SLITHERY HISTORY

Lizards reveal the millennia-old story of India’s grasslands

Quartz india
Quartz india

It is not very clear when grasslands spread in India, nor is it clear whether they evolved naturally or developed as a result of human activities. There is much debate between scientists who claim grasslands developed as humans cleared forests for agriculture, and others who think that grasses evolved as the Earth was subjected to different climatic changes.

One way to gain insights into the evolution of grasslands is to study the emergence of animals closely connected to them. In the case of grasslands, these animals are Ophisops, a genus of lizards from an ancient time that are restricted to open grassy habitats in India, and other arid parts of Turkey, Iran, Saudi Arabia, Libya, Tunisia, and Egypt—which scientists studying the geographical distribution of animals refer to as the Saharo-Arabian region.

The lizard-grassland connection

In a recent study, researchers from the National Centre for Biological Sciences in Bengaluru carried out genetic analyses to investigate the manner in which these lizards evolved, and also investigated the time period in which they spread across peninsular India.

Since Ophisops are restricted to grasslands, understanding the evolution of these lizards allowed the researchers to test two hypotheses related to the origins of Indian grasslands. The first hypothesis was that if Indian grasslands expanded at the same time as grasslands globally—which was four million to eight million years ago—the spread of Ophisops would date back to around roughly the same time period. The second hypothesis was if grasslands expanded only when humans started cultivation in the last 10,000 to 20,000 years, Ophisops would have only spread to areas cleared by humans in the more recent past.

The researchers collected specimens from 108 areas across India spanning a range of different habitats—from the Thar desert to the Western Ghats, the East and West coasts, and many parts of central India.

“We extracted DNA from 125 specimens collected from these localities and examined the similarities and differences between their DNA to understand the evolution of Ophisops,” said Ishan Agarwal, an evolutionary biologist and the lead author of the study.

Differences in DNA accumulate over time and hence the genetic divergence between two species can tell us how long ago they diverged from one another. “We also investigated at what rate species diversified through time, which can vary due to several factors including climate and available habitat,” said Agarwal.

The study also examined the relationship between Ophisops from India and those found in similar conditions in the Saharo-Arabian region. In their study, the researchers found that these lizards spread into India from the Saharo-Arabian part of the world between 23 million and 28 million years ago. This suggests that there were open areas available in India during that period, as these lizards are only found in open areas today. After coming to India, around 20 million years ago, the lizards split into two groups of big and small body sizes—big being more than 50 mm and small being less than 45 mm.

Genetic analyses of specimens collected from field sites and museums also found 25 new species of Indian Ophisops lizards when only five were previously known to science. Such findings are not uncommon among a group of organisms that are similar in appearance, and whose biological classification has not been evaluated with genetic methods.

“The homogeneity in habitat across their distribution range could be one of the reasons for the cryptic diversity,” said Varad Giri, a taxonomic expert on reptiles who was not part of the study. “The lizards have retained their body form across their range with limited or no changes to their appearance.”

The small-bodied species of Ophisops diversified rapidly around five million to nine million years ago, which corresponds to the time when grasslands were expanding globally. Around the same time—that is, during the late Miocene period—the Indian Subcontinent and other Asian regions went through a period of aridification. This opened up more dry arid areas, increasing the suitable habitat for these lizards to expand into. Thus the ancient past when these lizards spread suggests grasslands in India evolved millions of years ago.

Grasslands are of ancient origin

Of the many lizard species that evolved, the study also suggests that some members of the large-bodied group dispersed back into the Saharo-Arabian region, eventually evolving into new species. “It is the first time such an unusual bio-geographic pattern has been documented,” said Agarwal.

While several animals have dispersed from India to Southeast Asia, such a westward dispersal has not been documented previously. This could be because most research is focused on forest-dwelling species while the animals belonging to dry arid habitats are understudied. “When more studies find many groups of animals with a similar pattern you would infer that there was probably a broad geological or climatic event that facilitated this,” said Agarwal.

Grasslands are usually considered to harbour a low diversity of animals and are believed to be devoid of any unique diversity. But as this study suggests, grasslands may support many diverse understudied creatures.

Grasslands are among the most neglected ecosystems in India. In spite of 40% of the country’s natural habitats being covered with grasslands, they are poorly understood and often ill-treated. This study makes a case for grasslands being of an ancient origin, and highlights the urgent need for conservation of arid landscapes that support a wide array of creatures.

This post was first published on Scroll.in.

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