# Inbreeding in Theraphosids - That Old Chestnut



## mcluskyisms (Jan 24, 2010)

I’m interested in peoples views on inbreeding within theraphosids, I’ve read from time to time in various publications or within online forum posts that it seems to be frowned upon by many. I would like to know why?

Obviously inbreeding within most mammals, especially _**** sapiens_ can lead to vast problems for any offspring produced (looks disconcertingly towards the Royal Family). Although, saying that, they don’t tend to give birth, or lay eggs for want of a better word to hundreds of offspring in one go. 

Personally I don’t see any great problem with inbreeding arachnids or other various insects, I see it as there is so much offspring produced in each successful breeding that in the wild it is bound to happen, if direct inbreeding or indirect. Now some of you will say/argue that male theraphosids mature faster than the females from the same brood. Therefore that is natures way of stopping direct inbreeding occurring, although is this entirely true? 

I recall reading an article on a species of spider (cant recall the species I’m afraid). Where the reports suggests that would prefer copulation with a direct sibling over another unrelated mature male of the same species. 

In The Tarantula Keepers Guide by Schultz & Schultz (3rd Edition) there is a paragraph written where it loosely discusses inbreeding in “more rare species” is ok. That says to me that you shouldn’t inbreed other more available species and that inbreeding is the last resort. Why? 

Loads of people will probably think inbreeding is unethical, and that people should try and source unrelated males for breeding purposes. Reasons may include that inbred offspring are weaker or may have abnormalities etc. Although it seems there is no proof of this available within theraphosids 

What do other people think?


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## Hedgewitch (Feb 12, 2008)

Well a quick look at a couple of papers suggests that spiders can and do suffer from inbreeding depression, though not as much as vertebrates.

And while maturation times may keep siblings away from each other, the long lives of female mygales means that Mother-Son mating is relatively easy (especially considering low dispersal rates in tarantulas).

_Edit: However, while they show limited dispersal and movement over their lives, and live in small locally concentrated groups, males may travel long distances (one _A. hentzii_ was tracked over 1.7km) and allow for gene flow between communities, reducing amount of inbreeding._


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## Brandan Smith (Nov 17, 2010)

if it doesnt or wouldnt happen in the wild i say its a no-no


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## Darrell (Jan 4, 2011)

Shandy said:


> if it doesnt or wouldnt happen in the wild i say its a no-no


I agree. Sure if it happens in the wild then in captivity it shouldnt really matter, but there is no need for inbreeding when in captivity as males and females are usually readily avaiable i don't think it's right to allow it as it still could cause issues, just my opinion.


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## jaykickboxer (Feb 11, 2008)

Darrell said:


> I agree. Sure if it happens in the wild then in captivity it shouldnt really matter, but there is no need for inbreeding when in captivity as males and females are usually readily avaiable i don't think it's right to allow it as it still could cause issues, just my opinion.


It must happen In the wild,rodents can interbred with no ill effects lizards also h
Can how do u thinly all the Morphs were created for example in order to create the temper albino leopard gecko Ron temper collected loads of wc specimens bred them then bred all specimens bk to patents so as any traits not being shown could come out then out poped a albino the start of many of the Morphs today yet i see no ill effect with the geckos


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## Darrell (Jan 4, 2011)

jaykickboxer said:


> It must happen In the wild,rodents can interbred with no ill effects lizards also h
> Can how do u thinly all the Morphs were created for example in order to create the temper albino leopard gecko Ron temper collected loads of wc specimens bred them then bred all specimens bk to patents so as any traits not being shown could come out then out poped a albino the start of many of the Morphs today yet i see no ill effect with the geckos


True there i don't know to much about the subject myself but i agree with shandy on the fact that if it doesn't happen in the wild then it shouldn't be allowed in captivity, but if it does happen in the wild which as you have said there is a good possibility it does then fair enough lol


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## mcluskyisms (Jan 24, 2010)

Darrell said:


> True there i don't know to much about the subject myself but i agree with shandy on the fact that if it doesn't happen in the wild then it shouldn't be allowed in captivity, but if it does happen in the wild which as you have said there is a good possibility it does then fair enough lol


There is no proof that it doesn't happen in the wild, nor is there any proof that it leads to any defects or problems within the specimens created.


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## Bexzini (Oct 21, 2010)

mcluskyisms said:


> There is no proof that it doesn't happen in the wild, nor is there any proof that it leads to any defects or problems within the specimens created.


I must agree here actually obviously inbreeding with homosapiens is going to cause severe implications but with tarantulas I'm yet to see evidence that this doesn't hapen in the wild? But then again I don't know enough about tarantula genes to really comment on this scientifically. Maybe its frowned upon because people try to 'humanise' their animals so to speak and this causes them to attribute whats frowned upon in human society into tarantulas? Just a guess :lol2:

Someone should conduct some sort of longitudinal study to observe the effects!!


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## Willenium (Apr 17, 2008)

Another thing to consider is that within the hobby there can only be so many specimens before you inevitably begin to breed from the same bloodlines. This said, what's to say we haven't been unknowingly breeeding from related blood since the early days anyway?


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## Poxicator (Nov 14, 2007)

Ive seen this thread pop up in a number of forums, and often there's an argument that says there's no problems, that they've kept species of X and not seen any issues and plenty of other arguments that equally have little credibility. Who here has actually studied this? or gone much further than forums to get their information? used assumptions or other peoples opinions? infact who here has kept and bred tarantula long enough to have 3rd generation Ts?

In the wild almost all the specimens of a sac will die, and a huge percentage will die young, most as part of the food chain of others. If that were not the case we'd be overrun by tarantula, and any other animal you wish to attribute that argument to. The basic understanding is the Ts distribute and if they survive they'll find an area of a square metre in which to live. A large percentage of these will be male and eventually flee the area in search of females. The nearest females to them are likely to be from the same sac, so no point hanging around there. And the females wont mate with each other, so perhaps you can see how this argument falters.

I fail to see how a mammal can be used in this discussion. Quite simply too removed to have any bearing on it. However, whilst rodents will interbred readily in captivity its often the case that new blood is introduced as problems do occur.

To my mind the liklihood of it is far less than we imagine, the affects of it undertermined, and the reasons for doing so are merely of convenience. I don't buy 10 of one species to interbreed, I buy 10 to have waves of adults to breed with other generations.

For many species, especially the rare ones, we have a small gene pool, its common sense to mix this gene pool up and I don't need a report to tell me that.


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## jetski (Apr 7, 2008)

I can't comment on tarantulas but I have bred several species of praying mantis for around 10 or so generations with no noticeable ill effects so far and although I have several breeding pairs at anytime to try and mix it up as much as I can to stop the gene pool from getting any tighter, they all originally came from original siblings from the same ootheca


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## Guest (May 8, 2011)

Shandy said:


> if it doesnt or wouldnt happen in the wild i say its a no-no


Surely it should really be a case of "if it doesn't cause the animal harm or distress" it shouldn't happen. Theres alot that happens in captivity that doesn't in the wild (ie Mr Jiminy Cricket making his appearance in an enclosed space every friday at 4pm, for instance) so rather than chastizing something because its not "natural" we should try to ascertain if its detrimental or not.


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## Guest (May 8, 2011)

jetski said:


> I can't comment on tarantulas but I have bred several species of praying mantis for around 10 or so generations with no noticeable ill effects so far and although I have several breeding pairs at anytime to try and mix it up as much as I can to stop the gene pool from getting any tighter, they all originally came from original siblings from the same ootheca


By noticable affects what do you mean? deformities/mortalities? Ideally you should be looking at things like time to maturity, number of offspring, success rate of offspring etc to see if there is really anything going on here.

Its very difficult to assess this kinda thing in the hobbyist arena where its mostly anecdotal evidence, somebody should run an experiment or something really.


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## joeyboy (Jul 19, 2008)

I was under the impression that problems can occur with inverts as E.tiaratum in captivity started to have problems(too much parthenogenesis?) and so folks used new blood lines from imports?


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## mcluskyisms (Jan 24, 2010)

Well I have read on AB's that several _Holothele _and_ Heterothele_ species mature around the same times. I currently have groups of 6 _Holothele rondoni_ and also 5 _Heterothele villosella_ all of which are slings currently so I guess I shall see once I grow them on. With slight tinkering with temperatures and feeding schedules (if needed) once they are big enough to be sexed I intend to breed them.

: victory:


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## jetski (Apr 7, 2008)

Moonleh said:


> By noticable affects what do you mean? deformities/mortalities? Ideally you should be looking at things like time to maturity, number of offspring, success rate of offspring etc to see if there is really anything going on here.
> 
> Its very difficult to assess this kinda thing in the hobbyist arena where its mostly anecdotal evidence, somebody should run an experiment or something really.



I mean just that, "noticeable" all you have listed plus more, no noticeable effects. the reason I don't just say "no effects" is because I'm not arrogant enough to not admit its possible I have missed something. seriously though I have not noticed any changes and I have been looking because this is something I'm concerned with. I really don't think its difficult to assess, to a certain degree anyway


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## oliwilliams (Feb 23, 2010)

Why do people keep talking about inbreeding in humans? You only have to look to norfolk to see the results of that:whistling2:
I have tried to breed same ooth mantids by slowing down the males development and find that mating is much harder and less successful than with unrelated pairs. I wouldnt be surprised if it already happens in spiders though as animals change hands several times in their life and no one tracks where they go or come from must be cases of mother son breeding by now.


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## Hedgewitch (Feb 12, 2008)

jaykickboxer said:


> It must happen In the wild,*rodents can interbred with no ill effects* lizards also h
> Can how do u thinly all the Morphs were created for example in order to create the temper albino leopard gecko Ron temper collected loads of wc specimens bred them then bred all specimens bk to patents so as any traits not being shown could come out then out poped a albino the start of many of the Morphs today yet i see no ill effect with the geckos


Interbreeding and inbreeding are different.

However, assuming you mean inbreeding here, as it's the topic of the thread: like :censor: can they. Inbreeding in rodents comes up with deformity and reduced survivor-ship in short order (maybe looking at 2-3 generations of sibling inbreeding often).

Not sure about lizards but I've definitely heard people mention less vigour and shorter lifespans on the leo morphs as opposed to the wild-types. I'd need to see some sort of evidence though.


Whether or not tarantula inbreeding happens in the wild is kinda unknown, surely it happens from time to time, however we have no idea whether it happens with enough regularity to be detrimental. 

Remember, female tarantulas are often picky about the males they'll chose, many species live long lives. Female Ts can afford to reject males too closely related to them etc.

Loss of vigour _is _noted in habitually inbreeding lines of araneomorph spiders, usually communal species, where losses in strength and survival of offspring is offset _for a while_ by the care given in communal rearing of young. 

Some research is even suggesting that the short term benefits of communality leads to a repeated evolution of the trait followed by a swift extinction as generations of inbreeding takes its toll.

------

No obvious deformities have been cited as "evidence" against inbreeding effect in spiders and inverts, mind however that you may be looking at the wrong things. Say there are very homogeneous hox genes throughout a species and variation is found elsewhere. Inbreeding may show little in the way of deformity.
You may however find it in say; eventual size, speed of growth or more importantly: disease resistance. You know, that thing that may well be the entire reason most organisms above bacterial level reproduce sexually (only half your genes go on to the next generation, however there's less chance of all your offspring being wiped out by a cold down the line, the Red Queen hypothesis).


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## jetski (Apr 7, 2008)

yeah I have seen deformities from inbreeding in rodents first hand... but their mammals so i dont think that holds much of an argument in this case


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## jaykickboxer (Feb 11, 2008)

jetski said:


> yeah I have seen deformities from inbreeding in rodents first hand... but their mammals so i dont think that holds much of an argument in this case


I was always told u could breed kids bk to parents 5 times over I.don't jeep rodents just saying what I've been told by various people


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## jetski (Apr 7, 2008)

jaykickboxer said:


> I was always told u could breed kids bk to parents 5 times over I.don't jeep rodents just saying what I've been told by various people



in college I saw several one eyed gerbils, third or fourth generation I believe but could of been more I guess


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## mcluskyisms (Jan 24, 2010)

Hmmm, interesting opinions on this thread. I'm still gonna do it and hopefully put a few ill judged theories to bed along the way


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## Poxicator (Nov 14, 2007)

mcluskyisms said:


> Hmmm, interesting opinions on this thread. I'm still gonna do it and hopefully put a few ill judged theories to bed along the way


Out of interest how are you going to show there's no issues?
For any study to be of value it would have to have sound control, and examine a number of generations in comparison with a group that were not given to inbreeding?
Not trying to be smart, Im genuinely interested, although I am curious why so many flout caution.


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## OrigamiB (Feb 19, 2008)

joeyboy said:


> I was under the impression that problems can occur with inverts as E.tiaratum in captivity started to have problems(too much parthenogenesis?) and so folks used new blood lines from imports?


I have heard this aswell, I think it is the reason why so many nymphs die of sudden death syndrome and why E. Tiaratum isn't seen in the hobby as much as it used to be


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## Hedgewitch (Feb 12, 2008)

jetski said:


> yeah I have seen deformities from inbreeding in rodents first hand... but their mammals so i dont think that holds much of an argument in this case


Inbreeding is pretty deleterious to most higher animals. They should be pretty comparable I think.



Poxicator said:


> Out of interest how are you going to show there's no issues?
> For any study to be of value it would have to have sound control, and examine a number of generations in comparison with a group that were not given to inbreeding?
> Not trying to be smart, Im genuinely interested, although I am curious why so many flout caution.


As said before, traits you should probably be looking for are survivorship and disease resistance. For that you'd need access to 100+ inbred slings of a species (preferably for several generations for clearer results) and a comparable number of slings from wild caught stock collected from close but separate locations. 

To get meaningful results you'll need to keep all under as similar conditions as possible and note when and why spiders die, speed of growth, eventual size.

Other things to look at would be number of successful sacs and number of eggs that develop (number produced by females could potentially be a measure of fitness).

Remember, you're not looking for obvious deformity like spiders with egtra body parts etc. The results of inbreeding depression like this will most likely manifest at a molecular level.

Disease and parasite resistance are not easily tested in captivity.


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## bainsy (Feb 17, 2009)

Hedgewitch said:


> Inbreeding is pretty deleterious to most higher animals. They should be pretty comparable I think.
> 
> 
> 
> ...


Pretty much this. It would be a massive (and expensive) project to undertake in an amateur fashion. I'd be very interested in the results.


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## mcluskyisms (Jan 24, 2010)

Poxicator said:


> Out of interest how are you going to show there's no issues?
> For any study to be of value it would have to have sound control, and examine a number of generations in comparison with a group that were not given to inbreeding?
> Not trying to be smart, Im genuinely interested, although I am curious why so many flout caution.


Well as you obviously well know, I have no means to do this in a properly controlled fashion as it deserves, (we are mainly hobbyists with an interest) Although saying that I believe _any_ insight on the matter would be rather interesting. The way it would most likely be done is that if resulting slings from each inbred species go to small groups of dedicated hobbyists, and all records and information are kept and shared by each along the way. Then they themselves would rear and breed resulting offspring. Hopefully by the time generation 10 occurs the people in question will have good solid information regarding things like sac size, survival rate percentage and length of time to maturity within specimens. All information can then be put together, compared and written into document on the issue.

I personally believe most of the rarer CB stock in hobby (Even some of the least rare) have most likely been unknowingly (and knowingly) inbred. 
Many of the people who knowingly inbreed don't care to say they have due to a misconstrued general feeling that such actions are unsavory and bad for any offspring produced.


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## GlasgowGecko (Feb 23, 2008)

Measuring inbreeding depression, is not trivial, especially in the selectively neutral (or even positive) captive environment. Moreover, the traits which _can_ be used to measure fitness, are often a little subjective (particularly in captivity). Traits that one considers deleterious in a give environment, maybe neutral or beneficial in another. After-all, a selection pressure is environment specific. Sadly, none of the methods currently suggested in this thread, really allow adequate testing due to design.

The question becomes, is it reasonable to assume that inbreeding depression will occur, or can it be prevented?

Spiders (well, in fact anything with high fecundity) represent an ideal system for implementing strict selection to overcome potential fitness reduction. In fact, it is easily conceivable that an increase in fitness is possible via inbreeding with strict selection. Perhaps the nicest example of this is disease resistance (contrary to what is written above). Raising and inbreeding surviving offspring in the presence of a given disease or parasite can ensure fixation of resistance or tolerance which does not occur from random outcrossing. Mortality rate becomes very high in initial generations, but the fitness of surviving offspring (measured generally by fecundity in this group) will also be considerably higher than non-inbred lines in the presence of the same pressure. Of course, it takes a great deal of time to achieve this, and you must ensure that the selection pressure is appropriate for your goal, but it is certainly not impossible.

Does inbreeding occur in the wild? I think perhaps there is a little confusion between inbreeding (becoming homozygous at any given loci) and full-sibling mating. Any individual within a 'wild' population will be more related to any other individual within that population, than any individual picked at random from another population. Despite male roaming. Thus each mating within a population, constitutes the offspring in that generation being more related (number of homozygous loci) than the previous one. The key, is that 'mother nature' ensures strict selection pressure, and low survivorship, effectively purging deleterious recessive mutations.

Whether or not you _should_ do it or not (or are capable of ensuring appropriate selection, so that deleterious recessives are removed from the population) is a different matter entirely.

Andy


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## Guest (May 9, 2011)

mcluskyisms said:


> Well as you obviously well know, I have no means to do this in a properly controlled fashion as it deserves, (we are mainly hobbyists with an interest) Although saying that I believe _any_ insight on the matter would be rather interesting.


Without sounding like a dick or anything, or trying to put your efforts down etc etc... I'm afraid any data collected without rigorous controls, good samples and confidence levels would be more or less useless to make any firm claims.

Without something proper would be impossible to say for certain whether the outcome you're seeing is merely down to chance. You might see a trait, hell theres a good chance you will, but there'll just be too many confounding variables and too weak a confidence level for you to say what you're seeing is a real phenomena or an artefact of one on many variables.

Data collection really does need to be extremely rigorous to be useful.


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## mcluskyisms (Jan 24, 2010)

Thanks for that post Andy, I think you have made the most valid points in the thread.



Moonleh said:


> Without sounding like a dick or anything, or trying to put your efforts down etc etc... I'm afraid any data collected without rigorous controls, good samples and confidence levels would be more or less useless to make any firm claims.
> 
> Without something proper would be impossible to say for certain whether the outcome you're seeing is merely down to chance. You might see a trait, hell theres a good chance you will, but there'll just be too many confounding variables and too weak a confidence level for you to say what you're seeing is a real phenomena or an artefact of one on many variables.
> 
> Data collection really does need to be extremely rigorous to be useful.


Sadly I know this, and yeah as mentioned I haven't the proper resources at all to do it in such a manner that it would deserve. Although I still feel inclined to actually try inbreeding these species and see what results may come. I guess the main objective is to try a dis spell all the mystique surrounding inbreeding and to do so out in the open without trying to hide it.

People, as they always will can make of it what they like.


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## OrigamiB (Feb 19, 2008)

Moonleh said:


> Without sounding like a dick or anything, or trying to put your efforts down etc etc... I'm afraid any data collected without rigorous controls, good samples and confidence levels would be more or less useless to make any firm claims.
> 
> Without something proper would be impossible to say for certain whether the outcome you're seeing is merely down to chance. You might see a trait, hell theres a good chance you will, but there'll just be too many confounding variables and too weak a confidence level for you to say what you're seeing is a real phenomena or an artefact of one on many variables.
> 
> Data collection really does need to be extremely rigorous to be useful.


Nail on the head :no1: Any tests will have to be done under strict control, especially where it comes to inverts as the different keeping methods of everyone taking place in the test will all vary the growth and effects on the spider. Eventual deaths may be due to bad keeping or any other number of variables rather then a birth defect.... You really will need laboratory conditions for this to work!

I think this is an impossible question to answer unless you want to go and find someone to give you a research grant! Until then I think it is just safer to assume that inbreeding is bad, and it is better to introduce fresh genes into the gene pool (unless you take glasgow geckos example, but that would be hard to do on a hobbyist level, or on any level in captivity most likely)


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## mcluskyisms (Jan 24, 2010)

OrigamiB said:


> Until then I think it is just safer to assume that inbreeding is bad


That's the whole point of the thread, why just assume its bad?


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## 8and6 (Jan 19, 2010)

mcluskyisms said:


> That's the whole point of the thread, why just assume its bad?


i assume it's not a great thing to do because any species that the effects of inbreeding has been studied has shown detriment. any genetic anomalies enforced. they may not show in 1, 2 or even 3 generations, but they do occur eventually.
why assume that spiders are any different?
it's been proven in the Moth Epirrita autumnata to cause shortening of lifespan and a lowered immune response, especially in females

Read the full article here

and in freshwater shrimp colonies the information about colony crashes when no new genetic material is introduced is widely available. yes these are aquatic invertebrates, but invertebrates nonetheless.

using a 'cousin' of 5 generations removed is very different to inbreeding via a direct bloodline.

personally i will err on the side of caution, until a full and proper scientifically based study brings forth info either way.

we already 'mess' with nature as the majority of Ts wouldn't even make it to adulthood. Small and weak males are still used which wouldn't make it past a first pairing. Natural selection odds are cut hugely.

but to purposely inbreed without an outcross into another gene pool seems to me kind of......well.....self defeating.


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## GlasgowGecko (Feb 23, 2008)

[email protected] said:


> i assume it's not a great thing to do because any species that the effects of inbreeding has been studied has shown detriment. any genetic anomalies enforced. they may not show in 1, 2 or even 3 generations, but they do occur eventually.
> why assume that spiders are any different?
> it's been proven in the Moth Epirrita autumnata to cause shortening of lifespan and a lowered immune response, especially in females
> 
> ...


Interestingly, this is not entirely true ("...any species that the effects of inbreeding has been studied has shown detriment."), but what is important to remember, is that this study intended to demonstrate reduced fitness (due to _both_ inbreeding and out-crossing. Out-crossing depression is much more common than many realize). Simply because you can demonstrate that reduced fitness linked to mating strategy can occur, does not mean that there are not ways of preventing it (other than the obvious of course...). Inbreeding with strict selection can and does achieve this.

Of course you are right, there is a difference in the magnitude of alleles at which offspring will become homozygous if you consider breeding full-siblings when compared to less closely related individuals. But breeding full-siblings with strict selection allows you to purge the system (of hidden deleterious recessive alleles, previously present in heterozygotes) much quicker than by any other method.

Now I am not saying that this is the correct approach (quite the opposite in many cases), but it is certainly a valid approach. It does require very careful preparation, and strict rules however. Inbreeding depression is obviously worrying for many, however it is very beneficial for keepers of 'less common' species to be aware that there are ways to practice this technique safely - and in certain cases, it is almost essential.

Just for clarity, my main justification for arguing this point is not that I think people should do this, but that _IF_ it is attempted, people do it under appropriate conditions.

Andy


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## Poxicator (Nov 14, 2007)

GlasgowGecko said:


> ... there is a difference in the magnitude of alleles at which offspring will become homozygous if you consider breeding full-siblings when compared to less closely related individuals. But breeding full-siblings with strict selection allows you to purge the system (of hidden deleterious recessive alleles, previously present in heterozygotes) much quicker than by any other method.
> Andy


Out of interest, how would a hobbyist measure that?


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## GlasgowGecko (Feb 23, 2008)

Poxicator said:


> Out of interest, how would a hobbyist measure that?


Good question... The answer of course is not so straight forward (is anything?). Theoretically (and by this I mean mathematically, and not 'in theory') you can use simulation (mathematical modeling) to estimate inbreeding coefficient and its stocasticity over time (and based on various scenarios). OK, its complicated, but possible for hobbiest keepers logistically. Verifying it experimentally? Well thats not possible on this scale.

In essence, theory _should_ suffice here, as sharing 50% of your genes gives a significantly higher chance of becoming homozygous than sharing 10% (for example), and large numbers of offspring, theoretically allows you to select only those which do not express reduced fitness. 

Strictly speaking, if you have a population size of 50 adult pairs (unrelated), then you will increase your inbreeding coefficient by 1% per generation, which is almost the ideal scenario for captive breeding programs, as enforced selection _should_ allow you to maintain a viable population. Sadly, I suspect that in many species currently bred in the UK today, we don't have this 'ideal', and so we must accept some degree of inbreeding. Being prepared to deal with it, seems like half the battle to me.

Andy


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## Hedgewitch (Feb 12, 2008)

GlasgowGecko said:


> Measuring inbreeding depression, is not trivial, especially in the selectively neutral (or even positive) captive environment. Moreover, the traits which _can_ be used to measure fitness, are often a little subjective (particularly in captivity). Traits that one considers deleterious in a give environment, maybe neutral or beneficial in another. After-all, a selection pressure is environment specific. Sadly, none of the methods currently suggested in this thread, really allow adequate testing due to design.
> 
> The question becomes, is it reasonable to assume that inbreeding depression will occur, or can it be prevented?
> 
> Spiders (well, in fact anything with high fecundity) represent an ideal system for implementing strict selection to overcome potential fitness reduction. In fact, it is easily conceivable that an increase in fitness is possible via inbreeding with strict selection. Perhaps the nicest example of this is disease resistance (contrary to what is written above). Raising and inbreeding surviving offspring in the presence of a given disease or parasite can ensure fixation of resistance or tolerance which does not occur from random outcrossing. Mortality rate becomes very high in initial generations, but the fitness of surviving offspring (measured generally by fecundity in this group) will also be considerably higher than non-inbred lines in the presence of the same pressure. Of course, it takes a great deal of time to achieve this, and you must ensure that the selection pressure is appropriate for your goal, but it is certainly not impossible.


An interesting point, that inbreeding can fix positive traits. However that's looking at one trait verses overall fitness. Or at a surprising cost.

And interesting example from the human world is the mutation in some western Europeans that protects against HIV. Heterozygotes get an extra two years on average before HIV becomes AIDS (without treatment). Homozygotes are completely immune from HIV, they're very rare but completely safe from HIV... shame they're completely defenceless against west Nile virus.

To add to your point about possible benefits of inbreeding, a history of periods of inbreeding, in high fecundity animals like spiders, can lower the frequency of deleterious recessives in the population, which can lead to increased inbreeding tolerance in later generations.



> Does inbreeding occur in the wild? I think perhaps there is a little confusion between inbreeding (becoming homozygous at any given loci) and full-sibling mating. Any individual within a 'wild' population will be more related to any other individual within that population, than any individual picked at random from another population. Despite male roaming. Thus each mating within a population, constitutes the offspring in that generation being more related (number of homozygous loci) than the previous one. The key, is that 'mother nature' ensures strict selection pressure, and low survivorship, effectively purging deleterious recessive mutations.
> 
> Whether or not you _should_ do it or not (or are capable of ensuring appropriate selection, so that deleterious recessives are removed from the population) is a different matter entirely.
> 
> Andy


An interesting post altogether mate, and I see how the differences in selection pressure between the wild and captivity put a tack in the path of my experimental design. This needs thought.



mcluskyisms said:


> Thanks for that post Andy, I think you have made the most valid points in the thread.
> 
> 
> 
> ...


My only question about this is this: What are you comparing it against? Any observations are, for want of a better term, meaningless unless compared to something else. It'd be like trying to ascertain if someone was tall or not with no data about average heights and no one to compare them to.

----

To add to this all, I'd like to mention again that inbreeding depression _is_ noted in spiders:

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SpringerLink - Conservation Genetics, Volume 8, Number 5

http://www.scopus.com/record/displa...archTerm=TITLE-ABS-KEY(spider AND inbreeding)

Spiders themselves seem to think heterozygosity is a pretty big deal: http://www.scopus.com/record/displa...archTerm=TITLE-ABS-KEY(spider AND inbreeding)


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