How insect eating plants persuade insects to pollinate them

There have been quite a few articles about carnivorous plants just recently, and this one caught my eye.  It’s courtesy of the BBC Earth website, and I’ve linked this post to the original one.

Enjoy.

Karen

I tell myself
Hey only fools rush in and only time will tell
If we stand the test of time
All I know
You've got to run to win and I'll be damned if
I'll get hung up on the line

********

How insect eating plants persuade insects to pollinate them

Eating insects makes good evolutionary sense for plants living in barren soil with few nutrients. But how do the plants avoid eating the insect pollinators they rely on to reproduce?

·    By Yao-Hua Law

11 October 2016

Grubs gnaw roots, maggots munch fruits and caterpillars chew leaves. In textbook food chains, animals eat plants, not the other way round.But there are plant species that break this rule – at least 600 species of them on the last count. These are the carnivorous plants, and they routinely feast on insects, spiders, worms – even potentially small mammals.

Life for a carnivorous plant is challenging. They cannot very well march across the landscape in search of a meal. Dinner has to come to them. The plants have evolved sticky leaves, water pots and the like to catch animals, but how – if at all – do they lure their prey into these traps?

A study published in February 2016 shows for the first time that some carnivorous plants use smells to secure meals – validating an idea that Charles Darwin suggested 140 years ago.

Darwin worked on the sundews, a type of predatory plant with leaves covered in tentacles, each tentacle having a drop of sticky fluid at its tip. Darwin described the sticky leaves as"temporary stomachs"with which the plants catch live prey, break it down with acids, and "feed like animals".

Drosera spatulata. Pollinators are guided to the flowers by visual cues, and protected from the traps by spatial separation (Credit: Ashraf El-Sayed)

"It's common to analyse plant volatiles, so it's quite amazing that nobody has tested Darwin's hypothesis," says chemical ecologist Ashraf El-Sayed at the New Zealand Institute for Plant & Food Research Limited.

Studying sundews in New Zealand, El-Sayed's team found that one species, Drosera auriculata, uses smells to lure prey. Their leaves emit volatiles that beckon gnats, midges and mosquitoes.

"I was working on lure-and-kill tactics in pest management when I realised that wow, carnivorous plants have been at it for a very long time," says El-Sayed.

Carnivorous plants face a more profound problem: sex

Carnivory evolved independently at least six times across the plant kingdom.  Carnivorous plants live in places like bogs and rocky slopes where the soil – if there is any – is so nutrient-poor that few plants can survive.  Carnivorous plants eke out a living here because they converged on the same solution to the nutrient problem: animals are nutritious, so eat them.

But the path to meat-eating is costly. As plants transform their leaves into traps that can trick, bind, drown, and digest prey, they gradually become less effective for harnessing sunlight to produce energy. Therefore, most carnivorous plants grow slowly and stay small.

Beyond that carnivorous plants face a more profound problem: sex.

Drosera arcturi (Credit: Andreas Jürgens)

Like many plants, carnivorous plants produce flowers when they are ready to reproduce. Most of these flowers appear suitable for insect-pollination – again, in keeping with many plants.

The trouble is that many carnivorous plants trap and kill insects. They are faced with a unique dilemma called "pollinator-prey conflict": they need to eat insects without jeopardising their chances of being pollinated by insects.

The most obvious way to protect pollinators is to keep flowers away from traps

 For example, a carnivorous plant from Spain called Pinguicula vallisneriifolia could produce more seeds if its flowers receive more pollinators. But sticky leaves mere inches away from the flowers kill a good number of those pollinators.

The carnivorous plant's challenge is to avoid confusing the insects it needs to eat with the insects it relies on for pollination. Studies suggest that most carnivorous plants handle this challenge very well.
There is often very little overlap between the insects visiting flowers and those dying in traps.

Somehow, carnivorous plants can separate pollinators from prey.

A yellow pitcher plant (Sarracenia alata) (Credit: John Abbott/naturepl.com)

The most obvious way to protect pollinators is to keep flowers away from traps. Some carnivorous plants do this by making sure their flowers bloom and die before the traps open. A field survey of 560 Sarracenia alata pitcher plants found only five with flowers and pitchers active at the same time.

Many carnivorous plants seem to spare their pollinators

 There is another option. One-third of carnivorous plants have removed all risks of pollinator-prey conflict by growing their traps underwater and keeping their flowers above ground. Many carnivorous plants also raise their flowers on long stalks. Some researchers speculate that long stalks serve to distance pollinators from traps.

But the role of long stalks in protecting pollinators remains debated. Some plants extend their flowers on stalks even though pollinators cannot reach their traps: bladderworts (Utricularia), for instance, have stalked flowers despite the fact that their traps lie underground.

Furthermore, a survey of more than 50 sundew species } found that plants closer to ground grow longer stalks than those higher up. Some scientists argue that carnivorous plants evolve long stalks to better attract flying pollinators rather than to better protect them.

A greater bladderwort (Utricularia vulgaris) (Credit: Ingo Arndt/naturepl.com)

Whether or not their flowers are far from traps, many carnivorous plants seem to spare their pollinators. This suggests that the plants have another way to mitigate pollinator-prey conflict.

We suspected that the plants might be using other cues to guide the insects

We studied three sundew species with different distances between flowers and sticky leaves," says El-Sayed.

The sundews were lethal – less than 20% of insects caught on leaves escaped. But in all three species, less than 5% of insects caught on leaves were also found in flowers.

"We suspected that the plants might be using other cues to guide the insects," says El-Sayed.
El-Sayed found that Drosera auriculata – the species whose flowers grow closest to its leaves – has flowers that smell distinct from its leaves.

El-Sayed then exposed insects to synthetic blends of these odours. He found that flower odours attract floral visitors – insect pollinators – while leaf odours deter them. Only insects that the sundews usually eat are attracted by the leaf odours.

Some of these chemicals might help us manage pests

This means D. auriculata is the first carnivorous plant known to use odours both to lure prey and protect pollinators.

However, the other two sundews in El-Sayed's study, D. spatulata and D. arcturi, have scentless sticky leaves and flowers that grow further apart. Floral visitors prefer the white colour of flowers, while prey do not discriminate between flower and trap colours.

So instead of smells, D. spatulata and D. arcturi use visual signals and separation to protect pollinators.

Drosera auriculata. The flower and trap emit different odours, guiding pollinators safely to the flower (Credit: Friends of Black Hill/Morialta Inc)

"D. spatulata and D. arcturi grow in open sites. Their flowers are often the highest points around," says El-Sayed. Potential pollinators flying by would likely find the flowers easily even without odours. "Investing in odours to guide pollinators would not be cost-effective in these sundews."

 D. auriculata is the first carnivorous plant known to use odours both to lure prey and protect pollinators

 El-Sayed hopes that the discovery of carnivorous plant odours will stimulate new research and applications for the chemicals.

His team has now begun studying a pitcher plant that emits even more complex and distinct smells than those he found studying sundews. "Who knows? Some of these chemicals might help us manage pests," he says.

Carnivorous plants so captivated Darwin that he called them "the most wonderful plants in the world". After tens of millions of years of juggling hunger and sex, these wonderful plants have evolved into effective and selective killers. Their adaptations could well be a treasure vault that we have just begun to unlock.

Meet the man on a mission to save carnivorous plants

I saw this on the BBC Earth website, and thought it should be reproduced on my blog, as carnivorous plants are a passion of mine.

Karen


I tell myself
Hey only fools rush in and only time will tell
If we stand the test of time
All I know
You've got to run to win and 
I'll be damned if
I'll get hung up on the line

************************************

BBC Earth - Meet the man on a misson to save carnivourous plants

Many of these insect-eating plants are on the brink of extinction, but one researcher is trying to rescue them

·   By Lucy Jones

15 September 2016

Stewart McPherson is prepared to go a long way for his science: even into the grounds of a prison in the Philippines. "I had to be guided by murderers," he says.

His target was, appropriately enough, a plant that kills: a tropical pitcher plant called Nepenthes deaniana that traps and digests insects. "It hadn't been seen for nearly 100 years."

McPherson has been fascinated with carnivorous plants since childhood. As an eight-year-old he came across his first species in a British garden centre. Immediately fascinated, he started a collection. After a couple of years, he had filled the family conservatory with hundreds of different plants.

The young naturalist found carnivorous plants extraordinary – as many others have for centuries. But despite their startling abilities, carnivorous plants are also in profound danger.

"To think they are plants with highly modified specialist leaves that have adapted through evolution to attract, capture, kill and digest animals – in some cases as big as rats – is pretty amazing," says McPherson.

Nepenthes rajah sometimes traps rats (Credit: Stewart McPherson)

"To think they are plants with highly modified specialist leaves that have adapted through evolution to attract, capture, kill and digest animals – in some cases as big as rats – is pretty amazing," says McPherson.

The idea of flesh-eating plants has long captured the imagination, from Victorian fables of man-eating species to post-apocalyptic sci-fi with John Wyndham's The Day of the Triffids and the musical fantasy film Little Shop of Horrors.

These plants were mythical, of course. The thought of real-world carnivorous plant species once seemed impossibly implausible.

Over the last decade, he has climbed 300 mountains

So much so that when the great biologist Charles Darwin wrote about them in his 1875 book Insectivorous Plants, he was mocked for suggesting some plants were carnivorous.

"But of course he was right – as he always was – and he provided the evidence that showed these plants capture and kill animals," says McPherson.

Nepenthes deaniana was not seen for 100 years (Credit: Stewart McPherson)

McPherson always longed to see carnivorous plants in the wild so, after leaving university, he set out to various countries across the world to document them in a series of field guide books. 

Over the last decade, he has climbed 300 mountains, formally described 35 new carnivorous plants and rediscovered long-lost ones – like the Nepenthes deaniana in that Philippine jail.

Because, strange as it might seem, botanists and scientists often overlook carnivorous plants.

We had to eat frogs on the way back

"They haven't received as much attention as they deserve," says McPherson. "There are hundreds of them all over the globe that are underappreciated."

But, thanks to his and other researchers' efforts, that is changing. "In the last 10 years, more of these plants have been found than in any time in history."

Many species are found in remote, inaccessible areas of – for example – Malaysia, Indonesia and Western Australia. Some of these plants had been hard to assess because the environments they occupy are unstable and difficult to travel in.

This means McPherson has had to go to great lengths to explore carnivorous plant biology. On one "epic" trip to a remote mountain in Kalimantan in Southern Borneo, on the trail of Nepenthes pilosa, a species that had not been since 1899, McPherson and his team ran out of food.

Nepenthes pilosa has thick "hair", hence its scientific name (Credit: Stewart McPherson)

"We had to eat frogs on the way back," he says. "We'd go out each night with a torch and look out for their glowing eyes, and catch them for breakfast, lunch and dinner."

While compiling his book on pitcher plants, he travelled to Palawan, a little-known narrow island in the Philippines. As a result of political instability in the 1980s and 1990s, few botanists had travelled to Palawan and explored the spine of mountains that runs along its length.

It was a rich treasure trove for McPherson. "I went up all of the tallest mountains and found an undescribed species on almost every one – seven in total," he says.

It's lived there for tens of thousands of years, quite possibly millions of years, and no one has known or appreciated it

The most exciting of the new species was a giant pitcher plant on Mount Victoria that he named after David Attenborough (Nepenthes attenboroughii), because of the broadcaster's inspiring passion for the natural world. The plant is big enough to put your hand inside.

McPherson heard a story from a group of missionaries who returned after a fateful trip and said they had seen "giant cup plants". He became convinced they were talking about a new species of Nepenthes. "It was immediately clear that it was a brand-spanking-new species, because it was so gigantic."

"We felt absolute elation. It's wonderful contributing anything to science or knowledge. It's lived there for tens of thousands of years, quite possibly millions of years, and no one has known or appreciated it. It's humbling to know that a plant or animal has existed in habitats for years in silence, just slowly ticking along waiting to be noticed and appreciated."

Nepenthes attenboroughii is big enough to put your hand in (Credit: Stewart McPherson)

His team also found a newly-killed shrew in the plant. It had fallen in and drowned in the accumulated rainwater. Two weeks later when they returned, the shrew was a husk, digested by the plant's enzymes.

This kind of behaviour leads to the popular misconception that these plants are "rat-eating". It is actually more coincidental than that.

Many of them harbour little worlds of unique life within their pitchers

"It's not fair to say they deliberately kill [mammals], they do it through coincidence. Under very rare circumstances the same process by which they capture and kill insects, also works on [small mammals],"explains McPhearson.

We still do not know very much about how these plants engage with other animals. Many of them harbour little worlds of unique life within their pitchers: animals that live inside the traps and break down the prey that the plants capture.

And some carnivorous plants have close relationships with mammals and birds.

A fanged pitcher plant (Nepenthes bicalcarata) (Credit: Stewart McPherson)

For example, Nepenthes lowii gets much of its nutrition from tree shrews, just in a roundabout way. "The pitchers of N. lowii look like a toilet bowl. They trap the waste from birds and shrews that use it as a toilet," says McPherson.

A 2015 study suggested that a carnivorous pitcher plant in Borneo attracts bats with an ultrasound reflector, and provides a roost in exchange for their waste. The complex relationship between sundews, spiders and toads has recently been studied by scientists at the University of Maryland.

The parrot plant (Sarracenia psittacina) can capture tadpoles underwater with its lobster pot trap

There is a simple reason why carnivorous plants have such complicated relationships with animals. They usually live in nutrient-poor soil, so they have adapted to capture and digest animal prey to gain the nitrogen and other nutrients they need to survive and grow.

The beautifully ornate sundew (Drosera), for example, captures its prey with sticky, glue-like tentacles. Once an insect is stuck, the plant will fold down, trap and kill its victim. These bright reddish-crimson sundews are even found growing wild in the UK, in the bogs across the country.

Pitcher plants use pitfall traps instead of sticky tentacles. Often pitchers are vividly coloured in red and yellow, with intricate patterns. This elaborate display attracts insects, which slip down the waxy linings into the fluid below and drown.

The pitcher plant Nepenthes bicalcarata looks particularly sinister. It has two "fangs" projecting beneath its lid. There are many theories as to how these thorns profit the plant. Charles Clarke at the University of New England in Armidale, Australia, suggests they may attract insects – there is nectar in the tips.

Carnivorous plants can even capture prey underwater. The aquatic waterwheel plant uses a snap trap, similar to the Venus flytrap. It snaps shut on mosquito larvae and small crustaceans called copepods which are digested by enzymes released by the plant. The parrot plant (Sarracenia psittacina) can capture tadpoles underwater with its lobster pot trap.

Nepenthes platychila has a limited range (Credit: Stewart McPherson)

Unfortunately, the beauty and strange prey-catching adaptations these plants have evolved make them attractive to poachers. Many of them are already critically endangered, which means McPherson and other botanists are racing against time to describe species before they disappear. Many are endangered and some are already extinct.

People in Europe and North America want specifically different ones, which drives people to go up the mountains, rip them out and bring them back

Although it is a common sight in garden centres, the Venus flytrap (Dionaea muscipula), perhaps the most iconic of carnivorous plants, risks extinction in the wild. The plant occurs only in a small range around Wilmington, North Carolina. Illegal poaching is a factor in long-term population decline.

The rarest carnivorous plants can command the highest value – sometimes thousands of dollars per plant – and many of these species live in economically-deprived regions.

"Everyone has mobile phones and the internet for eBay, so there's a massive trade in the world of rare plants, and it gets bigger and bigger every year," says McPherson. "People in Europe and North America want specifically different ones, which drives people to go up the mountains, rip them out and bring them back to sell locally and internationally."

Alongside poaching, shrinking habitats due to logging, mining, agriculture, new roads and other developments is taking its toll. Because many of the plants live in narrow altitudes and ranges, they can become extinct quickly if habitats change.

There may only be a few thousand Nepenthes rajah in the wild (Credit: Stewart McPherson)

Climate change could also be an issue in the future because many carnivorous plants have such narrow ranges.

To combat the decline and conserve some of the rarest plants, McPherson set up Ark Of Life in 2010. "Many species of Nepenthes are increasingly at risk of becoming extinct and in some cases little is being done."

If we don't maintain a permanent collection for them, that's it for this species, they're gone

Nepenthes rigidifolia, for example, may be the closest plant to extinction. "It's pretty much wiped out in the wild," says McPherson. "The only known wild population currently consists of one plant."

Similarly, there may only be a couple of thousand Nepenthes rajah left in the wild. This huge pitcher plant is endemic to Malaysian Borneo, and has occasionally trapped lizards, birds and frogs. The species is well protected in Malaysia's Kinabalu National Park. Even so, a landslide last year completely destroyed one of four populations, bringing it a step closer to the brink.

The challenge in conserving Nepenthes and certain other carnivorous plants is that the plants are single-sex, meaning an individual plant only has male sexual organs or female sexual organs, not both. That means you need multiple specimens of each sex to have a viable population.

A botanic garden in Holland looks after the Ark of Life collection of around 50 male and female plants. "It's small but they're really important for plants that are extinct or nearly extinct in the wild – they're the rarest of the rare," says McPherson.

The only known wild population currently consists of one plant

"Nepenthes clipeata and N. rigidifolia are the most important," he says. "Both appear to be in serious trouble and if we don't maintain a permanent collection for them, that's it for this species, they're gone. In 50 years all the people who currently cultivate them will have died."

To build up a permanent conservation collection of strains of each plant, McPherson looks for cuttings from people who already have them in horticulture. It is perfectly fine to have legal carnivorous plants at home and there are many legitimate breeders.

The IUCN launched a fundraising campaign at the end of 2015 to help complete the assessment of carnivorous plants, estimating that only 20% of species have so far been formally documented. A report in 2014 said that the primary objective was the assessment of Nepenthes species, in line with the focus of McPherson's Ark of Life.

A shield-leaved pitcher plant (Nepenthes clipeata) (Credit: Stewart McPherson)

There are other promising developments, too. The law was recently strengthened in North Carolina to make poaching wild Venus flytraps a felony rather than a misdemeanour.

Despite extensively searching for several days, McPherson found only four adult clumps and just three small juvenile ones

McPherson has just returned from an expedition to see how the rare Nepenthes clipeata is faring in Indonesian Borneo. This species is the most imperilled of all carnivorous plants. The only mountain on which it occurs has suffered rampant poaching, and has been extensively burnt during recent years, pushing N. clipeata to the brink.

Despite extensively searching for several days, McPherson found only four adult clumps and just three small juvenile ones.

Our pollution might be turning these unique plants vegetarian

The situation is just as bleak for Nepenthes kelam, another carnivorous plant native to Indonesian Borneo. It occurs only near the summit of Mount Kelam on the island. McPherson's investigations on the mountain suggest it is close to extinction in the wild.

Human behaviour has a significant impact on carnivorous plants and it remains to be seen how the most endangered species will survive and adapt in the world.

In 2012, scientists found that  sundew plants in Swedish bogs were cutting back on their fly-catching because they could find nitrogen in the more polluted areas. The plants are so finely tuned to their environments that any changes can affect the way they prey and eat.

So what is the future for carnivorous plants? Some species that occur in non-vulnerable places will be fine. But for those that are restricted to small, isolated locations, the situation is critical. A poacher could wipe out an entire population in a single trip. "It's a battle that in some cases we're quickly losing," says McPherson.