Updated
A female dragon, with dappled markings like shadows through leaves, tilts her head and waves her arm.
It is not a friendly wave. It is water dragon sign language for the middle finger.She's communicating, clearly and vigorously and in a language that is now being translated so humans can understand.
ABC is streaming nature LIVE
Can't get to a park today? Check out #ABCWildOz — an intimate and unedited window into the remarkable lives of Australian wildlife.
"Social behaviour has been studied in mammals and in birds, but reptiles not so, because I think we've undermined them," says Dr Celine Frere, a senior research fellow at the University of the Sunshine Coast, who has been studying water dragons for eight years.
"But I have to say, that they exhibit social complexities that are similar to what I have studied in dolphins and primates."When you try to understand the evolution of social behaviour … it probably started [millions of years ago] with reptiles."
The eastern water dragon is Australia's largest dragon species, and it comes from the same branch of the evolutionary tree as the iguana.
The first part of its scientific name Intellagama — intelligent lizard — is incredibly apt, as the dragons are clearly a species that lead a very complex life.
"You see that?" Dr Frere says, sprinkling flower petals on the ground near a gathering of dragons.
"That tail slapping is the male telling me to move away — to get out of his territory.
"I think that human encounters with wildlife are important — it has been shown that it increases mental health and wellbeing. So, the fact that we, in Brisbane, are so lucky to have so many different wild species living with us; I think we ought to be grateful, that we ought to start watching them, and listening to them."
Over the course of a morning, several dragons across Roma Street Parkland have uneasy standoffs with humans, who traverse through their patches of land and squeal when the dragons approach them.
Though humans might not realise it, the dragons are communicating about their neighbourhood politics with a series of head nods, arm waves and tail slaps. But with Dr Frere there to translate, it all starts to become clear.
"It's like watching the Bold and the Beautiful or Home and Away," Dr Frere says.
Several genetic fathers in one clutch of eggs
As with many animals, control of resources is a primary motivation, and for male eastern water dragons, one of those resources is females.He aims to guard the best territory possible, and he'll let females live in it with him, and defend the territory as a relative safe space for them.
The females are polyandrous — that is, they will mate with multiple males and when they lay a clutch, there may be several genetic fathers present in the eggs.
But they also have an incredibly complex hierarchy between females, policed by the largest females who will even be so bold as to tell the much larger males off.
Interestingly though, while the fight for dominance within your own territory is a given, as soon as the dragons move out of their own space, they become almost immediately subordinate. They know that they're the visitor, and they know the rules.
"I think that they're cognitively incredibly advanced — they have to remember who is whom within their territory. Who do they tolerate and who they do not tolerate," Dr Frere says.
"They also have to understand space really well, and special boundaries of their territories and who is next to them.
"To me — having studied mammalian social behaviour for many, many years — I think they are equal."
The dragons reign supreme, and look the like royalty too.
They're omnivores and will eat everything from flowers right through to smaller lizards, even their own offspring. It's literally a dragon eat dragon world, with the jaws of a mature male exerting the downward force of over 20 kilograms.
"There is extreme selective pressures on them for survival," Dr Frere says.
And that is compounded by where these particular dragons live: in the city.
Imagine Charles Darwin aboard the Beagle, sailing the seas across to the Galapagos and writing in his note books about finch beak forms across the different islands.
Now imagine pockets of parkland scattered across a city, separated by oceans of malls and high rises, troughs of highways and roads.
The dragons of Brisbane live on islands — just like Darwin's finches did.
And, on those islands they're in completely human-made ecosystems with leaf blowers, fertile garden beds and human-derived food, pesticides and mowers.
And they're in an environment with a completely different make up of plants, prey and predators than they've ever had to deal with in the natural arena.
Photo:
The females are polyandrous — that is, they will mate with
multiple males and when they lay a clutch, there may be several genetic
fathers present in the eggs. (Off Track: Ann Jones)
'The archipelagos of the Anthropocene'
It is a pressure cooker for evolution."I call it the archipelagos of the Anthropocene — this idea that city parks within cities are acting as islands. And potentially we are observing evolutionary processes that Darwin witnessed throughout his voyage," Dr Frere says.
"In fact, the populations in Brisbane city are extremely genetically different from one another. So much so, that it is to the extent of different human cultural backgrounds."For us, the first step to speciation is genetic differentiation. I can't tell you it will lead to a speciation event. But I think we need to be on the lookout because we're witnessing evolution as it's occurring.
"They are almost moving from being an arboreal species to a land-based species.
Dr Frere is studying the isolated dragon populations in Roma Street Parklands, City Botanic Gardens, South Bank and Mt Coot-tha Botanic Gardens in Brisbane.
The dragons' genetic differentiation within each site is manifested in physical characteristics — referred to as morphology.
"In Brisbane city, you have unique equal morphology, so that at every single park the dragons are slightly different morphologically from one another."
The Roma Street dragons are smaller, but have really big heads. The City Botanical Garden dragons are immense compared to eastern water dragons in the wild, but have smaller heads and shorter limbs.
They are starting to move away from being water dragons, and starting to be something else.
Dr Frere and her colleagues have been researching in depth for eight years, in part to prove that this isn't a case of a reduced genetic pool, of inbreeding, but rather the start of genetic differentiation leading to speciation.
They have found that the populations of dragons in the Brisbane parks, and in particular in Roma Street Parklands, are the highest densities of this type of water dragon in the world.
And that density is one of the factors that is driving the sexual selection for different body types than what we might expect.
Here, where the population lives so close to one and other, and territorial displays and fighting at borders takes more and more of the time of males, those who are fittest for the new comparative, close quarters living are surviving and procreating.
It is sexual selection for the fittest of this entirely new circumstance — metropolitan dragons.
The result is startling difference in sexual dimorphism between urban and non-urban populations — the city-living males are becoming huge.
On top of that, the females bury their eggs deeper than their non-urban counterparts, perhaps in response to predation (even by other dragons) or perhaps the fact that cities are now on average several degrees hotter than regional areas.
"Darwin considered that evolution would take millions of years," Frere says.
"But now we've entered what we call the Anthropocene. It's a new era where we as human have basically impacted every level of this planet.
"And we are driving environmental change so quickly that we are now witnessing what we call rapid evolution.
"Because species have to adapt so quickly to the changes that we are throwing at them, they're evolving at a pace that we can witness."Human development, in this case, has led to loss and growth in the natural world.
Many species, perhaps some that we will never even know of, could not cope with the fragmentation, the predation, the chlorine put into the water to combat cane toads. And they've vanished from our ecosystems.
But some of the eastern water dragons were robust enough to survive us.
But by surviving, and even thriving, they will eventually lose what it is to be defined as an eastern water dragon.
Check out the water dragons streaming right now on ABC Wild Oz.
No comments:
Post a Comment