouri, USA. We ranked models using an information-theoretic approach to determine whether forestry treatment, microhabitat (logs, canopy cover, leaf litter depth), or microclimate (temperature and soil moisture) best predicted juvenile survival and growth. We found that microhabitat and microclimate, but not forestry practices, were important for survival and growth. However, small sample sizes may have limited our ability to detect forestry treatment effects. Most associations with growth and survival involved microclimate variables. Effects of microhabitat showed positive associations of survival with canopy cover and downed wood and of growth with leaf litter depth. All effects varied by species/year and season, as is common for studies on the effects of forestry practices on amphibians, indicating that it would be useful to maintain a variety of different microhabitats and microclimates to support a diverse anuran community. Because juvenile survival is a population-regulating parameter for many amphibians, it may be prudent to focus on creating favorable microhabitats and microclimates within areas under active forest management. However, it would be useful to repeat this type of study in different eco-regions with different species to determine the generalizability of these results.

Evaluation of a waistband for attaching external radiotransmitters to anurans

ABSTRACTRadiotelemetry provides fine‐scale temporal and spatial information about an individual's movements and habitat use; however, its use for monitoring amphibians has been restricted by transmitter mass and lack of suitable attachment techniques. We describe a novel waistband for attaching external radiotransmitters to anurans and evaluate the percentages of resulting abrasions, lacerations, and shed transmitters. We used radiotelemetry to monitor movements and habitat use of wood frogs (Lithobates sylvaticus) in 2006 and 2011–2013 in Maine, USA; American toads (Anaxyrus americanus) in 2012 in North Carolina, USA; and, wood frogs, southern leopard frogs (L. sphenocephalus), and green frogs (L. clamitans) in 2012 in South Carolina, USA. We monitored 172 anurans for 1–365 days (56.4 ± 59.4) in a single year and 1–691 days (60.5 ± 94.1) across years. Our waistband resulted in an injury percentage comparable to 7 alternative anuran waistband attachment techniques; however, 12.5% fewer anurans shed their waistband when attached with our technique. Waistband retention facilitates longer monitoring periods and, thus, provides a greater quantity of data per radiotagged individual. © 2015 The Wildlife Society.

The deal with diel: Temperature fluctuations, asymmetrical warming, and ubiquitous metals contaminants

Climate projections over the next century include disproportionately warmer nighttime temperatures (“asymmetrical warming”). Cool nighttime temperatures lower metabolic rates of aquatic ectotherms. In contaminated waters, areas with cool nights may provide thermal refugia from high rates of daytime contaminant uptake. We exposed Cope's gray tree frogs (Hyla chrysoscelis), southern leopard frogs (Lithobates sphenocephalus), and spotted salamanders (Ambystoma maculatum) to five concentrations of a mixture of cadmium, copper, and lead under three to four temperature regimes, representing asymmetrical warming. At concentrations with intermediate toxicosis at test termination (96 h), temperature effects on acute toxicity or escape distance were evident in all study species. Asymmetrical warming (day:night, 22:20 °C; 22:22 °C) doubled or tripled mortality relative to overall cooler temperatures (20:20 °C) or cool nights (22:18 °C). Escape distances were 40–70% shorter under asymmetrical warming. Results suggest potentially grave ecological impacts from unexpected toxicosis under climate change.

Herpetofaunal community change in multiple habitats after fifteen years in a southwest Florida preserve, USA.

Herpetofaunal declines have been documented globally, and southern Florida, USA, is an especially vulnerable region because of high impacts from hydrological perturbations and nonindigenous species. To assess the extent of recent change in herpetofauna community composition, we established a baseline inventory during 1995-97 at a managed preserve in a habitat rich area of southwest Florida, and repeated our sampling methods fifteen years later (2010-11). Nine drift fence arrays were placed in four habitat types: mesic flatwood, mesic hammock, depression marsh, and wet prairie. Trapping occurred daily for one week during 7-8 sampling runs in each period (57 and 49 total sampling days, respectively). Species richness was maintained in mesic hammock habitats but varied in the others. Catch rates of several native species (Anaxyrus terrestris, Lithobates grylio, Anolis carolinensis, Nerodia fasciata) declined significantly. Other native species (Lithobates sphenocephalus, Siren lacertian, and Notophthalmus viridescens piaropicola) that were abundant in 1995-97 declined by greater than 50%. Catch rate of only two species (the nonindigenous Anolis sagrei and the native Diadophis punctatus) increased significantly. Hierarchical cluster analysis indicated similarity within habitat types but significant dissimilarity between sampling periods, confirming shifts in community composition. Analysis of individual species’ contributions to overall similarity across habitats shows a shift from dominance of native species in the 1990s to increased importance of nonindigenous species in 2010-11. Although natural population fluctuations may have influenced differences between the two sampling periods, our results suggest considerable recent change in the structure and composition of this southwest Florida herpetofaunal community. The causes are unknown, but hydrological shifts and ecological impacts of nonindigenous species may have contributed.

Skin bacteria provide early protection for newly metamorphosed southern leopard frogs (Rana sphenocephala) against the frog-killing fungus, Batrachochytrium dendrobatidis

An important concern for conservation biologists is the continuing loss of global biodiversity. This is especially true for amphibians, which are disappearing at an alarming rate. The emerging fungal pathogen, Batrachochytrium dendrobatidis (Bd), causes the skin disease chytridiomycosis and is a major contributor to amphibian population declines. Recent studies suggest that symbiotic skin bacteria provide some protection against Bd. Possible mitigation strategies include skin microbiome manipulation and bioaugmentation with potentially beneficial bacteria. Such approaches may employ a method to reduce resident bacteria on the skin to allow for new colonization. Using the southern leopard frog, Rana (Lithobates) sphenocephala, we show here that the skin of this species harbors a rich array of culturable bacterial species that inhibit Bd growth in␣vitro. Use of a potent antibiotic cocktail dramatically reduced culturable skin bacteria within 48h. Reduction of bacteria on post-metamorphic juvenile skin using this antibiotic cocktail resulted in an increased Bd skin burden within two weeks of Bd exposure and a higher Bd burden in those frogs that died. However, efforts to maintain a normal bacterial skin community using a semi-natural mesocosm-derived source of microbes failed to provide long term protection of these vulnerable frogs. Regardless of presence or absence of mesocosm-derived bacteria, Bd loads decreased over time in surviving frogs, suggesting the development of an adaptive immune defense. In this species, development of an antimicrobial peptide defense is delayed, and thus, the microbial community and adaptive immune defenses may provide protection at this critical period of development.

Effects of corticosterone on development and immunocompetence in Western Chorus Frogs (Pseudacris triseriata) and Southern Leopard Frogs (Lithobates sphenocephalus)

Abstract. Stress has been shown to impact the rate of development in many species of vertebrates, including amphibians, reptiles, and mammals. We investigated how treatments of corticosterone, a glucocorticoid stress hormone, would affect the development and immune function of the Western Chorus Frog (Pseudacris triseriata) and the Southern Leopard Frog (Lithobates sphenocephalus). These two species exhibit different metamorphic rates, and we specifically chose these species as we wanted to determine if stress during development had a different effect on species with substantially different developmental periods. Tadpoles in the treatment group were given doses of corticosterone (0.5 μM in their water) and tadpoles in the control group were not dosed with corticosterone. Following three weeks of treatment, a blood sample was collected from each tadpole for use in a Candida albicans killing assay to test constitutive immunity. The findings suggest that Western Chorus Frog tadpoles and Southern Leopard Frog...

The effects of a fungicide and chytrid fungus on anuran larvae in aquatic mesocosms

The amphibian disease chytridiomycosis, caused by the pathogenic fungus Batrachochytrium dendrobatidis (Bd), has been linked to significant amphibian declines over the past three decades. The most severe effects of the pathogen have been primarily observed in relatively pristine areas that are not affected by many anthropogenic factors.One hypothesis concerning improved amphibian persistence with Bd in disturbed landscapes is that contaminants may abate the effects of Bd on amphibians. Recent laboratory studies have shown that pesticides, specifically the fungicide thiophanate-methyl (TM), can kill Bd outside of hosts and clear Bd infections within hosts. Using aquatic mesocosms, we tested the hypothesis that TM (0.43mg/L) would alter growth and development of Lithobates sphenocephalus (southern leopard frog) tadpoles and Bd-infection loads in infected individuals. We hypothesized that the scope of such alterations and infection clearing would be affected by aquatic community variables, specifically zooplankton. TM altered zooplankton diversity (reduced cladoceran and increased copepod and ostracod abundances) and caused mortality to all tadpoles in TM-exposed tanks. In TM-free tanks, Bd-exposed tadpoles in high-density treatments metamorphosed smaller than Bd-unexposed, effects that were reversed in low-density treatments. Our study demonstrates the potential adverse effects of a fungicide and Bd on tadpoles and aquatic systems.