Download Present-day species of piranhas result from a marine incursion into

Sheet n°279 - November 2007
he factors that lead to
the appearance of new
species are still insufficiently
understood for a great many
animals. However, it is easier
to trace back the evolutionary history of those whose
biogeographical distribution
is well known. This is the
case for piranhas for which
the whole range of species
is endemic to South America.
Combining the results of phylogenetic analysis, elaborated
using mitochondrial DNA of
piranhas, with existing data
about successive geological upheavals that affected
ecosystems in the course of
the past 15 million years, a
research team involving IRD
scientists (1) has acquired a
better understanding of the
evolutionary history of this
sub-family of fish. About 4
million years B.P., rise in sea
level appears to have brought
about the isolation of small
populations of piranhas in the
upper reaches of the great
rivers. This situation favoured
speciation and hence the formation of the present species.
Such populations would then
have descended to colonize
the lowland waters of these
rivers following the regression of the Atlantic Ocean.
This hypothesis for colonization and diversification
comes in opposition to the
hitherto prevailing theory and
moreover suggests a younger age for current species
of piranhas than previously
thought.
© Adrien Leroy
T
Present-day species of piranhas result from
a marine incursion into the Amazon Basin
Serrasalmus hastatus from Rio Negro, Amazon Basin.
Piranhas inhabit exclusively the fresh
waters of South America. Their geographical distribution extends from the Orinoco
River basin (Venezuela) to the North, down
to that of the Paraná (Argentina) to the South.
Over this whole area, which also embraces
the entire Amazon Basin, biologists have
recorded 28 carnivorous species of these
fish. In spite of the evolutionary success of
this subfamily of fish, the mechanisms that
generated the species richness of this group
are still insufficiently known. A team from the
IRD, working in partnership with Bolivian and
Peruvian scientists, aimed to establish how
these species were able to evolve over the
past 15 million years. They consequently
took samples from around their whole distribution range. Between September 2002 and
June 2003, numerous specimens of piranhas
were collected from the Bolivian part of the
Amazon. Complementary sampling was then
conducted in the Brazilian and Peruvian
sectors, from the Orinoco in Venezuela, and
the São Francisco and the Paraná-Paraguay
in Brazil. The team selected 57 specimens
representative of 21 different species of
piranhas, from 15 collection points distributed
over the whole South-American hydrographic
network,.
Mitochondrial DNA (mtDNA) of piranhas has
a particularly high mutation rate and thus
could be used as a molecular basis for
reconstructing the evolution of the presentday species which are different yet very
close to one another. These techniques using
mtDNA sequences led to the conclusion that
the origin of the piranha species inhabiting
the rivers of South America today dates back
to some ancestor at only a few million years
B.P. Yet dating from fossils, whose morpho-
Institut de recherche pour le développement - 213, rue La Fayette - F-75480 Paris cedex 10 - France - www.ird.fr
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CONTACTS
Nicolas HUBERT,
Laboratoire d’Ecologie
Marine (ECOMAR)
Address: Université de la
Réunion, 15 avenue René
Cassin, BP 7151, 97715
Saint Denis Messag,
Cedex 9, France.
Tel : +33 (0) 2 62 93 80 80
Email : nicolas.hubert@
univ-reunion.fr
Jean-François RENNO
Research Unit
‘Caractérisation et valorisation de la diversité
ichtyologique pour une
aquaculture raisonnée
(CAVIAR)’
Address : IRD Peru,
Casilla 18-1209, Lima 18,
Peru
Tel: (51) (1) 441 32 23
Email: [email protected]
IRD PRESS CONTACT :
Gaëlle COURCOUX
+33 (0)1 48 03 75 19
[email protected]
INDIGO, IRD PHOTO
LIBRARY :
+33 (0)1 48 03 78 99
[email protected]
www.ird.fr/indigo
REFERENCES :
HUBERT Nicolas (2005)
Evolution de l'ichtyofaune en Amérique du
South: biogéographie
des characiformes et
phylogéographie des
piranhas Serrasalmus
Lacepède, 1803 et
Pygocentrus Müller et
Troschel, 1844. Doctoral
thesis, Muséum National
d'Histoire Naturelle, Paris.
HUBERT Nicolas,
DUPONCHELLE Fabrice,
NUNEZ Jesus, GARCIA
DAVILA C., PAUGY Didier,
RENNO Jean-François.
Phylogeography of
the piranha genera
Serrasalmus and
Pygocentrus : implications for the diversification of the Neotropical
ichthyofauna, Molecular
Ecology, 2007, 16 (10), p.
2115-2136. doi:10.1111/
j.1365-294X.2007.03267.x
KEY-WORDS : piranhas,
Amazon Basin, phylogeny
logies are strikingly similar to those of presentday piranhas, strongly suggests that this fish
subfamily already existed in South America’s
hydrographic system 25 million years ago.
The modern species must therefore stem from
a recent diversification. Further investigation
involving the construction of a phylogenetic
tree by categorizing the study’s 21 species
allowed phylogenetic relationships between
each of them to be established in order to test
alternative hypotheses for the diversification
that occurred over time. Examination of these
data alongside geological-scale changes that
have affected aquatic ecosystems with time
brought out evidence that marine incursions
played a fundamental role in the appearance
then the distribution of piranha species. Five
million years ago, the Atlantic Ocean advanced,
its waters finding their way far onto the Amazon
flood plain. The saline water invaded the
lowland expanse of the great river and penetrated its tributaries situated below 100 metres of
altitude, provoking the disappearance of many
species of freshwater fish. Some of these would
nevertheless have succeeded in finding refuge
at high altitude, in particular in rivers that flowed
on the Guianan and Brazilian shields. DNA analysis confirmed this hypothesis and showed that
the piranha populations present in the Amazon
flood plain but situated 100 metres above sealevel have been in existence for no more than
3 million years. Hitherto, certain specialists had
suggested that the present-day piranha species
had arisen in the lower sections of the great
rivers of South America. The scientists thought
that from centres of speciation, piranhas would
subsequently have dispersed to colonize the
more upstream reaches of the river system.
However, the results of the study give sustenance to another scenario. According to that
new hypothesis, during the marine incursion
phase some piranha populations would have
survived in the upstream parts of the network.
Such populations would have differentiated
into species–following the fragmentation of
their zone of distribution, but probably also in
response to ecological constraints specific to
the basin where they were kept in isolation from
each other. Once the ocean had regressed
again, 3 million years ago, these piranhas could
finally have dispersed downstream, finding their
way back to the Amazon’s lowland plain which
would have served as a gathering ground for
biodiversity. What now remains to be found
are the ecological parameters that could have
favoured the diversification of piranha populations so confined to the upper reaches of the
river network. One of the hypotheses advanced
highlights water quality as a factor in stimulating
ecological and morphological differentiation of
species. The field survey observations indicated
that some of the species were highly localized,
in both geographical and ecological terms. For
example, Serrasalmus hollandi is mostly found
in turbid, sediment-laden waters flowing down
from Andean mountain streams. In contrast, a
new species the biologists discovered, lives in
the same hydrographic basin but only in rivers
with crystal-clear waters bearing very little sediment content. However, water quality cannot be
considered as the sole factor behind speciation,
seeing that a third piranha species was found
living in either of these two categories of river.
The research results as a whole suggest that
the superimposition of factors linked to geographical history and ecological conditions,
intervening at different spatial and temporal
scales, is responsible for the diversification
of the piranhas. This is an evolutionary progression which should be transposable to other
fish communities inhabiting South American
waters.
Grégory Fléchet - DIC
Translation : Nicholas Flay
(1)
These
investigations
were
conducted
jointly with Institute of Molecular Biology and
Biotechnology, University Mayor San Andrés, La
Paz (UMSA - Bolivia), the Institute of Research
on the Peruvian Amazon (IIAP - Peru) and the
Laboratoire Génome, Populations, Interactions,
Adaptation (GPIA) in Montpellier.
©Nicolas Hubert
Sheet n°279 - November 2007
For further information
Plot on a map of South America of the limits of the
marine incursion (green dashed line) and piranhas’
potential refuge areas (red lines).
Grégory Fléchet, coordinator
Délégation à l’information et à la communication
Tél. : +33(0)1 48 03 76 07 - fax : +33(0)1 40 36 24 55 - [email protected]