CONTENT - International Society of Zoological Sciences

ICZ2008 – Abstracts S20
Chromosomal evolution in the Notothenia clade
(Acanthomorpha, Nototheniidae)
Catherine Ozouf-Costaz, Mélyne Hautecoeur 2 , Jean-Pierre
Coutanceau 1 , Céline Bonillo 1 , Laura Ghigliotti 3 , Agnès Dettai 1 , G.
Duhamel 2 and
Eva Pisano 3
1
CNRS-MNHN, UMR7138, Dpt Systématique et Evolution, Paris,
France
2
MNHN, UMR 5178 BOME, Dpt Milieux et Peuplements
Aquatiques, Paris, France
3
Universita di Genova, Dpt di Biologia, Genova, Italy
Antarctic fish suborder Notothenioidei (Acanthomorpha) exhibit a
high rate of endemicity and represent a well known model of
adaptive radiation in marine extreme environment. Within the
family Nototheniidae, the clade Notothenia includes Antarctic and
sub-Antarctic species, which display habitat ontogenic shifts
between larvae and juveniles (pelagic) and adults (that live in
shallow waters, and partly feed with algae). This phylum is clearly
separated from other nototheniid clades on the base of
morphological and molecular characters. It is characterized by
common traits in chromosome diploid numbers that are particularly
low (Notothenia coriiceps: 2n = 22; Notothenia rossii: 2n = 24;
Notothenia angustata: 2n = 26, Paranotothenia magellanica: 2n =
26, Paranotothenia microlepidota: 2n = 26), compared with the
most frequent diploid number occurring in notothenioid fishes (2 =
48). Their karyotypes are mainly composed of large metacentric
chromosomes arising from Robertsonian rearrangements. Only
one species, Notothenia (Indonotothenia) cyanobrancha, has 2n =
48 chromosomes and juveniles that become benthic at very early
stages. Its phylogenetic position is currently under revision with
several molecular markers. We present here a detailed analysis of
these species karyotypes, including location of 5S and 28S
ribosomal genes by FISH. Main chromosome characters have
been mapped onto the Notothenia cladogram, including extragroups
chosen among other nototheniid clades so that
chromosome changes and inter-relationships within this clade
could be re-discussed.
Natural and experimental sunken wood: analysis of
substrates and associated fauna
Marie Pailleret 1,2,3 , Nima Saedlou 3 , Catherine Privé-Gill 3 , Françoise
Gaill 1,2 and Magali Zbinden 1,2
1 Laboratoire « Systématique, évolution, adaptation », UMR 7138,
université Pierre et Marie Curie, bâtiment A, 4e étage, 7, quai
Saint-Bernard, 75252 Paris cedex 05, France ; 2 AMEX, UMR
7138, CNRS, Université Pierre et Marie Curie, IRD, MNHN, 4,
place Jussieu, 75252 Paris cedex 05, France ; 3 Laboratoire de
paléobotanique et paléoécologie, UMR 5143, MNHN, case postale
48, 57, rue Cuvier, 75231 Paris cedex 05, France
Samples of natural sunken wood collected near Vanuatu (>500 mdepth)
are identified based on histological observations in order to
know their diversity, to infer their geographical origin and to
appreciate their degradation state. Diversity of the associated
fauna is also studied. Investigation of eventual specific
associations between wood species and organisms constitute the
second step of the study. Preliminary results concern two wood
samples: they belong to two different families (Asteraceae or
Onagraceae for the first sample; Fabaceae for the second one);
they may have a local geographical origin as sample 1 may come
from Polynesia and sample 2 may be endemic from Vanuatu; no
degradation in their histological structure was observed. The two
selected samples showed completely different colonisation
patterns, which could be due to differences in chemical
composition, to a selection of wood by fauna or to time elapsed
since sinking. To bring comparative data, an in-situ experiment
was established off the Nouméa coast. Four species of wood and
three monocots were immersed at a depth of 900-1000 m during
20 months. The seven samples did not equally respond to the
immersion. One of them housed the most abundant and diversified
fauna, the other samples were mostly colonised by two taxa. Major
cell-wall degradation was also noticed on the densely colonised
sample.
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Bacterial symbioses in Nautiloids excretory organs: some
evolutionary and functional aspects
Mathieu Pernice 1 , Silke Wetzel 2 , Olivier Gros 3 , Gaute Lavick 2 ,
Renata Boucher-Rodoni 1 and Nicole Dubilier 2
1
UMR 5178 Biologie des Organismes Marins et Ecosystèmes,
Département Peuplements et Milieux Aquatiques, Muséum
National d’Histoire Naturelle, 55 rue Buffon, 75005 Paris, France
2
Max Planck Institute for Marine Microbiology, 28359 Bremen,
Germany
3
UMR 7138 Systématique, Adaptation, Evolution, Département de
Biologie, université des Antilles et de la Guyane B. P. 592, 97159
Pointe à Pitre Cedex, Guadeloupe, France
Symbiosis is an important driving force of metazoan evolution and
the study of symbiotic associations in ancient lineages might
provide further insight into the origin of several major adaptations.
In this respect, symbiotic associations concerning the excretory
organs of Nautilus (Cambrian origin: ca 500 mya), are of particular
interest. Indeed, conversely to what is known in others
cephalopods, in Nautilus most of the excretory processes (filtration,
reabsorption, secretion) are assumed by the highly specialized
pericardial appendages. In this study, we report that nautiluses
from various geographical areas (Nautilus macromphalus from
New Caledonia, and Nautilus pompilius from Philippines and from
Vanuatu) harbour a high density of betaproteobacteria and
spirochete phylotypes in their pericardial appendages. They were
characterized by using various molecular approaches (16S rRNA
phylogeny, CARD-FISH) and electron microscopy (TEM). This
dual symbiosis concerns the genus Nautilus as it is not related to
geographical origin of the specimens.
CARD-FISH analyses relate bacteria distribution to the functional
ultrastructure of the host organ, suggesting a symbiotic
contribution to the excretory metabolism. First analyses by using
ex-vivo incubations of the symbiotic complex in controlled medium
suggest a bacterial implication in nitrogen metabolism of the host.
Such symbiosis being rare among marine invertebrates, Nautilus
bacterial symbiosis provides a great opportunity to investigate the
influence of host-microbes interactions on a major physiological
adaptation during the course of marine invertebrates’ evolution.
Comparative phylogeography of deep-sea hydrothermal vent
species along the east pacific rise
Sophie Plouviez, Claire Daguin, Frédérique Viard, François Lallier
and Didier Jollivet
Equipe Ecophysiologie : Evolution et Adaptation Moléculaires,
Station Biologique, BP 74, 29680 Roscoff, France
Deep-sea hydrothermal vents are widely distributed along oceanic
ridges throughout the globe. Venting is caused by deep-sea water
infiltration into the oceanic basaltic crust where it is overheated
and charged of metallic elements. The hot uplifted fluid (around
350°C) is mixed to the cold and well-oxygenated bottom sea-water
and precipitated to form large sulfide edifices. Hydro! thermal vent
species are strictly associated with these sulfidic emissions as
their nutritional needs only rely on chemolithoautotrophic bacteria.
Deep-sea hydrothermal vent sites are highly fragmented and often
separated by hundreds of kilometres with a rapid and highly
variable turn-over both in time and space, which implies good
dispersal capacities in order to (re)colonize new habitats. Dispersal
is mainly restricted to the sea bottom layer along the ridge axis.
Consequently, breaks that offset ridge axis (like transform faults)
could disrupt gene flow and thus may promote genetic breaks,
geographic structure of populations and, ultimately speciation.
Here, we compared several phylogeographic patterns from
different gastropod and polychaete species in order to test the
possibility of vicariant processes and propose a global history of
colonisation of vent species along the East Pacific Rise (EPR).
First coalescence results using sequences of the Cytochrome
Oxydase I mit! ochondrial gene indicated low geographic structure
in nearly all studied species. Most networks displayed a star-like
structure of same age, suggesting a recent demographic
expansion. Breaks to gene flow are detected at different latitudes
and often shared between groups of species and could be
attributed to putative vicariant events.