Historical biogeography of Tyrrhenian land snails: the Marmorana-Tyrrheniberus radiation (Pulmonata, Helicidae).
ABSTRACT The few studies available on Tyrrhenian land snails support high diversification in the Italian Peninsula and groups structured mainly by vicariant events. Here we investigated the phylogeny of a conchologically diversified group of Tyrrhenian land snails assigned to the genera Marmorana and Tyrrheniberus. We constructed a molecular phylogeny by sequencing two commonly used mtDNA genes (cytochrome oxidase I and the large ribosomal subunit). We also carried out conchological and anatomical analysis. Morphological (shell and genitalia) and genetic data (mitochondrial genes) showed paraphyly of Marmorana. Plio-Pleistocene events in the Tyrrhenian area may have structured relationships between species at regional scale while isolation by distance probably played a role in diversification between populations on a local scale. Continental populations experienced dispersal during interglacial periods and fragmentation and reduction during the dry cold climatic phases. Areas inhabited by Apennine Marmorana could represent relict and/or glacial refugia, with extinction in some areas along the Apennines and survival in the south. The results support a reassessment of taxonomy both at genus and species level and call for further analysis.
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ABSTRACT: The lively debate about speciation currently focuses on the relative importance of factors driving population differentiation. While many studies are increasingly producing results on the importance of selection, little is known about the interaction between drift and selection. Moreover, there is still little knowledge on the spatial-temporal scales at which speciation occurs, that is, arrangement of habitat patches, abruptness of habitat transitions, climate and habitat changes interacting with selective forces. To investigate these questions, we quantified variation on a fine geographical scale analysing morphological (shell) and genetic data sets coupled with environmental data in the land snail Murella muralis, endemic to the Mediterranean island of Sicily. Analysis of a fragment of the mitochondrial DNA cytochrome oxidase I gene (COI) and eight nuclear microsatellite loci showed that genetic variation is highly structured at a very fine spatial scale by local palaeogeographical events and historical population dynamics. Molecular clock estimates, calibrated here specifically for Tyrrhenian land snails, provided a framework of palaeogeographical events responsible for the observed geographical variations and migration routes. Finally, we showed for the first time well-documented lines of evidence of selection in the past, which explains divergence of land snail shell shapes. We suggest that time and palaeogeographical history acted as constraints in the progress along the ecological speciation continuum. Our study shows that testing for correlation among palaeogeography, morphology and genetic data on a fine geographical scale provides information fundamental for a detailed understanding of ecological speciation processes.Molecular Ecology 11/2012; · 6.28 Impact Factor
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ABSTRACT: Aim We provide insights into one of the most widespread biological invasions by reconstructing the molecular phylogeographic history of non-native populations of the land snail Cornu aspersum in austral South America. The goals of this work were: (1) to examine the genetic diversity of native vs. non-native populations of C. aspersum; (2) to analyze the species’ history of dispersal and colonization in austral South America; (3) to compare the biogeographic patterns of native and introduced populations; and (4) to identify signs of population bottlenecks and /or multiple independent introductions that could explain the current genetic diversity. Location North Africa, northwest Europe, North America (California, U.S.), and South America (Chile). Methods Sequence data from mitochondrial Cytochrome b (Cytb) gene was obtained from C. aspersum individuals collected from two localities subject to recent introductions (Californian and Chilean populations in North and South America, respectively) and compared it with previously published data from the species’ native range (northeast and northwest Africa), as well as with data from a previous introduction (northwest Europe). Genetic variation within and among groups was quantified. Genetic structure was inferred by analysis of molecular variance (AMOVA). Phylogenetic and genetic diversity analyses were used to reconstruct phylogeographical patterns. Results Among the 204 sequences from native and non-native populations, we identified 111 haplotypes, from which only three were shared between American and European populations, and no haplotypes were shared between Africa and the introduced populations. The analysis of genetic distances placed European populations between American and African populations. The AMOVAs showed that most of the genetic variance is present within populations rather than among populations or among localities. Haplotype network and phylogenetic analyses consistently demonstrated the existence of two major clades, separating the Tunisian populations and the American populations. Conclusions Genetic diversity and genealogical relationships support the hypothesis of multiple introductions of C. aspersum into austral South America. At least a portion of the current genetic diversity of Chilean populations derives from North American and European (France, Italy and Spain) populations. Keywords: Alien species, biogeography, molluscs, agricultural pests, bottlenecks, multiple introductions.Evolutionary ecology research 01/2013; 15. · 0.92 Impact Factor
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ABSTRACT: The phylogenetic relationships among genera of the subfamily Ariantinae (Pulmonata, Helicidae), especially the sister-group relationship of Cylindrus obtusus, were investigated with three mitochondrial (12S rRNA, 16S rRNA, Cytochrome c oxidase subunit I) and two nuclear marker genes (Histone H4 and H3). Within Ariantinae, C. obtusus stands out because of its aberrant cylindrical shell shape. Here, we present phylogenetic trees based on these five marker sequences and discuss the position of C. obtusus and phylogeographical scenarios in comparison with previously published results. Our results provide strong support for the sister-group relationship between Cylindrus and Arianta confirming previous studies and imply that the split between the two genera is quite old. The tree reveals a phylogeographical pattern of Ariantinae with a well-supported clade comprising the Balkan taxa which is the sister group to a clade with individuals from Alpine localities. Additional lineages representing samples from southern Alpine localities as well as from Slovakia split from more basal nodes, but their relationships are not clearly resolved. To achieve more definitive conclusions concerning the geographical origin of Ariantinae, still more sequence data are needed to obtain a tree with better resolution of basal nodes. The genetic data also provided new insights concerning the genus Cepaea, which was used as one of the outgroup taxa. Cepaea vindobonensis is only distantly related to Cepaea nemoralis and Cepaea hortensis, the latter two being more closely related to Eobania vermiculata. Thus, in our tree, the genus Cepaea is paraphyletic. Key words: Cylindrus obtusus – phylogeny – phylogeography – Alpine land snails – shell morphology – histone genes – Cytochrome c oxidase subunit 1 – rRNAJournal of Zoological Systematics and Evolutionary Research 01/2013; · 1.80 Impact Factor