JC Voltolini writes:
> I am teaching ecology in a Brazilian university for undergrad Biology
> students and this year I would like to use texts (book chapters and articles)
> about "parasite and host ecology and evolution". In some classic ecology
> books this relationship is reffered more as a health problem reinforcing the
> parasites causing deseases but not using an ecological and evolutionary
> vision to explain patterns and processes in the relationship.
By chance, a new paper that you'll probably find of interest appeared on the
co-evolution of lice and men only a couple of days ago, "Pair of lice lost or
parasites regained: the evolutionary history of anthropoid primate lice," Reed
et al., 2007.
You can access the paper at:
http://www.biomedcentral.com/content/pdf/1741-7007-5-7.pdf
There was also a write-up of this article in this week's NY Times "Science
Times" that's actually more informative (and more entertaining) than the
original paper. I've included a copy of the article below.
Wirt Atmar
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March 8, 2007
In Lice, Clues to Human Origin and Attire
By NICHOLAS WADE
One of the more embarrassing mysteries of human evolution is that people are
host to no fewer than three kinds of louse while most species have just one.
Even bleaker for the human reputation, the pubic louse, which gets its dates and
residence-swapping opportunities when its hosts are locked in intimate embrace,
does not seem to be a true native of the human body. Its closest relative is the
gorilla louse. (Dont even think about it.)
Louse specialists now seem at last to have solved the question of how people
came by their superabundance of fellow travelers. And in doing so they have shed
light on the two major turning points in the history of fashion: when people
lost their body hair, and when they first made clothing.
Three kinds of louse call Homo sapiens their home, but each occupies a different
niche on the human body. The head louse, Pediculus humanus, lives in the forest
of fine hairs on the scalp. Its cousin, the body louse, lives not on the skin
but in clothes. And the exclusive territory of the pubic louse, Phthirus pubis,
is the coarser hairs of the crotch.
Lice are intimately adapted to their hosts and cannot long survive away from the
bodys blood and warmth. If their host evolves into two species, the lice will
do likewise. So biologists have long been puzzled over the fact that the human
head louse is a sister species to the chimpanzee louse, but the pubic louse is
closely related to the gorilla louse.
By comparing louse DNA, a team led by David L. Reed of the University of Florida
has now reconstructed how this strange situation probably came about. Dr. Reeds
team collected pubic lice from a public health clinic in Salt Lake City. Samples
of gorilla lice were obtained by members of the Mountain Gorilla Veterinary
Project, which provides free health care to gorillas in the wild.
The number of DNA differences between the gorilla louse and the pubic louse
indicates that they diverged some 3.3 million years ago, Dr. Reed and colleagues
report in todays issue of the journal Biomed Central Biology. Among people, the
pubic louse is usually spread by sexual contact, but the gorilla louse could
have been contracted in some other way.
Well never know if it was sex or something more tame, Dr. Reed said. What can
be said about the transfer, he believes, is that it signals human ancestors had
already lost their body hair by 3.3 million years ago, confining the human louse
to the head and leaving the groin open to invasion by the gorilla louse.
Archaeologists contend that human ancestors lost their standard ape body hair
when they left the shade of the forests for the hot, open savanna and needed
bare skin for efficient sweating. Adaptation to the savanna was well in place by
1.7 million years ago. But loss of body hair could have begun earlier, and Dr.
Reeds result suggests a time for when people first became naked.
If people first became nudists 3.3 million years ago, when did they start to
wear clothes? Surprisingly, lice once again furnish the answer. Though humans
may long have worn loose garments like animal skin cloaks, the first tailored
clothing would have been close-fitting enough to tempt the head louse to expand
its territory. It evolved a new variety, the body louse, with claws adapted for
clinging to fabric, not hairs.
In 2003, Mark Stoneking, a geneticist at the Max Planck Institute in Leipzig,
Germany, estimated from DNA differences that the body louse evolved from the
head louse about 107,000 years ago. The first sewn clothes were presumably made
shortly before this time.
Probing back even earlier in louse evolution, Dr. Reed and his colleagues report
that the two species of primate lice, Pediculus and Phthirus, probably diverged
from each other on an ape host 13 million years ago. The divergence may have
happened after the lice started to specialize in different parts of the body.
Some seven million years ago, this ancient ape species split into gorillas and
the ancestors of humans and chimps, with both lineages infected by both species
of lice. But Pediculus then fell extinct in its gorilla hosts, according to Dr.
Reeds reconstruction, and Phthirus vanished from the chimp-human ancestor.
Next, chimps and humans diverged, and their joint louse diverged with them into
Pediculus humanus and Pediculus schaeffi.
The last event in this history of human-louse cohabitation was the transfer of
the gorillas Phthirus louse to people.
Dr. Stoneking said Dr. Reeds reconstruction was pretty reasonable and said he
agreed that acquisition of the gorillas louse indicated people had lost their
body hair by then. The transfer doesnt have to be sexual, he said, but
presumably it does require reasonably close contact.
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