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Scientific bulletin n° 327 - September 2009
ew Caledonia is
considered as a priority
zone of global significance
for preservation of
biodiversity, owing to
the richness of its flora,
exceptional in character
but threatened. With the
aim of achieving better
understanding of the
evolution of this flora, a
phylogenetic study was
conducted on one of New
Caledonia’s emblematic
plant families1, the
Cunoniaceae, particularly
well adapted to miningaffected soils.
DNA sequencing of
species of the endemic
genus1 Codia enabled
IRD researchers and their
partners2 to show that
more than half of the 13
species of the genus could
be interspecific hybrids.
Some of them possess
new morphological
characteristics,
absent from the parent
species, a finding which
emphasizes the crucial
role of hybridization in the
diversification of these
plants.
At a time when the Earth’s
biodiversity is going
through a sixth great
extinction, it is important
to conserve the processes
which lead to the formation
of new species. In New
Caledonia, this involves
the preservation of such
situations as contact zones
between different soil
types, where ecologically
different species might
co-occur and hybridize.
© IRD
N
Conservation of the natural evolutionary process:
a vital factor for New Caledonian biodiversity
Spider diagram adapted to show the complex evolution of the genus Codia (Cunoniaceae),
endemic to New Caledonia, involving hybridization events.
Upper left: C. discolor, Upper right: C. jaffrei, lower left: C. triverticillata, lower right.: C. incrassata
The New Caledonia archipelago is considered as a biodiversity hotspot owing to
the richness and exceptional character of
its fauna and flora, both in its terrestrial and
marine environments. Its terrestrial flora
amounts to at least 3 300 species with 75 %
endemism, meaning the presence of
organisms found nowhere else in the world,
including five endemic flowering plant families1. This group of islands harbours representatives of numerous ancient lineages,
like Amborella, and 13 out of 19 species
of Araucaria (column pines), a lineage of
conifers abundant during the Mesozoic era,
between 251 and 65.5 millions years B.P.,
the age of the dinosaurs. This diversity is
now affected by a range of threats: invasive
species, habitat destruction by fire, mining
activities (for nickel), global warming, and
also urbanization. Now only an estimated
28 % of New Caledonian territory is covered
by primary vegetation.
To design an effective conservation plan, it
is necessary to understand how the plant
groups diversified in the course of evolution.
An essential step is to integrate several
different elements such as vegetation
types3, diversity of pollinators or soil types.
Such parameters can be studied by using
phylogenetic trees, retracing parental
relationships between the species. Few
studies are available for New Caledonia,
unlike flora from other geographical areas
such as Hawaii or South Africa.
Cunoniaceae, an emblematic family of
New Caledonia
The Cunoniaceae family gathers together
about 300 species of trees and shrubs,
divided among 26 genera1, the bulk of
them located in the Southern Hemisphere.
In New Caledonia, this family is particularly
richly represented with 88 species (including
Geissois racemosa, the faux-tamanou,
and Pancheria brunhesii, known as chêne
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F-13572 Marseille Cedex 02 - France - www.ird.fr
You can find IRD photos concerning this bulletin, copyright free for press,
on www.ird.fr/indigo
CONTACTS:
Yohan PILLON
Former PhD student at the IRD
[email protected]
Jérôme MUNZINGER
Researcher at the IRD
[email protected]
Laboratoire de Botanique
UMR 123 AMAP
Address:
Centre IRD de Noumea
BP A5 – 98848 Noumea cedex
New Caledonia
REFERENCES:
Pillon Y.,Munzinger J., Amir H.,
Hopkins H.C.F., Chase M.W.
Reticulate evolution on a
mosaic of soils: diversification
of the New Caledonian endemic
genus Codia (Cunoniaceae).
Molecular Ecology 18 (10),
p. 2263–2275, 2009
doi:10.1111/j.1365-294X.2009.04178.x
Pillon Y., Hopkins H.C.F., Bradford, J.C. Two new species of
Cunonia (Cunoniaceae) from
New Caledonia. Kew bulletin
63, p. 419–431, 2008
KEY WORDS:
Cunoniaceae, New Caledonia,
biodiversity, hybridization
rouge), all endemic, divided into seven
genera including three endemic ones. The
Cunoniaceae live in various types of habitat
on the islands and are especially diversified
on ultramafic soils, which are rich in iron
and magnesium minerals (mining-affected
terrain), otherwise scarcely favourable for
plant development, owing to the presence
of heavy metals (nickel), a high magnesium/
calcium ratio and low availability of water.
Importance of hybridization in Cunoniaceae diversification
A study of the molecular phylogeny was
conducted on Codia, an endemic genus,
by IRD researchers and their partners2.
The scientists sequenced4 three nuclear
genes for each of the 13 species of the genus.
More than half of them appear to be the
result of natural hybridizations between
what are considered as parental species
(C. jaffrei, C. nitida, C. incrassata, C. ferruginea). Interspecific hybridization can be
a speciation process, meaning it can
generate new species. Two plants of hybrid
origin have whorled leaves (three leaves
arranged around each node) whereas all
the parental species have opposite leaves
(two leaves per node). The Codia resulting
from hybridization can therefore show
characteristics the parent species do not
have, known as transgressive phenotypes,
a sign of the importance of hybridization in
morphological diversification of plants.
Conserving evolutionary processes like
natural hybridization
Preservation of the biodiversity, particularly that represented by the appearance
of new species which will replace those
set to disappear during the current crisis,
requires conservation of the processes that
favour speciation. In 2008, an IRD scientists and his research partners5 described
a new species of Cunoniaceae, Cunonia
koghicola, discovered on Mount Koghis,
the mountain ridges closest to Noumea.
The morphology of this species suggests a
hybrid origin. The probable parent species
would be Cunonia balansae, a single-leaved
species adapted to mining-affected terrain,
and Cunonia austrocaledonica, a tree with
composite leaves which develops on land
untouched by mining. The Mont Koghis
Forest covers a geological complex zone
where different soil types form a mosaic with
a great diversity of vegetation types: mining
maquis, niaouli savannah (composed of
broad-leaved paper bark, a tree present in
New Caledonia and Australia), rainforest
on peridotite, serpentine and sedimentary
rock formations. Such interfaces provide the
opportunity for plants with different ecological
requirements to co-exist and hybridize, and
should be conserved for their role as a cradle
of biodiversity.
Mina Vilayleck - DIC
Translation - Nicholas FLAY
1. The classification of living organisms is determined
according to successive levels of hierarchy: a species
belongs to a genus which itself is a member of a
family.
2. This research work was conducted jointly with
researchers of the University of New Caledonia,
Noumea and the Royal Botanic Gardens at Kew in
the United Kingdom.
3. A vegetation type denotes a community of plants
which manifest a characteristic physical configuration
and determines a particular landscape.
4. Sequencing consists of determining the order of
DNA nucleotides making up genes.
5.T his study was conducted in partnership with
researchers of the Renewable Energy Development
Institute at Willits in the USA and the Royal Botanic
Gardens at Kew in the United Kingdom.
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Cunonia koghicola, a species discovered on the
Mount Koghis range and described in 2008.
© IRD / Yohan Pillon
© IRD / Yohan Pillon
Scientific bulletin n° 327 - September 2009
For further information
Mount Koghis and its ridges, viewed form Noumea.
These uplands have a mosaic of soil types favourable for
hybridization between plant species.
Gaëlle Courcoux, coordinatrice
Délégation à l’information et à la communication
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