Bright ideas about parasites

The Hamilton-Zuk hypothesis for parasite-mediated sexual selection in animals has generated much controversy. To resolve the arguments it will be necessary to incorporate many more details of the biology, ecology and evolution of hosts and parasites into studies of sexual selection.     

Evolution of the ATP-binding-cassette transmembrane transporters of vertebrates

The ATP-binding-cassette transmembrane transporters (ABC transporters) known from vertebrates belong to four major subfamilies: (1) the P- glycoproteins (Pgp); (2) the cystic fibrosis transmembrane conductance regulators (CFTR); (3) the Tap proteins encoded with the major histocompatibility complex of mammals; and (4) the peroxisomal membrane proteins. Both Pgp and CFTR have a structure suggesting a past internal gene duplication; a phylogenetic analysis indicated that these duplications occurred independently, while an independent tandem gene duplication occurred in the case of the Tap family. Both the Pgp and Tap proteins show evidence of relationship to bacterial ABC transporters lacking internal duplication, and both are significantly more closely related to the HlyB and MsbA families of transporters from purple bacteria than they are to ABC transporters from nonpurple bacteria. The simplest hypothesis to explain this observation is that eukaryotic Pgp and Tap genes are descended from a mitochondrial gene or genes that were subsequently translocated to the nuclear genome. The Pgp genes of eukaryotes are characterized by a remarkable degree of convergent evolution between the ATP-binding cassettes of their N- terminal and C-terminal halves, whereas no such convergence is seen between the two halves of CFTR genes or between the duplicated Tap genes. Exon 13 of the CFTR gene, which encodes a putative regulatory domain not found in other ABC transporters apart from CFTR, showed high levels of both synonymous and nonsynonymous difference in comparisons among different mammalian species, suggesting that this region is a mutational hot spot.      

Evidence for the presence of β-lactamase inStreptomyces glaucescens and its inhibition by sodium clavulanate

Streptomyces glaucescens is shown to possess -lactamase activity which is inhibitable by clavulanate. This is important in regard to its use as a cloning host for enzymes of \-lactam biosynthesis.     

Three-Dimensional Trabecular Alignment Model

The Shear-slip Mesh Update Method (SSMUM) is being used in flow simulations involving large but regular displacements of one or more boundaries of the computational domain. We follow up the earlier discussion of the method with notes on practical implementation aspects. In order to establish a benchmark problem for this class of flow problems, we define and report results from a two-dimensional viscous flow around a rotating stirrer in a square chamber. The application potential of the method is demonstrated in the context of biomedical design problem, as we perform an analysis of blood flow in a centrifugal left ventricular assist device, or blood pump, which involves a rotating impeller in a non-axisymmetric housing.     

Sexual dimorphism and intra-populational colour pattern variation in the aposematic frog Dendrobates tinctorius

Despite the predicted purifying role of stabilising selection against variation in warning signals, many aposematic species exhibit high variation in their colour patterns. The maintenance of such variation is not well understood, but it has been suggested to be the result of an interaction between sexual and natural selection. This interaction could also facilitate the evolution of sexual dichromatism. Here we analyse in detail the colour patterns of the poison frog Dendrobates tinctorius and evaluate the possible correlates of the variability in aposematic signals in a natural population. Against the theoretical predictions of aposematism, we found that there is enormous intra-populational variation in colour patterns and that these also differ between the sexes: males have a yellower dorsum and bluer limbs than females. We discuss the possible roles of natural and sexual selection in the maintenance of this sexual dimorphism in coloration and argue that parental care could work synergistically with aposematism to select for yellower males.