Climate structuring of Batrachochytrium dendrobatidis infection in the threatened amphibians of the northern Western Ghats, India.

Batrachochytrium dendrobatidis (Bd) is a pathogen killing amphibians worldwide. Its impact across much of Asia is poorly characterized. This study systematically surveyed amphibians for Bd across rocky plateaus in the northern section of the Western Ghats biodiversity hotspot, India, including the first surveys of the plateaus in the coastal region. These ecosystems offer an epidemiological model system since they are characterized by differing levels of connectivity, edaphic and climatic conditions, and anthropogenic stressors. One hundred and eighteen individuals of 21 species of Anura and Apoda on 13 plateaus ranging from 67 to 1179 m above sea level and 15.89 to 17.92° North latitude were sampled. Using qPCR protocols, 79% of species and 27% of individuals tested were positive for Bd. This is the first record of Bd in caecilians in India, the Critically Endangered Xanthophryne tigerina and Endangered Fejervarya cf. sahyadris. Mean site prevalence was 28.15%. Prevalence below the escarpment was 31.2% and 25.4% above. The intensity of infection (GE) showed the reverse pattern. Infection may be related to elevational temperature changes, thermal exclusion, inter-site connectivity and anthropogenic disturbance. Coastal plateaus may be thermal refuges from Bd. Infected amphibians represented a wide range of ecological traits posing interesting questions about transmission routes.

Micro-habitat distribution drives patch quality for sub-tropical rocky plateau amphibians in the northern Western Ghats, India.

The importance of patch quality for amphibians is frequently overlooked in distribution models. Here we demonstrate that it is highly important for the persistence of endemic and endangered amphibians found in the threatened and fragile ecosystems that are the rocky plateaus in Western Maharashtra, India. These plateaus are ferricretes of laterite and characterise the northern section of the Western Ghats/Sri Lanka Biodiversity Hotspot, the eighth most important global hotspot and one of the three most threatened by population growth. We present statistically supported habitat associations for endangered and data-deficient Indian amphibians, demonstrating significant relationships between individual species and their microhabitats. Data were collected during early monsoon across two seasons. Twenty-one amphibian taxa were identified from 14 lateritic plateaus between 67 and 1179m above sea level. Twelve of the study taxa had significant associations with microhabitats using a stepwise analysis of the AICc subroutine (distLM, Primer-e, v7). Generalist taxa were associated with increased numbers of microhabitat types. Non-significant associations are reported for the remaining 9 taxa. Microhabitat distribution was spatially structured and driven by climate and human activity. Woody plants were associated with 44% of high-elevation taxa. Of the 8 low-elevation taxa 63% related to water bodies and 60% of those were associated with pools. Rock size and abundance were important for 33% of high elevation specialists. Three of the 4 caecilians were associated with rocks in addition to soil and stream presence. We conclude the plateaus are individualistic patches whose habitat quality is defined by their microhabitats within climatic zones.

Combinatorial Wnt control of zebrafish midbrain-hindbrain boundary formation.

Wnt signaling is known to be required for the normal development of the vertebrate midbrain and hindbrain, but genetic loss of function analyses in the mouse and zebrafish yield differing results regarding the relative importance of specific Wnt loci. In the zebrafish, Wnt1 and Wnt10b functionally overlap in their control of gene expression in the ventral midbrain-hindbrain boundary (MHB), but they are not required for the formation of the MHB constriction. Whether other wnt loci are involved in zebrafish MHB development is unclear, although the expression of at least two wnts, wnt3a and wnt8b, is maintained in wnt1/wnt10b mutants. In order to address the role of wnt3a in zebrafish, we have isolated a full length cDNA and examined its expression and function via knockdown by morpholino antisense oligonucleotide (MO)-mediated knockdown. The expression pattern of wnt3a appears to be evolutionarily conserved between zebrafish and mouse, and MO knockdown shows that Wnt3a, while not uniquely required for MHB development, is required in the absence of Wnt1 and Wnt10b for the formation of the MHB constriction. In zebrafish embryos lacking Wnt3a, Wnt1 and Wnt10b, the expression of engrailed orthologs, pax2a and fgf8 is not maintained after mid-somitogenesis. In contrast to acerebellar and no isthmus mutants, in which midbrain and hindbrain cells acquire new fates but cell number is not significantly affected until late in embryogenesis, zebrafish embryos lacking Wnt3a, Wnt1 and Wnt10b undergo extensive apoptosis in the midbrain and cerebellum anlagen beginning in mid-somitogenesis, which results in the absence of a significant portion of the midbrain and cerebellum. Thus, the requirement for Wnt signaling in forming the MHB constriction is evolutionarily conserved in vertebrates and it is possible in zebrafish to dissect the relative impact of multiple Wnt loci in midbrain and hindbrain development.