Nov. 14, 2019
Heres thething about bats: They can fly. And they do that in the dark.
Those twofactors make bats, which make up 20 percent of the mammal species, extremelydifficult to study.
Geneticist Faith Walker and wildlife ecologist Carol Chambers wanted a better look at the 1,406 known species of bats, so after years of trying to meet the bats where they were, the two Northern Arizona University researchers instead turned to what the bats left behind: feces. Research into bat guano led to the creation of the Species from Feces assay, which can test DNA from bat guano and tell the researchers which species of bats live in a particular area.
Poop doesnt fly around in the dark and its easy tocollect, said Walker, who along with Chambers is co-director of the BatEcology and Genetics Lab at NAU. You can walk around in theday with a collection kit in one hand and a cup ofcoffee in the other andsample in 10 leisurely minutes, instead of the tour de force required by mistnetting (when we net bats we often have four cars, eight people and are outuntil midnight eating Oreos to stay awake). Hence, the fecal methodisfriendlier to bats and us, and it givesa broader timeframe forthe bat species that were using a roost.
Since publishing the Speciesfrom Feces research in 2016, which enabled theresearchers to correctly identify 92 percent of bats to the species level (theother 8 percent can be identified to genus) throughout the world for whichgenetic data are available, theyve helped other researchers and wildlifemanagers use the assay to better understand local populations. However, theywondered what else they could learn from fecalpellets, which they call the gold nuggets of wildlife biology thanks to theirwealth of information about biodiversity, diet and disease without the need fortrapping, handling or even observing the animals in question.
A lot, asit turns out, which led Walker, Chambers and a host of collaborators from NAUand the American Museum of Natural History (AMNH) to A Fecal Sequel: Testingthe limits of a genetic assay for bat species identification, published todayin PLOSOne.
Thefollow-up study asked a number of different questions, all of which centeredaround potential obstacles in extracting usable DNA from bat guano:
Walker,who was the lead author on the paper, connected the various questions anddetermined what was needed to move forward with the various arms of the study. Then-mastersstudent Abby Tobin used her work in both ecology and caving to study howdifferent gate types at the entrances of abandoned mines influence bats use ofthe mines. Colin Sobek, a genetics research specialist with the Schoolof Forestry and the Pathogen and Microbiome Institute and genetics Ph.D.student Dan Sanchez have been part of the Species from Feces researchfor years and extracted and tested the DNA in the lab. Viacheslav Fofanov,a professor in the School of Informatics, Computing, and Cyber Systemsmasterminded the lab test for the species rarity question. Nancy Simmons,curator in the Department of Mammalogy at AMNH, conducted bat research in theNeotropics.
To test the assay in a variety of circumstances, researchers stored fecal pellets in both a high-humidity cave and a low-humidity cave near Flagstaff and let them age for up to 30 months. Every six months they would go into the caves and retrieve a subset of pellets, then run the assay on pellets at six, 12, 18, 24 and 30 months. For the rarity test, the team collected pure guano from three bat species and combined the pellets into mock communities, with the rare bat guano represented as a minuscule ratio to the other two. To determine the utility of the assay as a survey tool, they collected single samples of 200 pellets from more than 40 abandoned mines across the Southwest and performed visual surveys; they did the same at bat roosts in archaeological sites in the Belizean tropics.
Onthe whole, the results werent surprising, Walker said. The assay identifiedthe rare bat DNA and verified that humidity contributed to more rapiddegradation than time. It also added to what the original research showed: TheSpecies from Feces assay is an exceptional tool for conducting bat surveys atroosts.
Thebiggest surprise came from the gold nuggets found in the tunnels of Mayatemples. Walker said two of the three bat species found there feed onvertebratesthey found DNA from a local rodent in the guano of the big-earedwoolly bat and cow DNA in the guano of the vampire bat. They also found DNA ofthe teardrop mosquito fish in almost all of the Belizean tunnels, which likelycame from ponds from which bats drink. Thats significant because it shows batsthemselves acting as an environmental DNA filter.
Importantly,our work illustrated that our assay performs well in the tropics, but likelyrequires feces that is relatively fresh (less than 12 months old), Walkersaid. For the tropics it would be best to collect guano from active roosts.DNA does well in dry and dark conditions. Were lucky that for mostsubterranean systems in the U.S. Southwest we have exactly that.
Werealso lucky to have the bat species that we do, she said. Bats are a criticalpart of the ecosystem, and theyre in danger both from changing habitat andfrom a deadly fungus sweeping the nation.
Most people appreciate bats because of the ecosystemservices they provide, particularly eating insects. Insectivorous bats eat anenormousnumber of insects (a single little brown bat can eat up to 1,000mosquitoes an hour, according to Bat Rescue), which can include crop pests andpathogenvectors likemosquitoes, Walker said. In Flagstaff, withWest Nile virus detected last summer, we should be particularly appreciative ofbats. However, the fungal disease called white-nose syndrome iskillingmillions of bats in the U.S. and is now on the West Coast and Texas. It hasntyet arrived in Arizona, and we dont know for certain which species will beimpacted. Hence, having a genetic tool that can be used to rapidly surveysubterranean roosts is important and will allow us to better understand batspecies presence before and after the disease arrives.
Walkerdeveloped this assay to extract DNA from feces and test it to identify thespecies from which it came. Although scientists have been testing fecal DNA fortwo decades, Species from Feces was revolutionary in the extent of the coverageresearchers got across the entire taxonomic order of bats, how reliable andprecise the assay is and the ease with which researchers can now study bats. Theynot only identified which bat species use particular roosts, but scientistsalso have used the Species from Feces assay to confirm visual identificationsof captured bats, identify bat carcasses at windfarms, screen fertilizer todetermine the species that contributed guano, detect nectar-feeding bats fromsaliva on agave flowers and evaluate the effect gates on the entrance to mineshave on neighboring bat populations.
The Species from Feces team has done work for more than 100 federal and state agencies, universities, museums and environmental consultancies in the past three years. Additionally, this assay has expanded well beyond bats; the lab does a lot of mammalian diet work and has identified plant and animal diet in everything from African lions and leopards to wombats and kangaroos to mule and pronghorn to giraffes and hippos. Walker will soon add a 31,000-year-old giant ground bolus sloth to that list to determine if she can identify what the animal ate.
Read more:
New research from NAU team expands the answers we can get from bat guano - NAU News
