Rana Clamitans Research Articles

Effects of Invasive Western Mosquitofish and Ammonium Nitrate on Green Frog Tadpoles

Invasive fish frequently negatively affect amphibian populations around the world. In agricultural regions of the world, the effects of invasive fish on amphibians may coincide with pollution by agricultural fertilizers. We conducted a mesocosm experiment to examine the potential independent and interactive effects of introduced Western Mosquitofish (Gambusia affinis) and ammonium nitrate, an agricultural fertilizer, on Green Frog (Lithobates clamitans) tadpoles. Mosquitofish had a negative effect on the survivorship of Green Frog tadpoles. Green Frog tadpoles from mesocosms with mosquitofish were larger than tadpoles from mesocosms without mosquitofish, possibly due to a thinning effect that reduced intraspecific competition, as well as increased primary productivity. Ammonium nitrate additions did not affect survivorship in Green Frogs. However, Green Frog tadpoles in ammonium nitrate addition treatments were larger than those from treatments without ammonium nitrate addition, possibly due to increased phytoplankton abundance. In conclusion, mosquitofish and ammonium nitrate addition each had independent and additive effects on Green Frog tadpoles, but there was no evidence for significant interactions between these two stressors. Our results suggest that environmental stressors can have additive effects in some systems and that introduced fish predators may have greater impacts on amphibian populations than low level chemical contamination.

Characterization of Gene Expression Endpoints During Postembryonic Development of the Northern Green Frog (Rana clamitans melanota)

Postembryonic development of a larval tadpole into a juvenile frog involves the coordinated action of thyroid hormone (TH) across a diversity of tissues. Changes in the frog transcriptome represent a highly sensitive endpoint in the detection of developmental progression, and for the identification of environmental chemical contaminants that possess endocrine disruptive properties. Unfortunately, in contrast with their vital role as sentinels of environmental change, few gene expression tools currently exist for the majority of native North American frog species. We have isolated seven expressed gene sequences from the Northern green frog (Rana clamitans melanota) that encode proteins associated with TH-mediated postembryonic development and global stress response, and established a quantitative real-time polymerase chain reaction (qPCR) assay. We also obtained three additional species-specific gene sequences that functioned in the normalization of the expression data. Alterations in mRNA abundance profiles were identified in up to eight tissues during R. clamitans postembryonic development, and following exogenous administration of TH to premetamorphic tadpoles. Our results characterize tissue distribution and sensitivity to TH of select mRNA of a common North American frog species and support the potential use of this qPCR assay in identification of the presence of chemical agents in aquatic environments that modulate TH action.

Factors determining the in vitro emergence of sexual stages of Hepatozoon clamatae from erythrocytes of the Green Frog (Rana clamitans)

Sexual reproduction of apicomplexan parasites in haematophagous arthropods requires that intracellular sexual stages of these protozoa escape vertebrate erythrocytes in the blood meal. Although cues that signal sexual stages of the human malaria parasite (Plasmodium falciparum Welch, 1897) to emerge from erythrocytes are well documented, such signals are poorly known for other blood-dwelling Apicomplexa. The objective of this comparative study was to investigate conditions required to induce in vitro emergence of sexual stages of Hepatozoon clamatae (Stebbins, 1905) from frog erythrocytes. Blood was drawn from Green Frogs (Rana clamitans Latreille in Sonnini de Manoncourt and Latreille, 1801 = Lithobates clamitans clamitans (Latreille in Sonnini de Manoncourt and Latreille, 1801)) infected with H. clamatae and treated with solutions of various concentrations of saline, pH, and xanthurenic acid at different temperatures. Hypertonic saline solutions of 200 and 222 mmol/L at pH 7.4 and 7.7 elicited emergence of nearly 100% of gamonts from frog erythrocytes, but at pH 8.0 resulted in decreased emergence. Solutions containing 1, 10, and 100 μmol/L xanthurenic acid increased gamont emergence at saline concentrations of 156, 178, and 244 mmol/L, but decreased emergence at 200 and 222 mmol/L. Gamont emergence increased as incubation temperatures increased from 18 to 26 °C. These results suggest that conditions necessary for emergence of sexual stages of bloodstream Apicomplexa from erythrocytes vary among genera.

Specific time of exposure during tadpole development influences biological effects of the insecticide carbaryl in green frogs (Lithobates clamitans)

The orchestration of anuran metamorphosis is initiated and integrated by thyroid hormones, which change dynamically during larval development and which may represent a target of disruption by environmental contaminants. Studies have found that some anurans experience increased rates of development when exposed to the insecticide carbaryl later in larval development, suggesting that this insecticide could affect thyroid hormone-associated biological pathways. However, the time in development when tadpoles are sensitive to insecticide exposure has not been clearly defined nor has the mechanism been tested. In two separate studies, we exposed recently hatched green frog (Lithobates clamitans) tadpoles to a single, three day carbaryl exposure in the laboratory at either 2, 4, 8, or 16 weeks post-hatching. We examined the impact of carbaryl exposure on mRNA abundance patterns in the brains of frogs following metamorphosis months after a single three day exposure (experiment 1) and in tadpole tails three days after exposure (experiment 2) using cDNA microarrays and quantitative real time polymerase chain reaction (QPCR) analyses. For tadpoles reared through metamorphosis, we measured tadpole growth and development, as well as time to, mass at, and survival to metamorphosis. Although carbaryl did not significantly impact tadpole development, metamorphosis, or survival, clear exposure-related alterations in both tail and brain transcript levels were evident when tadpoles were exposed to carbaryl, particularly in tadpoles exposed at weeks 8 and 16 post-hatching, indicating both short-term and long-term alterations in mRNA expression. These results indicate that carbaryl can have long-lasting effects on brain development when exposure occurs at sensitive developmental stages, which may have implications for animal fitness and function later in the life cycle.

Arsenic species and uptake in amphibians (Rana clamitans and Bufo americanus)

Total arsenic concentrations and the chemical form, or species, of arsenic were determined in amphibians (Rana clamitans and Bufo americanus) collected from a site with elevated arsenic concentrations in Nova Scotia, Canada. Frog legs had significantly elevated total arsenic concentrations at a contaminated site when compared with a nearby background site and a calculation of the estimated daily intake rates of arsenic indicates that both diet (invertebrate intake) and water absorption are important sources of arsenic for these adult organisms. Body burdens of tetramethylarsonium were similar for both the contaminated and background site, with up to 50% of the total arsenic contained in frog legs in the form of the tetramethylarsonium ion.

Laboratory and field exposure of two species of juvenile amphibians to a glyphosate-based herbicide and Batrachochytrium dendrobatidis

Herbicides are commonly used in agriculture and silviculture to reduce interspecific competition among plants and thereby enhance crop growth, quality, and volume. Internationally, formulations of glyphosate-based herbicides are the most widely used herbicides in both these sectors. A large amount of work has focused on the effects of these herbicides on amphibians. Several laboratory and mesocosm studies have demonstrated that various formulations of glyphosate herbicides can be acutely toxic to larval and juvenile amphibians at concentrations at the upper end of environmental realism. However, to date there has been little work done investigating such effects in natural systems, limited work on juvenile amphibians, and only a few studies have investigated interactions with other stressors. We conducted a 16day field experiment in which juveniles of two amphibian species (Lithobates clamitans and Lithobates pipiens) were exposed to the herbicide Roundup WeatherMax™ at four application rates (0, 2.16, 4.32 and 8.64kg a.e./ha) to investigate effects on survival, liver somatic index (LSI), body condition, and incidence of disease caused by Batrachochytrium dendrobatidis (Bd). In a separate 16day laboratory experiment, we exposed juvenile L. clamitans to both the herbicide and Bd. Results of our studies showed that this particular herbicide formulation had no effect on juvenile survival, LSI, body condition, or disease incidence, nor was there an interaction between exposure to herbicide and exposure to the disease in tests which closely mimic real world exposure scenarios. These experiments suggest that Roundup WeatherMax as typically used in agriculture is unlikely to cause significant deleterious effects on juvenile amphibians under real world exposure conditions.

Elucidating Predator–Prey Interactions Using Aquatic Microcosms: Complex Effects of a Crayfish Predator, Vegetation, and Atrazine on Tadpole Survival and Behavior

Habitat structure is known to influence community interactions, but its role in amphibian communities is unclear. Our objective was to examine the effect of vegetative habitat structure, in the presence or absence of a crayfish predator (Orconectes rusticus) and the herbicide atrazine, on Green Frog (Rana clamitans) tadpoles reared in 10-L microcosms in the laboratory. Crayfish predators reduced Green Frog survival and affected activity levels and microhabitat use differently depending on the presence or absence of vegetation. In treatments with vegetation, activity levels were greater when the crayfish predator was absent, but in treatments without vegetation activity levels did not differ between predation treatments. Moreover, when a crayfish predator was present, tadpoles in treatments without vegetation spent more time at the water surface than tadpoles in treatments with vegetation. This preference for the water surface may have been a compensatory behavioral change to avoid predation because it was less likely that crayfish would be able to reach the upper portion of the tank in the absence of vegetation. Atrazine exposure did not significantly influence susceptibility of Green Frog tadpoles to crayfish predators or alter the impact of vegetation. We found that vegetative habitat structure can mediate predator–prey interactions; however, contrary to previous studies we found that the presence of vegetation may benefit the crayfish predator and result in both lethal and sublethal effects on tadpole prey.

Disease risk in temperate amphibian populations is higher at closed-canopy sites.

Habitat loss and chytridiomycosis (a disease caused by the chytrid fungus Batrachochytrium dendrobatidis - Bd) are major drivers of amphibian declines worldwide. Habitat loss regulates host-pathogen interactions by altering biotic and abiotic factors directly linked to both host and pathogen fitness. Therefore, studies investigating the links between natural vegetation and chytridiomycosis require integrative approaches to control for the multitude of possible interactions of biological and environmental variables in spatial epidemiology. In this study, we quantified Bd infection dynamics across a gradient of natural vegetation and microclimates, looking for causal associations between vegetation cover, multiple microclimatic variables, and pathogen prevalence and infection intensity. To minimize the effects of host diversity in our analyses, we sampled amphibian populations in the Adirondack Mountains of New York State, a region with relatively high single-host dominance. We sampled permanent ponds for anurans, focusing on populations of the habitat generalist frog Lithobates clamitans, and recorded various biotic and abiotic factors that potentially affect host-pathogen interactions: natural vegetation, canopy density, water temperature, and host population and community attributes. We screened for important explanatory variables of Bd infections and used path analyses to statistically test for the strength of cascading effects linking vegetation cover, microclimate, and Bd parameters. We found that canopy density, natural vegetation, and daily average water temperature were the best predictors of Bd. High canopy density resulted in lower water temperature, which in turn predicted higher Bd prevalence and infection intensity. Our results confirm that microclimatic shifts arising from changes in natural vegetation play an important role in Bd spatial epidemiology, with areas of closed canopy favoring Bd. Given increasing rates of anthropogenic habitat modification and the resulting declines in temperate and tropical frogs, understanding how vegetation cover and disease interact is critical for predicting Bd spread and developing appropriate management tools for wild populations.

Mate attraction by male anurans in the presence of traffic noise

AbstractWe previously found that males of two anuran species – Hyla versicolor and Rana clamitans – alter their mating calls in response to traffic noise. To test whether these alterations compensate for an effect of traffic noise on mate attraction, we (1) recorded a male calling at a quiet site; (2) played traffic noise at the same male and recorded its altered call; (3) used these recordings to attract females to a trap at sites either with or without broadcast traffic noise. The calls produced without traffic noise attracted fewer females when they were played at sites with traffic noise than when they were played at sites without noise. However, the calls of the same individuals produced with traffic noise attracted as many females at sites with noise as at sites without noise, and they attracted as many females as did the call of the same male made without noise and played at sites without noise (the ‘natural’ situation). Therefore, for these species, traffic noise does not affect mate attraction; males change their calls to compensate for a potential effect of traffic noise on mate attraction. A third species – Bufo americanus – does not alter its call in response to traffic noise, and its call made in the absence or presence of traffic noise was equally able to attract females in the absence or presence of traffic noise, indicating that traffic noise does not negatively affect mate attraction. Therefore, it appears that traffic noise does not negatively affect mate attraction in these three species of anurans. We suggest that, if our results apply to anurans in general, the previously documented negative effects of roads on anuran populations are likely caused mainly by road mortality. If this is true, road mitigation for anurans should focus mainly on reducing this mortality.

A silviculture application of the glyphosate‐based herbicide VisionMAX to wetlands has limited direct effects on amphibian larvae

Herbicides are commonly used in agriculture and silviculture to reduce interspecific competition among plants and thereby enhance crop growth, quality, and volume. Internationally, glyphosate-based herbicides are the most widely used herbicides in both of these sectors. Laboratory and mesocosm studies have demonstrated that some formulations are toxic to amphibian larvae below concentrations that approximate predicted maximal or "worst-case" exposure scenarios. However, field studies have not found evidence of toxicity at these concentrations. The authors conducted a replicated field experiment involving 10 naturalized wetlands split in half with an impermeable plastic barrier to assess the direct toxicity of a glyphosate formulation commonly used in silviculture (VisionMAX™). The herbicide formulation was applied directly to the surface of one side of each wetland at one of two target aqueous exposure rates (high = 2,880, low = 550 µg acid equivalents [a.e.]/L), and the other side was left as an untreated control. The survival and growth of green frog larvae (Lithobates clamitans) were assessed for two years following herbicide treatment. The herbicide did not have a negative impact on survival or growth of L. clamitans larvae at either treatment level. In fact, mean larval abundance was typically greater in the treated sides than in control sides within the year of herbicide application. These results indicate that typical silviculture use of VisionMAX poses negligible risk to larval amphibians, likely because the combined effects of sorption and degradation in natural wetlands limit the exposure magnitude and duration.

Effects of Terrestrial Buffer Zones on Amphibians on Golf Courses

A major cause of amphibian declines worldwide is habitat destruction or alteration. Public green spaces, such as golf courses and parks, could serve as safe havens to curb the effects of habitat loss if managed in ways to bolster local amphibian communities. We reared larval Blanchard's cricket frogs (Acris blanchardi) and green frogs (Rana clamitans) in golf course ponds with and without 1 m terrestrial buffer zones, and released marked cricket frog metamorphs at the golf course ponds they were reared in. Larval survival of both species was affected by the presence of a buffer zone, with increased survival for cricket frogs and decreased survival for green frogs when reared in ponds with buffer zones. No marked cricket frog juveniles were recovered at any golf course pond in the following year, suggesting that most animals died or migrated. In a separate study, we released cricket frogs in a terrestrial pen and allowed them to choose between mown and unmown grass. Cricket frogs had a greater probability of using unmown versus mown grass. Our results suggest that incorporating buffer zones around ponds can offer suitable habitat for some amphibian species and can improve the quality of the aquatic environment for some sensitive local amphibians.

Impact of an insecticide changes with amount of leaf litter input: Implications for amphibian populations

Changes in percentage of forest cover can influence nutrient levels in aquatic systems and change abiotic conditions that may influence species. The authors examined how increasing amounts of leaf litter influenced toxicity of the insecticide carbaryl using larval green frogs (Rana clamitans) in outdoor mesocosm ponds. Insecticides can have direct negative effects on individual physiology and behavior and indirect effects on the food web, which can result in trophic cascades. They predicted that direct effects of the insecticide would dominate when nutrients were low (resulting in negative impacts on amphibian development and survival), whereas indirect effects could offset direct effects when nutrients were more abundant through a trophic cascade that leads to more food for tadpoles (resulting in positive effects on amphibian development and survival). The authors found support for this hypothesis: first, total green frog survival was greatest with increased leaf litter input in the presence of carbaryl. Additionally, most green frogs that reached metamorphosis were from ponds with high leaf litter input and carbaryl. Second, the impact of carbaryl on developmental stage and tadpole mass varied depending on the amount of leaf litter present. With high amounts of leaf litter, carbaryl had a positive impact on development and growth; in contrast, with low amounts of leaf litter, carbaryl had negative or no effects on tadpole development and mass. The present study suggests that differences in nutrient levels between ponds exposed to pesticides could play a role in amphibian population dynamics.

Ameliorative effects of sodium chloride on acute copper toxicity among Cope's gray tree frog (Hyla chrysoscelis) and green frog (Rana clamitans) embryos

Urban stormwater runoff is composed of a mixture of components, including polycyclic aromatic hydrocarbons, metals, deicing agents, and many others. The fate of these chemicals is often in stormwater detention ponds that are used by amphibians for breeding. Among aquatic organisms, the toxic mechanism for many metals involves interference with active Na(+) and Cl(-) uptake. Addition of cations has been shown to reduce the toxicity of metals among some aquatic organisms through competitive inhibition, but no studies have investigated the interaction between NaCl and Cu among amphibian embryos and larvae. To determine the degree to which NaCl may ameliorate the toxicity of Cu to amphibian embryos and larvae, the authors exposed Hyla chrysoscelis (Cope's gray treefrogs) and Rana (Lithobates) clamitans (green frogs) to seven levels of Cu and NaCl in fully factorial experiments. When exposure was in artificial hard water, Cu was highly toxic to both species (96-h median lethal concentration [LC50] of 44.7 µg/L and 162.6 µg/L for H. chrysoscelis and R. clamitans, respectively). However, approximately 500 mg/L of NaCl eliminated Cu toxicity over the range of Cu concentrations used in the experiments (maximum 150 µg Cu/L for H. chrysoscelis and 325 µg Cu/L for R. clamitans). The current results suggest that NaCl is likely responsible for the toxic effects of NaCl and metal mixtures that might be typical of runoff from road surfaces in northern latitudes.

Interactive effects of roads and weather on juvenile amphibian movements

We investigated whether paved roads adjacent to 16 ponds acted as barriers to movements of juvenile wood frogs (Lithobates sylvaticus), green frogs (Lithobates clamitans), mole salamanders (Ambystoma laterale, A. maculatum), and American toads (Anaxyrus americanus) in eastern New Brunswick, Canada. Using pitfall traps and drift fences, we recorded captures of juveniles dispersing away from their natal ponds into forest habitat (pondside fences) or across the road (roadside fences) over two field seasons. To explain variations in abundance of dispersers among sites, we measured several road-associated variables including traffic intensity and roadside habitat structure, pond quality, and weather variables. We estimated the activity patterns (across 4-day periods) and seasonal abundance of juveniles in transit between ponds and terrestrial habitat using generalized linear mixed models. For all groups, activity across 4-day periods increased with either total precipitation or minimum air temperature. However, road-associated variables were also important for some species. Mole salamander activity was lowest next to roads. Wood frog activity increased with minimum air temperature, but the effect was weakest at roadside fences (minimum air temperature × fence position interaction). Seasonal abundance of most groups varied with habitat structure or pond hydroperiod. Green frog abundance decreased with increasing traffic intensity, but abundance was higher at roadside fences than pondside fences. In contrast, wood frog seasonal abundance tended to be lowest at roadside fences. We conclude that road-associated disturbances are detectable at fine temporal scales and that amphibian responses to such variables can be influenced by weather variables.

Comparative toxicity of two glyphosate formulations (original formulation of Roundup® and Roundup WeatherMAX®) to six North American larval anurans

The toxicity of two glyphosate formulations (the original formulation of Roundup® and Roundup WeatherMAX®) to six species of North American larval anurans was evaluated by using 96-h static, nonrenewal aqueous exposures. The 96-h median lethal concentration values (LC50) ranged from 1.80 to 4.22 mg acid equivalent (ae)/L and 1.96 to 3.26 mg ae/L for the original formulation of Roundup and Roundup WeatherMAX, respectively. Judged by LC50 values, four species were more sensitive to Roundup WeatherMAX exposures, and two species were more sensitive to the original formulation. Two of six species, Bufo fowleri (p < 0.05, F = 14.89, degrees of freedom [df] = 1) and Rana clamitans (p < 0.05, F = 18.46, df = 1), had significantly different responses to the two formulations tested. Increased sensitivity to Roundup WeatherMAX likely was due to differences in the surfactants or relative amounts of the surfactants in the two formulations. Potency slopes for exposures of the original formulation ranged from 24.3 to 92.5% mortality/mg ae/L. Thresholds ranged from 1.31 to 3.68 mg ae/L, showing an approximately three times difference in the initiation of response among species tested. For exposures of Roundup WeatherMAX, slopes ranged from 49.3 to 84.2% mortality/mg ae/L. Thresholds ranged from 0.83 to 2.68 mg ae/L. Margins of safety derived from a simulated direct overspray were above 1, except for one species in exposures of Roundup WeatherMAX. Laboratory data based on aqueous exposures are conservative because of the lack of environmental ligands; however, these tests provide information regarding the relative toxicity between these two Roundup formulations.

Invasive shrub alters native forest amphibian communities

Although invasive plants can have transformative effects on native plant communities, studies of the consequences of plant invasion for native fauna are generally restricted to primary consumers. Here we investigate whether an invasive shrub, Lonicera maackii, impacts native amphibians and evaluate evidence for the role of invasive plant-induced alteration of forest understory microclimate as a mechanism driving amphibian responses to L. maackii invasion. We sampled amphibian communities in forest plots with high or low density of L. maackii, and monitored microclimate (temperature and humidity at ground level) in the same forest plots. Amphibian species richness and evenness were lower in invaded plots. Invasion also resulted in shifts in amphibian species composition. Mean daily maximum temperature and mean daily temperature were lower in invaded plots, and counts of the Green frog Lithobates clamitans were marginally negatively related to mean daily temperature. Our work illustrates how an invasive ecosystem engineer may affect native organisms with which it shares no trophic connection, and suggests that changes in microclimate may be one mechanism by which alien plants affect communities where they invade.

Seasonal Microhabitat Selection and Use of Syntopic Populations of Lithobates okaloosae and Lithobates clamitans clamitans

Abstract Quantifying and comparing habitat selection of related, syntopic species may help elucidate how species partition resources and compete. The Florida Bog Frog (Lithobates okaloosae) is endemic to northwestern Florida and is syntopic with the more widely distributed Bronze Frog (Lithobates clamitans clamitans). Our objective was to determine whether these closely related frogs selected different microhabitat characteristics at male calling sites, which in turn may influence successful reproduction or survival. From 2006 to 2008, we quantified microhabitat characteristics of male calling sites used by both species on Eglin Air Force Base, Florida. We created a suite of a priori models and used paired logistic regression to assess each species' habitat selection. Further, we compared habitat characteristics from each species' most highly supported model to directly compare habitat use. Model selection indicated that calling sites for L. okaloosae were best described by habitat features related to mic...

Exposure of juvenile green frogs ( Lithobates clamitans) in littoral enclosures to a glyphosate-based herbicide

The majority of studies on the toxicity of glyphosate-based herbicides to amphibians have focused on larval life stages exposed in aqueous media. However, adult and juvenile amphibians may also be exposed directly or indirectly to herbicides. The potential for such exposures is of particular interest in the littoral zone surrounding wetlands as this is preferred habitat for many amphibian species. Moreover, it may be argued that potential herbicide effects on juvenile or adult amphibians could have comparatively greater influence on overall recruitment, reproductive potential and thus stability of local populations than effects on larvae. In this experiment, juvenile green frogs ( Lithobates clamitans) were exposed to two concentrations (2.16 and 4.27 kg a.e./ha) of a glyphosate-based herbicide formulation (VisionMax ®), which were based on typical application scenarios in Canadian forestry. The experimental design employed frogs inhabiting in situ enclosures established at the edge of small naturalized wetlands that were split in half using an impermeable plastic barrier. When analyzed using nominal target application rates, exposure to the glyphosate-based herbicide had no significant effect on survival, body condition, liver somatic index or the observed rate of Batrachochytrium dendrobatidis infection. However, there were marginal trends in both ANOVA analysis and post-hoc regressions regarding B. dendrobatidis infection rates and liver somatic index in relation to measured exposure estimates. Results from this study highlight the importance of field research and the need to include multiple endpoints when examining potential effects of a contaminant on non-target organisms.

Juvenile green frog (Rana clamitans) predatory ability not affected by exposure to carbaryl at different times during larval development

Larval exposure to pesticides can occur at different times during development and can negatively impact amphibian fitness. We examined the effects of larval green frog (Rana clamitans) exposure to carbaryl at 2, 4, 8, or 16 weeks of development on juvenile predatory ability. We did not find evidence that predatory ability was affected by exposure to carbaryl, which suggests that carbaryl does not have latent effects on the predatory performance of green frogs in subsequent life stages.

Genetic evidence of contemporary hybridization in one of North America's rarest anurans, the Florida bog frog

When a widespread species is sympatric with a rare, geographically restricted conspecific, recurrent gene flow can pose the risk of extinction for the latter. This can occur via genetic swamping, where the occurrence of hybrids eventually replaces the numerically less abundant species. We took a molecular genetic approach to quantify the occurrence and degree of contemporary hybridization between two species of frog co-occurring in a small geographic area in northwest Florida, USA. The Florida bog frog Lithobates okaloosae is a small ranid limited in distribution to a few acidic seepage and steephead streams that feed the Yellow, Shoal and East Bay river drainages in Walton, Okaloosa and Santa Rosa counties, Florida. The bronze frog Lithobates clamitans is a widespread (Eastern North America) congener. Data from nine microsatellite loci and 350 frogs were analyzed using Bayesian clustering (structure) and a Bayesian hybrid classification method implemented in newhybrids. Power to detect hybrids with the dataset was assessed through simulations. Both methods detected hybrids in similar proportions (5–10%), including congruent confirmation and rejection of samples previously classified as putative hybrids based on phenotypic characteristics. However, the nine loci lacked sufficient power to differentiate among F1 and backcrossed individuals, leaving open the question of the extent of genetic introgression. Longitudinal genetic monitoring is recommended to evaluate whether the observed level of hybridization represents a long-term threat to the distinction of one of North America's most geographically restricted frogs.