Temperature stress increases hybrid incompatibilities in the parasitic wasp genus Nasonia

Hybrid incompatibilities, measured as mortality and sterility, are caused by the disruption of gene interactions. They are important post-zygotic isolation barriers to species hybridization, and much effort is put into the discovery of the genes underlying these incompatibilities. In hybridization studies of the haplodiploid parasitic wasp genus Nasonia, genic incompatibilities have been shown to affect mortality and sterility. The genomic regions associated with mortality have been found to depend on the cytotype of the hybrids and thus suggest cytonuclear incompatibilities. As environmental conditions can affect gene expression and gene interaction, we here investigate the effect of developmental temperature on sterility and mortality in Nasonia hybrids. Results show that extreme temperatures strongly affect both hybrid sterility (mainly spermatogenic failure) and mortality. Molecular mapping revealed that extreme temperatures increase transmission ratio distortion of parental alleles at incompatible loci, and thus, cryptic incompatible loci surface under temperature stress that remain undiscovered under standard temperatures. Our results underline the sensitivity of hybrid incompatibilities to environmental factors and the effects of unstable epistasis.     

Topological and dynamical properties of Azurin anchored to a gold substrate as investigated by molecular dynamics simulation

A classical molecular dynamics study of the electron transfer protein azurin, covalently bound to a gold substrate through its native disulphide group, is carried out at full hydration. With the aim of investigating the effects on the protein structure and dynamics as induced by the presence of an electric field, simulations are performed on neutral, positively and negatively charged substrates. A number of parameters, such as the average structure, the root mean square deviations and fluctuations, the intraprotein hydrogen bonds and solvent accessible surface of the protein, are monitored during 10 ns of run. The orientation, the height and the lateral size of the protein, with respect to the substrate are evaluated and compared with the experimental data obtained by scanning probe nanoscopies. The electron transfer properties between the copper redox center and the disulphide bridge bound to the substrate are investigated and briefly discussed.     

A high-resolution comparative radiation hybrid map of equine chromosome 4q12-q22

In this study, we present a comprehensive 5000-rad radiation hybrid map of a 40-cM region on equine chromosome 4 (ECA4) that contains quantitative trait loci for equine osteochondrosis. We mapped 29 gene-associated sequence tagged site markers using primers designed from equine expressed sequence tags or BAC clones in the ECA4q12-q22 region. Three blocks of conserved synteny, showing two chromosomal breakpoints, were identified in the segment of ECA4q12-q22. Markers from other segments of HSA7q mapped to ECA13p and ECA4p, and a region of HSA7p was homologous to ECA13p. Therefore, we have improved the resolution of the human-equine comparative map, which allows the identification of candidate genes underlying traits of interest.     

Citric acid production by Aspergillus niger on wet corn distillers grains

AIMS: To determine which citric acid-producing strain of Aspergillus niger utilized wet corn distillers grains most effectively to produce citric acid. METHODS AND RESULTS: Citric acid and biomass production by the fungal strains were analysed on the untreated grains or autoclaved grains using an enzyme assay and a gravimetric method respectively. Fungal citric acid production on the grains was found to occur on the untreated or autoclaved grains. The highest citric acid level on the grains was produced by A. niger ATCC 9142. The autoclaved grains supported less citric acid production by the majority of strains screened. Biomass production by the fungal strains on the untreated or autoclaved grains was quite similar. The highest citric acid yields for A. niger ATCC 9142, ATCC 10577, ATCC 11414, ATCC 12846 and ATCC 26550 were found on the untreated grains. Treatment of the grains had little effect on citric acid yields based on reducing sugars consumed by A. niger ATCC 9029 and ATCC 201122. CONCLUSIONS: It is feasible for citric acid-producing strains of A. niger to excrete citric acid on wet corn distillers grains whether the grains are treated or untreated. The most effective citric acid-producing strain of A. niger was ATCC 9142. SIGNIFICANCE AND IMPACT OF THE STUDY: The study shows that the ethanol processing co-product wet corn distillers grains could be utilized as a substrate for the commercial production of citric acid by A. niger without treatment of the grains.     

Genetic structure and evolutionary history of a diploid hybrid pine Pinus densata inferred from the nucleotide variation at seven gene loci

Although homoploid hybridization is increasingly recognized as an important phenomenon in plant evolution, its evolutionary genetic mechanisms are poorly documented and understood. Pinus densata, a pine native to the Tibetan Plateau, represents a good example of a homoploid hybrid speciation facilitated by adaptation to extreme environment and ecological isolation from the parents. Its ecologically and reproductively stabilized nature offers excellent opportunity for studying genetic processes associated with hybrid speciation. In this study, we investigated the levels and patterns of nucleotide variation in P. densata and its putative parents. Haplotype composition, gene genealogies, and the levels and patterns of nucleotide variation gave further support to the hybrid nature of P. densata. Allelic history, as revealed by our data, suggests the ancient nature of the hybrid preceding elevation of the Tibetan Plateau. We detected more deviations from neutrality in P. densata than in the parental species. Thus, at least some of the evolutionary forces that have shaped the genetic variation in P. densata are likely to be different from those acting upon parental species. We speculate that when populations of P. densata invaded new territories, they had elevated rates of response to selection in order to develop traits that help them to survive and adapt in the new environments.     

A statistical framework to discover true associations from multiprotein complex pull-down proteomics data sets

Experimental processes to collect and process proteomics data are increasingly complex, and the computational methods to assess the quality and significance of these data remain unsophisticated. These challenges have led to many biological oversights and computational misconceptions. We developed an empirical Bayes model to analyze multiprotein complex (MPC) proteomics data derived from peptide mass spectrometry detections of purified protein complex pull-down experiments. Using our model and two yeast proteomics data sets, we estimated that there should be an average of about 20 true associations per MPC, almost 10 times as high as was previously estimated. For data sets generated to mimic a real proteome, our model achieved on average 80% sensitivity in detecting true associations, as compared with the 3% sensitivity in previous work, while maintaining a comparable false discovery rate of 0.3%. Cross-examination of our results with protein complexes confirmed by various experimental techniques demonstrates that many true associations that cannot be identified by previous approach are identified by our method.     

Adjuvants enhance the biological control potential of an isolate of Colletotrichum gloeosporioides for biological control of sicklepod (Senna obtusifolia)

In greenhouse experiments, unrefined corn oil, Silwet L-77, and an invert emulsion were tested as adjuvants with the mycoherbicidal fungus Colletotrichum gloeosporioides, a weakly virulent pathogen of sicklepod (Senna obtusifolia). A 1:1 (v/v) fungus/corn oil tank mixture containing 0.2% (v/v) Silwet L-77 surfactant reduced the dew period requirements for maximum weed infection and mortality from 16 to 8 h, and delayed the need for free moisture for greater than 48 h. This formulation also resulted in the ability of the pathogen to infect and kill weeds in larger (>5 leaf) growth stages. The invert emulsion resulted in similar effects upon these parameters. These results suggest that invert emulsions, unrefined corn oil and Silwet L-77 surfactant greatly improve the bioherbicidal potential of this pathogen for control of sicklepod, a serious weed pest in the southeastern US.     

When invaders meet locally adapted types: rapid moulding of hybrid zones between sculpins (Cottus, Pisces) in the Rhine system

Hybrid zones are commonly studied to dissect the processes that drive divergence among lineages, which have incomplete barriers of reproduction. Most hybrid zones have existed for an extended time making inferences on the initial mode of formation difficult. It is a priori unclear how fast a nascent hybrid zone would form as a response to endogenous and exogenous factors. We have studied several hybrid zones between two lineages of sculpins (Cottus spp.), which emerged due to a recent range expansion of one of the lineages along the river Rhine in the early 1990s. Applying a dense sampling across two contact areas and using a highly informative set of 45 microsatellite markers we found pronounced genetic structure. Steep genetic clines suggest that strong selective forces have shaped the respective hybrid zones from the beginning. We find that the zones are coupled to ecological transitions from small streams to larger rivers. The width of these zones is much smaller than estimates of annual individual dispersal distances, as estimated outside of the hybrid zones. The pattern is apparently not strongly affected by pre- or postzygotic reproductive isolation because numerous backcross hybrids occur within the zones. This suggests that strong natural selection acts against immigrant genotypes. The study exemplifies how local adaptation can play a key role in preventing admixture in dependence of the ecological context.     

Hybrid origin of a swordtail species (Teleostei: Xiphophorus clemenciae) driven by sexual selection

The swordlike exaggerated caudal fin extensions of male swordtails are conspicuous traits that are selected for through female choice. Swords are one of only few examples where the hypothesis of a pre-existing bias is believed to apply for the evolution of a male trait. Previous laboratory experiments demonstrated that females prefer males with longer swords and even females from some swordless species show an affiliation for males of sworded species. Earlier phylogenetic studies based on maternally inherited mitochondrial DNA placed the sworded southern swordtail Xiphophorus clemenciae with swordless platies, contradicting its morphology-based evolutionary affinities. The analyses of new nuclear DNA markers now recover its traditional phylogenetic placement with other southern swordtails, suggesting that this species was formed by an ancient hybridization event. We propose that sexual selection through female choice was the likely process of hybrid speciation, by mating of platy females with males of an ancestral swordtail lineage. In artificial crosses of descendent species from the two potential ancestral lineages of X. clemenciae the hybrid and backcross males have swords of intermediate lengths. Additionally, mate choice experiments demonstrate that hybrid females prefer sworded males. These experimental lines of evidence make hybridization through xeno-specific sexual selection by female choice the likely mechanism of speciation.     

Comparing peripheral olfactory coding with host preference in the rhagoletis species complex

Recent studies have shown that flies from sympatric populationsof Rhagoletis pomonella infesting hawthorn, apple, and floweringdogwood fruit can distinguish among unique volatile blends identifiedfrom each host. Analysis of peripheral chemoreception in Rhagoletisflies suggests that changes in receptor specificity and/or receptorneuron sensitivity could impact olfactory preference among thehost populations and their hybrids. In an attempt to validatethese claims, we have combined flight tunnel analyses and singlesensillum electrophysiology in F₂ and backcross hybrids displayinga variety of behavioral phenotypes. Results show that differencesin peripheral chemoreception among second-generation adultsdo not provide a direct correlation between peripheral codingand olfactory behavior. We conclude that either the plasticityof the central nervous system in Rhagoletis can compensate forsignificant alterations in peripheral coding or that peripheralchanges present subtle effects on behavior not easily detectablewith current techniques. The results of this study imply thatthe basis for olfactory behavior in Rhagoletis has a complicatedgenetic and neuronal basis, even for populations with a recentdivergence in preference.