Archive for the ‘evolution’ tag
Plant rhododendrons to protect from bugs
Plants emit compounds to both attract and repel insects. Plants planted near rhododendrons can absorb and emit chemicals given off by rhododendrons to protect themselves from insects.
Scandinavian Scientists have discovered that a species of tree defends itself from herbivore attack by using chemicals emitted by neighbouring plants. The study, published today in New Phytologist, reveals how a species of birch tree adsorbs chemical compounds from neighbouring marsh tea plants, Rhondodendron tomentosum, in a unique ‘defence by neighbour strategy.’
The team from Finland, led by Prof. Jarmo Holopainen from the University of Eastern Finland, were conducting studies into emissions of forest and peat land plants when they discovered previously unreported compounds for mountain birch from their foliage emissions. The compounds were emitted by a species of rhododendron growing nearby.
“It is well known that many plant species start to emit chemical compounds after damage by herbivores,” said the co-author Dr. Sari Himanen, from Agrifood Research Finland. “In an earlier study we accessed the compounds emitted from mountain birch following Moth feeding damage and we found that some of the trees growing next to Rhondodendron tomentosum also emitted residual amounts of the compounds ledene, ledol and palustrol. This resulted in the idea to experimentally test whether these sticky semivolatiles could actually protect neighbouring birch trees from the attention of attacking herbivores such as feeding moths. Based on experimentation in the field, in a natural habitat and in the laboratory, we discovered that a novel, potentially also ecologically meaningful effect for neighbour-emitted foliage-adsorbed semi-volatiles might take place in a boreal environment.”
Plant emissions can have several roles, including the attraction or deterrence of herbivores. Some cause an indirect defence by attracting a herbivorous natural enemy, but it is extraordinary for one plant to benefit directly from another plant’s emissions.
Read more Plants discover the benefits of good neighbors in strategy against herbivores
Trees retaliate when their fig wasps don’t service them
It would seem trees are not as dumb as they first appear. When wasps try to lay eggs from outside the flower with out pollinating the flower, instead of inside the flower while spreading pollen the trees drop the fruit containing the baby wasps to death.
While trees often drop unpollinated flowers, they will often hold onto the galls containing the wasps and provide themselves with a future generation of pollinators.
Figs and fig wasps have evolved to help each other out: Fig wasps lay their eggs inside the fruit where the wasp larvae can safely develop, and in return, the wasps pollinate the figs.
But what happens when a wasp lays its eggs but fails to pollinate the fig?
The trees get even by dropping those figs to the ground, killing the baby wasps inside, reports a Cornell University and Smithsonian Tropical Research Institute study published in the Proceedings of the Royal Society B (published online Jan. 13). ( read more read more about tree retaliation )
More information
Abstract
Download the paper (pdf)
Plant and insect co-evolution
I recently attended a Lunch Bunch at Mercer on ‘Insect and Plant Interactions’, if you have a chance to hear that talk I strongly recommend it.
In your garden is an evolutionary arms race that has gone on since plants and insects first appeared on earth. Sometimes there are truces, sometimes one or both will adapt, and sometimes it’s all out war.
Plants have developed many defense mechanisms to protect themselves from herbivore insects ( about half of all insects ) including chemical toxins, physical barriers, trickery, but sometimes resort to a symbiotic relationship with the insect.
Some plants can send warnings to other plants when they are under attack by insects. These warnings are volatile organic compounds the leaves release into the air. Nearby plants sense the compounds and begin to ramp up their toxin production. This saves the plant from spending energy making toxins when they are not needed. Trees attacked by pine bark beetles will do this, legumes are also know to release warning chemicals when under attack.
Sometimes plants release chemicals that attract beneficial insects for pollination or to attack herbivores. Some plants create chemicals that make them undigestable to insects. Other plants release compounds to repel insects ( deet ). Some common beans create toxins that when eaten by caterpillars will prevent proper butterfly development. Nicotine is a toxin to ward off tobacco pests.
Physical barriers take the form of thorns ( roses ), hairs ( lamb’s ear ), thick walled leaves ( cactus), and grit on the leaves (bamboo). Plants that are wounded may release antibacterial chemicals and cell strengtheners to wounded areas.
Trickery by plants is more common than you’d expect. The passionflora vine has little nodules at the base of the leaves. These nodules look like butterfly eggs. When butterflies mistake these for other butterfly eggs, they move on and look for a less crowded place to lay their eggs.
Some plants have gone proactive and eat the insects. ( Venus flytraps, pitcher plants ). These plants either trap by trickery or close when a trigger hair is touched and capture, dissolve and eat the insect.
Waterlilies sacrifice a bee for each pollination. In the first stage the lily holds water in the cup. The bee arrives to drink but drowns because the plant has put surfactant into the water. The pollen that the bee has carried from previous flowers is released to fertilize the murderer. The next day the flower opens, dries and produces its own pollen for the next bee to collect and carry off.
Other plants are slightly less proactive predators. Pipevines attract flies who climb into the flower and are trapped in the bulb at the bottom by hairs that face in along the tube. After the fly created a ruckus getting covered in pollen the flower relaxes in the morning to let the fly escape and pollinate the next pipevine flower.
There are many symbiotic relationships, flowers have colors in visible and infrared light as well as scents and shapes to attract bees. Some like bluebonnets change color to announce whether there is nectar remaining.
Others give off heat and or less pleasant scents to attract beetles and flies. ( Sago, stapeliads, aroids )
Some plants provide shelter for ants who in turn protect the plant from other predators and feed the plant. Some ant species will even strip bare competing foliage plants.
Many species of plants and insects have developed a one to one relationship, wipe out the insect and you wipe out the plant species. ( yucca, Senita cactus/moth )
Insects continue to evolve ways around plant defenses including neutralizing or becoming resistant to plant toxins. For instance monarch butterfly caterpillars feed on toxic milkweed, black swallow tail butterflies on pipevines. Sometimes these insects use the ingested toxin to become toxic to their own predators.
Clever carnivorous insects will hang out on a plant, wait for the plants predator insect and have it for dinner. Some like ranching ants will milk and ranch the aphids that feed on a plant.
Sometimes only one or a few insects can eat a given plant, providing no food for competing insect species. (monarchs and milkweed ). Others like locusts, adapt to eat anything and everything in their path. Yet other insects can evolve to learn to eat the parts of the plants that do not contain a toxin.
All of which makes the garden a fascinating place.
More information for the curious:
Ecological Genomics of Plant-Insect Interactions
Plant insect interactions: An evolutionary arms race
Quaternary period
This time starts 3 million years ago and leads us into the age of humans. The world is still cooling at the start of this time, but that gives way to global warming. The world cools and the world warms several times in this period. Ice ages last about 100,000 years, followed by about 100,000 of global warming as the earth wobbles in its travels about the sun. The continents are pretty much where they are today.
Neaderthals appear about 250,000 years back. Homosapiens about 180,000 years ago. Our earliest cave paintings are about 30,000 years old, which is when our Neaderthals disappear, and the ice begins to retreat and continues to do so to this day.
The last ice age ends about 10,000 years ago. As the world warms the first farms appear about 6500 years after ago.
Flowering seed bearing plants are spreading rapidly. At 30 million years back herbaceous plants with flowers show up. They can better handle changing seasons.
Pine trees, grape vines, oaks and spruces are spreading.
Insects and plants are co-evolving together. Our first nectar eating birds and bats appear. Plants that were fertilized by wind give way to insect fertilizing plants. Some grasses and trees revert back to wind fertilization.
See also:
Milankovitch Cycles and Glaciation
