Genetic diversity and zoo conservation

SealPup said:
Never did I say they weren't on their last legs, nor did I say such was impossible.

Rather that after a bottleneck, the descendants are not the same as the ancestor: genetic diversity has been lost, and thus future potential to evolve as regards things like disease resistance. Does anyone think the Sumatran rhino might realistically have been saved by captive breeding when it was attempted? Or we will see Asian cheetahs all over India one day?
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But none of those mentioned species are on their last legs.

You mention bottlenecks and then you mention Cheetahs, are you aware that Cheetahs once underwent a natural bottleneck long ago? And the species still survived and even thrived until Human influences pushed them back. True bottlenecks certainly don't help the future of a species, but they do not mean inevitable extinction.

Perhaps the Sumatran Rhino was already a lost cause when captive breeding was attempted, but the point is it was attempted and that is better than doing nothing and most certainly counts as a cooperative conservation effort by several zoos. Could something have been done much earlier? Perhaps. Is the story of the Sumatran Rhino ending happily? Probably not- but that does not mean last ditch efforts and captive breeding programs involving low genetic diversity are useless. The Mauritius Kestrel is the best example given so far. While another member on here could give you a much better summary of the story, the entire surviving population is descended from two captive birds. Is the genetic diversity extremely low? Yes, but that species is now surviving back in the wild again and I do not believe inbreeding depression is a proving to be much of a problem with them. Of course most species would not fare quite as well, but that doesn't mean these actions are mute. I mentioned the Kihansi Spray Toad earlier. Less than 70 individuals were left in the captive population by the time they went Extinct in the Wild and their husbandry needs were worked out. Today there have been thousands bred in captivity and a reintroduction program is currently at work.

~Thylo
 
Just think in the cheetah, that passed a thin bottleneck about 10000 years ago and in current millenium is doing very fine with very big populations (now endangered again but due to human factors unrelated with their genetic diversity). Or just think in how well would recover the species mentioned before (Nene, Pere David's deer, European and American bison, etc) if the human-induced threats would not persist in their native ranges. Without mongooses in Hawaii, Nene would be plentiful. And just think on species saved from just two individuals (Mauritius kestrel, black robin) that today are doing fine, to the point to be ever no longer Critically endangered and coming back to Endangered for both species.
 
FBBird said:
What's wrong with Laysan Teal? Such a restricted population on a barely habitable island is always going to be at risk. However, it's common in aviculture, so we have a good reserve population -- I've bred quite a lot of them myself.
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The extremely low genetic diversity of Laysans makes them a classic example where inbreeding might become a time bomb in the long term. Yes, you can have a numerous population with low genetic diversity, but that lack of diversity is still crippling when change strikes.

Think of the difficulty Tassie devils had developing resistance to transmissable cancer; some are immune so there will be survivors, but next time there is a disease outbreak, will devils withstand that one too?
 
SealPup said:
The extremely low genetic diversity of Laysans makes them a classic example where inbreeding might become a time bomb in the long term. Yes, you can have a numerous population with low genetic diversity, but that lack of diversity is still crippling when change strikes.

Think of the difficulty Tassie devils had developing resistance to transmissable cancer; some are immune so there will be survivors, but next time there is a disease outbreak, will devils withstand that one too?
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And your point is?
 
I notice you like to selectively respond to the counter arguments made against your claims...

I'd imagine the Laysan Teal are a poor example when it comes to the problems with inbreeding. The population is likely somewhat resistant to its affects due to its very small endemic range.

~Thylo
 
I did not say they were resistant to a specific disease, I meant inbreeding probably won't affect the similarly to how many other species are affected due to the fact that they're endemic to an island that's about 1 mile by 1.5 miles in size. There's bound to be a certain amount of natural inbreeding and low genetic diversity to begin with.

~Thylo
 
SealPup said:
Its cumulative, is the point. Genetid diversity is an important part of adaptability.

Thylo: resistant - to which specific disease?
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It is likely that many species with a restricted range, and necessarily inbred because of it, have already gone extinct. Species like Laysan Teal and Mauritius Kestrel are probably survivors that have come through more than one genetic bottleneck over the years, and are pretty resilient. We see this in laboratory animals, where those inbred lines that don't go extinct, thrive and become standard tools of research.
 
SealPup said:
Because genetic diversity = long term prognosis. Some actions give humans a warm glow inside, but merely delay what had become inevitable.
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SealPup said:
but such last minute interventions have borne little fruit in return for financial outlay, largely because the patient's health was already in steep decline.
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SealPup said:
But after a crisis point, nothing is really cured. Keep fighting for someone whose death is imminent anyway? Or turn away, and help where you can.
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SealPup said:
Never did I say they weren't on their last legs, nor did I say such was impossible.
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SealPup said:
The extremely low genetic diversity of Laysans makes them a classic example where inbreeding might become a time bomb in the long term. Yes, you can have a numerous population with low genetic diversity, but that lack of diversity is still crippling when change strikes.
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SealPup said:
but next time there is a disease outbreak, will devils withstand that one too?
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SealPup said:
Its cumulative, is the point. Genetid diversity is an important part of adaptability.
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The SealPup philosophy in summary:

"Screw anything which is already in decline, they're a lost cause. Same goes for anything which *might* be in decline. Only bother saving the things which don't need saving yet. Anything with low genetic diversity doesn't deserve a chance."

:P
 
TeaLovingDave said:
The SealPup philosophy in summary:

"Screw anything which is already in decline, they're a lost cause. Same goes for anything which *might* be in decline. Only bother saving the things which don't need saving yet. Anything with low genetic diversity doesn't deserve a chance."

:p
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I will explain the lemurs they should try again then. Leave Madagascar and when they try to colonize the island again to bring a few more along when rafting away from Africa. Because they were doomed from the beginning...
 
And yet every consevation message, about the extinction of the thylacine, nowadays stresses the low genetic diversity as a factor in their extinction.

And no, rafting is not a one off event. Where rafting happens, ie. on the Amazon, it is regular occurrence. There is no reason to think one family of proto-lemurs came on a single raft. In the Eocene-Oligocene currents and vegetation types were more amenable to rafting, populations were topped up from the mainland.
 
SealPup said:
And yet every consevation message, about the extinction of the thylacine, nowadays stresses the low genetic diversity as a factor in their extinction.

And no, rafting is not a one off event. Where rafting happens, ie. on the Amazon, it is regular occurrence. There is no reason to think one family of proto-lemurs came on a single raft. In the Eocene-Oligocene currents and vegetation types were more amenable to rafting, populations were topped up from the mainland.
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1. That low genetic diversity was one of the factors in thylacine extinction does not mean that this will always be the case for all animals, enough examples of the contrary are available including humanity... It is all about chance here that you have a higher/lower chance of survival doesn't mean that the one with the lower survival chance always goes extinct.

2. It would actually be nice to come with evidence of all your wild claims, because we would need 1000s of rafting events to make your theory true and I have yet to see a reason for that to be the case. This does not only go for lemurs but for all island taxa that arrived in that way...
 
SealPup said:
And yet every consevation message, about the extinction of the thylacine, nowadays stresses the low genetic diversity as a factor in their extinction.
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Exactly. Low genetic diversity is indeed a factor that can contribute to the extinction of a species and an important one at that. But low genetic diversity doesn't equal inevitable extinction. Several members have pointed out lots of examples of taxa that are seemingly doing fine despite a genetic bottleneck in the recent past. Examples include Lord Howe Island stick insect, pink pigeon, Mauritius kestrel, Père David's deer, both species of Bison, black robin and your favourite, laysan ducks.

Edit: seems like @lintworm was just ahead of me :D
 
Depending on your definition of where to mark the transition from one species to another, one could argue that *all* species start off with only a few founders..... in which case every species on the planet can be written off as doomed :p
 
lintworm said:
1. That low genetic diversity was one of the factors in thylacine extinction does not mean that this will always be the case for all animals, enough examples of the contrary are available including humanity... It is all about chance here that you have a higher/lower chance of survival doesn't mean that the one with the lower survival chance always goes extinct.

2. It would actually be nice to come with evidence of all your wild claims, because we would need 1000s of rafting events to make your theory true and I have yet to see a reason for that to be the case. This does not only go for lemurs but for all island taxa that arrived in that way...
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Wild claims??? Where rafting on vegetation is a thing, its observed all the time ie. iguanas rafting into the Caribbean, or all kinds of animals in Amazonia. It has an element of chance each time, not just the rafting but the survival and colonisation - but where it happens, its actually commonplace, and in other parts of the world it isn't a factor at all.

And some animals are likelier rafters/survivors than others, murids and skinks being examples par excellence. Why do you think monkeys in ISEA stop their distribution where they do? Have you noticed its the crab eating macaques at the extremes, on not just one but several islands? Their lifestyle and sleeping preferences predispose them to accidental rafting all the time. Would have been the same with the first lemurs - like the crabeaters, they would have ended up on rafts more than once, if any founder populations could raft across at all in the Palaeogene.
 
TeaLovingDave said:
Depending on your definition of where to mark the transition from one species to another, one could argue that *all* species start off with only a few founders..... in which case every species on the planet can be written off as doomed :p
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Usually from a healthy population, tho. Unless one believes in the Adam and Eve myth.
 
SealPup said:
Wild claims??? Where rafting on vegetation is a thing, its observed all the time ie. iguanas rafting into the Caribbean, or all kinds of animals in Amazonia. It has an element of chance each time, not just the rafting but the survival and colonisation - but where it happens, its actually commonplace, and in other parts of the world it isn't a factor at all.
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Except the slight problem that all available evidence suggests that rafting to Madagascar was anything but commonplace, Madagascar is separated by several hundreds of kilometres of treacherous waters (at least 450 km and often more), distances much bigger than the Caribbean or the Amazon. It was actually so hard to cross that barrier that only 4 mammalian ancestor species (except flying bats and swimming hippopotami) made the cross successfully over a period of about 40 million years. It was so hard to cross that man colonized Madagascar not from nearby east Africa, but from Malaysia as you probably know and that only within the last 2000 years (though they had to deal with a different monsoon pattern, making it even more difficult). So all evidence at hand suggests that rafting across the Mozambique channel was extremely tough and it is thus highly unlikely large populations could cross within a small time period. Do they all descend from one pregnant female, probably not, but it almost can't have been much more given the rarity of successful crossings....
 
SealPup said:
Usually from a healthy population, tho. Unless one believes in the Adam and Eve myth.
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....except you were claiming that any bottleneck means the resulting population is not healthy - and as I noted above the classic concept of speciation rather relies on the newly-emerging species starting out with only one or two founders (in the case of random mutation) or becoming isolated from the uber-species. Both would comprise a genetic bottleneck.

You cannot have it both ways!
 
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