UCLA scientists discover new evolutionary relationship

Monday, 7/14/97 UCLA scientists discover new evolutionary
relationship RESEARCH: DNA findings may clarify man’s place in
chain of life, origin

By Kathryn Combs Daily Bruin Contributor "Where do we come
from?" The most experienced and knowledgeable scientists cannot
answer this question with 100 percent surety, making the origin of
man one of the most controversial and hotly-contested topics in
modern science. However, due to a recent discovery, UCLA
researchers may be a step closer to fully understanding the
relationship between members of the animal kingdom and from where
we descended. Beginning in 1994, Anna Marie Aguinaldo, a UCLA
graduate student, performed the original research work associated
with this discovery. She and her colleagues hypothesized that
arthropods and nematodes, two distinct groups in the evolutionary
tree, are more closely related than previously thought. As a result
of DNA analysis, they theorized that arthropods and nematodes
descended from a single supergroup called Ecdysozoa. "I started
looking at Tardigrades, a group also known as Water Bears," said
Aguinaldo, explaining that this group has always been considered a
sister group to the arthropods. "(Water Bears) have a unique
characteristic. Under very unfavorable environmental conditions,
they are able to retreat into a crypto-biotic stage,"she continued,
explaining that they were basically able to hibernate for long
periods of time during the absence of water. "I was studying those
using molecular sequencing to see how they were related to
arthropods," she added. The Water Bear, only one of the organisms
that Aguinaldo studied, enabled her to develop her methods for
further research. By comparing the DNA of organisms from the
nematode and arthropod groups, she determined that many of the
organisms along the evolutionary tree seemed to be closely related.
"All (Groups: Nematodes and arthropods) share a common property:
They all moult,"said James Lake, a professor in the department of
molecular, cellular and developmental biology. "Our hypothesis –
that all moulting animals are in one large family – starts to
explain the fossil record," he continued. Arthropods are considered
to be the most diverse animal group. However, their relationships
with other organisms have, to date, been unclear. Due to new
methods, scientists have been able to look closer at this group.
Researchers, including Lake and Aguinaldo, used the 18S ribosomal
DNA sequences to compare various animal groups. They first cloned
and sequenced the gene, and then used methods of comparative
analysis to determine the similarities between the groups. Before
genetic analysis was used to compare animal groups, scientists used
physical characteristics to differentiate groups. The hypothesis
that nematodes are related to arthropods has important implications
for developmental genetic studies. "The position of the nematodes
on the phylogenetic (evolutionary) tree is of fundamental interest
because nematodes are animals, of which a great deal is known,"
said professor David Jacobs with the department of biology.
"(Nematodes provide) a great model system. Since this is one of the
model systems, it is really important to medical research and
zoology how these different animals are related." "This research is
very interesting because it is controversial and it is a difficult
area to research. They, the researchers, may very well be correct,"
said Jacobs. Lake said that this research is significant because it
provides humans with clues as to where they descend from. "Now we
are at the stage where we have worked out the major relationships
between animals (because) it’s important to tell us where we came
from and how our bodies function," said Lake. "Clearly the
evolution of all multicellular animals is important," concluded
Lake.