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In brief–
Wobble killed off mammal species
Clues to disease in stink bug baby food HOLD your nose. The contents of
the humble stink bug’s gut might
help explain how disease-causing
bacteria originate.
Along with their eggs, plataspid
stink bugs lay a packet of gut bacteria
which the nymphs eat. As the nymphs
develop, their guts divide: the top
becomes a blind sac for digesting
plant juice, while the bottom end
swells into a fermentation chamber
where the bacteria provide the stink
bugs with vital nutrients.
Takema Fukatsu and colleagues at
the Institute of Advanced Industrial
Science and Technology in Tsukuba,
Japan, constructed a DNA family tree
of the bacteria species found in
different stink bug species to show
how the bacteria were related. To
their surprise, the tree was identical
to one for the stink bugs themselves,
showing that bacteria and insects had
evolved in lockstep (PLoS Biology,
DOI: 10.1371/journal.pbio.0040337).
This was completely unexpected
for bacteria living free in an insect’s
gut. Moreover, the bacteria have the
same shrunken genomes and other
changes seen in disease bacteria such
as chlamydia. The team thinks these
changes reflect the way bacteria
adapt to a host, whether as helpers
or as parasites. “This is likely to
provide insights into the evolution of
bacterial pathogens,” Fukatsu says.
The way the plataspids deliver
capsules of bacteria to their eggs will
allow researchers to investigate this
further by manipulating the host and
bacteria separately.
MAMMALIAN species are known
to last an average of 2.5 million
years before being snuffed out,
but nobody had been able to
figure out why. The reason, it
turns out, may be linked to
regular wobbles in Earth’s orbit.
Jan van Dam from Utrecht
University in the Netherlands and
colleagues reached this
conclusion after studying the
fossil record of rodents from
central Spain over a 22-million-
year span. This showed a link
between rodent extinction events
and the climate record.
Changes in the Earth’s tilt and
the shape of its orbit lead to climate
cycles of around 1.2 and 2.4 million
years. At their extremes both
these cycles cause global cooling,
expansion of polar ice sheets and
changes in rainfall patterns. The
extinction peaks coincided with
global cooling maxima, while new
appearance peaks coincided with
periods of stable climate (Nature,
DOI: 10.1038/nature05163).
“Changes in seasonality
associated with the astronomical
variations – harsh winters, dry
summers – are really a matter of
life and death to mammals,” van
Dam points out.
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It’s a hobbit… no, it’s a human… no, it’s a hobbit
18 | NewScientist | 14 October 2006 www.newscientist.com
Maggots, just what the doctor orderedIT’S not a treatment for the faint-
hearted. Now it seems that not only
do maggots eat away the dead tissue
from wounds and allow healing to
begin, they also secrete a fluid
containing enzymes to speed up the
healing process.
Stephen Britland at the University
of Bradford, UK, and his colleagues
applied extracts of maggot juice
to layers of cells that mimic skin.
When circular “wounds” were created
in the cell layers, those exposed to
the maggot extracts healed fastest
(Biotechnology Progress, DOI: 10.1021/
bp0601600).
Closer analysis revealed that
protease enzymes in the juice caused
specialised repair cells to move more
swiftly and freely to the wound site.
“They all march in unison and fill
the hole significantly quicker,” says
co-author David Pritchard of the
University of Nottingham.
The team now hopes to produce
wound dressings impregnated with
purified maggot extracts, which
would protect the wound and speed
up healing without the yuck factor of
the maggots. “You could get the
benefits without the insects
themselves,” says Britland.
They have already created a
prototype gel which healed wounds
just as quickly as applying the maggot
extracts directly.
THE battle over the “hobbit” that
lived 18,000 years ago on the
Indonesian island of Flores is
taking on epic proportions
worthy of The Lord of the Rings.
On one side is Robert Martin of
the Field Museum of Natural
History in Chicago, who says the
existence of a species of small-
brained dwarf human is a fantasy.
Instead, he argues, the fossil is
merely a stone-age human with a
mild form of microcephaly, a
disease which stunts brain
development and is associated
with small stature. And he says
the stone tools found at the site
were made by regular Homo
sapiens (Anatomical Record,
DOI: 10.1002/ar.a.20394).
Recently, however, Colin
Groves of the Australian National
University, Canberra, argued that
Homo floresiensis has the wrong
shape of skull for a human with
microcephaly and is therefore a
separate species (Journal of
Human Evolution, vol 51, p 360).
“There’s no sign of anything but
H. floresiensis on Flores at the end
of the Pleistocene,” he says.
Dean Falk of Florida State
University, Tallahassee, seems to
agree – according to her research
the skull lacks features shared by
10 modern humans with
microcephaly. “The brain is a
combination of features I’ve
never seen in any other primate.”
Further studies of the fossil
are unlikely to resolve the
argument without new material,
says Chris Stringer of the Natural
History Museum in London.
“We need a second skull to see
what the variation is.” Only
then will we know if the hobbit
with the chimp-sized brain
was one of a kind or belonged to
an unexpected branch of the
human tree.