Pocket Science – back-scratching disabled chimps and free-falling aphids

By Ed Yong | August 9, 2010 9:00 am

Not Exactly Pocket Science is a set of shorter write-ups on new stories. It is meant to complement the usual fare of detailed pieces that are typical for this blog.

Chimp see, chimp do – back-scratching technique passes among disabled chimps

Tinka’s hands are paralysed. His fingers are permanently flexed, he can’t bend his wrists and to top it all off, he has a chronic skin condition. His body itches frequently and without dextrous hands, he can’t scratch himself properly. Fortunately, Tinka is an ingenious fellow. He uses his motionless hands to grab a liana (a thick, woody vine) and, stretching it taut, he rubs his itching body against it. Tinka’s a chimpanzee and he has found a way of getting to those hard-to-reach places, like a human towelling their back.

Tinka’s a member of the Sonso chimp community in Uganda, which has high rates of disability, inflicted by man-made snares. The snares were intended for duiker and bush pig, but with hundreds in the area, some chimps inevitably got caught. The snares have been removed but not before they inflicted permanent handicaps on a third of the Sonso chimps. But from this tragedy came an opportunity to study the spread of cultural traditions in wild chimps – an opportunity that’s been seized by Catherine Hobaiter and Richard Byrne form the University of St Andrews.

It’s clear that chimps can pick up new traditions from one another in captivity but their ability to do so in the wild is unclear. In natural conditions, it’s very hard to spot the birth of a new behaviour and to identify the individual who started it. It’s also difficult to work out if others are copying the innovator or just performing acts that were already within their repertoire. But Tinka bucks the trend. His liana-scratch technique is his invention. No other chimp in Sonso, or anywhere else in Africa, does the same thing. And Hobaiter and Byrne have found that at least 6 other chimps have taken up the technique, all of whom lived in the same area as Tinka.

There’s no element of active teaching here. After merely watching Tinka perform his special move, the apeing apes could do it themselves sometime later. Chimp see, chimp do. What’s more, many of these imitators aren’t handicapped and the technique doesn’t seem to offer them any benefits – they could just scratch or groom themselves if they wanted. Hobaiter and Byrne think that this is just a “behavioural fad”, reflective of the chimpanzee’s natural predilection for copying its peers.

Reference: PLoS ONE: http://dx.doi.org/10.1371/journal.pone.0011959

More on chimp cultures from me

Aphids drop and roll when they detect mammal breath

For a colony of aphids, there can be few fates as humiliating as being suddenly eaten by a passing goat. Plant-eating mammals pose a great threat to plant-eating insects. One chomp can unwittingly take out an entire colony. But as hungry mammals get closer, they give off a warning –hot, wet breath. Pea aphids take this as a cue to stop, drop and roll – they let go of their plant en masse and fall away from the jaws of death.

Moshe Gish discovered this unusual strategy by allowing a goat to feed on alfalfa plants infested with pea aphids. He found that, at the last minute, two-thirds of the colonies dropped to the ground. When he flicked the leaves, only a quarter of the colonies dropped off and when he cast a shadow overhead, they did nothing. It was the animal’s breath that did it.

The aphids also drop when they sense predators like ladybirds, but they do so more quickly and consistently when they sense mammal breath. Gish could even make individual aphids abandon leaf by directing a puff of goat or human breath at them using a tube. By playing around with these artificial puffs, he found that it wasn’t the presence of any particular chemical that did the trick, but the combination of heat and humidity.

This is the first time that anyone has found an animal that defends itself against being accidentally eaten by plant-eaters. The ability to detect mammal breath isn’t unique to aphids though – mosquitoes use the same skill to find a blood meal, while other insects and arthropods respond to the hot and humid vapours by releasing toxic chemicals. But for the generally defenceless pea aphid, mammal breath means only one thing: drop or die.

Reference: Current Biology, citation to be confirmed

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Comments (7)

  1. Nemesis

    I know people who probably couldn’t figure that out.

  2. Tiger

    A good chance to also get a glimpse into early human evolution. If humans are as closely connected genetically to chimps and other great apes as suggested, maybe the adoption of better ways to do the simple things in life is the way man evolved to be the dominant species. If man were to disappear, it is likely that some species of great apes could still rival the porpoise as being the replacement species.

  3. Chiral

    So, how close to the aphids do you have to get? I am around aphid colonies a lot and have never seen this, even when I get within a few inches.

    I’m definitely going to try blowing on them now.

  4. I wonder if the next time someone who smokes breathes in my face when talking to me I can cite the aphid as I drop and roll…worth trying!

  5. Chris M.

    @Chiral, I’d bet it varies depending on the type of aphid; the ones that inhabit roses, trees, or other less large-herbivore-friendly habitats are probably not as willing to drop off at a breath.

  6. This was only tested in two species of aphid out of a total of 4,400 or so. I could probably have made that clearer in the text, I suppose.

  7. (on the aphid versus mammal’s breath thing)
    Now I am imaging a happy future where phytophagous insects are effectively driven off crops not by chemical cocktails, but simply by having human volunteer blow on plants. Ooh, it would be so good…


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