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October 18, 2005 — CHAPEL HILL -- In a new study of cichlid fish descended from
others caught in East Africa’s Lake Tanganika, scientists have made
some surprising observations about how those animals respond to changes
in their environments known as "social opportunities."
Sabrina S. Burmeister, assistant professor of biology at the University
of North Carolina at Chapel Hill’s College of Arts and Sciences, and
colleagues found that subordinate male fish underwent a radical and
rapid transformation when more dominant males were removed.
we took dominant cichlid males from an experimental tank, subordinate
males started becoming dominant themselves in as few as two minutes,"
Burmeister said. "Their colors -- blue and yellow -- got much brighter,
a black stripe we call an eye bar appeared near their eyes, and they
became much more aggressive than they were before. The remaining males
also quickly paid a lot more attention to females because for the first
time, they had an opportunity to reproduce."
No one had any idea
before that perceived changes in their social status could begin
altering animals’ behavior and appearance so quickly, she said.
Previous studies had shown the changes took as long as a week and were
associated with increased fertility.
Burmeister’s report on her
experiments, conducted at Stanford University, appears in the November
issue of the scientific journal PloS Biology, which is being released
today (Oct. 17). Co-authors are Drs. Erich D. Jarvis and Russell D.
Fernald, neurobiologists at Duke University and Stanford, respectively.
research is part of a larger effort to understand some of the most
intriguing questions in all of biology -- how did brains evolve and how
can the environment change an animal’s physiology through actions on
Such studies are relevant to humans since the hormones
and genes involved are close to identical, she said. Obviously, such
internal gene activity studies cannot be done directly in humans.
observing the striking changes in appearance and personality,
Burmeister and colleagues turned their attention to the inner workings
of the fish’s gene-hormone interactions by analyzing brain tissue.
gene we focused on, egr-1, was a good candidate for study because it
controls expression of other genes," Burmeister said. "We found that
perception of social opportunity caused more egr-1 to be expressed in
the hypothalamus, a region of the brain that controls fertility. We
believe that in our fish, egr-1 turns on expression of a second gene,
GnRH1, which produces a hormone necessary for reproduction."
basic mechanisms that control reproduction in fish and in humans are
the same and may be in all vertebrates, she said. The brain’s
hypothalamus links the nervous system to hormonal systems.
physiology is often influenced by environmental factors, including
social cues, the scientist said. "In humans, one of the best examples
came from work by Dr. Martha McClintock showing that the menstrual
cycles of women were influenced by olfactory cues from other women.
Another group found that the timing of ovulation in women is influenced
by olfactory cues from men."
In humans and many other mammals,
olfactory cues -- various odors --provide important information about
the social environment, Burmeister said. The situations are analogous
-- social cues from the environment influence the reproductive system
through GnRH neurons and create a "cascade" of molecular interactions
that result in increased fertility.
The National Institutes of Health and the National Science Foundation supported the research.
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