World Congress of Malacology Antwerp ... - Unitas Malacologica

population to consist primarily of young individuals, the oldest specimens being completely absent.
This suggests that the population is at its developing stage.
Genetic variability in the Mediterranean interstitial gastropod Pontohedyle milaschewitchii
(Opisthobranchia, Acochlidiomorpha)
Werth, Sigrid M.; Steiner, Gerhard
University of Vienna, Faculty of life sciences, Center of Zoology, Department of Evolutionary
Biology, Molecular Phylogenetics, Althanstrasse 14, A-1090 Vienna, Austria,
Email: michiwerth@gmx.net; Gerhard.Steiner@univie.ac.at
Pontohedyle milaschewitchii Golikov & Starobogatov, 1972 is a widely distributed mesopsammic,
dioecious species with internal fertilization and direct development. The dispersal potential is,
therefore, low and considerable genetic differentiation among population to be expected. The present
study aims to investigate the genetic variability of this species and to test the genetic conductivity
between populations of different parts of the Mediterranean. Samples were collected from two
separate sites at Croatian (Northern Adriatic Sea) and Ligurian coast (North-west Italy). A fragment
about 1900 bp of the mitochondrial genome containing partial cytochrome c oxidase subunit 1,
tRNA-Val, and partial 16S rRNA genes is used as genetic marker. The results reveal high genetic
variability within P. milaschewitchii: all 29 haplotypes are unique. They cluster in six haplotype
groups: three are limited to the Italian coast, one is limited to the Croatian coast. Two haplotype
groups are present at both locations. This indicates limited gene flow between these geographically
widely separated populations. Additional sequences from these locations and further analyses will
help to increase our understanding of the genetic conductivity and population structure of
Pontohedyle milaschewitchii.
Molluscan radiations and extinctions in Miocene Amazonian long-lived lake Pebas
Wesselingh, Frank P.
Naturalis, P.O. Box 9517, 2300 RA, Leiden, The Netherlands,
Email: wesselingh@naturalis.nnm.nl
During the Miocene, spectacular diversifications of endemic mollusc and ostracod faunas occurred in
a huge (> 1 million km 2 ) long-lived complex of lakes and wetlands, known as the Pebas system, that
occupied most of present-day western Amazonia. The anatomy of the mollusc radiations and
extinctions are documented, based on an improved ecological and stratigraphic framework. The
Pebas fauna diversified from possibly one ancestral cochliopid gastropod species and two corbulid
species about 23 million years ago into a fauna of approximately 75 co-occurring endemic species
about 12 million years ago. Evolutionary innovations in cochliopid gastropods and corbulid bivalves
are documented and their significance is discussed. It is demonstrated that the mollusc were able to
expand into ecological niches where dysoxia, high predation pressure and unconsolidated bottoms
dominated. Episodic marine incursions did modify the diversity, but did not interrupt the continuity
of the fauna as a whole. The non-endemic components of the Pebas fauna have a Neotropical
signature. The Pebas fauna became largely extinct by the onset of the modern Amazon River system,
circa 8-10 million years ago. The Pebasian mollusc development provides an excellent example of
the documentation of evolution and its context in a long-lived lake.
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