Date: Posted 12/24/2001

Stanford Researchers Develop System For Field Testing Mechanisms Of Evolution

STANFORD, Calif. - Evolutionary biology has always faced a major hurdle - how to
test a process that takes place over thousands, if not millions, of years.
Researchers at Stanford University may have come up with a solution. Genetic
mutations and the possible mechanisms underlying evolution have been studied in
laboratory animals for decades, said David Kingsley, PhD, professor of
developmental biology and assistant investigator for the Howard Hughes Medical
Institute. The challenge has been to find a means of applying what scientists
know to be true in the lab to systems in the natural world. In a paper published
Dec. 20 in the journal Nature, Kingsley and his team propose that a small spiny
fish called the three-spine stickleback, and the gene-linkage map of the fish's
chromosomes that the team has developed, may be the tools evolutionary
biologists have been needing. 

The key, according to Kingsley, was to find two populations, that unlike
laboratory bred mice and rats, would have traits that had evolved naturally and
yet could still be cross-bred. 

"What we needed were two species that had diverged fairly recently, had distinct
morphological differences, were fast-growing and easy to keep in the
laboratory," said Kingsley. It was also important to find two species, Kingsley
said, that could produce viable offspring in the lab even if they would not
naturally mate in the wild. The group's intent was to develop a map of the
inheritance patterns showing the links between genes from one generation to
another. According to Kingsley, it is a system used to study genetics in
laboratory-bred mice, but he wanted to develop a system that could test
inheritance patterns, mutations, and ultimately the mechanisms underlying
evolution in natural populations. 

"It's part of an age-old debate," Kingsley said. "Does evolution occur through
infinitesimally small genetic changes involving a very large number of genes, or
does it occur through changes of large effect associated with a smaller number
of genes?" In the lab, according to Kingsley, much of the focus is on single
gene mutations of large effect, but how does this apply to evolution as it
occurs naturally? Kingsley and his team turned to the genetic architecture of
two populations of sticklebacks for some answers. 

"What made sticklebacks so appealing was that not only did they meet our
criteria from a molecular and genetics standpoint, but their ecology and
behavior has also been widely studied by many other researchers," Kingsley said. 

To develop the gene-linkage map of the fish's genome, Kingsley's team first
designed a marking system that would allow them to follow the inheritance
patterns of various genes from one generation to the next. Using the markers,
the team crossbred two populations - a near-shore invertebrate feeding species
and an open-water plankton feeding species. They followed the patterns of
inheritance through several generations, developing a genome-wide gene linkage
map. Next, they used the map to analyze the genetic basis for a number of
evolutionary changes that occurred in the two populations, such as the amount of
body armor, the number of gill rakers and the length of the stickleback's
spines. 

Kingsley said they found a number of parallels between traditional laboratory
genetics and the traits they examined in the stickleback populations. For
example, many of the traits could be traced to major chromosome regions -
indicating that evolution can occur through changes of large effect, not just as
a series of small changes. Their findings also indicate that genetic control of
body regions appears to be modular. The genes that control the length of the
first dorsal spine, for instance, are located on different chromosome regions
from the genes that control the length of the second dorsal spine. This is not
surprising, said Kingsley, because it follows previous findings of the genetic
control of mouse skeleton development. As anyone who plays with Legos can
testify to, a modular body plan greatly increases the options for tweaking
designs over time. 

"The goal of this project was to develop a system that makes it possible to
bring what we know in the laboratory about molecular genetics and begin applying
it in the field to evolutionary theory and ecology," said Kingsley. The initial
results, he said, suggest that these fish can now be used for detailed genetic
studies of the mechanisms that control vertebrate evolution. 

Other authors on the paper include first author Catherine Peichel, PhD, research
associate with the Howard Hughes Medical Institute and Stanford Department of
Developmental Biology, as well as Kirsten Nereng, PhD, Kenneth Ohgi, PhD, Bonnie
Cole, and Pamela Colosimo, PhD, from the Stanford Department of Developmental
Biology, Alex Buerkle, PhD, from the Department of Biology at the University of
Wisconsin - Eau Claire, and Dolph Schluter, with the Zoology Department and
Centre for Biodiversity at the University of British Columbia. 

Stanford University Medical Center integrates research, medical education and
patient care at its three institutions - Stanford University School of Medicine,
Stanford Hospital & Clinics and Lucile Packard Children's Hospital. For more
information, please visit the Web site of the medical center's Office of News
and Public Affairs at http://mednews.stanford.edu. 

Note: This story has been adapted from a news release issued by Stanford
University Medical Center for journalists and other members of the public. If
you wish to quote from any part of this story, please credit Stanford University
Medical Center as the original source. You may also wish to include the
following link in any citation:
http://www.sciencedaily.com/releases/2001/12/011221080921.htm

Source:
Stanford University Medical Center
(http://med-www.stanford.edu/MedCenter/MedSchool/)

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