Jackson’s Chameleon Natural History

In 1972, a group of about 36 (the information is sketchy) Yellow-crested Jackson’s Chameleons escaped a pet store owner’s back yard in Oahu of the Hawaiian Islands. They subsequently dispersed and have established a feral population on not only Oahu, but on Maui, Kauai, and Hawaii

Upon the shutting down of exports from Kenya in 1981, the US continued to bring Jackson’s Chameleons from Hawaii in for the pet trade. Hawaii has since made export illegal in order to discourage other enterprising individuals from releasing animals into the Hawaiian Islands as their own personal breeding project for harvesting later. This has not slowed the availability of these animals in the US. Whether the yellow-crested Jackson’s Chameleons sold here are smuggled from Hawaii or are harvested from breeding populations introduced on the mainland, both are illegal and you are unlikely to get a straight answer as to the origin of your chameleon! At this point in time, there are exports allowed from Kenya. These mostly go to Europe as the price of Hawaiian Jackson’s Chameleons is much lower than Kenyan “Xanths” in the US and there is little awareness of a difference.

Since the early 2000s some long time chameleon keepers began to speak of differences they were noticing in the Hawaiian populations that were more and more frequent. There began to be talk of possible inbreeding effects. These observed differences were

  • Body size: It appeared that the individuals from Hawaii tended towards being smaller
  • Rostral horns: There were more individuals with horn being “upturned” instead of coming out straight forward.
  • Preocular horns: Founder stock has parallel preocular horns (horns above the eyes) as the standard while the Hawaiian population can have horns that go out at an angle.
  • Thinner horns in the Hawaiian population

The minimum number of individuals to start a viable population is considered to be from 50 individuals to over 1000 that are all able to mate and reproduce. Our best estimates place the original Hawaiian population at 36 and it is unknown what the sex ratio was or how many survived to breed. The best case scenario is that there were 36 gravid females and 36 subsequent bloodlines that could mate. Even at best case, inbreeding depression would be expected.

The Hawaiian population has an advantage over captive inbreeding in that there is a strong component of selective breeding by the environment. In captivity, inbred animals go on to breed if they possess a certain color enjoyed by humans or other aspect that is tangential, or even unhealthy, to surviving. The environment cares nothing for aspects that do not support surviving. Thus there is a strong factor in selecting out only the strongest individuals to go on to breed. This dynamic certainly slows inbreeding depression. Of course, we must also take into account that the pressure of natural selection in Hawaii is not intense. The rapid growth of the population is a result of lack of natural predators, abundance of food, and a relatively mild climate. As reptiles are a relatively new addition to the Hawaiian islands and so there was no space for a reptile predator to develop. Introduced cats are the best the islands can throw at these chameleons. This is unfortunate for the prey items of the Jackson’s Chameleon and has created a concern with wildlife officials regarding the possibility of Hawaiian species being wiped out by Jackson’s chameleons and the host of other introduced species that have no natural predators there.

As expected with isolated populations, there are shifts being noticed in physical appearance. There is, to this date, no published scientific study into the divergence between the founder and frontier populations. The most specific information we have is from herpetologist Petr Necas who specializes in chameleons. (He is also an advisor to this webpage). Through his visits to Hawaii and Kenya his observations were that the Hawaiian population, overall, had smaller individuals and their horns had a greater tendency to point in directions other than straight ahead. Both are pointers towards inbreeding. The Hawaiian horns, he noted, were also thinner but this could be due to different minerals in the environment. Kenyan dust that is whipped up and deposited on leaves where Jackson’s Chameleons drink contains calcium, while the Hawaiian soil is volcanic and does not contain calcium. It could be that the issue with horns has a heavy nutritional influence.

It is important to note that these differences are observed over a wide number of individuals. This is not to say that every Hawaiian Jackson’s Chameleon has a smaller body or misdirected horns just as not every Kenyan Jackson’s Chameleon gets to its maximum size or has straight horns. The genetics come from the same founder stock and will have the same variations. The observation is that the Hawaiian population is showing these traits over a wider number of individuals in the population. In fact, from personal observation, the largest Jackson’s Chameleon I have seen was from the Hawaiian stock.

The warning signs are there. The Jackson’s Chameleon population in Hawaii is diverging. They are dealing with a limited genetic base and are working to evolve to be more suited to their new environment. There will continue to be heated debate over Hawaiian genetics and how different they are from the founder stock. The bottom line is that it is just logical that there would be differences. There are almost 50 generations from limited genetics selected for in a different environment. Argument can be made as to the extent of the differences and whether these are “weaker” or not, but they will be different and they will continue to diverge in an environment they were not originally designed for. Nature does this with varying levels of success. The species most able to evolve wins the epoch.

The Kenyan Xanth Project was established to bring founder genetics back into the US captive environment. This group of keepers and breeders saw the value of continuing our captive husbandry with founder genetics from Kenya. If you are interested in being part of this program please check out the Kenyan Xanth Project page.