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Why Kenyan chameleons shine brighter in Hawaii

by Coffee Table Science
Image source: https://istockphoto.com

Jackson’s chameleons, a species of chameleon that was brought to Hawaii from a population in Kenya to be sold as pets. In a matter of decades, Jackson’s chameleons have populated the island of Hawaii and evolved in significant ways from their parent species, developing brighter colors to help in social interaction at the cost of being more conspicuous to predators.

Martin J. Whiting is a professor of animal behavior in the School of Natural Sciences at Macquarie University, Australia. His research focuses on the underlying mechanisms of animal behavior and how it affects the animal’s ecological fitness. Recently, Dr. Whiting and colleagues published their findings on Jackson’s chameleons in Science Advances.

CTS: Can you briefly describe your relevant findings for our readers who haven’t encountered your article?

MW: The main finding is that chameleons that are originally from East Africa, in this case near Mt. Kenya or the slopes of Mt. Kenya were inadvertently introduced into Hawaii through the pet trade, and in the space of 50 to 60 generations, these chameleons have become much brighter when they signal to each other, so when they use social signals such as courtship signals or when they signal to rivals, these signals are much brighter and more conspicuous.
They’re also more conspicuous to potential predators, so things back in East Africa that would eat them would include snakes and a whole range of birds, but in Hawaii, there are no snakes and very few birds that might actually eat them. So what’s happened is that they don’t have the same predation risk in Hawaii and as a result, natural selection has relaxed, and [the chameleons] essentially evolved these much brighter colors which can give them an advantage in a social context or a reproductive context. These signals are also more conspicuous against the background vegetation in Hawaii.

Chameleon color signal change in response to different social stimuli. (A) A dominant male in display coloration (B) A subordinate male that lost a contest (C) Two males fighting (D) A courting male in full display color, while the female has turned to a contrasting color, rejecting the male.
Image source: https://www.science.org/doi/10.1126/sciadv.abn2415

CTS: Why is it important to study species that change color dynamically (such as the chameleon) compared to colorful animals whose appearances are fixed?

MW: Well, I wouldn’t say that studying one is any more important than the other. It’s just that in terms of evolution and processes that drive the evolution of color, we have a better understanding of animals that have, should we say, more fixed color or color that doesn’t change dynamically over seconds or minutes or hours. So that’s why the chameleon work is quite valuable because there’s just been very little work done in that context. Chameleons are fairly well-studied in that we know how they change color, and we know a fair bit about their color signals in general, but nobody’s really looked at how they can change in these different environments, so from that perspective it’s more interesting.

CTS: The article mentioned that the evolutionary changes in Jackson’s chameleons came about rapidly. Do you expect them to continue to evolve in the same ways?

MW: That’s a good question. It’s really hard to know because it might be that there’s a particular threshold for these bright, conspicuous signals where they’re very effective, and then above that, it might not make too much of a difference. It’s kind of like when you’re a billionaire, if you’ve got a billion dollars do you really need another billion because you’re not going to probably spend that first billion in any case. It’s kind of like that – it may not make too much of a difference. Also, often there’s a cost – a developmental cost or some physiological cost and so you wouldn’t just carry on getting brighter and brighter, for example.

CTS: What purposes, if any, do the three horns on male chameleons serve, other than competing with other male chameleons?

MW: Well I would say that’s actually the primary function is really to win contests in the quest to mate with females. There’s no other real function there. Having said that there could be an advantage if it’s attacked by a predator, it might be that a snake, there’s some protection they can be used to protect against predators to some degree. It wouldn’t really help the chameleon against a raptor, for example

Experimental setup for behavioral trials. Image source: Martin J. Whiting, Macquarie University

CTS: The article also specifically looks at the color change in male chameleons. Do females change color, and if so, has the female population of Jackson’s chameleons experienced similar evolutionary changes?

MW: Chameleons are actually very anti-social and they are quite hostile to other chameleons unless they are ready to mate, and even then once the deed is done they will move away from one another. Females will often signal aggressively to other individuals and when they get … if you approached a female chameleon or if another chameleon was on the scene, they often turn into these stress colors and start rocking back and forth and threatening these other individuals. They certainly do change color quite dramatically, but they don’t have these lemon-yellow colors that the males use in courtship and to fight other males, and that’s why we focused on the males and not the females, but I wouldn’t expect that their color change would be much different. Although it’s a good question, it would be worth looking at whether the way they respond to a predator has changed.

CTS: To your knowledge, have Jackson’s chameleons had any major negative impact on the Hawaiian ecosystem?

MW: I’m not too sure – I know that some tree snails occasionally get eaten by chameleons. I would say that they might have an impact on species that are already quite threatened… But typically, most of the chameleons are in quite disturbed areas where you no longer get very many endangered species. Unfortunately, the island of Oahu, where they’re most common and which is the island they first colonized, is really quite degraded and transformed. You need to get to the peaks of mountaintops to find remnant vegetation, so I wouldn’t say that the chameleons have a very much of an impact on the Hawaiian ecosystem.

CTS: What were some of the major challenges you faced when working with the chameleons?

MW: Well just logistics for one thing. We had to set up research projects in foreign lands and that takes a lot of work and you need to get permits, animal ethics approvals, and things like that. So there’s a lot of work in setting things up. The actual work went very well, which is not always the case.

CTS: Would you consider or recommend getting one as a pet?

For a start, I would only ever recommend getting a captive-bred chameleon, not a chameleon that’s been collected from the wild because those populations are often vulnerable. I would only recommend getting one as a pet if you are able to get one legally and one that is captive-bred but having said that chameleons actually need a lot of care.

If you are a budding naturalist and interested a lot in learning about chameleons and chameleon behavior then you could consider getting one, but you have to bear in mind that they require a lot of special care. They’re quite a high-maintenance animal. Unfortunately, lots of people get chameleons as pets and they’re not prepared to look after them and then they die! I mean that’s a very common thing to happen. So they need UV light and they need to be misted and there’s a lot of general care. So I would just say: think very carefully about it if you’re going to go that route. But certainly, never get one that is not captive-bred or not obtained legally.

CTS: What do you enjoy most about studying the social behavior of lizards?

MW: Well it’s really just the excitement of making new discoveries, the excitement of answering questions. Getting to know the animal and learning about the animal and just, you know, satisfying an intense interest in animal behavior would be what I really enjoy. Certainly when it involves fieldwork and studying animals in the wild in their natural habitat that’s really enjoyable to me.

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