RESEARCH IN BRIEF
A Costa Rican
zebra tarantula
Aphonopelma
seemanni.
BIOMIMETICS
P HOTO : MPI
FOR
M ETALS R ESEARCH
Adhesion Unlimited
The thought of a hairy spider scurrying up a
wall would send a shiver down most people‘s
spines, but scientists at the Max Planck
Institute for Metals Research in Stuttgart are
fascinated by it. They recently discovered that
zebra tarantulas (Aphonopelma seemanni)
secrete adhesive silk fibers, called tarsal silk,
from their feet to help them to cling to smooth,
steep surfaces. This means that spiders have
three adhesion mechanisms: in addition to the
adhesive fibers, they also have tiny claws and
extremely fine microhairs. Inspired by these
microhairs – albeit from beetles and geckos –
the Stuttgart-based researchers joined forces
with Gottlieb Binder GmbH in Holzgerlingen to
develop an effective adhesive material based on
the biological model. The material has even
been successfully used to produce shoe soles
for climbing robots. (NATURE, September 28,
2006, and JOURNAL OF THE ROYAL SOCIETY INTERFACE,
October 17, 2006)
Spiders climb smooth vertical walls with seemingly no effort at all, and can even negotiate ceilings without a problem. This is because spiders,
like insects and geckos, have extremely thin hairs
that provide them with this remarkable adhesion
capability. In addition, their feet also have tiny
hook-like claws that grip onto rough surfaces. Scientists at the Max Planck Institute for Metals Research in Stuttgart have discovered that the zebra
tarantula A. seemanni uses a further special adhesion mechanism on very smooth surfaces: silk
glands on its feet produce adhesive silk fibers.
This previously unknown adhesion mechanism
raises questions about the evolution of spider silks.
Did the ancestors of modern spiders perhaps originally secrete silk only from their feet to increase
traction, and only later use it for webs? It will take
further investigations of the genes involved in
producing tarsal silk to resolve this.
In any case, the tarsal silk is formed from the
same proteineous material as spiders use to make
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RESEARCH IN BRIEF
RESEARCH IN BRIEF
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ASTROPHYSICS
In a Galactic Powerhouse
ET AL .
DR. STANISLAV GORB
Max Planck Institute
for Metals Research,
Stuttgart
Tel.: +49 711
689-3414
Fax: +49 711
689-3412
e-mail: s.gorb@
mf.mpg.de
F.N. O WEN
@ Contact:
(2000)
Physicists working on the H.E.S.S. project
have examined the engine behind galaxy M87.
The consortium, in which the Max Planck
Institute for Nuclear Physics in Heidelberg is a
participant, has found that the immediate
surroundings of the black hole at the center of
the radio galaxy emit very high energy (VHE)
gamma rays. The researchers have concluded
this from the fact that the intensity of the
radiation measured changes drastically over the
course of just a few days. The gamma rays must
therefore originate in a compact region located
in the very center of the galaxy – the only way
to reproduce the rapid flux fluctuations
observed from Earth. This gives scientists
insight into which processes the black hole
“engine” powers in its immediate vicinity.
(SCIENCE EXPRESS, October 26, 2006)
RADIO IMAGE :
M ETALS R ESEARCH
Microscopic
image of the
new adhesive
material‘s biomimetic surface
structure. The
material (green),
inspired by the
soles of insect
feet, sticks to
glass (blue).
travel over slightly rough surfaces; it‘s a fundamental problem with the adhesion mechanism,”
explains project leader Stanislav Gorb. Once removed, the material leaves no visible marks and
still sticks after it has been affixed and removed
hundreds of times. And, in contrast to adhesive
tape, when it‘s soiled, it can even be washed without losing its adhesiveness.
Potential applications for the new adhesive
material include protective foil for delicate glassware and reusable adhesive fixtures. Refrigerator
magnets are a thing of the past – microhairs
have arrived, and also stick to mirrors, cabinets
and windows. The material has also already performed well with heavier weights: a 120-gram
robot was able to climb a vertical glass wall with
the help of the artificial adhesive fibers attached
to its soles.
For the manufacture of the material, a mold
serves as a pattern – similar to baking a cake – in
which the required surface is stamped as a negative image. This is filled with a polymerizing mixture that is allowed to harden, and is subsequently separated from the mold. “It sounds easy, but it
was the result of a great deal of trial and error,”
says Gorb. The developers found the construction
of the microstructural “cake pan” to be the most
challenging, and exactly how it works remains a
trade secret. Optimizing the polymer mixture also
taxed the researchers: too liquid and it just flowed
out of the mold; too viscous and it wouldn‘t even
flow into the mold.
The researchers are currently attempting to further improve the material by refining the structures and, for example, getting
it to stick and unstick on demand, or displacing it in a specific direction. “However, the
research group still has a great
deal of work, since something
that functions in the laboratory
is a long way away from largescale production,” explains
Stanislav Gorb.
Through understanding the
adhesive hairs, all of the mechanisms that give spiders traction have been translated into
technological reality. However, the spider‘s own adhesion
technique is still far better
than the artificial ones: they
can freely switch methods to
match the requirements of
whatever surface they are negotiating. Such a combinatory
technique is currently being
developed in collaboration
with Roger Quinn‘s group at
Case Western Reserve University (Cleveland, USA).
●
I MAGE : H.E.S.S.;
their webs. However, the fibers are much finer,
only about a quarter of a millimeter thick and up
to 2.5 millimeters long. They adhere so reliably
that the spider can lift its dense mass of microhairs up off the surface when it secretes the adhesive silk. But it uses these adhesive fibers as a last
resort to gain traction, preferring to use its microhairs and not waste silk.
Unlike spiders, according to current findings, insects rely on their microhairs alone and have optimized their form. Spatula- and mushroom-shaped
ends on the hairs provide particularly good adhesion. Yet, while technology has long copied the
principles of sticking and tiny claws in Scotch tape
and Velcro, the microhair principle has still not
been exploited in everyday use. However, a team
of scientists led by Stanislav Gorb has become the
first to successfully mimic the principle of microhairs in an industrial adhesive material. The particularly high adhesive strength of this biomimetic structure is due to very fine hairs shaped like
tiny mushrooms. The researchers investigated the
feet of more than 300 different insect species, spiders and geckos before selecting the foot sole design of various types of beetles as a blueprint for
their material.
Just five square centimeters of the microstructured material can hold objects weighing a few
kilograms on glass walls with smooth surfaces; on
the ceiling, however, they can hold up to ten times
less weight. Smooth structures such as glass or
polished wood are good bases for such adhesive
strips – rough-textured wallpaper, in contrast,
hardly at all. “But insects also find it difficult to
of light, can make it here, since relativistic effects
strongly focus the gamma radiation in the direction of the plasma current. As the relativistic flow
of matter from the radio galaxy M87, 50 million
light-years away, is not directed toward the Earth,
there is less chance of measuring the VHE gamma
quanta. However, it is precisely these quanta that
the researchers in the H.E.S.S. team have now
measured. As the intensity of the radiation fluctuates very strongly, the relativistic flow of matter
cannot be its source: over the course of just a few
days, it increases and decreases at random. Such
fluctuations can be observed only when the light
takes less than a few days to travel from one end
of the source to the other.
“This is not much larger than the event horizon
of the supermassive black hole in the center of
M87,” says Matthias Beilicke, one of the partici-
VHE gamma rays are amazing:
their energies are higher than
visible light by a factor of a million times a million. However,
they are rare messengers from
space. Even from powerful sources, only about one gamma quantum, or one particle of light of
the appropriate energy, reaches
the Earth’s atmosphere per square
meter per month. And they can
be detected only indirectly: the
H.E.S.S. telescope in Namibia
identifies them using Cherenkov
light – light created by an air Left: Radio galaxy M87, as observed by H.E.S.S. in very high energy
shower triggered by the extrater- regime (color scale). The black lines represent the structure of M87 in
restrial gamma rays. The first in- the radio range. The gamma radiation looks distended, which is due
dications that M87 also glows in to the telescope’s precision.
gamma light were discovered by Right: The cutout shows an image of M87 in the radio range – at
astrophysicists as early as 1998 energies that are approximately 19 orders of magnitude lower than
those of the gamma rays. The cross marks the point at which H.E.S.S.
with the HEGRA telescopes. “The
measured the highest level of gamma radiation.
H.E.S.S. measurements have now
given these results a firm basis,” says Felix Aharopating scientists from the University of Hamburg.
nian, one of the participating physicists from the
“Relativistic effects that play a part in the blaMax Planck Institute in Heidelberg.
zars, the extragalactic sources previously proven
The H.E.S.S. team has now established that the
to exist, should be of less significance in the case
area immediately surrounding the black hole in
of M87. It is therefore highly likely that VHE
M87 is a previously unknown radiation source. Up
gamma radiation is coming from the immedito now, astrophysicists had detected gamma-ray
ate vicinity of the supermassive black hole in
light at these energies only from blazars. Blazars
the center of M87.
are galaxies that meet two conditions: first, a suHowever, physicists do not yet know exactly
permassive black hole at their center must work as
how the gamma rays are created. It may even be
an energy powerhouse – a characteristic of any
an as yet unknown mechanism – for example, hyactive galaxy. Second, the current of matter or
drogen nuclei close to a rotating black hole could
plasma that escapes the black hole’s vicinity must
be accelerated to extremely high energies and
be directed nearly precisely at the Earth. This is the
then radiate gamma quanta. “H.E.S.S. gives us
only way the gamma radiation, which is created
clear insight into the processes that take place in
by the matter moving rapidly at almost the speed
the galactic powerhouse,” says Felix Aharonian. ●
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@ Contact:
PROF. FELIX AHARONIAN
Max Planck Institute
for Nuclear Physics,
Heidelberg
Tel.: +49 6221
516-485
Fax: +49 6221
516-601
e-mail:
Felix.Aharonian@
mpi-hd.mpg.de
7
RESEARCH IN BRIEF
RESEARCH IN BRIEF
CELL BIOLOGY
QUANTUM CHEMISTRY
With the Strength of a New Heart
Photon Fusion
Newts can do something humans can’t: when
they lose a leg, they simply grow a new one. And
even an injured heart will regenerate completely.
Scientists at the Max Planck Institute for Heart
and Lung Research in Bad Nauheim want to
discover which cellular mechanisms make such
astonishing healing possible. One result of their
investigations: the heart muscle cells of newts
are exceptionally versatile. This knowledge could
help with the development of new cell therapies
for patients with damaged organs. (JOURNAL OF
CELL SCIENCE, 2006)
Notophthalmus viridescens, the green water
newt, usually lives in marshy areas of North
America. But it also feels quite at home in the
aquarium at the institute in Bad Nauheim – and
is one of the favorite animals there. Scientists in
Thomas Braun’s group are studying how the
newt’s damaged heart tissue renews itself and
how the organ regains its full strength – an ability that mammals do not possess. The heart of a
myocardial infarct patient is scarred and remains
permanently damaged.
Notophthalmus viridescens is spared such permanent consequences of a damaged heart,
cle-specific proteins are now being produced
again, as the scientists’ data shows. By this time,
the cells have redifferentiated again.
In culture, Braun and his colleagues were able
to detect a protein called phospho-H3 in the majority of cells. This protein appears in the G2 phase
of the cell cycle and signals that the heart muscle
cells are actively dividing again. From this, the researchers conclude that the newt heart regenerates without the help of stem cells. But apparently an injured heart does not heal using the same
mechanism as a detached leg, since a typical
wound healing tissue, a blastema, does not form
here. “The heart possesses only a relatively small
number of different cell types. This could be a reason why no blastema is required in heart tissue
reconstruction,” says Braun in explanation of
these results.
Blastema cells, similar to stem cells, can differentiate into various cell types. Heart muscle cells
are, in principle, versatile enough to also form
blastema cells, at least according to further investigations by the cell biologists in Bad Nauheim.
After limb amputation, they injected heart muscle
cells into the newly growing newt leg. In this environment, the heart muscle cells began to dedif-
Two greens make a blue: Researchers at the
Max Planck Institute for Polymer Research in
Mainz and the Sony Materials Science Laboratory in Stuttgart are creating one high-energy
blue photon from the sum of two low-energy
green photons by irradiating a solution of two
photoactive substances with green light. This
fusion process even works for photons from
sunlight. Previously, it was possible to convert
only low-energy coherent photons into higherenergy ones. The ability to
pair up sunlight photons
would help increase the
efficiency of solar cells.
(PHYSICAL REVIEW LETTERS,
October 4, 2006)
8
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@ Contact:
DR. MATTHIAS HEIL
Max Planck Institute
for Heart and Lung
Research (W.G.
Kerckhoff Institute),
Bad Nauheim
Tel.: +49 6032
996-2822
Fax: +49 6032
705-211
e-mail: presse@
mpi-bn.mpg.de
P OLYMER R ESEARCH
ferentiate and, at the same time, formed proteins
typical for blastema cells. After around 15 days,
they had actually developed into skeletal muscle
cells. Injected into a healthy newt leg, however,
the heart muscle cells underwent no changes. “We
suspect that the signal for dedifferentiation comes
from cells in the wound healing area,” explains
Braun. An enzyme – focal adhesion kinase – may
possibly be involved. It is phosphorylated in transplanted cells and therefore active. “When we fully
understand this mechanism, it may open up new
possibilities for treating heart attack patients,” the
researcher hopes.
●
FOR
thanks to the plasticity of the newt’s heart muscle cells. Biologists understand this as the ability
of cells to change under certain circumstances.
Specifically, when the organ is injured, the heart
muscle cells lose their characteristic properties
and dedifferentiate. “We have demonstrated that
this involves dramatic down-regulation of typical heart muscle cell proteins, such as the heavy
myosin chain and various troponins,” says Braun.
At the same time, the cells begin to feverishly
divide, rapidly building up new heart muscle
mass. After about two weeks, the newt’s heart
beats as if nothing had happened, since the mus-
P HOTO : MPI
P HOTO : MPI
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Left: After two weeks, heart muscle cells that were injected into a regenerating leg produce
proteins typical for skeletal muscle cells (green). The cells were previously stained with a red dye,
so the overlap results in the color orange.
Right: In contrast, just two days after injection, the heart muscle protein troponin T is no longer
detectable. The inset shows healthy heart tissue where troponin T is stained green.
one passes all of its energy to the other, which
thus becomes even higher in energy. However, it
relaxes to ground state again rapidly and emits a
blue photon in the process. Although this light
particle is higher in energy than the green light
originally radiated, in total, no energy is created.
Rather, the energy from two photons is combined
into one.
To ensure that the two photoactive substances
can achieve this together, the chemists must coor-
Solar cells can’t convert lowenergy, long-wave sunlight
to electricity, and that drastically lessens their efficiency. Scientists at the Max
Planck institute in Mainz
and the Sony Laboratory in
Stuttgart have now succeeded in converting longwave photons to high-energy short-wave photons – even
if they are from a common
light source like the Sun. In
this way, the part of light
energy that was previously
lost can now be used by solar cells.
The color of the photons shows that they have paired up. They flow
The researchers sent long- into the solution as green light and come back out as blue light.
wave green light through a
dinate them carefully. Above all, the excited ansolution of platinum octaethyl porphyrin and ditenna molecules must store the energy long
phenylanthracene. The two active substances comenough, and should not surrender it in any way
bined two green photons into one blue photon.
other than by transferring it to the emitter molePreviously, this pairing was possible only with phocules. The only thing that proved suitable as antons from a laser beam, although it was achieved
tennae were special metal-organic compounds
in a different way: bombarded with photons from
with a heavy metal atom in a complex including
a laser, some molecules take up two photons sian aromatic part. For triplet-triplet annihilation to
multaneously and then surrender one with higher
occur, the emitter molecule, in turn, must take the
energy. As the radiation from common light sourcenergy packets from the antenna molecules and
es is not sufficiently intense, it is very unlikely that
hold onto them until it encounters another extheir photons will pair up in this way.
cited emitter molecule.
The newly discovered cocktail of two photoacThe research team is now looking for more
tive substances combines photon partners from
substances that meet these requirements to
common light sources using a different mechaachieve fusion of photons of other light colors.
nism: triplet-triplet annihilation. Here, the molIn this way, they seek to make the energy of the
ecules from the platinum octaethyl porphyrin act
entire solar spectrum usable. At the same time,
as antennae for green light. They store the light
they are trying to integrate the photoactive subenergy in excited states and then pass it on to
stances into a polymer matrix in order to prepare
the diphenylanthracene, which puts these emitthe process for more direct application in upconter molecules into an excited state, as well. If two
verters for solar cells.
excited diphenylanthracene molecules collide,
●
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@ Contact:
STANISLAV BALOUCHEV
Max Planck Institute
for Polymer Research,
Mainz
Tel.: +49 6131
379-485
Fax: +49 6131
379-100
e-mail: balouche@
mpip-mainz.mpg.de
9
RESEARCH IN BRIEF
RESEARCH IN BRIEF
EVOLUTIONARY BIOLOGY
ATOMIC PHYSICS
The First Million Have Been Sequenced
Order in a Herd of Atomic Sheep
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It is the goal of several groups of researchers
throughout the world to create patterns with
electrons. They want to force conduction electrons
– the electrons that allow electrical current to
flow – into regular structures on the surface of
certain materials by planting the atoms selectively. In this way, they want to influence the growth
of thin films of materials. When new atoms, called
adatoms, are vapor-deposited on these electron
structures, they settle in some areas more than in
others. Their preference for specific areas depends
on where the density of electrons attracts or repels them. By tailoring the density of electrons,
physicists are hoping that they will be able to create thin films of material with predetermined
characteristics.
Researchers at the Max Planck Institute for Microstructure Physics in Halle, together with physicists from the Universities of Halle and Santiago
de Compostela in Spain, have investigated a special form of electron structure: they considered
electrons in a dense, closed ellipse of cobalt atoms
on a copper substrate. The conduction electrons
can be viewed as a gas or a liquid; ring-fenced by
the atoms, they create standing waves, like water
in a small pond.
The physicists calculated where additional vapor-deposited cobalt atoms would arrange themselves. In the process, they had to take into account that the new atoms would interact with the
cobalt atoms of the corral and with the trapped
electrons. According to their calculations, the cobalt adatoms preferred to move to the areas that
are more densely populated with electrons, as the
atoms here need less energy to settle than in places where there is low electron density. However, in
their simulations, the physicists can ensure order
in the corral only if the rate at which the atoms
are deposited is correct, the temperature is lower
than 253 degrees Celsius below zero and the corral is sufficiently closely packed.
The cobalt atoms arrange themselves in ellipses,
like waves in an electronic pond. The scientists
were able to create regular structures on the circles themselves using adatoms, which have a
greater ability to move at lower temperatures –
for example cerium atoms. This was similar to allowing a herd of atomic sheep to run into a corral
and the herd then obediently arranging itself into
evenly spaced concentric circles.
The scientists would now like to see the results
of the simulations confirmed in experiments. They
are confident that this can be achieved with normal scanning force microscopy, thus opening up
new paths to creating thin films.
●
@ Contact:
SANDRA JACOB
(Press Officer)
Max Planck Institute
for Evolutionary
Anthropology, Leipzig
Tel.: +49 341
3550-122
Fax: +49 341
3550-119
e-mail:
[email protected]
@ Contact:
M ICROSTRUCTURE P HYSICS
When the first Neanderthal bones were unearthed
in 1856, lots of questions were raised, particularly
about the demise of the Neanderthals – a topic
that is still hotly debated today. For a long time,
attempts to investigate this meant searching
through the dirt of millennia in dark caves for fossilized remains of these pre-humans. Scientists at
the Max Planck Institute for Evolutionary Anthropology and the American company 454 Life Sciences Corporation are now pursuing another
strategy: similar to a huge jigsaw puzzle, they
want to piece together the entire Neanderthal genome from fossilized DNA fragments. The first one
million base pairs have now been decoded – about
0.04 percent of the entire genome.
Direct comparisons between Neanderthals,
humans and chimpanzees show that, of all the
genetic changes between humans and chimpanzees, only about 7 percent arose after the
split between the human and Neanderthal lines.
This makes the question as to what effect these
small genetic differences had – that is, how, under the influence of a few genetic mutations,
our ancestors developed in different directions
– all the more exciting. “The Neanderthal ge-
Electrons and atoms can be confined into
atomic structures like sheep in a corral – which
is nothing new. However, physicists at the
Max Planck Institute for Microstructure Physics
in Halle have now discovered how to cause
the herds to arrange themselves in an orderly
fashion: when they give the atomic fence the
proper shape and choose the proper substrate,
temperature and several other parameters,
the randomly vapor-deposited atoms arrange
themselves in regular structures in the corral.
(PHYSICAL REVIEW LETTERS, November 2, 2006)
FOR
P HOTO : SPL-F OCUS
The bones of
this Neanderthal
were found at LaChapelle-auxSaints in France,
and are about
45,000 years old.
nome sequence could provide clues about regions in our own genome that have undergone
particularly marked changes since our separation from Neanderthals about 500,000 years
ago,” explains Pääbo. “Such regions were very
probably subject to strong positive selection,
and may well have played a crucial role in the
emergence of modern man.”
Like a prehistoric logbook, the DNA records
how the ancestral lines of humans and Neanderthals first diverged 500,000 years ago, and then
met up again about 45,000 years ago. At the moment, the evidence points to at least some occasional genetic mixing. The two species were
apparently not as clearly separated as previously
assumed. The researchers
found indications that especially male members of
modern humans had affairs
with Neanderthal females.
In about 30 percent of cases, Neanderthals share a
new gene variant with modern man – a value that is
too high to correlate with
the previous idea of a simple population split. And
since the differences in the
Neanderthal’s X chromosome are so much greater
than in the autosomes –
that is, the chromosomes
that are not sex chromosomes – the researchers
speculate that the gene flow was principally from
modern human males to Neanderthals. However,
more extensive sequencing of the Neanderthal
genome is still needed to test this hypothesis.
But for now, Svante Pääbo and his team have
impressively shown that their method works. Sequencing fossilized DNA is an extremely tricky
process, and for a long time the hurdles seemed
insurmountable: similar to ancient scrolls that decompose with the passage of time, DNA, too, becomes very fragile. In addition, it is always contaminated with huge amounts of foreign DNA
from bacteria and fungi that colonize the body
after death – and from those who work with the
fossils. Since human DNA and Neanderthal DNA
share so many similarities, and since it is precisely
the fine differences between them that need to be
determined, it is particularly catastrophic if human DNA is found on the bones. The 38,000-yearold fossilized bones from the Vinija cave in Croatia, however, were a lucky find for the researchers:
of the good 6 percent of hominid DNA, 99 percent
was actually of Neanderthal origin, and not contamination from researchers’ hands.
●
P HOTO : MPI
Did modern humans meet up with Neanderthals at some point, and did they perhaps
interbreed to produce fertile offspring? This
is one question that scientists in Svante
Pääbo’s group at the Max Planck Institute
for Evolutionary Anthropology want to answer.
Using a new technique developed in the US,
they have begun to decode the DNA of our
closest extinct relatives – and have now
finished the first million base pairs. A rough
draft of the entire Neanderthal genome is
expected to be available in two years, and
should provide information about which
genetic changes were key in evolving into
Homo sapiens. (NATURE, November 16, 2006)
PROF. DR.
PATRICK BRUNO
Max Planck Institute
for Microstructure
Physics, Halle
Tel.: +49 345
5582-763
Fax: +49 345
5582-765
e-mail: bruno@
mpi-halle.de
An elliptical
corral of cobalt
atoms planted on a
substrate of copper
atoms. The electrons in
the corral behave like
standing waves in a pond.
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RESEARCH IN BRIEF
Panorama
RESEARCH IN BRIEF
BEHAVIORAL BIOLOGY
Too Tame for This World
P HOTO : T HOMAS R ÖDL
Marine
iguanas on
the Galápagos
Islands.
12
The researchers thus took advantage of the Max
Planck Society’s research platform on the Galápagos Islands. Thomas Rödl described the extensive
preparations for this trip and his first impressions
in the 2/2003 issue of MAXPLANCKRESEARCH. These
Pacific islands are still an oasis for evolutionary
biologists. However, it is not only scientists who
are drawn here – more and more tourists visit this
unique archipelago every year: in 2005 the figure
was around 126,000, and the trend is increasing.
The problem: a large number of tourists and immigrants not only disturb many of the indigenous
animals on the Galápagos Islands, they also introduce alien animal and plant species that cause
great damage to local flora and fauna.
Rödl and his colleagues wanted to discover the
extent to which marine iguanas from different
populations and with different predator experiences diverge in their stress response and behavior. To this end, they carried out so-called harassment experiments in which they measured the
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animals’ flight initiation distance, chasing them
repeatedly over short distances and subsequently
capturing them to measure the corticosterone
levels in their blood. If the animal found the situation threatening – that is, stressful – then the
corticosterone hormone concentration in the
blood plasma rose within just a few minutes.
The scientists tested various island populations:
marine iguanas with no experience of predator
threat let humans approach them to within one to
two meters, and showed no increase in the stress
response even after sustained pursuit. Marine
iguanas familiar with predators but at low risk
showed elevated corticosterone levels only when
caught, and flight initiation
distances increased only in
those animals that had already
been caught once before. In
contrast, iguanas living with
acute predator pressure immediately responded to a harassment experiment with an increase
in
corticosterone
concentrations.
“Our experiments show that
the animals can increase their
flight initiation distance to
some degree and can activate
the corticosterone stress response,” explains Thomas Rödl.
“Apparently, the function of
the stress axis has been retained even over long evolutionary periods without pressure from predators, and can
be reactivated immediately
when predation reappears.” Marine iguanas can
apparently learn what a predator is, but they
are unable to effectively increase their flight
initiation distance. “We were able to recapture
the same animals up to six times in four weeks,”
says Rödl. No wonder, then, that the introduction of dogs and cats has drastically reduced the
population of marine iguanas on some islands.
This indicates that the ability to adapt to new
predators is not limited by the physiological system, but by constraints in behavior. “In the
course of evolution, with the absence of predators, selection possibly favored especially those
animals that avoided cost-intensive flight behavior, providing them with a fitness advantage,”
speculates Rödl. The scientists’ findings not only
provide the first clues to why tame animals have
become extinct on numerous continents, they
also provide conservationists with arguments to
support their plea for sustainable tourism on the
Galápagos Islands.
●
HIERARCHICAL STRUCTURE strengthens bones.
Scientists at the Max Planck Institute of Colloids
and Interfaces have discovered what makes bone
both elastically formable, but also extremely breakproof. The secret is its hierarchical structure: strain
applied to the bone as a whole is absorbed by elastically stretchable collagen fibers that shift against
each other via a type of adhesive layer, and then
transfer the strain to structures at the micron level
and ultimately pass it on to tiny apatite particles at
the nanometer level. These hard and brittle mineral particles are only a few nanometers in size and
can thus withstand greater strain than particles
measuring a few micrometers, which crack under
even slight strain. Accordingly, bone stability is due
to the fact that small mineral particles can carry a
higher breakage load than larger particles. On the
basis of these bone structure principles, it may be
possible to construct new materials for technical
applications. Furthermore, the research may provide insight into the pathological changes that occur at the molecular level during the progression
of osteoporosis.
@ Contact:
DR. THOMAS RÖDL
Max Planck Institute
for Ornithology,
Andechs
Tel.: +49 163
161 5373
Fax: +49 8152
373-133
e-mail: roedl@
orn.mpg.de
P HOTO : C HRISTOPH B ASSE
Marine iguanas on the Galápagos Islands live
without enemies – at least they did up until
150 years ago. Since then, they have had to
face dogs and cats on some islands of the
archipelago. Thomas Rödl from the Max Planck
Institute for Ornithology, and his colleagues
Silke Berger from the University of Ulm,
Michael Romero from Tufts University and
Martin Wikelski from Princeton University,
wanted to find out if these usually tame
animals are capable of adapting their behavior
and endocrine stress response to such newly
introduced foes. (PROCEEDINGS OF THE ROYAL SOCIETY
OF LONDON, B 274 (1609): 577-582 (2007)
NANOBARRIERS FILTER HYPERSONIC WAVES.
Researchers at the Max Planck Institute for Polymer Research have produced colloidal crystals
that absorb sound waves in the gigahertz frequency range. This extremely short-wave hypersound is created to some extent by the thermal
movement of atoms, and it contributes to thermal
conductivity in materials. It has a wavelength of
just nanometers, which means that, to block it,
structures with similar dimensions are required.
The scientists in Mainz arranged polystyrene
spheres with diameters of 200 to 300 nanometers
in regular layers on a glass substrate and connected them using silicone oil, producing colloidal
crystals that can absorb hypersonic waves in defined frequency ranges. Since they also influence
thermal conductivity, these crystals could be utilized to construct highly efficient thermal barriers.
In addition, they work as optical filters and could
be used to reciprocally modulate optical and
acoustic waves, as well as possibly to construct
acoustic lasers.
THE TRICKS EMPLOYED BY A PLANT PARASITE
are being investigated by an international research
team led by scientists at the Max Planck Institute
for Terrestrial Microbiology in Marburg. The parasite in question is Ustilago maydis, the pathogen
that causes corn smut. On corncobs, this fungus
causes monstrous tumors that, although not poisonous – they are even considered to be a delicacy
in Mexico – make the infected corn plants unsuitable for cornmeal or popcorn. The scientists have
now analyzed the genome of this parasite. Among
its some 7,000 genes, they have found some that,
on the one hand, enable the fungus to live at the
expense of its host plant without killing it and, on
the other hand, evade the plant’s defenses. The
identification of these key genes will enable Ustilago maydis to be used as a model for studying
the strategies of other biotrophic fungi, many of
which, including the economically important rust
fungus, are related to the corn smut pathogen.
Corn plays host: The Ustilago maydis fungus causes
corn smut. Researchers have now identified key
genes that play a role in infecting the plant.
SACRIFICED TO FIGHT INFECTION. When germs
enter the body, the first line of defense is formed
by neutrophile granulocytes. On the one hand,
these white blood cells act as phagocytes, cells
that “eat” the invader by ingesting it and using
aggressive enzymes to kill it. On the other hand, as
scientists from the Berlin Max Planck Institute for
Infection Biology discovered some time ago, the
granulocytes also use extra-cellular traps: they
produce web-like structures, composed of nucleic
acid and enzymes, in which bacteria and fungi are
caught and rendered harmless. The Berlin-based
researchers have now discovered how these webs
are produced. Inside the granulocytes, components of the destroyed pathogens cause the cell’s
nuclei and enzyme deposits to dissolve, and their
contents to mix. Thus, a tangled “ball” of DNA
threads and enzymes is created. As it perishes,
the granulocyte uses the last of its strength to
burst open its cell membrane and expel this
deadly web, which then unfolds to catch germs.
1/2007 MA
X
PL
A N C K
R
E S E A R C H
www
Further
information
is available at
www.maxplanck.de
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