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100 years ago: woolly bear caterpillars obey the law

The Guardian - Mon, 2017-09-04 07:30

Originally published in the Manchester Guardian on 4 September 1917

September 3
“Woolly bears,” in a fearful hurry, race across the road; they look as if they meant business or feared the wheel of passing vehicle or heedless boot. But the caterpillar knows nothing of danger, but merely acts as heredity has taught it; it must obey laws or go under in the struggle. Most insects need a wide distribution, for too restricted a feeding area may bring famine or degeneration; in one or other of their stages insects must get to a distance from congested districts or from ravaged food-plants. Naturally this distribution or migration takes place with many insects when, in their perfect stage, they are provided with wings, but some moths are slow-flying and lethargic, too busy with nectar-sipping and egg-laying to travel far, and in these the caterpillars make the journeys, getting over as much ground as they can before they find it necessary to spin cocoons.

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I have always wondered: why are some fruits poisonous?

The Conversation - Mon, 2017-09-04 06:05

It was all the apple's fault: we've been fascinated by poisoned fruit for a long time. Jacob Jordaens (1593–1678), The Fall of Man, via Wikimedia Commons

This is an article from I Have Always Wondered, a new series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au

Why are some fruits poisonous when the objective of fruit is, presumably, to be eaten so that the seeds can be widely distributed with nutritive manure? – Sev Clarke, Mt Macedon

Poison fruit has captured our imaginations for centuries. Snow White’s death sleep was induced by the evil queen’s gift of a poison-laced apple. It is rumoured that deadly nightshade, a plant with naturally occurring fruit toxins, was used to kill a Roman emperor and halt an invasion of Scotland. A deadly dose of ricin from castor beans was administered to a Bulgarian dissident via the tip of an umbrella.

More recently, scientists have been trying to understand why some fruits are naturally poisonous. From the vain queen’s point of view it makes sense to poison an apple and feed it to the fairest in the land. But why do some plants offer poison fruit that has the potential to harm – or at least deter – fruit-eating animals?

Fruiting plants and fruit-eating animals have “mutualistic relationships”, where each benefits from the other. Plants need to spread their seeds to colonise new territory, recolonise after disturbance, or avoid the dangers of staying at home (for example, if the parent plant harbours pests).

One way of doing this is to encase seeds in nutritious fruit pulp so that animals eat the fruit, digest the pulp, and later excrete the seeds with a helpful fertilising deposit of manure.

Animal-mediated (as opposed to wind- or water-mediated) seed dispersal can be particularly useful for getting seeds to specific locations. If you’ve ever wondered how parasitic mistletoe plants or strangler figs find their way onto branches high up in trees, fruit-eating birds are the answer. But why poison the pulp?

Birds spreading seeds are vital for many plants, so there has to be a very good reason to risk deterring them with toxic fruit. Matt MacGillivray/Flickr, CC BY Don’t you know that you’re toxic?

First, how do plants poison the pulp? Plants produce a range of chemical compounds, some of which have no apparent function in primary life-maintaining processes and so are called secondary compounds.

Potentially poisonous secondary compounds are produced either in the course of development from seed to adult plant, or in direct response to attacks from plant-eaters.

Poisons in fruit pulp are typically produced during development. Unripe fruit is often toxic to protect immature seeds from attack or premature dispersal, but ripe fruit with mature seeds can also be poisonous.

So how do we explain fruit that remains poisonous even when it’s ripe and ready for dispersal? One theory is that a low level of poison in fruit encourages fruit-eating animals to move away from the parent plant (avoiding additional poison), therefore carrying seeds further away.

In some cases toxins cause constipation, ensuring that seeds stay longer in the gut and so increasing the distance they are carried. In other cases – think of prunes – they act as laxatives to ensure the quick passage of seeds with minimal time for seed damage during digestion.

There is some evidence for these hypotheses, but they’re not the full story.

There’s good fruit-eating and bad fruit-eating

Not everything that eats fruit is good for the plant. Toxins in fruit might specifically target animals, microbes and fungi that damage its seeds, while being non-toxic to species that are good seed dispersers. The fruit of deadly nightshade is lethal to many mammals but apparently harmless to some birds, and Mediterranean buckthorn fruits are toxic to some insect pests but not seed-dispersing birds.

The fruit of deadly nightshade is poisonous to many mammals, but not the birds that carry its seeds. Andreas Rockstein/Flickr, CC BY-SA

But poisons often discourage seed destroyers and dispersers alike, so plants face a trade-off between deterring assailants and attracting the animals that safely disperse their seeds. Research so far suggests that how plants balance this trade-off depends on how long they hold onto fruit.

Highly nutritious and attractive fruit is quickly found and eaten as soon as it’s ripe: think of a plum tree stripped by fruit bats in a night or two. These fruits face less risk of damage before they’re safely eaten by the right animals, so protective toxins are less important and are therefore produced in lower quantities.

On the other hand, plants with less nutritious fruit, rarer or unreliable seed-dispersers, or more predators need to protect their vulnerable seeds with toxic fruit.

Finally, fruit might be poisonous simply because the rest of the plant is toxic. This is another trade-off some plants make: toxins that protect leaves from herbivores can also end up in the fruit.

Recent research suggests that poison fruit may ultimately result from adaptation to a range of animals consuming different plant parts, so we need to consider the whole plant and its interactions with various organisms to understand the origin and function of poison fruit.

Understanding how and why plants produce poison, in their fruit or elsewhere, has led to discoveries that are valuable for reasons other than murder and mayhem. Naturally occurring plant poisons have been used for a range of medical purposes from painkillers to antimalarial and anti-cancer agents, and there are potentially many more useful plant poisons yet to be discovered in the wild.

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Julian MacPherson Brown does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.

Categories: Around The Web

Freedom for Miss Simpson, the penguin found 2,000km from home

The Guardian - Mon, 2017-09-04 04:00

A Snares penguin from islands south of New Zealand is found wounded on a Tasmanian beach. Nine months’ nursing later, she tastes the open sea again

Just before dawn on a still morning in autumn a crowd of people gathers on a beach in southern Tasmania. They watch in tense silence as a small animal shuffles across the sand. This animal, a penguin, has been the focus of nine months of care, liaison and cooperation to get to this moment – she is being released and sent back out into her world. I am privileged to be included in the farewell crew, and share the jubilation and anxiety of the people around me, all of us hoping that she will remember her path home.

ABC Environment - Sat, 2017-09-02 12:05

The Earth has warmed by 1 degree. 2 degrees will bring with it awful consequences. Are we on track for getting the rise under control? Join Robyn Williams and a panel of energy experts at Brisbane’s World Science Festival.

Categories: Around The Web

The Guardian - Sat, 2017-09-02 00:59

The week’s top environment news stories and green events. If you are not already receiving this roundup, sign up here to get the briefing delivered to your inbox

Categories: Around The Web

Will European supermarkets act over Paraguay forest destruction?

The Guardian - Sat, 2017-09-02 00:48

NGO Earthsight reports charcoal from the Chaco region has been sold in Aldi, Lidl and Carrefour in Spain and Germany

No tropical forests anywhere in the world are being destroyed more rapidly than the Chaco stretching across Argentina, Bolivia and Paraguay. Not the Amazon in Brazil, nor in Indonesia, Malaysia or the Democratic Republic of Congo.

At least, that is according to a University of Maryland-led study published in 2013. And the carnage continues today. In July British NGO Earthsight released a report stating that “the latest available analysis [by Paraguayan NGO Guyra], covering January 2017, suggests that the rate of deforestation has kept pace since the Maryland paper. The Paraguayan Chaco is on course to lose more than 200,000 hectares of forest this year: an area the size of Manhattan every fortnight.”

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The week in wildlife – in pictures

The Guardian - Fri, 2017-09-01 23:07

Marabou storks, Kamchatka brown bears and playful lion cubs are among this week’s pick of images from the natural world

Categories: Around The Web

UK citizens are taking air pollution monitoring into their own hands

The Guardian - Fri, 2017-09-01 22:25

Thousands of people are using home air quality monitoring kits due to fears official figures are not capturing dangerous pollution levels, say Friends of the Earth

A growing number of citizens are monitoring local air quality because of fears official figures are not capturing “dangerous” levels of pollution.

The environmental charity Friends of the Earth has said 70 local groups are now using their testing kits and noted a “surprising” increase in people taking monitoring into their own hands.

Categories: Around The Web

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