Contact: Bob Nelson For immediate release
(212) 854-6580 December 19, 1997
Widespread Genus of Monkeys Gives Up
Genealogical Secrets to Columbia Researchers
Genetic detective work at Columbia University has unraveled the
complicated lineages of African and Asian macaques, a genus of cocker-spaniel-
sized monkeys that is more widespread than any other primate except humans.
New information about how, when and where the macaques spread across
three continents over the last 5 million years is expected to tell anthropologists
more about how other mammals dispersed and adapted to the same conditions.
Among the many findings is that the sole African member of the genus and
the widespread Asian long-tailed macaques have been inaccurately placed among
the other macaques. The study, which appears in the January 1998 issue of the
Journal of Human Evolution, clearly separates the Barbary ape of Morocco and
Algeria from the Asian macaques and finds no particular genetic affinity of the
Asian long-tailed macaques with other members of a species group that bears its
name. The researchers advocate abolishing that species group as a classification.
The study of all 19 living macaque species confirms that the genus is one of
the oldest among Asian monkeys, dating to at least 7 million years ago, and one of
the most successful, radiating from its home base in Africa to Europe and across
southern Asia, from eastern Afghanistan through Pakistan, India, southern
China, Burma, Thailand, Japan, Taiwan and the Indonesian archipelago.
The research was reported by Juan Carlos Morales, associate research
scientist at the Center for Environmental Research and Conservation at
Columbia, who conducted the genetic analysis, and Don J. Melnick, professor of
anthropology and biological sciences and director of the Center, who gathered
most of the field specimens for genetic analysis over a period of 20 years and
worked with Dr. Morales to interpret the results.
Because it shows how and where macaques spread most rapidly -
throughout Asia over the past 5 million years - the new work will serve as a road
map to Asian primate evolution, and to the evolution of many other mammalian
species in Asia during this time, according to its co-authors. Data on macaque
distribution at different periods in history will give researchers clues to what
factors influenced that distribution, and will be of most immediate use in helping
decipher the movements of two other widespread primate groups, the leaf
monkeys and the gibbons, the researchers said.
"With each successive genus that is analyzed in this manner, we will get a
better and better idea of exactly what was going on in this part of the world and
which geological and climatological events were more important than others in
shaping the evolutionary history and dispersal paths of a diverse group of
organisms, such as primates," Professor Melnick said.
Macaques invaded Asia in what appears to be a series of waves, each time
spreading and diversifying across the continent over a relatively short period of
time, according to the study's authors. Their rapid differentiation into different
species indicates that the environment was conducive to both colonization and
diversification. The many isolated species of macaques further indicates that
periodic lowering of sea levels allowed the spread and subsequent isolation of
macaques on what are now offshore islands. Glaciers and river systems probably
also contributed to the isolation of populations and creation of new species.
Macaques are members of the papionins, a group of old-world primates
that includes baboons, mangabeys and mandrills. The macaques have adapted to
a wide range of conditions, finding ecological niches at sea level and at 12,000 feet,
from semi-desert to cold mountain forest to low-lying tropical habitats.
"The macaques have spread to so many environments precisely because
they have conserved many of the generalized features of the old-world monkeys,"
Professor Melnick said. "As good generalists, they have filled many different
habitats with only small anatomical alterations of the skull and body. In many
ways, macaques are the Darwin's finches of the primate world."
In external appearance, the macaque family has no common defining
feature, leading to considerable confusion when appearance has been used to
classify them. There has even been some debate on whether macaques are a
single genus or two genera, and whether some species now classified as
macaques, such as the Barbary ape, rightfully belong in the genus. Until
Professor Melnick's and Dr. Morales' work, the accepted classification was the
one devised in 1976 by Jack Fooden of the Field Museum of Natural History in
Chicago, based on genital appearance. Body size, fur length and coloration, face
shape and tail length have also been used by others to identify macaque species.
The Fooden classification, while generally accurate, has placed Macaca
fascicularis, the long-tailed macaque, as the immediate ancestor of a small group
of Asian macaques that include the commonly-known rhesus monkey, from
which the Rh blood factor was isolated, the Japanese snow monkey and the
Taiwan monkey. In fact, the more recent Columbia studies find that the various
species thought to be closely related to the long-tailed macaque simply share with
it ancestral characteristics, and have no special genetic proximity to the long-tail.
The real ancestor of the rhesus, Taiwan and Japanese macaque lineage is the
rhesus monkey itself, the researchers believe. They advocate abolishing
fascicularis as a classification, and placing the long-tailed macaques as a more
distant ancestor to most of the mainland and offshore island Asian macaques.
Researchers examined the DNA in cell bodies called mitochondria, because
such DNA evolves relatively rapidly and is only transmitted through the maternal
line, making it a good indicator of recent genetic changes. They determined the
nucleotide composition of a segment of mitochondrial DNA, then compared the
results for genetic similarity and shared genetic changes to draw their
conclusions. The work was supported by the Center for Environmental Research
and Conservation at Columbia University and the National Science Foundation.
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