Evolutionary, biogeographic, and population genetic relationships of dreissenid mussels, with revision of component taxa

The identification of taxa and discernment of evolutionary relationships within the family Dreissenidae have been confounded by morphological plasticity as well as prior lack of a comprehensive DNA sequence data analysis. We thus analyzed the phylogenetic relationships of putative taxa (species and subspecies) in the genus Dreissena in relation to its nearest living relatives (Mytilopsis leucophaeata and Congeria kusceri) using DNA sequence data from the nuclear 28S RNA gene and three mitochondrial genes: cytochrome c oxidase subunit I (COI), 16S RNA, and cytochrome (cyt) b oxidase. Relationships resolved by maximum likelihood and Bayesian phylogenetic trees are robust and congruent and support division of Dreissena into three subgenera: Dreissena, Pontodreissena, and Carinodreissena. The subgenus Pontodreissena contains two species: Dreissena caputlacus and Dreissena rostriformis. Putative subspecies once proposed for D. rostriformis lack genetic divergence and likely should no longer be recognized; these include D. r. “bugensis” (the quagga mussel), D. r. “grimmi,” D. r. “distincta,” and D. r. “compressa.” The Pontodreissena then comprises the sister group (nearest relative) to a clade comprising the other two subgenera (Dreissena and Carinodreissena). The subgenus Carinodreissena contains the valid taxa Dreissena carinata and Dreissena blanci; both inhabit ancient lakes in the Balkan Peninsula. We consider the once recognized Dreissena “stankovici” and Dreissena “presbensis” to be synonyms of Dreissena carinata; DNA and morphological evidence supports this conclusion. The subgenus Dreissena includes two species, Dreissena polymorpha and Dreissena anatolica. D. anatolica is endemic to Turkey in lakes north of the Mediterranean, and D. polymorpha (the zebra mussel) has been widely introduced throughout much of Eurasia and North America, spreading from its native distribution in the Pontocaspian region. We additionally analyze population genetic variation for invasive and native populations of the zebra mussel D. polymorpha (using 11 nuclear DNA microsatellite loci) and the quagga mussel D. r. “bugensis” (using 9 microsatellite loci) across North America and Eurasia and compare our results with previous studies that used other markers. Results reveal significant genetic structuring of introduced populations from Eurasia and North America for both species. North American invasions of both species were founded from multiple source populations and a large number of propagules, showing no founder effects and substantial genetic diversity. In contrast, recently colonized quagga mussel populations from the Colorado River and California exhibit some founder effects. Genetic compositions of both species have changed over time at given colonization sites, with some populations adding alleles from adjacent populations, some losing them, and most retaining closest similarity to their original composition. In conclusion, these genetic data comprise a valuable baseline for resolving present and future invasion pathways for dreissenids, as well as interpreting patterns of distributions in their native ecosystems. © 2014 by Taylor & Francis Group, LLC

Engineering geological map of the Chiavari city area (Liguria, Italy)

An engineering geological map at a scale of 1:10,000 of the Chiavari city area (Northern Italy) – a major tourist and economic attraction of the Ligurian East Riviera – is presented in this paper. The municipality land shows an excellent geomorphological case-study of the well-known Ligurian coast: a floodplain, fairly wide and inhabited, formed by several floods of the two main rivers, a hill hinterland, reasonably inhabited, developed in marly limestones and sandy shales flysch and the coast – featuring cliffs and narrow pebbly beaches – deeply modified. This map was compiled by combining available geological data with a new engineering geomorphological field survey and including geotechnical data which were obtained from studies carried out for town planning and building purposes. On the basis of the critical review of the available lithostratigraphic data from drilling, as well as geotechnical and geophysical analyses carried out between 1981 and 2010 on the municipality land, an engineering geologica..