Moving to a city means adapting to different surroundings. And it's no different for lizards in Bengaluru city too, find scientists: Indian rock agamas here are changing their physiology — including lowering their testosterone levels — to adapt to urban life.
Some wild animals (including rock agamas which are usually found in the south Indian countryside) are at home in urban areas too. Some species are ‘exploiters’: using urban areas greatly to their advantage, they thrive better here. Others are ‘adapters’: making a few changes, they use the new areas, but only nearly as well as they do in their natural habitats. Identifying species as adaptors or exploiters helps assess the health of animals in disturbed areas and develop better management plans for them.
The standard way to find out if Bengaluru's agamas are adapters that can cope with urban life would be to observe their behaviour (many lizards change their behaviour in urban areas). However, Madhura Amdekar and her colleagues at Bengaluru’s Indian Institute of Science took a different approach: they studied agama physiology, for urbanisation does affect physiology and compromised physiological conditions would mean that the lizards are trying to adapt. They identified 41 urban lizards in Bengaluru city and 42 others in the rural Anthargange forest range, 60 km away. The team captured these lizards and measured their body conditions, parasite levels on the skin and cell-mediated immunity (a kind of immune response to foreign and potentially harmful substances) in the laboratory. They also studied hormone levels and heterophil-to-lymphocyte (H:L) ratios in the blood, which are indicators of stress and immunity levels.
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According to senior author Dr. Maria Thaker, “This approach of measuring several indicators simultaneously gives us a better understanding of how the body prioritises its response to challenges.”
Their results published in Frontiers in Ecology and Evolution show that urban lizards had lower testosterone levels and H:L ratios. This is a sign that they are coping with their urban surroundings, said lead author Amdekar.
“Testosterone, for instance, mediates fighting and aggression,” she said. “One small patch may hold many lizards in urban areas, so competition between them would be high. Lower testosterone levels would be crucial to adapt to such competition.”
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This is the first study to show that physiological measures can reveal whether a lizard species in an adapter or exploiter. However, it is crucial to use multiple measures of physiology to test this, added Amdekar.