Experimental setup for behavioral trials: The male on the left won this contest and is in full display color while the male on the right has lost this contest and turned brown (subordinate).Credit: Martin J. Whiting/Macquarie University/Sci. Adv. 8,2415 (2022)
Kenyan chameleons, accidentally introduced to Oahu, Hawaii in the 1970’s, where the lizards have no native predators, display flashier colors compared with members of the same species in their original habitat.
According to a new study published in Science Advances, a shipment of Jackson’s chameleons (Trioceros jacksonii xantholophus) thought to be 36 or fewer individuals, was sent from Kenya to Oahu destined for the pet trade. When the animals arrived in poor condition, they were left outdoors to recover – before they escaped and became established on the island.
While scientists have expected that animals’ social and sexual signals change when the threat of predation decreases, this phenomenon has seldom been observed in the wild and has remained particularly mysterious in species with the ability to change color. Scientists are only now beginning to understand how social and sexual signals change in response to rapid environmental change.
To study this phenomenon, the scientists performed a series of tests with chameleons in Oahu, where there are no snakes or lizard-eating raptors to prey on the species, as well as with members of the source population in Kenya. A total of 174 chameleons in Hawaii and 128 in Kenya were used.
They monitored how the different populations’ colours changed and found the chameleons in Hawaii have evolved signals that are more conspicuous to other chameleons. They did not undergo a radical color change but were rather more conspicuous as perceived by other chameleons, and they did show higher luminance contrast against the local background than Kenyan chameleons. The authors suggest this resulted from adaptations to the Hawaiian environment.
In the absence of predators, the chameleons from Hawaii were much more visible than
Kenyan chameleons when threatened by both bird and snake predators (fakes were used). The Hawaiian chameleons had higher luminance contrast against the local background to the visual system of the corresponding predator.
Thus, this novel finding raises the question of whether other animals that have convergently evolved dynamic colour signals, such as cephalopods, frogs, other lizards, and fishes, may be likewise influenced under the same circumstances.
