Granting Citizenship to the Striped Grass Skink Eutropis dissimilis

It may surprise you to know that there are lizards which look more like snakes. Called 'skinks', these lizards are small-legged and resemble snakes in both structure and locomotion. They lack the pronounced neck and long legs that are characteristic of “true lizards”, like the house lizards we share our homes with.

“Skinks of the genus Eutropis represent one of the most widespread and speciose lizard groups in tropical Asia,” mentions Aniruddha Dutta-Roy. Numerous recent studies have utilised a variety of genes and methods to reconstruct the evolutionary history of these lizards. However, these studies have not resolved the history of one widely distributed member, the Striped Grass Skink (Eutropis dissimilis).

Like many of their kind, striped grass skinks can grow back tails that they shed during a predatory attack. They are generally insectivores and prefer the safety of the underground, and sniff the air with their tongues. They are found across the vast landscapes Afghanistan, Pakistan, Northern India, Bhutan, Nepal, and Myanmar.

Aniruddha Datta Roy from Dr. Praveen Karanth’s Evolving Phyo-Lab in the Centre for Ecological Sciences at the Indian Institute of Science has established that the Striped Grass Skink is a member of the endemic Indian radiation of Eutropis.

Phylogenetics is the study of the evolutionary history of organisms and their interrelatedness. Phylogenetic investigations focus on the sequencing of the molecular structure of DNA from an organism. By identifying the key stretches of DNA (genes) to analyse, organisms can be divided up into different species based on the extent of differences between the DNA stretches. What you get is a kind of family tree depicting relationships between species.

For this study specimens of E. dissimilis were sampled from West Bengal and samples of E. novemcarinata obtained from the California Academy of Sciences Museum. The partial regions of two mitochondrial markers, one nuclear gene (from the DNA), and the RNA fingerprint protein were sequenced for inter species comparison. The sequences generated were compared published sequence data from species in the genus Eutropis, Dasia, Trachylepis and Emoia (a more distantly related lizard group).

Previously, morphological studies (studies which focus on the physical traits of the organism) supported the theory that the Striped Grass Skinks were descendants of the African group of skinks, Mabuya, which had dispersed to this region. Contrary to this, scientists from Karanth’s lab, working in collaboration with researchers from the University of Hawaii and the California Academy of Sciences have used this skink’s DNA to show that it definitely belongs to the Eutropis group, which is endemic to India.

Phylogenetic studies are important because they help in revealing interesting aspects of evolutionary history. They help in tracing the ancestry of a given species, which sometimes result in fascinating discoveries such as the genetic similarity between the hippopotamus and the whale. They also help in identifying if a species found in a location is there due to migration or due to local evolution. Evolutionary radiation refers to the increase in species diversity due to environmental stresses and opportunities over million year timescales.

It is interesting to note that the Eutropis dissimilis possesses a transparent window in the lower eyelid rather than a scaly eyelid which is present in most other Eutropis, and this is similar to all the species of Trachylepis (the Afro-Malagasy clade Mabuya). This leads to the fascinating conclusion: that these transparent lower eyelids, were acquired by the Striped Grass Skinks through isolated genetic mutation and the local environmental factors.

About the authors

Aniruddha Datta Roy and V Deepak are postdoctoral fellows and Praveen Karanth an Associate Professor at the Centre for Ecological Sciences, Indian Institute of Science Bangalore. Chinta Sidharthan is a researcher in Praveen Karanth's lab.

Collaborator Anthony Barley is at the University of Hawaii Manoa.

Contact: Aniruddha Roy

The paper appeared in the journal Zootaxa earlier this month.