American Bullfrog Lithobates Catesbeianus Research Articles

The first intermediate host of the invasive frog trematode Glypthelmins quieta in Japan.

Glypthelmins quieta is a frog trematode native to North and Central America. This trematode was recently detected in Japan in the American bullfrog Lithobates catesbeianus, which was introduced from North America to Japan. As the first intermediate host of G. quieta, typically a snail, has not yet been identified in Japan, we conducted a snail survey in eastern Japan to screen for an intermediate host using DNA barcoding based on the nuclear 28S ribosomal RNA and mitochondrial cytochrome c oxidase subunit 1. We sampled 3 different snail species, Orientogalba ollula, Physella acuta, and Sinotaia quadrata histrica (157 individuals in total), and only the freshwater snail Physella acuta, which is also believed to have been introduced from North America to Japan, had sporocysts of G. quieta in its hepatopancreas. The introduction of the intermediate and definitive hosts from North America may have facilitated the invasion of G. quieta into Japan.

Bombardier beetles repel invasive bullfrogs.

Invasive non-native predators negatively affect native species; however, some native species can survive the predation pressures of invasive species by using pre-existing antipredator strategies or evolving defenses against invasive predators. The American bullfrog Lithobates catesbeianus (Anura: Ranidae) has been intentionally introduced to many countries and regions, and has impacted native animals through direct predation. Bombardier beetles (Coleoptera: Carabidae: Brachininae: Brachinini) discharge chemicals at a temperature of approximately 100 °C from the tip of the abdomen when they are attacked by predators. This “bombing” can successfully repel predators. However, adults of a native bombardier beetle Pheropsophus (Stenaptinus) occipitalis jessoensis have been reportedly found in the gut contents of the introduced bullfrog L. catesbeianus in Japan. These records suggest that the invasive bullfrog L. catesbeianus attacks the native bombardier beetle P. occipitalis jessoensis under field conditions in Japan; however, the effectiveness of the bombing defense against invasive bullfrogs is unclear. To test the effectiveness of the bombing defense against bullfrogs, we investigated the behavioral responses of L. catesbeianus juveniles to P. occipitalis jessoensis adults under laboratory conditions. Contrary to previous gut content results, almost all the bullfrogs (96.3%) rejected bombardier beetles before swallowing them; 88.9% rejected the beetles after being bombed, and 7.4% stopped attacking the beetles before being bombed. Only 3.7% successfully swallowed and digested the beetle. All of the beetles collected from non-bullfrog-invaded sites could deter bullfrogs, suggesting that the pre-existing defenses of bombardier beetles played an essential role in repelling bullfrogs. When treated beetles that were unable to discharge hot chemicals were provided, 77.8% of bullfrogs successfully swallowed and digested the treated beetles. These results indicate that bombing is important for the successful defense of P. occipitalis jessoensis against invasive bullfrogs. Although invasive bullfrogs have reportedly impacted native insect species, P. occipitalis jessoensis has an existing defense mechanism strong enough to repel the invasive predators.

Global economic costs of herpetofauna invasions

Biological invasions by amphibian and reptile species (i.e. herpetofauna) are numerous and widespread, having caused severe impacts on ecosystems, the economy and human health. However, there remains no synthesised assessment of the economic costs of these invasions. Therefore, using the most comprehensive database on the economic costs of invasive alien species worldwide (InvaCost), we analyse the costs caused by invasive alien herpetofauna according to taxonomic, geographic, sectoral and temporal dimensions, as well as the types of these costs. The cost of invasive herpetofauna totaled at 17.0 billion US$ between 1986 and 2020, divided split into 6.3 billion US$ for amphibians, 10.4 billion US$ for reptiles and 334 million US$ for mixed classes. However, these costs were associated predominantly with only two species (brown tree snake Boiga irregularis and American bullfrog Lithobates catesbeianus), with 10.3 and 6.0 billion US$ in costs, respectively. Costs for the remaining 19 reported species were relatively minor (< 0.6 billion US$), and they were entirely unavailable for over 94% of known invasive herpetofauna worldwide. Also, costs were positively correlated with research effort, suggesting research biases towards well-known taxa. So far, costs have been dominated by predictions and extrapolations (79%), and thus empirical observations for impact were relatively scarce. The activity sector most affected by amphibians was authorities-stakeholders through management (> 99%), while for reptiles, impacts were reported mostly through damages to mixed sectors (65%). Geographically, Oceania and Pacific Islands recorded 63% of total costs, followed by Europe (35%) and North America (2%). Cost reports have generally increased over time but peaked between 2011 and 2015 for amphibians and 2006 to 2010 for reptiles. A greater effort in studying the costs of invasive herpetofauna is necessary for a more complete understanding of invasion impacts of these species. We emphasise the need for greater control and prevention policies concerning the spread of current and future invasive herpetofauna.

Infectious disease threats to amphibians in Greece: new localities positive for Batrachochytrium dendrobatidis.

In the early 2000s, numerous cases of European amphibian population declines and mass die-offs started to emerge. Investigating those events led to the discovery that wild European amphibians were confronted with grave disease threats caused by introduced pathogens, namely the amphibian and the salamander chytrid fungi Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal) and ranaviruses. In Greece, Bd was previously documented among wild amphibian populations in 2 different locations and 3 different species. However, no disease-related mass declines or mortality events have been reported. In this work, we build upon previous findings with new, subsequently obtained data, resulting in a 225-sample dataset of 14 species from 17 different locations throughout Greece, in order to examine the occurrence status of all 3 pathogens responsible for emerging infectious diseases in European amphibians. No positive samples for Bsal or ranavirus were recorded in any location. We confirmed the presence of Bd in 4 more localities and in 4 more species, including 1 urodelan (Macedonian crested newt Triturus macedonicus) and 1 introduced anuran (American bullfrog Lithobates catesbeianus). All insular localities were negative for Bd, except for Crete, where Bd was identified in 2 different locations. Again, no mass declines or die-offs were recorded in any Bd-positive area or elsewhere. However, given the persistence of Bd across Greece over the past ~20 yr, monitoring efforts should continue, and ideally be further expanded.

Presence of invasive American bullfrogs may reduce infectious disease in a native frog species.

Amphibians breeding in aquatic environments may encounter a myriad of threats during their life cycle. One species known to prey on native amphibians in aquatic habitats is the invasive North American bullfrog Lithobates catesbeianus, which, besides being a voracious predator and competitor, often acts as a pathogen carrier and disease superspreader because it tolerates high infection loads of the frog-killing fungus Batrachochytrium dendrobatidis (Bd). Here, we hypothesized that the presence of the bullfrogs in microcosms should either (1) decrease Bd disease severity in native frog species by discouraging them from using the aquatic environment, or (2) increase the mortality of the native species. We tested these 2 mutually exclusive hypotheses by co-housing the snouted treefrog Scinax x-signatus (native to our study area) with L. catesbeianus in the laboratory, exposing them to Bd, and using qPCR analysis to quantify the resulting Bd infection loads in the native frogs. Our experiment had the following replicated treatments: (1) native-only treatment (3 individuals of S. x-signatus), (2) native-predominant treatment (2 S. x-signatus + 1 L. catesbeianus), and (3) exotic-predominant treatment (1 S. x-signatus + 2 L. catesbeianus). We found that Bd infection loads in the native S. x-signatus were highest in the native-only treatment, and lowest in the exotic-predominant treatment, indicating that bullfrogs may discourage native frogs from occupying the aquatic habitat, thus reducing encounter rates between native frogs and the waterborne pathogen. This effect could be driven by the bullfrogs' predatory behavior and their high philopatry to aquatic habitats. Our results highlight that predation risk adds to the complexity of host-species interactions in Bd epidemiology.

Conformation and membrane interaction studies of the potent antimicrobial and anticancer peptide palustrin-Ca

Palustrin-Ca (GFLDIIKDTGKEFAVKILNNLKCKLAGGCPP) is a host defence peptide with potent antimicrobial and anticancer activities, first isolated from the skin of the American bullfrog Lithobates catesbeianus. The peptide is 31 amino acid residues long, cationic and amphipathic. Two-dimensional NMR spectroscopy was employed to characterise its three-dimensional structure in a 50/50% water/2,2,2-trifluoroethanol-d_{3} mixture. The structure is defined by an alpha-helix that spans between Ile^{6}-Ala^{26}, and a cyclic disulfide-bridged domain at the C-terminal end of the peptide sequence, between residues 23 and 29. A molecular dynamics simulation was employed to model the peptide’s interactions with sodium dodecyl sulfate micelles, a widely used bacterial membrane-mimicking environment. Throughout the simulation, the peptide was found to maintain its alpha-helical conformation between residues Ile^{6}-Ala^{26}, while adopting a position parallel to the surface to micelle, which is energetically-favourable due to many hydrophobic and electrostatic contacts with the micelle.

Direct and Latent Effects of Pathogen Exposure Across Native and Invasive Amphibian Life Stages.

Emerging infectious diseases are one of the multiple factors contributing to the current “biodiversity crisis”. As part of the worldwide biodiversity crisis, amphibian populations are declining globally. Chytridiomycosis, an emerging infectious disease, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is a major cause of amphibian population declines. This fungus primarily affects keratinized structures in larval, juvenile, and adult amphibians as well as heart function. However, we know little about how Bd can impact embryos as well as potential latent effects of Bd exposure over ontogeny. Using two different Bd strains and multiple exposure times, we examined the effects of Bd exposure in Pacific chorus frog (Pseudacris regilla), Western toad (Anaxyrus boreas) and American bullfrog (Lithobates catesbeianus) life stages. Using a factorial experimental design, embryos of these three species were exposed to Bd at early and late embryonic stages, with some individuals re-exposed after hatching. Embryonic Bd exposure resulted in differential survival as a function of host species, Bd strain and timing of exposure. P. regilla experienced embryonic mortality when exposed during later developmental stages to one Bd strain. There were no differences across the treatments in embryonic mortality of A. boreas and embryonic mortality of L. catesbeianus occurred in all Bd exposure treatments. We detected latent effects in A. boreas and L. catesbeianus larvae, as mortality increased when individuals had been exposed to any of the Bd strains during the embryonic stage. We also detected direct effects on larval mortality in all three anuran species as a function of Bd strain, and when individuals were double exposed (late in the embryonic stage and again as larvae). Our results suggest that exposure to Bd can directly affect embryo survival and has direct and latent effects on larvae survival of both native and invasive species. However, these impacts were highly context dependent, with timing of exposure and Bd strain influencing the severity of the effects.

Distribution Change of Invasive American Bullfrogs (Lithobates catesbeianus) by Future Climate Threaten Endangered Suweon Treefrog (Hyla suweonensis) in South Korea.

Simple SummaryThe American Bullfrog (Lithobates catesbeianus), known as one of the most problematic amphibians in the world, was introduced to South Korea in the 1970s. Although it has spread very rapidly over the past 50 years, there is no focused strategy to manage the frogs. With the introduction of American Bullfrogs into nature, numerous native species (mostly amphibians) are rapidly decreasing due to predation, a transmission of infectious diseases, and crossbreeding. In particular, the critically endangered Suwon treefrog (Hyla suweonensis) is the most affected by Bullfrogs. In this study, we modeled what environment the American Bullfrog settled in and how it could spread in the future. It was confirmed that the distribution of the two species overlaps in many areas at present, and the distribution of the American Bullfrog may spread to the distribution area of the Suwon treefrog according to future climate change. Through the results of this study, we intend to suggest a management direction for the spread of invasive species and the protection of endangered species. Our result could contribute to many countries that have problems with the American Bullfrogs at present and in the future.The American Bullfrog (Lithobates catesbeianus) has been imported into South Korea in earnest for food since the 1970s and introduced into nature due to release and escape. Accordingly, the influx and spread of American Bullfrogs are expected to have a direct impact on native species, but few related studies have been conducted on this. We predicted changes in the potential distribution and future distribution based on climate change scenarios to analyze how those changes affect critically endangered Suwon treefrogs. Suwon treefrog sites (63.9%, 78/122) overlapped with the distribution of Bullfrogs. According to the prediction of the future distribution of Bullfrogs, the overlapping of American Bullfrogs and Suwon treefrog will remain similar to the current level in the Representative Concentration Pathway (RCP) 4.5 scenario. On the other hand, in the RCP 8.5 scenario, the number of overlapping sites will increase to 72.1% (88/122) due to the spreading of the American Bullfrogs. The results show that climate change directly affects the distribution expansion of the American Bullfrogs but also indirectly can lead to an increased threat to Suwon treefrogs. In conclusion, our results strongly suggest why climate change should be actively addressed in terms of the spread of invasive species and the protection of endangered species.

Economic costs of invasive species in Germany

Invasive alien species are a well-known and pervasive threat to global biodiversity and human well-being. Despite substantial impacts of invasive alien species, quantitative syntheses of monetary costs incurred from invasions in national economies are often missing. As a consequence, adequate resource allocation for management responses to invasions has been inhibited, because cost-benefit analysis of management actions cannot be derived. To determine the economic cost of invasions in Germany, a Central European country with the 4th largest GDP in the world, we analysed published data collected from the first global assessment of economic costs of invasive alien species. Overall, economic costs were estimated at US$ 9.8 billion between 1960 and 2020, including US$ 8.9 billion in potential costs. The potential costs were mostly linked to extrapolated costs of the American bullfrog Lithobates catesbeianus, the black cherry Prunus serotina and two mammals: the muskrat Ondatra zibethicus and the American mink Neovison vison. Observed costs were driven by a broad range of taxa and mostly associated with control-related spending and resource damages or losses. We identified a considerable increase in costs relative to previous estimates and through time. Importantly, of the 2,249 alien and 181 invasive species reported in Germany, only 28 species had recorded economic costs. Therefore, total quantifications of invasive species costs here should be seen as very conservative. Our findings highlight a distinct lack of information in the openly-accessible literature and governmental sources on invasion costs at the national level, masking the highly-probable existence of much greater costs of invasions in Germany. In addition, given that invasion rates are increasing, economic costs are expected to further increase. The evaluation and reporting of economic costs need to be improved in order to deliver a basis for effective mitigation and management of invasions on national and international economies.

Anthropogenic habitat loss accelerates the range expansion of a global invader

AbstractAimUnderstanding the patterns and correlates of the range expansion of established alien species is crucial for predicting invasion impacts and developing effective control strategies. With accelerating globalization, it is key to identify the interactions of different global change processes, such as how land‐use change may influence range expansion, yet empirical studies remain limited.LocationLiuji Town, Jiangsu Province, China.MethodsWe first divided the study area into 128 grids with a resolution of 1 × 1 km and conducted visual encounter surveys over two years for a total of 492 water bodies to explore the establishment and range expansions of a global notorious invader, the American bullfrog Lithobates catesbeianus (Shaw, 1802) (= Rana catesbeiana (Shaw, 1802)) using generalized linear mixed models. Then, we investigated the residence time of the established bullfrogs in each water body based on a questionnaire survey. We quantified the habitat loss and range expansion of the past 30 years via GIS‐based spatial analysis and explored their temporal dynamics using the breakpoint regression technique.ResultsWe found that the area of suitable habitats was the most important variable positively related to the bullfrog establishment. There was a similar temporal trend of the range expansion and habitat loss, although the optimal time of habitat loss was slightly earlier than that of the great increase in bullfrog range expansion. Overall, the bullfrogs tended to expand faster with greater habitat loss after controlling for temporal non‐independence.Main conclusionsOur results demonstrated that loss of suitable habitats may facilitate invaders with faster range expansion to occupy the remaining limited resources. Alien species might thus accelerate invasions under human‐induced land‐use modifications in the era of global change. The time lag between range expansion and habitat loss is the golden window for preventing the spread of established alien species in disturbed habitats.

ACTIVE SEASON AND PRE-OVERWINTERING MICROHABITAT USE BY OREGON SPOTTED FROGS (RANA PRETIOSA) AND AMERICAN BULLFROGS (LITHOBATES CATESBEIANUS [RANA CATESBEIANA]) AT CONBOY LAKE NATIONAL WILDLIFE REFUGE, WASHINGTON

Conboy Lake National Wildlife Refuge (CLNWR) in Washington State supports one of the largest remaining populations of federally listed Oregon Spotted Frogs (OSF; Rana pretiosa). Invasive American Bullfrogs (Lithobates catesbeianus [Rana catesbeiana]), implicated in amphibian declines, are also abundant at CLNWR. Owing to the likely negative effect of this aquatic invader on the highly aquatic OSF, bullfrog control strategies are needed. One method is to limit habitat used by bullfrogs while retaining or enhancing OSF habitat, but for such an approach to be implemented, the 2 species must partition habitat sufficiently. We used radiotelemetry to characterize OSF and bullfrog active-season and pre-overwintering habitat in the human-engineered ditch system at CLNWR. We tracked 12 OSF and 10 bullfrogs from mid-to-late summer, recorded data on frog location and habitat, and analyzed movement patterns, niche breadth, and spatial differences between species. Based on minimum convex polygons, bullfrogs overlapped extensively with OSF habitat space in the ditch system. During the active season, niche analyses also showed extensive overlap in the species' vegetation associations, with selected exceptions at the microhabitat scale. However, each species used distinct pre-overwintering habitats. The small differences in active-season microhabitats and pre-overwintering habitats, and our relatively narrow study conditions, create uncertainty about these species' habitat use in a broader context. Nonetheless, these results underscore the challenge of managing an invasive species that is both a habitat generalist and congener and expose the need for further research to guide management approaches to favor OSFs at CLNWR.

Diet of the American Bullfrog Lithobates catesbeianus Naturalized on Okinawajima, Ryukyu Archipelago, Japan

Abstract: The diet of the nonnative American Bullfrog Lithobates catesbeianus occurring in Ogimi Village of Okinawajima, Ryukyu Archipelago, is investigated. Seventy two of 89 frogs (nine adults, five subadults, and 58 juveniles) captured had food items in its stomach. We identified a total of 64 taxa from 253 food items. Our analyses show that (1) the diet consists mainly of terrestrial prey, (2) mollusks and vertebrates are the essential prey groups for adults and subadults, and (3) odonates, mollusks, and arachnids are the main prey for juveniles. Such dietary habits are quite different from those of several conspecific nonnative populations in mainland Japan and other regions. Part of this is most likely related to the absence of the frog's favorite prey, nonnative American crayfish Procambarus clarkii, in the study area. We also confirm the predation of a poisonous newt Cynops ensicauda popei (Salamandridae) and several aquatic insects by this frog and present some implications for these results.

Predictor complexity and feature selection affect Maxent model transferability: Evidence from global freshwater invasive species

AbstractAimEcological niche models (ENMs) are widely used to address urgent real‐world problems such as climate change effects or invasive species; however, the generality of models when projected through space and/or time, that is transferability, remains a key challenge. Here, we explored the effects of complex predictors and feature selection on ENM transferability in a widely employed algorithm, Maxent, using five globally invasive freshwater species as case studies.LocationGlobal.MethodsWe modelled the global distributions of five notorious freshwater invasive species (African sharptooth catfish Clarias gariepinus, Mozambique tilapia Oreochromis mossambicus, American bullfrog Lithobates catesbeianus, red swamp crayfish Procambarus clarkii, and Australian redclaw crayfish Cherax quadricarinatus), using three predictor datasets of varying complexities derived from two commonly used climatic data sources (WorldClim and IPCC) and three methods of model tuning that differentially incorporated feature selection. Spatially explicit transferability assessments were then conducted using a suite of evaluation metrics previously used to quantify Maxent model performance.ResultsWe show that in the absence of detailed biological knowledge of focal species, simpler predictor datasets produce models that are more accurate than those calibrated using comprehensive “bioclimatic” datasets. Additionally, we find that tuning models for both optimal regularization parameters as well as feature‐class combinations led to the greatest increases in transferability and geographic niche conservatism. Results indicate a tenuous link between model transferability and Akaike's information criterion corrected for small sample sizes (AICc), suggesting that the indiscriminate use of AICc as an estimate of model parsimony may lead to erratic model performance.Main conclusionsOur findings demonstrate that methodological considerations can drastically affect the reliability of spatial and possibly temporal projections, which has severe implications when ENMs are used to infer species’ niches, and quantify ecological or evolutionary change across impacted landscapes.

Reproductive characteristics of American bullfrogs (Lithobates catesbeianus) in their invasive range of the Pacific Northwest, USA

Invasive species pose a major threat to global biodiversity. The effects of invasive species can be strongly influenced and potentially mediated by their reproductive characteristics, such as fecundity, egg production, and duration and number of reproductive events. Selection for smaller body size at first reproduction can also play a role in their establishment, facilitating colonization and spread. The American bullfrog, native to the eastern U.S. (Lithobates catesbeianus), is a species that has invaded more than 40 countries across 4 continents. This species has become especially prevalent in the western United States since its introduction in the early 1900s. This study characterized reproductive characteristics of bullfrogs with emphasis on the minimum size at which males and females reach sexual maturity in the Willamette Valley, Oregon, USA invasion range. We collected and dissected 121 individuals in 2013 and 2017, quantifying characteristics of sexual maturity including snout-vent length, total length, sex, tympanum diameter, presence of distended oviducts or eggs for females, and testes length and sperm activity in males. Our results showed that the minimum reproductive size of both males and females was smaller relative to bullfrogs in their native range as well as in populations across their invasive range. Reduction in size at reproductive maturity is likely impacting the invasive success of American bullfrogs and this study gives us insight on management actions to control the invasion. Applying this insight, managers can adjust their definition of reproductively active adults, increasing the target population of culling and other control methods.

A potential threat to amphibians in the European Natura 2000 network: Forecasting the distribution of the American bullfrog Lithobates catesbeianus

Freshwater biodiversity is declining at an accelerated pace. Climate change and associated global warming and changes in precipitation patterns, combined with the expansion of generalist -invasive species are two of the main threats. Niche-based models (NBMs) are becoming inevitable tools in invasive species risk assessment and in conservation decision-making. Lithobates catesbeianus is an invasive species globally known for its adverse ecological impacts on native amphibians and biodiversity. To assess species current and future climatic suitable areas at the global and European scales we used an ensemble forecasting approach. We considered six climatic variables, three timeframes (current, 2050, and 2070), and two CO2 emission scenarios. Temperature seasonality, minimum temperature of the coldest month, maximum temperature of the warmest month, and precipitation in the driest month were the most important variables predicting bullfrog occurrence. Globally currently 3.8% of land area is suitable for bullfrog and an increase of up to 5.2% in 2070 is expected. Increase in suitable areas is expected at higher latitudes, especially in North America and central Europe. Currently, 3.45% of total Natura 2000 area is suitable, and a predicted range gain of up to 355.93% (12.28%) is expected in the highest concentration scenarios predictions. This can indicate that the 64 native amphibian species present in the Natura 2000 network could be at increased risk. The choice of Natura 2000 for a geographic detailed analysis of the possible effects on native amphibians is due to its importance for habitats and wildlife conservation. Identification of its invasion-susceptible areas will allow resource and management practices optimization.

Aliens in the backyard: Did the American bullfrog conquer the habitat of native frogs in the semi-deciduous Atlantic Forest?

The American bullfrog Lithobates catesbeianus has a natural distribution in North America, but was spread by human activities in different regions around the world. It is listed as the most invasive amphibian species, affecting terrestrial and aquatic ecosystems and the community of native species. In addition, the American bullfrog is extensively associated with lethal pathogens, with high correlation of the presence of this species with population declines and extinctions. Here we test if this alien species has spread through the landscape, establishing populations at new locations. We used diverse methods including georeferencing of satellite images, ethnobiological interviews and field data to evaluate the dispersion and effects of L. catesbeianus introduction on amphibian composition, species number, and density of individuals in forest fragments in an Atlantic Forest landscape. We did not find any relationship between density of individuals, number of species or composition of the native anuran assemblages in forest fragments in relation to the presence or proximity of American bullfrog introduction points. Additionally, we found that the dispersion potential of this species in the studied landscape is zero, as it was only found in those fragments where it was specifically introduced 15 years ago. The species has not established new populations in the landscape. Although exotic, L. catesbeianus thrives in lentic habitats and has no apparent effect on the structural metrics of the native anuran assemblage. Despite this alien species exhibiting a capacity to adapt and survive at the point of introduction, its potential for propagation is limited probably by the fragmented terrestrial landscape and regional stream network.

Phenotypic variation in American bullfrogs (Lithobates catesbeianus) bred under intensive systems in Mexico: A preliminary report

Commercial bullfrog farming has increased steadily in Mexico from 1925 to satisfy both the national and international markets. However, intensive production systems are still scarce, and there is a need for information to help further advance their development. Therefore, this study aimed to characterize and compare morphometric and physiological traits of bullfrogs bred under intensive culture systems. Three-year-old breeding adults (n = 100) from five farms in three different states, and one-year old juveniles (n = 60) from two of these locations, were used in the study. The scaled mass index (SMI) was calculated by considering body weight and snout-vent length measurements. Hematocrit and white blood cell concentrations were determined in juveniles, and a leukocyte profile was established. Eight linear (based on measurements from photographs of the skull), plus one geometric, variables, were used for morphometric analyses. Results show that the SMI did not vary between localities or gender in juvenile frogs, while differences were found both between sexes (p &lt; 0.026) and between farms (p &lt; 0.001) in adult frogs. Hematocrit and neutrophil concentrations in juvenile individuals also differed between localities. Linear and geometric morphometric analyses in juvenile frogs showed differences between sexes (p &lt; 0.001) and between localities (p &lt; 0.001), the latter suggesting the existence of at least two morphotypes of this species. This study presents relevant information to help advance bullfrog farming in Mexico.

Moonlight rather than moon phase influences activity and habitat use in an invasive amphibian predator and its native amphibian prey

Predation affects population dynamics via both direct mortality and behavioural responses to the threat of death. Environmental factors are known to influence the activity of both predator and prey in amphibians by interacting with their physiological constraints. For instance, lunar cues (moonlight and moon cycle) influence amphibian predation risk and foraging efficiency. However, little information is available on how the moonlight affects activity and habitat use. Here, we investigated whether lunar light flux, environmental variables, and lunar phases influence abundance and habitat use in a predator-prey system consisting of an invasive predator (i.e., the American bullfrog Lithobates catesbeianus) and a native prey (i.e., the green frogs Pelophylax spp.). In accordance with both the “visual acuity” and “predation risk” hypotheses, the activity of the invasive predator was enhanced in moonlit nights, especially in open habitats, whereas the activity of the native prey species seemed to be not affected by the intensity of moonlight. Contrary to the “habitat-mediated predation risk hypothesis”, no suppressive effect of moonlight in open habitats was found for L. catesbeianus, this possibly evidencing the lack of perceived predation risk by this alien species. Moon cycle had no effect on American bullfrog abundance and weakly affected the activity of green frogs especially in open habitats between the first quarter and the full moon. Our study shows how moonlight, lunar phases and environmental parameters influence the behaviour and ecology of the American bullfrog and one of its native prey. Since indirect effects have the potential to moderate or amplify the impacts of invasive species on native populations, our findings could help to understand the spreading of American bullfrogs and to possibly mitigate their impacts on native fauna through habitat restoration.

Genome analysis of Ranavirus frog virus 3 isolated from American Bullfrog (Lithobates catesbeianus) in South America

Ranaviruses (family Iridoviridae) cause important diseases in cold-blooded vertebrates. In addition, some occurrences indicate that, in this genus, the same virus can infect animals from different taxonomic groups. A strain isolated from a Ranavirus outbreak (2012) in the state of Sao Paulo, Brazil, had its genome sequenced and presented 99.26% and 36.85% identity with samples of Frog virus 3 (FV3) and Singapore grouper iridovirus (SGIV) ranaviruses, respectively. Eight potential recombination events among the analyzed sample and reference FV3 samples were identified, including a recombination with Bohle iridovirus (BIV) sample from Oceania. The analyzed sample presented several rearrangements compared to FV3 reference samples from North America and European continent. We report for the first time the complete genome of Ranavirus FV3 isolated from South America, these results contribute to a greater knowledge related to evolutionary events of potentially lethal infectious agent for cold-blooded animals.

Effect of parasitism of Lernaea cyprinacea on tadpoles of the invasive species Lithobates catesbeianus

The introduction of invasive species is one of the greatest threats currently faced by natural ecosystems, causing ecological imbalances between native populations and transmission of a variety of diseases. We reported the interaction between two exotic species given by the parasitic infestation of the copepod Lernaea cyprinacea in the early stages of the development of the American bullfrog Lithobates catesbeianus in the central area of Argentina. In this paper we analysed the leukocyte profile of parasitized and non-parasitized tadpoles of L. catesbeianus with L. cyprinacea and their body condition (BC) as biomarkers of the health status of organisms. A total of 27 tadpoles of L. catesbeianus were analysed (12 non-parasitized and 15 parasitized). The lower BC recorded in parasitized organisms show a lower health status in these tadpoles, which could be affecting the metamorphosis and therefore impact at the population level. Leukocyte response of L. catesbeianus tadpoles to the parasitism of L. cyprinacea was found. Mature and immature lymphocyte frequencies and hematocrit were higher in parasitized compared to non-parasitized tadpoles, which is a typical response to the presence of parasites. However, eosinophils and monocytes were recorded at high frequencies in not parasitized tadpoles, which could be due to the important role played by these leucocytes in the metamorphosis of frogs. The results of this study constitute a first antecedent on leukocyte profile in aquatic stages of anurans during an ectoparasitosis and its possible implications for environmental health. The parasitism of L. cyprinacea influences the biology of the American bullfrog at both the individual and population levels. Parasitized individuals are not killed directly by the parasite, but they can create conditions for secondary infections, growth retardation, behavioral changes and, ultimately, reduce populations.