Download Tiger Gene Decline Threatens Species

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Celeste Begandy
CW-2
December 14, 2009
Research Paper
Tiger Gene Decline Threatens Species
Throughout this world, thousands of people dedicate their lives to preserve
animal and plant species on the brink of extinction. Among those diverse species, there
is the beautiful and majestic Panthera tigris, or simply known as the tiger. However, all
six of the eight remaining subspecies of this big cat are in danger of becoming a
permanent part of history (“Tiger Ecology”). While programs have replenished tiger
populations, the low levels of genetic diversity put the tigers in danger. Genetic diversity
means that a species has enough positive genes to be spread and continue producing a
healthy population (Arm 243). However, with human development occurring fast, wild
tigers are losing the genetic battle despite breeding efforts. Humans are affecting tiger
genetic variation by destroying habitats and employing selective breeding.
One of the main reasons for this lack of genetic diversity is the destruction of the
tiger’s natural habitat. The human populations in once undisturbed lands have
exploded, causing 75% of habitat loss and recent extinctions (Arm 243). Humans are
taking over the land and competing with tigers for natural resources they both use
(“Habitat Loss”). Tigers, like any animal, need access to water and prey that has been
uninfected by human development in order to survive. Only 7% of tigers roam freely in
their previously dominated territory, opposed to 40% of Asian lands they had ten years
ago (“Tiger Habitat Shrunk”). Species that exist in limited habitats with limited resources
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are more likely to become extinct (Arm 243). Also, the restricted populations of tigers
are less likely to survive environmental changes that occur. Not only does human
development pressure the current tiger populations, but also the genes of their future
cubs (Platt). Because of the rapid development of buildings and towns, tigers are finding
themselves with less territory to roam and claim. Instead of migrating to breed with
different tigers, most choose to stay within boundaries because they cannot travel past
human metropolises. Tigers are then forced to breed with the same mate or even
interbreed with cubs from previous litters (“Habitat Loss”). As a result, resources both
naturally and genetically are being lost. Without a habitat, wild tigers cannot survive.
This species is depending on a healthy habitat in order to keep the populations alive
and genetically stable.
Furthermore, scientific facts prove that it is difficult to raise a species from
extinction because these already low populations have fewer genes to go around,
opposed to non-endangered species (Frankham 1500-1508). Naturally, zoos try to help
by establishing solid populations of endangered animals through captive breeding
programs with often successful results. Captive tigers are showing more genetic
variation than wild tigers, simply because humans can carefully choose another captive
mate. However, these hand-raised tigers don’t necessarily help the tiger gene pool.
They can never be released into the wild; therefore, the wild populations still suffer with
the limited mates (Caccone). Even if captive tigers could be released into the wild, there
may not be a healthy habitat available to them (McRary).
Some of these breeding programs are not following the guidelines some tiger
advocates want. Wild tigers and hand-raised tigers are occasionally mixed to create
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some diversity. However, this tactic receives criticism for mixing lineages of zoo-raised
cats and their wilder counterparts (Ryder). Also, the breeding programs aren’t always
what they’re said to be. In China, two Siberian tigers attacked a zoo staff member
because of starvation. While the institute once played host to 300 other Siberians, the
zoo had a revenue loss due to the poor economy and could not afford to keep feeding
the tigers properly. Therefore, the Siberian pair was said to be overcome with hunger
and this was motivation for the attack (“Tigers Killed”). Other captive tiger attacks are
reported yearly around the world, often due to poor care or precaution taken by zoo staff
members. Events like these obviously slow down positive progress for tigers. People
arguing against the captive programs say that genetic variation is an important factor,
but more effort should be taken in the natural habitats, where the real survival takes
place (Frankham).
The exotic pet trade industry has also withheld species members from the world.
According to PETA, there are thousands of big cats, including the rarest subspecies, the
Siberian tiger, around the world. Eric Dinerstein, an author for tiger research, states that
there are “more tigers alive in private homes in the state of Texas than in the wild
worldwide (qtd. in “Tiger Habitat Shrunk”).” Because of illegal animal hoarding,
members of the species are not only kept out of the gene pool, but are also denied
proper care and feeding from an authorized facility.
Criticism of breeding programs does not necessarily come without reason. White
Bengal tigers, often thought to be a subspecies of tiger, are not subspecies at all. “Royal
Rare White Tigers” are actually a mix of Siberians and Bengals and are mostly products
of selective inbreeding. The white gene does occur occasionally in nature, but not often
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because it’s disadvantageous to the tiger’s survival. The white coat does not blend into
their surroundings, which makes hunting more difficult. The tigers are inbred to achieve
this beautiful defect for all of the wrong reasons. Their purposes are strictly for
aesthetics and entertainment – Las Vegas shows often feature these white cats since
their intelligence is not as substantial when compared to other tigers. Other defects
include immune deficiency, scoliosis, cleft palates, mental disabilities, and crossed
eyes; all of which are due to inbreeding (“Genetics of the White Tiger”). This is
something zoos like to keep out of the public eye and what many big cat lovers are
protesting.
On a lighter note, an example of positive population comeback is the Amur, or
Siberian, tiger. This is the largest cat of all of the subspecies, but also one of the most
endangered. There are 500 wild Amurs, which seems like a substantial number.
However, only about 35 of those tigers have stable, workable genes (Walker). The
Amur tiger experienced what researchers call a “genetic bottleneck” during the 1940’s
(Caccone). A bottleneck occurs when populations shrink to only a few members and
after they breed, all of their offspring have less diverse genes and makes them more
likely to inherit poor traits (Arm 243). Even after the Amur population rebounded, the
genetic variety was lost. Each generation has almost identical genes from the last,
which makes these tigers lose out on adapting to the environment (Walker). While the
Amurs are not showing any physical abnormalities from the lack of genes now, habitat
pressures could cause this to become more evident. Tigers must adapt to
environmental changes, but with the lack of genes, it makes survival harder than it
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needs to be (Platt). These facts urge conservationists to focus on not only population
numbers, but the number of genes in the pool.
In order for tigers to thrive, many problems need to be addressed. Habitat loss is
a serious matter needing thoughtful solutions. With human populations exploding,
especially in Asia, creating land for these felines is an issue itself. Seventy-five percent
of recent extinctions came from human development (Arm 246). Hunting and poaching
bans have improved populations, but it has not done much for tiger genes specifically
(Walker). Dr. Alan Rabinowitz, director of Science and Exploration programs at the
Wildlife Conservation Society, insists that tiger mating migration is the most crucial way
to save their population. He is proposing a “genetic corridor” to span along eight
countries to set aside tiger habitat. Rabinowitz wants countries to consider zoning
farming regions so tigers can pass through in order to expand their breeding territory
(“Genetic Corridors”). This study also revealed that two Amur tiger populations are
separated entirely, decreasing their chance for genetic diversity. A need to open these
regions is dire because the chance of reintroduction into original territories in China
could be lost if one group dies (Walker). Tigers that live in these limited regions are
more likely to become extinct. If the group receives a disease or genetic fault, the entire
population could be wiped out (Arm 245). Wild tigers can now only depend on habitat
and diverse populations to exist (Ryder).
Along with habitat protection, careful monitoring of captive and wild tiger DNA is
necessary. Knowing and understanding the tiger genome will help achieve stable
genetic diversity; therefore, creating a healthy species for generations. However, DNA
research is still uncertain and has many flaws. It is also a costly investment that many
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zoos and agencies do not posses. However, zoos can help by understanding
subspecies of tigers and preventing different categories to breed (“Tiger Conservation”).
Also, not buying or participating in exotic tiger trade, or in white tiger breeding can assist
this cause (“Inside the Exotic Animal Trade”).
While captive breeding programs and hunting bans have slightly repaired the
damages done by humans, more action is desperately needed to save these majestic
cats. Habitat protection and genetic variation should be carefully watched by those who
truly understand the importance of conservation. Tigers should also remain wild in order
to keep the genes of the whole species active (“Can Diversity Beat Adversity”). Healthy
populations of tigers can only survive with a prosperous habitat and diverse gene pool
in order to evolve and improve the entire species (Tiger Conservation).
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Works Cited
Arm, Karen. Environmental Science. Austin: Hold, Rinehart, and Winston, 2006. Print.
Caccone, Adalgisa, et al. “Potential Genetic Consequences of a Recent Bottleneck in
the Amur Tiger.” Conservation Genetics. 5.5 (2004): 707-713. Web. 13 Oct 2009
<http://www.springerlink.com>.
“Can Diversity Beat Adversity for Tigers?” Endless Forums. Web. 20 Oct 2009 <http://
network.nature.com/people>.
Frankham, Richard. “Relationship of Genetic Variation to Population Size in Wildlife.”
Conservation Biology 10.6 (Dec. 1996): 1500-1508. Web. Oct 30 2009
<http://www.jstor.org>.
“Genetic Corridors Are Next Step to Saving Tigers.” ScienceDaily 18 Feb 2008. Web.
20 Oct 2009 <http://www.sciencedaily.com>.
“Genetics of the White Tiger.” Big Cat Rescue. Web. 13 Oct 2009 <http://www.
bigcatrescue.org>.
“Habitat Loss.” The Tiger Foundation. Web. 30 Oct 2009<http://www.tigerfdn.com>.
“Inside the Exotic Animal Trade.” PETA. Web. 20 Oct 2009 <http://www.peta.org>.
McRary, Amy. “Zoos’ Plans Serve As Arks for Animals’ Survival.” Knoxville News
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<http://sks.sirs.com>.
Platt, John. “Rare Siberian Tigers Face Potential Genetic Bottleneck.” Scientific
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Ryder, Oliver A. “Forests of the Night: Refugia of Genetic Diversity in Wild Tigers.” 14
Aug 2009. San Diego Zoo’s Institute for Conservation Research. Web. 20 Oct
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2009 <http://www.Hcbi.nih.gov>.
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2009 <http://www.msnbc.msn.com>.
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bigcatrescue.com>.
Walker, Matt. “Amur Tigers on ‘Genetic Brink’.” BBC News. 2 July 2009. Web. 15 Oct
2009 <http://Newsvote.bbc.co.uk>.