Native Treefrogs Research Articles

Experimental evaluation of how biological invasions and climate change interact to alter the vertical assembly of an amphibian community.

While biotic-abiotic interactions are increasingly documented in nature, a process-based understanding of how such interactions influence community assembly is lacking in the ecological literature. Perhaps the most emblematic and pervasive example of such interactions is the synergistic threat to biodiversity posed by climate change and invasive species. Invasive species often out-compete or prey on native species. Despite this long-standing and widespread issue, little is known about how abiotic conditions, such as climate change, will influence the frequency and severity of negative biotic interactions that threaten the persistence of native fauna. Treefrogs are a globally diverse group of amphibians that climb to complete life-cycle processes, such as foraging and reproduction, as well as to evade predators and competitors, resulting in frog communities that are vertically partitioned. Furthermore, treefrogs adjust their vertical position to maintain optimal body temperature and hydration in response to environmental change. Here, utilizing this model group, we designed a novel experiment to determine how extrinsic abiotic and biotic factors (changes to water availability and an introduced predator, respectively) interact with intrinsic biological traits, such as individual physiology and behaviour, to influence treefrogs' vertical niche. Our study found that treefrogs adjusted their vertical niche through displacement behaviours in accordance with abiotic resources. However, biotic interactions resulted in native treefrogs distancing themselves from abiotic resources to avoid the non-native species. Importantly, under altered abiotic conditions, both native species avoided the non-native species %- more than they avoided their native counterpart. Additionally, exposure to the non-native species resulted in native species altering their tree climbing behaviours by and becoming more vertically dynamic to avoid the non-native antagonist. Our experiment determined that vertical niche selection and community interactions were most accurately represented by a biotic-abiotic interaction model, rather than a model that considers these factors to operate in an isolated (singular) or even additive manner. Our study provides evidence that native species may be resilient to interacting disturbances via physiological adaptations to local climate and plasticity in space-use behaviours that mediate the impact of the introduced predator.

Non‐native fish facilitate non‐native snails and alter food web structure in experimental pond communities

Abstract Contemporary ecosystems commonly support multiple non‐native species, which can alter community structure and directly or indirectly interact with one another. Novel interactions between invasive species can result in the facilitation or suppression of one or both invaders, making it important to understand the underlying mechanisms that affect invasion outcomes. Goldfish Carassius auratus and Chinese mystery snails Cipangopaludina chinensis have been introduced widely through the aquarium trade and co‐occur in their non‐native ranges. We used an outdoor mesocosm experiment to assess separate and combined effects of goldfish and mystery snails on urban pond community structure and to investigate whether goldfish and mystery snails affected one another positively, neutrally or negatively. We predicted that the distinct trophic levels of each species and the anti‐predator traits of mystery snails would lead to positive interactions between invaders and synergistic effects on the aquatic community. Goldfish directly increased turbidity and decreased filamentous algae, zooplankton, juvenile native snails and survival of amphibians via consumptive effects. Goldfish indirectly increased periphyton, phytoplankton and body size of surviving native green frogs Lithobates clamitans through trophic cascades and/or release from competition. Mystery snails had more subtle effects including reducing growth rates of native grey tree frogs Hyla versicolor, likely through competitive interactions. With goldfish present, mystery snails showed increased reproductive success (higher biomass of juveniles), likely due to indirect competitive release from other herbivores. In contrast to their effects on native snails, goldfish did not consume juvenile mystery snails, likely due to their unique traits (e.g. large size and shell thickness). Mystery snails slightly reduced goldfish growth but did not affect their survival. These results suggest unidirectional facilitation between invaders via indirect changes in the food web. Overall, our study found strong direct and indirect effects of invasive aquarium species, particularly goldfish, and provides experimental support for the invasional meltdown hypothesis within urban waterbodies, which are especially prone to invasions. Read the free Plain Language Summary for this article on the Journal blog.

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.

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.

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.

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.

Hydric Balance and Locomotor Performance of Native and Invasive Frogs

An animal’s physiology should be closely adapted to its environment to optimize organismal function, so physiological traits may be mismatched when animals are introduced to new locations. For introduced amphibians, mismatched traits involving hydric balance or performance across hydric states could have profound impacts on their abundance and distribution, and thus their invasion success. We examined susceptibility to dehydration in invasive Cuban treefrogs (Osteopilus septentrionalis) and two sympatric native treefrogs (Hyla spp.) in Florida, USA, by measuring rates of evaporative water loss, rates of water uptake, and sensitivity of locomotor performance to dehydration. Of the three species, Cuban treefrogs were the most susceptible to dehydration by experiencing the highest rate of evaporative water loss and lowest rate of water uptake. Green treefrogs (H. cinerea) were the most resistant to dehydration by losing water the slowest and gaining water the fastest, and squirrel treefrogs (H. squirella) were intermediate in rates of water loss and uptake. Dehydrating frogs by 20% of their fully hydrated body masses affected the locomotor performance of all species by decreasing maximum jump lengths, decreasing speed, and increasing successive jump lengths. The maximum jump lengths of Cuban treefrogs and green treefrogs were more sensitive to dehydration than those of squirrel treefrogs. Despite this sensitivity, Cuban treefrogs still outperformed both native species in maximum jump length and speed, even when controlling for body size. Consequently, the performance of dehydrated Cuban treefrogs was similar to that of fully hydrated native treefrogs. Our results suggest that Cuban treefrogs are more susceptible to dehydration and its effects than several native competitors; however, they may be able to at least partly compensate for these effects with their large body size, superior locomotor performance, and strong affinity for refugia. Our findings highlight different strategies used by frogs to maintain water balance and suggest that Cuban treefrog densities may be higher in areas with greater moisture availability and habitat complexity, including urban and densely forested areas. Native treefrogs may experience stronger competition and predation from Cuban treefrogs in these areas, which supports anecdotal reports of native frog declines.

Lack of Behavioral and Chemical Interference Competition for Refuges among Native Treefrogs and Invasive Cuban Treefrogs (Osteopilus septentrionalis)

The introduction of a novel competitor can dramatically alter community dynamics, and competition-mediated impacts often result from biological invasions. Interference competition can be especially problematic as a source of methodological bias for studies seeking to evaluate population and community-level impacts of invasive species. We used polyvinyl chloride (PVC) refugia to conduct laboratory trials to determine whether behavioral or chemical cues of invasive Cuban treefrogs (Osteopilusseptentrionalis) interfere with artificial refuge use by conspecifics or treefrogs native to Florida (USA). We found no evidence of behavioral or chemical competition for refuges by Cuban treefrogs or native treefrogs. The inability of native treefrogs to avoid chemical cues from Cuban treefrogs, despite living sympatrically with the invasive treefrogs for 10–20 years, has important implications for predation risk.

Establishment of the exotic invasive Cuban treefrog (Osteopilus septentrionalis) in Louisiana

The Cuban treefrog, Osteopilus septentrionalis, is native to Cuba, the Bahamas, and the Cayman Islands, and is invasive in areas where it has been introduced and established in the Caribbean as well as Florida. Despite repeated occurrences in several states over many years, it was not believed that Cuban treefrogs had successfully established outside of Florida in the mainland United States. From mid-September to mid-November 2017, we captured and removed 367 Cuban treefrogs in just four surveys in New Orleans, Louisiana. The impacts of this population on native treefrogs in this area is unknown but possibly severe as indicated by the paucity of observations of native treefrogs during our surveys. Eradication of this seemingly established population is improbable, but continued surveys will facilitate learning about the ecology and genetics of this novel population.

The effect of newt toxin on an invasive snail

Invasive species are well documented to impact native species where they are introduced. In the Santa Monica Mountains, a native species of amphibian, the California newt (Taricha torosa) possesses a neurotoxin, tetrodotoxin (TTX) that is considered a chemical defense against predation but also appears to facilitate ecological processes and specifically affect freshwater macroinvertebrate behavior. A recently introduced invasive species, the New Zealand mud snail (Potamopyrgus antipodarum), is known to negatively affect ecosystems it invades and means to control its proliferation once introduced are limited. Given the ecological role of newt neurotoxin, we hypothesized that TTX may impact P. antipodarum behavior and tested its effects upon snail movement in laboratory assays and in-stream experiments. When snails were exposed to ecologically realistic TTX concentrations and newt chemical cues that contain TTX they moved significantly less and distance was significantly reduced relative to controls. In a natural stream, significantly more P. antipodarum moved out of areas exposed to newt chemical cues relative to snails in the presence of native tree frog cues (Pseudacris cadaverina). Our results suggest that California newts may help limit the spread of P. antipodarum in streams where T. torosa is both able to persist and possess adequate chemical defenses.

Toxic, invasive treefrog creates evolutionary trap for native gartersnakes

Possession of unique defensive toxins by nonindigenous species may increase the likelihood of creating evolutionary traps for native predators. We tested the hypothesis that nonindigenous, toxic Cuban Treefrogs (Osteopilus septentrionalis) have created an evolutionary trap for native, generalist snakes. Additionally, we explored the possibility that populations of snakes that co-occur with Cuban Treefrogs have responded in ways that allow them to escape potential trap dynamics. To evaluate a potential fitness cost of consuming Cuban Treefrogs, we monitored growth of 61 wild-caught Common Gartersnakes (Thamnophis sirtalis) fed exclusive diets of either Cuban Treefrogs, native Green Treefrogs (Hyla cinerea), or native Golden Shiners (Notemigonus crysoleucas). Snakes in the Cuban Treefrog diet treatment gained less than half the mass of those consuming native prey, and Cuban Treefrogs were significantly less digestible than native prey. There was no difference in the response of gartersnakes to prey scent cues of Cuban Treefrogs and Green Treefrogs. Our results indicate that Cuban Treefrogs likely represent an evolutionary trap for snakes because consumption of these frogs carries fitness costs, yet snakes fail to recognize this prey as being costly. We found no difference in growth or response to prey cues between snakes from invaded and non-invaded regions, suggesting snakes have not responded to escape trap dynamics. Interactions of native snakes and Cuban Treefrogs support the idea that introduced species with novel toxins may increase the likelihood of evolutionary trap formation.

PREDATION ON NATIVE ANURANS BY INVASIVE VERTEBRATES IN THE ATLANTIC RAIN FOREST, BRAZIL

Anurans are usually preyed upon by other vertebrates, but in a few cases higher vertebrates serve as food for anuran species. This complexity in predator-prey interactions makes predicting the impacts of interactions difficult, especially when we are dealing with novel interactions imposed by non-native species. Introduced predators may have dramatic effects on resident species, which have not co-evolved with the introduced ones, since they provide a new environmental stress. On the other hand, the scarcity of studies and our consequent lack of understanding prevent us from taking the actions necessary to protect the native fauna into megadiverse places. Therefore, in the present paper we intent to provide new data on novel predator-prey interactions involving native and non-native species in the Brazilian Atlantic Rain Forest. In the first predatory event an individual of Rattus rattus was observed attempting to prey on two individuals of Rhinella icterica . In the second predatory event a tadpole of the native tree frog Hypsiboas sp. was found in the stomach contents of an individual of Micropterus salmoides . Non-native predators are one of the causes for amphibian population declines worldwide and the negative impacts of introduced vertebrates are probably more significant than we can detect. Additionally, in Brazil, information about the impacts caused by introductions of non-native species is accumulating slowly. Therefore, basic bits of evidence, as reported here, are necessary and may serve as a starting point for future investigations that explore the novel interactions and negative impacts caused by invasive species. We must improve our knowledge base and provide data regarding non-native predator-prey interactions with a view to clarify their biological aspects and to enable species conservation.

Raising a racket: invasive species compete acoustically with native treefrogs

Environmental noise is increasing worldwide, limiting the space available for species to send and receive important acoustic information. Many invasive species produce acoustic signals that alter the spectrotemporal characteristics of available signalling space. This provides an opportunity to test ideas about competitive exclusion by quantifying whether species with shared requirements for acoustic resources will become excluded or partition resource use to permit coexistence. We conducted a field playback experiment to test whether native treefrogs (green treefrogs, Hyla cinerea; pine woods treefrogs, Hyla femoralis) modify their acoustic behaviour to minimize acoustic competition from chorus noise of the invasive Cuban treefrog, Osteopilus septentrionalis. We demonstrate that noise from an invasive species differentially affects the vocal behaviour of native species. Those with similar calls (H. cinerea) shortened calls, called louder and persisted calling in response to masking stimuli while those with different calls (H. femoralis) did not modify behaviour. This evidence suggests that acoustic competition by invasive O. septentrionalis has altered the acoustic community structure, identifying acoustic competition as a mechanism by which invasive species can impact communities. Furthermore, these results broaden the concept of noise pollution, demonstrating fitness-relevant consequences of noise produced by invasive species.

Quantifying Anuran Microhabitat Use to Infer the Potential for Parasite Transmission between Invasive Cane Toads and Two Species of Australian Native Frogs

Parasites that are carried by invasive species can infect native taxa, with devastating consequences. In Australia, invading cane toads (Rhinella marina) carry lungworm parasites (Rhabdias pseudosphaerocephala) that (based on previous laboratory studies) can infect native treefrogs (Litoria caerulea and L. splendida). To assess the potential of parasite transmission from the invader to the native species (and from one infected native frog to another), we used surveys and radiotelemetry to quantify anuran microhabitat use, and proximity to other anurans, in two sites in tropical Australia. Unsurprisingly, treefrogs spent much of their time off the ground (especially by day, and in undisturbed forests) but terrestrial activity was common at night (especially in anthropogenically modified habitats). Microhabitat overlap between cane toads and frogs was generally low, except at night in disturbed areas, whereas overlap between the two frog species was high. The situations of highest overlap, and hence with the greatest danger of parasite transmission, involve aggregations of frogs within crevices by day, and use of open ground by all three anuran species at night. Overall, microhabitat divergence between toads and frogs should reduce, but not eliminate, the transmission of lungworms from invasive toads to vulnerable native frogs.

Impacts of acoustic competition between invasive Cuban treefrogs and native treefrogs in southern Florida

The natural acoustic environment has undergone substantial changes over the past century due to human activities, creating novel soundscapes. Much research has focused on the impacts of anthropogenic noise on acoustic communication, including noise from transportation, construction, energy development, and defense. The impact of acoustic invasive species has been largely overlooked in bioacoustic studies on the behavioral and ecological consequences of noise. We conducted a passive monitoring experiment and a playback experiment to quantify the impact of invasive Cuban treefrog (Osteopilus septentrionalis) acoustic signals on the acoustic environment and on native treefrog acoustic behavior. Our results show that Cuban treefrog chorus altered the soundscape in Everglades National Park and affected the acoustic behavior of native treefrogs. Collectively, these results suggest that acoustic invasive species are important yet rarely considered sources of noise that can have ecological consequences at scales ranging from the individual to the ecosystem.

Competing tadpoles: Australian native frogs affect invasive cane toads (Rhinella marina) in natural waterbodies

AbstractThe cane toad (Rhinella marina) is one of the most successful invasive species worldwide, and has caused significant negative impacts on Australian fauna. Experimental work in the laboratory and in mesocosms has shown that tadpoles of native frogs can affect survival, size at metamorphosis and duration of larval period of cane toad tadpoles. To test if these effects occur in nature, we conducted a field experiment using two temporary ponds where we set up enclosures with tadpoles of native green tree frogs (Litoria caerulea) and cane toads in treatments with a range of densities and combinations. The presence of green tree frog tadpoles significantly decreased the growth rate of toad tadpoles and increased the duration of their larval period in both ponds; in one pond, frog tadpoles also significantly reduced the body length and mass of metamorph toads. Toad tadpoles did not have any significant negative effects on green tree frog tadpoles, but there was strong intraspecific competition within the latter species: increased frog tadpole density resulted in increased larval period and reduced survival, growth rate and size at metamorphosis for frogs at one or both ponds. Our results are encouraging for the possibility of using native frogs as one component of an integrated approach to the biological control of cane toads.

Benefits and costs of using a lungworm parasite to control invasive toads in Australia

Pizzatto & Shine (2012) noted the serious impacts that the introduced cane toad Rhinella marina has caused to its predators in Australia. The toad’s range is expanding at an increasing rate and additional negative consequences are predicted. Control measures have been ineffective or in some cases have not been tried. Female toads have a very high fecundity, and the species has a high potential growth rate. High removal rates of the toad population are needed to eliminate the species, suggesting that physical removal is not practical (Shine & Doody, 2010). One approach to controlling the toad species is biological control, which has been effective in some cases in Australia and elsewhere (Saunders et al., 2010). Biological control usually involves introduction of a species that in its native range controls the population of the pest species. However, introducing an exotic species as a biocontrol agent can have negative effects on nontarget species and potentially on ecosystem function (Simberloff & Stiling, 1996). Use of a native species as a biological control agent eases these concerns, but may involve a protocol to increase the abundance and distribution of a native control agent. In the case of the cane toad, one goal of biocontrol can be slowing the rate of expansion. Individuals at the leading edge of expansion have greater locomotor endurance, and the authors suggest that this may be due to escape from a lungworm parasite that infects toads behind the leading edge. Therefore, the authors test aspects of a general hypothesis that posits that lungworm parasites can be used as a biocontrol agent to slow the toads’ advance. This may not be an entirely satisfactory solution, but slowing the toads’ advance might buy time to develop other ways to control the species’ numbers. As the lungworm is already present in the toads and likely was present in the toads when they were introduced to Australia in 1935, it is not considered an exotic species. The authors suggest that one way to increase the prevalence of lungworm infection is to infect a native tree frog species, Litoria caerulea, which does not seem to be negatively affected by the parasite. They also propose three primary assumptions necessary for biocontrol to work in this case: the parasite does not harm the tree frogs, the tree frogs can maintain an infection over the long term, and infective larvae of the parasite can be transmitted to cane toads and reduce viability of the toads. They test aspects of these assumptions in their paper. Pizzatto and Shine showed that the tree frogs were infected at a 50% rate at the end of the experiment, and this was after placing the lungworm in the mouths of the frogs. All parasite-exposed frogs survived, and their growth rate was not different from that of uninfected controls. It would be important to compare the growth of infected frogs and uninfected frogs as the ‘parasite-exposed’ treatment apparently contained frogs that were not infected or had cleared the infection. Of those frogs that were infected, they had on average a low intensity (1.67 parasites per frog). It is unclear that this intensity would have the desired effect of transmission of larvae to toads. To test for transmission to the toads, lungworm larvae were put in boxes housing five toads. About half of the toads were infected under these laboratory conditions. In terms of fitness effects on the toads, there was no survival difference between infected and uninfected, no difference in body mass and no difference in sprint speeds. The authors did find that toads exposed to lungworms had lower stamina than did controls. Laboratory conditions are likely to maximize transmission of parasites as toads were under high density conditions, and their movements were constrained. However, under these conditions, parasite prevalence in frogs and toads averaged 50%. Importantly, only minor fitness effects were seen in the toads. Based on these results, it seems doubtful that control would be effective in nature. There are other reasons to be skeptical that biocontrol would be effective in this case. Is the lungworm a factor in population control in other parts of the toads’ range where prevalence is high? If not, why would it be expected to work bs_bs_banner

Is Typhoid Mary a good role model?

Cane toads, Bufo marinus, are among the iconic poster children of invasive species, in part thanks to Mark Lewis’s 1988 Australian documentary, ‘Cane Toads: An Unnatural History’, and subsequent follow-up, ‘Cane Toads: The Conquest’. Unfortunately, the conquest in his latest video refers to what the cane toads have achieved, not the Australians’ efforts to control them, despite the impressive research program of Rick Shine and his colleagues at the University of Sidney, among others. In this issue’s featured paper, Pizzatto & Shine (2012) show that a lungworm parasite of the invasive cane toad, apparently brought to Australia along with the toad, can infect native green tree frogs, Litoria caerulea, with no evident detrimental effect on the frogs. These frogs can maintain the infection for up to 120 days postexposure, and infective lungworm larvae in the native frogs’ feces can then infect cane toads, substantially reducing their stamina. This leads to the intriguing suggestion that biological control of the cane toad could be undertaken by deliberately infecting these native frogs, which could then disseminate the lungworm to the cane toads, as a sort of ‘Typhoid Mary’ – an asymptomatic carrier of the pathogen that, while remaining healthy, spreads disease to others. The authors are not ready to advocate this approach in this system, ‘except in areas of high conservation value where toads are likely to have major impacts’, primarily on the grounds of possible undetected effects on green tree frog viability and secondarily on animal welfare grounds – although if, in fact, the parasite has no effect on green tree frogs, it is not clear how infecting them is imposing suffering. A more important reason to avoid the ‘Typhoid Mary’ approach in this case would seem to be because a close relative of the green tree frog, the splendid tree frog (Litoria splendida), has been found to be very sensitive to this lungworm parasite, at least in laboratory trials (Pizzatto & Shine, 2011a). I wonder if the likelihood of spread to L. splendida by deliberately infected L. caerulea would actually be greater than spread to cane toads, considering the two native frogs are congeners. The concept is certainly novel, and we need novel ways to control invasive pests. However, this approach, while using a native species to spread the parasite, ultimately depends on the use of an exotic organism. Although it is true that many parasites and parasitoid insects are quite host specific, unfortunately, this is not always the case. A parasitoid fly introduced as a biological control agent for gypsy moth and other pest Lepidoptera was subsequently found to impact populations of several native giant silk moth species in North America (Boettner, Elkinton & Boettner, 2000). Other examples of negative effects of biological control agents are cited by Howarth (1991), Simberloff & Stiling (1996) and Barratt et al. (2010). Current regulations emphasize the need for host specificity of any introduction, and concern for non-target impacts is more and more a concern in the regulatory environment (Hajek, McManus & Junior, 2007; Barratt et al., 2010). The cane toad is also an iconic poster child for biological control gone wrong, and in our efforts to control it, we must ensure that things are not made worse – if that is possible. Typhoid Mary unknowingly spread the bacteria that cause typhoid fever to other members of her own species, as a rather unsanitary cook to a whole series of human families. A possible approach in the cane toad system might be to take heavily infected cane toads and release them at the invasion front (where the lungworm is often absent), or otherwise enhance the level of lungworm parasites, if this can be done in a way that would not significantly increase the toad population – perhaps by releasing small infected metamorphs that would likely be cannibalized by larger cane toads (Pizzatto & Shine, 2011b). So far, efforts to identify a truly cane toad-specific pathogen for use as a biological control agent have been unsuccessful, as have been efforts to induce autoimmunity and disrupt metamorphosis (Pallister et al., 2011). Alarm pheromones and translocation of parasitic lungworms to the invasion front may provide new tools in the management of this damaging pest species (Saunders et al., 2010). Unfortunately, at present, a truly effective and safe ‘integrated toad management’ program still seems elusive.

Using Combined Morphological, Allometric and Molecular Approaches to Identify Species of the Genus Raillietiella (Pentastomida)

Taxonomic studies of parasites can be severely compromised if the host species affects parasite morphology; an uncritical analysis might recognize multiple taxa simply because of phenotypically plastic responses of parasite morphology to host physiology. Pentastomids of the genus Raillietiella are endoparasitic crustaceans primarily infecting the respiratory system of carnivorous reptiles, but also recorded from bufonid anurans. The delineation of pentastomids at the generic level is clear, but the taxonomic status of many species is not. We collected raillietiellids from lungs of the invasive cane toad (Rhinella marina), the invasive Asian house gecko (Hemidactylus frenatus), and a native tree frog (Litoria caerulea) in tropical Australia, and employed a combination of genetic analyses, and traditional and novel morphological methods to clarify their identity. Conventional analyses of parasite morphology (which focus on raw values of morphological traits) revealed two discrete clusters in terms of pentastome hook size, implying two different species of pentastomes: one from toads and a tree frog (Raillietiella indica) and another from lizards (Raillietiella frenatus). However, these clusters disappeared in allometric analyses that took pentastome body size into account, suggesting that only a single pentastome taxon may be involved. Our molecular data revealed no genetic differences between parasites in toads versus lizards, confirming that there was only one species: R. frenatus. This pentastome (previously known only from lizards) clearly is also capable of maturing in anurans. Our analyses show that the morphological features used in pentastomid taxonomy change as the parasite transitions through developmental stages in the definitive host. To facilitate valid descriptions of new species of pentastomes, future taxonomic work should include both morphological measurements (incorporating quantitative measures of body size and hook bluntness) and molecular data.

Range Expansion and Food Habits of Rana nigromaculata Introduced to Hokkaido, Japan

Abstract: A field survey was made in 2006 for the exotic black-spotted pond frogs Rana nigromaculata in central Hokkaido, northern Japan. The result suggested a prominent range expansion of this frog since the previous survey in 1997. Examinations of stomach contents from 140 frogs yielded 662 prey items that almost entirely consisted of invertebrate preys, such as lepidopteran larvae, water striders (Gerridae), and spiders (Araneae). The result suggests a fairly little impact, if any, of this accidentally introduced frog upon the native tree frog Hyla jponica through direct predation.