Sunday, 10 May 2015

Lizards 11: Bearded Dwarf Chameleon

Bearded Dwarf Chameleon - in center of picture
While panther chameleons are among the larger species of chameleon, many species have become miniaturised in the course of their evolution and are generally referred to as pygmy or dwarf chameleons. This has happened on at least two separate occasions, resulting in the dwarf chameleons of mainland Africa and the even smaller leaf chameleons of Madagascar. As a result of their small size and limited capacity to disperse, there are almost certainly many more species of these marvelous little lizards than are currently described.

Recently Bristol Zoo has put on show one of the more widely kept and bred of these miniature chameleons, the Bearded Pygmy Chameleon Rieppeleon brevicaudatus, which grows to a maximum of 8cm. Many other dwarf chameleon species are even smaller – the Madagascan Brookesia have several species with a snout-vent length of only 15mm, making them some of the smallest lizards in the world.  As with the other miniature chameleons, they are specialized for living in low growing bushes and leaf litter of the forest floor. Part of this specialization is a body form which resembles one of the dead leaves that their habitat is full off. Some other species of dwarf chameleon are camouflaged in shades of green instead, and disguise themselves as moss.

Such small lizards feed on equally small invertebrates, about the size of fruit flies or hatchling crickets, and like their larger relatives they catch them with their extensible tongue. Such small animals are also vulnerable to many other predators, not only, or even especially, vertebrates – large spiders, centipedes, scorpions, praying mantids and ants are  just some of the  invertebrate predators they face. Perhaps to ward these off, dwarf chameleons can “buzz”, vibrating in an apparent warning signal to potential attackers.

Unlike many species, dwarf chameleons are not especially antisocial. Males are aggressive with each other as are many other kinds of lizard, but females tolerate each other and even roost together at times.

Some chameleon species are livebearing, but R.brevicaudatus is an egg layer. Clutch sizes in captivity are up to 4 eggs, usually less, which are buried in the soil. Incubation varies with temperature, but is usually around 90 days. I am not sure if they have temperature-dependent sex determination as many reptiles do, and it appears that both means of determining gender of offspring are thought to occur in other chameleon species. The newly hatched babies are of course minute, and feed on even smaller invertebrates than the adults.

Bearded Dwarf Chameleons are reasonably fast growing and prolific, which they need to be as they are unfortunately quite short lived. In the wild they are probably effectively annual, but in captivity they can live up to 3 years.

At present R.brevicaudatus is listed by the IUCN as Least Concern. They are however widely collected for the pet trade, which results in heavy mortality, and deforestation is probably also a threat to local populations. As some of these may represent additional new species, as a minimum any hobbyists keeping the species should try to keep locality data on the parentage of their animals.

Next time, the third of the three chameleon species kept at Bristol, the Mediterranean or Common Chameleon.

(images are mine)

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