According to Brown University researcher Dr Christopher Anderson, small chameleon species project their tongues further than large species, achieving projection distances of 2.5 body lengths.
The rosette-nosed chameleon Rhampholeon spinosus – a small (up to 50–55 mm snout-vent length, 3 – 3.5 g), tree-dwelling chameleon – can stick out its tongue with a peak acceleration 264 times greater than the acceleration due to gravity. Image credit: Philip L. Shirk et al., doi: 10.1111/ddi.12239.
“Chameleons employ a power amplification mechanism to ballistically project their tongue as far as two body lengths from their mouth to capture prey. To do so, the tongue is rapidly accelerated off the hyoid with the tongue subsequently traveling to the prey on its momentum alone,” Dr Anderson said.
Writing in the journal Scientific Reports, he reports that ballistic tongue projection in the rosette-nosed chameleon (Rhampholeon spinosus) produced a peak acceleration 264 times greater than the acceleration due to gravity.
“I show peak accelerations as high as 2,590 m/s2, or 264 g, and peak muscle mass-specific power values up to 14,040 W/kg in a 47 mm long individual of Rhampholeon spinosus,” Dr Anderson wrote in the paper.
“Tongue projection distances as high as 2.5 body lengths in a 47 mm long specimen of Rhampholeon spinosus were recorded. Similarly, tongue projection distances longer than 2 body lengths were also recorded in Brookesia superciliaris, Rieppeleon brevicaudatus and Trioceros hoehnelii, all of which are smaller than 90 mm long.”
Dr Anderson wanted to find the upper limit of chameleon tongue performance. To do that, he gathered individuals of 20 species of widely varying sizes in his lab.
Then he perched them one by one in front of a camera that shoots 3,000 frames a second. For each measurement, a cricket hung off a small dangling mesh to tempt the tongue to emerge. When it did, he could measure the distance the tongue went, the elapsed time, and the speed and the acceleration at any given time.
“In total, 279 feeding events from 55 different individuals were analyzed. This sample represented 20 chameleon species in nine genera, covering approximately 10 percent of the species-level and 75 percent of the genus-level diversity of the chameleon family,” Dr Anderson said.
What he noticed across all his measurements and analysis was that the smaller the chameleon, the higher the peak acceleration, relative power, and distance of tongue extension relative to body size. Larger chameleons produced impressive motions, too, but not compared to their smaller cousins.
“The results make physical and evolutionary sense. All of the chameleons have the same catapult-like apparatus for launching the tongue, but proportional to their size, smaller chameleons have a bigger one than larger chameleons,” Dr Anderson said.
The evolutionary reason why tiny chameleons are proportionately better equipped for feeding is presumed to be because, like all small animals, they need to consume more energy per body weight to survive.
“So little chameleons must be especially good at catching their insect meals – their tongues have to burst out unusually fast and far to compete for all that needed nutrition,” Dr Anderson said.
“For these reasons, it will often benefit researchers to look at the little guys when studying physical performance. Prior studies of chameleon tongue acceleration had measured much lower peak values because they only looked at much larger chameleons.”
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Christopher 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
