CONTENT - International Society of Zoological Sciences

ICZ2008 – Abstracts S2
Connectivity and speciation processes in an oceanic
seamounts system: comparative phylogeography of
Gastropods with contrasting reproductive strategies
Magalie Castelin 1 , Philippe Bouchet², Marie-Catherine Boisselier 1
and Sarah Samadi 1
1 Department of Systematic and Evolution, The Natural History
Museum, Paris 43 rue Cuvier 75005, France;
2 Department of Systematic and Evolution, The Natural History
Museum, Paris 55 rue Cuvier 75005, France;
Species distribution and speciation processes in the deep-sea
remain largely unknown. It has been suggested that seamounts,
which vary greatly in their faunal assemblage and display many
original species, may be center of speciation. Their spatial
distribution represents a fragmented habitat, which may locally
increase speciation rate by breaking up species in small isolated
populations. Another viewpoint suggests that seamounts, which are
highly productive oases, receive large trophic input that allow
abundance of species and multiplication of ecological niches. As
such, seamounts could serve as suitable place for parapatric
speciation by accommodating species to colonize new ecological
niche. The phylogeographic survey of seven Gastropods species
with contrasted reproductive strategies from seamounts near New
Caledonia reveals patterns supporting either allopatric or parapatric
speciation models. Allopatric diversification pattern is found for
organisms with low dispersal abilities, whereas parapatric pattern is
observed for a couple of species with high dispersal abilities. In this
last case the two species have distinct bathymetric distribution.
The geography of speciation
Jerry Coyne
CNRS, Avenue de la Terrasse, 91198, Gif-sur-Yvette, France
One of the most contentious areas of speciation is its biogeography:
do populations usually need to be geographically isolated to become
new species, or can those species form in the presence of some
gene flow. In this talk I review the theory and data bearing on the
likelihood of parapatric and sympatric speciation in nature,
concentrating on work that has been done in the last five years.
Ecological adaptation retraced by molecular changes in
Odorant Binding Proteins (OBP) in the Drosophila simulans
complex
Jean-Luc Da Lage 1 , Delphine Legrand 1 , Takashi Matsuo 2 and Marie-
Louise Cariou 1
1
LEGS, CNRS, avenue de la Terrasse, bâtiment 13, 91198, Gif-sur-
Yvette, France
2
Department of biological sciences, Tokyo Metropolitan University,
Tokyo, Japan
Adaptation to an exclusive food resource provides an evolutionary
advantage and may lead to reproductive isolation. Among the closely
related species of the simulans complex, Drosophila simulans and D.
mauritiana are generalist while D. sechellia evolved as a strictly
specialized species on the toxic ripe fruit of Morinda citrifolia
(Rubiaceae). The OBP family plays a major role in odor recognition,
and the Obp57d/e region is clearly involved in the attraction of D.
sechellia to its host plant. We thus performed a population genetics
analysis to detect selection signature in the three species. Selection
was found in D. sechellia and, unexpectedly, in D. mauritiana, but
not in D. simulans. In addition, tissue-specific expression patterns of
the two genes Obp57d and Obp57e were investigated and compared
among species in the presence or absence of the toxic resource.
Linking fine scale molecular analysis with biological traits, this study
provides an interesting insight in the comprehension of the
mechanism of adaptation.
S2 - Mechanisms of speciation
- 11 -
The relative importance of habitat choice and assortative mating
during rapid ecological divergence
Fabrice Eroukhmanoff 1 , Sébastien Guéchot 2 , Anders Hargeby 3 and
Erik I. Svensson 1
1
Section for Animal Ecology, Ecology Building, Lund University, SE-
223 62 Lund, Sweden
2
Sup Agro, 2 Place Pierre Viala, 34060 Montpellier, France
3
Division of Biology, Linköping University, 581 83 Linköping,
Sweden
The question of when and how diverging populations start restraining
gene flow is critical to the understanding of the origin of species
(Schluter 2000, Rundle et al. 2000). Assortative mating might
emerge early on during divergence, but under intense selection,
migration modifications are favored and will lead to rapid speciation
(Yukilevich & True 2006). If habitat choice is strong enough between
populations inhabiting different environments, this will lead to
allopatric speciation. Reproductive isolation might then emerge
secondarily through reinforcement (Yukilevich & True 2006). These
two types of barriers to gene flow can interfere with each other if they
evolve jointly and it is quite uncertain how well gene flow is limited
under this scenario. We studied two ecotypes of a freshwater isopod
(Asellus aquaticus), which started to diverge in parallel in two lakes
of southern Sweden twenty years ago (Hargeby et al. 2004). We
report that populations from different ecotypes are sexually isolated
but not populations from similar ecotypes, regardless of whether they
originate from the same or different lakes. In addition, we provide
evidence that habitat isolation between ecotypes has also evolved in
at least one lake, and now constitutes the main barrier to gene flow
between ecotypes. In conclusion, the early and simultaneous
emergence of sexual and habitat isolation has efficiently restrained
gene flow during this rapid divergence event. However, our study
reveals that rather than assortative mating (Nosil et al. 2002), habitat
choice could play an acute role in the early stages of ecological
speciation.
Feeding habit causes divergence of skull shape in bats
Allowen Evin 1,2 1, 2
and Michel Baylac
1
MNHN – CP 50, Origine, Structure et Evolution de la Biodiversité,
45 rue Buffon, 75005 Paris, France
2
Plate-Forme de morphométrie, IFR 101, MNHN – CP 50, 45 rue
Buffon, 75005 Paris, France
Within the bat species complex of Myotis myotis, M. blythii and M.
punicus, studies using 3D geometric morphometrics have shown that
skull evolution does not match molecular phylogeny (Evin et al. 2007;
2008). Since some of the observed patterns of skull evolution implied
different regions of the skull that are potentially linked with feeding,
we hypothesized that this divergence, between phylogeny and
phenotypic similitude, could result from functional convergences.
To test this hypothesis we investigate the patterns of skull variation
within and between taxa. Most cases reveal that the patterns of
species evolution closely follow within-species patterns of variability,
i.e. the least-resistance lines of evolution as defined by Schluter
(1996). The single exception is that of M. blythii whose patterns of
differenciation diverged, implying skull parts that are involved in
mastication process. A closer examination of the within and between
patterns of skull differenciation using Marroig & Cheverud's test
(2004) for selection and drift indicates that some components of skull
shape variation are compatible with selection. These components
correspond to the separation of M. blythii from the rest of the
complex and they deal with skull parts specifically involved in
mastication. Finally, we used a partial-least squares approach to
analyze the covariation between skull variation and feeding habits.
Once the effect of diet removed, the residual shapes match closely
the phylogenetic relationships.
All investigations therefore are congruent with a divergence of M.
blythii by diversifying selective pressures related to feeding habits.