Paper on Hybrid Animals in zoos with special reference to Orang Utans

[Guest guest]

http://findarticles.com/p/articles/mi_m1200/is_n12_v147/ai_16795968/ Caste-off

orangs: controversy surrounds implications of a hybrid label - interbreeding

Sumatran and Bornean orangutans - Cover Story Science

News<http://findarticles.com/p/articles/mi_m1200/>,

March 25, 1995 <http://findarticles.com/p/articles/mi_m1200/is_n12_v147/> by

Janet Raloff <http://findarticles.com/p/search/?qa=Janet+Raloff>

 

Caste-Off Orangs

 

Controversy surrounds

 

implications of a hybrid label

 

By JANET RALOFF

 

At the tender age of 9 months, Chantek left his mother in Atlanta to live in

a trailer next to the music building on the University of Tennessee campus

in Chattanooga. There, his surrogate family toilet trained the inquisitive,

red-haired youngster and taught him language, how to clean his

bedroom, andthe deportment necessary to ride in cars, visit parks,

and eat burgers at the local fast- food chain. Eventually, this quiet,

strapping boy even received an allowance -- one he could bank or spend at

his discretion on treats. In many ways, Chantek lived much of his first 9

years like any ordinary child in the United States. But Chantek is an

orangutan, and his every action and reaction has been recorded and studied

as part of an ongoing examination of how these quiet, slow-moving -- some

would say highly intellectual -- apes think and behave. Acculturation to

human society did not prevent Chantek from slipping back into the

traditional world of captive orangutans when he returned home to the Yerkes

Primate Research Center in 1986. Indeed, he fathered a child 3 years later.

 

But this healthy, 18-year-old representative of an endangered species will

never sire again -- at least if internationally recognized primate

conservation policies prevail.

 

The reason? Chantek's mother hailed from Borneo, his father from Sumatra.

That makes Chantek a biological hybrid as well as a cultural one. The

American Association of Zoological Parks and Aquariums (AZA) adopted a

policy 10 years ago to stop interbreeding Sumatran and Bornean orangutans --

and to prevent any of AZA's hybrid offspring (now numbering 51) from

reproducing. The organization's 55 member zoos and primate conservation

centers with orangutans all adopted the policy, though some " accidental "

births did occur through 1991, observes Lori A. Perkins, a conservation

biologist at Zoo Atlanta who coordinates AZA's species survival plan for

orangutans.

 

Four other international umbrella organizations that oversee endangered

species management also to this policy, which now affects the

reproduction -- and status -- of 192 hybrid orangutans worldwide. Biologists

avoid crossbreeding captives because zoo animals are intended to represent

their wild brethren. Hybrids " don't have any biological meaning, " observes

Zoo Atlanta director Terry Maple, himself an orangutan researcher.

" [They're] a man-made creation. "

In fact, he says, " nobody wants them -- isn't that a pretty darn good reason

not to produce any more? "

 

 

The survey, completed in 1985, showed that orangutans born in the wild carry

the same inversion on both copies of chromosome 2 - - an SS pair in

Sumatrans, a BB pair in Borneans. Hybrids with wild-born parents carry one

of each, or SB.

 

While these inversion patterns provided a marker for wild-born orangutans'

island of origin, they couldn't establish how genetically divergent the two

groups are. Are the differences equivalent to races in humans? Do they

signal subspecies as dissimilar -- and therefore as unnatural for mating --

as Sumatran and Siberian tigers? Or do they represent distinct species, such

as the chimpanzee and bonobo (pygmy chimpanzee)?In 1990, researchers at the

National Cancer Institute in Frederick, Md., helped pinpoint the answer,

Perkins says. A study led by Stephen J. O'Brien and Dianne N. Janczewski

compared several hundred proteins -- reflecting several hundred genes --

from Sumatran and Bornean orangutans. It showed that genetic differences

between the two kinds of orangutans were 5 to 10 times greater than the

differences between the tiger subspecies. Ryder followed up on these data 2

years ago with a report on his chromosome 2 typing for 144 captive

orangutans -- including 58 born in the wild. He also analyzed variations in

the mitochondrial DNA of 14 of the orangutans, including six each from

Borneo and Sumatra.

 

Mitochondrial DNA is located outside a cell's nucleus and is inherited only

from the mother. In addition, it mutates more frequently than nuclear DNA.

For this reason, anthropologists use mutation patterns in mitochondrial DNA

to construct evolutionary trees of relationships within and between species.

Together, the two forms of genetic information established that the

chromosome 2 inversion distinguishes two taxonomically distinct lines, Ryder

says. And the roughly 3 percent variation between Sumatran and Bornean DNA

sequences suggests that gene flow between the two islands ended

approximately 1.5 million years ago, Ryder and Leona G. Chemnick conclude in

the September-October 1993 Journal of Heredity.

 

Last year, O'Brien and NCI colleague Lu Zhi reported similar findings from

their newest orangutan studies -- also involving mitochondrial DNA. Their

data suggested that " the extent of difference between Bornean and Sumatran

populations was consistent with species-level divergence. "

 

Case closed? Not necessarily, according to data unveiled at the AAAS meeting

by C. Cam Muir of Simon Fraser University in Vancouver, British Columbia.

Muir finds no compelling difference between the mitochondrial DNA of wild

Bornean and captive Sumatran orangutans.

 

When he plotted the animals' genetic trees, Muir found that, rather than

occupying different branches, the orangutans shared various limbs, depending

on which sequence of genetic material he analyzed.

 

In contrast to earlier studies, Muir told Science News, his relies

ondifferences obtained by actually sequencing genes, as opposed to

differences

inferred from variations in the proteins that genes code for and other

indirect data. So presumably, he says, his data may prove a bit better at

distinguishing changes.

 

Overall, he believes, " use of the term 'hybrid' is improper because these

are not two species. "

 

That interpretation could change, he concedes, once he has expanded his

analysis to include more genes -- including some from the nucleus --

andseveral hundred more wild orangutans.

 

But even if Sumatran and Bornean orangutans constitute separate species or

subspecies, Muir fears that a ban on crossing them in captivity may

dangerously restrict the gene pool, potentially making the animals less fit

and more prone to extinction.For populations numbering in the thousands, he

says, " there is an advantage to keeping distinct populations separate,

because in mixing them you could lose some critical genetic diversity. "

However, " the opposite is true once you get below a threshold number

anddon't have a full representation of genetic types. " Muir worries

that

maintaining captive Sumatrans and Borneans separately risks falling below

that threshold.

 

Anthropologist Colin P. Groves of Australian National University in Canberra

worries about a related problem. In analyzing orangutan skulls, he has found

bigger differences between those from Borneo's three geographically isolated

groups than between any of those populations and the orangutans in Sumatra.

 

Groves not only agrees that Borneans and Sumatrans are distinct subspecies

and should not be interbred, he also says that " eventually, we'll be

proposing that these [bornean populations] be formally recognized as

subspecies. " The Bornean skull differences he has observed are not visible

in living animals. So unless someone finds a genetic marker, he argues, the

ongoing repatriation to the wild of recently captured orangutans (usually

from the illegal pet trade) should be halted or altered. Otherwise,

well-intentioned game managers may hybridize animals in the wild.

 

He also argues that zoos and other game managers should attempt to establish

that Borneans paired for mating trace back to the same geographically

distinct parent population.

 

" I've been hearing that speculation [about Bornean subspecies] for about 5

years, " says Perkins, who coordinates orangutan breeding in North America.

But if it turns out to be true, she told Science News, " I don't know what I

would do with the information. "

 

Only 82 Bornean orangutans are managed under the AZA program, Perkins notes.

Even if roughly equal numbers came from each of the three populations, " I

don't know that it would be smart to subspeciate them, " she says. The number

in each group might become too small to ensure a healthy degree of genetic

diversity.

 

Moreover, " I'd have no basis on which to separate them, " she points out,

because records of where orangutans were captured are spotty at best. " So

our only options now are to just breed them as Borneans or to not breed any

Borneans -- which would send the [captive] population into a crash from

which it probably would not recover. "

 

But veterinarian William B. Karesh of the Wildlife Conservation Society,

which operates the Bronx Zoo in New York, suspects that Perkins has no

reason to worry. He says unpublished genetic data from a study of 50

wild-born orangutans in Asia on which he and O'Brien's team are

collaborating suggest that Borneo's various populations may have been

geographically isolated for a long time -- at least 250,000 years. And while

they do appear to be dividing into subspecies, Karesh says, " they don't yet

qualify, really, as subspecies. " In practical terms, he says, when

reintroducing a Bornean captive to the wild, " if you knew where the animal

came from, it would be nice to return it to that gene pool. But if you

don't, we're not really disturbing nature that much. " For zoo animals, which

will never return to the wild, the issue becomes even less important, he

suspects.

 

Groves disagrees, noting that, at a minimum, the size of orangutans varies

between Borneo's populations -- and " size matters with adult male orangs. "

Because big males tend to dominate, smaller ones from Borneo's Malaysian

region may not succeed in attracting mates if introduced into the island's

Indonesian southwest, where they would have to compete against bulkier kin.

And so the debate rages.

 

What difference does being a crossbreed make? At the AAAS meeting, several

speakers mentioned the fact that some hybrid animals have been sterilized.

There were also passing references to the practice of removing hybrids from

display and banishing them to the less stimulating environs of a zoo holding

cell after the AZA policy went into effect.Such charges spark Perkins' ire.

" We do not stick hybrids in the back of zoos, " she maintains. " They stay in

the social groups they've been in and engage in a complete range of

behaviors -- even copulation. " You could call every AZA institution in the

orangutan program " and they would tell you they don't keep [hybrids] any

differently. " And, she adds emphatically, " as long as I'm the

[speciessurvival plan] coordinator, they will not. " Perkins concedes

that some males

have received a vasectomy, which may not prove reversible. But most

institutions now rely on timed- release hormone implants to prevent sexually

active hybrid females from conceiving. Remove that implant, she notes,

" andthe females are fertile again. " Even if one s to not

mongrelizing

purebred populations, hybrids needn't remain childless. Groves suggests

sending fertile hybrids to major, responsible zoos that could not otherwise

afford orangutans, such as several in India.

 

Ethel Tobach of the American Museum of Natural History has another idea.

Many uninhabited Southeast Asian islands are ecologically similar to Borneo

and Sumatra. " It would be great to put hybrids on such an island and study

them there. "

 

Groves agrees that " if you reintroduce them way outside their known modern

range -- such as in the Malay Peninsula -- you can do what you like because

there would be no population to disrupt. "

 

But Maple argues that " the only reason we've been interbreeding [orangutans]

is out of ignorance. If nature isn't making Sumatran- Bornean crosses, "

heargues, " why should we? "

COPYRIGHT 1995 Science Service, Inc.

COPYRIGHT 2004 Gale Group