Mating strategies based on foraging ability: an experiment with grasshoppers

Female mate choice and the benefits of this behavior are criticalaspects of Darwinian sexual selection, but they are seldom documentedbecause it is difficult to identify the male trait(s) that femalesmay be seeking. We conducted experiments with grasshoppers (Melanoplussangutnipes: Orthoptera, Acrididae) to examine this behavior.Males that feed more intensively and select a diet mix thatpermits greater food intake (food intake per body mass per time)in laboratory trials were preferentially selected by females.These better foraging males on average provide greater paternalinvestment (greater spermatophore mass) to the female, whichincreases her reproductive rate (eggs produced per body massper time). However, paternal investment may not entirely explainfemale choice of better foraging males, because these maleswere still selected even if they had their food intake restrictedor had been allowed to recently mate, which reduces spermatophoreproduction. Furthermore, males change their mating strategyin response to female choice and the foraging abilities of surroundingmales. Poorer foraging males attempt forcible copulation ratherthan displaying and allowing female choice. A male will facultativelyswitch between these strategies depending on the foraging abilitiesof the surrounding males. While females attempt to reject forciblecopulation, forcible copulation reduces the frequency with whichfemales successfully copulate with better foraging males. Therefore,males that are less "attractive" to females adopt alternativemating strategies to counter female choice which would excludethem from mating.[Behav Ecol 7: 438–444 (1996)]     

Phylogeography of Bufo marinus from its natural and introduced ranges.

The marine toad, Bufo marinus, has a broad natural distribution extending from the south-west of the USA to southern Peru and the central Amazon. It was introduced to several localities in the Caribbean and Pacific Oceans to control sugar cane pests. We sequenced 468 bp of mitochondrial DNA (mtDNA) containing the ND3 gene, and flanking tRNA genes from toads spanning the broad natural and introduced ranges. Consistent with the known history of introductions and expected effects of serial bottlenecks, mtDNA within introduced populations in Hawaii and Australia was uniform and most closely related to samples from eastern Venezuela and French Guiana. However, mtDNA nucleotide diversity in the geographic region spanning the source areas is also relative low (0.18-0.46%) and the absence of variation in the introduced populations precludes quantitative assessment of the reduction in genetic diversity. Unexpectedly, there was a large phylogeographic break (5.4% sequence divergence) within the natural range separating populations east and west of the Venezuelan Andes. We hypothesize that the two major lineages of B. marinus were isolated by the uplift of the eastern Andean cordillera which was completed approximately 2.7 Ma. Another species of the marinus group, B. paracnemis, had mtDNA paraphyletic, with marinus, being nested within the eastern lineage. Thus, at least one speciation event within the marinus group postdates the split within marinus. These findings suggest that the taxonomy of B. marinus should be re-evaluated and that the search for pathogens to control Australian populations should be conducted in populations from both lineages in the natural range.     

Increasing cell biomass in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> increases recombinant protein yield: the use of a respiratory strain as a microbial cell factory

Background  

Recombinant protein production is universally employed as a solution to obtain the milligram to gram quantities of a given protein required for applications as diverse as structural genomics and biopharmaceutical manufacture. Yeast is a well-established recombinant host cell for these purposes. In this study we wanted to investigate whether our respiratory Saccharomyces cerevisiae strain, TM6*, could be used to enhance the productivity of recombinant proteins over that obtained from corresponding wild type, respiro-fermentative strains when cultured under the same laboratory conditions.     

A complete lipopolysaccharide inner core oligosaccharide is required for resistance of Burkholderia cenocepacia to antimicrobial peptides and bacterial survival in vivo

Burkholderia cenocepacia is an important opportunistic pathogen of patients with cystic fibrosis. This bacterium is inherently resistant to a wide range of antimicrobial agents, including high concentrations of antimicrobial peptides. We hypothesized that the lipopolysaccharide (LPS) of B. cenocepacia is important for both virulence and resistance to antimicrobial peptides. We identified hldA and hldD genes in B. cenocepacia strain K56-2. These two genes encode enzymes involved in the modification of heptose sugars prior to their incorporation into the LPS core oligosaccharide. We constructed a mutant, SAL1, which was defective in expression of both hldA and hldD, and by performing complementation studies we confirmed that the functions encoded by both of these B. cenocepacia genes were needed for synthesis of a complete LPS core oligosaccharide. The LPS produced by SAL1 consisted of a short lipid A-core oligosaccharide and was devoid of O antigen. SAL1 was sensitive to the antimicrobial peptides polymyxin B, melittin, and human neutrophil peptide 1. In contrast, another B. cenocepacia mutant strain that produced complete lipid A-core oligosaccharide but lacked polymeric O antigen was not sensitive to polymyxin B or melittin. As determined by the rat agar bead model of lung infection, the SAL1 mutant had a survival defect in vivo since it could not be recovered from the lungs of infected rats 14 days postinfection. Together, these data show that the B. cenocepacia LPS inner core oligosaccharide is needed for in vitro resistance to three structurally unrelated antimicrobial peptides and for in vivo survival in a rat model of chronic lung infection.     

Morphometric analysis of the isolated calcium-tolerant cardiac myocyte

Summary Using morphometric analysis of thin sections and freeze-fracture replicas, the ultrastructure of isolated rat myocytes prepared by collagenase digestion (Powell et al. 1980) was compared with that of myocytes fixed by perfusion of intact myocardium. The volumes of myofibrils, mitochondria, nuclei, sarcoplasmic reticulum and lipid droplets in the isolated myocytes did not differ from those of their counterparts in the intact heart, but the volume occupied by transverse tubules was apparently reduced. The isolated cells had significantly shorter sarcomeres than did cells in the intact tissue, and this was associated with an altered topography of plasma membrane surface folds at the level of the Z-lines. Plasma membrane intramembrane particles were randomly distributed and showed the same numerical density on the E-faces of both isolated and intactheart myocytes. However, P-face particle density was slightly reduced in the isolated cells. It is concluded that the few differences detected in the isolated cells do not reflect any fundamental derangement of their properties.     

Bacteriocin Production by Transformable Group H Streptococci

Group H streptococci (strain Challis) which are competent for transformation release a bacteriocin into liquid medium which is bacteriocidal for another group H streptococcus (strain Wicky). The streptocin (STH(1)) is resistant to treatment with deoxyribonuclease and ribonuclease but is sensitive to trypsin, phospholipase C, and alkaline phosphatase. Such enzyme sensitivity experiments indicate that the bacteriocin may be a complex molecule (protein and lipid) containing phosphate groups essential for activity. STH(1), which is readily distinguishable from competence factor and bacteriophage activity, appears to have no role in the initiation of the competent state in strain Wicky. The presence of this factor in Challis culture supernatant fluids indicates that a reevaluation of earlier studies performed with the Challis-Wicky transformation system may be necessary.