Vicariance patterns in the Mediterranean Sea: east–west cleavage and low dispersal in the endemic seagrass Posidonia oceanica

Aim The seagrass, Posidonia oceanica is a clonal angiosperm endemic to the Mediterranean Sea. Previous studies have suggested that clonal growth is far greater than sexual recruitment and thus leads to low clonal diversity within meadows. However, recently developed microsatellite markers indicate that there are many different genotypes, and therefore many distinct clones present. The low resolution of markers used in the past limited our ability to estimate clonality and assess the individual level. New high‐resolution dinucleotide microsatellites now allow genetically distinct individuals to be identified, enabling more reliable estimation of population genetic parameters across the Mediterranean Basin. We investigated the biogeography and dispersal of P. oceanica at various spatial scales in order to assess the influence of different evolutionary factors shaping the distribution of genetic diversity in this species. Location The Mediterranean. Methods We used seven hypervariable microsatellite markers, in addition to the five previously existing markers, to describe the spatial distribution of genetic variability in 34 meadows spread throughout the Mediterranean, on the basis of an average of 35.6 (± 6.3) ramets sampled. Results At the scale of the Mediterranean Sea as a whole, a strong east–west cleavage was detected (amova) . These results are in line with those obtained using previous markers. The new results showed the presence of a putative secondary contact zone at the Siculo‐Tunisian Strait, which exhibited high allelic richness and shared alleles absent from the eastern and western basins. F statistics (pairwise θ ranges between 0.09 and 0.71) revealed high genetic structure between meadows, both at a small scale (about 2 to 200 km) and at a medium scale within the eastern and western basins, independent of geographical distance. At the intrameadow scale, significant spatial autocorrelation in six out of 15 locations revealed that dispersal can be restricted to the scale of a few metres. Main conclusions A stochastic pattern of effective migration due to low population size, turnover and seed survival is the most likely explanation for this pattern of highly restricted gene flow, despite the importance of an a priori seed dispersal potential. The east–west cleavage probably represents the outline of vicariance caused by the last Pleistocene ice age and maintained to this day by low gene flow. These results emphasize the diversity of evolutionary processes shaping the genetic structure at different spatial scales.     

Sexual reproduction and developmental adaptations in Xanthoria parietina

Thalli of Xanthoria parietina have been grown in cultures in the natural environment. In early phases of development the fungus associates with foreign algae and only later forms a symbiosis with Pseudotrebouxia . The lichen is shown to have a very effective mechanism for distribution by sexual spores followed by relichenization.     

Uptake and metabolism of taurine in the green alga Chlorella fusca

Taurine entered the alga Chlorella fusca Shihira et Krauss strain 21l-8b via a pH and energy-dependent system ("permease"). Transport followed triphasic kinetics from 10⁻⁶ to 10⁻² M with K_m values for taurine of 5.4 × 10⁻⁵, 4.1 × l0⁻⁴ and l.5 × 10⁻³ M. This uptake system was specific for sulfonic acids and showed no affinity for α- and β -amino acids or Na⁺; thus the permease of C. fusca is different from all known taurine transport systems with respect to structural specificity and lack of Na⁺ -dependence. Uptake was not observed in sulfate-grown algae but developed as a response to sulfate limitation within 2 h. Sulfate addition caused a rapid decline in taurine transport capacity. Labeled taurine was rapidly metabolized in C. fusca to sulfate and ethanolamine, suggesting oxidative hydrolysis as the mechanism of C-S bond cleavage. Further incorporation of these catabolic products in C - and S -metabolism was demonstrated. Taurine catabolism was also detected in other green algae and some cyanobacteria.     

NAD(P)H oxidase and peroxidase activities in purified plasma membranes from cauliflower inflorescences

An NAD(P)H oxidase activity stimulated by phenolic compounds has been investigated in purified plasma membranes (pm) and in an intracellular membrane (icm) fraction depleted in plasma membranes, both obtained from a microsomal fraction from cauliflower inflorescences ( Brassica oleracea L.). The phenolic compounds salicylhydroxamic acid (SHAM), ferulic acid, coniferyl alcohol, n -propyl gallate, naringenin, kaempferol and caffeic acid all strongly stimulated the activity. Peroxidase (EC 1.11.1.7), or a peroxidase-like enzyme, was responsible for the NAD(P)H oxidase activity, which proceeded through a free-radical chain reaction and was inhibited by catalase (EC 1.11.1.6), superoxide dismutase (EC 1.15.1.1) and KCN. Most of the total activity was soluble; however, the membrane-bound activity was highly enriched in the pm compared to the icm. The catalase activity was 6 times higher in the icm-fraction than in the pm-fraction, but this was not the reason for the much lower phenol-stimulated NADH oxidase activity in the icm. Peroxidase activity measured with o -dianisidine and H₂O₂ had about the same specific activities in the pm-and icm-fractions.
Neither the phenol-stimulated NADH oxidase nor the peroxidase activity could be washed away from the pm even by 0.7 M NaCl, indicating that these activities are truly membrane-bound. SHAM as well as the other phenolic compounds capable of stimulating the NADH oxidase reaction were potent inhibitors of blue light-induced cytochrome b -reduction in the pm fraction.     

The ultrastructure of chemolithoautotrophic Gallionella ferruginea and Thiobacillus ferrooxidans as revealed by chemical fixation and freeze-etching

By using sodium thioglycolate to dissolve the high amount of excreted stalk material in axenic cultures of the chemolithoautotrophic iron bacterium Gallionella ferruginea, the ultrastructure of Gallionella cells from pure cell suspensions could be studied without any loss of viability or disturbance by dense ferric stalk fibers, and compared with Thiobacillus ferrooxidans, also grown chemolithoautotrophically with ferrous iron as energy source. Both organisms were chemically fixed or freeze-etched. Particular structural differences between these iron-bacteria could be ascertained. G. ferruginea possesses intracytoplasmic membranes and soluble d-ribulose-1,5-bisphosphate-carboxylase, whereas T. ferrooxidans contains carboxysomes but no intracytoplasmic membranes; Gallionella forms poly--hydroxybutyrate and glycogen as storage material; T. ferrooxidans produces only glycogen. Both organisms also differ from each other with respect to the freeze fracture behaviour of the cell envelope layers. Whereas the cells of T. ferrooxidans exhibit a characteristic double cleavage, exposing the plasmic fracture face and exoplasmic fracture face of the outer membrane and cytoplasmic membrane, the exceptionally thin multilayered cell envelope of G. ferruginea revealed a particularly intimate association between the layers, resulting in a visualisation of the supramolecular organisation of only the inner fracture face of the cytoplasmic membrane. The results are discussed predominantly in relation to the extremely distinct environments of both organisms.     

Assignment of autosomal dominant spinocerebellar ataxia (SCA1) centromeric to the HLA region on the short arm of chromosome 6, using multilocus linkage analysis.

A 7-generation kindred with the HLA-linked form of spinocerebellar ataxia (SCA1) was studied to determine whether the SCA1 gene maps centromeric or telomeric to the HLA loci. The DNA markers flanking the HLA-(A-B) region were used for polymorphism studies and multilocus linkage analysis. These two markers are the cDNA for the beta-subunit of HLA-DP, which is centromeric to HLA-(A-B), and the cDNA for coagulation factor XIIIa (F13A), which is telomeric to HLA-(A-B). Haplotypes were constructed using multiple polymorphisms for these two DNA markers, and pairwise linkage analysis revealed a maximum lod score of 2.18 for SCA1 versus HLA-DP at a recombination fraction of .05 and a maximum lod score of 0 for SCA1 versus F13A at a recombination fraction of .50. A possible crossover between HLA-(A-B) and HLA-DP was identified, but lack of samples from key individuals hampered the analysis. To clarify the phase and improve the analysis, the two chromosomes 6 for the crossover individual were separated in somatic cell hybrids. The results strongly favored the probability that the crossover occurred between HLA-(A-B-DR) and HLA-DP with SCA1 segregating with HLA-DP, consistent with a location centromeric to HLA-(A-B). Multilocus linkage analysis was used to evaluate further the location of SCA1 relative to F13A, HLA-(A-B), and HLA-DP; the results indicated that the SCA1 gene locus is centromeric to HLA-DP with odds of 46:1 favoring this most likely location over the second most likely location, i.e., telomeric to HLA-(A-B) between the HLA complex and F13A.     

Longitudinal age changes in a fishermen population of West Bengal

The longitudinal anthropological age changes in a sample of coastal fishermen in West Bengal are discussed. The results show that some traits follow the trends observed in ageing of Western populations, for instance nasal length and breadth continue to increase throughout life in both sexes. Stature follows also the trend generally observed: a decrease occurs indeed from 35 years of age in both sexes, the decline is becoming higher with increasing age. The typical ecological conditions of our population influence the rate of change in other traits, such as weight and biacromial diameter. Weight is known to be influenced by the nutritional status and the way of life. It explains that in our study of males an early increase of weight and biacromial diameter is observed first and a decrease afterwards. In females, however, a decrease is observed already from 35 years of age. This kind of analysis was only possible with the help of longitudinal data and in a well defined population: only longitudinal data is free from the effect of secular changes and of selective death.