All these slugs, we MUST be doing something wrong...

[carol]

Yea, I don't mean that any one line or morph is more prone to infertility, its just that the few hatchlings that survive a mostly infertile clutch are much more likely to grow and bred(and pass it on) in captivity that in the wild, where you need to have so many because in reality so many die. No matter if it is amel or lav some pass more fertile than others but we still breed the less fertile causing it to bite us in the rear later. Lets face it when is the last time we went to buy an awesome colored or patterned corn and said "But wait a minute, how big of a clutch did he/she come from?" Thanks everyone for their 2 cents.

 

[tschofie]

Serpentile Darwinism

/If those genes are so detrimental, they shouldn't be so
/common in the wild gene pool, so it would take quite a
/lot of "non-selective" breeding for them to become so
/common.

Sounds a little like asking why, say, tay-sachs is so much more common in, oh, the Jewish population than in the rest of the world. Or why Cystic fibrosis is more common in westerners. Or why lactose intolerance is more common in eastern populations. Whatever original event that happened to cause an increase in the bad allele within those populations (like a bottleneck or founder effect) certainly occurred a very, very long time ago. And that population has, er... "interbred" with all kinds of other populations since then, for generations and generations. But still the disease is more prevalent.

So if amels indeed all come from just one animal, well, that's one heck of a bottleneck. It means that EVERY amel, if you draw a family tree large enough, can trace its lineage back to one individual sometime in the last, oh, 30 generations or so. That would be like... if 800 years ago some guy washed up on an undiscovered continent along with a couple willing ladies, and they had lots of kids, and even though other people washed up or sailed to the continent, they all married descendants of the original arrivals. So now today, *everyone* on our pretend continent is related to (at the very least) that one original male.

Unless that male just-so-happened to be carrying no destructive alleles at all (unlikely, since the average human carries some five to twenty-five recessive alleles for diseases of varying nastyness and lethality, and I can't imagine snakes are much different) then the frequency of those alleles within our little contintent population *must be* much higher than in the larger, outbred population. The bad alleles may not be following the amel trait around, but they are *more common* in the population that derived from that first daddy snake.

That in itself probably causes a lot of the infertility and non-feeding hatchlings. (In the wild an individual with a bad allele in a relatively randomly mating population is less likely to run into a mate who is *also* heterozygous for the same diseased allele. The allele is just less frequent.)

There's actually a term for this effect. "Inbreeding Depression" is the decline in mean fitness of a population, due to the increase in homozygosity and the increase in frequency of individuals carrying recessive genetic diseases. (Note that it doesn't exclude remarkably healthy or super fertile individuals! It just means that the *average* is becoming less fit.) It happens any time any population is not allowed to breed absolutely randomly, which almost never happens, and the only way to stop it is to balance it out with environmental selective pressure, where only the very strongest and most adapted survive. In the wild, females prone to eggbinding die, kinked babies die, eggbound females die, males with low fertility don't pass their genes on, females that lay eggs which rot and stink and attract preditors have their clutches eaten and don't pass on their genes, and so on and so on.

So, because there is little selective pressure and a non-randomly breeding population of corns, I'm willing to bet that inbreeding depression is probably happening to captive corn snakes.

Theoretically, it is also happening to humans. Personally, I'm really, *really* glad there aren't a lot of environmental pressures selecting against poorly adapted humans in most countries anymore. I mean, I know I wouldn't have made the cut.

'Course, all that healthful excercise out in the wild surely plays a role, too. Oh, now I'm all confused. And how the heck did my "R" key get sticky? It's just my R key and I think I need a nap and grumblegrumblegrumble.... K. I really am going now.

Cheers,
TS


*****

Reality is merely an illusion, albeit a very persistent one.
- Albert Einstein (1879-1955)

 

[Clint Boyer]

Sounds good to me ....

Inbreeding depression is a reality that we have to deal with in this hobby. Hopefully we will be able to weed those types of things out when they become a problem. But, of course, there are some things that are just not meant to be, but that won't keep us from trying

 

[Rich Z]

Hmm, I'm not sure I agree with all of this.

How dispersed are corn snake populations in the wild these days? Most are likely to be island communities surrounded by unnatural barriers created by mankind. Even in true island populations (the Florida Keys, for instance), do we really see or has anyone noticed an increase in problems that could be pointed to as having inbreeding as the causative agent?

I suspect corn snakes don't move around much from their home territory. So that implies that a healthy population of corn snakes will naturally be inbred to a substantial degree. There may be some occasional stragglers come in, but for the most part I think an environment that is favorable to corn snakes (good food supply, low instance of predation, etc.) would remain relatively stable in the core (relation wise). If a captive facility has a good supply of unrelated stock to start with, I suspect that the problems associated with inbreeding would actually be LESS than that experienced in the wild with proper management of the captive stock. The difference being is that in the wild, the failures (genetically speaking) never get to been seen by us before they die off. But this still would not explain the low incidence (in my experience) with eggs collected from wild caught females producing substandard (healthwise) individuals.

It would certainly be interesting to investigate various populations of corns in the wild and be able to determine just how closely related they tend to be. I think that by the definitions we are using, we would find them all to be heavily inbred. Afterall, the genetic stew needs to be concentrated for the POSITIVE mutations to take hold. If the individuals are too widely dispersed, then the odds of evolution having any effect would be dramatically reduced.

IMHO.

 

[tschofie]

Hmm...

Absolutely. Badly adapted snakes, in the wild, die. Even the snakes related to the badly adapted ones die. For instance, perhaps the reason one never finds clutches with bad eggs in the wild is that clutches that contain bad eggs smell, and attract more preditors. Environmental pressure goes a long ways towards keeping a population from showing the nastier effects of its inbreeding.

So as for collecting good females... what happens to the fertility rate if you breed two wild caught snakes together? Does fertility go down the longer they've been in captivity, or does it stay high? What happens if you breed a wild caught female to a captive born male, or vice versa? Does it seem to matter how old the male or female was when he/she was caught?

Just wondering... Does anyone know how the total population of wild cornsnakes compares to the total population of captive cornsnakes? Any guesses?

All kinds of questions. Sorry,
TS

 

[Serpwidgets]

Ahh, this thread is getting better all the time. ))))

Sounds a little like asking why, say, tay-sachs is so much more common in, oh, the Jewish population than in the rest of the world.

According to the "out of Africa" theory, the entire human population is only something like 5000 generations old. I would guess (seriously, I have no clue) that corns have been exposed to a lot stronger natural selection pressures, and for a lot more generations. Also, being more common is relative. According to the Gale encyclopedia of medicine, "About one out of every 3,600 babies born to Ashkenazi Jewish couples will have the disease." (Yes, I'm a geek and had to look it up online, hehe) This makes for 1 in 900 couples that are both "het" which means that something on the order of 1 in 225 people of that 'breeding group' are actually carrying the gene. The "problems" we have in corns seem a lot more common than that, and the wild populations have to deal with serious selection pressures.

Compare with how uncommon the allele for amelanism is in wild corns. It doesn't totally add up, in my mind anyway. Ya know what I mean?

Absolutely. Badly adapted snakes, in the wild, die. Even the snakes related to the badly adapted ones die.

That's part of the original point I was trying to make, that badly adapted snakes in the wild die off, therefore because of this deselection, detrimental alleles (especially dominant ones of course) should be uncommon in wild snakes to begin with. The smaller the breeding group, the more pressure there is on those with the "bad" recessive genes because they are more likely to breed with another carrier and suffer the 25% loss of offspring.

And the wild is where our gene pool has come from. From what I've heard the majority of corns are only a handful of generations away from wild ancestors.

Another thing that is interesting, which just occured to me, is that inbred populations, as Rich mentioned, might have had their "bad genes" cleaned up by the process. Meanwhile, some other population of cornsnakes that doesn't interbreed with the first group has also cleaned out theirs, but I imagine it's possible when you put group A with group B that some "never-before-seen" combination of alleles could also cause problems.

So as for collecting good females... what happens to the fertility rate if you breed two wild caught snakes together? Does fertility go down the longer they've been in captivity, or does it stay high?

I'd be very interested in seeing results from such experiences. My money is on "B-fertility will go down the longer they're in captivity."

I believe that inbreeding can be, and in some cases is, a large factor. But IMO that doesn't explain all of the differences we are seeing between wild and captive corns. IMO our husbandry is not as optimal as it could be. Not that we neglect our animals or anything; I just think we don't know enough yet to provide optimal environments for them.

Heh, I'm on my 3rd beer, so take it all with a grain of salt... oh wait, salt is for tequila. ;-)

 

[LizS]

I have a question (and I'm only on my first beer): would snakes in the wild eat the slugs? And those caught while pregnant who lay eggs in captivity, have they been observed while laying to rule out slug eating? Because if they eat their slugs it would definitely affect the observed results.

 

[carol]

Re: Hmm...

Absolutely. Badly adapted snakes, in the wild, die. Even the snakes related to the badly adapted ones die. For instance, perhaps the reason one never finds clutches with bad eggs in the wild is that clutches that contain bad eggs smell, and attract more preditors. Environmental pressure goes a long ways towards keeping a population from showing the nastier effects of its inbreeding.

Yes wonderful, just what I was trying to say but you did a much better job explaining. Thanks!

 

[Serpwidgets]

Does any body know if the trait for infertile eggs is dominant, recessive, or codominant. This could also be a factor.

Assuming it's a single trait, it would most likely be recessive. Anything that is destructive that expresses itself when heterozygous is so much more likely to be deselected from the wild population long before we ever get our hands on it.

However, I don't think it would be a single trait. There are probably a lot of things that could contribute to infertility. Think about all the things that go into making healthy sperm, and any genetic factor (or combination of factors) that affects any one of those things could have an effect.

For example, say one population of cornsnakes has sperm that are slower swimmers because they have less energy. Then there's another population of cornsnakes that has slow swimmers because of their shape. Alone, these wouldn't be such a big factor, but if both traits are present in the same animal's sperm, those sperm might never get to their destination.

The thing that's frustrating is that there could be a gazillion and one factors. I think a genome map would be mighty helpful.