Four faculty members at the University of Tennessee, Knoxville, have been elected 2024 Fellows of the American Association for the Advancement of Science. AAAS Fellows are elected to a lifetime appointment annually by their peers on the AAAS Council in recognition of their extraordinary achievements.
At the far end of the Northwestern Hawaiian Islands lies Kuaihelani – also known as Midway Atoll – a small set of islands home to the world’s largest albatross colony. Over a million albatrosses return to Kuaihelani each year to breed. These seemingly pristine islands appear safe, but there’s a predator lurking among the seabirds.
House mice (Mus musculus) — the same kind that may be in your residence — have started to attack and kill albatrosses, eating them alive as they sit on their nests. I’m an ecologist who’s been studying the mystery behind these murderous mice.
Once the site of intense warfare during World War II, Kuaihelani is now a national wildlife refuge.
Without predators such as cats, rats or mongooses, Kuaihelani provides a safe haven for millions of nesting and migratory birds, including mōlī (Phoebastria immutabilis), also known as Laysan albatrosses. These seabirds, each about the size of a goose, nest in nearly the exact same spot each year, producing only one egg annually.
In the winter nesting season of 2015, bird-counting volunteers and biologists began seeing gruesome bloody wounds on nesting mōlī. At first, they found only a few mōlī with these mysterious injuries, which included severe chewing along the neck and even scalping. In the weeks that followed, they found dozens of injured mōlī, then hundreds.
Biologists were stumped. Had a black rat escaped off a docked boat? Had a peregrine falcon blown in with the latest winter storm? Desperate to identify the culprit, biologists set up game cameras around nesting mōlī.
The cameras captured bizarre nighttime footage of mice crawling and chewing on the backs and heads of mōlī. It was the first time a house mouse had ever been observed attacking a live adult, nesting albatross.
Mōlī, like many seabirds, have evolved without predators on remote islands. As a result, such seabirds are often oddly unafraid and curious – pulling on researchers’ shoelaces or nibbling at our clipboards. This phenomenon is called “island naïveté” and, however charming, can spell disaster when nonnative predators such as rats and cats are introduced to islands. Lacking innate caution, even the largest seabirds can become the defenseless prey of predators as small as a mouse.
During World War II, the islands of Kuaihelani were cleared and covered with wartime infrastructure. Both black rats and house mice were inadvertently introduced at this time. Soon, the rats began decimating populations of burrowing seabirds.
When the military importance of Kuaihelani faded in the 1990s, management of the atoll was transferred to the U.S. Fish and Wildlife Service. Rats were successfully eradicated in 1996, but mice remained. Thought to be small and harmless, they didn’t generate much concern until 2015.
Although scientists may never know exactly why mice began to attack and kill mōlī, we have some ideas.
Due to climate change, Kuaihelani has experienced increasingly erratic precipitation, sometimes resulting in long dry spells or intense downpours. During dry periods, vegetation quickly dies back. It’s likely the usual food items for mice, namely seeds and bugs, decline during these periods. In order to survive, mice need to find a different food source.
On an island with millions of birds, seabird carcasses are plentiful and attract a rich community of bugs, including cockroaches, isopods and maggots. Mice appear to have quite an appetite for these critters and likely feed on seabird carcasses at the same time. The transition from scavenging dead seabirds to attacking live ones that don’t fight back is only a small step.
As mouse attacks on nesting mōlī escalated from 2015 on, it was clear something needed to be done – and fast. The solution was to get rid of the mice, which, unfortunately, is much easier said than done.
Mouse eradication is a challenging and risky conservation endeavor that requires years of research and careful planning. Ideally, rodenticide, a type of poison used to kill rodents, should be offered when mice are most hungry and likely to eat it. This requires knowing exactly what they are eating and when those food sources are scarce.
By extracting and sequencing DNA from mouse poop and analyzing stable isotopes – a technique that identifies unique chemical fingerprints of organisms – my colleagues and I could figure out what organisms mice were eating and in what quantities. We found that mice on Sand Island of Kuaihelani mainly eat bugs (about 62% of their diet), followed by plants (27%) and finally albatross (likely mōlī, about 12%). The Fish and Wildlife Service identified July as the best time for the eradication attempt, since seabird density is typically lowest then.
Because of COVID-19 disruptions, the eradication attempt was delayed until July 2023, when the nonprofit organization Island Conservation and the Fish and Wildlife Service meticulously applied rodenticide in multiple rounds. At first, it seemed to be working. But in the weeks that followed, a few mice were spotted – then more. By September 2023, the eradication was declared unsuccessful.
Some conservation practitioners believe eradication should be attempted again, but others worry about creating mice resistant to rodenticide. When generations of rodents are exposed to rodenticide repeatedly, they may start to carry genetic mutations resulting in resistance to the poison, making future eradication efforts ineffective.
Without a doubt, mice on Kuaihelani have already been exposed to rodenticide for a long time. When Kuaihelani – or Midway Atoll – was a naval base, rodenticide was likely applied in and around buildings and residences. The rat eradication in 1996 was another exposure. I’m currently researching whether the mice on Kuaihelani already have these genetic mutations.
The worries about rodenticide-resistant mice aren’t limited to Kuaihelani. Around the world, especially in Europe, there are more and more cases of rodents carrying resistance. Rodents continue to have severe and widespread ecological effects on islands worldwide.
For now, I’m focused on helping the mōlī of Kuaihelani survive. But our research may also help inform the growing challenge of resistant mice around the world.
Wieteke Holthuijzen, Ph.D. Candidate in Ecology and Evolutionary Biology, University of Tennessee
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Read the article here: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0293092
Dr. Angela Chuang, formerly of the Riechert lab, was consulted for this NY Times article on Joro Spiders, and whether current research is in fact proving how shy the species can be.
https://www.nytimes.com/2023/05/19/science/joro-spiders.html
https://artsci.utk.edu/dialogue/studying-the-mysterious-of-the-microbiome/?utm_source=newsletter&utm_medium=email&utm_content=noopener%20noreferrer&utm_campaign=TN%20Today
EEB Graduate Student Wieteke Holthuijzen received the best PhD poster award at the 50th Annual Meeting of the Pacific Seabird Group and also received the Chairs Choice Award for assistance in organizing the conference. Per their website, “The Pacific Seabird Group (PSG) is a society of professional seabird researchers and managers dedicated to the study and conservation of seabirds…PSG members include biologists, wildlife managers, post-docs, students and conservation biologists from 16 countries including the United States, Mexico, Canada and Japan. PSG annual meetings and publications provide forums where members can share their findings on all research topics related to Pacific seabirds, and discuss local and large scale conservation issues.”
Title: Determining arthropod consumption by Laysan Ducks to inform non-target mitigation efforts during rodent eradication
Authors: Wieteke Holthuijzen, Carmen Antaky, Beth Flint, Jonathan Plissner, Coral Wolf, Holly Jones
Abstract: The critically endangered koloa pōhaka (Laysan Duck, Anas laysanensis) in the Northwestern Hawaiian Islands has wild populations on Kamole (Laysan Island), Kuaihelani (Midway Atoll NWR), and Hōlanikū (Kure Atoll). Although its population and distribution have increased since its listing in 1967, the koloa pōhaka faces a new risk on Kuaihelani: non-target poisoning via a pending House Mouse (Mus musculus) eradication. After mice were observed attacking and depredating mōlī (Laysan Albatross, Phoebastria immutabilis) on Sand Island of Kuaihelani in 2015, plans to eradicate mice with rodenticide were quickly developed. To reduce exposure to rodenticide, ducks will be captured and translocated to Eastern Island (mouse-free) during eradication activities. Even so, ducks may risk secondary poisoning by ingesting arthropods that feed on brodifacoum bait. Therefore, it is crucial to monitor rodenticide residue in arthropods to determine when koloa pōhaka can be safely released post-eradication. Because duck diet is unknown on Kuaihelani, we used next-generation sequencing (NGS) to identify which arthropods ducks consume. We found that Sand Island’s ducks most frequently consume cockroaches (Blattodea), freshwater ostracods (Cyprididae), midges (Chironomidae), and isopods (Porcellionidae). Notably, Sand Island’s ducks consume entirely different arthropods from ducks on Kamole, which mainly eat flies (Diptera) and brine shrimp (Anostraca, Artemia sp.). Our study adds to the literature on the biology and ecology of translocated koloa pōhaka populations by using advanced techniques to uncover their diet with a high degree of taxonomic precision. In addition, our study serves as a model for risk mitigation during invasive rodent eradications.
Thirty volunteers came out to help remove invasive plants from Deans Woodlot (near Alcoa Highway, south of UT’s main campus) at the end of March. Everyone had a great attitude and was eager to remove invasive plants! Below are a some pictures of before, after, and the mound of material removed.
(View the related Tennessee Today press release.)
Newly discovered much earlier reproduction of this forest pest may explain why it is invasive, reveal why control has failed, and impede future control.
Hemlock woolly adelgid (Adelges tsugae) infestation on the underside of an eastern hemlock (Tsuga canadensis) branch in Knox County, Tennessee.
A sap-feeding insect native to Asia, the hemlock woolly adelgid (Adelges tsugae) or HWA was first found in 1951 in eastern North America, where it has since devastated native hemlock populations. HWA does not kill hemlocks in its native range, and why it devastates hemlocks in eastern North America has not been determined.
Like its aphid relatives, HWA has a complex life cycle. Reproduction alternates through several sexual and asexual generations. Each generation is made up of a variety of life forms. Completing two generations each year on hemlock, adults lay eggs that hatch from March through June, then develop though four stages before they mature and lay eggs that hatch from May through July. Until now, scientists documented HWA eggs hatching only from March through July.
Hemlock woolly adelgid (Adelges tsugae) 1st instar nymphs, called “crawlers,” emerging from a “woolly” mass where an adult female lays eggs inside.
The newly documented activity occurred in eastern Tennessee during and after record high temperatures, attributed to global climate change and El Niño conditions, where December’s average mean was 53°F with 14 days at least 65°F. Although not proven to be the reason for this newly documented HWA activity, temperature likely contributed in some way. Temperature influences the rate of insect development, distribution, and abundance. Higher temperatures shorten life cycle stages, sometimes increasing the number of generations each year. More generations create more offspring and may increase insect populations. Alternatively, insect populations may crash when put out of sync with their hosts or when they develop new interactions preventing their survival.
Hemlock woolly adelgid (Adelges tsugae) eggs revealed inside “woolly” mass.
When University of Tennessee researchers Christy Leppanen and Daniel Simberloff discovered eggs hatching in December, they followed populations and determined that this winter’s HWA populations reproduced earlier and more quickly than previously documented.
Reproduction outside of recognized cycles can counteract management because control relies on accurate predictions of pest reproduction, knowing what life stages are present when, so they can be targeted at the most effective times. We are caught by surprise when pests break the rules.
“We visit only a few locations out of the introduced range that extends from Georgia to Maine and couldn’t have been so lucky to happen across the first instance of early winter reproduction,” Leppanen said. “This likely occurred before, possibly increasing populations at times or in numbers that overwhelmed existing population controls, including beetles deliberately introduced to eat them, and contributed to HWA’s escalation from ‘introduced’ to ‘invasive’ in the East.”
Hemlock woolly adelgid (Adelges tsugae) 1st instar nymphs implanted to feed at the base of eastern hemlock needles.
Events like this challenge current HWA control focused on matching natural enemies like the introduced beetles with HWA population cycles. Control using natural enemies has not yet proven successful, possibly because HWA reproduction has not been sufficiently synchronized with enemies able to respond in time, place, and densities necessary to reduce HWA populations. And while earlier reproduction that occurs regularly is predictable, reproduction on the fly in response to changing conditions, such as temperature fluctuations, is difficult to anticipate. So, the frequency and regularity of “extragenerational” reproduction must be understood.
After their discovery, Leppanen sent a mass email to a group of HWA researchers and managers on December 31, 2015, New Year’s Eve. An immediate response came via dozens of “Out of Office” replies. Simberloff asks, “Could similar events in other years have gone unrecorded because HWA life cycles were not synchronized with researcher activity periods?”
Dr. Christy Leppanen is a Postdoctoral Research Associate working in the laboratory of Dr. Daniel Simberloff, the Nancy Gore Hunger Professor of Environmental Studies, in the Department of Ecology and Evolutionary Biology at the University of Tennessee.
Old growth eastern hemlock (Tsuga canadensis) in Knox County, Tennessee.
Fresh, vibrant eastern hemlock (Tsuga canadensis) growth in Knox County, Tennessee.
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