Professional Herpetoculture for the Pet Trade

A Discussion About Hybridization

Introduction

At VMS, we frequently get inquiries and comments regarding the hybridization of captive reptiles. Many of these comments border on near-hysteria, others simply state that hybridization is unethical. In one case, the writer gave the impression that the world would end if additional hybrids of any type are produced. Yet while writing such a letter, that same person may have a domestic cat curled up in his or her lap. The writer is blissfully unaware that this cherished pet is most likely a descendant of an intra-specific hybrid, a cross between the African Wild Cat (Felis sylvestris lybica) and the Asian Wild Cat (Felis sylvestris sylvestris). In fact, some scientists believe that both Pallas's Cat (Felis manul) and Sand Cat (Felis margarita) may also have contributed to the domestic cat gene pool as ancestors of longhaired cats. In any event, all of this would have taken place thousands of years ago and the world is still turning.

But one thing is pretty obvious in all these cases. Each and every writer seems completely ignorant of what a hybrid truly is, and even more ignorant of the benefits of hybridization. Sure, there can be a few 'downsides' to hybrids, but even these have little merit in an argument. Think about that while you go let the dog out. Did you know your canine friend is a hybrid? In his case, there appear to be so many ancestors which contributed to his genetic pool that scientists cannot even agree on which or how many there might be. Yet no dog-lover would ever consider abandoning Fido simply because he's not 100% pure Wolf!

So perhaps we need to shed a little light on the myths surrounding hybridization.

What Is A Hybrid?

Figure 1: a Zeedonk, a hybrid created by crossing a Zebra and a Donkey

The word hybrid is a term applied by plant and animal breeders to the offspring of a cross between two different subspecies or species. Hybrids between different species within the same genus are sometimes known as interspecific hybrids. Hybrids between different sub-species within a species are known as intra-specific hybrids. Hybrids between different genera are sometimes known as intergeneric hybrids.

The mule, the hybrid steer, and hybrid corn are examples of hybrids produced by breeders, but some animal species may cross-breed in the wild, as the gray wolf and coyote sometimes do.

Hybrids are often named by the portmanteau method, combining the names of the two parent species. Illustrated here (Fig. 1), a zeedonk is a cross between a Zebra and a Donkey. Since the traits of hybrid offspring often vary depending on which species was mother and which was father, it is traditional to use the father's species as the first half of the portmanteau. For example, a Liger is a cross between a male Lion and a female Tiger, while a Tigon is a cross between a male Tiger and a female Lion.

Some other common animal interspecies hybrids are:

  • Mule, a cross of female Horse and a male Donkey.
  • Hinny, a cross between a female Donkey and a male Horse.
  • Zeedonk or Zonkey, a Zebra/Donkey cross.
  • Beefalo/cattalo, a cross of an American Bison and a domestic Cow. This is a fertile breed, although the two species are in different genera (Bison and Bos, respectively).
  • Wolfdog, the cross between a domestic Dog and a Wolf. Fertile Canid hybrids occur between coyotes, wolves, dingos, jackals and domestic dogs. Depending on the author, dogs and wolves may be considered the same species, making wolfdogs a non-hybrid.
  • Bengal cat, a recent cross between the Asian Leopard cat and the domestic Cat, one of many hybrids between the domestic cat and wild cat species.

Why Hybridize?

Hybridization between cultivars or varieties is often used in agriculture to obtain greater vigor or growth (heterosis). The first generation often shows greatly increased vigor and a better yield primarily because many genes for recessive, often deleterious, traits from one parent are masked by corresponding dominant genes in the other parent. Many of the hybrid reptiles produced in today's marketplace also show the positive effects of hybrid vigor. Larger babies, with stronger feeding responses, are often produced.

The offspring can display traits and characteristics of both parents. This is a common reason for hybridizing captive reptiles. Combining two forms with attractive appearances to create a third intermediate form which may be still more uniquely attractive is a common goal. Many breeders also use hybridization as a means to introduce desired mutations into species not currently exhibiting them. One of the first projects along these lines was the use of albino Ruthven's Kingsnakes (Lampropeltis ruthveni) to introduce the albino gene to the closely related Gray Banded Kingsnake (L. alterna). By carefully selecting the resulting offspring for appearance similar to the Gray Banded Kingsnake, breeders were able to produce albino specimens nearly identical to pure Gray Banded Kingsnakes.

The possibility of natural interbreeding and the production of fertile offspring is an indicator of the genetic closeness of the two species. An understanding of the true relationships between species can be enhanced through the process. DNA compatibility is certainly a more accurate indicator of close relationships than mere anatomy...

The Downsides

The offspring of an interspecific or intergeneric cross may be sterile. Sterility is often attributed to the different number of chromosomes the two species have, for example donkeys have 62 chromosomes, while horses have 64, mules and hinnies have 63. Mules, hinnies, and other normally sterile interspecific hybrids normally cannot produce viable gametes because the extra chromosome cannot make a homologous pair at meiosis, meiosis is disrupted, and viable sperm and eggs are not formed. However, fertility in both female mules and hinnies has been reported with a donkey as the father.

Loss of 'purity of race'. This is the most common argument presented against hybridization, and it has a bit of merit. However, such argument is often carried to extremes. It's generally broken into a few concepts, most of which are misleading:

  • "The genetic purity of the race will be lost and the resulting specimens will be unfit for repatriation into the wild population". Lemme clue you in on this: Absolutely NO specimens ever kept in the pet trade will ever be used for repatriation of a species in the wild, period. First, releasing any animal into the wild without authorization is already illegal in most states and many countries. Second, projects along these lines are carefully monitored by the relevant AAZPA approved Taxon Advisory Groups and relevant wildlife agencies. The requirements to be met for such projects are exhausting and you can believe me when I state that your pet snakes will never be used for such purposes.
  • "The genetic purity of the captive population will be destroyed forever". Often this argument is presented along with the idea that genetic information about hybrids sold will be lost or misunderstood by keepers acquiring future generations of these animals.
  • First, let me state that anybody producing hybrids does indeed have an obligation to accurately label them as such to prevent accidental introduction of undesired or unwanted genes into the population. That's just professional etiquette. I think the same data should accompany sales of known pure races as well. We've got the same obligation to maintain details of purity as we do of impurity.
  • Here's a secret for you: Unless your animals are pure descendants of known 'locality specific' specimens their purity is already highly questionable anyway. This is the reason that the TAG groups mentioned above were formed to oversee captive release projects. The minute you take your pure 'Jasper County Cornsnake' and breed it to a pet albino, you've lost the guarantee of purity forever, even though both are cornsnakes.
  • "Hybrids are trash". Yeah, whatever. Sharing such a factually presented opinion carries zero weight with anybody. You should have joined the high school debate team, you might have learned a thing or two about presenting your point. Foreign car enthusiasts have been saying bad things about domestic vehicles for years now, and vice versa. Come to think of it, so have Ford vs. Chevy owners. Guess what: Nobody cares about your sticker showing some kid wearing a Ford shirt urinating on a Chevy when they are shopping for a new vehicle. There's millions of happy owners of all these brands of vehicles. Moral of the story: If you don't like it don't buy it. This is America and that's your freedom of choice. So is expressing your opinion, just try not to sound like an idiot or waste other people's time when doing so.

I Don't Like Hybrids What Can I do About it?

Honestly, the number of uneducated/unprofessional/unscrupulous dealers and breeders out there is huge and any form of monitoring is impractical. If genetic purity is important to you, spend the extra time and money seeking out specimens from reputable dealers. Is a dealer producing hybrids disreputable? Certainly not, provided he or she is accurately labeling the hybrids as such. In fact, such a dealer is probably among the most reputable, as such labeling illustrates the dealer's understanding of the importance of such accuracy in labeling. Thus you can probably put greater faith in such a dealer when he or she labels something as pure! There's no point in sending a scathing letter of protest to a dealer just because he produces hybrids. He's probable more educated and informed on this subject than you are, and you just come off looking like an idiot.

About 'Mystery' Snakes

All of the above discussion centers upon snakes that are known to be hybrids. But each year a number of potential new mutations are brought to light. Often such snakes are quickly labeled as hybrids by the public - without regard to some factual information that must first be considered. Let's talk about a few of those, using a snake suspected of being a hybrid between a Cornsnake (Pantherophis [Elaphe] guttata guttata) and Gray Ratsnake (Pantherophis [Elaphe] obsoleta spiloides) as an example:

  • First, before quickly labeling some other breeder's efforts as "a trashy hybrid", you need to ask yourself if you are really an authority on the subject? Or even an educated non-authority? A specie is described to science by authorities on the subject, using only known locality specimens which are then held in museum study collections for permanent reference. The original specimen utilized to describe a new specie is designated as the holotype, while additional supporting specimens used are termed paratypes. These papers and specimens are the ONLY acceptable definition of a pure specimen, as defined by science. Anyone casting opinions on the purity of any specimen MUST consult these references before doing so or they have zero authority on the subject. In the case of our example snake, the following documents would be required: Elaphe guttata guttata (LINNAEUS 1758) and Elaphe obsoleta spiloides (DUMêRIL, BIBRON & DUMêRIL 1854). It would be wise to consult additional reference materials from subsequent authors as well.
  • Second, notice that these papers and all subsequent papers require use of the original specimens collected from known locality for original and future discussion as reference. There's a reason for that. As future authors study the population dynamics of a specie, the group as a whole may be split into several sub-species or even species. The original names applied would then apply only to the specimens from the original population.
  • In the case of our Cornsnake example, several subspecies have been described over the years, and some have later been split off into separate species. Some subspecies have later been discarded as being erroneous. Thus, 'pure' cornsnakes of today, may actually be intra-specific hybrids of former subspecies or future subspecies. Consider breeding say, a known locality Jasper County (Okeetee) Cornsnake to a known locality Pine Island Charcoal Cornsnake to create known 'pure' Charcoal Cornsnakes. Should future scientists decide the Pine Island population represents a new subspecies, your 'pure' corns would now be hybrids. It's all a matter of definition and viewpoint.
  • My point here is that if you don't have a clear and factual understanding of what a pure Cornsnake or Gray Ratsnake actually is, you are certainly in no position to cast judgment on our example.
  • Third, understand that NO captive bred snake can ever be used as a holotype or paratype for a specie or subspecies description. The reason for this is the possibility of non-natural appearance caused by embryonic development issues or mutation. Simply put, if a genetic mutation such as albinism can appear in captive specimens of our two example snakes, then other mutations can certainly appear as well. Some of these may not be apparent to the layman or even to the scientist, perhaps being subtle differences in structure, body shape, or scalation. Thus such specimens are disqualified from such use by necessity.
  • An obvious example of this (related to our example, as well) are the occasional scale-less specimens of Cornsnake and Gray Ratsnake produced in captivity. With scale counts and scale patterns a vital part of the scientifically descriptive process, it should be obvious that captive bred specimens are unfit for use as a holotype or paratype.

With all of this in mind, several concepts should be accepted:

  • It is apparent that simply stating that a specimen 'looks like a hybrid' has no validity at all, especially when using captive bred stocks for comparisons. The comparison specimens considered 'pure' are not valid by scientific standards.
  • The simple fact that the specimen being accused of being hybridized is captive-bred renders any such statement unusable. The specimen itself is not valid by scientific standards to be used as comparison, even if against the holotypes of the species in question.
  • With the above two concepts understood, the ONLY acceptable method of defining a specimen with certainty as a hybrid would be to perform DNA sequencing on the holotypes of the two species in question, as well as the potential hybrid.

Something to Consider

Is genetic purity really all that important? I mean we are talking about pet populations here. As discussed above, my cat is a hybrid and I love her all the same. In fact, I'm pretty sure I would not feel the same way if she were a pure African Wild Cat (Felis sylvestris lybica). I suspect I'd spend all my time getting stitches after trying to pet her....

But in the case of the cat, we have many perfectly happy owners of hybrids and known lines of pure race animals maintained by hobbyists and zoos. It'll be Ok to get to this point with reptiles too, we just aren't there yet - so the arguments rage on.

The Future?

At some point, the domestication of captive reptiles is going to be accepted as fact. There are already more known morphs of cornsnake available than there are for the parakeet (which is already considered domesticated by most states), With many agencies, evidence of hybridization plays a role in the definition of domestication and with current trends in legislation outlawing the keeping of wildlife, declaring our little herp friends as domestic animals may play a key role in preserving our ability to keep these animals.

As you've read, there are both good and bad points about hybridization to consider and in reality it is simply another tool in the toolbox of breeders that can be used wisely to create some new and unique herps for pet keepers to enjoy.