Grantee Research Project Results

The Thin Line Between Health and Disease: Determining the Effects of Climate Change on Amphibians’ Skin Microbial Communities

EPA Grant Number: F13B20412
Title: The Thin Line Between Health and Disease: Determining the Effects of Climate Change on Amphibians’ Skin Microbial Communities
Investigators: Muletz, Carly Rae
Institution: University of Maryland - College Park
EPA Project Officer: Packard, Benjamin H
Project Period: September 2, 2014 through September 2, 2016
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2013) RFA Text |  Recipients Lists
Research Category: Fellowship - Biological Sciences , Academic Fellowships

Objective:

Objective 1: Determine how different temperatures (13 °C, 17 °C and
21 °C) affect the skin bacterial community on red-backed salamanders, Plethodon cinereus, and their susceptibility to disease over time. Objective 2: Determine how exposure to a fungal pathogen (Batrachochytrium dendrobatidis, Bd, implicated in worldwide amphibian decline) affects the skin bacterial community on P. cinereus over time. Objective 3: Determine if there is a relationship between changes in the skin bacterial community due to temperature and disease susceptibility.

Approach:

A laboratory experiment will be conducted with 84 red-backed salamanders, using temperature (13 °C, 17 °C, 21 °C) and disease treatments (pathogen+, pathogen-) in a full factorial design (N = 14 per treatment). All salamanders will be swabbed at collection (Day 0) and thereafter at each swabbing event (every 2 weeks) until the end of the experiment at Day 100. The mass and length of each individual will be measured at each swabbing event to determine salamander body condition. On Day 40, all salamanders will be exposed either to the fungal pathogen Bd or to a sham following standard procedures. DNA will be extracted from swabs to determine Bd infection load (using quantitative PCR) and bacterial diversity (using high-throughput sequencing of the 16s rRNA gene). The QIIME pipeline and several packages in R will be used to perform multivariate analyses.

Expected Results:

As temperature increases, it is expected that the number of bacterial spe- cies will decrease, including anti-Bd bacteria, selecting for only a subset of the bacterial taxa with higher temperature optima (homogenization), which will increase in abundance. Functionally important anti-Bd bacteria will be identified from a database of bacteria found on salamander skin that kill Bd in culture. As temperature increases, salamander susceptibility to Bd infection is expected to increase (in pure culture, Bd typically grows similarly between 13 and 21 °C). Salamander susceptibility to Bd infection and associated disease will be determined by comparing salamander body condition, survival and pathogen load among treat- ments. Increased salamander susceptibility to Bd infection is expected to correlate to a reduction in (entire and anti-Bd) bacterial richness and abundance. It is assumed that temperature does not affect salamander immunity, because research indicates that Bd paralyzes amphibians’ immune responses regardless of temperature.

Potential to Further Environmental/Human Health Protection

Knowing how woodland salamanders and their associated bacteria will respond to temperature changes and pathogen exposure, especially in hotspots of biodiversity like the Appalachian Mountains, is important for planning management actions and understanding how ecosystem functions may change. Knowing how bacterial community structure influences disease outcome in amphibians is important for developing a broader understanding of how resident bacteria on animal hosts (including humans) influence disease outcome of the host.

Supplemental Keywords:

amphibians, microbiome, wildlife disease

Progress and Final Reports:

2015

Final