The FLYzards

The Draco Lizard appears in Episode 3 of Planet Earth II Season 1. In the documentary, Attenborough describes how Draco lizards can fly up to 30 meters at a stretch to avoid combat or search for food. In this particular instance in the documentary, a Draco lizard is shown surveying a tree for food. However, it soon realizes the tree is occupied by another Draco Lizard. Instead of battling the bigger, threatening lizard for his territory, the smaller lizard chooses to glide away and try his luck on another tree. The Draco lizard belongs to the genus Draco and primarily inhabits the rainforests of Southeast India and Southeast Asia [1]. Because these lizards tend to live and find food on trees that are hundreds of feet tall, gliding is one of the many evolutionary mechanisms they have evolved to optimize their ecological niche. Researchers studying these unique creatures have hypothesized that the lizard developed the patagium, a membrane that connects its forelimbs to its hindlimbs, to avoid injury when zipping from tree to tree; it helps them slow down their velocity when they fall [2]. This is an example of natural selection in action. Since the Draco Lizard habitat consists of tall, majestic trees, falling can be extremely dangerous. Natural selection led to the development of gliding. As a result, the lizards are able to avoid falling and consequently extract the most resources from their environment.

Dracos exhibits other interesting adaptations as well. One behavioral characteristic of Draco lizards is bobbing. As seen in the documentary, the bobbing occurs automatically as a consequence of seeing another Draco lizard. This bobbing happens by simultaneously bending and straightening the forelegs. It is hypothesized that bobbing is a threat display to fend off enemy competition [3]. Another important morphological characteristic of the Draco lizard is its dewlap, a flap of skin under the throat that extends outwards under certain circumstances. One particular instance in which the dewlap is shown is in courtship behaviors [4]. The males use these dewlaps in courtship rituals, and studies have shown that larger dewlap sizes are positively correlated with reproductive success. Therefore, sexual dimorphism is seen in Draco Lizards; males tend to be larger than females, and also have longer dewlaps [5]. So next time you are in Southeast Asia, look out for these iconic creatures – they may fly right over your head!

by Tarun Swaminathan, Rishabh Surana and Neal Patel

Planet Earth II, Season 1, Episode 3, starting at approximately 8:50

 References

1. Mori A & Hikida T. 1994. Field observations on the social behavior of the flying lizard, Draco volans sumatranus, in Borneo. Copeia 1: 124-130.
2. McGuire JA & Dudley R. 2011. The biology of gliding in flying lizards (Genus Draco) and their fossil and extant analogs. Integrative and Comparative Biology 51:983-990
3. Hairston, N. 1957. Observations on the Behavior of Draco volans in the Philippines. Copeia 4: 262-265.
4. Font EF & Rome LC. 1990. Functional morphology of dewlap extension in the lizard Anolis equestris (Iguanidae). Journal of Morphology 206: 245-258.
5. Srichairat N, Duengkae P, Jantrarotai P & Chuaynkern Y. 2016. Sexual dimorphism in the spotted flying lizard Draco maculatus (Gray, 1845) (Squamata: Agamidae) from Thailand. Agriculture and Natural Resources 50: 120-124.