Size matters

Smallest chameleon discovered in Madagascar

Brookesia nana

Reptilia: Chamaeleonidae

Brookesia nana sp. nov., in life.  Male holotype (ZSM 1660/2012). By Frank Glaw, Jörn Köhler, Oliver Hawlitschek, Fanomezana M. Ratsoavina, Andolalao Rakotoarison, Mark D. Scherz & Miguel Vences - Glaw, F., Köhler, J., Hawlitschek, O. et al. Extreme miniaturization of a new amniote vertebrate and insights into the evolution of genital size in chameleons. Sci Rep 11, 2522 (2021). doi:10.1038/s41598-020-80955-1. Creative Commons License: CC BY 4.0

Who isn’t fascinated by chameleons, beginning with their amazing ability to change colors?   This talent famously allows chameleons to blend into their surroundings, but is valuable in more ways than camouflage, with uses varying among species and situations.  For example, bright colors can be an aggressive signal to other chameleons, while darker ones may communicate submission. They also use color to regulate their body temperature.  Dark colors absorb light and heat better than lighter colors that reflect it, allowing these animals to raise or lower their temperature in spite of being cold-blooded. Some chameleons undergo color changes specifically aligned with what a particular predator is capable of seeing.

Chameleons have remarkable foot anatomy reminiscent of a condition in birds called zygodactyly.  Their five toes are arranged into two functional groups.  On front legs, the two outer toes form one group, and three inner toes the second.  On hind legs this is reversed, with two inner toes and three outer toes forming the two groups.  Either way, the groups of toes oppose one another enabling a firm grasp on branches.  This grip, combined with prehensile tails, and bodies that are laterally compressed, putting their center of gravity over their midline — and the branch on which they stand, make them superbly adapted for an arboreal life.  Other striking features include their characteristic swaying gate, stereoscopic vision, enabled by eyes that pivot and focus independently, and a long, projectile tongue, expert at catching insect prey.

The earliest fossil record for a chameleon is from China, about 60 million years ago.  Today, chameleon species are found in diverse habitats including tropical lowland and montane rainforests, savannahs and deserts.  They are distributed from the Middle East, southern India and Sri Lanka to northern Africa and southern Europe.  Nearly half of the approximately 200 named species of chameleons are endemic to the island nation of Madagascar.  A couple of species have been introduced to other areas, accounting for feral populations found in Hawaii, California, Florida and Texas.

Variation in size among chameleon species is quite impressive.  Among the largest, Parson’s chameleon, Calumma parsonii, has a body length of about 27 inches.  The smallest species are only about one thirtieth as long.  Setting a new record for being small is the recently named species Brookesia nana.  A photo taken by the scientists who named the species pictures this chameleon, less than an inch in length, perched on a finger-tip (above).  Females measure in at a scant 19mm and males are even smaller, only about 14 mm. For the metrically challenged, there are 25 mm in one inch.

Miniaturization has evolved at least twice among squamate reptiles, producing the tiniest of all amniote animals.  One is the genus Sphaerodactylus, the dwarf geckos of Central America, and the other the dwarf chameleons of Madagascar belonging to the genus Brookesia that includes the newly named species.

And, while we’re talking about size, there is something else noteworthy about this little lizard.  Males of the species — how can I put this delicately? — could give a race horse feelings of inadequacy.  The length of the hemipenis (herpetology speak for the male sex organ) in chameleons varies from 6.3% of body length to 32%, in the related species Brookesia tuberculata.  The new species measures in at a respectable 18.5%, or about one-fifth the total body length.  The reason that miniaturized species have proportionately larger genitalia than their larger-sized counterparts remains a matter of controversy.  In species like Brookesia nana, it is speculated that males need proportionately larger genitalia to be mechanically compatible with females of the species, which are larger.  Much remains to be learned about the sex lives of chameleons.

Cute, bizarre and exotic, it is easy to understand the attraction of keeping a chameleon as a pet.  But a disturbing amount of international trade in chameleons is illicit and threatens their survival in the wild.  While some live a decade, many species live only three to five years in nature.  Sadly, their lives are frequently much shorter in captivity.  Dr. Christopher Anderson, a herpetologist at the University of South Dakota, summed up the sobering situation succinctly: “The two main threats to chameleons in Madagascar are habitat loss and… the international pet trade” (as quoted in Mongabay, link below).  Legal export of a limited, regulated number of chameleons exists, but many thousands of chameleons are collected illegally each year to meet the high demand of the pet industry.  With so much habitat already destroyed or severely altered in Madagascar, this avoidable added threat to remaining populations is an unethical business that should be abolished.  No one who cares about these amazing animals should participate in or condone their illegal trade.

Further Reading

Glaw, F., Kohler, J. Hawlitschek, O., Ratsoavina, F. M., Rakotoarison, A., Scherz, M. D., and M. Vences (2021) Extreme miniaturization of a new amniote vertebrate and insights into the evolution of genital size in chameleons.  Scientific Reports 11: 2522. 

Scarffe, Chris (2021) Pet trade relies on ‘disposable’ wild chameleons from Madagascar.  Mongabay, 20 January.