Research topics

Evolution of parental care

Sexual selection

Reproductive ecology

Kin recognition and inclusive fitness

Mate choice

Aposematism and mimicry

Phylogenetics

Biogeography

Chytridiomycosis in Peru

 

 

 

 

 

Chytridiomycosis in Peru

Over the last 30 years, scientists around the globe have observed dramatic declines and extinctions of amphibians. Recently, the Global Amphibian Assessment (GAA) demonstrated that amphibians are the most threatened group of vertebrates, with at least 32.5% considered threatened under IUCN Red List criteria (IUCN Species Survival Commission 2004, Stuart et al. 2004). One of the most puzzling observations about many of these declines is that they are occurring in pristine habitats where no obvious cause can be determined. In fact, “enigmatic” declines are known to comprise at least 48% of all known declines (Stuart et al. 2004), which means that solely preserving habitats is not an effective means of protecting many amphibians. Within the last decade, many of these amphibian declines have been linked to the spread of the emerging chytrid pathogen (Lips et al. 2006).

Two hypotheses have been proposed to explain where this fungus originated and how it is spreading. The “novel pathogen hypothesis” (Berger et al. 1998), proposes that Bd is a novel pathogen that is spreading globally (similar to the human epidemics of AIDS or SARS) and is associated with high levels of mortality (Berger et al. 1998; Skerratt et al. 2007). The second hypothesis, known as the “emerging endemic hypothesis,” proposes that Bd was present in the environment in a saprobic or sporitic form before outbreaks, but environmental change induced a pathogenic state or provided better conditions for growth of the organism (Rachowicz et al. 2005, Pounds et al. 2006). Regardless of which hypothesis Bd researchers support, they all agree that it is an important driver of amphibian declines and is responsible for massive amphibian population declines and extinctions worldwide. However, despite the ominous implications of this devastating disease, monitoring efforts for chytridiomycosis have been sparse and sporadic at best, especially in areas of high species diversity and endemism such as South America and Asia (Duellman 1999, Ron 2005).

The earliest record of Bd in South America is from Ecuador (1980; Ron and Merino-Viteri 2000), but Bd has been detected in most of the South American countries where samples have been analyzed (Carnaval et al. 2006). Intensive monitoring efforts in Ecuador have documented the effects of Bd infection in montane endemic populations of frogs (genus Atelopus), where it has caused widespread extinction at both the population and species level (Ron and Merino-Vitteri 2000; La Marca et al. 2005). Other Ecuadorian species have also been affected, as documented by intensive monitoring at seven different sites (Bustamante et al. 2005).

In Brazil, the first record of Bd (1981; Carnaval et al. 2006) comes from the Atlantic Forest region. Interestingly, this record coincides with several historical reports in this area of unexplained declines (Carnaval et al. 2006). Bd has been well studied in this region, and so far 21 species have been found to be infected (Carnaval et al. 2006, Toledo et al. 2006); however, other regions throughout the country remain under-sampled, including areas that were predicted to be suitable for disease establishment by environmental niche modelling (Ron 2005).

In contrast to Ecuador and Brazil, comparatively little effort has been spent monitoring Bd infection in amphibian populations from Peru and other South American countries (Lips et al. 2005), even though Ron (2005) identified the eastern Andean slopes of Peru and Bolivia (through niche modeling) as one of the new world regions with highest suitability for Bd establishment. The cordilleras that make up the transition zone between the Andes Mountains and Amazonian lowlands are one of the most species rich regions on earth (Fjeldsa and Rahbek 2006). Amphibian species richness and regional endemicity are particularly high for this area (Duellman 1982). In fact, the area is unrivalled in terms of amphibian biodiversity (Duellman 1999). Given its location, situated along the majority of the Andean massif, and encompassing vast tracts of transition zone cordilleras, Peru has a larger proportion of amphibian biodiversity than any other country worldwide. The emergence of Bd in this region potentially poses a grave risk to this biodiversity.

To date, very little work has been done to monitor the prevalence of Bd infection in Peruvian amphibians. The first report of Bd in Peru comes from four Telmatobius marmoratus collected in 2002; these frogs were from a high elevation site (4450m) in the Cordillera Vilconota in southern Peru where declines had been previously reported by the local Quechua herders (Seimon et al. 2005). Informal observations by several Peruvian researchers in northern Peru suggest that populations of the frog genus Atelopus have undergone unexplained declines, and Bd was detected in Atelopus pulcher in the Cainarachi Valley in 2003 (Lötters et al. 2005). A more recent investigation at a high elevation site (5348m) in the southern Andes near Lake Sibinacocha reported the presence of Bd in two anuran species (Telmatobius marmoratus, Pleurodema marmorata), and showed that increased mortality in at least one species could be linked to Bd (Seimon et al. 2007).

We are currently investigating the prevalence of Bd throughout Peru in order to obtain a “snapshot” of the current distribution of this devastating disease. Additionally we plan to investigate which environmental and ecological factors are associated with chytrid prevalence and pathogenicity, to determine if there is a correlation between disease resistance and DNA sequence variation in host MHC class II genes, and to compare the genetic structure of Bd isolates from geographically dispersed sites throughout Peru to test the validity of the two competing hypothesis about the origin of Bd.

 

Influential Bd Papers

Hyatt A.D., Boyle, D.G., Olsen, D.B., Berger, L., Obendorf, D., Dalton, A., Kriger, K., Hero, M., Hines, H., Phillott, R., Campbell, R., Marantelli, G., Gleason, F., & Colling, A. 2007. Diagnostic assays and sampling protocols for the detection of Batrachochytrium dendrobatidis. Diseases of Aquatic Organisms 73:175-192.

Lips, K.R., Brem, F., Brenes, R., Reeve, J.D., Alford, R.A., Voyles, J., Carey, C., Livo,L., Pessier, A.P. & Collins, J.P. 2006. Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community. PNAS 103:3165-3170.

Morehouse, E.A., James, T.Y., Ganley, A.R.D., Vilgalys, R., Berger, L., Murphy, P.J., & Longcore, J.E. 2003. Multilocus sequence typing suggests that chytrid pathogen of amphibians is a recently emerged clone. Molecular Ecology 12: 395-403.

Rachowicz, L.J., Hero, J.M., Alford, R.A., Taylor, J.W., Morgan, J.A.T., Vredenberg, V.T., Collins, J.P. & Briggs, C. 2005. The novel and endemic pathogen hypothesis: competing explanations for the origin of emerging infectious diseases of wildlife. Conservation Biology 19:1441-1448.

Ron, S.R. 2005. Predicting the Distribution of the Amphibian Pathogen Batrachochytrium dendrobatidis in the New World. Biotropica 37: 209-221.

Seimon, T.A., Seimon, A., Daszak, P., Halloys, S.R.P., Schloegel, L.M., Aguilar, C.A.,Sowell, P., Hyatt, A.D., Konecky, B., & Simmons, J.E. 2007. Upward range extension of Andean anurans and chytridiomycosis to extreme elevations in response to tropical deglaciation. Global Change Biology 13:288-299.