From: LARRY KLAES (ljk4@msn.com)
Date: Thu Nov 07 2002 - 07:56:31 PST
----- Original Message -----
From: cunews@cornell.edu
Sent: Wednesday, November 06, 2002 5:15 PM
To: CUNEWS-LIFE_SCIENCE-L@cornell.edu; CUNEWS-SCIENCE-L@cornell.edu
Subject: Cornell News: Old mole-rats
Mole-rat Methuselahs, at 26 years old and counting, bolster
evolutionary theory of aging, says Cornell biologist
FOR RELEASE: Nov. 6, 2002
Contact: Roger Segelken
Office: 607-255-9736
E-mail: hrs2@cornell.edu
ITHACA, N.Y. -- Virtually hairless, venerably wrinkled and very
nearly blind, naked mole-rats -- those homely rodents from
underground Africa -- remind some zoo-goers of little old men.
The resemblance is more than coincidence. They really are really old
males -- and females, too -- biologists report in an article
scheduled for November publication in the Journal of Zoology (Vol.
258, Part 3). Many naked mole-rats (Heterocephalis glaber) in
laboratory colonies in the United States and South Africa have lived
more than 20 years, and some are at least 26 years old, making them
by far the oldest small rodents in captivity.
That distinction won't get them birthday greetings from the
president. But their species is being hailed as a perfect exemplar
for the evolutionary theory of senescence (or aging), which explains
why some bodies wear out before others. Senescence theory also tries
to explain, for example, why gerbils live only a couple of years,
humans regularly live eight to nine decades and redwood trees for
millennia.
"Whatever kind of organism it is, it's going to senesce," says Paul
Sherman, a professor of neurobiology and behavior at Cornell
University. "Of course, good food and exercise, proper medical care
and avoiding risky behaviors may extend lives a bit. But nothing we
can do in our lifetimes or many more to come is likely to stop
senescence." Evolutionary biologists define the term as the
persistent decline in fitness components with age, due to internal
physiological deterioration.
In the paper, "Extraordinary life spans of naked mole-rats," Sherman
and his South African colleague Jennifer U.M. Jarvis report that
laboratory mole-rats have survived nearly three decades, making their
life spans about 10 times longer than other similar-size rodents.
"Life spans of naked mole-rats offer strong support for evolutionary
theories of aging," Sherman notes.
Evolutionary biologists agree there are two types of causes for the
end of life. The proximate (or immediate) cause, such as drowning or
essential body parts wearing out, gets reported in newspaper
obituaries, whereas the ultimate (or long-term) cause, the genetic
explanation for death, gets discussed in scholarly scientific papers,
and Sherman offers this explanation for the difference:
"Most people attribute aging solely to wear-and-tear on individuals'
bodies. We know about oxidative damage to DNA and cells, so we tend
to say things like, 'He died because his heart failed.' True, that's
the proximate cause of death, but it doesn't explain why a person's
heart lasted much longer than a gerbil's heart. Senescence theory
does: Long before a particular man or gerbil was born, natural
selection had acted on the genomes of their species to cause gerbils'
bodies to senesce more rapidly than humans' bodies.
"Proximate and ultimate explanations for senescence are not
alternative, they are complementary," Sherman adds. "The first
identifies specific physiological mechanisms whose breakdown results
in senescence. The second explains how natural selection has acted to
maintain or fail to maintain those mechanisms."
The Cornell researcher has studied colonies of naked mole-rats living
in transparent plastic tunnel systems in his laboratory since 1979,
first at the University of California-Berkeley and then in Ithaca.
Jarvis has done the same for her mole-rats at the University of Cape
Town. The animal-care protocols they pioneered have helped zookeepers
worldwide to display the intriguing creatures for the education of
the general public.
In nature, naked mole-rats are known to live at least 10 years. "We
think they live longer in the laboratory than they do in the wild
because they're safer here, but they're pretty safe in nature, too,"
Sherman says. One of the factors contributing to the evolution of
longer life spans is reduced extrinsic mortality, which Sherman
defines as causes of death that are outside an animal's control, such
as drowning in a flash flood or being devoured by a snake. In nature,
naked mole-rats are largely protected from sources of extrinsic
mortality by inhabiting subterranean burrows in extremely hard soils.
Protection is enhanced by cooperative defense against predators. As a
result, naked mole-rats have evolved genetic traits that make them
more resistant to senescence than similar-sized, solitary,
surface-dwelling rodents. Indeed, the only rodent known to live as
long as the naked mole-rat is the African porcupine Hystrix
brachyura, which is protected by its large body size and quills.
The diminutive naked mole-rat has something else going for it:
greater fecundity with advancing age. "A large, old breeding female
mole-rat gives birth to an incredible number of young and continues
to do so year after year," Sherman says. "Our record for a laboratory
female is 28 pups in one litter and more than 900 pups in a
lifetime." Fecundity seems related to body size, Sherman adds, noting
that mole-rat queens, like queens in honeybees and termites, are
considerably larger than workers in their colonies. Fecundity is
important because if old individuals can make disproportionate
reproductive contributions, there will be strong selection to
postpone senescence.
While naked mole-rats are models that support senescence theory, they
are not perfect role models for humans. Senescence occurs,
simultaneously, on all aspects of any organism, which means there is
no single gene for aging or for youth. "Senescence theory," says
Sherman, "tells us why the fountain of youth still eludes us -- and
probably always will."
-30-
The web version of this release, with accompanying photos, may be
found at http://www.news.cornell.edu/releases/Nov02/old_moles.hrs.html
Cornell University News Service
Surge 3
Cornell University
Ithaca, NY 14853
607-255-4206
cunews@cornell.edu
http://www.news.cornell.edu
This archive was generated by hypermail 2.1.2 : Thu Nov 07 2002 - 08:20:30 PST