Adaptive differentiation of body size in speciating mole rats

Summary We report the body weight of 1,653 subterranean mole rats comprising 12 populations and 4 chromosomal species (2n=52, 54, 58 and 60) of the Spalax ehrenbergi superspecies in Israel. The sample was collected from 1970 to 1985 and includes all captured animals with a minimal age of 10 months. The results indicated the following. (a) Body weight of males was significantly higher than that of females. (b) There is a southward latitudinal gradient in body size. Northern animals living in cooler and more productive mesic environments are larger than southern animals living in warmer and less productive xeric environments. (c) The interspecific differences for each sex are statistically significant. (d) Body size is negatively correlated with temperature variables, and positively correlated with plant cover (reflecting productivity or food resources) and rainy days. (e) The best predictors of body size, explaining up to 87% of the variation in size included various combinations of temperature variables and plant cover.We conclude that in both adaptation and speciation natural selection is a major agent of differentiation of body size in accordance with multiple factors, primarily temperature and food resources operating on the energetics balance.     

Coevolution of A and B genomes in allotetraploid Triticum dicoccoides.

Data is presented on the coevolution of A and B genomes in allotetraploid wheat Triticum dicoccoides (2n = 4x = 28, genome AABB) obtained by genomic in situ hybridization (GISH). Probing chromosomes of T. dicoccoides with DNA from the proposed A/B diploid genome ancestors shows evidence of enriching A-genome with repetitive sequences of B-genome type. Thus, ancestral S-genome sequences have spread throughout the AB polyploid genome to a greater extent than have ancestral A-genome sequences. The substitution of part of the A-genome heterochromatin clusters by satellite DNA of the B genome is detected by using the molecular banding technique. The cause may be interlocus concerted evolution and (or) colonization. We propose that the detected high level of intergenomic invasion in old polyploids might reflect general tendencies in speciation and stabilization of the allopolyploid genome.     

Origin and evolution of assortative mating in actively speciating mole rats

The origin and evolution of positive assortative mating in the actively speciating subterranean mole rats of the Spalax ehrenbergi superspecies in Israel, may be deciphered by comparing female mate preference in the laboratory between ancestral and derivative species. Estrous females of the recent derivative of speciation (chromosomal species 2n = 60) showed trimodal mate preference distribution significantly differing from a normal curve. Females consisted of three phenotypes, comprising negative, low positive, and high positive preference for homospecific males. By contrast, mate preference in encounters of ancestral species (2n = 52, 54, and 58) showed a prevalence of a positive homospecific mate preference. It is suggested that the three modal distribution is explicable even on the basis of one major gene with three genotypes. The evolution of ethological reproductive isolation proceeded presumably from a high polymorphism in the most recent derivative of speciation towards increasing monomorphism of positive assortative mating among ancestral species. If an assortative mating locus combines with sexual selection of the frequent male adapted optimally to the local environment, then speciation and adaptation will be tightly linked in the evolution of mole rats.     

Congruent mammalian trees from mitochondrial and nuclear genes using Bayesian methods

Analyses of mitochondrial and nuclear gene sequences have often produced different mammalian tree topologies, undermining confidence in the merit of molecular approaches with respect to "traditional" morphological classification. The recent sequencing of the complete mitochondrial genomes of two additional rodents (Spalax judaei and Jaculus jaculus) and one lagomorph (Ochotona princeps) has prompted us to reinvestigate the issue. Using Bayesian phylogenetics, we found phylogenetic relationships between mammalian species highly congruent with previous results based on nuclear genes. Our results show the existence of four primary lineages of placental mammals: Xenarthra, Afrotheria, Laurasiatheria, and Euarchontoglires. Relationships between and within these lineages strongly suggest that the gene trees may also be congruent with the underlying species phylogeny.     

The Group-Specific Component/Vitamin D Binding Protein (GC/DBP) in Jewish Population Groups. Distribution of common and rare alleles. Description of a new variant GC1C51

The distribution of GC phenotypes and alleles was determined in six Jewish population groups from Israel. In Jews of eastern Europe, central Europe and North Africa, the allele distribution was similar to that of European non-Jewish populations. GC^*2 frequencies were considerably lower in Jews of the Middle East and highest in Jews of the Balkan area (Rumania and Bulgaria). A new rare GC variant allele, hitherto not encountered, was observed in six Jewish individuals of various countries of origin. This variant was classified as GC 1C51.     

Adhesion characteristics of chondrocytes cultured separately and in co-cultures with synovial fibroblasts.

The present study was designed to investigate the adherence mechanism(s) and behaviour of cultured chondrocytes under various culturing conditions, co-culturing with fibroblasts, or growth in the presence of conditioned medium either of fibroblasts or chondrocytes. The findings obtained indicate that chondrocyte time-adhesion curves and the final percentiles of attached cells to a plastic substrate are much slower and lower respectively than those of anchorage dependent cell types. The poorest adhesion occurs employing chondrocytes originated from suspension cultures, as compared to chondrocytes grown in monolayers. No interference with chondrocyte adhesion was found by inhibiting the production of proteoglycan (PG). Puromycin and to a lesser degree actinomycin but not cytosine arabinoside interfered with chondrocyte adhesion, suggesting the importance of protein synthesis in this process. The nature of proadhesion modifying molecules in synoviocytes conditioned media and antiadhesive agents in chondrocyte conditioned media suggests that both substances are heat labile, non-dialyzable, protein containing factors.     

The architecture of Rhodobacter sphaeroides chromatophores

The chromatophores of Rhodobacter (Rb.) sphaeroides represent a minimal bio-energetic system, which efficiently converts light energy into usable chemical energy. Despite extensive studies, several issues pertaining to the morphology and molecular architecture of this elemental energy conversion system remain controversial or unknown. To tackle these issues, we combined electron microscope tomography, immuno-electron microscopy and atomic force microscopy. We found that the intracellular Rb. sphaeroides chromatophores form a continuous reticulum rather than existing as discrete vesicles. We also found that the cytochrome bc₁ complex localizes to fragile chromatophore regions, which most likely constitute the tubular structures that interconnect the vesicles in the reticulum. In contrast, the peripheral light-harvesting complex 2 (LH2) is preferentially hexagonally packed within the convex vesicular regions of the membrane network. Based on these observations, we propose that the bc₁ complexes are in the inter-vesicular regions and surrounded by reaction center (RC) core complexes, which in turn are bounded by arrays of peripheral antenna complexes. This arrangement affords rapid cycling of electrons between the core and bc₁ complexes while maintaining efficient excitation energy transfer from LH2 domains to the RCs.