Fine-scale genetic structure, co-founding and multiple mating in the Australian allodapine bee (Exoneura robusta)

Despite the role of Australian native bees in important ecological processes, surprisingly little is known of their population structuring. In this study five microsatellite loci were used to investigate genetic structuring of the allodapine bee Exoneura robusta sampled from four locations (maximum pairwise distance c . 35 km) in the Mountain Ash forests of Victoria. Although E. robusta would seem to have high dispersal ability, several analyses show significant population subdivision and a strong pattern of isolation-by-distance from which limited gene flow was inferred. Limited gene flow was not associated with inbreeding at the within-colony level, and within-colony genetic structure implied co-founding, multiple breeding pairs and some degree of reproductive skew. Strong population structure at such fine scales suggests that substantially divergent populations are likely within the extensive distribution currently ascribed to E. robusta .     

Male-offspring-specific, haplotype-dependent, nonrandom cosegregation of alleles at loci on two mouse chromosomes

F(1) backcrosses involving the DDK and C57BL/6 inbred mouse strains show transmission ratio distortion at loci on two different chromosomes, 11 and X. Transmission ratio distortion on chromosome X is restricted to female offspring while that on chromosome 11 is present in offspring of both sexes. In this article we investigate whether the inheritance of alleles at loci on one chromosome is independent of inheritance of alleles on the other. A strong nonrandom association between the inheritance of alleles at loci on both chromosomes is found among male offspring, while independent assortment occurs among female offspring. We also provide evidence that the mechanism by which this phenomenon occurs involves preferential cosegregation of nonparental chromatids of both chromosomes at the second meiotic division, after the ova has been fertilized by a C57BL/6 sperm bearing a Y chromosome. These observations confirm the influence of the sperm in the segregation of chromatids during female meiosis, and indicate that a locus or loci on the Y chromosome are involved in this instance of meiotic drive.     

Mutants of FtsZ targeting the protofilament interface: effects on cell division and GTPase activity

The bacterial cell division protein FtsZ assembles into straight protofilaments, one subunit thick, in which subunits appear to be connected by identical bonds or interfaces. These bonds involve the top surface of one subunit making extensive contact with the bottom surface of the subunit above it. We have investigated this interface by site-directed mutagenesis. We found nine bottom and eight top mutants that were unable to function for cell division. We had expected that some of the mutants might poison cell division substoichiometrically, but this was not found for any mutant. Eight of the bottom mutants exhibited dominant negative effects (reduced colony size) and four completely blocked colony formation, but this required expression of the mutant protein at four to five times the wild-type FtsZ level. Remarkably, the top mutants were even weaker, most showing no effect at the highest expression level. This suggests a directional assembly or treadmilling, where subunit addition is primarily to the bottom end of the protofilament. Selected pairs of top and bottom mutants showed no GTPase activity up to 10 to 20 microM, in contrast to the high GTPase activity of wild-type FtsZ above 1 muM. Overall, these results suggest that in order for a subunit to bind a protofilament at the 1 microM K(d) for elongation, it must have functional interfaces at both the top and bottom. This is inconsistent with the present model of the protofilament, as a simple stack of subunits one on top of the other, and may require a new structural model.     

Variation in the ribosomal internal transcribed spacers and 5.8S rDNA among five species of Acropora (Cnidaria; Scleractinia): patterns of variation consistent with reticulate evolution

The ITS sequences of Acropora spp. are the shortest so far identified in any metazoan and are among the shortest seen in eukaryotes; ITS1 was 70-80 bases, and ITS2 was 100-112 bases. The ITS sequences were also highly variable, but base composition and secondary structure prediction indicate that divergent sequence variants are unlikely to be pseudogenes. The pattern of variation was unusual in several other respects: (1) two distinct ITS2 types were detected in both A. hyacinthus and A. cytherea, species known to hybridize in vitro with high success rates, and a putative intermediate ITS2 form was also detected in A. cytherea; (2) A. valida was found to contain highly (29%) diverged ITS1 variants; and (3) A. longicyathus contained two distinct 5.8S rDNA types. These data are consistent with a reticulate evolutionary history for the genus Acropora.      

Putting the heat on sex determination

Sex determination and differentiation are inherently fascinating to both layperson and geneticist. Major advances have accelerated interest in the molecular genetic events mediating these processes in nematodes, flies, mice and humans. Far less attention has been paid to those organisms, particularly reptiles, where sex is determined by environmental cues. However, recent experimental evidence suggests that the two modes of sex determination may not only share common genetic elements, but may also be regulated by similar mechanisms. We argue that the ability to manipulate sex by temperature provides a particularly suitable model for exploring the molecular basis of this fundamental biological process.