Some Brisbane reptiles double in size because of which park they live in: study - Via Herp Digest

Sydney Morninng Herald, 4/27/17 by Amy Mitchell Whittington

Water dragons living in separate parks across Brisbane have evolved differently from one another in a process likened to the Galapagos Islands evolution recorded by Charles Darwin, a Queensland researcher says.

The first "clue" was a DNA variation across 570 eastern water dragons at South Bank, Roma Street Parkland, the City Botanic Gardens and Mt Coot-tha Botanic Gardens monitored by University of Sunshine Coast Senior Research Fellow Dr Celine Frere.

"That was the first clue to tell us there was something going on in the city that was not your conventional type of evolution," Dr Frere said.

Studies revealed there were also physical differences between each population that lived within kilometres of each other.

The study, published in the journal Molecular Ecology, found males varied in overall size, while females varied in terms of head and leg size, Dr Frere said.

"The animals at the city botanical gardens, they are by far the largest animals and they seem to have, in relation to body size, shorter limb length than other parts," she said.

"In contrast, the animals we found at Mount Coot-tha botanical garden are smaller in size but they have longer back limbs.

"At Roma Street Parkland the animals are quite small but they have larger heads and shorter limbs whereas the animals at South Bank are also fairly small but they have smaller heads and longer limbs.”

While Dr Frere did not know why this species had evolved so differently in a short time – over 32 generations in "lizard time" or since the city's development in the mid to late 1800s – she suggested landscape and microhabitat variations were likely factors.

"The simplest explanation is to think of each city park as being quite a unique ecosystem and different to one another," she said.

"Each of these city parks are different ecosystems, are geographically isolated ... we could look at city parks as islands in a jungle of concrete that make up this archipelago that has similar evolutionary processes like the Galapagos."

Dr Frere said the heaviest male caught during the study, from the City Botanic Gardens, weighed 1.4 kilograms, almost double that of males caught in native habitats.

"This is a common thread when you study island evolution: they say (gigantism) is a biological phenomenon where the size of an animal when isolated on an island increases dramatically compared to its mainland relative," she said.

Dr Frere said the staggered process by which the parks were developed – Mt Coot-tha opened in the 1970s while South Bank opened in the 1980s – could have also influenced the variation.

"Anthropogenic pressures, while they do extensive damage to biodiversity, they are recognised as one of the more significant selective pressures that results in rapid evolution," she said.

"We talk about this idea that cities may be representing these theatres for rapid evolution because animals that do live within cities have to drastically change their way of life.”

So what is the next step in this evolutionary expedition?

"We are going to study the ecology of these parks in much more detail, the thermal landscape and the 3D landscape ... looking also at the biodiversity composition in terms of diet and how these animals are negotiating these landscapes by GPS tracking them and looking at their fine-scale movements across a few days," she said.

"We often thought of this as an urban versus non-urban dichotomy … but here it is to show we go even deeper than that, it is every dragon within every city park (being) extremely different to other dragons in another city park."