World Congress of Malacology Antwerp ... - Unitas Malacologica

Ecological character displacement among endemic Baikal gastropods
Sitnikova, Tatiana Ya 1 ; Köhler, Frank 2 ; Riedel, Frank 3
1. Limnological Institute SD RAS, Ulan-Batorskaya 3, Irkutsk, 664033, Russia,
Email: sit@lin.irk.ru
2. Museum für Naturkunde, Humboldt-Universität, Invalidenstr. 43, 10115 Berlin, Germany,
Email: Frank.Koehler@museum.hu-berlin.de
3. Freie Universität Berlin, Interdisciplinary Centre for Ecosystem Dynamics, Malteserstr., 74-100,
Haus D, 12249 Berlin, Germany,
Email: paleobio@zedat.fu-berlin.de
Parabaikalia oviformis (Caenogastropoda: Rissooidea: Baicaliidae) represents a widely distributed
endemic species living on sandy substrates within the cold water zones of the Lake Baikal littoral. It
must be assumed that the deep basins of Lake Baikal represent a barrier in respect of direct gene flow
between populations living on opposite sides of the lake. In some parts of the lake P. oviformis
coexists with the closely related species P. florii. In order to evaluate the influence of competition on
the morphology of these two species, shell variability and female reproductive systems have been
investigated in 220 specimens of P. oviformis and in 83 specimens of P. florii. The comparative
analysis of individuals from the southwestern littoral revealed that the morphologies of the
reproductive systems of the two species are very similar. There are, however, significant differences
in size (shell and soft parts), that of P. florii being 1.5-2 times larger compared to P. oviformis. These
size differences appear to reflect the main reproductive isolation between the two species.
Competition for food resources is limited by a different depth distribution, most individuals of P.
oviformis dwelling in shallower water than P. florii. On the other hand, individuals of P. oviformis
living along the eastern littoral of central Baikal, where P. florii does not compete, are much larger
compared to the southwestern population and here reach the size of P. florii. We therefore assume the
existence of an ecological character displacement between these species, according to the
phenomenon that closely related species develop size differences where they occur jointly while
these differences do not occur between populations which are spatially clearly separated. This study
was carried out within the State Program N 7.9.1.3 and supported by SB RAS project N 11.14
(“Biodiversity…”), RFBR project N 05-04-97258 and by the Deutsche Forschungsgemeinschaft.
Diversity of terrestrial snails in Papua New Guinea: Have we only scratched the surface?
Slapcinsky, John
University of Florida, Department of Zoology and Florida Museum of Natural History,
P.O. 117800, Gainesville, Florida, USA,
Email: slapcin@flmnh.ufl.edu
Tropical forests harbor the richest terrestrial faunas on the planet. Until recently, however, land snails
were thought by some to be more diverse in temperate habitats. It is now becoming apparent that
tropical snails are relatively poorly sampled and far more diverse than previously reported. Recent
surveys (2002-2005) of terrestrial snails in Papua New Guinea have uncovered a rich land snail fauna
with many narrow range endemics that may reflect the country's complex geological history and
numerous isolated mountains and islands. In fact, over 75% of the approximately 100 species from
the three largest islands in the Louisiade Archipelago are endemic to single islands and nearly half of
these taxa are undescribed. Similarly, species from mountains, many created by the accretion of
offshore island terranes onto mainland New Guinea also display high levels of endemism. The fauna
of higher elevations is especially poorly known and in many places entirely endemic and
undescribed. Small to moderately sized species of Charopidae, Rhytididae, and Helicarionidae are
especially poorly sampled. Each of these families contains large radiations with many new species.
For example, only 14 species of the endemic charopid genus Paryphantopsis were known before
these surveys, which uncovered an additional 15 species, all of which appear to be endemic to single
mountain chains or islands. Slug species are also poorly sampled especially the rathousiid slug genus
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