Contributed by: James Baxter-Gilbert (PhD Student from Macquarie University, NSW)
The Australian Water dragon (Intellagama lesueurii) is a large lizard species common along the eastern coast of Australian ranging from Queensland to Victoria. There are two subspecies described: the Eastern Water Dragon (Intellagama lesueurii lesueurii) living in the northern extent of the range, and the Gippsland Water Dragon (Intellagama lesueurii howittii) living in the south1. The males of this species are larger in size and will defend a territory, displaying a bright red chest coupled with head-bobbing and arm-waving to communicate to other males to stay away. Females will regularly mate with multiple males to ensure genetic diversity of her eggs; a single clutch of eggs may have 2-3 different fathers2 divided between 6-18 eggs.
At night these lizards typically take shelter either in the trees, in a burrow, or floating in water with just their nostrils exposed. This penchant for bobbing in the water is likely the reason that early European explorers had described seeing crocodiles in the waterways around Gippsland, however this myth was debunked once the Water Dragon as a species was properly studied and described.
Since these lizards are common along waterways, they can often be found in close proximity to urban areas, as well as the bush. This means that Water Dragons provide a very unique opportunity for researchers to study how urbanisation and the ‘human landscape’ affects species, and how these creatures can adjust themselves to survive alongside people, a feat very difficult for most types of animal.
One of the most prominent drivers of biodiversity loss around the world is habitat degradation and fragmentation resulting from human development and urbanization3. Reptiles as a whole have suffered some of the most substantial population losses of all vertebrates4; however, there are certain reptile species that thrive in urban landscapes. What allows certain reptiles to survive and exploit urban landscapes where most cannot? Urban areas are a novel landscape that can select for particular life-history and behavioural characteristics for certain species, including high behavioural flexibility5 (e.g. bolder or more exploratory), altered stress physiology6 (e.g. reducing the level of stress hormones expressed), modified morphologies7 (e.g. longer limbs and toes), and increased reproductive output8 (e.g., more eggs produced).
Currently, research is being conducted by James Baxter-Gilbert and Dr. Martin Whiting (www.whitinglab.com/) from the Lizard Lab at Macquarie University in Sydney to examine if urban Eastern Water Dragon populations are able to thrive because of population-level adaptations to the selective pressures of city life. In answering this question, the research hopes to better understand how wildlife copes with the challenges of an ever increasing anthropogenic world.
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References
1) Cogger, H. (2014). Reptiles and amphibians of Australia. CSIRO PUBLISHING.
2) Frère, C.H., Chandrasoma, D. & Whiting, M.J. (2015) Polyandry in dragon lizards: inbred paternal genotypes sire fewer offspring. Ecology and Evolution. doi: 10.1002/ece3.1447
3) McKinney, M.L. (2002). Urbanization, biodiversity, and conservation: The impacts of urbanization on native species are poorly studied, but educating a highly urbanized human population about these impacts can greatly improve species conservation in all ecosystems. Bioscience, 52(10), 883-890.
4) Böhm, M., et al. (2013). The conservation status of the world’s reptiles. Biological Conservation, 157, 372-385.
5) Moule, H., Michelangeli, M., Thompson, M.B., & Chapple, D.G. (2015). The influence of urbanization on the behaviour of an Australian lizard and the presence of an activity–exploratory behavioural syndrome. Journal of Zoology. [online]. DOI: 10.1111/jzo.12288
6) French, S.S., Fokidis, H.B., & Moore, M.C. (2008). Variation in stress and innate immunity in the tree lizard (Urosaurus ornatus) across an urban–rural gradient. Journal of Comparative Physiology B, 178(8), 997-1005.
7) Winchell, K.M., Reynolds, R.G., Prado‐Irwin, S.R., Puente‐Rolón, A.R., & Revell, L.J. (2016). Phenotypic shifts in urban areas in the tropical lizard Anolis cristatellus. Evolution, 70(5), 1009-1022.
8) Lucas, L.D., & French, S.S. (2012). Stress-induced tradeoffs in a free-living lizard across a variable landscape: consequences for individuals and populations. PloS one, 7(11), e49895.