Potential for climate effects on the size-structure of host–parasitoid indirect interaction networks

Communities of insect herbivores are thought to be structured mainly by indirect processes mediated by shared natural enemies, such as apparent competition. In host–parasitoid interaction networks, overlap in natural enemy communities between any pair of host species depends on the realized niches of parasitoids, which ultimately depend on the foraging decisions of individuals. Optimal foraging theory predicts that egg-limited parasitoid females should reject small hosts in favour of future opportunities to oviposit in larger hosts, while time-limited parasitoids are expected to optimize oviposition rate regardless of host size. The degree to which parasitoids are time- or egg-limited depends in part on weather conditions, as this determines the proportion of an individual''s lifespan that is available to foraging. Using a 10-year time series of monthly quantitative host–parasitoid webs, we present evidence for host-size-based electivity and sex allocation in the common secondary parasitoid Asaphes vulgaris. We argue that this electivity leads to body-size-dependent asymmetry in apparent competition among hosts and we discuss how changing weather patterns, as a result of climate change, may impact foraging behaviour and thereby the size-structure and dynamics of host–parasitoid indirect interaction networks.     

PCR–SSCP: A Method for the Molecular Analysis of Genetic Diseases

Single strand conformation polymorphism (SSCP) is a reproducible, rapid and quite simple method for the detection of deletions/insertions/rearrangements in polymerase chain reaction amplified DNA. All the details for the use of PCR–SSCP are presented in the direction of genetic diseases (β-thalassaemia, cystic fibrosis), optimum gel conditions, sensitivity and the latest modifications of the method, which are applied in most laboratories. This non-radioactive PCR–SSCP method can be reliably used to identify mutations in patients (β-globin, CFTR), provided suitable controls are available. Moreover, it is widely used for mutation identification in carriers (β-thalassaemia, cystic fibrosis), making it particularly useful in population screening.     

Paternal effects on seed germination: a barrier to the genetic assimilation of an endemic plant taxon?

We used a crossing experiment to investigate post-zygotic barriers that might limit introgression between a pair of closely-related, gynodioecious plant species--the widespread weed Silene vulgaris and the local Swedish endemic S. uniflora ssp. petraea. The study not only considered the effects of hybridization on conventionally-used (primary) fitness components such as seed set and progeny survival, but also provided a test for the effects of interspecific hybridization on characters with more subtle or habitat-specific effects on fitness. We detected highly significant paternal effects on seed germination properties, with the germination characteristics of hybrid seed resembling those of the species that served as the pollen donor. These paternal effects on germination represent a potentially strong barrier to interspecific introgression in the two species' natural habitats, where an inappropriate germination response in the habitat of the maternal parent may lead to the failure of seedling establishment. Interspecific crosses had weak or variable effects on progeny survival, flowering and sex ratio, but these effects could not be interpreted in terms of barriers to introgression. Our results indicate that nuclear restorers in S. vulgaris have the capacity to suppress cytoplasmic male-sterility genes in its endemic congener.     

Inheritance and genetic mapping of two nuclear genes involved in nuclear–cytoplasmic incompatibility in peas (Pisum sativum L.)

Genetic analysis was performed to finely map and assess the mode of inheritance of two unlinked nuclear genes Scs1 and Scs2 involved in incompatibility of the nuclear genome of the cultivated pea Pisum sativum subsp. sativum with the cytoplasm of the wild pea of the subspecies P. sativum subsp. elatius, accession VIR320. Based on the segregation of genotypes in the progeny of the test-crosses, we concluded that if the cytoplasm was inherited from the wild pea VIR320, the Scs1 allele from the cultivated pea was gametophyte lethal and sporophyte recessive lethal. The Scs2 allele from the cultivated pea reduced male gametophyte viability. In homozygote, Scs2 from cultivated parent brought about nuclear–cytoplasmic conflict manifested as chlorophyll deficiency, reduction of blade organs, and low pollen fertility of about 20%. In heterozygote, Scs1 and Scs2 genes reduced pollen fertility by ca 50 and 30%, respectively. The Scs1 and Scs2 genes involved in nuclear–cytoplasmic incompatibility were genetically mapped. The distance between the markers bordering Scs1 comprised about 2.5 cM on linkage group III. The map distance between the bordering markers in the neighborhood of Scs2 varied substantially from cross to cross in the range of 2.0–15.1 cM on linkage group V.     

Count Bayesian models for genetic analysis of in vitro embryo production traits in Guzerá cattle

Four models for in vitro embryo production traits in Guzerá cattle were compared: Gaussian (untransformed variable – LIN and transformed in logarithmic scale – LOG), Poisson (POI) and zero-inflated Poisson (ZIP). Data consisted of 5716 ovum pick-up and in vitro fertilization records performed in 1205 cows from distinct regions of Brazil. Analyzed count traits were the number of viable oocytes (N_OV), number of grade I oocytes (N_GI), number of degenerated oocytes (N_DG), number of cleaved embryos (N_CLV) and number of viable produced embryos (N_EMB). Heritability varied from 0.17 (LIN) to 0.25 (POI) for N_OV; 0.08 (LOG) to 0.18 (ZIP) for N_GI; 0.12 (LIN) to 0.20 (POI) for N_DG; 0.13 (LIN) to 0.19 (POI) for N_CLV; 0.10 (LIN) to 0.20 (POI) for N_EMB depending on the considered model. The estimated repeatability varied from 0.53 (LOG) to 0.63 (POI) for N_OV; 0.22 (LOG) to 0.39 (ZIP) for N_GI; 0.29 (LIN) to 0.42 (ZIP) for N_DG; 0.42 (LIN) to 0.59 (POI) for N_CLV; 0.36 (LIN) to 0.51 (POI) for N_EMB. The goodness of fit, measured by deviance information criterion and mean squared residuals, suggested superiority of POI and ZIP over Gaussian models. Estimated breeding values (EBV) obtained by different models were highly correlated, varying from 0.92 for N_OV (between LIN-POI) and 0.99 for N_GI (between POI-ZIP). The number of coincident animals on the 10% top EBV showed lower similarities. We recommend POI and ZIP models as the most adequate for genetic analysis of in vitro embryo production traits in Guzerá cattle.     

Effect of arsenic–phosphorus interaction on arsenic-induced oxidative stress in chickpea plants

Arsenic-induced oxidative stress in chickpea was investigated under glasshouse conditions in response to application of arsenic and phosphorus. Three levels of arsenic (0, 30 and 60 mg kg^?1) and four levels of P (50, 100, 200, and 400 mg kg^?1) were applied to soil-grown plants. Increasing levels of both arsenic and P significantly increased arsenic concentrations in the plants. Shoot growth was reduced with increased arsenic supply regardless of applied P levels. Applied arsenic induced oxidative stress in the plants, and the concentrations of H₂O₂ and lipid peroxidation were increased. Activity of superoxide dismutase (SOD) and concentrations of non-enzymatic antioxidants decreased in these plants, but activities of catalase (CAT) and ascorbate peroxidase (APX) were significantly increased under arsenic phytotoxicity. Increased supply of P decreased activities of CAT and APX, and decreased concentrations of non-enzymatic antioxidants, but the high-P plants had lowered lipid peroxidation. It can be concluded that P increased uptake of arsenic from the soil, probably by making it more available, but although plant growth was inhibited by arsenic the P may have partially protected the membranes from arsenic-induced oxidative stress.     

Analysis of trait–performance–fitness relationships reveals pollinator-mediated selection on orchid pollination traits

Premise

The role of pollinators in evolutionary floral divergence has spurred substantial effort into measuring pollinator-mediated phenotypic selection and its variation in space and time. For such estimates, the fitness consequences of pollination processes must be separated from other factors affecting fitness.

Methods

We built a fitness function linking phenotypic traits of food-deceptive orchids to female reproductive success by including pollinator visitation and pollen deposition as intermediate performance components and used the fitness function to estimate the strength of pollinator-mediated selection through female reproductive success. We also quantified male performance as pollinarium removal and assessed similarity in trait effects on male and female performance.

Results

The proportion of plants visited at least once by an effective pollinator was moderate to high, ranging from 53.7% to 85.1%. Tall, many-flowered plants were often more likely to be visited and pollinated. Given effective pollination, pollen deposition onto stigmas tended to be more likely for taller plants. Pollen deposition further depended on traits affecting the physical fit of pollinators to flowers (flower size, spur length), though the exact relationships varied in time and space. Using the fitness function to assess pollinator-mediated selection through female reproductive success acting on multiple traits, we found that selection varied detectably among taxa after accounting for sampling uncertainty. Across taxa, selection on most traits was stronger on average and more variable when pollination was less reliable.

Conclusions

These results support pollination-related trait–performance–fitness relationships and thus pollinator-mediated selection on traits functionally involved in the pollination process.     

Plant-mediated effects on an insect–pathogen interaction vary with intraspecific genetic variation in plant defences

Baculoviruses are food-borne microbial pathogens that are ingested by insects on contaminated foliage. Oxidation of plant-derived phenolics, activated by insect feeding, can directly interfere with infections in the gut. Since phenolic oxidation is an important component of plant resistance against insects, baculoviruses are suggested to be incompatible with plant defences. However, plants among and within species invest differently in a myriad of chemical and physical defences. Therefore, we hypothesized that among eight soybean genotypes, some genotypes would be able to maintain both high resistance against an insect pest and high efficacy of a baculovirus. Soybean constitutive (non-induced) and jasmonic acid (JA)-induced (anti-herbivore response) resistance was measured against the fall armyworm Spodoptera frugiperda (weight gain, leaf consumption and utilization). Indicators of phenolic oxidation were measured as foliar phenolic content and peroxidase activity. Levels of armyworm mortality inflicted by baculovirus (SfMNPV) did not vary among soybean genotypes when the virus was ingested with non-induced foliage. Ingestion of the virus on JA-induced foliage reduced armyworm mortality, relative to non-induced foliage, on some soybean genotypes. Baculovirus efficacy was lower when ingested with foliage that contained higher phenolic content and defensive properties that reduced armyworm weight gain and leaf utilization. However, soybean genotypes that defended the plant by reducing consumption rate and strongly deterred feeding upon JA-induction did not reduce baculovirus efficacy, indicating that these defences may be more compatible with baculoviruses to maximize plant protection. Differential compatibility of defence traits with the third trophic level highlights an important cost/trade-off associated with plant defence strategies.     

Distinguishing the effects of selection from demographic history in the genetic variation of two sister passerines based on mitochondrial–nuclear comparison

Determining the mechanisms responsible for the distribution of genetic diversity in natural populations has occupied a central role in molecular evolution. Our study was motivated by the unprecedented observation that a widespread Eurasian flycatcher, Ficedula albicilla, exhibited no variation at the mitochondrial DNA (mtDNA) ND2 gene in 75 individuals sampled over a 5000-km distance. In contrast, its sister species, F. parva, had low but considerably higher levels of mtDNA variation. We assessed whether natural selection or demographic factors could explain the absence of mtDNA variation in F. albicilla. Eighteen nuclear genes were sequenced to estimate the two species'' phylogeographic histories, and for comparison to the mtDNA data. Multilocus coalescence analyses suggested that F. albicilla experienced a population expansion perhaps following a population bottleneck. Simulations based on this demographic history, however, did not replicate the extremely low level of mtDNA variation. Historical range changes based on ecological niche models also failed to explain the observed mtDNA patterns. Neutrality tests (DHEW and ML-HKA) suggested a non-neutral pattern in the mtDNA of F. albicilla. We found a transmembrane-skewed distribution of nonsynonymous substitutions between the two species, three of which caused functional change; the results implied that positive selection could have targeted mtDNA. Several lines of evidence support selection rather than demographic history as the main force influencing the patterns of mtDNA variation. Despite the influence of natural selection, many of the phylogeographic inferences derived from mtDNA were robust, including species limits and a high level of gene flow among populations within species.     

Intraspecific variation in fruit–frugivore interactions: effects of fruiting neighborhood and consequences for seed dispersal

The extent of specialization/generalization continuum in fruit–frugivore interactions at the individual level remains poorly explored. Here, we investigated the interactions between the Neotropical treelet Miconia irwinii (Melastomataceae) and its avian seed dispersers in Brazilian campo rupestre. We built an individual-based network to derive plant degree of interaction specialization regarding disperser species. Then, we explored how intraspecific variation in interaction niche breadth relates to fruit availability on individual plants in varying densities of fruiting conspecific neighbors, and how these factors affect the quantity of viable seeds dispersed. We predicted broader interaction niche breadths for individuals with larger fruit crops in denser fruiting neighborhoods. The downscaled network included nine bird species and 15 plants, which varied nearly five-fold in their degree of interaction specialization. We found positive effects of crop size on visitation and fruit removal rates, but not on degree of interaction specialization. Conversely, we found that an increase in the density of conspecific fruiting neighbors both increased visitation rate and reduced plant degree of interaction specialization. We suggest that tracking fruit-rich patches by avian frugivore species is the main driver of density-dependent intraspecific variation in plants’ interaction niche breadth. Our study shed some light on the overlooked fitness consequences of intraspecific variation in interaction niches by showing that individuals along the specialization/generalization continuum may have their seed dispersed with similar effectiveness. Our study exemplifies how individual-based networks linking plants to frugivore species that differ in their seed dispersal effectiveness can advance our understanding of intraspecific variation in the outcomes of fruit–frugivore interactions.

     

Genetic mouse models of Huntington’s disease: focus on electrophysiological mechanisms

The discovery of the HD (Huntington’s disease) gene in 1993 led to the creation of genetic mouse models of the disease and opened the doors for mechanistic studies. In particular, the early changes and progression of the disease could be followed and examined systematically. The present review focuses on the contribution of these genetic mouse models to the understanding of functional changes in neurons as the HD phenotype progresses, and concentrates on two brain areas: the striatum, the site of most conspicuous pathology in HD, and the cortex, a site that is becoming increasingly important in understanding the widespread behavioural abnormalities. Mounting evidence points to synaptic abnormalities in communication between the cortex and striatum and cell–cell interactions as major determinants of HD symptoms, even in the absence of severe neuronal degeneration and death.     

Direct evidence for opposite effects of D-glucose and D-glyceraldehyde on cytoplasmic pH of mouse pancreatic β-cells

The effects of D-glucose, D-glyceraldehyde, glibenclamide, D-600, NH₄⁺ and high concentrations of K⁺ on cytoplasmic pH (pH_i) were investigated in dispersed and cultured pancreatic -cells fromob/ob mice. The cytoplasmic pH was measured with the fluorescent H⁺-indicator quene 1. The average pH_i value in resting -cells was 6.71. Addition of 20 mM of the physiological stimulus D-glucose increased pH_i with 0.05 units. Both glibenclamide and high concentrations of K⁺ decreased pH_i. The latter effects were completely reversed by D-600, supporting the notion that free cytoplasmic Ca²⁺ can be involved in the regulation of pH_i. In contrast to D-glucose, 10mM of D-glyceraldehyde decreased pH_i by 0.09 units, an effect persisting even in the presence of D-600. From the present study it is evident that D-glyceraldehyde and D-glucose have opposite effects on pH_i in pancreatic -cells.     

Effects of cytoplasmic genes on sperm viability and sperm morphology in a seed beetle: implications for sperm competition theory?

Sperm competition theory predicts that sperm traits influencing male fertilizing ability will evolve adaptively. However, it has been suggested that some sperm traits may be at least partly encoded by mitochondrial genes. If true, this may constrain the adaptive evolution of such traits because mitochondrial DNA (mtDNA) is maternally inherited and there is thus no selection on mtDNA in males. Phenotypic variation in such traits may nevertheless be high because mutations in mtDNA that have deleterious effects on male traits, but neutral or beneficial effects in females, may be maintained by random processes or selection in females. We used backcrossing to create introgression lines of seed beetles (Callosobruchus maculatus), carrying orthogonal combinations of distinct lineages of cytoplasmic and nuclear genes, and then assayed sperm viability and sperm length in all lines. We found sizeable cytoplasmic effects on both sperm traits and our analyses also suggested that the cytoplasmic effects varied across nuclear genetic backgrounds. We discuss some potential implications of these findings for sperm competition theory.     

Fractionation of nuclear and cytoplasmic ribonucleic acids from rat tissues on the methylated albumin–kieselguhr column

1. The conformation of RNA was found to affect its behaviour on methylated albumin-kieselguhr chromatography. The less regular the secondary structure of RNA, the more tightly it binds to the methylated albumin-kieselguhr column. 2. The presence of various denaturing agents (such as urea or perchlorate) in the medium while RNA was adsorbed on the column increased the resolving power of the technique as exemplified by the separation of rat liver rRNA into two distinct peaks. A special procedure for selective adsorption of the cytoplasmic DNA-like RNA on the preparative scale has been developed. Polyribosomal mRNA (rapidly labelled RNA formed in the presence of small doses of actinomycin D) can also be adsorbed selectively by the column. 3. A type of tissue specificity was detected in nuclear RNA from rat liver, kidney, thymus and spleen by using a modified salt and temperature gradient for the chromatographic fractionation (Lichtenstein, Piker & Shapot, 1967; Shapot, Lichtenstein & Piker, 1967). It was also found that cytoplasmic RNA from the different rat tissues contained no tenaciously bound fraction at all, whereas it constituted about 50% of the nuclear RNA. The problem of the possible biological function of the tenaciously bound fraction is discussed.     

Analysis of the cytotoxic effects of ruthenium–ketoconazole and ruthenium–clotrimazole complexes on cancer cells

Ruthenium-based compounds have intriguing anti-cancer properties, and some of these novel compounds are currently in clinical trials. To continue the development of new metal-based drug combinations, we coupled ruthenium (Ru) with the azole compounds ketoconazole (KTZ) and clotrimazole (CTZ), which are well-known antifungal agents that also display anticancer properties. We report the activity of a series of 12 Ru–KTZ and Ru–CTZ compounds against three prostate tumor cell lines with different androgen sensitivity, as well as cervical cancer and lymphoblastic lymphoma cell lines. In addition, human cell lines were used to evaluate the toxicity against non-transformed cells and to establish selectivity indexes. Our results indicate that the combination of ruthenium and KTZ/CTZ in a single molecule results in complexes that are more cytotoxic than the individual components alone, displaying in some cases low micromolar CC₅₀ values and high selectivity indexes. Additionally, all compounds are more cytotoxic against prostate cell lines with lower cytotoxicity against non-transformed epidermal cell lines. Some of the compounds were found to primarily induce cell death via apoptosis yet weakly interact with DNA. Our studies also demonstrate that the cytotoxicity induced by our Ru-based compounds is not directly related to their ability to interact with DNA.