Osteopilus Septentrionalis Research Articles

Parasite spillover to native hosts from more tolerant, supershedding invasive hosts: Implications for management

AbstractIntroduced hosts are capable of introducing parasite species and altering the abundance of parasites that are already present in native hosts, but few studies have compared the tolerances of native and invasive hosts to introduced parasites or identified the traits of introduced hosts that make them supershedders of non‐native parasites.Here, we compare the effects of a nematodeAplectana hamatospiculathat is native to Cuba but appears to be introduced to Florida on the native Floridian treefrog,Hyla femoralis, and on the Cuban treefrog (CTF),Osteopilus septentrionalis. We were particularly interested in CTFs because their introduction to Florida has led to reported declines of native treefrogs.In the laboratory, infection withA. hamatospiculacaused a greater loss in body mass ofH. femoralisthan CTFs despiteH. femoralisshedding fewer total worms in their faeces than CTFs. Field collections of CTFs,H. femoralis, and another native Floridian treefrog,H.squirella(Squirrel treefrog) from Tampa, FL also showed that CTFs shed more larval worms in their faeces than both native frogs when controlling for body size. Hence, the non‐native CTF is a supershedder of this non‐native parasite that is spilling over to less tolerant native treefrogs.Any conservation intervention to reduce the effects of CTFs on native treefrogs would benefit from knowing the traits that contribute to the invasive host being a supershedder of this parasite. Hence, we conducted necropsies on 330 CTFs to determine how host sex and body size affect the abundance ofA. hamatospicula, and two other common parasites in this species (acuariid nematodes and trematode metacercariae).There was a significant linear increase inA. hamatospiculaand encysted acuariids with CTF body size, but there was no detectable relationship between host body size and the intensity of metacercariae. Female CTFs were bigger, lived longer and, on average, had moreA. hamatospiculathan male CTFs.Synthesis and applications. These results of the study suggest that there is parasite spillover from the invasive Cuban treefrog (CTF) to native treefrogs in Florida. Additionally, at least some of the adverse effects of CTFs on native treefrogs could be caused by the introduction and amplification of this introduced parasite, and female and larger CTFs seem to be amplifying these infections more than males and smaller CTFs, respectively, suggesting that management could benefit from targeting these individuals.

Early-life exposure to Ivermectin alters long-term growth and disease susceptibility.

Ivermectin is a broad-spectrum antiparasitic medicine, which is often used as a treatment for parasites or as a prophylaxis. While studies have looked at the long-term effects of Ivermectin on helminths, studies have not considered the long-term impacts of this treatment on host health or disease susceptibility. Here, we tracked the effects of early life Ivermectin treatment in Cuban tree frogs (Osteopilus septentrionalis) on growth rates, mortality, metabolically expensive organ size, and susceptibility to Batrachochytrium dendrobatidis (Bd) infection. One year after exposure, there was no effect of Ivermectin exposure on frog mass (X21 = 0.904, p = 0.34), but when tracked through the exponential growth phase (~2.5 years) the Ivermectin exposed individuals had lower growth rates and were ultimately smaller (X21 = 7.78, p = 0.005; X21 = 5.36, p = 0.02, respectively). These results indicate that early life exposure is likely to have unintended impacts on organismal growth and potentially reproductive fitness. Additionally, we exposed frogs to Bd, a pathogenic fungus that has decimated amphibian populations globally, and found early life exposure to Ivermectin decreased disease susceptibility (disease load: X21 = 17.57, p = 0.0002) and prevalence (control: 55%; Ivermectin: 22%) over 2 years after exposure. More research is needed to understand the underlying mechanism behind this phenomenon. Given that Ivermectin exposure altered disease susceptibility, proper controls should be implemented when utilizing this drug as an antiparasitic treatment in research studies.

Batrachochytrium salamandrivorans Can Devour More than Salamanders.

Batrachochytrium salamandrivorans is an emerging fungus that is causing salamander declines in Europe. We evaluated whether an invasive frog species (Cuban treefrog, Osteopilus septentrionalis) that is found in international trade could be an asymptomatic carrier when exposed to zoospore doses known to infect salamanders. We discovered that Cuban treefrogs could be infected with B. salamandrivorans and, surprisingly, that chytridiomycosis developed in animals at the two highest zoospore doses. To fulfill Koch's postulates, we isolated B. salamandrivorans from infected frogs, exposed eastern newts (Notophthalmus viridescens) to the isolate, and verified infection and disease by histopathology. This experiment represents the first documentation of B. salamandrivorans chytridiomycosis in a frog species and substantially expands the conservation threat and possible mobilization of this pathogen in trade.

The Louisiana Amphibian Monitoring Program from 1997 to 2017: Results, analyses, and lessons learned.

To determine trends in either frog distribution or abundance in the State of Louisiana, we reviewed and analyzed frog call data from the Louisiana Amphibian Monitoring Program (LAMP). The data were collected between 1997 and 2017 using North American Amphibian Monitoring Program protocols. Louisiana was divided into three survey regions for administration and analysis: the Florida Parishes, and 2 areas west of the Florida parishes called North and South. Fifty-four routes were surveyed with over 12,792 stops and 1,066 hours of observation. Observers heard 26 species of the 31 species reported to be in Louisiana. Three of the species not heard were natives with ranges that did not overlap with survey routes. The other two species were introduced species, the Rio Grande Chirping Frog (Eleutherodactylus cystignathoides) and the Cuban Treefrog (Osteopilus septentrionalis). Both seem to be limited to urban areas with little to no route coverage. The 15 most commonly occurring species were examined in detail using the percentage of stops at which they observed along a given survey and their call indices. Most species exhibited a multimodal, concave, or convex pattern of abundance over a 15-year period. Among LAMP survey regions, none of the species had synchronous population trends. Only one group of species, winter callers, regularly co-occur. Based on the species lists, the North region could be seen as a subset of the South. However, based on relative abundance, the North was more similar to Florida parishes for both the winter and summer survey runs. Our analyses demonstrate that long-term monitoring (10 years or more) may be necessary to determine population and occupancy trends, and that frog species may have different local demographic patterns across large geographic areas.

Asymmetric cross-strain protection for amphibians exposed to a fungal-metabolite prophylactic treatment.

Chytridiomycosis, an infectious disease of amphibians caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), poses an imminent conservation threat. The global spread of Bd has led to mass mortality events in many amphibian species, resulting in at least 90 species' extinctions to date. Exposure to Bd metabolites (i.e. non-infectious antigenic chemicals released by Bd) partially protects frogs during subsequent challenges with live Bd, suggesting its use as a prophylactic treatment and potential vaccine. However, we do not know whether Bd metabolite exposure protects against strains beyond the one used for treatment. To address this knowledge gap, we conducted a 3 × 2 experiment where we exposed adult Cuban treefrogs, Osteopilus septentrionalis, to one of three treatments (Bd metabolites from California-isolated strain JEL-270, Panamá-isolated strain JEL-419, or an artificial spring water control) and then challenged individuals with live Bd from either strain. We found that exposure to Bd metabolites from the California-isolated strain significantly reduced Bd loads of frogs challenged with the live Panamá-isolated strain, but no other treatments were found to confer protective effects. These findings demonstrate asymmetric cross-protection of a Bd metabolite prophylaxis and suggest that work investigating multiple, diverse strains is urgently needed.

Amphibian species vary in their learned avoidance response to the deadly fungal pathogen Batrachochytrium dendrobatidis

Abstract Lethal and sublethal effects of pathogens should theoretically select for host avoidance of these pathogenic organisms. Some amphibians can learn to avoid the pathogenic fungus Batrachochytrium dendrobatidis (Bd) after one infection‐clearance event. Here, we investigated whether four taxonomically distinct amphibians, Cuban tree frogs Osteopilus septentrionalis, southern toads Anaxyrus (Bufo) terrestris, greenhouse frogs Eleutherodactylus planirostris and pine woods tree frogs Hyla femoralis, exhibited any innate or learned avoidance of Bd on a moist substrate and, if so, what cues they used to identify the fungus. Cuban tree frogs, pine woods tree frogs and greenhouse frogs did not appear to exhibit detectable innate or learned avoidance of Bd. However, southern toads learned to avoid Bd after only one exposure. Southern toads avoided any treatment containing Bd metabolites but did not avoid treatments that lacked Bd metabolites even when dead zoospores were present. Bd metabolites appeared to be the cues that amphibians use to avoid Bd. These metabolites may have a distinct smell or may cause discomfort, which would be consistent with a classical or Pavlovian conditioning response. Synthesis and applications. Not all species of amphibians respond the same way to Bd exposure; some can learn to avoid Bd and the metabolites it produces, while others do not. These findings have important implications for both management practices and policy, and should be considered when developing disease models and conservation plans for amphibians.

Diet of a community of frogs in an agroecosystem in western Cuba

The study of frog diets in agricultural areas enables us to recognize their role in terrestrial food webs as predators of invertebrates, which can become crop pests or disease transmission vectors for humans. The present study examines the diet composition of three syntopic frog species occurring in one agroecosystem in Cuba, and their interspecific trophic interactions. The fieldwork was in Zea mays and Colocasia esculenta crops in Pinar del Río province, Cuba, in August, 2020. The frogs were measured and stomach-flushed in situ, and released at the site of capture. Niche overlap between species was calculated. Fifty-two frogs were captured and 43 (82.7%) had prey in their stomachs. Eleutherodactylus goini had the highest rate of prey/stomach and the broadest diet diversity while Osteopilus septentrionalis had the lowest rate and the narrowest diet diversity. High diet overlap was detected between Eleutherodactylus species. The most consumed prey were Lepidoptera, Hymenoptera, and Blattodea. The diet data suggests that these species could be important biological controls of the invertebrate community in the studied agroecosystems. This indicates a positive impact of these native frogs to the crops by controlling noxious and damaging invertebrates.

Invasive Cuban Treefrogs (Osteopilus septentrionalis) Have More Robust Locomotor Performance Than Two Native Treefrogs (Hyla spp.) in Florida, USA, in Response to Temperature and Parasitic Infections

Introduced species pose a threat to biodiversity, and ecological and physiological factors are important in determining whether an introduced species becomes successfully established in a new region. Locomotor performance is one such factor that can influence the abundance and distribution of an introduced species. We investigated the effects of temperature and parasitism by the intestinal nematode Aplectana hamatospicula on the maximum jump distance and endurance in one invasive and two native treefrogs in Florida, USA. We collected frogs from the wild, estimated their parasite loads, and tested their locomotor performance at three temperatures. Contrary to expectations, invasive Cuban treefrogs (Osteopilus septentrionalis), which are adapted to a warmer climate in the Caribbean, outperformed pinewoods treefrogs (Hyla femoralis) and squirrel treefrogs (H. squirella) at each temperature, even when controlling for body size differences. In all three species, maximum jump distance was positively related to temperature, and this relationship was stronger for larger frogs. Parasites influenced both the maximum jump distance and endurance of frogs. In all three species, larger frogs jumped farther maximum distances than smaller frogs, but this relationship was stronger when frogs had lower, rather than higher, parasite loads. Parasitism had little effect on endurance in invasive frogs, but it tended to decrease the endurance of native frogs at high temperatures. Furthermore, at low temperatures, the lengths of consecutive jumps of infected native frogs tended to increase, suggesting that parasites limited the distances of initial jumps. Effects of temperature and parasites on the locomotor performance of frogs could influence their abilities to forage, escape predators, and disperse. The tremendous locomotor performance of O. septentrionalis, which is maintained across temperatures and parasite loads, likely contributes to the invasion success of this species.

Manual mass spectrometry de novo sequencing of the anionic host defense peptides of the Cuban Treefrog Osteopilus septentrionalis.

Host defense peptides accumulated in the skin glands of the animals constitute the basis of the adaptive and immune system of amphibians. The peptidome of the Cuban frog Osteopilus septentrionalis was established using tandem mass spectrometry as the best analytical tool to elucidate the sequence of these peptides. Manual interpretation of complementary collision-induced dissociation (CID), higher energy collision-induced dissociation (HCD), and electron transfer dissociation (ETD) tandem mass spectra recorded with an Orbitrap Elite mass spectrometer in liquid chromatography/mass spectrometry (LC/MS) mode was used to sequence the peptide components of the frog skin secretion, obtained by mild electrostimulation. Although the vast majority of amphibian peptides discovered so far are cationic, surprisingly only anionic peptides were identified in the skin secretion of the Cuban frog Osteopilus septentrionalis. Mass spectrometry allowed the sequences to be established of 16 representatives of new peptide families: septenins 1 and septenins 2. The highest sequence coverage when dealing with these anionic peptides was obtained with CID normalized collision energy 35 and HCD normalized collision energy 28. Mirror-symmetrical peptides are sequenced using N-terminal acetylation. Acetylated Ser is reliably distinguished from isomeric Glu by the loss of ketene from b-ions containing the corresponding residue. Calculations of the physicochemical and structural properties of the discovered anionic septenins 1 and 2 allowed the mechanism of their interaction with microbe cells to be postulated.

The application of community ecology theory to co-infections in wildlife hosts.

Priority effect theory, a foundational concept from community ecology, states that the order and timing of species arrival during species assembly can affect species composition. Although this theory has been applied to co-infecting parasite species, it has almost always been with a single time lag between co-infecting parasites. Thus, how the timing of parasite species arrival affects co-infections and disease remains poorly understood. To address this gap in the literature, we exposed postmetamorphic Cuban tree frogs (Osteopilus septentrionalis) to Ranavirus, the fungus Batrachochytrium dendrobatidis (Bd), a nematode Aplectana hamatospicula, or pairs of these parasites either simultaneously or sequentially at a range of time lags and quantified load of the secondary parasite and host growth, survival, and parasite tolerance. Prior exposure to Bd or A. hamatospicula significantly increased viral loads relative to hosts singly infected with Ranavirus, whereas A. hamatospicula loads in hosts were higher when coexposed to Bd than when coexposed to Ranavirus. There was a significant positive relationship between time since Ranavirus infection and Bd load, and prior exposure to A. hamatospicula decreased Bd loads compared to simultaneous co-infection with these parasites. Infections with Bd and Ranavirus either singly or in co-infections decreased host growth and survival. This research reveals that time lags between co-infections can affect parasite loads, in line with priority effects theory. As co-infections in the field are unlikely to be simultaneous, an understanding of when co-infections are impacted by time lags between parasite exposures may play a major role in controlling problematic co-infections.

UNA RANA ARBORÍCOLA (Osteopilus septentrionalis, HYLIDAE) DEPREDANDO A UN TOMEGUÍN DE LA TIERRA ENJAULADO (Tiaris olivaceus) EN CUBA

Abstract.-We are reporting the first case of predation of a Cuban Treefrog (Osteopilus septentrionalis) on a confined caged bird, a Yellow-faced Grassquit, (Tiaris oilivaceus) in central Cuba. We comment about predation on aquarium fish too. Both cases of predation are not reported previously.

The potential role of reproductive interference in the decline of native green treefrogs following Cuban treefrog invasions

Reproductive interference is increasingly implicated in the decline of native taxa following alien species invasions. We examined reproductive interference in the context of acoustic modulation of hormone levels and declines in native green treefrogs (Hyla cinerea) following invasions of Cuban treefrogs (Osteopilus septentrionalis) in the southeastern United States. The motivation for our study stemmed from similarities in spectro-temporal properties of Cuban treefrog courtship calls and green treefrog aggressive calls. The aggressive calls of green treefrogs stimulate glucocorticoid production in rival conspecific males, which suppresses androgen production and reproductive behavior. We thus hypothesized that native male green treefrogs exposed to advertisement calls of this invasive species exhibit increased levels of circulating glucocorticoids. We found that broadcast aggressive calls of green treefrogs stimulated glucocorticoid production in conspecific males but that Cuban treefrog vocalizations did not increase glucocorticoid levels in green treefrogs. In natural choruses, the density of calling male green treefrogs and the proportion of non-calling males were positively correlated with glucocorticoid levels and negatively correlated with androgens, whereas body size was positively correlated with androgens. After controlling for these variables, there was no evidence that hormone levels or behavior differed in choruses of green treefrogs in the presence and absence of Cuban treefrogs. Together, our results suggest that interactions among male green treefrogs modulate hormone levels but that the presence of Cuban treefrogs, calling or not, is not altering levels of glucocorticoids or androgens in breeding male green treefrogs.

Predation by a Cuban Treefrog (Osteopilus septentrionalis) and a Domestic Cat (Felis catus) on Tropical House Geckos (Hemidactylus mabouia) in Central Cuba, with a Review of Predators and Vertebrate Prey of Tropical House Geckos

Predation by a Cuban Treefrog (Osteopilus septentrionalis) and a Domestic Cat (Felis catus) on Tropical House Geckos (Hemidactylus mabouia) in Central Cuba, with a Review of Predators and Vertebrate Prey of Tropical House Geckos

Elucidating mechanisms of invasion success: effects of parasite removal on growth and survival rates of invasive and native frogs.

Identifying the mechanisms underlying biological invasions can inform the management of invasive species. The enemy release hypothesis (ERH) suggests that invasive species have a competitive advantage in their introduced range because they leave behind many of their predators and parasites from their native range, allowing them to shift resources from defenses to growth, reproduction, and dispersal. Many studies have demonstrated that invasive species have fewer parasites than their native counterparts, but few studies have tested whether the loss of these natural enemies appears to be a primary driver of the invasion process.To test the ERH, we conducted a mark-recapture study in which we used an anthelmintic drug to successfully reduce parasitic worms in invasive Cuban treefrogs (Osteopilus septentrionalis) and native treefrogs (Hyla spp.) at half of 12 wetlands, marking nearly 4,200 frogs. If the ERH is supported, we would expect that treating for parasitic worms would have a greater benefit to native than invasive hosts.Growth and survival rates of invasive and native treefrogs responded similarly to the anthelmintic treatment, suggesting that the Cuban treefrog's release from parasitic worms does not appear to significantly contribute to its invasiveness in established areas. Instead, it appears that the overall faster rates of growth and maturation, higher survival rates, and larger body sizes of Cuban treefrogs that we observed may contribute to their expansion and proliferation.Synthesis and applications. Although Cuban treefrogs have a lower diversity of parasitic worms in their invasive than native range, this does not appear to significantly contribute to their invasion success in areas where they have been established for more than 20 years. This suggests that any manipulation of parasites in invasive or native hosts would not be an effective method of controlling Cuban treefrogs or reducing their impacts. Further research into other hypotheses is needed to explain the Cuban treefrog's success and help guide management actions to reduce their spread and negative impacts. Our study demonstrates that enemy release may not be a primary driver of invasiveness, highlighting the need for more experimental tests of the enemy release hypothesis to examine its generality.

Effects of elevated salinity on Cuban treefrog Osteopilus septontrionalis aldosterone levels, growth, and development

ABSTRACT Amphibians are increasingly challenged with salinization due to factors such as elevated sea level associated with climate change, the use of road salts, and lowering of water tables. Aldosterone is a steroid hormone that is produced by the adrenal cortex and is involved in osmotic regulation and may play an important role in amphibian acclimation to elevated salinity. We studied the effects of salinity on growth, development, and aldosterone levels in Cuban treefrog (Osteopilus septentrionalis) tadpoles. Gosner stage, growth rates, and aldosterone levels were determined for tadpoles among three salinity treatments (1.0, 2.5, and 3.5 ppt) over a six-week period. It appears that Cuban treefrog tadpoles have the ability to respond to high salt levels with decreased aldosterone secretion; however, in order to survive high salt concentrations, trade-offs in growth and development must occur to regulate osmotic functions.

The effects of traffic noise on tadpole behavior and development

Traffic noise is known to negatively affect many wildlife species by interfering with foraging behavior. Frogs often lay their eggs in roadside ditches because they are predator-free, but it is possible that traffic noise could reduce the survival and fitness of tadpoles, creating an ecological trap. In a series of lab experiments, we tested whether traffic noise has a negative impact on tadpole feeding behavior, whether this is mediated by changes in tadpole activity, and whether there is any impact on tadpole growth rate or metamorphosis. Traffic noise exposure significantly reduced the amount of food consumed by Cuban Treefrog (Osteopilus septentrionalis) tadpoles. Traffic noise exposure also increased the activity level of both Southern Toad (Anaxyrus terrestris) and Cuban Treefrog tadpoles, which could possibly make them more noticeable to predators in the wild. However, these behavioral changes were not associated with changes in growth rate or timing of metamorphosis. We caution, however, that this study aimed to isolate the specific impact of traffic noise, and did not investigate other road effects that may be damaging to tadpoles.

Post-hurricane relief facilitates invasion and establishment of two invasive alien vertebrate species in the Commonwealth of Dominica, West Indies

Invasive alien species (IAS) are a main driver of current global change and contribute significantly to decreases in biodiversity worldwide. To prevent new introductions and establishment of IAS, it is important to identify mechanisms of incursion. On 18 September 2017, Hurricane Maria, a category-5 Atlantic storm, made landfall on the Commonwealth of Dominica causing widespread destruction. Responding to the post-hurricane situation, countries and organizations provided a large range of aid including funds, medical and security support, and relief supplies. Here we report the incursion and establishment of two vertebrate IAS on Dominica during the aftermath of Hurricane Maria—the Common Green Iguana (Iguana iguana) and Cuban Treefrog (Osteopilus septentrionalis)—representing a 20% increase in vertebrate alien species on Dominica. We also report observations of Venezuela Snouted Treefrogs (Scinax x-signatus). Collectively, these species were found at four sites spread along the Caribbean and south coast of Dominica, within or near ports of entry. Invasions of I. iguana and O. septentrionalis are especially worrisome given their known impacts on native species on other Caribbean islands. Though understandable given the human impact caused by severe weather events, these incursions suggest that biosecurity is not implemented by aid-facilitating countries and organizations. With the predicted increase in hurricane intensity and frequency, we suggest basic biosecurity and training programs to reduce incursion threats of IAS during future relief and recovery initiatives. For Dominica, we recommend mitigation programs with additional biological surveys to control and better understand the number of incursion and their impact on post-Maria Dominica.

Metabolites produced by Batrachochytrium dendrobatidis alter development in tadpoles, but not growth or mortality.

The mass decline of amphibian populations poses a serious threat to global biodiversity and ecosystem stability. The pathogenic fungus Batrachochytrium dendrobatidis (Bd) has contributed to the extirpation and extinction of hundreds of amphibian species worldwide. Bd produces potentially damaging metabolites during the host infection process that may affect amphibian growth and development, even in the absence of infection. In this experiment, Cuban tree frog Osteopilus septentrionalis tadpoles and adults were exposed once to either artificial spring water (ASW) or Bd metabolites (n = 31 tadpoles per treatment and n = 30 and 20 adults per treatment, respectively). Tadpoles exposed to Bd metabolites alone developed faster than those exposed to ASW; however, there was no difference in tadpole length, weight change, or mortality between treatments. Despite the faster developmental speed, metabolite exposure did not reduce tadpole weight or length (compared at Gosner stages 27, 29, and 31). There was no effect of treatment on adult size or mortality. These results indicate that both tadpole and adult O. septentrionalis do not appear to be negatively impacted by exposure to non-infectious Bd-contaminated water. In fact, tadpoles developed faster when exposed to metabolites and were of equal size as those in their stage cohort, implying a potential long-term benefit if faster development allows them to leave Bd-infected waters sooner.

The effects of tail damage on tadpole development and leaping ability after metamorphosis in Cuban tree frogs (Osteopilus septentrionalis)

Tadpoles have many predators in the wild and are able to escape from them because the structure of their tail allows it to tear off if attacked. We examined the effects of tail damage in the early tadpole stages on the leaping and swimming abilities of Cuban tree frogs after metamorphosis. We obtained 120 Cuban tree frogs, and to simulate predation, we initially removed a piece of the top of the tadpole tails in one experimental group, cut off a piece of the bottom of the tadpole tails in the second experimental group, and did not make any cuts to tails of the control group. Following tail regeneration by all tadpoles in both experimental groups, we treated all experimental tadpoles as one group, and simulated a second predation event by removing 10% of the distal tip of the tail. After tadpoles completed metamorphosis, they were subjected to a swimming endurance test and subsequent measurement of their leaping abilities. We found no significant effect of tail damage on the leaping abilities of frogs after metamorphosis, and no significant difference in body size at metamorphosis among the groups. The experiment was then replicated and tested tadpole corticosterone (CORT) levels to determine if tadpoles exhibited stress from the tail damage. We found significantly elevated CORT levels in tadpoles with tail damage compared to the tadpoles without tail damage. We conclude that the regeneration abilities of the Cuban tree frog tadpoles afford them the opportunity to survive minor predation events and recover with no apparent long-lasting ill effects even though they were physiologically stressed from the damage. These abilities likely contribute to the Cuban tree frogs' success as an invasive species throughout the Florida peninsula.

Innate immunity and antioxidant costs of low temperatures in native green treefrogs (Hyla cinerea) and invasive tropical Cuban treefrogs (Osteopilus septentrionalis)

Thermal tolerance plays a role in the geographic range over which different species can survive, and temperature fluctuations can affect amphibian physiology. We studied physiological costs associated with low temperatures in green treefrogs (Hyla cinerea), which are native to the United States, and tropical, non-native Cuban treefrogs (Osteopilus septentrionalis) that have invaded Florida. Specifically, we examined variation in innate immunity and skin antioxidant capacity. To complete the study, 107 treefrog tadpoles were raised through metamorphosis and, as young frogs, divided into a control group maintained at room temperature of approximately 24°C and an experimental group at approximately 8°C. Individuals in the low temperature group were placed in the cold temperatures for 6-8 hours per day for 14 days to simulate early fall nocturnal ambient temperatures in northern regions of states along the Gulf of Mexico in the United States. Cuban treefrogs had a significantly greater survival rate than green treefrogs in the control group, but there was no significant difference in survival between experimental groups. We also found that each species was negatively affected by low temperatures, with a decrease in bacterial killing ability and antioxidants on their skin, but the Cuban treefrogs were affected to a much greater extent. These findings suggest that the spread of Cuban treefrogs into areas north of their current invasive range may be slowed by physiological costs of low temperatures, but we do not expect significantly greater mortality rates associated with cold alone than treefrogs already occupying such a range.