Le journal de l'IRD
n° 60 june-july-august 2011
Translator: Nicholas Flay
Abstracts for the international issue
p. 1, 8 and 9 News
p. 4 Partners
Interview
The good combination…
Excerpt from an interview with Hania Zlotnik, Head of the
Population Division of the United Nations Department of
Economic and Social Affairs. Her unit has just published a report
on the different predictions for world population growth in the
XXIst Century.
F
p. 2 News
Apomixis
Fishing for sand
in the River Niger
M
assive extraction of
sand and gravel from
the bottom of the River Niger
is cutting the river bed upstream by several centimetres
every year. Little has been
known about this phenomenon but researchers have
recently gained insights into the problem. The severe disturbance caused is having
serious impacts on agriculture, fishing and access to water.
he International Conference on
Preventive Archaeology in Cameroon (Yaoundé, 24 to 26 May 2011)
presented substantial proof of the
benefits of prevention work. This
approach takes advantage of excavation conducted for development projects and gives specialists the opportunity to intervene before any damage is done to
important heritage sites. About 600 sites have been discovered and thousands of objects
collected, which will help reconstruct Cameroon’s long history. For 10 years an IRD researcher, with his colleagues from the Universities of Ngaoundéré and Yaoundé, has been
investigating the country’s subsoil with the aim of saving traces of the past, just as precious as the minerals of Africa coveted the world over. The review of their work, published in 2010, gives clear insights on the period stretching over the past 50 000 years.
p. 7 Research
Biodiversity in the páramos
f you ask the people of Quito, the capital of Ecuador, what the páramos mean
to them, there is a high chance that one
word comes back constantly in their
replies: “agua”, “water”. Páramo is a
grassland ecosystem, perched at between
4000 and 5000 m altitude, and indeed it
plays a fundamental role in storing water from rainfall and glaciers and regulating
downstream water flow. Throughout the tropical Andes in fact, a substantial part of
the water supply for crop irrigation systems, urban areas and hydro-electric dams is
provided and regulated by the páramos. The plant and animal biodiversity of this environment is prominently involved in these hydrological mechanisms, through the contribution they make to the formation of favourable organic soils. This biodiversity is the
source of vital ecosystem services and is at the centre of attention of scientists, who
are seeking to assess the already noticeable impact of climate change on its fragile
equilibrium.
p. 3 News
p. 10 Research
Crossing Asian and African rice
to feed the planet
Infections as origins
for cancer
A
R
team of biologists is seeking to increase
yields of Asian rice by taking advantage of
genes from African rice. A recent study published in the journal PLoS One presents clues
towards this objective. To achieve it, the scientists must overcome an obstacle.
Although the two cultivated rice species originate from the same Asian parent, a reproductive
barrier emerged between them in the course of
their evolution. Crossing the Asian Oryza sativa
with the African Oryza glaberrima is still possible, but that would give rise to a sterile plant, as its male gametes –the pollen
grains– are not viable. Similarly, in practically all cases the female gametes contained in the flower are rendered sterile. Yet on occasions such female cells are found
to be fertile. Why are these rare hybrid individuals fertile whereas the others
are not? A crucial question, for which the research team has recently found an
answer.
© IIRD / G. Jourdain
© IRD / J.-P Montoroi
T
I
p. 3 News
© IRD / L. Ferry
O
Archaeologists also do
prevention work
ecent statistics for the number of
cancer deaths in the developing
countries show the size of the issue. The
scale of the problem gives justification for
intensifying research effort. In this
situation the specific link between certain
viruses and certain cancers raises the opportunity to check the progress of these
diseases. Awareness of this came only relatively recently. In the early 1970s,
the number of cancers provoked by parasites or viruses was estimated at 1%.
The World Health Organization now considers that 20% of cancers are due to
infectious agents and all indications point to an increase in this figure in the
coming years. IRD research teams and their partners, equipped with the knowledge acquired of pathologies of the North and of the countries of the South, are
taking hold of the question. They draw for example on the methods developed
for Aids control, since cancers sometimes occur along with HIV infection and
that infection aggravates the risk of developing practically all the other types of
cancer.
p. 13 Worlds
Origins
of writing
W
ake up, Champollion! A dozen specialists
of graphic forms of predynastic Egypt
could bring into question two of the most common theories about the origin of writing. The proceedings of the symposium where they met some
months ago at Aix en Provence will undoubtedly
cause shockwaves as soon as they are published.
Contrary to what has been thought up to now,
Egypt does not owe its writing to Mesopotamia.
This upsets a common theory, resumed by a wellknown maxim Lux ex oriente, which states that
writing culture came out of Mesopotamia, then
spread to Egypt and the rest of the world. The
research team postulate that the two civilizations
invented the early forms of writing in parallel, with
little time between them and to serve comparable
economic and political purposes.
✆naturexpose.com / O. Dangles et Fr. Nowicki
© IRD / J.B erthaud
SAS: What part do the countries of the South play in the demographic dynamics
building up towards the end of the XXIst Century ?
Haina Zlotnik: The part played by the countries with high fertility, which are all in the
South and count among them all the least advanced countries, is prominent in the projections for the demographic growth to come. But you have to bear in mind that not all
the countries of the South are in this situation, far from it, and many of them already have
a birth rate below the threshold replacement rate.
States with high fertility, which amount to 58 and are at the crux of the global population
issue, share some common characteristics. They suffer or have recently suffered from poor
governance, cannot manage to develop really democratic structures and sometimes live
under high political instability. Many have gone through long drawn out conflicts or are
still confronted with them. Specialist experts put forward two main theories to explain the
high fertility these countries are experiencing. One of them assumes that, in such areas
where economic with persistent economic underdevelopment, a large number of children
per family is thought to be a kind of insurance for the parents’ old age. In the same way,
the multiplication of births in a household is seen as so many chances that one of the children will manage to do well and support the rest of the family. The other explanation,
more macro-economic, is that these countries, both poor and not very organized, do not
provide adequate services for health in general and family planning in particular.
p. 5 Partners
© IRD / R. Oslisly
The parasitic wasp Dinocampus coccinellae gives all the signs of being a
manipulator. It lay its eggs in its ladybird host’s abdomen and then uses it
as a food source for its larva. But it also
uses the beetle for guarding its cocoon. Although it is common in hymenoptera to use other insects for laying
their eggs, it is much less so for the larval development to leave the host
alive. Even less frequent for this host
then to be “manipulated” to serve as
a bodyguard. Once the D. coccinellae
larva reaches maturity, it emerges from
the ladybird to weave its cocoon between the beetle’s legs and stays there
until the wasp is formed.
© CIAT / D. Noguera
Sciences au Sud : What are the major trends that emerge from your report on the
future evolution of the world’s population?
Haina Zlotnik: First, we have to realize that currently there are highly contrasting situations depending on the country, with highly variable fertility rates. So, 42 % of people live
in countries which are no longer renewing their population, 40 % in countries where the
birth rate reaches or exceeds generation replacement level and only 18 % in countries
with high fertility. Birth rate may well not rise in the countries of the first two groups, and
therefore it is the demographic dynamics of the countries in the third group which will
determine future trends. We consider that a just a small variation in this index in the countries where it is highest, more or less around 0.5 children per woman, can have substantial effects on the world population in the long term. We have therefore proposed three
possible scenarios for the future, which by 2100 would lead to some very different situations. In the case of a continuous low fertility, world population would tend to decrease,
going from nearly 7 billion people at present to only 6 billion towards the end of the century. Following the high-level hypothesis, the world population would be heading towards
16 billion. Or if the intermediate scenario prevailed, at the end of the century there could
be 10 billion inhabitants on Earth. And these additional 3 billion, compared with the present population, would practically all come from the countries with high fertility.
Manipulating wasp
ver 400 wild species make their
young all by themselves: certain
plants produce seeds by cloning. In botanists’ jargon, this is apomixis, meaning
“without mixing”, without fertilization
or genetic recombination, and the
daughter plants become exact copies of
the mother plant. Transferring this rather
unusual method of asexual reproduction
to crop plants –most of which reproduce
sexually– would perpetuate the agriculturally advantageous genes. This is a
considerable challenge requiring a feat
of science and technology but research
scientists are now getting closer. They
recently demonstrated in a study published in the journal Cell that it would be
possible to make species such as maize
or wheat “apomictic” by stimulating the
embryo to undergo development totally
àodf maternal origin.
arming practices alternative to the intensive usage of fertilizers, particularly welcome for tropical soils often poor in organic
matter and nutritive mineral elements, are
proving their worth. An example is the incorporation of crushed wood charcoal (biochar)
in soil to imitate the highly fertile dark earths
created by Pre-Columbian peoples. Biochar is a highly stable material and persists in the
soil for many centuries. It gives the soil such advantages as improved cation exchange
capacity, organic matter retention and modified micro-organism communities. Another
helpful practice consists in keeping up high earthworm densities in cultivated soils.
These worms generally favour plant growth by their various actions. They bring in
nutrient elements, stimulate microbiological activity, control pathogenic agents,
liberate plant hormones, favour symbioses and increase soil porosity. The latter facilitates root development and increases soil oxygen availability, their effect best known
to farmers. However, this ecological engineering approach may not be compatible with
modern crop plant varieties, selected for maximum production under a regime of high
fertilizer input and in soils poor in fauna. This has been demonstrated by Columbian
and French scientists on five varieties of rice.
© IRD / G. Graff
© UN / E. Debebe
✆ CNRS IRD / M. Bélanger Morin
p. 1 News