How urban lizards are changing their lifestyles to make cities their home6 min read . Updated: 17 Sep 2017, 04:36 PM IST
Rock agamas are flexible, smart, and eager to live in harmony with humans
Rock agamas are flexible, smart, and eager to live in harmony with humans
Five years ago, on her way back from the National Centre for Biological Sciences (NCBS) in Bengaluru, where she often attended seminars, Anuradha Batabyal stopped by to observe brightly-coloured lizards.
Even as a student of zoology, she had never before seen yellow and vermilion lizards bobbing their heads and doing push-ups on wayside rocks. “My interest grew when I saw them again around Nandi Hills and Devarayanadurga," says Batabyal.
At that time, she didn’t know that Indian rock agamas, a species of lizards, would become the subject of her doctorate at the Indian Institute of Science (IISc) in Bengaluru. For a doctoral student in India, lizard behaviour is a rare subject to pursue.
“Relatively few Indian researchers have studied reptile behaviour; lizards, even fewer," says Kartik Shanker, an evolutionary ecologist who is currently the director of the Ashoka Trust for Research in Ecology and the Environment (ATREE), Bengaluru.
According to the 2011 Census, 31.6% of the Indian population is urban. The United Nation’s World Urbanization Prospects estimates that by 2050, at least half of the country’s populace would have moved to cities.
Urbanization causes large continuous habitats to fragment into smaller, incongruent areas due to the eruption of roads and buildings, consequently eating up a lot of grassy and soil-rich patches, which are essential for the survival of animals.
To examine the effects of rapid urbanization in Indian metropolises like Bengaluru, Batabyal, under the guidance of ecologist and assistant professor Maria Thaker, chose to study its impact on Psammophilus dorsalis, aka the rock agama. The agama’s habitat has so far been identified in and around South India.
Batabyal and Thaker compared the escape strategies and social communications of rural and urban rock agamas to see how they are changing their lifestyles to make cities their home.
A majority of their suburban live specimens were picked up from the Sahakar Nagar and Jakkur area of Bengaluru and the rural ones from Kolar. While in the laboratory, the lizards were fed ants and crickets.
“Rock agamas do not eat dead prey, so we had to make sure to get them live organisms," Batabyal reveals.
In cities, they tend to live on construction sites and vacant plots and unlike their rural cousins, they also need to develop skills to escape unfamiliar predators like cats and dogs.
When they aren’t socially active, males look patchy yellow-brown with yellow lips. An indistinct orange to black stripe runs from behind their eyes to the end of the tail. Females are always light brown, half the size of males and fit easily in a human palm. They are fairly inconspicuous, blending well with rocks and stone walls in urban spaces.
In the absence of any referral studies on colour changes within the species, Batabyal learnt everything about her lizard from scratch. She observed that during their interactions with both sexes, male lizards change colour rapidly. “Within a few seconds to a minute, from dull yellow they turn to a bright yellow or orange, depending on what they are communicating," she says.
At first, she hypothesized that the colour changes could be for the sake of camouflaging, just like chameleons. Later, only when the interactions between male and female were studied, did she find that males use a different set of colours to communicate with both sexes. When he gets into a fight with another male, his body turns bright yellow and the band becomes orange. While courting a female, he turns bright orange to red, with his band taking a deep black colour.
Even though male rock agamas are conspicuously coloured only during their mating season twice a year, colouration is a big trade-off for lizards—bright colours attract mates, but also predators. Yet, the female chooses her partner based on its colour intensity.
“The brighter the colour, the faster they can sprint and the harder they bite, so another male who may be wanting to get into a squabble would think twice before wasting his energy with a brightly coloured male," Batabyal says.
“Being colourful and sexy holds importance for the female, but equally significant for her is that her partner can evade its predator and survive, despite its colours," she adds. Since it would be dearer for a species to lose an egg-bearing female to a predator, a female agama is never coloured.
Batabyal and Thaker found that the city-bred male agamas change colour slowly and are generally duller than their rural counterparts. Along with her supervisor, she speculates in her recent study that the urban lizards possibly do not need to signal as hard as they do in rural settings, as they find themselves closer to each other in fragmented habitats. This may also be leading to more frequent interactions with their own, reducing their sensitivity to communication.
In yet another study with Shashank Balakrishna (also Thaker’s student), they found that urban rock agamas are more accustomed to seeing humans in their vicinity and therefore, comfortable letting them come close. Unlike their rural kin, who flee as soon as they sense a human advancing, urban agamas wait until humans approach quite close before making a quick run for the closest hiding spot. “They capitalize on the diversity of structures and hiding places in a city," Thaker says.
“Think of escape strategies as loss and benefit," says Batabyal. “If a lizard is looking for a mate, feeding, or even basking in the sun, it checks how much threat the approaching human holds before running."
Rural lizards behave differently. “Owing to open spaces in rural areas, they have to run a lot before they find a rock crevice to hide, so they don’t take a chance," adds Batabyal.
To check their survival skills in cities, the researchers also looked at their cognitive ability, specifically, how quickly they acquire knowledge about changing habitats. “We found that urban lizards can learn faster about hiding spaces and are equally quick to unlearn this information if the spot becomes unsafe," Batabyal says.
For rural lizards, the number of safe spaces is few, so they don’t use this skill.
Just like every organism, lizards too have a unique place in the food chain. “They keep the population of insects in check and are food for higher vertebrates," says Dr Varad Giri, facility in-charge, Museum and Field Stations Facility, NCBS, who wasn’t involved with Batabyal’s studies.
It is, therefore, essential to study their behaviour and find out what threatens their survival and what they can adapt to, so that they can be conserved. If they are wiped out, part of the food chain will collapse.
While species diversity in lizards is studied in India, research on their behaviour is lacking. “For many reptile groups, species identities are uncertain, so it is hard for a researcher to examine their behaviour. In other instances, the student may not be able to find a suitable mentor," says Shanker, who wasn’t involved with Batabyal’s studies.
“Most studies on urbanization either discuss its negative impact on wildlife or the kind of animal diversity urban spaces can support," says Shanker.
Batabyal’s and Thaker’s studies indicate that rock agamas are flexible, smart, and eager to live in harmony with humans. All they need are rocky habitats, soil to lay their eggs and some vegetation, so that insects are available as food.
“We want to tell the world that lizards are really cool organisms," says Thaker. “You don’t need to go online to see them; just look around and you’ll find them doing fascinating things near you," adds Batabyal.
“Indian lizards are not venomous—nothing in India in lizard form can kill humans, so it’s time we stop killing and shooing them away," says Thaker.
Priti Salian is a Bengaluru-based freelance journalist who has written for The Guardian, CNN.com and Al Jazeera, among others. Check out her work at www.pritisalian.com.
Comments are welcome at email@example.com