An expedition to the African island of Madagascar has uncovered the world’s smallest chameleon.
Adult members of the leaf chameleon species Brookesia micra grow to less than 30 millimeters, from nose to tip of the tail, and are found only on the islet of Nosy Hara, just off the extreme northern edge of Madagascar. As its distribution is limited to this tiny islet, the species may represent an “extreme case of island dwarfism.”
The ‘snout-to-vent’ length (i.e., from the tip of the nose to just before the tail begins) in B. micra males is just 16 mm, with both sexes growing no larger than 30 mm, making it one of the smallest amniote (egg-originating) invertebrates ever discovered. It’s tiny size just barely beats out the smallest lizard species: the gecko lizard, Sphaerodactylus ariasae, which has a snout-vent length (SVL) of at most 18 mm and a total length (TL) of 33 mm.
Unlike their larger, and more colorful, arboreal relatives, the 26 currently recognized species of Brookesia (4 of which are newly discovered) typically dwell and forage on the ground amongst the leaf litter, and are thus a dullish brown color, or rarely, a slightly greenish color. They are active day feeders and retire to the lowest branch perches at night for sleeping. It is here that they are most easily discovered by scientists; they were simply spotted by flashlight and plucked from their perches while sleeping.
For an endothermic amniote — a reptilian species that maintains a constant body temperature — B micra may represent the lower limit on the mass/surface-area relationship required for this adaptation. This is because maintenance of a constant body temperature requires an increasing proportion of the energy budget as this ratio decreases. Put simply: small size means less metabolic activity (per cell) to generated the heat needed. Even the smallest hummingbirds and bats reach a minimum size of 30 to 50 mm.
Size extremes in Nature — gigantism and miniaturization — are of great interest to animal scientists insofar as they represent the ecological and morphological constraints that the natural world places on organisms. The biggest animals are generally well-known, but it’s the most miniature of animals that, naturally, go unnoticed for the longest time. Just last year, the smallest species of frog (Paedophryne amauensis) was discovered in Papua New Guinea.
According to Glaw et al, in their PLoS ONE paper Rivaling the World’s Smallest Reptiles: Discovery of Miniaturized and Microendemic New Species of Leaf Chameleons (Brookesia) from Northern Madagascar:
“Miniaturization has been postulated to constitute an important pre-adaptation for evolutionary novelties that may lead to the evolution of entirely new patterns of organismal organization. Miniaturized tetrapods are often characterized by reduced and simplified adult morphologies; often the diminutive species resemble juveniles or subadults of larger related taxa.
Miniaturization is also sometimes associated with an evolutionary loss of skull bones and phalangeal elements, and with other features such as relatively larger braincases. Such features probably often reflect functional constraints and paedomorphosis.” (i.e., the retention of youthful characteristics into adulthood)
In addition to B. micra, three other species of the Brookesia minima clade were discovered on this recent, Malagasy expedition: Brookesia confidens from Ankarana, B. desperata from Forêt d’Ambre, and B. tristis from Montagne des Français.
Researcher conducted molecular phylogenetic analyses (based on one mitochondrial and two nuclear genes) and compared these to all nominal species in the B. minima group, including one additional species (B. tuberculata from Montagne d’Ambre in northern Madagascar). Results showed they all form a strongly supported clade (a more general taxonomic grouping) comprised of separate evolutionary lineages. This suggests that these species have diversified in geographical proximity in this small area.
In addition to Brookesia, two other genera, Calumma, and Furcifer, constitute the three genera of chameleons occurring on the island of Madagascar, a major biological ‘hot spot’, and which harbors about 80 of the world’s approximately 185 nominal chameleon species.
Chameleon photos and Map: (Brookesia micra, and others) The authors (Glaw et al), PLoS ONE, supporting material.
Additional photo: (Paedophryne amauensis, smallest frog) Rittmeyer EN, Allison A, Gründler MC, Thompson DK, Austin CC