Olpidium gregarium, a chytrid fungus affecting rotifers populations in Rio Grande Reservoir, São Paulo State, Brazil

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Endemic infection of the amphibian chytrid fungus in a frog community post-decline

The chytrid fungus Batrachochytrium dendrobatidis has been implicated in the decline and extinction of numerous frog species worldwide. In Queensland, Australia, it has been proposed as the cause of the decline or apparent extinction of at least 14 high-elevation rainforest frog species. One of these, Taudactylus eungellensis, disappeared from rainforest streams in Eungella National Park in 1985-1986, but a few remnant populations were subsequently discovered. Here, we report the analysis of B. dendrobatidis infections in toe tips of T. eungellensis and sympatric species collected in a mark-recapture study between 1994 and 1998. This longitudinal study of the fungus in individually marked frogs sheds new light on the effect of this threatening infectious process in field, as distinct from laboratory, conditions. We found a seasonal peak of infection in the cooler months, with no evidence of interannual variation. The overall prevalence of infection was 18% in T. eungellensis and 28% in Litoria wilcoxii/jungguy, a sympatric frog that appeared not to decline in 1985-1986. No infection was found in any of the other sympatric species. Most importantly, we found no consistent evidence of lower survival in T. eungellensis that were infected at the time of first capture, compared with uninfected individuals. These results refute the hypothesis that remnant populations of T. eungellensis recovered after a B. dendrobatidis epidemic because the pathogen had disappeared. They show that populations of T. eungellensis now persist with stable, endemic infections of B. dendrobatidis.

Landscape context influences chytrid fungus distribution in an endangered European amphibian

Wildlife disease is an emerging threat to biodiversity. The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis, has been documented in over 500 amphibian species globally. Understanding conditions under which amphibians are vulnerable to Bd is important for evaluating species risk and developing surveillance strategies. Here, we investigate the spatial distribution of Bd infection in the ephemeral pond-breeding yellow-bellied toad Bombina variegata, a species of high conservation concern in the European Union. We sampled 550 toads from 60 ponds in a traditional agricultural landscape in Southern Transylvania, Romania. Overall, Bd prevalence was low in B.variegata, but infected toads were widely dispersed through the landscape and were found in a quarter of all sampled ephemeral ponds. At the pond level, increased Bd occurrence was associated with short distances to perennial water sources and high forest cover. These findings suggest that perennial water sources may act as source habitat for Bd, with amphibian movements resulting in Bd spillover into ephemeral ponds. Increased Bd occurrence in ponds surrounded by high levels of forest cover is likely related to cooler and wetter conditions that are more favourable for Bd. Throughout the study landscape, patchy environmental suitability for Bd appears to restrict the pathogen to a subset of B.variegata habitat. Ephemeral ponds in open landscapes, without nearby perennial habitat, likely provide an environmental refuge from Bd, where the risk of infection is low. From a conservation perspective, these findings highlight the importance of maintaining ephemeral ponds in open landscapes, but these are currently threatened by land-use change.

Decline and re-expansion of an amphibian with high prevalence of chytrid fungus

The disease chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is a key driver of global amphibian declines. While chytridiomycosis can cause extinction, many susceptible species persist after an initial period of decline, albeit with reduced abundance and distribution. Emerging evidence indicates that amphibian abundance can recover within remnant populations, but to date, the capacity of amphibian populations to re-expand into historically occupied habitat has received limited research attention. We surveyed 145 sites in 2011 and 2012 to determine if populations of the whistling tree frog (Litoria verreauxii verreauxii) have re-expanded compared with historical data from 1975-1976, 1990 and 1996. L. v. verreauxii underwent a major range contraction likely caused by chytridiomycosis between the first two time periods. Populations have recently re-expanded, with 39 new sites colonised despite high prevalence of Bd. We suspect that changes in disease dynamics have resulted in the increased coexistence of L. v. verreauxii and Bd. Habitat attributes at sites that retained frogs for the duration of the study indicate that high quality habitat may contribute to buffering against population level effects of Bd. Colonised sites had more coarse woody debris, suggesting a possible habitat management strategy to encourage range expansion for this species. Given sufficient time and adequate source populations in high quality habitat, it is possible that other amphibian species may re-expand from chytridiomycosis-induced declines. This provides an impetus for the protection of historical, but currently unoccupied amphibian habitats and highlights the importance of maintaining high quality habitat to help species survive novel shocks such as pandemic diseases.

Inconclusiveness of chytridiomycosis as the agent in widespread frog declines

Although there is considerable evidence to support the hypothesis that the chytrid fungus Batrachochytrium dendrobatidis is the primary agent responsible for widespread declines in amphibian populations, particularly rainforest frog populations in Australia and Central America, I argue the case has not yet been made conclusively. Few specimens were collected at the time of population declines, so it may never be possible to conclusively determine their cause. It remains unclear whether the pathogen is novel where declines have occurred. Although it is not necessary that the infection be novel for it to be implicated in declines, if a preexisting pathogen has only recently caused extinctions, cofactors must be important. Whether the pattern of outbreaks represents a wave of extinctions is unclear, but if it does, the rate of spread in Australia is implausibly high for a waterborne pathogen, given the most likely estimates of epidemiological parameters. Although B. dendrobatidis is an amphibian pathogen according to Koch's postulates, the postulates are neither necessary nor sufficient criteria to identify a pathogen. The following key pieces of information are necessary to better understand the impact of this fungus on frog communities: better knowledge of the means and rate of transmission under field conditions, prevalence of infection among frog populations, as distinct from morbid individuals, and the effect of the fungus on frogs in the wild. It is crucial to determine whether there are strains of the fungus with differing pathogenicity to particular frog species and whether host-pathogen coevolution has occurred or is occurring. Recently developed diagnostic tools bring into reach the possibility of addressing these questions and thus developing appropriate strategies to manage frog communities that may be affected by this fungus.

Enigmatic faunal declines at La Selva, Costa Rica: Patterns and processes in a collapsing neotropical herpetofauna

Amphibian populations are declining even in pristine areas in many parts of the world, and in the Neotropics most such enigmatic amphibian declines have occurred in mid- to high-elevation sites. However, amphibian populations have also declined at La Selva Biological Station in the lowlands of Costa Rica, and similar declines in populations of lizards have occurred at the site as well. To set the stage for describing amphibian declines at La Selva, I thoroughly review knowledge of amphibian decline and amphibian conservation in Central America: I describe general patterns in biodiversity, evaluate major patterns in and ecological correlates of threat status, review trends in basic and applied conservation literature, and recommend directions for future research. I then synthesize data on population densities of amphibians, as well as ecologically similar reptiles, over a 35-year periods using quantitative datasets from a range of studies. This synthesis identifies assemblage-wide declines of approximately 75% for both amphibians and reptiles between 1970 and 2005. Because these declines defy patterns most commonly reported in the Neotropics, it is difficult to assess causality evoking known processes associated with enigmatic decline events. I conduct a 12-month pathogen surveillance program to evaluate infection of frogs by the amphibian chytrid fungus, an emerging pathogen linked to decline events worldwide Although lowland forests are generally believed to be too warm for presence or adverse population effects of chytridiomycosis, I present evidence for seasonal patterns in infection prevalence with highest prevalence in the coolest parts of the year. Finally, I conducted a 16-month field experiment to explore the role of changes to dynamics of leaf litter, a critical resource for both frogs and lizards. Population responses by frogs and lizards indicate that litter regulates population densities of frogs and lizards, particularly those species with the highest decline rate. My work illustrates that sites that are assumed to be pristine are likely impacted by a variety of novel stressors, and that even fauna within protected areas may be suffering unexpected declines.

Low impact of chytridiomycosis on frog recruitment enables persistence in refuges despite high adult mortality

The global chytridiomycosis pandemic caused by the pathogen Batrachochytrium dendrobatidis (. Bd) is implicated in the apparent extinction or severe decline of over 200 amphibian species. Many declined species now only persist in isolated remnant populations. In this study we examine how remnant populations coexist with Bd, focusing on disease impact on adult survival and recruitment potential in the chytridiomycosis-threatened frog Litoria verreauxii alpina. Using skeletochronology we found that the adult male population in both 2011 and 2012 was dominated by a two year old age cohort. The lack of recruitment into the three year old cohort in 2012 indicates that annual adult survival is very low. Combined with high Bd prevalence and heavy infection burdens, the pathogen appears to drive almost complete mortality of breeding adults over their first breeding season. However, adults successfully mate prior to large increases in disease prevalence that occurs during the breeding season. Infection prevalence among tadpoles and juveniles is low. Exposure to warm water could provide a mechanism for avoiding or clearing Bd infection. Relatively low Bd prevalence in juveniles prior to dispersal into terrestrial habitat indicates that Bd has minimal impact on early life history stages. As such, recruitment is probably high, allowing populations to persist despite low adult survival. This dependence on reliable annual recruitment may explain why remnant populations persist in permanent ponds rather than ephemeral ponds that were historically occupied. New management strategies that focus on increasing recruitment may provide a way forward for the management of disease-threatened amphibian species.

High adult mortality in disease-challenged frog populations increases vulnerability to drought

Pathogen emergence can drive major changes in host population demography, with implications for population dynamics and sensitivity to environmental fluctuations. The amphibian disease chytridiomycosis, caused by infection with the fungal pathogen Batrachochytrium dendrobatidis (Bd), is implicated in the severe decline of over 200 amphibian species. In species that have declined but not become extinct, Bd persists and can cause substantial ongoing mortality. High rates of mortality associated with Bd may drive major changes in host demography, but this process is poorly understood. Here, we compared population age structure of Bd-infected populations, Bd-free populations, and museum specimens collected prior to Bd emergence for the endangered Australian frog, Litoria verreauxii alpina (alpine tree frog). We then used population simulations to investigate how pathogen-associated demographic shifts affect the ability of populations to persist in stochastic environments. We found that Bd-infected populations have a severely truncated age structure associated with very high rates of annual adult mortality. Near-complete annual adult turnover in Bd-infected populations means that individuals breed once, compared with Bd-free populations where adults may breed across multiple years. Our simulations showed that truncated age structure erodes the capacity of populations to withstand periodic recruitment failure; a common challenge for species reproducing in uncertain environments. We document previously undescribed demographic shifts associated with a globally emerging pathogen and demonstrate how these shifts alter host ecology. Truncation of age structure associated with Bd effectively reduces host niche width, and can help explain the contraction of L. v. alpina to perennial waterbodies where the risk of drought-induced recruitment failure is low. Reduced capacity to tolerate other sources of mortality may explain variation in decline severity among other chytridiomycosis-challenged species and highlights the potential to mitigate disease impacts through minimising other sources of mortality.

Reservoir-host amplification of disease impact in an endangered amphibian

Emerging wildlife pathogens are an increasing threat to biodiversity. One of the most serious wildlife diseases is chytridiomycosis, caused by the fungal pathogen, Batrachochytrium dendrobatidis (Bd), which has been documented in over 500 amphibian species. Amphibians vary greatly in their susceptibility to Bd, with some species tolerating infection, while others experience rapid mortality. Reservoir hosts - species that carry infection while maintaining high abundance, but are rarely killed by disease - can increase extinction risk in highly susceptible, sympatric species. However, whether reservoir hosts amplify Bd in declining amphibian species has not been examined. We combine a laboratory study with field surveys, disease sampling, and statistical modeling to investigate the role of reservoir hosts in chytridiomycosis dynamics and species decline in an amphibian community in south-eastern Australia. We show that the non-declining common eastern froglet (Crinia signifera) is a reservoir host for Bd, with laboratory animals carrying intense infection burdens over 12 weeks and the majority of wild sampled individuals carrying intense infections. We find that the presence of C. signifera is strongly associated with Bd prevalence in the sympatric, IUCN red-listed northern corroboree frog (Pseudophryne pengilleyi). Consistent with disease amplification by a reservoir host, we find that P. pengilleyi has declined from areas with high C. signifera abundance. Our results suggest that when reservoir hosts are present, population declines can continue long after the initial emergence of Bd, highlighting an urgent need to assess extinction risk in remnant populations of other declined amphibian species. Reintroductions and in situ management strategies must focus on identifying reservoir hosts and minimizing exposure of threatened species.

Long-term endemism of two highly divergent lineages of the amphibian-killing fungus in the Atlantic Forest of Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Stability of endoglucanases from mesophilic fungus and thermophilic bacterium in acidified polyols

Recent developments in chemical pretreatments of lignocellulosic biomass using polyols as co-solvents (e.g., glycerol and ethylene glycol) at temperatures less than 100 °C may allow the effective use of thermostable and non-thermostable cellulases in situ during the saccharification process. The potential of biomass saccharifying enzymes, endoglucanases (EG) from a thermophilic bacterium (Thermotoga maritima) and a mesophilic fungus (Trichoderma longibrachiatum), to retain their activity in aqueous buffer, acidified glycerol, and acidified ethylene glycol used as co-solvents at pretreatment temperatures at or below 100 °C were examined. The results show that despite its origin, T. longibrachiatum EG (Tl-EG) retained 75% of its activity after exposure to 100 °C for 5 min in aqueous buffer while T. maritima EG (Tm-EG) retained only 5% activity. However, at 90 °C both enzymes retained over 87% of their activity. In acidified (0.1% (w/w) H2SO4) glycerol, Tl-EG retained similar activity (80%) to that obtained in glycerol alone, while Tm-EG retained only 35%. With acidified ethylene glycol under these conditions, both Tl-EG and Tm-EG retained 36% of their activity. The results therefore show that Tl-EG is more stable in both acidified glycerol and ethylene glycol than Tm-EG. A preliminary kinetic study showed that pure glycerol improved the thermal stability of Tl-EG but destabilized Tm-EG, relative to the buffer solution. The half-lives of both Tl-EG and Tm-EG are 4.5 min in acidified glycerol, indicating that the effectiveness of these enzymes under typical pretreatment times of greater than 15 min will be considerably diminished. Attempts have been made to explain the differences in the results obtained between the two enzymes.