Lupine Invasions

Roadsides, ditches, and railway lines in Norway are awash with colour right now.  The lupines are in bloom, and the dense swathes of purple, pink, and white blossoms stacked into perfect pillars brighten the countryside. I love the vibrant colours, but have to stop to remind myself that these are not the friendly wildflowers of my Canadian childhood.

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Lupinus polyphyllus is a wildflower in Canada, but is an invasive species in Europe that has taken over ditches and roadsides with its beautiful blossoms. Photo by: Merja partanen.

The big-leaved lupine is native to western Canada, but in Norway and the rest of Europe it is an introduced invader. In many European countries, lupines have escaped from household gardens where they were originally planted for their vivid blossoms. Once on the loose, they rapidly colonize disturbed habitats like roadsides where they are particularly well adapted to spread and thrive. What makes them so well adapted to spread? Nutrient poor soils in marginal habitats are less of a barrier to lupines than most native plants because of its two specialized mechanisms for acquiring essential nutrients like nitrogen, phosphorous and potassium. Symbiotic bacteria occur in specialized nodules on lupine roots where they convert atmospheric nitrogen into forms the plant can use. In addition, the roots themselves release massive amounts of carboxylic acid into the soil, facilitating the uptake of phosphorous. Their efficient nutrient scavenging actually allows lupines to enrich the soil they colonize. The plants are biennial, surviving only two years and shedding all of their leaves in winter, introducing new, nutrient rich organic material into the soils, which gradually makes them more amenable for other species to live in too.

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As far as invaders go, lupines are not all bad. Their showy blossoms can attract pollinators and maintain pollinator populations, increasing visits to native plants in the area too. Photo by: Richard Griffin

However once established the effects of this invader are mixed. Despite enriching soils and making habitats more suitable for other species, lupines do not share well with others. The overall number of plant species in areas invaded by lupines actually decreases as  the quick-growing, tall lupines shade later-emerging, shorter native plants and outcompete them.   Lupines also produce a wide variety of alkaloid compounds in their leaves that can persist in soils and are thought to negatively impact the germination of seeds from other species of plants. By preventing seeds from germinating around them, the lupines further decrease the biodiversity in areas they invade. And it’s not just other plants that can be negatively impacted by lupine invasions. In Finland, lupines have a bottom-up effect on the ecosystem, decreasing the number and diversity of moths and butterflies occurring in invaded areas too, as they are a poor food source for these insects. Nevertheless, not all species suffer from the presence of these invaders. With their large concentrations of showy flowers, lupines can act as a ‘magnet species’, attracting and sustaining large populations of bumble bees, which can then increase the number of pollinator visits to co-occurring native plants with potential knock-on effects on their reproductive success. Still, as beautiful as they may be, the lupines out my window in Norway are perturbing the ecosystem, and would be better left at home in Canada!

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Responsible Citizens Catch Fish and Climb Trees

I’m sitting, staring intently at the red and white striped bobber floating just at the surface of the water. It rocks soporifically in time with the boat lulling me to near sleep until my five year old eyes are distracted by the shiny blue dragonflies tracing lazy figure eights overhead. That’s when it happens. The rod jolts in my hands and I panic as I see the tip of it arcing towards the water, the red and white float barely visible in the green depths. The ensuing chaos makes minutes seem like seconds. I furiously crank the reel. A vague shadowy outline emerges in the murky water and turns suddenly to fins and teeth. Impossibly, the shadow is then in my hands: slimy, and supple, a white belly and spotted sides. Just as quickly it is over. A splash and a flip of the tail disappearing into the depths. My first fish. I am hooked.

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The number of children in Japan having formative experiences with nature has declined substantially in just ten years time. This phenomenon is not isolated and is occurring in many countries worldwide. Graph from Soga and Gaston 2016

Catching a fish for the first time was a formative moment in my own life, but worldwide, fewer and fewer children are experiencing this. And it’s not just limited to fishing. With urbanization and modernization, people, especially children, are becoming increasingly disassociated from nature. It is a phenomenon known as ‘extinction of experience’. From Japan to the United Kingdom to Australia to the United States, the numbers are telling: over the course of just ten years, there have been consistent declines of up to 20% in the number of children who have had core experiences with nature, including everything from birdwatching to tree climbing to fishing.

 

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Simple experiences like climbing trees or catching fish help children to form permanent bonds with nature and makes them more likely to become environmentally responsible citizens. Photo by Louis Cahill Photography

Why should the number of children visiting parks, watching birds, and climbing trees concern us? Put simply, children that experience nature form bonds with it. Interactions with the natural world are strongly linked to positive mental and physical health outcomes: people that walk their dogs in nature reserves, have lunch outside in the park, stop to smell the flowers and watch the birds, or spend the weekend hiking or fishing are happier and healthier. Not only that, they are more engaged with environmental issues and more likely to have pro-environmental attitudes and behaviours. People who are in contact with nature are more likely to recycle,  donate money to environmental causes, and to support pro-environment legislation that is also vital for conserving those ecosystems that provide essential services to society like conserving wetlands that help to maintain clean drinking water reserves. And it doesn’t take a lot to elicit these effects. Just a few positive experiences with nature can result in substantial, long-term changes to a person’s attitudes and behaviours. The moral of the story? For the sake of yourself and society, get out and enjoy nature, whether it is forest, mountains, beaches, or the neighbourhood park!

 

Want to know more about ‘the extinction of experience’ check out this research paper or chapter 4 of the most recent white paper on nature from the UK government.   

 

 

 

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Planning the Perfect Alien Invasion

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There are alien invaders just outside your back door, but they probably aren’t of the extraterrestrial variety. Image by Carrol MacDonald

It sounds like a conspiracy theory: there are invaders all over the world, lurking in plain sight. The thought of it immediately calls to mind fantastical Dr. Who-worthy plots where little green martian men wear the skins of humans and walk among us while they plot the ultimate destruction of all mankind. In truth, the alien invaders outside your doorstep are (most likely) not of the extraterrestrial variety. For hundreds, even thousands of years, plants, animals, and microbes have been hitchhiking with humans as they move around the world. These alien species find themselves in new habitats and even on new continents with a world of opportunity in front of them. Each launches an invasion into these new habitats. Some find limited success, barely able to eke out a living in their new home. Others become invasive species, exploding in numbers and spreading widely, dominating, out-competing, and even exterminating the existing native plants and animals.

In a study published this month in Ecology Letters, a group of French researchers has asked the question “What makes an alien invasion successful?”.  To do this, the researchers quite literally looked at the invaders outside their backdoors, and focused on the 10 million hectares of grasslands that are found in France. They analysed a massive amount of information from 50 000 grassland vegetation plots that have been surveyed by botanists over the last 20 years. More than 1 million individual plants have been identified, representing over four thousand different species! Among these thousands of grassland species were 160 alien invaders – plant species that had been introduced from other places intentionally through agriculture and horticulture, or by accident through the movement of humans and goods. The scientists scored the success of these invaders: how big their local populations were and how pervasive they had become in different habitats. They then used mathematical modeling to identify those characteristics associated with the most successful invasions.

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Can you spot the invaders? The most successful alien plant species have similar functional roles and are closely related to their native counterparts. Photo by: Xiao Lin

You might think that the best invasion involves brute force domination, with bigger, stronger alien species out-competing the puny locals, but the researchers found this was rarely the case. The majority of successful invading plants are shorter than the surrounding native plants and do not have larger leaves, meaning their success can’t be attributed to cutting off surrounding native plants’ access to light. Instead successful plant invasions are more of a stealth attack. The best invaders actually resemble native species: they are closely related and share similar functional roles to members of the existing community. The scientists hypothesize that this high degree of similarity between invaders and locals is a result of environmental filtering over very large habitat scales. The invaders must have many of the same ecological adaptations as the locals in order to survive in that habitat’s combination of climatic and geologic conditions.

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Goldenrod, Solidago canadensis, is a particularly successful invader in French grasslands. Photo by: Kim Starr.

However, on smaller scales, the similarities between invaders and locals end. Invasions are won with strength in numbers, and successful alien species are typically make many, small, light seeds that are easily transported to new places and can quickly take advantage of any available patch of dirt. The invader’s short stature means they are less likely to be eaten by herbivores, and are better competitors for real-estate, crowding out native species. Persistence pays off in invasions too, and the best invaders get an early start. The more time that has lapsed since the introduction of an alien plant, the more likely it is to have found a foothold and become pervasive in its new community.

The researchers analyses have not only pinpointed what makes alien species successful when they invade a grassland, but the model they have developed also allows them to assess the invasive potential of newly introduced alien species. Armed with this kind of information, authorities will be able to identify high-risk invaders early and manage the developing invasions, hopefully preventing invaders from exterminating the locals. Although these researchers may not have discovered the key to protecting earth from hostile extraterrestrials, their work contributes to preserving native biodiversity.

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Roses are Red, Violets are Blue

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Violets are blue, but that’s not the half of the story. Photo by: Marie L. Davey

Valentine’s Day may have passed, but it is still evidenced by the discounted chocolate and wilting roses in the shop windows, and the childhood rhyme “Roses are red, violets are blue…” that is echoing incessantly in my head. The repeated rhyme has gotten me thinking: of all the things about Viola to remark on, their sometimes blue colour is probably their least remarkable quality!

 

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Cleistogamous flowers growing from the roots of a violet. These flowers will never develop coloured petals or open, and will self-pollinate underground. Photo by: Juliet Blankespoor

Why are violets the perfect token of affection for your favourite biologist? It’s all about reproduction. Viola species can produce showy flowers worthy of a Valentine’s gift that range in colour from blue to purple, white or yellow. These flowers are known as chasmogamous, a term derived from the greek words for ‘open marriage’. They are open to the world and any available violet in it, allowing for cross pollination as insects and the wind carry pollen between different Viola flowers. However, some violet species also produce a second type of flowers underground that are pale and never open their petals. These cleistogamous (‘closed marriage’) flowers are self-pollinated and receive no genetic input from other individuals. Eventually, the mature seeds of these cleistogamous flowers will be released directly into the soil, or near the soil surface. This production of cleistogamous flowers is thought to be a ‘backup method’ to ensure successful seed production even when pollinators are scarce and seed and flower predation are high.

It’s not just the production of hidden flowers that makes violets unique. The genus also has evolved two dispersal methods to ensure that its seeds find new territories to colonize. Most species have a form of ballistic dispersal, whereby contraction of the seed pod as it dries eventually shoots the seeds up to several metres away from the mother plant.

Those violets that do not have a ballistic dispersal mechanism have evolved instead a complex, mutually beneficial partnership with ants, a phenomenon called myrmechory. The ants act as seed carriers, depositing the Viola seeds in new locations around the forest, but not before they have collected payment by gnawing off the fatty, lipid rich protuberance at the base of the seeds called an elaiosome. Myrmechorous Viola species have drooping flowers on weak stems that bend to the ground under the weight of the developing seed capsule. When the seed capsule finally opens, it spills the seeds out into a pile on the soil, rather than flinging them forcibly from the mother plant. The seeds produce a compound called 1,2-diolein that acts as a signal to foraging ants. Attracted by the smell of the seeds, the ants collect them and take them back to the nest, where larvae are fed the elaiosomes, and the seeds are then deposited in refuse piles at the nest entrances or the borders of the ants’ territory where they eventually germinate. The relationship between the violets and ants is finely tuned. The plant has evolved to release its seeds early in the season, before the peak in abundance of other, more attractive food sources for the ants, and the seed capsules open during the period of highest ant activity, which coincides with the lowest levels of activity of seed predators like rodents. Violets benefit in a number of secondary ways from ant dispersal too. The chewing behaviour of the ants can actually break the dormancy of the seeds, improving their germination rates, and the refuse piles the ants leave the seeds in represent nutrient enriched microsites that are favourable for growth. Violets may be blue, but it is their reproductive biology that makes them fascinating!

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New Year’s Resolutions

 

A recent open letter in Nature from scientists at the University of Exeter raised a lurking issue about environmental sustainability in research just in time for scientists looking to make New Year’s resolutions. The authors highlight that the average lab scientist produces just under a tonne of plastic waste in their annual quest for knowledge, and they call on funding agencies to introduce incentives to foster greener lab practices.

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Hundreds, sometimes thousands of plastic pipette tips are used and thrown away every day in molecular biology laboratories. Photo by: Rajiv Shah

One tonne of plastic. That’s equivalent of enough barrels of oil needed to make gasoline to drive a car for 2 weeks. The statistic immediately brings to mind my first experiences with a molecular biology lab and the conflict it created with my environmental consciousness. As an undergraduate I was involved with sustainability groups on campus, and I spent many hours visiting friends at the campus ‘eco-house’. I also worked part time for the molecular biology professor who was responsible for getting our department’s brand new robotic microarray machine up and running. For months, I spent a couple of hours every day placing thousands of plastic pipette tips in racks, sterilizing them, and then gathering up the 100 L garbage bags full of the pipette tips used the previous day and hauling them down to the dumpsters. Having me rack tips bought in bulk was comparatively ‘environmentally friendly’ because it meant our hundred or so tip boxes were re-used instead of being thrown out as they were emptied, but I still shuddered at the sheer amount of plastic thrown out every morning. It’s not a new issue. Single use plastics or ‘consumables’ are an integral part of many branches of science. Whether it is pipette tips for molecular biologists, plastic sampling bottles for limnologists, or centrifuge tubes for chemists, disposable plastics are considered a key time- and labour-saving component of lab science. Admittedly, some of the plastic waste generated at the lab bench is biohazardous and unsuitable for recycling, but much of it is clean plastic that has touched nothing more dangerous than water or alcohol. It’s no question, the possibility for re-use or recycling is definitely there.

But is it really up to funding agencies to drive more sustainable practices in scientific laboratories? My own take on the issue is that meaningful change will only come from changing the behaviour of scientists themselves. My institution, like hundreds of others, already has ‘green lab’ recycling programs in place for uncontaminated plastics, cardboard, Styrofoam and glass. Still in the molecular biology labs, plastic pipette tip boxes and cardboard packaging from microcentrifuge tubes inevitably find their way into the garbage can standing at the end of the lab bench rather than the recycling bins a few feet away at the door of the lab. Although technologies are available for cleaning pipette tips for re-use, I have yet to work at an institution that has a system in place, or encounter anyone who has included one of these machines in a grant application or equipment funding bid, and implementing this kind of system would inevitably encounter some resistance on the grounds of time and labour costs. Funding agencies effectively operate at arms length from actual day to day lab operation and have little ability to check up on lab practices and whether claims made in grant applications have actually translated to improved sustainability in science labs. It seems doubtful that any initiative originating at that level could really result in effective change. It is scientists themselves that need to step up and make a New Year’s resolution to green their lab practices.

Looking for ideas on how to improve your own lab practices? Check out this post from Southern Fried Science or get in touch with your university’s sustainability office.

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Christmas Cannons

Nothing says Christmas in my house like the smell of sibling rivalry, so it seems appropriate to share a biology-themed sibling showdown that includes a Christmas favourite. When it comes to decking the halls, any interior decorator will tell you the European mistletoe I recently wrote about is the golden child, no contest. Ask a biologist, and sibling rivalry steps in. My personal favourite? The ugly cousin: the Dwarf American mistletoe, Arceuthobium. It might not be much to look at, but biologically, it’s a beautiful parasite.

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The dwarf American mistletoe is a parasite of conifer trees. Because it derives most of its nutrition from its host, it no longer produces leaves of its own and makes little chlorophyll in its stems, making it a yellow-green colour. Photo by: Stan Shebs

Unlike their flashy European cousins that are all greenery and shiny berries, Arceuthobium is a dense, leafless bush of branching coral-like, sickly yellow-green stems that parasitize conifer trees. The dwarf American mistletoe has evolved to exploit its hosts more thoroughly than its European cousin, doing away with its own leaves and instead sucking most of its nutrition out of its host. But what Arceuthobium lacks in physical appeal, it makes up for in speed. The plants’ fruits are small, dark, swollen egg-shaped protuberances at the tip of arching stems. Upon first glance, they hardly seem capable of the physical feats they perform. The dwarf American mistletoe has explosive seed dispersal and these tiny fruits, no more than 5 mm in diameter, are powerful cannons that accelerate mistletoe seeds at speeds of up to 25 m/s. By comparison, the fastest mammal in the world, the cheetah, has a top speed that is only marginally faster at 30 m/s. The mistletoe can shoot its seeds up to 20 m away, which would be the equivalent of a human being able to throw a baseball more than half a kilometer. Considering there can be more than 2 million mistletoe fruits on a single host tree, an infected forest is a veritable army of seed-cannons.

 

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Ripe dwarf Mistletoe fruits with the abscission zone visible as a slightly darkened line at the base of the fruit. Photo from de Bruyn et al. 2015

The mechanism behind this explosive dispersal is unique among the plant world. The greenish fruits of the American mistletoes contain seeds surrounded by specialized tissues called viscin. As the fruit matures, these cells swell with water, raising the pressure within the fruit. A layer of cells at the base of the fruit where it joins the stem are programmed to die during the ripening of the fruit, creating a weak layer that is called the abcission zone. The increasing pressure in the fruit will eventually cause the fruit to suddenly separate from the stem at the abcission zone, ejecting the seeds violently. However, what makes this method of seed dispersal so unique is the mechanism that triggers it. Recent research has demonstrated that Arceuthobium fruits increase in temperature by as much as 2 degrees Celsius in the ten minutes before dispersal occurs. This sudden accumulation of heat seems to act as an internal trigger, although the mechanism by which the signal is translated is not fully understood. While dwarf American mistletoe may not have the romantic Christmas charm of its European cousin, its spectacular physical feats make it a stand out species nonetheless.

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Mistletoe Magic

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The European mistletoe is a hemiparasite that steals water and nutrients from host trees, but whose green leaves photosynthesize and produce sugars as well. Photo by: Hans Braxmeier

T’is the season here at the BioPhiles and this week’s species extraordinaire is the European Mistletoe of Christmas carol fame, Viscum album. Its dark green foliage and shiny white berries make it perfect for decking the halls and creating holiday romance, but from a biologist’s point of view, this Christmas standby is no slouch, either. Like all mistletoes, it is a parasite of other tree species and its roots have been modified into specialized structures called haustoria that penetrate the host’s bark, allowing it to divert water and nutrients from its host. Despite being a perfectly adapted thief, the European Mistletoe is considered a hemiparasite because it still retains the ability to photosynthesize and is not dependent on its hosts for all of its nutrition. Nevertheless, heavy mistletoe infections can drastically alter the physiology of their hosts, decreasing water use efficiency, and increasing nitrogen demands. This can ultimately change total biomass production of the tree as well as the relative proportions of leaves, wood, and roots it produces.

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Mistletoe seeds are surrounded by sticky viscin that helps them to adhere to branches where they can germinate and infect new trees. Photo by: M. Fagg

The white berries produced by mistletoe are another highly adaptive feature of this plant. The seeds inside the berry are surrounded by sticky flesh called viscin, which contains sugars and long, tightly coiled fibres called cellulose microfibrils. This combination of molecules allows viscin to both stick and stretch. Viscin is a sort of botanical superglue: it doesn’t dissolve in water and isn’t easily broken down by heat, light, or even the digestive tract of birds. When birds eat the mistletoe berries, the seeds that are defecated out are as sticky as when they went in, allowing them to adhere to whatever branch the bird was sitting on when it answered the call of nature. Not all of the seeds make it that far either. The sticky viscin coating often leaves mistletoe seeds stuck to the beaks of birds, which induces preening behaviour. The bird will wipe its face against branches until the offending seed comes off, and the viscin will glue the seed to the branch where it can germinate and start a new infection. This is where bird behaviour becomes important in shaping mistletoe populations. The plants largely depend on birds to disperse their seeds. Because birds prefer to visit trees with tasty mistletoe bushes growing on them, a positive feedback loop initiates, whereby mistletoe populations become concentrated in small patches, and trees have multiple infections. From a biologist’s point of view, the magic in the mistletoe has nothing to do with Christmas cheer, it’s parasitism and adaptation.

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A positive feedback loop driven by bird behaviour means that a tree with one mistletoe infection is likely to develop more. This poplar tree has many globe shaped mistletoe plants growing on its branches. Photo by Stefan Schweihofer

 

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