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Résumé :
Les Rhinolophidae sont des chauve-souris de l’Ancien Monde
qui ont connu une radiation rapide voici 5 millions d’années.
Dans cet article, Togga Kingston et Stephen J. Rossiter étudient
le système d’écholocation de certaines populations
(Rinolophus philippinensis) et montre que celui-ci a connu des modifications
génétiques récentes. Or, ce système
très particulier de gestion des ultrasons sert à la
fois à repérer les insectes et à communiquer.
Le changement dans la quête des ressources et l’appariement
assorti (assortative mating) impliqué par la nouveau mode
de communication ont pu conduire à des spéciations
au cours de l’évolution.
Abstract :
Evolutionary divergence between species is facilitated by ecological
shifts, and divergence is particularly rapid when such shifts also
promote assortative mating. Horseshoe bats are a diverse Old World
family (Rhinolophidae) that have undergone a rapid radiation in
the past 5 million years. These insectivorous bats use a predominantly
pure-tone echolocation call matched to an auditory fovea (an over-representation
of the pure-tone frequency in the cochlea and inferior colliculus)
to detect the minute changes in echo amplitude and frequency generated
when an insect flutters its wings. The emitted signal is the accentuated
second harmonic of a series in which the fundamental and remaining
harmonics are filtered out. Here we show that three distinct, sympatric
size morphs of the large-eared horseshoe bat (Rhinolophus philippinensis)
echolocate at different harmonics of the same fundamental frequency.
These morphs have undergone recent genetic divergence, and this
process has occurred in parallel more than once. We suggest that
switching harmonics creates a discontinuity in the bats' perception
of available prey that can initiate disruptive selection. Moreover,
because call frequency in horseshoe bats has a dual function in
resource acquisition and communication, ecological selection on
frequency might lead to assortative mating and ultimately reproductive
isolation and speciation, regardless of external barriers to gene
flow.
© Nature
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Commentaire Eurekalert (www.eurekalert.org)
Changes to insect-seeking
calls of horseshoe bats may drive new species formation
(Boston) -- It may not matter whether there is a mountain high
enough or a river wide enough to keep members of a species apart.
New species may diverge and form because of something as fundamental
as a call to dine.
According to new research by Tigga Kingston, a research associate
in the Department of Geography at Boston University, and Stephen
Rossiter, a National Environment Research Council research fellow
in the School of Biological Sciences at Queen Mary, University of
London, geographical barriers may not be necessary for speciation.
In their study of one species of bat in Southeast Asia, the scientists
found that the bats were diverging into exclusive groups primarily
because of acoustic differences in the calls they make to locate
the insects they eat.
Their finding challenges long-standing theory that geographical
barriers are the mechanism by which new species evolve. This new
perspective on an old controversy appears in the June 10 issue of
Nature.
For centuries, theorists have debated how new species form. Traditional
thought holds that speciation occurs over long periods of time as
a result of interbreeding among members of a group that are, for
one reason or another, isolated from other members of the same population.
If, for example, geologic activity changed an area so that mountains
rose and split a region populated by a species of bat, the bat populations
on either side of a mountain would no longer be able to breed together.
Their genetic information, including changes that lead to physical
or behavioral adaptations to the demands of their environments,
would no longer be pooled. Future generations of bats found on one
side of the mountain would.
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