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.

TAKA

HIRO

HOS

OKAW

A

SUKR

EE SU

KPLA

NG/R

EUTE

RS

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.