Zoology has a discipline: evolution; zoology is vertically integrated, concerned with biological organisation at the level of organisms in their environment, organs, tissues, cells and molecules. This blog meanders through the animal kingdom, from aardvarks and anoles, through mouse and man, to zorillas and zebras.
Wednesday, 22 June 2016
The Case of the ‘Electric’ Chameleon
Chameleons never cease to fascinate and I have never been more fascinated than on one day in 1989. I was sitting with David Blatchford in his house. Bob Bustard called in on his way home and had with him a chameleon of the genus Rhampholeon. He showed us what happened when one gently touched the chameleon on the back. There was a tingling that felt like an electric current. We could not decide whether the tingling was the result of minute vibration of the scales or whether there really was some form of electrical discharge. Since the effect seemed to wear off with repeated touching and then, after a period of rest, return, we could not really rule out some electricity.
The next day I wrote to Richard Keynes FRS (1919-2010), my old boss and then Professor of Physiology at Cambridge, the world expert on bioelectricity from his work on electric eels, to see if he had come across such phenomena in a terrestrial animal; he hadn’t but told me what equipment I would need if I came across a Rhampholeon again. I didn’t, that is not until we we were walking back to camp from watching a family of Western Lowland Gorillas in the Republic of Congo in 2014 when our guide spotted this one on the path.
Rhampholeon spectrum. Republic of Congo 2014
Lacking a handy oscilloscope and knowing how much chameleons hate to be touched we left this one to go on its way.
Over the years I have kept and handled ten species of chameleon. In none of them nor in some wild ones in Madagascar did I encountered the same phenomenon. I have, though, kept it in the back of my mind and when I was looking through the excellent book, Mountain Dragons by Jan Stipala1 (2014) I realised that the phenomenon had been reported. In describing Rhampholeon boulengeri he wrote: ‘Known to produce vibrations as a defence mechanism when touched’.
A Google search then produced the following statement for each species of Rhampholeon and Rieppeleon (the latter genus was split recently from the former) in The Kenya Reptile Atlas: ‘Moves slowly, may sham death, if handled will produce a burst of vibrations, like an electric shock, caused by exhaling minute amounts of air’. Similarly, in Reptiles and Amphibians of Southern Africa8: Some species in this genus have a peculiar defensive strategy: when touched or restrained, the chameleon may suddenly vibrate. ‘This vibration is said to feel like a small electrical shock and is intended to startle a predator’. The owners of Lewa House north of Mount Kenya reported in the blog in 2013:
A few days ago as Calum walked down to the Lewa House pool he noticed a stick on the path that seemed to “fall over” as he got near it – on closer inspection he realised it was a chameleon! The first one we (or anyone we know) has seen on Lewa?
It’s called a Kenyan Pygmy-Chameleon (Rhampholeon kersteni) and has an interesting tactic of vibrating violently when picked up—something that Calum discovered when he handled it for the first time! It vibrates so much that a person who found one near the Kenyan coast thought that the chameleon had given them an electric shock?!
In Somali folklore it is said that if a Camel touches one of these chameleons the vibrations will kill the camel! We released our camel slaying chameleon back in to the bush safe and sound.
But who first described the phenomenon? in which chamaeleons does it occur? And is there any experimental evidence, as opposed to supposition, as to its adaptive significance?
The first reference I can find is to Edouard-Raoul Brygoo (1920-2016) in 19712. He, while working at the Pasteur Institute in Madagascar, observed in three species of Brookesia: ‘une certaine vibration perceptible au toucher mais pratiquement inaudible. Cette vibration n'a jamais été constatée avec des Chamaeleo’.
Dick Hillenius (1927-1987) of Amsterdam in a paper published in 19863 observed the same behaviour in Rhampholeon kersteni. Later, in describing a new species from Malawi (R. chapmani) Colin R. Tilbury described4 what happened when two adult males were placed in close proximity:
When 2 of the adult males were placed in close proximity to each other, they dorso-laterally flattened their bodies to about 3 mm in width and gave a lateral display accompanied by a rhythmical swaying to and fro of the whole body. The head and neck regions of both males turned a pale powder blue and the eyelids a bright white. The rest of the body remained a drab grey brown. Off-white gular interstitial skin was exposed and one male gaped his jaws displaying yellow buccal membranes. In addition to this, both chameleons produced short bursts of a «buzzing» vibration that was easily felt through the twig on which they were perched. These vibrations appear to be generated by the chameleons exhaling minute amounts of air.
In describing other new species from Tanzania, Mariaux & Tilbury (2006)5 noted in R. viridis: ‘When handled these chameleons produced an easily felt “buzzing” vibration, particularly if touched lightly on the back’.
In addition to any possible rôle in deterring predators, another function for ‘vibration’ has been suggested. Kenneth Barnett, Reginald Cocroft and Leo Fleishman noted6 that when Veiled Chamaeleons, Chamaeleo calyptratus, were touched they produced a vibration emanating from the body anterior to the front legs. They suggested that, because these vibrations could be detected in the plants on which they were living and were produced by males in the presence of females, the vibrations could be vegetation-borne communication signals to other chamaeleons. They recorded the frequencies of the vibrations. However attractive a suggestion that may be, experimental evidence has not been produced to indicate that the putative receiver of the putative signal actually perceives the vibration in the vegetation or is influenced by it. Since C. calyptratus is the one species that is easy to keep and breed in captivity, such studies should be possible to do. It should also be possible to determine whether the vibration in this relatively large species is produced by the same means as that in the small Rhampholeons and Brookesias.
There are more recent reports of ‘vibration’ in some other species of chameleon7.
While I want to stress that there is a lack of experimental evidence for any of the suggestions of a function for the phenomenon, nor for the mechanism or mechanisms of its production, I want to return to Bob Bustard’s female Rhampholeon. We could see no sign of any movement of the skin nor could we hear any sound being emitted. If the skin were just vibrating with minute oscillations, then would the pointed scales invoke the same feeling in other animals as it did in our fingers? And can we completely discount the discharge of static electricity, possibly building up on scales as they rub together during respiration? There are experiments there waiting to be done.
1 Stipala J. 2014. Mountain Dragons. In Search of Chameleons in the Highlands of Kenya. Jan Stipala. ISBN 978-0-9928176-0-2.
3 Hillenius D. 1986. The relationship of Brookesia, Rhampholeon and Chamaeleo (Chamaeleonidae, Reptilia). Bijdragen tot de Dierkunde 56, 29-38
4 Tilbury CR. 1992. A new dwarf forest chameleon (Sauria: Rhampholeon Günther 1874) from Malawi, central Africa. Tropical Zoology 5, 1-9. http://dx.doi.org/10.1080/03946975.1992.10539176
5 Mariaux J, Tilbury CR. 2006. The pygmy chameleons of the Eastern Arc range (Tanzania): Evolutionary relationships and the description of three new species of Rhampholeon (Sauria: Chamaeleonidae). Herpetological Journal 16, 315-331.
6 Barnett KE, Cocroft RB, Fleishman LJ, 1999. Possible communication by substrate vibration in a chameleon. Copeia 1999, 225-228.
7 Stuart-Fox D. 2014. Chameleon behavior and color change. In, The Biology of Chameleons, edited by Tolley KA & Herrel A, p 115-130. Berkeley: University of California Press. 8 Schmidt W. 2006. Reptiles and Amphibians of Southern Africa. Cape Town: Struik.