Extinction Of Amphibian Species Research Articles

Reconstructing historical and contemporary disease dynamics: A case study using the California slender salamander

The fungal disease chytridiomycosis, caused by the pathogen Batrachochytrium dendrobatidis (Bd), has been implicated in the extirpation and extinction of amphibian species throughout the world. Recent Bd epizootics (i.e. epidemics in wildlife) have driven hundreds of species to near-extinction. Several species in California have been severely affected by Bd epizootics, but most work has focused on aquatic species. Our study focused on the most abundant and widespread terrestrial amphibian species in California, the California slender salamander, Batrachoseps attenuatus. This species is known to be infected by Bd, but little is known of its disease dynamics. We examined the effect of disease history on contemporary disease dynamics by combining retrospective tests for Bd emergence in museum specimens with contemporary field-collected infection data from the same locations. We found that Bd rapidly emerged in B. attenuatus and exhibited a non-linear pattern of spread throughout Northern California, and that modern-day persistence was negatively correlated with time since first detection of infection. To understand what factors are associated with Bd emergence, we correlated standard environmental variables (e.g. temperature, precipitation) from Bd-positive sites with Bd prevalence. We also compared and contrasted the degree of sociality between B. attenuatus populations that were recently Bd-infected with those that had a longer history of infection. We found that Bd infection in B. attenuatus was positively associated with distance to nearest lentic aquatic habitat, suggesting that aquatic carriers of Bd may be important in prevalence of pathogen within terrestrial B. attenuatus populations. Among our 14 field sites, we also found that recently infected populations had larger group sizes, after standardizing for population density, than populations that had been infected over multiple decades. This result suggests that sociality may facilitate disease spread in terrestrial hosts and that populations with longer exposure to this pathogen may evolve away from the ancestral condition of sociality.

Chytrid fungus infections in laboratory and introduced Xenopus laevis populations: assessing the risks for U.K. native amphibians

The chytrid fungus Batrachochytrium dendrobatidis (Bd) is notorious amongst current conservation biology challenges, responsible for mass mortality and extinction of amphibian species. World trade in amphibians is implicated in global dissemination. Exports of South African Xenopus laevis have led to establishment of this invasive species on four continents. Bd naturally infects this host in Africa and now occurs in several introduced populations. However, no previous studies have investigated transfer of infection into co-occurring native amphibian faunas. A survey of 27 U.K. institutions maintaining X. laevis for research showed that most laboratories have low-level infection, a risk for native species if animals are released into the wild. RT-PCR assays showed Bd in two introduced U.K. populations of X. laevis, in Wales and Lincolnshire. Laboratory and field studies demonstrated that infection levels increase with stress, especially low temperature. In the U.K., native amphibians may be exposed to intense transmission in spring when they enter ponds to spawn alongside X. laevis that have cold-elevated Bd infections. Exposure to cross-infection has probably been recurrent since the introduction of X. laevis, >20years in Lincolnshire and 50years in Wales. These sites provide an important test for assessing the impact of X. laevis on Bd spread. However, RT-PCR assays on 174 native amphibians (Bufo, Rana, Lissotriton and Triturus spp.), sympatric with the Bd-infected introduced populations, showed no foci of self-sustaining Bd transmission associated with X. laevis. The abundance of these native amphibians suggested no significant negative population-level effect after the decades of co-occurrence.

Environmental Refuge from Disease-Driven Amphibian Extinction

Species that are tolerant of broad environmental gradients may be less vulnerable to epizootic outbreaks of disease. Chytridriomycosis, caused by the fungus Batrachochytrium dendrobatidis, has been linked to extirpations and extinctions of amphibian species in many regions. The pathogen thrives in cool, moist environments, and high amphibian mortality rates have commonly occurred during chytridiomycosis outbreaks in amphibian populations in high-elevation tropical rainforests. In Australia several high-elevation species, including the armored mist frog (Litoria lorica), which is designated as critically endangered by the International Union for the Conservation of Nature (IUCN), were believed to have gone extinct during chytridiomycosis outbreaks in the 1980s and early 1990s. Species with greater elevational ranges disappeared from higher elevations, but remained common in the lowlands. In June 2008, we surveyed a stream in a high-elevation dry sclerophyll forest and discovered a previously unknown population of L. lorica and a population of the waterfall frog (Litoria nannotis). We conducted 6 additional surveys in June 2008, September 2008, March 2009, and August 2009. Prevalences of B. dendrobatidis infection (number infected per total sampled) were consistently high in frogs (mean 82.5%, minimum 69%) of both species and in tadpoles (100%) during both winter (starting July) and summer (starting February). However, no individuals of either species showed clinical signs of disease, and they remained abundant (3.25 - 8.75 individuals of L. lorica and 6.5-12.5 individuals of L. nannotis found/person/100 m over 13 months). The high-elevation dry sclerophyll site had little canopy cover, low annual precipitation, and a more defined dry season than a nearby rainforest site, where L. nannotis was more negatively affected by chytridiomycosis. We hypothesize this lack of canopy cover allowed the rocks on which frogs perched to warm up, thereby slowing growth and reproduction of the pathogen on the hosts. In addition, we suggest surveys for apparently extinct or rare species should not be limited to core environments.

Distribution and risk factors for spread of amphibian chytrid fungus Batrachochytrium dendrobatidis in the Tasmanian Wilderness World Heritage Area, Australia

Chytridiomycosis is an emerging infectious disease caused by the pathogen Batrachochytrium dendrobatidis (Bd) and is the cause of the decline and extinction of amphibian species throughout the world. We surveyed the distribution of Bd within and around the Tasmanian Wilderness World Heritage Area (TWWHA), a 1.38 million ha area of significant fauna conservation value, which provides the majority of habitat for Tasmania's 3 endemic frog species (Litoria burrowsae, Bryobatrachus nimbus and Crinia tasmaniensis). Bd was detected at only 1 (3%) of the 33 sites surveyed within the TWWHA and at 15 (52%) of the 29 sites surveyed surrounding the TWWHA. The relatively low incidence of the disease within the TWWHA suggests that the majority of the TWWHA is currently free of the pathogen despite the fact that the region provides what appears to be optimal conditions for the persistence of Bd. For all survey sites within and around the TWWHA, the presence of Bd was strongly associated with the presence of gravel roads, forest and < 1000 m altitude--factors that in this study were associated with human-disturbed landscapes around the TWWHA. Conversely, the presence of walking tracks was strongly associated with the absence of Bd, suggesting an association of absence with relatively remote locations. The wide distribution of Bd in areas of Tasmania with high levels of human disturbance and its very limited occurrence in remote wilderness areas suggests that anthropogenic activities may facilitate the dissemination of the pathogen on a landscape scale in Tasmania. Because the majority of the TWWHA is not readily accessible and appears to be largely free of Bd, and because Tasmanian frogs reproduce in ponds rather than streams, it may be feasible to control the spread of the disease in the TWWHA.

Amphibian chytridiomycosis: strategies for captive management and conservation

Dramatic declines and extinctions of amphibian species have occurred worldwide over the last three decades owing to the introduction of chytridiomycosis. This emerging infectious disease is caused by the chytrid fungus Batrachochytrium dendrobatidis, a virulent water‐borne pathogen of many amphibian species. It has caused epidemic waves of high mortality as it spread through susceptible wild populations in Australia, North, Central and South America, and New Zealand, and is now endemic in surviving populations in these continents and in Europe and Africa. The prevalence of chytridiomycosis in the international amphibian trade is high and import of infected frogs into zoos has caused disease epidemics in established amphibian collections. Management of disease spread requires effective national and international quarantine and control strategies. Although B. dendrobatidis is susceptible to a range of commonly used disinfectants, there is no universally effective treatment regime for infected amphibians. Zoological institutions can play a key role in preventing pathogen spread between captive facilities, and in disease surveillance, captive‐breeding and reintroduction programmes, to limit the impact of this formidable disease on wild amphibian populations.

The diversity of amphibian species in water bodies of Kozienice Forest

Abstract: In the years 2003–2005, the diversity of amphibian species in Kozienice Forest was analyzed. Thirteen species of amphibians were found in 91 different water habitats. The most common were Rana esculenta , R. temporaria and Bufo bufo, the rarest Triturus vulgaris , B. viridis and T. cristatus. We confirmed the presence of all species which had been found in this area in the beginning of 70s. Beside the check-list of amphibians of this area, we recognized their preferences for several important features of the studied water habitats. The most obvious, was the tendency of green frogs, for inhabiting large and stable water bodies. The differences in species diversity and relative abundance between Kozienice Landscape Park and other protected forests were discussed. Key words: amphibians, distribution, Kozienice Landscape Park, habitat preferences, species richness I NTRODUCTION Sudden extinctions of amphibian species and decline of their local populations have been observed for the last 20–30 years. Since early1990s, many studies have focused on global patterns of amphibian declines (Barinaga 1990, Wake 1991, Pechmann & Wilbur 1994). It is suspected that several interacting causes rather than one common reason have led amphibian populations and species to extinction. Six major hypotheses existing in the literature may be sorted into two categories. The first category indicates factors that directly interact with amphibian population, like land use changes, commercial over-exploitation, emerging infectious diseases and alien species. To the second category belong factors which indirectly affect amphibians: chemical pollutions, increased UV radiation and global climate change (Collins & Storfer 2003). Published papers have reported declining populations and extinction of amphibian species everywhere: in South and North America (Stebbins & Cohen 1995, Pounds et al. 1997, Lips 1998, 1999), in Australia (Laurance et al. 1996) and in Europe (Blab & Vogel 1999). It is well documented, particularly for Western Europe, that once common species have now become rare and live in isolated populations (Honegger 1978, Terhivuo 1981, Blab et al. 1984, Thielcke et al. 1991). In Poland, the dynamics of amphibian declines have not been so well documented as in West European countries. Nevertheless, in some areas this decline was well documented (Juszczyk 1987, Berger 2000, Rafinski & Tabasz 2001, Glowacinski & Rafinski 2003). For example, in Niepolomnice Forest, during twenty years, in the 70s and 80s of twentieth century, the number of amphibians was reduced by 90%, from 2000 to 150–300 individuals per one hectare (Glowacinski & Witkowski 1970, Witkowski 1978, Glowacinski 2003). Similarly, in agricultural landscape of Wielkopolska (Western Poland) during about ten years in the late 60s and early 70s the number of amphibians was reduced from 300 to dozen or so individuals per one hectare (Berger 1987, Rybacki & Berger 1997). Also in protected natural areas, population

Successful Recovery of Motility and Fertility of Cryopreserved Cane Toad (Bufo marinus) Sperm

The recent decline and extinction of amphibian species is a worldwide phenomenon without an identified cause or solution. Assisted reproductive technologies, including sperm cryopreservation, are required to manage endangered amphibian species and preserve their genetic diversity. This study on the Anuran amphibian (Bufo marinus) was undertaken to determine the feasibility of cryopreservation of amphibian sperm. Sperm suspensions for cryopreservation were prepared by macerating testes in cryoprotective additives of 10% (w/v) sucrose or 10% (w/v) sucrose containing either 10, 15, or 20% (v/v) glycerol or 10, 15, or 20% (v/v) dimethyl sulfoxide (Me2SO). Suspensions were then cooled to −85°C using a controlled rate cooler, stored in LN2, and thawed in air. The motility and fertilization rate of cryopreserved suspensions and unfrozen control suspensions in Simplified Amphibian Ringer were compared. Sucrose alone had no cryoprotective effect. All other treatments showed varying degrees of recovery of motility and fertilizing capacity. High rates of recovery of motility and fertilizing capacity were observed with 15% Me2SO (68.9 ± 3.8 and 60.5 ± 4.7%) and 20% glycerol (58.0 ± 5.9 and 81.4 ± 4.3%), respectively. Motility and fertilization rates were similar with Me2SO but diverged with glycerol as cryoprotectant. The data demonstrate the feasibility of using sperm cryopreservation with amphibian species.