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101105091811.htm
Evolution by Religious Selection: Mexican Cavefish Develop Resistance to Toxin
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Top: Atlantic molly. Bottom: Ceremony in the Cueva del Azufre. (Credit: Michael
Tobler (top); Mona Lisa Productions (bottom))
ScienceDaily (Nov. 5, 2010) A centuries-old religious ceremony of an
indigenous people in southern Mexico has led to small evolutionary changes in a
local species of fish, according to researchers from Texas A&M University.
Since before the arrival of Christopher Columbus to the New World, the Zoque
people of southern Mexico would venture each year during the Easter season deep
into the sulfuric cave Cueva del Azufre to implore their deities for a
bountiful rain season. As part of the annual ritual, they release into the
cave's waters a distinctive, leaf-bound paste made of lime and the ground-up
root of the barbasco plant, a natural fish toxin. Believing the cave's fish to
be gifts from their gods, they scoop up their poisoned prey to feed upon until
their crops are ready to harvest.
However, a team of researchers led by Dr. Michael Tobler, an evolutionary
ecologist at Oklahoma State University, and Dr. Gil Rosenthal, a biology
professor at Texas A&M, has discovered that some of these fish have managed not
only to develop a resistance to the plant's powerful toxin, but also to pass on
their tolerant genes to their offspring, enabling them to survive in the face
of otherwise certain death for their non-evolved brethren.
Their findings recently were published in the online journal Biology Letters.
Tobler has been studying the small, cave-dwelling fish species known as the
Atlantic molly or Poecilia mexicana and its uncanny ability to survive in the
toxic sulfur environment of Cueva del Azufre since 2004. He earned his Ph.D.
from the University of Zurich in 2008 and spent the next two years as a
postdoctoral research associate at Texas A&M, studying under Rosenthal and Dr.
Kirk Winemiller, a professor in wildlife and fisheries science, as part of a
two-year, $79,000 Swiss National Science Foundation Postdoctoral Fellowship.
After learning about the Zoque people's sacred ritual and witnessing the event
firsthand in 2007, Tobler and Rosenthal decided to investigate the effects of
this peculiar ceremony on the mollies and their habitat. Ironically, it was the
last ceremony ever held, as the Zoques ended the practice that year due to
political pressure from the government, which sought to preserve the cave as a
hotbed for tourism and potential revenue.
"We wanted to do a lab experiment where we exposed fish from different parts of
the creek to barbasco," Tobler says. "Some of these fish had been more exposed
than others."
In March 2010, the team collected molly specimens from two different areas of
the cave annually exposed to the barbasco toxin as well as from two different
areas upstream, further away from the Zoque's ritual. With both groups of fish
in a single tank, they then introduced the barbasco root to determine how both
groups would react.
They found that the mollies annually exposed to the barbasco indeed were more
resistant than the fish further upstream -- to the extent that they were able
to swim in the noxious water nearly 50 percent longer. Tobler and Rosenthal's
group concluded that human beings had, over time, not only affected molly
population dynamics, but also inadvertently kick-started the evolutionary
process of natural selection as well. Mollies able to tolerate the poisonous
conditions survived and passed those traits to their offspring, resigning those
that perished to their fate of serving as a ceremonial feast for the Zoque.
"The cool thing is that this ceremony has gone on a long time and that the fish
responded to it evolutionarily," Tobler says. "Lots of species couldn't live
with these changes. It highlights how nature is affected by human activity."
Rosenthal contends that the idea of imposing evolutionary divergence on a
species at an extremely localized spatial scale is not a new concept. In fact,
he says, it's been happening since the beginning of humankind and that the idea
of the "noble savage" is passé.
"We tend to have this wonderful Pocahontas idea that before Europeans came in,
everything was pristine and in harmony with nature and that all of the changes
in our environment have been post-industrialization," he explains. "No. People
have been changing the environment forever."
Moreover, Rosenthal says, once a species has become genetically adapted to
human presence, it is not very easy to suddenly reverse.
Their ritual since banned, the Zoques still perform a mock ceremony each Easter
season. Tobler, however, would like to see the Zoque's original ceremony
resume, but in a way that is sustainable to nature as well as other cave
inhabitants. The key, he and Rosenthal believe, is to find a balance between
human activity and their environment. In the case of the Zoques, it may mean a
few limitations on barbasco usage for their ritual, such as releasing the toxin
only 50-to-60 meters into the cave rather than 100 meters.
Pending further resolution, Tobler will continue his research with the mollies
at Oklahoma State, where they are housed in a special tank built to safely
imitate their sulfuric living conditions in Cueva del Azufre.
"We need to understand what the impact really is on these fish rather than
eliminate the ceremony completely," Tobler says. "We want to hopefully find a
balance between the cultural practices of these people and the ecosystem."
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Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily
staff) from materials provided by Texas A&M University.
Journal Reference:
1. M. Tobler, Z. W. Culumber, M. Plath, K. O. Winemiller, G. G. Rosenthal.
An indigenous religious ritual selects for resistance to a toxicant in a
livebearing fish. Biology Letters, 2010; DOI: 10.1098/rsbl.2010.0663
Need to cite this story in your essay, paper, or report? Use one of the
following formats:
APA
MLA
Texas A&M University (2010, November 5). Evolution by religious selection:
Mexican cavefish develop resistance to toxin. ScienceDaily. Retrieved November
5, 2010, from http://www.sciencedaily.com /releases/2010/11/101105091811.htm
Note: If no author is given, the source is cited instead.
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