The tension is palpable. The first athlete is placed on the starting line and the official timer, Dr Anthony Herrel, resets the stopwatch on his smartphone. Once given the go-ahead, Dr Krystal Tolley tickles the yellowy-green chameleon’s tail and the two-inch reptile springs into action. About 10 seconds later, after reaching the end of the 1-metre dowel in a season’s best time, it returns to the resting area and the next competitor is given a chance to strut its stuff.
In the coming days, 120 Knysna dwarf chameleons (Bradypodion damaranum) – male and female, from forest habitats, gardens and parks – will be put through their paces in a series of speed and endurance challenges that the scientists refer to as the Chameleon Olympics. They will run on horizontal and vertical dowels of varying diameter; have the strength of their bite and gripping forces measured in newtons, and be tested on their ability to thermoregulate along a course that has a temperature gradient.
At the end of each day, the specimens will be released back into their habitats, and the scientists will set off with headlamps and cloth bags to capture the next batch of Olympians.
Pitting urban chameleons against rural ones is the latest in a series of tests on South Africa’s 17 species of dwarf chameleons. These comprise “a really fascinating study system”, says Herrel, because of the way that they demonstrate evolution in action. Despite being extremely similar genetically and living in adjacent habitats, Knysna dwarf chameleons living in forests are almost twice as heavy as – and much more colourful than – members of a closely related and as yet unnamed species that live in open fynbos (heath or shrubland) habitats and thus have to be smaller and drabber to avoid detection by predators.
In their quest to find out whether urban chameleons have adapted physically to cope with the urban habitats they now face (gardens, golf courses, parks, etc), the scientists need to “measure things that are going to make a difference in their everyday lives”, says Herrel, a research director based at the National Museum of Natural History in Paris, who has devised fitness and performance tests for lizards, frogs and even chickens.
The chameleon’s ability to run on different diameter dowels is one such test, as gardens – with their trees, shrubs, fences and phonelines – have a far greater variety of perch sizes and angles than forests. Being able to keep their body at the correct temperature is another, as the urban habitat is less thermally buffered than the forest and thus prone to greater temperature extremes.
The chameleons are a great example of adaptive radiation – a process where organisms diversify rapidly from an ancestral species into a multitude of new forms, usually because of a change in the environment. “Tens of millions of years ago, South Africa had a lot more forest,” explains Tolley, a principal scientist at the South African National Biodiversity Institute. As the trees gave way to fynbos or grassland, chameleons had to choose – adapt or die.
Now urbanisation is dishing up the same dilemma. Early indicators are that the Knysna dwarf chameleons are again changing their physical characteristics to adapt to city life. Preliminary test results show that the urban chameleons perform better across all three diameters of dowel, while the forest chameleons are really quick on the thicker dowels but slower on the skinniest ones. And although the city dwellers seem to prefer the same temperatures as their counterparts from the forest, they have learned to change their behaviour to find shade on hot days.
In the coming months, Tolley, Herrel and a team of researchers will be hosting the games in Port Elizabeth and Durban with the eastern Cape dwarf chameleon (Bradypodion ventrale) and the KwaZulu-Natal dwarf chameleon (Bradypodion melanocephalum), respectively. Several of South Africa’s big cities boast chameleon populations. But there are also many species of chameleon that wouldn’t be caught dead in a city. What Tolley really wants to know is what the species that can adapt to urban environments have in common.
One theory is that natural variation within the gene pool of a species means specimens with certain characteristics – eg shorter or perhaps longer limbs – are better suited to city life and are more successful at breeding with one other. This results in the gene pool slowly changing.
Alternatively, individuals already have the versions of genes they need to develop the ideal traits – it’s just a matter of activating them. In this case, a simple ecological flick can result in limbs becoming longer or shorter in a matter of a few (chameleon) generations.
While it’s too early to say for sure which process is at play with the dwarf chameleons, Tolley says that sequencing the chameleon’s genome will provide a definitive answer.
“These days we talk a lot about how ecosystems can provide services to humanity,” says Herrel, giving the example of forests capturing CO2. For these big-ticket functions to continue, however, “the entire ecosystem has to remain intact … All the way down to the dwarf chameleons.”