phipps@garth.UUCP (Clay Phipps) (04/06/90)
[The following thread has been abducted from "sci.environment" and crossposted in "sci.bio"; it seems to belong more there than here.] In article <6451@crdgw1.crd.ge.com>, oconnordm@CRD.GE.COM (Dennis M. O'Connor) wrote: >In [an earlier article], vac@sam (Vincent Cate) wrote: >] >] frozen woolly mammoths [have been found] in remarkable condition ... >] the DNA is intact in many of the cells. >] The idea is ... to clone a mammoth. ... I'd be more interested in Georg Steller's sea cow (Hydrodamalis gigas): an inhabitant of North Pacific waters until 1 or 2 centuries ago, as long as we're fantasizing about bringing extinct animals back. It's simply not possible to "restore" the Pacific coast of the U.S. to its hypothetical prehuman state without including that critter. And *please* leave that "greatest white shark" (Carcharodon megalodon) DNA alone wherever you found it :-). >[...] mammoth cloning [...] can't bring back the species >unless clones from many different ex-mammoths could be made. >Even a dozen individuals wouldbe too few. >The same applies to endangered species. >Once the gene pool is reduced to a few dozen individuals (living or dead), ^^^^^^^^^^^ >it becomes nearly impossible to really resurrect the species. Then I suppose that you have already given up on the California condor (Gymnogyps californianus). As of March 23, there were only 33 California condors known still alive, and 2 fertile eggs known--on this entire planet, all in captivity. Those counts were provided by a biologist at the U.S. Fish and Wildlife Service (USFWS) Ventura Endangered Species Recovery Office (VESRO), which oversees the California condor recovery program. The Andean condor, whose appearance is similar to the California condor, is neither the same species nor even in the same genus. >Cheetahs provide an example of this from nature. >Theory has it that [the world-wide(?) cheetah population was] >reduced to 200 or so individuals about 10,000 years ago. >As a result, cheetahs will always teeter on the brink of extinction : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ It would be a far greater service to this "science" news-group to present data on the world-wide distribution and status (esp. with regard to rate of change) of populations of cheetahs world-wide, than to offer a statement that has the distinct ring of long-term fund-raising rhetoric. The phrase "teeter on the brink of extinction" is sometiomes applied to sea otters in California, who were reduced to a guesstimated 50 individuals sometime early in this century. A systematic survey of their population in Spring 1989 produced a *count* of 1864 individuals (source: USFWS). The Spring 1990 survey should produce a count approximately the same as the year A.D., and could break 2000 (source: me; I've followed those surveys very closely over the last few years), if recent observed population growth rates continue. I posted more complete data on the counts and growth rates back in July. >they are so close to genetically identical, >they lack the diversity to survive sudden ecological change. My understanding is that loss of viable habitat (especially important because of the consequent reduction in carrying capacity) is a far greater threat than anything else to the survival of most animal populations (is there significant disagreement on this ?). There are notable exceptions: the fundamentally nonrenewable poaching of African elephants for their ivory. I'm not convinced that the cheetahs are *practically* any worse off than a lot of other animals retaining much greater genetic diversity. Cheetahs could certainly be hit hard by a sudden or cyclic disease, but I *suspect* that encroachment by Homo sapiens is their biggest problem now. Can someone elaborate on the world-wide plight of cheetahs ? -- [The foregoing may or may not represent the position, if any, of my employer, ] [ who is identified solely to allow the reader to account for personal biases.] [Besides, this article was written and posted way after normal business hours.] Clay Phipps Intergraph APD: 2400#4 Geng Road, Palo Alto, CA 94303; 415/852-2327 UseNet (Intergraph internal): ingr!apd!phipps UseNet (external): {apple,pyramid,sri-unix}!garth!phipps EcoNet: cphipps
oconnordm@CRD.GE.COM (Dennis M. O'Connor) (04/06/90)
phipps@garth (Clay Phipps) writes:
] In article <...> oconnordm@CRD.GE.COM (Dennis M. O'Connor) wrote:
] >In [an earlier article], vac@sam (Vincent Cate) wrote:
] > ] ...
] >[...] mammoth cloning [...] can't bring back the species
] >unless clones from many different ex-mammoths could be made.
] >Even a dozen individuals wouldbe too few.
] >The same applies to endangered species.
] >Once the gene pool is reduced to a few dozen individuals (living or dead),
] ^^^^^^^^^^^
] >it becomes nearly impossible to really resurrect the species.
]
] Then I suppose that you have already given up on the California condor
] (Gymnogyps californianus).
]
] As of March 23, there were only 33 California condors known still alive,
] and 2 fertile eggs known--on this entire planet, all in captivity. ...
]
] The Andean condor, whose appearance is similar to the California condor,
] is neither the same species nor even in the same genus.
Your rigth, I have given up hope for the California condor. I appreciate
and support the heroic efforts of those trying to ressurect the species,
but in a thousand years ( a blink of the eye ) I doubt there will be
even one member of the species left.
This is why I feel we have to be more vigilant in protecting the genetic
diversity that remains in our ecosystem.
] >Cheetahs provide an example of this from nature.
] >Theory has it that [the world-wide(?) cheetah population was]
] >reduced to 200 or so individuals about 10,000 years ago.
] >As a result, cheetahs will always teeter on the brink of extinction :
] [...]
] >they are so close to genetically identical,
] >they lack the diversity to survive sudden ecological change.
]
] My understanding is that loss of viable habitat (especially important
] because of the consequent reduction in carrying capacity) is a far greater
] threat than anything else to the survival of most animal populations
] (is there significant disagreement on this ?). There are notable exceptions:
] the fundamentally nonrenewable poaching of African elephants for their ivory.
]
] I'm not convinced that the cheetahs are *practically* any worse off
] than a lot of other animals retaining much greater genetic diversity.
] Cheetahs could certainly be hit hard by a sudden or cyclic disease, but
] I *suspect* that encroachment by Homo sapiens is their biggest problem now.
] Can someone elaborate on the world-wide plight of cheetahs ?
I agree with you on the short-term threat. But take the long-term
perspective : change is inevitable, and without diversity in a population
a single adverse change can destroy the entire population. Now there
is some recovery of diversity from mutation, but you won't recover
the original diversity that made the species what it was ; instead, if you
are lucky, you evolve a new species.
Look at the agri-corporation mono-cultures that blight our farmland :
( okay, I'm waxing poetic, I'm sorry ) In the past, single diseases
hafve destroyed entire counties worth of crops. This was because
every genetically-identical plant in those counties had essentially
the same resistance to any particular disease : once a lethal disease
appeared, it propogated like wildfire.
The same could happen to cheetahs or California condors. The same DID
happen to the Clydesdale population of the US in the 1960's -- new blood
from Europe, imported by Annheiser-Busch, renewed and expanded the
gene pool and population level of the breed. Eventually, it is probable
that cheetah and condor will also fall victem to such an epidemic.
And it is sad.
Extinction is forever. So is the los of characteristcs (i.e. narrowing)
of the gene pool of a species. Even if I'm wrong, isn't it better
too assume I'm right until we know better ?
--
Dennis O'Connor OCONNORDM@CRD.GE.COM UUNET!CRD.GE.COM!OCONNOR
"Let's take a little off the top ... a bit off the sides ...
trim the back a bit ... Surprise ! You've been bald-ed !"knox@whittaker.rice.edu (Robert G. Knox) (04/12/90)
Admittedly species can be in trouble for many reasons, but cheetahs are a good example of why numbers and habitat aren't enough. Due to having lost nearly all their genetic diversity "unrelated" cheetahs might as well be clones of one another. Skin grafts are not rejected between unrelated animals, which suggests vulnerablity to disease (a bug which can kill one can kill them all, etc.). More importantly at present, cheetahs have very poor reproductive success--either in captivity or in the wild. The explanation for poor reproductive success comes from studies of inbreeding in animals or plants that generally outbreed. Most outbred individuals carry a range of rare deleterious genes that are receessive in their effects. When switched to breeding with close relatives, some of these genetic alleles are lost, by chance, but others end up "homozygous"--in that form the genes are deleterious and would be normally eliminated by natural selection, but there's no alternative! The cheetahs are stuck with whatever made it through a past population "bottleneck" until new mutations replenish the supply of genetic variation (a very slow process). The lesson for conservation is that it's not enough to save the "last" CA condor, blue whale, or panda. By then it will usually be too late for long-term survival without our (expensive) help. We need to act early to preserve viable populations--large enough to include and sustain genetic diversity. Otherwise all we save are living museum specimens, genetically crippled descendants of formerly viable species. [Hope the tone isn't too pedantic. I'm new at this net stuff :-) For a readable report on the situation with cheetah genetics, see _BioScience_ vol.36, pp. 358-362. An overview of genetics for wildlife conservation appears in the March 1990 _BioScience_, vol.40,no.3,pp 167-171.] Re: bringing back extinct species, perhaps old pelts, skins, etc. collected before loss of genetic diversity could be used to reconstruct the DNA sequences of the lost genetic alleles and the diversity engineered back in, gene by gene. But the biotechnology isn't quite there yet, and even when it is . . . now you're talking about *really* expensive help!