Giant meat-eating plants prefer to eat tree shrew poo
By Matt Walker Editor,
Botanists have discovered that the giant montane pitcher plant of Borneo has a pitcher the exact same size as a tree shrew's body.
But it is not this big to swallow up mammals such as tree shrews or rats.
Instead, the pitcher uses tasty nectar to attract tree shrews, then ensures its pitcher is big enough to collect the feeding mammal's droppings.
Details of the discovery are published in the journal New Phytologist.
Pitcher plants have elaborate structures which entice creatures such as ants or spiders into a precarious position, from which they fall into a fluid-filled trap, where they drown and are ingested.
These arthropods are thought to provide the plant with vital nitrogen and phosphorus, which it cannot obtain any other way.
Pitchers are the largest carnivorous plants, and the largest pitchers grow in Borneo.
One, known as Nepenthes rajah, is believed to be the largest meat-eating plant in the world, growing pitchers that can hold two litres of water if filled to the brim.
This plant's pitcher is so big that they are reputed to catch vertebrates.
"This species has always been famous for its ability to trap rodents, but I've been looking at the pitchers of this species on and off since 1987, and I've never seen a trapped rat inside," says Dr Charles Clarke, an expert on carnivorous plants based at Monash University's Sunway Campus in Selangor, Malaysia.
"This made me wonder: if it is large enough to trap rats, but it only traps them very rarely, it is likely that the pitchers are large because of some other reason?"
To find out, Dr Clarke and colleagues Ms Lijin Chin of Monash University and Dr Jonathan Moran of Royal Roads University in Victoria, British Columbia, Canada turned their attention to tree shrews, which inhabit the same forest as N. rajah.
They did so after noticing that tree shrews, which are a similar size to rodents but most closely related to primates, sometimes left faeces in the traps of large pitchers.
"All of a sudden we realised that there may be some relationship between big pitchers and tree shrews," says Dr Clarke.
"So we decided to look at the pitcher geometry."
What they found "totally blew us away", says Dr Clarke.
N. rapah pitchers have huge orifices, but they also grow large concave lids held at an angle of about 90 degrees away from the orifice.
The inside of these lids are covered with glands that exude huge amounts of nectar.
Most importantly, the distance from the front of the pitcher's mouth to the glands corresponds exactly to the head to body length of mountain tree shrews.
The same is true for two other species of large meat-eating pitcher plant, N. lowii and N. macrophylla that are also visited by tree shrews.
However, the pattern does not hold for other pitcher species not associated with the small mammals.
"In order for the tree shrews to reach the exudates, they must climb onto the pitchers and orient themselves in such a way that their backsides are located over the pitcher mouths," explains Dr Clarke.
The tree shrews then appear to defecate as a way of marking their feeding territory.
That suggests these supposedly "meat-eating" plants have evolved a mutualistic relationship with tree shrews.
The tree shrews get nectar, a valuable food source, and in return, the plants get to catch and absorb the tree shrew's faeces which likely supplies the majority of nitrogen required by the plant.
These particular species of pitcher also live in the highlands where insects and other arthropods are more scarce.
Such creatures would normally provide the nitrogen needed by the pitcher, forcing it to evolve its huge size to attract tree shrews instead.
"150 years after the discovery of N. rajah, we finally have an explanation for why the largest carnivorous plant in the world produces such big pitchers," says Dr Clarke.
Dr Clarke says it is the "neatest" discovery he has made in more than 20 years of studying Nepenthes meat-eating plants.
"The findings should radically alter how we look at these plants," he says.
He believes there is much we still have to learn about the true habits of carnivorous plants.
They suspect another highland species, N. ephippiata, likely feeds on faeces too, as may a huge meat-eating plant called N. attenboroughii which was only discovered last year.
In the lowlands of Borneo, bats roost in the pitchers of yet more Nepenthes species, suggesting these plants may too feed off the faeces of other small mammals.
Giant 'meat-eating' plant found
Matt Walker Editor,
A new species of giant carnivorous plant has been discovered in the highlands of the central Philippines.
The pitcher plant is among the largest of all pitchers and is so big that it can catch rats as well as insects in its leafy trap.
During the same expedition, botanists also came across strange pink ferns and blue mushrooms they could not identify.
The botanists have named the pitcher plant after British natural history broadcaster David Attenborough.
They published details of the discovery in the Botanical Journal of the Linnean Society earlier this year.
Word that this new species of pitcher plant existed initially came from two Christian missionaries who in 2000 attempted to scale Mount Victoria, a rarely visited peak in central Palawan in the Philippines.
With little preparation, the missionaries attempted to climb the mountain but became lost for 13 days before being rescued from the slopes.
On their return, they described seeing a large carnivorous pitcher plant.
That pricked the interest of natural history explorer Stewart McPherson of Red Fern Natural History Productions based in Poole, Dorset, UK and independent botanist Alastair Robinson, formerly of the University of Cambridge, UK and Volker Heinrich, of Bukidnon Province, the Philippines.
All three are pitcher plant experts, having travelled to remote locations in the search for new species.
So in 2007, they set off on a two-month expedition to the Philippines, which included an attempt at scaling Mount Victoria to find this exotic new plant.
Accompanied by three guides, the team hiked through lowland forest, finding large stands of a pitcher plant known to science called Nepenthes philippinensis, as well as strange pink ferns and blue mushrooms which they could not identify.
As they closed in on the summit, the forest thinned until eventually they were walking among scrub and large boulders
"At around 1,600 metres above sea level, we suddenly saw one great pitcher plant, then a second, then many more," McPherson recounts.
"It was immediately apparent that the plant we had found was not a known species."
Pitcher plants are carnivorous. Carnivorous plants come in many forms, and are known to have independently evolved at least six separate times. While some have sticky surfaces that act like flypaper, others like the Venus fly trap are snap traps, closing their leaves around their prey.
Pitchers create tube-like leaf structures into which insects and other small animals tumble and become trapped.
The team has placed type specimens of the new species in the herbarium of the Palawan State University, and have named the plant Nepenthes attenboroughii after broadcaster and natural historian David Attenborough.
"The plant is among the largest of all carnivorous plant species and produces spectacular traps as large as other species which catch not only insects, but also rodents as large as rats," says McPherson.
The pitcher plant does not appear to grow in large numbers, but McPherson hopes the remote, inaccessible mountain-top location, which has only been climbed a handful of times, will help prevent poachers from reaching it.
During the expedition, the team also encountered another pitcher, Nepenthes deaniana, which had not been seen in the wild for 100 years. The only known existing specimens of the species were lost in a herbarium fire in 1945.
On the way down the mountain, the team also came across a striking new species of sundew, a type of sticky trap plant, which they are in the process of formally describing.
Thought to be a member of the genus Drosera, the sundew produces striking large, semi-erect leaves which form a globe of blood red foliage.
Note: When you wonder if life exists on other planets, just take a look at the diversity of life on our own world, Earth. That should be your first clue.