World Congress of Malacology Antwerp ... - Unitas Malacologica

Global patterns of diversity and speciation in tropical marine mollusks
Williams, Suzanne; Reid, David
Natural History Museum, London SW7 5BD, UK,
Email: s.williams@nhm.ac.uk; d.reid@nhm.ac.uk
Today, the Indo-West Pacific (IWP) is the largest marine biogeographic province and the richest in
terms of species diversity, especially for shallow water marine invertebrates. The origin of this
diversity and the timing of its appearance are of particular interest because it has been suggested that
the tropics are the source of many evolutionary novelties and that they have provided a species pool,
from which temperate regions were populated.
Molecular phylogenies for the genus Turbo and for the subfamily Turbininae were used to assess the
consequences of temperature regime and tectonic events on the diversification of turban shell species,
with particular focus on the IWP. Both Bayesian and parsimony analyses of the subfamily recovered
five clades and suggested that temperate habitat is an ancestral character in at least four. Therefore, in
contrast to most fossil evidence for molluscs, the tropics are not acting as a source of genetic
diversity for temperate and polar regions. Instead it appears likely that the latitudinal gradient in this
group is best explained by higher rates of diversification in the tropics.
Phylogenetic analyses of the genus Turbo in combination with the fossil evidence suggest that
present day IWP is behaving as both a cradle of diversity (with new species originating in situ) and a
museum of diversity (with lineages that pre-date its isolation also being maintained). A period of
rapid diversification in the IWP was observed to begin approximately 24-25 Ma in both Turbo and
the tropical periwinkles, Echinolittorina, corresponding to the time period when Australia and New
Guinea collided with Southeast Asia. These tectonic events resulted in increased shallow water
habitat and a mosaic of different habitats able to support a large number of taxa within the small
central IWP area, resulting in what is commonly known as the ‘centre-of-diversity’.
Non-reciprocal hybridization against asymmetric introgression of mtDNA in Snails
Wiwegweaw, Amporn 1 ; Asami, Takahiro 2
1. Department of Biology, Shinshu University, Matsumoto 390-8621, Japan,
Email: ampornwiwegweaw@yahoo.com
2. Email: asami99@shinshu-u.ac.jp
Population surveys with molecular markers often reveal that introgression is ordinary between related
species. It leads to recent concerns of genetic pollution through hybridization with introduced aliens.
Non-reciprocal introgression of mtDNA has naively been thought to indicate the direction of
hybridization with no biological examination. Here we show that simple interpretation of
introgression detected by molecular markers misleads us to a wrong conclusion of non-reciprocal
hybridization. The terrestrial pulmonates Bradybaena pellucida (BP) and B. similaris (BS) can clearly
be distinguished only by penial surface structure. BP is endemic to western Japan, while BS from
overseas has been introduced to most lowlands. Our survey of mtDNA haplotypes in eastern Japan
has detected introgression significantly more frequently across collection sites of BP than of BS,
regardless of allopatry or sympatry. This pattern of introgression would normally be interpreted that
mtDNA leaks from BS to BP more often or easily than vice versa, with little doubt of hybrid
production by BS. On the contrary, we found that BS seldom produces hybrids, despite simultaneous
reciprocal copulation with BP. The latter instead produces hybrids with no breakdown. Then, another
ordinary interpretation is that BS leaks mtDNA by backcrossing with hybrids. We again, however,
found that BS copulates with a hybrid but does not reproduce, while the hybrid partner does. These
crossing experiments indicate that mtDNA leakage from BS to BP cannot be easier or frequent than
vice versa, against the ordinary interpretations. The frequent detection of introgression from BS to BP
could only be explained by carry-over of alien haplotypes by BP that has recently expanded
distribution, or by frequent dispersals of BS into BP populations. Out results exemplify that
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