Genetic signature of the colonisation dynamics along a coastal expansion front in the damselfly Coenagrion scitulum

1. Many insects are expanding their distribution range polewards as a result of climate change, which has been shown to be associated with founder effects leading to a reduction in genetic diversity and an increase in genetic differentiation. These spatial genetic patterns may arise from colonisation from a broad expansion front or a limited neighbourhood after a stepping stone model of dispersal. The temporal persistence of such founder effects are poorly understood, mainly because studies looking at the fine‐scale initial temporal dynamics of the genetic signature of a range expansion are rare. 2. Using microsatellite markers, we performed a detailed spatiotemporal genetic analysis of the range expanding damselfly Coenagrion scitulum (Rambur) along a coastal axis during the first years after colonisation. 3. A decrease was in (private) allelic richness when going northwards along the coastline, which is consistent with a scenario of cumulative founder events. In spite of the spatiotemporal dynamics in the observation records of the species along the coastline, the spatial genetic data indicated a major contribution from the broad expansion front during the colonisation of the coastline rather than a stepping‐stone colonisation process. 4. The fine‐scale temporal dynamics of the range expansion indicated the absence of persistent founder effects and instead showed considerable temporal instability in genetic indices at the more northern edge populations. This may be explained by genetic immigration and admixture from the broad expansion front in this active disperser.     

Genetic Association between H-2 Gene and Testosterone Metabolism in Mice

SEVERAL characters involved in sexual dimorphism or male reproductive performance are influenced by genetic factors that are linked with the histocompatibility-2 (H-2) system of the mouse. These factors influence sperm cell production and function^1–4 interstrain differences in relative weights of vesicular gland and testis^4,5, immune response to the male-specific histocompatibility antigen^6,7 and an androgen-dependent allotypic serum protein designated Slp⁸. Our finding of an H-2 linked gene influencing the size of such male hormone-dependent organs, as is the vesicular gland and testis, suggested that the amount of testosterone in plasma may be influenced by an H-2 linked gene. Whereas the genetic control of some hormonally determined traits is considered to be polygenic^9,10, other data indicate some endocrine variation is due to allelic substitution at a single locus or very few loci^11–14. These genes in the mouse genome have not yet been located.     

Endophyte-induced Verticillium protection in tomato is range-restricted

Endophytes, bacterial, fungal or viral, colonize plants often without causing visible symptoms. More important, they may benefit host plants in many ways, most notably by preventing diseases caused by normally virulent pathogens. Previous studies have shown that an isolate of V. dahliae from eggplant, Dvd-E6, can colonize tomato endophytically, producing taller and more robust tomato plants while providing protection against a virulent V. dahliae, race 1 (Vd1) isolate. Expression analyses suggest this requires interplay between Dvd-E6 and the plant that involves resistance and defense genes. To examine the possibility of a broader effect, dual interactions have been further examined with a more distantly related pathogen, Verticillium albo-atrum (Vaa). The results indicate Dvd-E6 colonization selectively modifies the expression of specific tomato genes to be detrimental to Vd1 but not Vaa, providing evidence that Verticillium-induced protection is range-restricted.Key words: cross-protection, endophyte, lycopersicon, tolerance, VerticilliumAn “endophyte” commonly is defined as a “fungus or bacterium living within plants without causing visible symptoms of disease”; a “pathogen” is regarded as “a disease causing biological agent”. Historically, plant biologists have tended to consider these as two very different and distinct classes of organisms but accumulating evidence now suggests that the boundaries between mutualism and parasitism are not as defined as previously thought. Many organisms can occupy both ecological niches¹ depending on the genotype of the host, the genotype of the organism itself and interaction with the environment. Indeed, this “dual life style” may be a significant factor in the evolutionary dynamics of pathogen resistance, tolerance and susceptibility.²One of the more recent additions to the growing list of dual life style (endophyte/pathogen) fungi is Verticillium dahliae,³ a causal agent of vascular wilt disease or early dying syndrome in a broad range of the plant species.⁴ When Verticillium infects a plant three different host responses can occur: resistance, susceptibility or tolerance. The phenomenon of tolerance has been associated with Verticillium spp. for decades but research on mechanisms governing the development of the plant/Verticillium interaction has focused on the compatible and incompatible interactions and little is known about the tolerant state (reviewed in ref. ⁵). In a recent series of papers we have identified an isolate of Verticillium dahliae, known as Dvd-E6, that colonizes tomatoes, cv Craigella, resulting in a stable tolerant condition, that we have used as a model system to investigate the biological and molecular bases of plant tolerance to Verticillium spp. The Craigella/Dvd E6 interaction has a number of interesting but unanticipated properties. Host plants tend to be taller and more robust than their uninfected counterparts⁶ and colonization of Craigella by Dvd-E6 provides protection against its virulent Verticillium dahliae race 1 (Vd1) cousin, limiting both Vd1 colonization and symptom development during dual infections.⁷ Such attributes normally are associated with plant/endophyte partnerships, strongly suggesting that under some conditions, Verticillium dahliae can assume an endophytic role. Apparently interplay between Dvd-E6 and the plant establishes protection against the virulent Vd1.⁷Many endophytic infections provide protection for the host against a broad range of pathogens.¹ To test the ability of Dvd-E6 infection to protect Craigella against a more distantly related Verticillium pathogen we have now examined dual interactions with Verticillium albo-atrum (Vaa). Susceptible Craigella⁸ seedlings again were inoculated at the 4-leaf stage by dipping the roots in Vd1, Dvd-E6 or Vaa conidial suspensions (1 × 10⁷ spores/ml in 0.5% gelatin solution) to establish homogeneous interactions (reviewed in ref. ⁷). For dual interactions, seedlings were inoculated with Dvd-E6 spores at the 3-leaf stage and reinoculated at the 4-leaf stage with either Vd1 or Vaa spore suspension to establish the mixed infections. Control seedlings were root dipped in gelatin solution alone. Plants were scored for symptom expression on a 0 (no symptoms) to 5 (plant dead) scale as described by Shittu and co-workers (2009) and the top two-thirds of the stems harvested at 5 and 10 days post inoculation (d.p.i.) for extraction and fungal DNA assays.^7,9All experimental results are summarized in Figure 1. At 10 d.p.i., the disease scores for Dvd-E6-infected plants were approximately one-third that of the Vd1-or Vaa-infected plants. More interesting were the symptoms in the dual interactions, Dvd-E6/Vd1 mimicking the tolerant plants with low disease and Dvd-E6/Vaa-infected plants exhibiting the highest disease scores, similar to Vd1-or Vaa-infected plants. When the amount of fungal DNA in the stems was assessed, the total fungal biomass in both dual infections as well as the Dvd-E6 and Vd1-infected plants at 5 and 10 dpi was similar (light and dark gray bars), the amount of Vaa being somewhat lower. In the mixed infections, however, most of the DNA (>90%) was of Dvd-E6 origin (white bars). More important, the Vd1 DNA level in Dvd-E6/Vd1 plants was substantially reduced relative to plants infected with Vd1 alone while the Vaa DNA levels stayed about the same in the single and double infections. This indicates that Vd1 colonization is restricted⁷ by the presence of Dvd-E6 while Vaa is not.Open in a separate windowFigure 1Comparison of symptoms and levels of V. dahliae 1 or V. albo-atrum DNA in susceptible Craigella tomato simultaneously infected with V. dahliae Dvd-E6. Individual (E6, Vd1 and Vaa) and mixed (E6/Vd1 and E6/Vaa) infections were established as previously described.⁷ Plants were scored (upper) at 5 (light gray bars) and 10 (dark gray bars) dpi for symptoms (i.e., disease scores ± SD) or assayed⁷ for total levels of Verticillium DNA (i.e., ng/g plant tissue ± SD) in the stems (lower). In mixed infections levels for each fungus also were determined (black and white bars, respectively). Results summarize the data for 9–12 plants per time point for each interaction.These results demonstrate that Dvd-E6 infection protects Craigella tomatoes against colonization by and symptom development from Vd1 but not Vaa. Past studies often have suggested that the protective effect stems from an endophyte-induced activation of systemic acquired resistance (SAR) in the host providing protection against a broad range of pathogens.¹⁰ However, in the tolerant CS//Dvd-E6 interaction the protective effect appears to be targeted more directly, allowing Dvd-E6 to effectively restrict it''s virulent cousin, Vd1. In this context, it may be important that both of the Verticillium dahliae isolates from tomato are endemic to Ontario^7,11 and potentially in direct competition, while Verticillium albo-atrum from tomato is not. Previous molecular analyses suggested that the protective effect provided by Dvd-E6 colonization requires a genetic interplay with the host, selectively modifying the expression of specific tomato genes to be detrimental to Vd1. The experimental results presented here provide evidence that Verticillium-induced protection is restricted in range.     

1H, (13)C, and (15)N NMR stereochemical study of cis-fused 7a(8a)-methyl and 6-phenyl octa(hexa)hydrocyclopenta[d][1,3]oxazines and [3,1]benzoxazines

Four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3]oxazines, five 8a-methyl octa(or hexa)hydro[3,1]benzoxazines, two 6-phenyl hexahydro[3,1]benzoxazinones, and 8a-methyl hexahydro[1,3]benzoxazinone, all cis-fused, were prepared and their stereostructures studied by various one- and two-dimensional (1)H, (13)C, and (15)N NMR spectroscopic methods. In solution, the cyclopentane-fused 2-oxo derivatives and the 1,3-benzoxazinone were found to attain exclusively the N-in/O-in conformation, whereas the 6-phenyl 2-oxo/thioxo derivatives were found to be present predominantly in the N-out conformation. The C-2 unsubstituted and the 2-oxo/thioxo 7a/8a-methyl derivatives were all present in solution as a rapidly interconverting equilibrium of the N-in and N-out conformations. The C-2 methyl derivatives were each found to be interconvertable mixtures of epimers (at C-2) with the N-in conformer predominating for one epimer and the N-out conformer predominating for the other, with both predominating conformers having the C-2 methyl group equatorially orientated. The substituent on the nitrogen (H or Me) was found to be always predominantly equatorial with respect to the heteroring, except for the epimeric 2-methyl derivatives with N-out conformations where steric constraints and the generalized anomeric effect resulted in the axial orientation of the C-2 methyl being favored.     

Isolation and cross‐familial amplification of 41 microsatellites for the brook charr (Salvelinus fontinalis)

The brook charr (Salvelinus fontinalis; Osteichthyes: Salmonidae) is a phenotypically diverse fish species inhabiting much of North America. But relatively few genetic diagnostic resources are available for this fish species. We isolated 41 microsatellites from S. fontinalis polymorphic in one or more species of salmonid fish. Thirty‐seven were polymorphic in brook charr, 15 in the congener Arctic charr (Salvelinus alpinus) and 14 in the lake charr (Salvelinus namaycush). Polymorphism was also relatively high in Oncorhynchus, where 21 loci were polymorphic in rainbow trout (Oncorhynchus mykiss) and 16 in cutthroat trout (Oncorhynchus clarkii) but only seven and four microsatellite loci were polymorphic in the more distantly related lake whitefish (Coregonus clupeaformis) and Atlantic salmon (Salmo salar), respectively. One duplicated locus (Sfo228Lav) was polymorphic at both duplicates in S. fontinalis.     

In vivo and in vitro characterization of novel microparticulates based on hyaluronan and chitosan hydroglutamate

This study examined the application of previously characterized microparticles composed of hyaluronan (HA) and chitosan hydroglutamate (CH) as well as novel microparticles consisting of both polymers (HA/CH) to improve the nasal delivery of a model drug. The rabbit bioavailabilities of gentamicin incorporated in HA, CH, and HA/CH microparticles were increased 23-, 31-, and 42-fold, respectively, compared with the control intranasal solution of gentamicin, indicating that all test microparticles were retained for longer periods on the nasal mucosa of the rabbits as supported by previous in vitro dissolution as well as frog palate mucoadhesion studies, thereby improving drug absorption. The higher bioavailabilities of CH-based formulations (CH and HA/CH) suggest the penetration-enhancing effects of CH may also be partially responsible for the improvement. A model was developed, based on a glass impinger device, to deliver dry powder formulations reproducibly onto the surface of cultured cell monolayers. In vitro permeability and fluorescence microscopy studies on the tight junctions of the 16HBE14o- cell lines further confirmed the ability of CH-based formulations to enhance penetration. Furthermore, the in vitro absorption profile from cell culture studies was consistent with those determined from in vivo studies. The complementary effect from the mucoadhesive nature of HA coupled with the penetration-enhancing effects of CH makes the novel HA/CH formulation a promising nasal delivery system.     

Seedling Nitrate Reductase Activity and Nitrate Partitioning in Maize (Zea mays L.) Strains Divergently Selected For Post-anthesis Leaf-Lamina Nitrate Reductase Activity

Two experiments were conducted to evaluate the effects of phenotypicrecurrent selection for high and low post-anthesis leaf-laminain vivo NRA on nitrate uptake, nitrate partitioning and in vitroNRA of seedling roots and leaves. In Experiment 1, intact plantsof cycle 0, 4, and 6 of the high and low NRA strains were grownon NH₄-N for 11 d, then exposed to 1.0 mol m^–3 KNO₃, andcultures sampled at 6 h and 28 h (induction and post-inductionperiods). Nitrate uptake, tissue nitrate concentration and invitro NRA were determined. The pattern of response to selectionin seedling leaf NRA was similar to that observed for in vivoNRA of field grown plants. Leaf NRA increased between 6 h and28 h. Root NRA was not affected by selection or sampling time.Treatments differed in total fresh weight but not in reductionor uptake of nitrate per unit weight, indicating a lack of correspondencebetween NRA and reduction and supporting the idea that concomitantreduction by NR is not obligatorily linked to nitrate influxin the intact plant. In Experiment 2, dark-grown plants of cycle 0, and 6 of thehigh and low NRA strains were cultured without N, detopped onday 6, transferred the following day to 0-75 mol m^–3 KNO₃and sampled at 6 h and 28 h. In contrast to Experiment 1, selectionpopulations differed in nitrate reduction and root NRA, whichby 28 h reached higher average levels than root NRA of intactplants. Translocation and reduction were inversely related amongstrains within each sampling time. The high level of translocationin detopped plants of the low NRA strain was difficult to reconcilewith its low leaf NRA level of Experiment 1. It is suggestedthat nitrate transport in detopped roots is altered relativeto the intact system in a way which permits greater NRA inductionand nitrate reduction. The results indicate that nitrate partitioningby detopped root systems should be interpreted with caution. Key words: Zea, nitrate reductase activity, nitrate uptake, nitrate reduction, nitrate partitioning, selection