Tuesday, May 28, 2024

Climate change is moving tree populations away from the soil fungi that sustain them

SPUN (SOCIETY FOR THE PROTECTION OF UNDERGROUND NETWORKS)

An ectomycorrhizal mushroom on the forest floor in Patagonia — IMAGE:
AN ECTOMYCORRHIZAL MUSHROOM ON THE FOREST FLOOR IN PATAGONIA
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CREDIT: SPUN/MATEO BARRENENGOA

As our planet warms, many species are shifting to different locations as their historical habitats become inhospitable. Trees are no exception – many species’ normal ranges are no longer conducive to their health, but their shift to new areas that could better sustain them has been lagging behind those of other plants and animals. Now, scientists show that the reason for this lag might be found belowground. A study published in PNAS on May X, shows that trees, especially those in the far north, may be relocating to soils that don’t have the fungal life to support them.

Most plants form belowground partnerships with mycorrhizal fungi, microscopic, filamentous fungi that grow in the soil and connect with plant roots to supply plants with critical nutrients in exchange for carbon. Most large coniferous trees in northern latitudes form relationships with a kind of mycorrhizal fungi called ectomycorrhizal fungi.

“As we examined the future for these symbiotic relationships, we found that 35% of partnerships between trees and fungi that interact with the tree roots would be negatively impacted by climate change,” says lead author Michael Van Nuland, a fungal ecologist at the Society for the Protection of Underground Networks (SPUN).

The trees most at risk of this climate mismatch in North America are those in the pine family, find the authors. Areas of particular concern are the edges of species ranges where trees often face the harshest conditions. Here, the authors discovered that trees with higher survival rate in these locations have more diverse mycorrhizal fungi, a sign that these symbioses may be critical for helping trees withstand the effects of climate change.

“Ectomycorrhizal fungi have a different relationship to climate than ectomycorrhizal trees do,” says co-author Clara Qin, a data scientist at SPUN. “We are finding evidence that the trees have to answer for these differences.”

The study sheds light on how climate change might be affecting symbioses. “While we expect climate-driven migrations to be limited by abiotic factors like the availability of space at higher latitudes and elevations, we don't usually account for biotic limitations like the availability of symbiotic partners,” says Qin.

“It’s absolutely vital that we continue to work to understand how climate change is affecting mycorrhizal symbioses,” says Van Nuland. “These relationships underpin all life on Earth – it’s critical that we understand and protect them.”

***

Download the full paper here.

This research was funded by a National Science Foundation grant awarded to Kai Zhu and Kabir Peay (NSF Awards 1926438, 2244711)

PNAS, Van Nuland et al., “Climate mismatches with ectomycorrhizal fungi contribute to migration lag in North American tree range shifts”

The Society for the Protection of Underground Networks (SPUN) is a scientific research organization with a mission to map and preserve Earth’s fungal networks. In collaboration with researchers and local communities, SPUN is accelerating efforts to protect the underground ecosystems largely absent from conservation and climate agendas. To learn more about SPUN, visit: https://spun.earth/.

A giant pine tree growing on Corsica, where climate change effects are extreme

CREDIT

SPUN/Quentin van den Bossche

Cortinarius spp., a mycorrhizal mushroom.

CREDIT

SPUN/Mateo Barrenengoa

JOURNAL

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2308811121

METHOD OF RESEARCH

Data/statistical analysis

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Climate mismatches with ectomycorrhizal fungi contribute to migration lag in North American tree range shifts

ARTICLE PUBLICATION DATE

27-May-2024

New research shows soil microorganisms could produce additional greenhouse gas emissions from thawing permafrost

COLORADO STATE UNIVERSITY

As the planet has warmed, scientists have long been concerned about the potential for harmful greenhouse gasses to seep out of thawing Arctic permafrost. Recent estimates suggest that by 2100 the amount of carbon dioxide and methane released from these perpetually frozen lands could be on par with emissions from large industrial countries. However, new research led by a team of Colorado State University microbiome scientists suggests those estimates might be too low.

Microorganisms are responsible for the process that will generate greenhouse gasses from thawing northern peatlands, which contain about 50% of the world’s soil carbon. For now, many of the microbes in this environment are frozen and inactive. But as the land thaws the microbes will “wake up” and begin to churn through carbon in the ground. This natural process, known as microbial respiration, is what produces the carbon dioxide and methane emissions forecasted by climate modelers.

Currently, these models assume that this community of microorganisms — known as a microbiome — will break down some types of carbon but not others. But the CSU-led work published this week in the journal Nature Microbiology provides new insight into how these microbes will behave once activated. The research demonstrates that the soil microbes embedded in the permafrost will go after a class of compounds previously thought to be untouchable under certain conditions: polyphenols.

“There were these pools of carbon — say, donuts, pizza and chips — and we were comfortable with the idea that microbes were going to use this stuff,” said Bridget McGivern, a CSU postdoctoral researcher and the paper’s first author. “But then there was this other stuff, spicy food; we didn’t think the organisms liked spicy food. But what our work is showing is that actually there are organisms that are eating it, and so it’s not going to just stay as carbon, it’s going to be broken down.”

More carbon being broken down by microbial respiration will produce additional greenhouse gas emissions. But this new finding has other implications, too. Some scientists had previously theorized that adding polyphenols to the thawing Arctic permafrost could potentially “turn off” these microorganisms altogether, effectively trapping a massive cache of potentially problematic carbon in the ground. The concept is known as the enzyme latch theory.

That no longer appears to be a viable option, said Kelly Wrighton, associate professor in the College of Agricultural Sciences’ Department of Soil and Crop Sciences, whose lab led the work. “Not only did we think these microbes didn’t eat polyphenols,” Wrighton said, “we thought that if the polyphenols were there it was like they were toxic and would lock the microbes into inactivity.”

The soil microbiome has often been considered something of a black box due of its complexity. Wrighton hopes this new information about the role of polyphenols in permafrost helps shift that perception. “I’d like to move past these black box assumptions,” she said. “We can’t engineer solutions if we don’t understand the underlying wiring and plumbing of a system.”

Probing the permafrost in Sweden

Unlocking the relationship between soil microbes and polyphenols has been years in the making for McGivern, who began examining this topic while working on her doctoral degree in Wrighton’s lab in 2017.

McGivern started with a simple question. Scientists presumed that without oxygen, soil microbes could not break down polyphenols. Gut microbes, however, don’t need oxygen to churn up the compound — that’s how humans extract healthy antioxidant benefits from polyphenol-rich substances such as chocolate and red wine. McGivern wondered why the process would be different in soils, a question that is particularly relevant to permafrost or waterlogged lands that contain little or no oxygen.

“The motivation for a lot of my Ph.D. was how could these two things exist?” McGivern said. “Organisms in our gut can breakdown polyphenols but organisms in the soil can’t? The reality was that nobody in soils had really ever looked at it.”

McGivern and Wrighton successfully tested the theory in a lab experiment and published a proof of concept study in 2021. The next step was testing it in the field. The team gained access to core samples from a research site in northern Sweden, a place that scientists have used for years to examine questions related to permafrost and the soil microbiome.

But before McGivern could look for evidence of polyphenol degradation in the core samples, she first had to create a database of gene sequences that corresponded to polyphenol metabolism. McGivern mined thousands of pages of existing scientific literature, cataloging the enzymes in cattle, the human gut, and some soils that were known to be responsible for the process. Once she built the database, McGivern compared the results to the gene sequences expressed by the microbes in the core samples. Sure enough, she said, polyphenol metabolism was happening.

“What we found was that genes across 58 different polyphenol pathways were expressed,” McGivern said. “So, we’re saying not only can the microorganisms potentially do it, but they actually are, in the field, expressing the genes for this metabolism.”

Still, more work is needed, McGivern said. They don’t know what might constrain the process or the rates at which the metabolism is happening — both important factors for eventually quantifying the amount of additional greenhouse gas emissions that could be released from permafrost.

“The whole point of this is to build a better predictive understanding so that we have a framework we can actually manipulate,” Wrighton said. “The climate crisis we’re facing is so fast. But can we model it? Can we predict it? The only way we’re going to get there is to actually understand how something works.”

JOURNAL

Nature Microbiology

DOI

10.1038/s41564-024-01691-0

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

A cache of polyphenol metabolisms discovered in peatland microbiomes

ARTICLE PUBLICATION DATE

28-May-2024

Prenatal exposure to air pollution associated with increased mental health risks

UNIVERSITY OF BRISTOL

A baby’s exposure to air pollution while in the womb is associated with the development of certain mental health problems once the infant reaches adolescence, new research has found. The University of Bristol-led study, published in JAMA Network Open today [28 May], examined the long-term mental health impact of early-life exposure to air and noise pollution.

Growing evidence suggests air pollution, which comprises toxic gases and particulate matter, might contribute to the onset of mental health problems. It is thought that pollution could negatively affect mental health via numerous pathways, including by compromising the blood-brain barrier, promoting neuroinflammation and oxidative stress, and directly entering the brain and damaging tissue.

Despite youth being a key period for the onset of these problems, until now, relatively few studies have investigated the associations of air and noise exposure during early life with mental health.

In this new study, researchers sought to examine the long-term impact of air and noise pollution exposure during pregnancy, early childhood and adolescence on three common mental health problems: psychotic experiences (including hallucinations, such as hearing or seeing things that others cannot, and delusions, such as having very paranoid thoughts), depression and anxiety.

To investigate this, the team used data from over 9,000 participants from Bristol’s Children of the 90s birth cohort study (also known as the Avon Longitudinal Study of Parents and Children), which recruited over 14,000 pregnant women from the Bristol area between 1991 and 1992, and has followed the lives of the women, the children and their partners ever since.

By linking participants’ early childhood data with their mental health reports at the ages of 13, 18 and 24 years, researchers were able to use this to map against outdoor air and noise pollution in South West England at different time points.

Researchers found that relatively small increases in fine particulate matter during pregnancy and childhood were associated with more psychotic experiences and depression symptoms many years later in teenage years and early-adulthood. These associations persisted after considering many related risk factors, such as family psychiatric history, socioeconomic status, and other area-level factors such as population density, deprivation, greenspace and social fragmentation.

The team found that every 0.72 micrograms per cubic meter increase in fine particulate matter (PM2.5) during pregnancy and childhood was associated with an 11 per cent increased odds and 9 per cent increased odds for psychotic experiences, respectively; while exposure in pregnancy was associated with a 10 per cent increased odds for depression. In contrast, higher noise pollution exposure in childhood and teenage years was subsequently associated with more anxiety symptoms.

Dr Joanne Newbury, Sir Henry Wellcome Postdoctoral Research Fellow in the University’s Bristol Medical School: Population Health Sciences (PHS) and the study’s lead author, said: “Childhood, adolescence, and early adulthood are critical periods for the development of psychiatric disorders: worldwide, nearly two-thirds of those affected become unwell by the age of 25. Our findings add to a growing body of evidence – from different populations, locations, and using different study designs – suggesting a detrimental impact of air pollution (and potentially noise pollution) on mental health.

“This is a major concern, because air pollution is now such a common exposure, and rates of mental health problems are increasing globally. Given that pollution is also a preventable exposure, interventions to reduce exposure, such as low emissions zones, could potentially improve mental health. Targeted interventions for vulnerable groups including pregnant women and children could also provide an opportunity for more rapid reductions in exposure.

“It is important to emphasise that these findings, by themselves, do not prove a causal association. However, other recent studies have shown that low emissions zones appear to have a positive impact on mental health.”

The research, which involved researchers from King’s College London, University College London and Cardiff University, was funded by the University of Bristol, Wellcome, Economic and Social Research Council (ESRC), Medical Research Council (MRC), National Institute for Health and Care Research (NIHR), and the Natural Environment Research Council (NERC).

JOURNAL

JAMA Network Open

DOI

10.1001/jamanetworkopen.2024.12169

METHOD OF RESEARCH

Observational study

SUBJECT OF RESEARCH

People

ARTICLE TITLE

Air and noise pollution exposure in early life and mental health from adolescence to young adulthood

ARTICLE PUBLICATION DATE

28-May-2024

Air and noise pollution exposure in early life and mental health from adolescence to young adulthood

JAMA NETWORK

About The Study: Early-life air and noise pollution exposure were prospectively associated with three common mental health problems (psychotic experiences, depression, and anxiety) from adolescence to young adulthood in this longitudinal cohort study. There was a degree of specificity in terms of pollutant-timing-outcome associations. Interventions to reduce air and noise pollution exposure (e.g., clean air zones) could potentially improve population mental health. Replication using quasi-experimental designs is now needed to shed further light on the underlying causes of these associations.

Corresponding Author: To contact the corresponding author, Joanne B. Newbury, Ph.D., email joanne.newbury@bristol.ac.uk.

To access the embargoed study: Visit our For The Media website at this link https://media.jamanetwork.com/

(doi:10.1001/jamanetworkopen.2024.12169)

Editor’s Note: Please see the article for additional information, including other authors, author contributions and affiliations, conflict of interest and financial disclosures, and funding and support.

# # #

Embed this link to provide your readers free access to the full-text article This link will be live at the embargo time http://jamanetwork.com/journals/jamanetworkopen/fullarticle/10.1001/jamanetworkopen.2024.12169?utm_source=For_The_Media&utm_medium=referral&utm_campaign=ftm_links&utm_term=052824

About JAMA Network Open: JAMA Network Open is an online-only open access general medical journal from the JAMA Network. On weekdays, the journal publishes peer-reviewed clinical research and commentary in more than 40 medical and health subject areas. Every article is free online from the day of publication.

JOURNAL

JAMA Network Open

Wind farms are cheaper than you think – and could have prevented Fukushima, says global review

UNIVERSITY OF SURREY

Offshore wind could have prevented the Fukushima disaster, according to a review of wind energy led by the University of Surrey.

The researchers found that offshore turbines could have averted the 2011 nuclear disaster in Japan by keeping the cooling systems running and avoiding meltdown. The team also found that wind farms are not as vulnerable to earthquakes.

Suby Bhattacharya, Professor of Geomechanics at the University of Surrey’s Department of Civil and Environmental Engineering, said:

“Wind power gives us plentiful clean energy – now we know that it could also make other facilities safer and more reliable. The global review finds that greener really is cheaper – thanks to falling construction costs and new ways to reduce wind turbines’ ecological impact.”

One of the report’s starkest findings was that new wind farms can produce energy over twice as cheaply as new nuclear power stations.

The lifetime cost of generating wind power in the UK has fallen dramatically, from £160/MWh to £44/MWh. This includes all the costs of planning, building, operating and decommissioning the wind farm over its entire life.

By comparison, the UK Government agreed to pay £92.50/MWh for energy produced at Hinkley Point C nuclear power station.

Professor Bhattacharya said:

“What makes wind so attractive is that the fuel is free – and the cost of building turbines is falling. There is enough of it blowing around the world to power the planet 18 times over. Our report shows the industry is ironing out practical challenges and making this green power sustainable, too.”

Although less power is generated in calmer conditions, the electricity generated could be stored in batteries – as planned for the Ishikari project off the coast of Hokkaido, Japan. Or it could be used to produce hydrogen from seawater – giving us the fuel of the future.

The research is published in the journal National Institute Economic Review.

JOURNAL

National Institute Economic Review

DOI

10.1017/nie.2024.5

METHOD OF RESEARCH

Systematic review

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

GREENER IS CHEAPER: AN EXAMPLE FROM OFFSHORE WIND FARMS

ARTICLE PUBLICATION DATE

28-May-2024

Imperceptible sensors made from ‘electronic spider silk’ can be printed directly on human skin

Peer-Reviewed Publication

UNIVERSITY OF CAMBRIDGE

Imperceptible sensors made from ‘electronic spider silk’ can be printed directly on human skin — VIDEO:
RESEARCHERS HAVE DEVELOPED A METHOD TO MAKE ADAPTIVE AND ECO-FRIENDLY SENSORS THAT CAN BE DIRECTLY AND IMPERCEPTIBLY PRINTED ONTO A WIDE RANGE OF BIOLOGICAL SURFACES, WHETHER THAT’S A FINGER OR A FLOWER PETAL.
THE FIBRES, AT LEAST 50 TIMES SMALLER THAN A HUMAN HAIR, ARE SO LIGHTWEIGHT THAT THE RESEARCHERS PRINTED THEM DIRECTLY ONTO THE FLUFFY SEEDHEAD OF A DANDELION WITHOUT COLLAPSING ITS STRUCTURE.
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CREDIT: UNIVERSITY OF CAMBRIDGE

Researchers have developed a method to make adaptive and eco-friendly sensors that can be directly and imperceptibly printed onto a wide range of biological surfaces, whether that’s a finger or a flower petal.

The method, developed by researchers from the University of Cambridge, takes its inspiration from spider silk, which can conform and stick to a range of surfaces. These ‘spider silks’ also incorporate bioelectronics, so that different sensing capabilities can be added to the ‘web’.

The fibres, at least 50 times smaller than a human hair, are so lightweight that the researchers printed them directly onto the fluffy seedhead of a dandelion without collapsing its structure. When printed on human skin, the fibre sensors conform to the skin and expose the sweat pores, so the wearer doesn’t detect their presence. Tests of the fibres printed onto a human finger suggest they could be used as continuous health monitors.

This low-waste and low-emission method for augmenting living structures could be used in a range of fields, from healthcare and virtual reality, to electronic textiles and environmental monitoring. The results are reported in the journal Nature Electronics.

Although human skin is remarkably sensitive, augmenting it with electronic sensors could fundamentally change how we interact with the world around us. For example, sensors printed directly onto the skin could be used for continuous health monitoring, for understanding skin sensations, or could improve the sensation of ‘reality’ in gaming or virtual reality application.

While wearable technologies with embedded sensors, such as smartwatches, are widely available, these devices can be uncomfortable, obtrusive and can inhibit the skin’s intrinsic sensations.

“If you want to accurately sense anything on a biological surface like skin or a leaf, the interface between the device and the surface is vital,” said Professor Yan Yan Shery Huang from Cambridge’s Department of Engineering, who led the research. “We also want bioelectronics that are completely imperceptible to the user, so they don’t in any way interfere with how the user interacts with the world, and we want them to be sustainable and low waste.”

There are multiple methods for making wearable sensors, but these all have drawbacks. Flexible electronics, for example, are normally printed on plastic films that don’t allow gas or moisture to pass through, so it would be like wrapping your skin in cling film. Other researchers have recently developed flexible electronics that are gas-permeable, like artificial skins, but these still interfere with normal sensation, and rely on energy- and waste-intensive manufacturing techniques.

3D printing is another potential route for bioelectronics since it is less wasteful than other production methods, but leads to thicker devices that can interfere with normal behaviour. Spinning electronic fibres results in devices that are imperceptible to the user, but without a high degree of sensitivity or sophistication, and they’re difficult to transfer onto the object in question.

Now, the Cambridge-led team has developed a new way of making high-performance bioelectronics that can be customised to a wide range of biological surfaces, from a fingertip to the fluffy seedhead of a dandelion, by printing them directly onto that surface. Their technique takes its inspiration in part from spiders, who create sophisticated and strong web structures adapted to their environment, using minimal material.

The researchers spun their bioelectronic ‘spider silk’ from PEDOT:PSS (a biocompatible conducting polymer), hyaluronic acid and polyethylene oxide. The high-performance fibres were produced from water-based solution at room temperature, which enabled the researchers to control the ‘spinnability’ of the fibres. The researchers then designed an orbital spinning approach to allow the fibres to morph to living surfaces, even down to microstructures such as fingerprints.

Tests of the bioelectronic fibres, on surfaces including human fingers and dandelion seedheads, showed that they provided high-quality sensor performance while remaining imperceptible to the host.

“Our spinning approach allows the bioelectronic fibres to follow the anatomy of different shapes, at both the micro and macro scale, without the need for any image recognition,” said Andy Wang, the first author of the paper. “It opens up a whole different angle in terms of how sustainable electronics and sensors can be made. It’s a much easier way to produce large area sensors.”

Most high-resolution sensors are made in an industrial cleanroom and require toxic chemicals in a multi-step and energy-intensive fabrication process. The Cambridge-developed sensors can be made anywhere and use a tiny fraction of the energy that regular sensors require.

The bioelectronic fibres, which are repairable, can be simply washed away when they have reached the end of their useful lifetime, and generate less than a single milligram of waste: by comparison, a typical single load of laundry produces between 600 and 1500 milligrams of fibre waste.

“Using our simple fabrication technique, we can put sensors almost anywhere and repair them where and when they need it, without needing a big printing machine or a centralised manufacturing facility,” said Huang. “These sensors can be made on-demand, right where they’re needed, and produce minimal waste and emissions.”

The researchers say their devices could be used in applications from health monitoring and virtual reality, to precision agriculture and environmental monitoring. In future, other functional materials could be incorporated into this fibre printing method, to build integrated fibre sensors for augmenting the living systems with display, computation, and energy conversion functions. The research is being commercialised with the support of Cambridge Enterprise, the University’s commercialisation arm.

The research was supported in part by the European Research Council, Wellcome, the Royal Society, and the Biotechnology and Biological Sciences Research Council (BBSRC), part of UK Research and Innovation (UKRI)

Imperceptible sensors made fro [VIDEO] |

When printed on human skin, the fibre sensors conform to the skin and expose the sweat pores, so the wearer doesn’t detect their presence. Tests of the fibres printed onto a human finger suggest they could be used as continuous health monitors.

CREDIT

University of Cambridge

JOURNAL

Nature Electronics

DOI

10.1038/s41928-024-01174-4

ARTICLE TITLE

Imperceptible augmentation of living systems with organic bioelectronic fibres

ARTICLE PUBLICATION DATE

24-May-2024

Survey reveals growing support for changing Australia Day date

Reconciliation Day on May 27 the favoured alternative

Peer-Reviewed Publication

UNIVERSITY OF SOUTH AUSTRALIA

Support for retaining 26 January as Australia’s national day of celebration appears to be slipping, according to a new survey that shows growing numbers of people are open to changing the date out of respect for First Nations people.

The University of South Australia survey of 559 Australian citizens reveals that 67% do not mind when Australia Day falls, as long as there is a dedicated day for national celebration. Reconciliation Day on 27 May was the most popular alternative date.

This contrasts with a 2019 poll by ANU researchers showing 70% support for 26 January and a subsequent 2022 survey by the Institute of Public Affairs, where 65% of people said Australia Day should be celebrated on 26 January.

The new study, published in Analyses of Social Issues and Public Policy, also drew out some of the factors influencing people’s views, suggesting that racism, patriotism, traditionalism and age all play a part.

“Those open to changing the date were in favour of an alternative date that did not offend First Nations’ people,” says lead researcher, UniSA Psychology (Honours) graduate Eliza Mortimer-Royle.

“The most popular option was moving the current date to 27 May, which is Reconciliation Day. Another possibility was 1 January, marking the date in 1901 when Australia became a nation.”

Younger respondents who were taught a different version of Australian history than older survey participants were more likely to support a date change.

“In recent years, the school curriculum has focused on how Aboriginal and Torres Strait Islander people experienced colonisation as an invasion, leading to subsequent oppression and degradation, including major loss of life, land, culture, community and history. That contrasts with the version of history that older Australians learned at school, which was from a European perspective.

“It is not surprising that these different perspectives on Australia’s history may affect how people feel towards celebrating 26 January, which marks the arrival of the First Fleet on Gweagal and Gameygal Land.”

Australia Day has been commemorated since 1935 and celebrated nationally as a public holiday since 1994, but it’s a subject of contention for many Aboriginal and Torres Strait Islanders, as well as a growing number of non-Indigenous Australians.

In recent years, Australia Day protests have become increasingly commonplace, with many recognising 26 January as an annual Day of Mourning, Invasion or Survival. The date has been protested by Aboriginal and Torres Strait Islanders since as early as 1938.

“There is a consensus that a date change will improve the inclusivity of Australia Day celebrations and lessen the ongoing negative impact that 26 January has on First Nations communities,” Mortimer-Royle says.

The study is the first to investigate predictors of Australians’ attitudes towards 26 January, while simultaneously exploring whether interventions could result in a date change.

Notes to editors

“Pride and prejudice: what influences Australians’ attitudes toward changing the date of Australia Day” is published in Analyses of Social Issues and Public Policy. DOI: 10.1111/asap.12399. It was authored by Eliza Mortimer-Royle, Dr Stephanie Webb, Dr Sarven McLinton, Associate Professor Yvonne Clark and Michael Watkins.

JOURNAL

Analyses of Social Issues and Public Policy

DOI

10.1111/asap.12399

METHOD OF RESEARCH

Survey

SUBJECT OF RESEARCH

People

ARTICLE TITLE

Pride and prejudice: what influences Australians’ attitudes toward changing the date of Australia Day

Freshwater mussels: Investigating the remarkable reproductive cycle of Michigan's threatened mollusks

UNIVERSITY OF MICHIGAN

Photos and graphic

Michigan is home to 43 species of native freshwater mussels, 30 of which are considered to be at risk of extinction. Among the many factors that threaten the hard-shelled bottom dwellers are competition from invasive zebra and quagga mussels, water pollution, and—especially—dams.

The Huron River in Southeast Michigan, for example, has 19 dams on its main stem and at least 96 across its entire drainage. Damming completely transforms a river's ecology, replacing native mussel-rich shoal, riffle, and pool habitats with less suitable lake-like reservoirs.

Two University of Michigan biologists led a recent freshwater mussel study based on fieldwork along the Huron River and the River Raisin, also in Southeast Michigan. The study, published May 24 in the journal PeerJ, investigates freshwater mussels' remarkable reproductive cycle, which includes the use of fleshy "mantle lures" by pregnant females to attract nearby fish and "infect" them with mussel larvae.

The study's lead author, Trevor Hewitt, conducted the fieldwork for his doctoral dissertation in the U-M Department of Ecology and Evolutionary Biology. The senior author, Diarmaid Ó Foighil, is a professor in the department and was Hewitt's adviser.

What background information would someone who is completely unfamiliar with your field need to know to understand the findings of your study?

Hewitt: Freshwater mussels undergo an obligate parasitic larval development in which pregnant females must infect a suitable fish host with her young. The mussel larvae typically attach to the host fish's gills, and after two to four weeks they metamorphose into juveniles and drop to the riverbed. Many mussel species are host specialists, infecting just one or a few species of fish, and utilizing distinct host infection strategies.

One of the most striking strategies involves use of a mantle lure. This is a pigmented tissue flap displayed by pregnant females to mimic a host prey item (a small fish, an invertebrate, etc.), eliciting an attack by the host fish and resulting in its infection.

Mantle lure displays are a remarkable and understudied example of mimicry in nature that occurs in many of our streams and rivers each spring and summer.

What exact research question did you set out to answer, and what methods did you use?

Hewitt: Our research focused on the mantle-lure diversity present in one mussel species, the wavy-rayed lampmussel, which is found from Michigan to Alabama. This mussel uses smallmouth bass as its primary fish host and, most unusually, it has two highly distinctive types of mantle lures.

One, previously termed "darter-like," resembles a small fish called a darter, complete with eye spots, mottled body coloration and prominent marginal extensions including a tail. The other, previously termed "worm-like," is uniformly bright orange underlain with black. Both lure forms, or morphs, co-occur throughout the animal's range.

Our research aims were to: 1) confirm that the mantle lure diversity represents a true polymorphism, meaning a clearly different form within a population of the species; 2) investigate its ecological persistence through time; 3) identify the range of putative model species targeted by this mimicry system in a natural population; and 4) determine whether the two mantle lure morphs differ in their display behavior in addition to their pigmentation and morphology.

What are the most important findings of your study, and how do they go beyond previous studies of this topic?

Ó Foighil: We were able to demonstrate that the mantle lure morph diversity in this species is a true polymorphism using two independent criteria: evolutionary trees based on genomic data and inheritance of both morphs within a captive-raised brood—the first such record in freshwater mussels.

Using museum specimens from a River Raisin population, we found that the polymorphism appears stable over ecological time frames. The ratio of the two lure morphs in 2017 was consistent with that of museum samples collected at the same site six decades earlier.

We were able to identify likely model species for the mantle lure variants—meaning the species of fish or invertebrates the mantle lures mimic—within the River Raisin mussel population. Four main darter-like lure motifs visually approximated four co-occurring darter fish species, and the worm-like lure resembled the North American medicinal leech. Darters and leeches are typical prey of smallmouth bass.

Using a GoPro camera, field recordings were made of the darter and leech lure display behaviors in the River Raisin and the Huron River. The displays were largely similar despite the pronounced difference in lure appearance and in model species, implying that the mimicry is only skin deep.

Were there any big surprises?

Hewitt: There were several big surprises. Most important was the unexpected discovery of within-brood mantle lure polymorphism, meaning that different forms of the mantle lure were found within a single group of offspring laid by a female mussel. This critical result was hard-earned, requiring infection of fish hosts and two years of juvenile mussel culture at the Alabama Aquatic Biodiversity Center.

Another surprise was the discovery of 1950s mussel samples from our River Raisin study site in the U-M Museum of Zoology's mollusk collection. The mantle lures on these old specimens were still intact, and they enabled us to compare the ratio of the leech lure morph to the darter lure morph over a 60-plus-year period.

What are the main implications or potential applications of these findings?

Ó Foighil: Discovery of discrete within-brood inheritance of the mantle lure polymorphism is particularly exciting because it implies potential control by a single genetic locus. Virtually nothing is known about the regulatory genes that control mantle lures, representing a significant knowledge gap. Our results identify the wavy-rayed lampmussel as a promising study system to identify the regulatory genes controlling a key adaptive trait of North American endangered freshwater mussels.

The other authors of the PeerJ study are Paul Johnson and Michael Buntin of the Alabama Aquatic Biodiversity Center and Talia Moore of the University of Michigan. The work was financially supported with block grant funding through U-M's Rackham School of Graduate Studies, the Dr. Nancy Williams Walls award for field research, and the State Wildlife Grant Program.

Study: Polymorphism in the aggressive mimicry lure of the parasitic freshwater mussel Lampsilis fasciola (DOI: 10.7717/peerj.17359)

U-M Museum of Zoology mollusk collection

Alabama Aquatic Biodiversity Center

JOURNAL

PeerJ

DOI

10.7717/peerj.17359