Professor Damhnait McHugh and an international team of researchers received a $100,000 grant from Colgate’s Picker Interdisciplinary Science Institute to unravel the mystery of an invasive worm species spreading across Ireland.
In the northeast corner of Ireland, about an hour’s drive from Dublin, there is a collection of ancient passage tombs tucked among the rolling farmland of the Boyne Valley. Dating back more than 5,000 years, these neolithic tombs are older than the Egyptian pyramids and contain some of the world’s earliest evidence of prehistoric human cultures. The burial sites are ensconced in kerbstones, large and sometimes decorated rocks that were covered with earth to form imposing grass-covered knolls.
Each burial mound has a single entrance that opens into a network of subterranean passageways, which have long been a source of archaeological intrigue and Irish folklore. But for Raab Family Chair and Professor of Biology Damhnait McHugh, these burial sites contain a far more titillating mystery than the inscrutable inscriptions carved on their entrance: They are home to Prosellodrilus amplisetosus, a small earthworm so far out of its natural environment that she was willing to travel across 3,000 miles of open ocean just to see it.
This was how, on a rainy day last fall, McHugh found herself trudging across the sodden pastures of the Boyne Valley accompanied by European ecologist Olaf Schmidt. Every so often, McHugh and Schmidt would stop and plunge the shovels they carried with them deep into the earth. Each time, they were astonished to see that the dirt was alive, packed with writhing specimens of P. amplisetosus.
“We couldn’t believe that we were finding so many,” says McHugh. “They were under hedgerows, in the middle of fields, under trees, and in horse pastures. It was astounding.”
The presence of earthworms in the Boyne Valley was not remarkable in itself. Ireland is home to 26 native species of earthworm, which play a vital role in maintaining the health of its natural ecosystems by recycling nutrients trapped in the soil. But the 2-centimeter long earthworm that McHugh had come to see is not counted among them. In fact, this worm is only endemic to the temperate Aquitaine region of southern France and northern Spain. And yet here they were, squirming in McHugh’s hand and burrowing through the fertile Irish soil more than 600 miles from their native habitat.
How this small worm traveled so far north — to say nothing of how it came to thrive in such a radically different environment — is a mystery and potentially the beginning of a big problem. Today, little is known about the impact that P. amplisetosus has on the Irish environment. Perhaps the worm is throwing fragile ecosystems out of balance by competing with endemic species for scarce resources or releasing vast quantities of carbon stored in the soil. Supported by a $100,000 research grant from Colgate’s Picker Interdisciplinary Science Institute, McHugh, Schmidt, and three of their Spanish colleagues are determined to get to the bottom of these questions. Along the way, they hope to get a glimpse of evolution happening in real time and a better understanding of the profound impact that climate change has on the invisible world beneath our feet.
One of the main questions that McHugh and her colleagues want to answer is when and how P. amplisetosus arrived in Ireland. Schmidt first discovered the worm on an urban farm in Dublin 2012, and, since then, it has been discovered at two additional sites — including the Boyne burial complex — all within 50 miles of one another. Did the worm slowly migrate north over the course of decades or centuries, or was it accidentally imported in the soil of plants growing on the urban farm?
“There was movement between Spain and Ireland thousands of years ago, so maybe they came in on a boat when Ireland was first being farmed,” says McHugh. “It’s probably very far-fetched, but I love thinking about that. It’s fun to make up these stories and test them as hypotheses.”
Around the time of Schmidt’s discovery, McHugh was leading a research project on a different invasive species, the jumping worm, which is normally found in Japan and Korea, but had begun to appear in New York and other areas of the eastern United States. McHugh and her colleagues at Colgate were attempting to discover how the jumping worm had leapt out of its natural environment and started spreading across the states. Their research project continues to this day.
Last summer, during a chance meeting with Schmidt at an earthworm ecology conference in France, McHugh realized that her research on the jumping worm could potentially help Schmidt unravel the mystery of the invasive worm he had discovered in Ireland. The duo agreed to collaborate on a new research project that could apply McHugh’s genetic sequencing techniques to better understand the trajectory P. amplisetosus.
“If we can get enough information from the DNA that reflects a historical mutation that’s passed on from one generation to the next, I can begin to build these family trees,” says McHugh. “The idea was that we might be able to use these shared genetic traits to tease apart the invasion history itself.”
The second major question McHugh and her colleagues hope to answer is how P. amplisetosus has managed to not just survive but thrive in Irish soils, and the impact that it’s having on its new environment. Its native habitat in southern France and northern Spain is about 3 degrees warmer on average than Dublin. Ireland should, by all accounts, be a hostile environment for a worm accustomed to a mediterranean climate. Instead, at each site where Schmidt has encountered the worm in Ireland, he found well-established populations in the soil. This suggested that the worm had adapted to the relatively harsh Irish environment or that the island’s climate had warmed enough to support the worm.
“We’re bringing together all our different areas of expertise to try and tackle these kinds of questions,” says McHugh. “And if we can figure it out for this species of invasive worm, maybe we can apply it to some other similar scenarios.”
To answer these questions, McHugh and her colleagues are leveraging sophisticated genomic sequencing techniques. Over the course of their two-year study, they will collect dozens of specimens of P. amplisetosus from sites in Ireland as well as its native habitat. The genetic differences between these worms may hold telltale clues that can reveal how the worm came to Ireland and what led to its proliferation.
For example, if McHugh and her colleagues compare DNA mutations from worms found in Spain and those found in Ireland and discover two distinct genetic lineages, this would suggest that these worms have likely been in Ireland for a very long time because these kinds of distinct genetic lineages can only emerge over many generations. Or they might find common variations in specific genes between Irish and Aquitaine worms, which would suggest that the Irish worms are genetically adapting — that is, evolving — to survive in a cooler northern climate.
For now, these remain open questions, but McHugh and her colleagues are optimistic that their research will not only help us understand the history of this particular worm, but also the impact of climate change and invasive species more broadly.
“What we’re interested in is what happens if you tinker with an ecosystem either through climate change or through the introduction of a different species,” says McHugh. “It may not be bad, but it could change things in ways we don’t anticipate. There are many groups of small organisms that are hidden from us in the soil, and they are critical to the health of the ecosystem so it’s important to have baselines so we can understand what will happen when things start changing.”
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