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Could human interference be affecting a lizard’s signalling and escape behaviour?

June 23,2017
Artificial models of rock agamas from Prof. Thaker's lab
Read time: 7 mins

Photo: Siddharth Kankaria / Research Matters


Urbanisation, coupled with industrialisation has transformed our entire world. Today, there is an unprecedented rise in the number of people flocking to the cities from villages in search of a better future, thus leading to a rapid change in the landscape of cities and our quality of life. But, have you ever wondered how this has affected our fellow creatures?

This is one aspect of Anuradha Batabyal and Prof. Maria Thaker’s study on the South Indian Rock Agama (Psammophilus dorsalis). The South Indian Rock Agama is a lizard that is found commonly in semi-arid regions and suburban areas of South India. In a non-suburban setting, they can be seen basking on rocky boulders interspersed with scrub vegetation. From snout to the tip of the tail, males can grow up to 25 cm, while females are smaller. A characteristic feature of this lizard is the development of conspicuous colouration in males during the breeding season.

In a couple of recent studies published by Ms. Batabyal, Prof. Thaker and their team, the researchers have focused on understanding two aspects of the rock agamas and how urbanisation has influenced them. The first focuses on how these lizards communicate with colour and whether this colour change is affected by urbanisation. The other looks into how urbanization affects escape strategies employed by these lizards and their use of habitat.

For the study, the researchers captured alive male and female lizards from rural as well as from urban settings during the breeding season and kept them in laboratory conditions similar to the lizards’ habitat in the wild. Colour changes and behaviour were compared under different social conditions: when males were allowed to interact with a female, another male, and when alone.

While it was previously known that males of the South Indian Rock Agama changed colours during the breeding season, Ms. Batyabal and Dr. Thaker were surprised to find how context specific and rapid these colour changes were.

To study the colour change during social interactions, the researchers measured the percentage of reflectance of the dorsal and the lateral side of the lizard’s body. This was done using a flexible fibre optic probe, which was taped to the body of the lizard and connected to a spectrometer.

So one could say that the researchers had put a sort of spectrometer backpack on the lizards! The reason for this is that the colour change is also affected by stress and handling and so, putting on the probe during the social interaction would have affected the measurement of colour change.

By measuring the percentage of reflectance, the researchers were measuring the amount of light of a particular range of wavelength being reflected from the lizard’s body. For example, if the colour of a part of the lizard’s body changed from yellow to red, then by measuring the amount of light reflected by that part of the body in the range of wavelength that results in red light, a person would be able to find out the intensity of the red colour exhibited by the lizard.

The researchers found that during interactions with females where they displayed courtship behaviour, a band along the dorsal (top) side of the body changed from patchy yellow to orange or red, while bands along the lateral sides (either sides) of the body changed from patchy orange to black. During interactions with other males where they displayed aggressive behaviour, the lizard’s dorsal band changed to a brighter yellow and the lateral bands to a brighter orange. During normal conditions, the colours remained mostly brown and patchy like the patterns on rocks from their natural habitat.

Also, using digital videography and photography, they measured the speed of the colour changes and found that colour change during aggressive behaviour was much faster than during courtship behaviour.

The researchers observed specific differences between rural and urban lizards. During courtship behaviour, it was found that rural males showed greater intensity of colour change than urban males. And during interactions with other males, it was found that rural males were faster in changing their colours than urban males.

The researchers suggest that intensity of colour change could be a signal of male quality for females, while rate of colour change could be a signal of male dominance. When asked what could be the reason for the difference between rural and urban lizards, Prof. Thaker says, “We think that the local crowding in the remnant habitats that are suitable for them, and the overall stress of living in the city, may be the reason why the intensity of their colour-based communication has lessened. Lizards in urban Bangalore do not get as intensely coloured and are slower to change their colours during social interactions.”

The other study focused on how human activities due to urbanisation have impacted the lizard’s escape strategies. What makes the urban environment different for the lizards is that it is much more complex, with a lot more perch and refuge options, say the researchers. They believe that this, coupled with a habituation to human interference, would make the lizards less averse to perceived risks.

To study the escape behaviour, “predator attacks” were staged in the lizards’ habitat, where the same observer wearing dull olive clothes on sunny days would walk in a straight line towards the lizards at a speed of approximately 1.5 m/s. Another observer would record the location of the initial perch and the path taken to the refuge. Later, FID (Flight Initiation Distance) -- the distance between the initial perch and the first observer when the lizard starts to flee, the hiding duration, perch height and type, refuge type and perch-to-refuge distance were calculated.

The researchers found that females allowed observers to get much closer to them as compared to males, because they were dull coloured and stayed still to be unseen, unlike the males. Rural males initiated escape much earlier than urban males, while there was not much difference between Flight Initiation Distance of females across habitats.  Hiding duration was similar for all lizards across habitats.

Lizards were also captured and taken to the laboratory, where they were made to run on a racetrack. It was found that males, which are the bigger sex, were faster than females, but there was no significant difference in speed between members of the same sex across habitats.
It’s also worth noting that all the captured lizards were returned to their original habitats after the period of study.

The difference in Flight Initiation Distance between rural and urban males, according to Anuradha Batabyal, is because the urban lizards have learnt to recognise what is and what isn’t dangerous. While many species are not able to cope with the changing environment, it seems obvious that these lizards have found a way.

Prof. Thaker remarks, “The world is not easily divided into ‘pristine natural areas’ and ‘human dominated areas’. Especially in India, as we expand our cities and convert natural ecosystems to human use, we are rapidly losing species. So, when we saw that this lizard lives in and around Bangalore, in our gardens and on our walls, we were excited to understand how they were coping. If we understand how flexible they are to life in the city, and what they need, we have a better shot at co-existing with them.”

Prof. Thaker definitely makes a point. There is so much magic in our surroundings that we never take notice of. But it is a part of us. The more we understand how and why our fellow creatures survive, the better it is for all of us.