Ecological and morphological differentiation among cryptic evolutionary lineages in freshwater limpets of the nominal form-group Ancylus fluviatilis (O.F. Müller, 1774)

The phylogeny and potential mode of speciation of the river limpet Ancylus fluviatilis (Basommatophora) was examined using mitochondrial DNA sequences from 16S ribosomal RNA, cytochrome c oxidase subunit I (COI) and nuclear DNA from internal transcribed spacer (ITS-1) regions from 103 populations across Europe. Four highly divergent lineages were observed within Ancylus. Clade 1, representing the nominal taxon Ancylus fluviatilis (O.F. Müller, 1774), is mainly found in central and northern Europe, Clade 2 is present in a single Portuguese population, Clade 3 is distributed on the Canary islands, North Africa and the eastern Mediterranean region, whereas Clade 4 inhabits the Northern Mediterranean coasts. Phylogenetic analyses revealed an overall consistent topology of nuclear and mitochondrial gene trees. Based on a molecular clock, we estimated that the basic radiation occurred in the late Pliocene. Although clades differ significantly in size independent shell shape, morphological differentiation of lineages is not feasible without genetic data. Environmental data related to climate (precipitation, temperature, etc.) showed a significant differentiation of clades. Clade 1 dwells in relatively colder and more stable habitats than Clades 3 and 4, whose habitats in turn differ in a low or high amount of precipitation during spring and autumn, respectively. Based on the combined data sets on mitochondrial DNA, nuclear DNA, morphological and ecological differentiation, we conclude that Ancylus represents a cryptic species complex of reproductively and genetically isolated lineages. In addition, the joint analysis suggests that ecological speciation is probable to explain current patterns.

Evidence for survival of Pleistocene climatic changes in Northern refugia by the land snail Trochoidea geyeri (Soós 1926) (Helicellinae, Stylommatophora)

BACKGROUND

The study of organisms with restricted dispersal abilities and presence in the fossil record is particularly adequate to understand the impact of climate changes on the distribution and genetic structure of species. Trochoidea geyeri (Soós 1926) is a land snail restricted to a patchy, insular distribution in Germany and France. Fossil evidence suggests that current populations of T. geyeri are relicts of a much more widespread distribution during more favourable climatic periods in the Pleistocene.

RESULTS

Phylogeographic analysis of the mitochondrial 16S rDNA and nuclear ITS-1 sequence variation was used to infer the history of the remnant populations of T. geyeri. Nested clade analysis for both loci suggested that the origin of the species is in the Provence from where it expanded its range first to Southwest France and subsequently from there to Germany. Estimated divergence times predating the last glacial maximum between 25-17 ka implied that the colonization of the northern part of the current species range occurred during the Pleistocene.

CONCLUSION

We conclude that T. geyeri could quite successfully persist in cryptic refugia during major climatic changes in the past, despite of a restricted capacity of individuals to actively avoid unfavourable conditions.

Phylogeographic history of the land snail Candidula unifasciata (Helicellinae, Stylommatophora): fragmentation, corridor migration, and secondary contact

We studied sequence variation in 16S rDNA in 204 individuals from 37 populations of the land snail Candidula unifasciata (Poiret 1801) across the core species range in France, Switzerland, and Germany. Phylogeographic, nested clade, and coalescence analyses were used to elucidate the species evolutionary history. The study revealed the presence of two major evolutionary lineages that evolved in separate refuges in southeast France as result of previous fragmentation during the Pleistocene. Applying a recent extension of the nested clade analysis (Templeton 2001), we inferred that range expansions along river valleys in independent corridors to the north led eventually to a secondary contact zone of the major clades around the Geneva Basin. There is evidence supporting the idea that the formation of the secondary contact zone and the colonization of Germany might be postglacial events. The phylogeographic history inferred for C. unifasciata differs from general biogeographic patterns of postglacial colonization previously identified for other taxa, and it might represent a common model for species with restricted dispersal.

Separating historic events from recurrent processes in cryptic species: phylogeography of mud snails (Hydrobia spp.)

The present study combines methods that were designed to infer intraspecific relationships (e.g. nested-clade analysis (NCA), mismatch distributions and maximum likelihood gene flow analysis) to analyse historic events and recurrent processes in the cryptic mud snail species Hydrobia acuta and H. glyca. Specifically, we test the proposed allopatry of cryptic species and whether the peculiar range-subdivision of the putative subspecies H. a. acuta and H. a. neglecta is a result of long-distance dispersal or continuous range expansion. The NCA indicates a past fragmentation of the two H. acuta subspecies as well as past fragmentations within H. glyca. Gene-flow analyses show extensive gene flow in an E-W direction (towards the Atlantic) in the Mediterranean H. a. acuta, generally low gene flow in a W-E direction in the Atlantic H. a. neglecta and complex gene-flow pattern in a N-S but also in a S-N direction (against the Gulf Stream) in H. glyca. Based on these data and supportive ecological and oceanographical data, we hypothesize that the separation of the two H. acuta subspecies was not caused by long-distance dispersal but by a range shift and/or range expansion of the closely related competitor H. glyca as a result of an interglacial warming with a subsequent range shift in H. acuta. Moreover, our data do not show evidence for a long-term, stable sympatry of Hydrobia species, supporting the concept of allopatric relationships within cryptic radiations. NCA and gene-flow analyses indicate that the only sympatric population found in our study is the result of a recent dispersal event from the nearby Mediterranean. It is assumed that allopatric relationships in ephemeral Hydrobia populations constitute an evolutionary advantage relative to competition, recruitment and re-establishment of habitats. Mechanisms that could be of relevance for maintaining allopatry are discussed.

Phenotypic evolution and hidden speciation in Candidula unifasciata ssp. (Helicellinae, Gastropoda) inferred by 16S variation and quantitative shell traits

In an effort to link quantitative morphometric information with molecular data on the population level, we have analysed 19 populations of the conchologically variable land snail Candidula unifasciata from across the species range for variation in quantitative shell traits and at the mitochondrial 16S ribosomal (r)DNA locus. In genetic analysis, including 21 additional populations, we observed two fundamental haplotype clades with an average pairwise sequence divergence of 0.209 +/- 0.009 between clades compared to 0.017 +/- 0.012 within clades, suggesting the presence of two different evolutionary lineages. Integrating additional shell material from the Senckenberg Malacological Collection, a highly significant discriminant analysis on the morphological shell traits with fundamental haplotype clades as grouping variable suggested that the less frequent haplotype corresponds to the described subspecies C. u. rugosiuscula, which we propose to regard as a distinct species. Both taxa were highly subdivided genetically (FST = 0.648 and 0.777 P < 0.001). This was contrasted by the partition of morphological variance, where only 29.6% and 21.9% of the variance were distributed among populations, respectively. In C. unifasciata, no significant association between population pairwise FST estimates and corresponding morphological fixation indices could be detected, indicating independent evolution of the two character sets. Partial least square analysis of environmental factors against shell trait variables in C. u. unifasciata revealed significant correlations between environmental factors and certain quantitative shell traits, whose potential adaptational values are discussed.

Dynamic microsatellites in transcribed regions of gastropod mitochondrial 16S rDNA

Length variations of repetitive sequences in different AT-rich loop-coding regions of mitochondrial 16S rDNA in two gastropod species were discovered during intraspecific haplotype surveys. Examination of the discrete length variation of the basic repeat unit in a phylogenetic framework led to the conclusion of a microsatellite-like mutational dynamic. The observations suggest that the presence of a repetitive sequence structure alone is sufficient to trigger this dynamic.

Northern blot analysis of simple repetitive sequence transcription in plants

The presence of simple repetitive sequence motifs in RNA from various plant species was probed by Northern blot analysis. Hybridization of total, poly(A)(+)- and poly(A)(-)-RNA with microsatellite-complementary oligonucleotide probes revealed distinct bands with most but not all probe/species combinations, demonstrating the presence of di-, tri- and tetranucleotide repeat motifs in plant transcripts. Only trinucleotide repeat-derived hybridization signals were found to be enriched in the poly(A)(+)-fraction. The quality of Northern blot signals proved to be highly dependent on hybridization stringency. Thus, under the stringency conditions usually applied for oligonucleotide hybridization, some probes [(GT)8, (CAC)5, (TCC)5, and (CCTA)4] cross-hybridized to bands corresponding in size to 18S and/or 26S rRNA. Cross-hybridization to rRNA was significantly reduced at higher stringencies. These results stress the importance of carefully adjusting the hybridization conditions in Northern blot analysis of simple sequence transcripts.

Synthesis of precursors of C4 and C5 cumulenones

Bicyclo[2.2.l]hept-5-en-2-one was condensed with 2,2-dimethyl-1,3-dioxan-4,6-dione in the presence of titanium tetrachloride/pyridine to yield 5-(bicyclo[2.2.1]hept-5'-en-2'-ylidene)-2,2-dimethyl-1,3- dioxan-4,6-dione (6a) which on pyrolysis at 520-560�/0.01 mm gave acetone, carbon dioxide, cyclopentadiene and butatrienone. In the same way 5-(7'-oxabicyclo[2.2.1]hept-5'-en-2'-ylidene)-2,2- dimethyl-1,3-dioxan-4,6-dione (6b) was prepared from 7-oxabicyclo[2.2.1]hept-5-en-2-one and on pyrolysis at 570�/0.01 mm it gave acetone, carbon dioxide, furan and butatrienone. Alkylation of 2-trimethylsiloxybicyclo[2.2.1]hepta-2,5 with phenylthiomethyl chloride with titanium tetrachloride as catalyst followed by condensation with 2,2-dimethyl-1,3-dioxan-4,6-dione gave an endo/exo mixture of 5-(3'-phenylthiomethylbicyclo[2.2.1]hept-5'-en-2'-ylidene)-2,2-dimethy 1-1,3-dioxan- 4,6-dione. The structure of the endo isomer was established by X-ray crystallography. Oxidation of the phenylthiomethyl compound with m-chloroperbenzoic acid yielded the sulfoxide which was converted by boiling in carbon tetrachloride into 5-(3'-methylenebicyclo[2.2.l]hept-5'-en-2'-ylidene)- 2,2-dimethyl-1,3-dioxan-4,6-dione (8). Preliminary studies on the fragmentation of compound (8) have shown that at 450�/0.01 mm it is converted into acetone, carbon dioxide and products showing ketene absorption at 2140 cm-1. The formation of pentatetraenone has not been established with certainty. The 3'-phenylsulfonylmethyl, phenylselenyl and methyl derivatives of (6a) are also described.

[The value of acetylsalicylic acid for the prevention of postoperative thromboembolic complications]

All studies on the value of acetylsalicylic acid for the prevention of postoperative thromboembolic complications have been evaluated. Controlled, prospective and randomized studies have been analyzed only where the incidence of postoperative deep vein thrombosis or pulmonary emboli was proven by objective diagnostic methods such as the fibrinogen test, phlebography or autopsy. In 6 studies there is no significant reduction in the incidence of deep vein thrombosis in general surgical and orthopedic patients after acetylsalicylic acid prevention. One study, though it has definite methodological defects, does suggest a significant reduction in the number of postoperative fatal pulmonary emboli in 120 patients with fractures of the upper end of the femur. On the basis of all these data, the prevention of postoperative thromboembolic complications by means of acetylsalicylic acid cannot be recommended.