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January 14, 2016 Archives

In 2012 the world was introduced to some of the smallest-known vertebrates: tiny chameleons. My good friend Grant wrote about them at the time, & I set an essay assignment for my first-years on these tiny beasties. How tiny is tiny? The following images are from the original paper, published in PLoS one by Glaw, Kohler, Townsend & Vences, 2012.

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Brookesia micra sp. n. from Nosy Hara, northern Madagascar. (A) adult male on black background, showing orange tail colouration; (B) juvenile on finger tip; (C) juvenile on had of a match; (D) habitat along a small creek on western flank of Nosy Hara, where part of the type series was collected. doi: 10.1371/journal.pone.0031314.g008

Anyway,Science News has an article on the speed with which chameleons shoot out their tongues to capture prey. It's based on this paper by Christopher Anderson, published in Scientific Reports.

When a chameleon shoots out its tongue, the movement's driven not only by muscle contraction but by utilising the potential energy stored in stretched elastic tissues. This allows the animal

to release energy more rapidly than by muscle contraction directly, thus amplifying power output. Chameleons employ such a mechanism to ballistically project their tongue up to two body lengths, achieving power outputs nearly three times greater than those possible via muscle contraction.

Noting that small animals are often capable of greater performance in the same feat than larger ones (think about the relative heights that fleas can jump, for example, or the loads that ants are capable of carrying), Anderson hypothesised that smaller chameleons would be able to outperform larger ones when it came to thrusting out their tongues.

To test this, he watched feeding by chameleons from 20 different species, and found that smaller species could indeed reach further: 2.5 times  body length in an individual just 47mm long. And they also achieved much greater accelerations: while larger species send forth their tongues at accelerations as high as 486 m s-2, the smaller ones Anderson studied managed far greater acceleration and power:

peak accelerations of 2,590 m s-2, or 264 g, and peak power output values of 14,040 W kg-1

The interesting question here is, why? Why can smaller chameleons shoot their tongues our further & faster? The answer may lie in the animals' metabolic rates: smaller chameleons will have higher mass-specific metabolic rates, and better feeding effectiveness could mitigate the impact of this. Anderson's data support this: because they also have proportionately longer jaws, larger tongues & associated structures, and higher relative tongue projection distances, 

small chameleons have effectively increased the relative size of their entire feeding apparatus. In doing so, small chameleons have increased the functional range of their prey capture mechanism, and are likely able to capture and process larger prey items than they would otherwise be able to if their muscle cross sections and jaws were not disproportionately large for their body size. This inference is supported by the selection of proportionately larger prey items by the smaller of two morphological forms in Bradypodion. These patterns are thus consistent with those that would be predicted for mitigating metabolic scaling constraints, which may be involved in driving the observed morphological scaling patterns.

Dr Anderson has produced a number of videos showing just what happens when a chameleon strikes, and has kindly given permission for me to use one of them here: 

C.V.Anderson (2016) Off like a shot: scaling of ballistic tongue projection reveals extremely high performance in small chameleons. Scientific Reports 6, article number 18625. doi: 10.1038/srep18625

 

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Recent Comments

  • Ken McLeod : It's not as if the University of Woolongong wasn't aware read more
  • Alison Campbell: We're testing the "Curiosity Stream" subscription documentary service at the read more
  • ifthethunderdontgetya™³²®©: They are fascinating beasties. Along with butterflies, my favorite summertime read more
  • Alison Campbell: @ Tsu Dho Nimh - yes, the mind boggles. I read more
  • Alison Campbell: @ Michael: apparently not, if the comments in various on-line read more
  • Alison Campbell: @ Grant - tempting to see if the Masters is read more
  • Tsu Dho Nimh: "It was used in the fight against smallpox for ~150 read more
  • Michael Edmonds: Since when has "academic freedom" been equated with "I can read more
  • Grant: Eh, that Masters is from the School of Health Sciences. read more
  • Alison Campbell: Beggars belief that the pertussis thing wasn't picked up on read more