Boa constrictor breeding with related bloodlines - boa inbreeding

Aspiring breeders often debate over whether it is advisable to acquire several animals from the same litter.

It is a fact that the successful breeding of unrelated boas promotes and maintains genetic variety. Unfortunately, purebred boas and pythons are not produced in a manner that would allow for the attitude: „In order to avoid inbreeding, I’m going to take the female from breeder A and the male from breeder B“.

Most of the time, someone who is interested in a somewhat rare species or subspecies of boa or python has to be glad if


a) there is a successful breeder in your country, and if

b) there still are specimens available from that litter

In addition, it is often the case that captive-bred animals from different breeders still originate from the same bloodline, and are therefore related to one another.

Bottom line: There often is little choice other than to breed blood-related animals. However, this is not necessarily always a disadvantage.

One factor that speaks for breeding siblings of boas and pythons to one another is the higher likeliness of a successful mating. In blood-related animals, one can be certain that the same housing conditions trigger the breeding behavior at the same time. The ancestors of unrelated animals may come from different parts of the distribution area, and they may therefore show breeding behavior at different points in time, as the triggers of such may differ. If this is the case, the breeding will not be successful.

Ulrich Sieling, who is one of the pioneers of breeding pure boas and pythons in Germany (e.g. Boa c. occidentalis, Epicrates cenchria, Morelia viridis and Corallus caninus) told the author that he has bred siblings of rosy boas (Lichanura trivergata trivergata) up into the sixth (!) generation, without ever receiving any noticeable defects in the offspring.

On the contrary, Mr. Sieling mentioned that his offspring got larger and stronger, and that his litter sizes increased continuously. He made the same observations with Epicrates cenchria and Morelia viridis, in which he bred siblings up to the F3 generation.

Why is that? Maybe the study of the British scientists that was published in January 2001 offers a suitable explanation. They determined that in some cases, incest may have some advantages. They examined the genetic code of a small horde of cattle from northern England. These so-called Chillingham-cows have been known since the 13th century.

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According to certain documents, they have been inbreeding exclusively for the last 300 years.
The genetic analysis confirmed this documentation: in all examined cows, 24 of 25 genetic markers were identical. According to one of the researchers, there would have been no more than 18 identical markers in a normal horde. By this, the Chillingham-cows could almost considered to be clones.
Despite this massive inbreeding, the animals are healthy and keep on reproducing. The researchers therefore believe that the inbreeding has resulted in a loss of unsuitable genetic variants in this case (Source: Nature, Vol. 409, No. 6818, 18.1.01, p 303 / New Scientist, 18.1.01).

Mr. Sieling further referred to the fact that boas and pythons inhabit specific home ranges and it is therefore likely that reproduction among related animals is quite common in the wild. The many island forms of boas and pythons also need to be considered in this context. Due to their isolated distribution areas, they do not have the chance to expand their gene pool, but nevertheless are of great health and vitality, as long as they do not cross paths with a specimen of the genus Homo sapiens. By the way, Ulrich Sieling is not the only one who has bred siblings into the third generation without any apparent defects. An acquaintance of ours did the same with Acrantophis dumerili, and all the produced offspring was completely normal as well.

It is generally worth discussing whether incest is as much of a problem in reptiles as it is in mammals, as the former are on a lower evolutionary level than the ladder.

However, there is also a negative example from the U.S. that shows that inbreeding in reptiles can cause defects. Increasing numbers of one-eyed albino Boa constrictors have been produced there recently, the cause of which is without a doubt a defective gene that came into play through massive inbreeding and has been widely distributed through this.
That is exactly the problem: If the genetic properties of the animal contain a defective gene, it does not necessarily manifest in its offspring. It may be eradicated if the genetic material is mixed with that of a “genetically healthy” animal. However, this is not the case when related animals produce offspring, as they both carry the defective gene. In that case, it is certainly possible for the young to show defects.

The fact that this happened to occur in albino Boa constrictor is not surprising. Out of pure greed, the main concern was to produce as many of these as possible, just to make money. The ideal way to reach this goal happens to be inbreeding to the excess. We don’t want to fail to mention that some snake keepers are crazy about those freak animals. In the section "artificial boas" you will find out what else certain “breeders” produce, and what the mainstream taste of the herp enthusiasts in the U.S. is like.