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The Indian star tortoise (Geochelone elegans) is a sight to behold, with its obsidian shell and the striking Sun-yellow star patterns adorning it. These tortoises are hardy herbivores and are popular as exotic house pets — but they shouldn’t be. It’s illegal to own one in India but also unethical since they are vulnerable in the wild.
Endemic to the subcontinent, Indian star tortoises reside in arid pockets of northwest India (bordering Pakistan), South India, and Sri Lanka. However, members of the species have also been found in people’s homes as far afield as Canada and the U.S. The increasing demand for them as pets has entangled them in one of the largest global wildlife trafficking networks.
The Indian star tortoise is listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and in Schedule I of the Wildlife (Protection) Act 1972, which provides the highest level of protection to animals in Indian law. Despite this, officials have already seized hundreds of tortoises being smuggled through the Chennai and Singapore airports and across the India-Bangladesh border this year.
Wildlife biologist Sneha Dharwadkar, cofounder of an NGO called Freshwater Turtles and Tortoises of India, is worried unscientific releases of the seized tortoises could worsen their fate. “We can no longer simply take confiscated tortoises and release them in nearby forests,” Dharwadkar wrote in an email.
To find an alternative, researchers from the Wildlife Institute of India and Panjab University explored the diversity and natural distribution in India by sequencing the genomes of Indian star tortoise in zoos, wildlife reserves, and protected areas.
The study identified two genetically distinct groups of Indian star tortoises: northwestern and southern.
The genetic divergences showed up as differences in physical features that could inform strategies on where and how to release and conserve rescued tortoises, Subhasree Sahoo, a PhD student at the Wildlife Institute of India, Dehradun, and first author of the study, said.
Millions of years ago, Geochelone, the group that includes the Indian star tortoise, spread across the Indian subcontinent after the latter split from the Gondwana supercontinent and collided with Eurasia.
Over time, parts of the subcontinent became arid and encouraged the growth of savannahs and open grasslands in northwestern and peninsular India, which are now the tortoises’ natural habitats.
But the creation and expansion of savannahs came at the expense of humid forests: the increasingly seasonal nature of the monsoons restricted them to parts of southwest India and Sri Lanka. This separation of humid and dry areas paralleled the splitting of the tortoises into northern and southern groups about 2 million years ago.
To find genetic evidence of this split, the researchers of the new study collected tortoise tissue samples from 14 locations.
“These tortoises are very rare to encounter, so I chose the rainy season because that’s the breeding season. They’re the most active. That’s also what poachers do,” Sahoo said. With the help of frontline forest staff and local communities living near the tortoises’ natural range, she was able to collect 38 samples from northwestern India and 44 from southern India.
Researchers prefer tortoises’ blood samples for genetic testing but even small mistakes when drawing blood can cause profuse bleeding. This is manageable in controlled environments like zoos or wildlife reserves, and less so in the wild.
“When I was in Kakatiya Zoo in Telangana, a zookeeper told me, ‘Madam, why do you want to take blood? You can take the scutes, right? They come off very easily’,” Sahoo said. Scutes are keratin layers found on the tortoises’ limbs, neck, and shell. “I peeled off some scute from the zoo in Kakatiya and tested [it] in the lab, and it worked just fine.”
Once collected, the researchers extracted DNA from the tissue samples. Then they sequenced the mitochondrial genes cytochrome B and NADH dehydrogenase 4. The gene for cytochrome B is highly conserved and used to identify subspecies-level differentiation and later to detect smaller genetic variations between the samples.
The searchers also screened 10 microsatellite markers: short DNA sequences that repeat in a particular location in the genome. They serve as a genome’s fingerprint and are helpful to identify how individuals of the same species are related, how they mate, and recent changes in their population.
The results revealed that even after illegal poaching and unscientific releases, the northwestern group remains largely genetically unchanged whereas the southern group is highly diverse.
“For a long time, on-ground practitioners have suspected the presence of at least two evolutionarily significant units, or ESUs — populations of organisms considered distinct for conservation purposes,” Dharwadkar said. “This paper provides a reliable confirmation of that.”
Sandeep Kumar Gupta, nodal officer at the Wildlife Institute of India, Dehradun, and corresponding author of the study said that since different Indian star tortoises are found in different areas, it’s crucial to not mix the populations during release. Doing so might lower their genetic diversity and depress breeding rates.
Sahoo also raised the concern of shell-pyramiding in captive-bred star tortoises. These tortoises develop pyramid-shaped shells instead of the dome-like shells in the wild due to nutritional deficiencies, and can further complicate mating and breeding issues.
Gupta also emphasised greater public awareness of the legality of keeping certain species as pets and the importance of adhering to national laws on this front. Overall, the team expressed belief in its paper that the findings could benefit both national and international agencies with evidence-based conservation of the Indian star tortoise.
Sanjukta Mondal is a chemist-turned-science-writer with experience in writing popular science articles and scripts for STEM YouTube channels.
Published - December 09, 2024 05:30 am IST