Urbanisation and Shifting Phenotypes Behavioural, Physiological and Cognitive Strategies of the Indian Rock Agama Psammophilus Dorsalis
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Humans directly or indirectly cause changes in the environment, and urbanisation is currently one of the most important threats to biodiversity. Urbanisation exposes organisms to novel pressures that are drastically different from those in their native habitats, as human modification rapidly and dramatically changes natural environments, alters habitats as well as shifts resources and predator communities. Organisms can cope with the novel challenges by modifying their behaviour, physiology, morphology and cognition. To understand the impacts of urbanisation on phenotypic traits, the goal of my research was to study the social and survival strategies of the Indian rock agama, Psammophilus dorsalis. Using a combination of field and laboratory-based experiments, I examined differences in signal-receiver dynamics in communication, anti-predator strategies, stress physiology, and spatial learning. Social interactions in this species involve rapid physiological colour changes and behavioural displays. My work shows that colour patterns are diametrically different between courtship and aggressive interactions. Males change their dorsal body region to red, and their lateral body region to black when courting females, whereas these regions turn yellow and orange respectively when fighting with competitive males. Regardless of social context, suburban males express lower colour contrast and are also slower to change colours than rural males. Using robotic lizard stimuli, I found that receiver responses match the population-specific intensity of male signals. For the first time in any lizard species, I find that perception and responsiveness to motion and colour are lateralized in different ways. Psammophilus dorsalis is left visual field dominant when responding to social display colours, but motion stimuli elicit similar responses from both visual field. Along with shifts in colour signalling strategies, stress physiology and social behavioural display was also affected by urbanisation. Suburban males had significantly higher circulating corticosterone levels during both control conditions and immediately following social interactions compared to rural males. Proportion and rate of courtship displays was also significantly lower in suburban males compared to rural males. In the field, escape strategies of males, but not females differed between suburban and rural populations, such that suburban males were more tolerant of simulated predator attacks than rural males. As expected from their cryptic body patterns, females, regardless of habitat, relied more heavily on crypticity rather than flight to minimize predation risk. Suburban males also had stronger cognitive skills, as spatial learning and reversal learning in suburban males was faster than in rural males. In sum, differences in these behavioural, physiological, and cognitive responses of suburban and rural populations of lizards demonstrated in my thesis, indicate human-induced changes in selective pressures that support shifted survival and reproductive strategies. Psammophilus dorsalis promises to be an excellent system to further examine the specific selective pressures that shift in urban landscapes. The study of multiple integrated phenotypic traits in response to urbanisation gives a broader perspective as to how a species can flexibly adapt to rapid environmental disturbances, which is currently one of the greatest threats to biodiversity worldwide.