What Constititutes Inbreeding?

[Skiploder]

Dear Skip,

First, let me say that I have read a good many of your posts, and thanked you in a very many of them. Your husbandry recommendations are spot on, and I have nothing but the highest regard for you. In all honesty, you are one of the most consistently excellent posters on this site. All of your posts are intelligent, well thought out, and backed by what must be decades of real life experience. Though some people may complain about the tone of your posts, I think they would be better off just taking your advice. It is clear that you care deeply about the health and well being of your animals, and other keepers animals. It is also obvious that you are highly ethical in your standards of treatment for these animals.

Still, in this post, there are several things that I must disagree with you on. After reading your blog, and many of your very helpful posts on this and other forums, I get the feeling that your experience is mostly In vitro (behind glass). Mine is In Situ (at the location). Before changing careers and becoming a gunsmith, I was a very poor(monetarily) and lonely globe trotting Tropical Field Biologist. This gives me a very different perspective on the nature of gene flow. It is clear to me that you have an extremely organized mind. No doubt your collection is housed in a facility that is designed to take as many of the variables out of the husbandry equation as possible. This is an excellent trait in a keeper and breeder, but it has mislead you greatly when you tried to extrapolate into the wild.

First, in the wild there is no great keeper ensuring that conditions are optimal. In fact, conditions are often shockingly unstable. It is not uncommon to go to a location one month and find a huge number of a species, only to return a few months later and find the population has vanished. This occurs because something in the environment changed and the area is no longer habitable. The animals (unless they are insects) usually don't just die, they migrate. Migration can happen for a number of reasons: Changes in environment, interspecies competition (two species in the same niche cannot co exist, so they either partition the niche or one species leaves), intraspecies competition (males fight for females, or individuals fight for territories), seasonal changes, prey animal migration etc.

Second, in the wild offspring often cannot cohabit in the same environment as adults. This is especially true in many reptiles, where offspring have a different diet from adults. Offspring often are forced to travel in order to find suitable territory not already occupied by adults. During these early migrations, most youth are killed by disease, stranded in fatal environments, or are eaten by predators.

Third, in the wild animals do not hold onto territories for very long. A snake may obtain a territory with prime food sources and basking spots, only to be eaten by an eagle or hawk the next day. After the demise of this serpent, another snake will simply move into the territory to replace it.

Fourth, most animals have sophisticated ways of selecting mates. These mechanisms include a wealth of chemo-sensory clues that humans can't really understand, mate competition, and sperm selection to name a few. This differs greatly from the herp breeder's rack where the breeder pairs off snakes without regard to the rich mate selection strategies that have evolved in snakes.

Your 120 acre model does not take many of these factors into account. First, your 120 acres is static and stable, which in the wild (especially if there is any human involvement) just doesn't happen all that much. That territory may expand, contract, or move completely. Your cohort of 312 snakes will constantly be changing as well. Some snakes will persist in the environment for a great deal of time, others will be forced out, succumb to disease, be eaten etc. Over a four or five year period it would not be unusual to see as much as fifty to sixty percent of the individuals turn over. Of course, unless there is a very sharp divide between your 120 acres and contiguous territories there will be tremendous gene flow between contiguous territories.

Also of great importance is mate choice. Female snakes don't have to mate with specific males in the wild. They can choose which males to mate with. Many female snakes can also store sperm and choose when and if to use stored sperm. In many species, this decreases sibling mating, since siblings tend to have similar chemical signatures and most organisms seem programed to select mates with different chemical signatures.

Now let us look very carefully at one of your statements, "Now, with the exception of some select species, snakes are fairly limited in their roamings and wanderings. That's sort of how locality variants are formed - as well as intergrades. Gopher snakes in Contra Costa County have subtle differences compared to those in Alameda County. Some pituophis vary within localities." This statement is only partly correct, and in large degree incorrect. It is true that many snakes are limited in there ability to wander, and that there are locality specific variants. The variants are actually the result of natural selection eliminating phenotypic traits that are maladaptive for the environment. This does not mean that outside genotypes are being eliminated. In fact though all the snakes in an area may look the same, they may be genetically very variable. Your claim that intergrades are formed by limited roaming is completely incorrect. Since an intergrade cannot happen without gene flow, intergrades are actually proof of gene flow, outbreeding, and breeding continuity across the species in general.

In short unless we build a wall around your 120 acres, screen in the top, and post guards every few feet to make sure that no snakes enter or leave the 120 acres, there will be considerable migration in and out of your 120 acres. So the breeding pool over time is not as limited as you are suggesting. Even in a limited breeding pool, there are biological safeguards in place to limit inbreeding.

So though it is true that inbreeding does occur in wild populations, it is much lower than expected from your model. Furthermore, inbreeding depression is a very real and measurable problem. It occurs whenever humans try to line breed for specific traits. It also occurs in the wild when a population bottle necks. Inbred individuals have shorter life spans and are more prone to diseases than outbred animals. Limited genetic diversity can be extremely dangerous, especially if a new disease emerges. Many of the inbred animals and plants humans use today experience severe mortality do to infections that are seldom seen or unknown in wild populations with diverse genetics.

If we are not careful to protect the genetic diversity of captive bred populations, those populations could be at risk for increased mortality and reduced disease resistance.

Your statements about lifestyle diseases and selecting for maladaptive traits that are linked to color morphs people find attractive are spot on. I think our many Spider breeders could take a strong lesson from you.

Thank you again for the many fantastic posts you have contributed and will contribute to this forum.

Sincerely,

David

Actually, your assumption is partially wrong, but I do thank you for your thoughtful reply. While I have never been a paid biologist, my mentor was one and at one point my job took me to many places around the world. When I got to these places, I spent a lot of time field herping and wandering around with local herpers and biologists.

I didn't really get into a lot of things in this thread and I was not suggesting a model. The basic concept was to illustrate to people who gnash their teeth at the suggestion of inbreeding that it does occur naturally and in some areas, it occurs much more than others.

When I worked in Australia I was shown a wonderful map by Bill Messick regarding how a. ramsayi intergrades and localities slowly occur then subtly change over time starting at the edges of a range and then leisurely make the way inwards. Without going into to much detail here the idea is that there are a higher percentage of intergrades at the natural range interlap. There is more diversity at that interlap than at the center of the species range.

However over time, that edge interlaps with the next area inwards into the range. The process is both inwards and outwards. In time it leads to diversity throughout the range, but not equally in all parts of the range. As one variant affects change on it's neighbor, it is in turn being affecting by it's neighbors. The visual I always had was of a wave, strong as it hits the shallows, then slowing down as it hits the beach. That image was formed by that locality map. Whether the analogy is 100% accurate or not is up for debate.