The Unpredictably Variant Amazon Tree Boa

The Amazon Tree Boa (Corallus hortulanus), or ATB, has become increasingly popular in the herpetological hobby world, yet little is still known about their genetics. While several species of the Corallus complex are popular among hobbyists – C. hortulanus, C. batesii, & C. caninus – many are still very rare due to low demand or CITES restrictions – C. annulatus, C. cookii, C. grenadensis, C. ruschenbergerii, & C. cropanii. This has led to several very tight-nit communities working with these animals – case in point: the Amazon Alliance (www.boakindom.com).

They are being exported and bred at a faster pace than ever before, with more morphs than ever before – albeit only 4 proven. Although there are several hobbyists, including myself, working to prove out ATB genetics, many are happy to just pair up random animals and see what pops out. This creates a lot of interesting ammies, but does not help with determining color and pattern inheritance.

Now some genetics. ATBs come in a variety of patterns and a mélange of colors – and now you can even find some morphs. First, a little background on what we do know. There are garden, halloween, and colored ammies. Garden ATBs are those that have base colors that are darker – any shade of brown, grey, granite, black, or rust. Halloween ATBs are a form of garden that start off with red/orange on their dorsal scales, which then disappears with age. In the long run, there is nothing different between them and “normal” garden (that we know of). If it were a logic problem: All Halloween ATBs are gardens, but not all gardens are Halloween phase. Then there are colored ATBs. These are the yellows, oranges, and reds – they may be heavily patterned, have slight speckling, or no pattern at all.

Typical "garden" phase ATB with granite coloration and heavy patterning

 From the morph list: there are tigers, calicos, hypos, & leopards. Tiger ammies are due to a dominant gene that presents as striping along the dorsal scales. There are garden (Halloween included) and colored tigers with various colored stripes. Several calico lines are being worked with. They’ve so far been proven to be dominant as well, producing heavily mottled ammies. Hypo ammies have only been proven by one breeder so far – GCR – and are a codominant trait with a super form. The heterozygous form produces solid colored ammies that have faint colored banding and develop black speckling with age – I work with a pair that may carry these genes. The super form is an off-white colored ammie that also seems to develop some yellow and black. The last known morph is the leopard phase ATB. This has supposedly been proven to be a recessive trait, but with the second generation leopard offspring differing in form. The first generation have dorsal splotches, are darkly colored, have metallic eyes, and can darken and lighten throughout the course of a day. Second generation leopards have similar characteristics but are solid silver/black/gray. To me, it would seem as if they are also codominant, but I have yet to work with any – although I possess a pair that may be leopards. On the unproven list, there are several lines of possible calicos, some candycane atbs (a name of a proven calico line that has also been given to a lot of ammies that have colored banding), and Aztec ammies – a line with an aberrant dorsal patterning that extends onto the sides somewhat.

Possible first generation Leopard Boa

There hasn’t been much work breeding similarly colored and patterned individuals together, and even when that is done the offspring seem random in outcome: two differently colored gardens producing yellow and orange patterned offspring; two coloreds producing all gardens or patterned individuals; two mottled ammies producing gardens and coloreds; or a garden and colored producing everything under the sun. Since they are so variable, with no predictable outcomes (aside from the proven morphs), I believe their patterns and colors to be polygenic. That is, I think their patterns and their colors are determined by several sets of alleles , like human skin color, as opposed to one set or alleles, like the proven morphs. It works similar to skin pigments in humans, which is why we have a range of skin colors and not just one or the other. With that being said, I think body color, head color, patterning, speckling, and eye color are all windows into their genetics. I’m currently trying to pair up my ATBs with individuals that are as close to the same as possible.

Hopefully this year, some of the genetics behind Amazon Tree Boas will begin to be understood. We’ll then start to see ammies with cleaner patterns and probably see some new morphs proven out. It will also just be an overall benefit to the herpetological world, gaining some insight into another unique arboreal boa.