Heroic Algae Might Help Cancer Research, Nature, H. Gee 
Some animals sacrifice themselves in order to save
their children and thereby increase the chance of passing on their
genes to future generations. Others will give up the prospect of
having their own children if it helps the survival of closely
related progeny. Humans even went all the way to encourage young
men to die for their country as kamikaze pilots or with the
slogan: "Dulce et decorum est pro patria mori".
Where in evolution did this genetic strategy first emerge?
Antonio Miralto from the Stazione Zoologica "Anton Dohrn" in
Naples, Italy, and colleagues studied diatoms, single-celled algae
that float in the sunlit surface waters of the world and which
form the base of the food chain. They discovered an astonishing
defense strategy of the diatoms against copepods, small
crustaceans that are the pre-eminent grazers on diatoms. While
other plants or prey animals evolved poisons or chemicals that
would make them unattractive to predators diatoms display a
different strategy of individual self-sacrifice: Diatoms turn into
copepod baby-killers the moment they are eaten. They do this by
producing substances that kill baby copepods before they even
hatch. These substances are believed to work by interfering with
the network of proteins within the cell that controls how it
divides. This strategy is highly effective: While under normal
circumstances about 90% of the copepod eggs hatch this rate drops
to 12% for copepods when they were feeding on diatoms.
Since the diatom chemical suppresses cell division it also
might be helpful to develop new drugs against cancer: Cancer
tissue and embryos have in common that their cells are relatively
un-differentiated and divide rapidly. Therefore and drug that
slows or stops cell division will primarily affect cancer (and
embryo) cells.
The
diatoms of death,
Henry Gee, Nature science update 11 Nov.
1999
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J. Doyne Farmer, a chaos physicist by training, has
always been interested in using scientific methods to make money:
As a student he built a computer to predict the outcome of
roulette, later he used methods from non-linear dynamics and
complexity theory to play the stock markets. In a commissioned
article for Computing in Science & Engineering he reviews some
of the theoretical methods behind "econo-physics" and
computational finance. The central object of study is the
log-return function, which tells you how much you can expect an
investment at a given time will return a certain amount of time
later. Already in the 1960s Benoit Mandelbrot and others
recognized that log-return histories are better described by
fractal curves than by traditional statistical processes.
Today we know from millions of analyzed transactions that the
story is a little more complex: no low dimensional chaotic
attractors appear to describe the data although nonlinearities (a
precondition of chaos) are clearly present. Instead of simple
fractals one needs multi-fractals to describe the scaling
properties of the data. In good physics tradition the
econo-physicists are not too shy to introduce new technical terms
like "fat tails" and even a "smile". Instead of econometric models
the simulations are done based on models of economic agents. As a
return of this theoretical investment one seems to get a better
understanding of phenomena like "clustered volatility" and
"information cascades".
To convince skeptics that econophysics is not just another
academic sand-box Farmer mentions en passant the success of the
Prediction Company that he co-founded: " According to many
mainstream economists, the highly statistically significant
profits we made should have been impossible."
Physicists
Attempt to Scale the Ivory Towers of Finance, Santa Fe
Institute Working Papers 99-10-073, J. Doyne Farmer
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"When a female mammal makes the transition from virginity
to motherhood, she is forced to refocus her activities
dramatically. She must adapt to a multitude of new demands by her
offspring or risk losing a significant metabolic and genetic
investment. She needs to find and remember the location of food
stores, water sources and nest sites, and be able to exploit them
to her offspring's advantage. The performance of these tasks may
depend on a sharpening of her cognitive abilities."
Kinsley et al. could show that for rats the rearing of pups is
not only a new challenging task for the mother that makes it
necessary for her to learn many new things but that she is
supported in mastering this new challenge with the help of
hormone-induced modifications to the hippocampus. That means part
of her brains change so that it becomes easier for her to adapt
and learn the many new tasks.
To some this might invoke the vision of a drug that acts like a
Nuremberg funnel and allows learning without the hard work that
goes with traditional cramming. But the authors state clearly that
the activity of raising the pups itself exposes the brain to rich
sensory events that have effects on brain structure and function
that are similar to those caused by other types of enriched
physical environments.
But alone the possibility of hormonal facilitation of learning
and retention of what has been learns open up new ways for
education and future treatment of learning disorders.
Motherhood
improves learning and memory, Nature
402, 137 (1999), C.H. Kinsley et al.
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Perceptual learning is well known in psychology. If the
brain is repeatedly required to distinguish between pictures of
faces or patterns, for example, its performance improves. This
contrasts with the other prevailing theory -- that training
diminishes the amount of 'internal noise' or interference produced
by the nervous system.
Bennett's group then studied how practice influenced the
subjects' abilities to identify the pictures.
The team found that when they added little or no artificial
'external noise' (the interference that was deliberately
superimposed on the pictures), the performance of the subjects was
limited only by the amount of internal noise. Bennett and
colleagues conclude that perceptual learning probably results from
enhanced 'signal strength' -- an improvement in the way the
neurons in the brain represent a stimulus.
Practice
makes perfect, RACHEL SMYLY, Nature
science update, 11 Nov. 1999
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Noise is traditionally seen as undesirable pollution of a
signal. The discovery of stochastic resonance phenomena shows that
under certain conditions noise can actually improve the quality of
a signal. Since our natural environment contains many sources of
noise it is no surprise that many organisms have adapted to this
situations and use stochastic resonance to their own advantage.
The article by Sbitnev reports simulation of a simple model of
a neuronal system that is exposed to external noise. They could
confirm that it indeed shows the characteristic signature of
stochastic resonance.
Abstract: The phase transition with respect to the intensity of
a -correlated noise source has been studied in a coupled map
lattice that simulates the excitability of field-type neural
tissues [7]. The entropy of lattice states versus this
control parameter undergoes a qualitative change at the phase
transition point. Its behavior is linear on one side of this point
and it transforms to a cubic-root form on the other side. An
enormously increasing susceptibility to external perturbation in
the vicinity of the phase transition point leads to an observed
existence of stochastic resonance in this region. Complexity
induced by the external subthreshold periodic signal reaches a
maximum at the phase transition point.
Noise
Induced Phase Transition in a Two-dimensional Coupled Map
Lattice, Complex Systems, Valery I.
Sbitnev
-
It has been well established that an ant colony uses
chemical (pheromone) traces for communication between its members.
The resulting communication structures allow the ant colony to
behave as self-organized, coherent super-organism that learns and
behaves as a unit. Almost all of the ants (workers and soldiers)
are daughters of the queen (yes, even soldier ants are female,
contrary to the movie antz) and have given up their chance to have
their own offspring. The total number of neurons that cooperate in
this way in an anthill are comparable to the number of neurons in
a human brain.
The structure of the trails is therefore of central importance
for the survival of the colony. It is known that the trail
structure is modified as the colony learns about the distribution
of its food resources. The paper by Solé et al. addresses
the question about the mechanisms that actually determine the type
of trails that will be established. They use an agent-based model
with simple behavioral rules for each ant and the pheromone
distribution. Their resulting simulated patterns are not only
"strikingly similar" to observed patterns but they also change
their structure from multi-branched fractal to structures with
only a few branches as a function of parameters in a way that
agrees with one's expectations.
Abstract: "Army ant colonies display complex foraging raid
patterns involving thousands of individuals communicating through
chemical trails. In this paper we explore, by means of a simple
search algorithm, the properties of these trails in order to test
the hypothesis that their structure reflects an optimized
mechanism for exploring and exploiting food resources. The raid
patterns of three army ant species, Ection hamatum, Ection
burchelli, and Ection rapex, are analyzed. The respective diets of
these species involve large but rare, small but common, and a
combination of large but rare and small but common, food sources.
Using a model proposed by Deneubourg et al. (1989), we simulate
the formation of raid patterns in response to different food
distributions. Our results indicate that the empirically observed
raid patterns maximize return on investment, that is, the amount
of food brought back to the nest per unit of energy expended, for
each of the diets. Moreover, the values of the parameters that
characterize the three optimal pattern-generating mechanisms are
strikingly similar. Therefore the same behavioral rules at the
individual level can produce optimal colony-level patters. The
evolutionary implications of these finding are discussed."
Pattern
Formation and Optimization in Army Ant
Raids, Santa Fe Institute Working
Paper 99-10-074
-
Termites under attack from fungi send out an alarm
signal warning the rest of the colony to run away. The insects
signal danger by frantically waggling their heads, sending shock
waves through the nest.
Dampwood termites (Zooteropsis angusticollis) nest in rotting
logs and trees, eating the very homes they live in. "It produces a
vibration," says Traniello. "It's a seismic signal." Other
termites sense this signal in their legs.
How
termite head-bangers outwit a
fungus, New Scientist, Matt Walker,
13 November 1999
-
Two reports in this week's issue of Science (pp.
1377
and 1381)
bolster the notion that immune cells never forget. The immune
cells in question are T cells, which spring into action to kill
infected cells or orchestrate other immune responses when other
cells "present" them with an appropriate antigen, together with a
so-called MHC protein. The new work shows that memory T cells
don't need to repeat this experience: They persist and maintain
their ability to recognize their specific antigens, even when put
into mice that have been genetically altered to eliminate the MHC
proteins, which makes antigen presentation impossible.
Memory
T Cells Don't Need Practice,
Science, M. Hagmann
Accelerated Virus Evolution in IV Drug Users, New Scientist
Intravenous drug abusers are harbouring a virus that is
evolving 300 times faster than usual and could turn nasty,
scientists warn. Several drug users infected with the normally
harmless virus have already developed a devastating neurological
disorder, although a firm link between the virus and the disease
is yet to be confirmed.
Marco Salemi and Anne-Mieke Vandamme at the Rega Institute for
Medical Research in Leuven, Belgium, and William Hall at
University College Dublin in Ireland, say needle sharing has made
the virus epidemic among drug users. The virus is called HTLV-II.
The virus has been picked up in drug users in the US, Asia and
Europe, where between 5 and 10 per cent of users are infected. In
drug users, however, this rate is 300 times faster.
In
the works: A deadly disease may be evolving in the veins of
junkies, New Scientist, Matt Walker,
13 November 1999, Source: Proceedings of the National Academy
of Sciences (vol 96, p 13 253)
-
We are used to recognizing complex patterns in space with
our eyes and complex structures in time with our ears. There is
some evidence that dolphins can also "hear" complex patterns in
space with their sonar. With stereo- or quadrophony we are used to
get a vague idea about the spatial locations of soendsources. A
new level of realism in reconstructing complex three dimensional
acoustic images has been achieved by simultaneous recording from
several "pickup" points of an instrumunt followed by massive
digital sound processing. The results apparently are convincing:
"And when it comes to reproducing the three-dimensional aspects
of a string quartet, the complexity of the sound pattern radiated
by just a single violin shows what the physicists were up
against.
Studies by Dr. Gabriel Weinreich of the University of Michigan,
have revealed that at sound frequencies below about 850 hertz, or
oscillations per second, roughly a G sharp an octave and a half
above middle C, a violin radiates its sound almost uniformly in
all directions. But above that point, with higher frequencies and
thus higher notes, the violin has what Weinreich calls directional
tonal color, meaning that the instrument emits sound louder in
some directions and softer in others, with patterns that are
different at nearly every frequency.
"All of that is folded into what we call the violin sound,"
Weinreich said.
Such complexities in each of the individual instruments meld
together in a way that depends on how they are arranged on the
floor or stage, creating the dynamic, three-dimensional, acoustic
presence of a string quartet. "
A
New Dimension in Recorded Music, New
York Times, James Glanz, November 16, 1999
Humpback Whale Songs and the Environment, Nature, P. Ball
Humpback whale songs are among the most complex, evolving
sound patterns that animals (or most humans) produce. They are up
to half an hour long, are shared by every singer living in the
same ocean and they slowly change over years like the charts of
human pop music. It is still not completely clear why humpback
whales sing at all. Apparently not to attract females: According
to research of Louis Herman's group in Hawaii "singers" are
typically much smaller than "escorts", males that most likely mate
with females. On could therefore talk of these whale songs as
"humpback whale blues".
The work by Mercado and Frazer seems to confirm the idea that
the singers are not necessarily interested in a large audience.
They calculated "how different frequencies propagate in the waters
off Hawaii. They find that because of the complexities of sound
reflection and distortion, lower frequencies actually travel worse
than higher ones. So, they say, "humpback whales should produce
higher frequencies rather than lower frequencies if they want
their sounds to go farther".
But is this really what the whales want? The researchers found
that the best frequencies for long-ranged propagation are not the
ones actually produced by the whales, which seem to prefer singing
rather lower than this. Yet the mammals are clearly capable of
singing at this ‘optimal’ pitch -- so why don’t
they?"
Sounding
out the science of whale song, Nature,
Science update, Philip Ball
