Batrachochytrium dendrobatidis (Bd ) is a chytrid fungus that causes chytridiomycosis in amphibians. Only named in 1999, Bd is a proximate driver of declines in global amphibian biodiversity. The pathogen infects over 350 species of amphibians and is found on all continents except Antarctica. However, the processes that have led to the global distribution of Bd and the occurrence of chytridiomycosis remain unclear. This review explores the molecular, epidemiological, and ecological evidence that Bd evolved from an endemic ancestral lineage to achieve global prominence via anthropogenically mediated spread. We then consider the major host and pathogen factors that have led to the occurrence of chytridiomycosis in amphibian species, populations, and communities.

Global emergence of Batrachochytrium dendrobatidis and amphibian chytridiomycosis in space, time, and host.

Amphibians are in decline worldwide. However, their patterns of diversity, especially in the tropics, are not well understood, mainly because of incomplete information on taxonomy and distribution. We assess morphological, bioacoustic, and genetic variation of Madagascar's amphibians, one of the first near-complete taxon samplings from a biodiversity hotspot. Based on DNA sequences of 2,850 specimens sampled from over 170 localities, our analyses reveal an extreme proportion of amphibian diversity, projecting an almost 2-fold increase in species numbers from the currently described 244 species to a minimum of 373 and up to 465. This diversity is widespread geographically and across most major phylogenetic lineages except in a few previously well-studied genera, and is not restricted to morphologically cryptic clades. We classify the genealogical lineages in confirmed and unconfirmed candidate species or deeply divergent conspecific lineages based on concordance of genetic divergences with other characters. This integrative approach may be widely applicable to improve estimates of organismal diversity. Our results suggest that in Madagascar the spatial pattern of amphibian richness and endemism must be revisited, and current habitat destruction may be affecting more species than previously thought, in amphibians as well as in other animal groups. This case study suggests that worldwide tropical amphibian diversity is probably underestimated at an unprecedented level and stresses the need for integrated taxonomic surveys as a basis for prioritizing conservation efforts within biodiversity hotspots.

https://www.pnas.org/content/pnas/106/20/8267.full.pdf

Vast underestimation of Madagascar's biodiversity evidenced by an integrative amphibian inventory

Amphibian populations around the world are experiencing unprecedented declines attributed to a chytrid fungal pathogen, Batrachochytrium dendrobatidis Despite the severity of the crisis, quantitative analyses of the effects of the epidemic on amphibian abundance and diversity have been unavailable as a result of the lack of equivalent data collected before and following disease outbreak We present a community-level assessment combining long-term field surveys and DNA barcode data describing changes in abundance and evolutionary diversity within the amphibian community of El Cope, Panama, following a disease epidemic and mass-mortality event The epidemic reduced taxonomic, lineage, and phylogenetic diversity similarly We discovered that 30 species were lost, including five undescribed species, representing 41% of total amphibian lineage diversity in El Cope These extirpations represented 33% of the evolutionary history of amphibians within the community, and variation in the degree of population loss and decline among species was random with respect to the community phylogeny Our approach provides a fast, economical, and informative analysis of loss in a community whether measured by species or phylogenetic diversity

https://www.pnas.org/content/pnas/107/31/13777.full.pdf

Epidemic disease decimates amphibian abundance, species diversity, and evolutionary history in the highlands of central Panama

Tropical biotas provide excellent settings in which to explore mechanisms of evolutionary diversification, yet these processes remain poorly understood. Pioneering work on biodiversity patterns and diversification processes in other tropical regions has recently been complemented by studies in Madagascar. Here we review diversity models and diversification mechanisms proposed for the fauna of this island and the perspectives for testing them. Madagascar has a diverse biota that has evolved in isolation, and is characterised by regionally pronounced and locally steep environmental gradients, common patterns of microendemism across taxa and numerous evolutionary radiations. These characteristics establish Madagascar as a promising system for the study of pattern and process in species diversification.

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Madagascar as a model region of species diversification.

Fully-sampled phylogenies of squamates reveal evolutionary patterns in threat status

Frogs from Madagascar constitute one of the richest groups of amphibian fauna in the world, with currently 238 described species; caecilians and salamanders are absent [1]. Several frog radiations of the island are species-rich and parallel lemurs and tenrecs in their astonishing morphological and ecological diversity. According to the Global Amphibian Assessment (GAA), Madagascar ranks as the country with the 12th highest amphibian species richness [2,3] (see also http://www.globalamphibians.org), but this is likely an underestimate, because an additional 182 candidate species have been identified since [1]. Diversity is concentrated in rainforests and can locally reach over 100 species. Impressively, 100% of the autochthonous species and 88% of the genera are strictly endemic to Madagascar and its inshore islands [1]. Most of these species belong to two radiations of astonishing ecomorphological and reproductive diversity, the mantellids and the scaphiophrynine plus cophyline microhylids [4,5] (Figure 1).

/pdf/the-challenge-of-conserving-amphibian-megadiversity-in-375d8ncefb.pdf

Samuel Furrer

Papers

The Challenge of Conserving Amphibian Megadiversity in Madagascar