The role of habitat in structuring Halipegus occidualis metapopulations in the green frog

The transmission dynamics of the trematode Halipegus occidualis in its definitive host, Rana clamitans, have been examined over a 5-yr period in a North Carolina pond. The breeding season of green frogs coincides with the period of worm recruitment, during which time male frogs are territorial and females show strong site fidelity. This site fidelity allows inferences to be made regarding the suitability of a particular habitat for worm transmission based on frog infection intensities within that habitat. Four foci of infection were identified in the pond by plotting worm infrapopulation size against site of host capture. Sites within infection foci are characterized by shallow water and emergent vegetation, factors favorable for overlapping distributions of the 4 hosts in the life cycle of H. occidualis. Consistent year-to-year worm prevalences and intensities, despite fluctuations in frog population size, are thought to be the result of a relatively constant proportion of the frog population being present in infection foci each year. Removal of worms from heavily infected frogs in the fifth year resulted in further heavy worm recruitment by treated frogs suggesting that site selection can predispose a frog to heavy infection. Further, the sum of removed parasites and those recruited after parasite removal by treated frog hosts was higher than worm infrapopulations observed in previous years, indicating that worm density regulates parasite infrapopulation size in heavily infected frogs.     

Echinostome infection in green frogs (Rana clamitans) is stage and age dependent

The increasing threat of emerging infectious diseases in both wildlife and humans has spurred interest in the causes of disease emergence, including the role of anthropogenic change. A prior field study of infection patterns in amphibians suggests that echinostome infection may be an emerging disease of green frogs Rana clamitans living in urbanized environments. We examined the impact of echinostome infection on green frog tadpoles at a wide range of developmental stages (Gosner stage 25–39). Echinostome infection was associated with green frog mortality rates of up to 40% in an early developmental stage, and none in later developmental stages. Tadpoles exposed to higher echinostome doses exhibited higher edema rates, a potential sign of compromised renal function. Histopathological analysis further supported the hypothesis that echinostome-induced tadpole mortality resulted from compromised renal function. Given that the timing of highest cercarial shedding can coincide with the most vulnerable stages of green frog tadpole development, echinostomes could significantly impact green frog survival in nature.     

Habitat distribution and predation on a western population of terrestrial Leiopelma (Anura: Leiopelmatidae) in the northern King Country,New Zealand

Abstract

A new population of terrestrial Leiopel‐matid frog was discovered in the Whareorino Forest, northern King Country, New Zealand, in 1991. Searches were carried out from June 1991 to December 1993 to determine the species present and to document variation in external morphology, habitat, and local distribution. These confirmed that a terrestrial frog resembling L. archeyi is present in the area, as well as Hochstetter's frog Leiopelma hochstetteri and the introduced Australian hylid frog Litoria aurea.

In Whareorino Forest, the terrestrial Leiopelma was mostly above 500 m altitude and L. hochstetteri above 350 m. The terrestrial Leiopelma occupies sites under rocks and logs in forest. It also occurs in vegetation, such as crown fern Blechnum discolor, tree fern Cyathea smithii, hook grass Uncinia uncinata, and rice grass Microlaena avenacea. Egg clusters of this frog were found in crown fern and tree fern, as well as under stones.

The terrestrial Leiopelma is susceptible to predation by Litoria aurea and rats. This is the first documented evidence of predation on Leiopelma on the New Zealand mainland. The future of this small remnant Leiopelma population is uncertain, and further investigation of the impact of anuran and mammalian predators is needed.     

Presence of the amphibian chytrid fungus Batrachochytrium dendrobatidis in threatened corroboree frog populations in the Australian Alps

Since the early 1980s, the southern corroboree frog Pseudophryne corroboree and northern corroboree frog P. pengilleyi have been in a state of decline from their sub-alpine and high montane bog environments on the southern tablelands of New South Wales, Australia. To date, there has been no adequate explanation as to what is causing the decline of these species. We investigated the possibility that a pathogen associated with other recent frog declines in Australia, the amphibian chytrid fungus Batrachochytrium dendrobatidis, may have been implicated in the decline of the corroboree frogs. We used histology of toe material and real-time PCR of skin swabs to investigate the presence and infection rates with B. dendrobatidis in historic and extant populations of both corroboree frog species. Using histology, we did not detect any B. dendrobatidis infections in corroboree frog populations prior to their decline. However, using the same technique, high rates of infection were observed in populations of both species after the onset of substantial population declines. The real-time PCR screening of skin swabs identified high overall infection rates in extant populations of P. corroboree (between 44 and 59%), while significantly lower rates of infection were observed in low-altitude P. pengilleyi populations (14%). These results suggest that the initial and continued decline of the corroboree frogs may well be attributed to the emergence of B. dendrobatidis in populations of these species.     

Transmission of Batrachochytrium dendrobatidis to wood frogs (Lithobates sylvaticus) via a bullfrog (L. catesbeianus) vector

Chytridiomycosis, an emerging infectious disease caused by the chytrid fungus Batrachochytrium dendrobatidis, threatens anuran populations worldwide. Effects of B. dendrobatidis on frog species are variable. Some species typically develop nonlethal infections and may function as carriers; others typically develop lethal infections that can lead to population declines. Nonlethal infections in the bullfrog (Lithobates catesbeianus) are well-documented. In contrast, recently metamorphosed wood frogs (L. sylvaticus) can die from chytridiomycosis. We conducted an ex-situ experiment between May and July 2010 to determine whether B. dendrobatidis-infected bullfrogs could transmit the fungus to wood frog tadpoles when the two species shared a body of water. We tested for B. dendrobatidis infections with quantitative polymerase chain reactions (qPCR) in a subsample of the wood frog tadpoles and in all metamorphosed wood frogs and compared risk of death of froglets exposed and unexposed to infected bullfrogs. We detected B. dendrobatidis sporadically in subsampled treatment tadpoles (nine of 90, 10%) and frequently in treatment froglets (112 of 113, 99.1%). Pooled risk of froglet death was higher (P<0.001) in treatment enclosures than in control enclosures. Our results indicate that, at the low infection loads bullfrogs tend to carry, swabbing for PCR analyses may underestimate prevalence of B. dendrobatidis in this species. We highlight bullfrog disease screening as a management challenge, especially in light of exotic bullfrog colonies on multiple continents and large-scale global trade in this species. We document the importance of quantifying lethal and sublethal effects of bullfrog vectors on B. dendrobatidis-susceptible species.     

Cryptosporidiosis associated with emaciation and proliferative gastritis in a laboratory-reared South African clawed frog (Xenopus laevis)

A 2-year-old emaciated female South African clawed frog (Xenopus laevis) was euthanized because of chronic weight loss. At necropsy, there was no evidence of bacterial, fungal or viral disease; however, the histopathologic findings indicated a proliferative gastritis and the presence of numerous cryptosporidial stages throughout the intestinal tract. Crytosporidial oocysts were present in the water taken from the aquarium housing the infected frog and were likely shed by the sick frog; however, the exact source of the oocysts could not be identified. Water samples from other frog aquaria in the facility did not contain cryptosporidial oocysts. Some Cryptosporidium species are important zoonotic pathogens and, to our knowledge, this is the first report of disease associated with Cryptosporidium infection in a laboratory Xenopus laevis.     

Unlikely Remedy: Fungicide Clears Infection from Pathogenic Fungus in Larval Southern Leopard Frogs (Lithobates sphenocephalus)

Amphibians are often exposed to a wide variety of perturbations. Two of these, pesticides and pathogens, are linked to declines in both amphibian health and population viability. Many studies have examined the separate effects of such perturbations; however, few have examined the effects of simultaneous exposure of both to amphibians. In this study, we exposed larval southern leopard frog tadpoles (Lithobates sphenocephalus) to the chytrid fungus Batrachochytrium dendrobatidis and the fungicide thiophanate-methyl (TM) at 0.6 mg/L under laboratory conditions. The experiment was continued until all larvae completed metamorphosis or died. Overall, TM facilitated increases in tadpole mass and length. Additionally, individuals exposed to both TM and Bd were heavier and larger, compared to all other treatments. TM also cleared Bd in infected larvae. We conclude that TM affects larval anurans to facilitate growth and development while clearing Bd infection. Our findings highlight the need for more research into multiple perturbations, specifically pesticides and disease, to further promote amphibian heath.     

Altitudinal distribution of chytrid (Batrachochytrium dendrobatidis) infection in subtropical Australian frogs

The disappearance of amphibian populations from seemingly pristine upland areas worldwide has become a major focus of conservation efforts in the last two decades, and a parasitic chytrid fungus, Batrachochytrium dendrobatidis, is thought to be the causative agent of the population declines. We examined the altitudinal distribution of chytrid infections in three stream‐dwelling frog species (Litoria wilcoxii, L. pearsoniana and L. chloris) in southeast Queensland, Australia, and hypothesized that if B. dendrobatidis were responsible for the disappearance of high‐altitude frog populations, infection prevalence and intensity would be greatest at higher altitudes. Overall, 37.7% of the 798 adult frogs we sampled were infected with B. dendrobatidis, and infections were found in all the populations we examined. Contrary to our initial hypothesis, we found no consistent evidence that high‐altitude frogs were more likely to be infected than were lowland frogs. Further, the intensity of fungal infections (number of zoospores) on high‐altitude frogs did not differ significantly from that of lowland frogs. Batrachochytrium dendrobatidis appears to be capable of infecting frogs at all altitudes in the subtropics, suggesting that all populations are at risk of decline when conditions favour disease outbreaks. We did find evidence, however, that chytrid infections persist longer into summer in upland as compared with lowland areas, suggesting that montane amphibian populations remain susceptible to disease outbreaks for longer periods than do lowland populations. Further, we found that at high altitudes, temperatures optimal for chytrid growth and reproduction coincide with frog metamorphosis, the life‐stage at which frogs are most susceptible to chytrid infections. While these altitudinal differences may account for the differential population‐level responses to the presence of B. dendrobatidis, the reason why many of southeast Queensland's montane frog populations declined precipitously while lowland populations remained stable has yet to be resolved.     

A genetic component of resistance to fungal infection in frog embryos

The embryo has traditionally been considered to completely rely upon parental strategies to prevent threats to survival posed by predators and pathogens, such as fungi. However, recent evidence suggests that embryos may have hitherto neglected abilities to counter pathogens. Using artificial fertilization, we show that among-family variation in the number of Saprolegnia-infected eggs and embryos in the moor frog, Rana arvalis, cannot be explained by maternal effects. However, analysed as a within-females effect, sire identity had an effect on the degree of infection. Furthermore, relatively more eggs and embryos were infected when eggs were fertilized by sperm from the same, compared with a different, population. These effects were independent of variation in fertilization success. Thus, there is likely to be a significant genetic component in embryonic resistance to fungal infection in frog embryos. Early developmental stages may show more diverse defences against pathogens than has previously been acknowledged.     

Neuropeptide Y (NPY)-like immunoreactive amacrine cells in retinas of frog and goldfish

Summary The distribution of neuropeptide Y (NPY)-like immunoreactivity in rat, rabbit, chick, frog and goldfish retinas was investigated by immunohistochemistry. Positive results were observed only in the frog and goldfish retinas. NPY immunoreactivity was associated with a small population of amacrine cell bodies in the inner nuclear layer and cell processes in the inner plexiform layer of both retinas. In the frog retina, three distinct layers containing immunoreactivity were observed in the inner plexiform layer. In contrast, the immunoreactivity in the same area of the goldfish retina was more or less separated into two layers. Convincing evidence could not be found for the co-existence of NPY-like material with other putative transmitter-like substances in the two retinas.Radioimmunoassay revealed the presence of small amounts of NPY-like immunoreactivity in the rabbit retina; the goldfish and frog retinas contained significantly more immunoreactive material. High performance liquid chromatography of the immunoreactive material in frog and goldfish retinas showed each retina containing different molecular forms of NPY-like proteins, neither of which resembled porcine NPY or PYY.The endogenous NPY-like material of the frog retina can be released by potassium depolarisation in a calciumdependent way. In view of all these data an NPY-like protein must now be considered a potential retinal transmitter.     

Population Patterns of a Riparian Frog (Rana swinhoana) Before and After an Earthquake in Subtropical Taiwan

We compared the population dynamics of a riparian ranid frog, Rana swinhoana, before (1996–1999) and after (1999–2001) a strong earthquake. This earthquake caused little disturbance to the vegetation and landscape of the study site but the stream and ponds dried up within a week. Nearly all frogs marked (1002 of 1004) before the earthquake had disappeared after the earthquake. Smaller, unmarked frogs began to appear in stream habitats about 9 mo after the earthquake, and the frog population was much smaller than it was before the earthquake. Population dynamics and temporal and spatial distribution of frogs before and after the earthquake correlated closely with the hydrology of the stream and ponds. The movement patterns of frogs before and after the earthquake were similar, suggesting frog behavior did not change in response to drastic changes in hydrology, and frogs continued to exhibit strong site-fidelity. Following the earthquake, stream water volume was much lower, especially in the summer, which allowed the normally winter-breeding frogs to breed year-round. Results demonstrate that a population of R. swinhoana can disappear suddenly as the result of a natural disturbance. We propose that anuran species that exhibit strong site-fidelity are particularly susceptible to extirpation of local populations because frogs may lack the behavioral plasticity to respond to sudden water depletion.     

Indications of recent changes in status in the British Isles of the frog (Rana temporaraia) and the toad (Bufo bufo)

Two surveys are described which were designed to provide information on changes in status in the British Isles of the frog ( Rana temporaria L.) and the toad ( Bufo bufo L.). Questionnaires were distributed asking for information and conclusions are based on replies referring to 1079 localities and 314 individual breeding sites. Replies indicated that the frog decreased slightly over most of the British Isles during the 1940s and 1950s, and suffered considerable declines over most of England throughout the 1960s. Moderate declines occurred in Scotland and Northern Ireland during the last half of the decade. Declines for the toad probably followed a similar pattern.
The garden pond was the only habitat in which either species increased. Both the frog and the toad decreased markedly in breeding sites on agricultural land in the early 1960s, but during the late 1960s declines were less severe.
The main reason for the declines has probably been loss of suitable wetland habitat due to sites being filled in, drained or physically modified in some way. Insecticides are only likely to have been harmful in sites where unusually high pollutant concentrations occurred. Other possible contributory factors are discussed and of these road mortality is perhaps the most important. Recent declines for the frog were significantly related to human population density.     

Feeding preferences in 2 disjunct populations of tiger snakes, Notechis scutatus (Elapidae)

Variations at both the genetic and phenotypic levels play animportant role in responses to food and food-related stimuli.Knowledge of such variations is crucial to understanding howpopulations adapt to changing environments. We investigatedthe dietary preferences of 2 tiger snake populations and comparedthe responses of diet-naive animals (laboratory-born neonates),diet-controlled animals (laboratory-reared juveniles), and naturaldiet–experienced animals (wild-caught adults) to visualand chemical cues from 6 prey types (mouse, skink, silver gull,chicken, shearwater, and frog). The mainland population inhabitsa swamp, feeds mostly on frogs, and suffers heavy predation.The second population inhabits a small nearby offshore islandwith no standing water (no frogs); feeds mostly on skinks, mice,and, as adults, silver gull chicks; and suffers no known predation.Although different prey are eaten in the 2 populations, adultwild-caught snakes from both populations showed a significantpreference for 3 types of prey (frog, mouse, and chick), irrespectiveof their natural diet. Neonates responded to all prey cues morethan they did to control stimuli in both populations. However,the island neonates showed significantly higher interest insilver gull chick stimuli (the main prey of the island adultsnakes) than did their mainland conspecifics. Laboratory-bredjuveniles displayed behavioral plasticity by significantly increasingtheir response to mice after being fed baby mice for 7 months.We conclude that genetic-based differences in food-related cuesare important in tiger snakes but that they are also capableof behavioral plasticity. Island adult and neonate snakes exhibitedresponses to prey types no longer consumed naturally (frog),suggesting that behavioral characters may have been retainedfor long periods under relaxed selection. Island neonates showeda strong interest in a novel prey item (silver gull). This resultcomplements previous work describing how island snakes havedeveloped the ability to swallow larger prey than usual, aswell as seemingly developing a taste for them.     

Habitat fragmentation causes bottlenecks and inbreeding in the European tree frog (Hyla arborea)

A genetic study of the European tree frog, Hyla arborea, in Denmark was undertaken to examine the population structure on mainland Jutland and the island of Lolland after a period of reduction in suitable habitat and population sizes. The two regions have experienced the same rate of habitat loss but fragmentation has been more severe on Lolland. Genetic variation based on 12 polymorphic DNA microsatellites was analysed in 494 tree frogs sampled from two ponds in Jutland and 10 ponds on Lolland. A significant overall deviation from Hardy-Weinberg expectations could be attributed to three ponds, all on Lolland. This was most probably caused by an inbreeding effect reducing fitness, which was supported by the observed significant negative correlation between larva survival and mean F(IS) value and mean individual inbreeding coefficient. A significant reduction in genetic variation (bottleneck) was detected in most of the ponds on Lolland. Population-structure analysis suggested the existence of at least 11 genetically different populations, corresponding to most of the sampled population units. The results indicated that the populations were unique genetic units and could be used to illustrate the migration pattern between newly established ponds arisen either by natural colonization of tree frogs or by artificial introduction. A high degree of pond fidelity in the tree frogs was suggested. A severe fragmentation process reducing population size and fitness within some of the populations probably caused the significant reduction in genetic variation of tree frog populations on Lolland.     

Presence of Batrachochytrium dendrobatidis in feral populations of Xenopus laevis in Chile

Batrachochytrium dendrobatidis (Bd) is a causal agent of disease and population decline of amphibian populations, and the extinction of several anuran species worldwide. Diverse hypotheses have been provided for the emergence of this fungus in different continents, ranging from global climate change to the vectoring of Bd via the international trade in amphibian species. In order to address these hypotheses, it is important to assess the current distribution of Bd in the context of introduced non-native amphibian species. We sampled several populations of the African clawed frog Xenopus laevis across its distribution in Chile in order to detect the presence of B. dendrobatidis and evaluate the role of this frog as a potential vector. In three of ten sites sampled, individuals harbored B. dendrobatidis infection, with an overall prevalence of infection across the studied populations of 24% (14 positive out of 58 analyzed specimens). The rapid spread exhibited by this frog within Chile suggests that transpecific transmission of the pathogen is possible, perhaps jeopardizing native species. This finding indicates the urgent need to establish long-term monitoring population programs in order to allow early detection disease-driven changes in the sizes of native populations, allowing the prompt application of conservation practices.     

Phylogeography of the rice frog, Fejervarya multistriata (Anura: Ranidae), from China based on mtDNA D-loop sequences

The rice frog, Fejervarya multistriata, is an amphibian widely distributed in China. In this study, we sampled the species across its distributional area in China and sequenced the mtDNA D-loop to investigate the genetic diversity and geographical pattern of the frog population. The results revealed 38 haplotypes in the population, with K2P values varying from 0.19% to 4.22%. Both a phylogenetic analysis and a nested clade analysis (NCA) detected two geographically isolated lineages respectively distributed around the Yangtze drainage (Yangtze lineage) and the south of China (southern lineage). NCA inferred a contiguous range expansion within the Yangtze lineage and allopatric fragmentation within the southern lineage, which might be partly due to the limited samples from this lineage. Accordingly, Fu's Fs test also indicated a population expansion after glacial movement. Therefore, we assumed that the species history responding to glacial events shaped the present population pattern of F. multistriata on the Chinese mainland.     

Microsatellite DNA markers for the Chinese wood frog (Rana chensinensis) and tests for their cross-utility in 15 ranid frog species

We developed 22 microsatellite markers for the Chinese wood frog (Rana chensinensis) to study the impact of landscape features on its population structure. Thirty‐four individuals from one breeding site were examined and 14 loci were polymorphic. The number of alleles, expected heterozygosity and observed heterozygosity varied from two to 14, from 0.0833 to 0.9118, and from 0.1376 to 0.8667, respectively. Cross‐species amplification was tested for 15 ranid frog species. The Plateau brown frog, Rana kukunoris (n = 23), was successfully amplified at 18 loci, and 15 were polymorphic with number of alleles varying from two to 18. Ten other species were also amplified at a limited number of loci.     

The population ecology of a self-maintaining colony of the Common frog (Rana temporaria)

A population of the Common frog ( Rana temporaria L.) which was self-maintaining for food, subject to the minimum of interference and derived from one batch of spawn, was kept for nearly seven years in an enclosure of 65 m² in which cover was provided by a pile of humified plant litter and by herbaceous vegetation. The seasonal pattern of activity, and observations on feeding and other aspects of behaviour are described. Hibernation took place in the plant litter when the only water available was in concrete pools up to 18 cm in depth, but there was evidence of preference for an underwater site for hibernation after a well vegetated concrete pond 50 cm deep had been provided. Individuals which could be readily observed were found to adopt fixed resting places during the summer. Breeding first occurred at the age of three years. Censuses made possible by aggregation for this purpose and also, in the last winter of the study for hibernation under water, indicated a population of 26 individuals at the age of three years, falling to 16 at the age of six years. A second cohort raised a year after the main population and under the same environmental conditions was eliminated: the reason for the failure of any of its members to survive is discussed. A provisional estimate is made of the population metabolism during the latter part of the study and a comparison is made with that of small homeotherms. Attention is drawn to the advantages of the low metabolic rate permitted by poikilothermy for small insectivorous land vertebrates.     

Characterization of a virion protein kinase as a virus-specified enzyme.

Antibodies which completely inhibited the enzymatic activity of the protein kinase associated with virions of frog virus were obtained by immunization of rabbits with the purified enzyme. This inhibition provided a specific probe for the frog virus protein kinase, since this antiserum had no inhibitory effect on a variety of other protein kinases, including the activity of uninfected cells, or the protein kinase associated with vesicular stomatitis virus or vaccinia virus cultivated in the same cell line as frog virus. The frog virus protein kinase was characterized as a virus-specified protein on the basis of the following observations: (a) the virion protein kinase was antigenically distinct from essentially all of the protein kinase expressed in uninfected cells; (b) following infection by frog virus more than a 15-fold increase was detected in the specific activity of intracellular protein kinase and most of this activity was antigenically related to the virion enzyme; (c) when frog virus was grown in cells derived from widely different species, the antigenic and biochemical specificities of the virion protein kinase remained identical; and (d) screening of cells infected with different temperature-sensitive mutants of frog virus indicated that certain viral mutants failed to synthesize this protein kinase when cultivated at the nonpermissive temperature.