Sympatric occurrence of diverged mtDNA lineages of Pityogenes chalcographus (Coleoptera, Scolytinae) in Europe

Differentiation among the European populations of the six-toothed spruce bark beetle Pityogenes chalcographus was observed for the first time in the 1970s as mating males from Northern Europe with females from Central Europe led to a significant decline in fecundity. Morphological examination revealed that P. chalcographus can be separated into two European races. Here, we investigated the genetic background of this separation by analysing 39 populations ( n  = 695), sequencing almost the complete cytochrome oxidase I gene (1543 bp) and applying single-strand conformation polymorphism. Phylogenetic analysis of 58 haplotypes yielded three major clades with a maximum sequence divergence of 2.33%, indicating that the demographic events took place in the late Pleistocene. These results support the hypothesis of allopatric divergence of the mtDNA lineages, which postglacially came into sympatric existence in Europe. However, as a result of partial crossing incompatibility the diverged lineages retained their genetic identity during postglacial times.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 331–340.     

{alpha}Melanocyte Stimulating Hormone: Chemical Nature and Mechanism of Action

Melanotropin (-MSH) is a tridecapeptide, Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH₂,synthesized and secreted by the pars intermedia of the vertebratepituitary. This peptide hormone is derived from pro-opiomelanocortin,a precursor protein which contains within its structure thesequences of other melanotropic peptides (- and rß-MSH,corticotropin), and possibly other hormones. -MSH is the physiologicallyrelevant melanotropin secreted by the pituitary and in mostvertebrates plays the essential role in adaptive color changesthrough its action on integumental chromatophores. The initial actions of -MSH are mediated at the level of themelanocyte membrane and involve signal transduction from receptorto adenylate cyclase on the intracellular surface of the membrane.This results in elevated cytosolic cyclic AMP levels followedby melanosome dispersion within dermal melanocytes and melanogenesiswithin epidermal melanocytes. The action of -MSH on dermal melanocytesrequires calcium for transduction of signal and cyclic AMP production.Melanosome dispersion per se does not, however, require extracellularcalcium. Structure-function studies of -MSH analogues and fragmentshave provided important insights relative to the structuralrequirements of the hormone for receptor binding and transduction.Substitution of certain residues within -MSH has led to thedevelopment of melanotropins that exhibit extraordinary potencyand prolonged biological activity     

The GIRK1 Brain Variant GIRK1d and Its Functional Impact on Heteromultimeric GIRK Channels

Four isoforms of GIRK channels (GIRK1–4) have been described in humans. In addition, several splice variants of more or less unknown function have been identified from several tissues and species. In our study, we investigated the structure and function of a new variant of GIRK1 that has been isolated from rat brain. Because of wide similarities with a previously described variant, we also named it GIRK1d. This variant lacks a region corresponding to exon 2 of full-length GIRK1, leading to a truncated GIRK1 that lacks the main part of the C-terminus. To study GIRK1d we used the Xenopus laevis expression system, the two-electrode voltage clamp method, and confocal laser scan microscopy. We found that our GIRK1d variant preferentially binds GIRK2 or GIRK4 over GIRK1. Furthermore, it largely reduces conductances mediated by GIRK1/2 or GIRK1/4 hetero-multimeric channels when coexpressed and nearly totally abolishes currents when replacing GIRK1 in hetero-multimeric channels.     

Night-time sun-compass behaviour of honey bees at the equator

ABSTRACT. In accordance with the peculiarities of the sun's azimuthal path near the equator, African honey bees observed in their night-time dances apparently allowed for the azimuth moving backwards at night relative to its day-time movement. In several cases the bees evidently inferred the actual azimuthal position of the sun, rather than the one that would result from extrapolating a uniform movement of the sun.     

Short allele dominance as a source of heterozygote deficiency at microsatellite loci: experimental evidence at the dinucleotide locus Gv1CT in Gracilaria gracilis (Rhodophyta)

In this study, we compared the genotypes obtained at a microsatellite locus using two methods of amplification and detection of variation in a set of individuals belonging to the red alga haplo-diploid species, Gracilaria gracilis . The methods varied in their capacity to detect longer alleles in heterozygotes, resulting in an apparent heterozygote deficiency. We attributed this bias in favour of short alleles to competition leading to the preferential amplification of shorter alleles (short allele dominance). To test this hypothesis, we created artificial heterozygotes (mixtures of two haploid DNA samples) and showed that long alleles already less intense than short alleles, 'suffer' more from being in association.     

Trypanosoma cruzi: Flow Cytometric Analysis. I. Analysis of Total DNA/Organism by Means of Mithramycin-Induced Fluorescence1,2

ABSTRACT. Total DNA/organism was determined by flow cytometry on stocks of 33 single-cell-isolate clones and one strain of mithramycin-stained Trypanosoma cruzi. Interstrain differences in mean total DNA/group of 34% and interclone differences in total DNA/organism of 41% were found. Microspectrofluorometric analyses of the trypomastigote stage of selected clones confirmed the flow cytometry data and indicated that the total DNA/organism differences were due to differences in DNA of both the nucleus and kinetoplast with the nucleus being the major contributing factor. These data imply that the potential for genetic diversity in T. cruzi may be very large.