Chameleons introduced to Hawaii in 1972 have started flaunting brighter colours, probably because they have fewer predators to hide from
11 May 2022
Kenyan chameleons that were introduced to Hawaii half a century ago have evolved flashier colours, probably because they have fewer predators to hide from.
Jackson’s chameleons (Trioceros jacksonii xantholophus) are native to Kenya and, like other chameleons, change colour depending on their context.
Males turn yellow to attract females or to signal their dominance to other males. They switch to green and brown at other times to blend in with vegetation and avoid being noticed by predatory birds and snakes.
In 1972, about 36 Jackson’s chameleons were imported from Kenya by a pet shop owner in Hawaii. He placed them in his back garden, but they escaped. Since Hawaii has few animals that can prey on them, they were able to establish themselves widely.
Martin Whiting at Macquarie University in Sydney, Australia, and his colleagues wondered whether being released from this predation pressure led to changes in the chameleon’s colour displays.
To test this, they conducted experiments using male Jackson’s chameleons collected from Hawaii and Kenya. They exposed each individual to another male, a female, a model bird and a model snake, then observed their colour changes in response.
The Hawaiian and Kenyan chameleons both turned yellow when they encountered another male or a female, but the yellow of the Hawaiians was about 30 per cent brighter, as measured by an instrument called a spectrophotometer.
When exposed to the bird and snake models, both groups changed colour to blend in to their environment, but the Hawaiian chameleons did this less effectively.
The Hawaiians have probably become worse at camouflaging themselves since they no longer need to, says Whiting. “That’s how natural selection works – if you don’t use it, you lose it.”
With predators mostly out of the equation, the chameleons may have evolved brighter yellow displays to increase their chances of attracting mates and reproducing, he says.
This evolution has occurred in just 50 to 65 generations, which is “pretty quick”, says Whiting. “But it is becoming increasingly apparent that evolution can occur over much shorter time periods than we previously thought.”
Other studies, for example, have found that lizards can evolve longer legs within six months after being experimentally introduced to new islands.
Journal reference: Science Advances, DOI: 10.1126/sciadv.abn2415
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