Observations on the introduction of Verticillium chlamydosporium and other parasitic fungi into soil for control of the cereal cyst-nematode Heterodera avenue

Isolates of Verticillium chlamydosporium and a sterile fungus added to soil on ground oat grain reduced the numbers of Heterodera avenae on wheat by between 26 and 80%. Nematode populations in uninoculated soil increased from 15 eggs/g soil before planting to 218 eggs/g after harvest. V. chlamydosporium was isolated from oat grain that had been air-dried and milled before introduction into soil. Applications of the fungi on attapulgite clay or as suspensions of mycelium and spores in water had no effect on nematode multiplication. The effect of the fungi on numbers of H. avenae eggs was similar in autoclaved and non-sterilised soil. V. chlamydosporium added on attapulgite clay to a calcareous sand and a calcareous silty loam could be re-isolated after at least 6 months. Some isolates colonised the roots of wheat without causing lesions or affecting the dry weights of shoots or roots. These results indicate that V. chlamydosporium may be useful for the biological control of cyst nematode pests.     

The evolution of parasite host range in heterogeneous host populations

Theory on the evolution of niche width argues that resource heterogeneity selects for niche breadth. For parasites, this theory predicts that parasite populations will evolve, or maintain, broader host ranges when selected in genetically diverse host populations relative to homogeneous host populations. To test this prediction, we selected the bacterial parasite Serratia marcescens to kill Caenorhabditis elegans in populations that were genetically heterogeneous (50% mix of two experimental genotypes) or homogeneous (100% of either genotype). After 20 rounds of selection, we compared the host range of selected parasites by measuring parasite fitness (i.e. virulence, the selected fitness trait) on the two focal host genotypes and on a novel host genotype. As predicted, heterogeneous host populations selected for parasites with a broader host range: these parasite populations gained or maintained virulence on all host genotypes. This result contrasted with selection in homogeneous populations of one host genotype. Here, host range contracted, with parasite populations gaining virulence on the focal host genotype and losing virulence on the novel host genotype. This pattern was not, however, repeated with selection in homogeneous populations of the second host genotype: these parasite populations did not gain virulence on the focal host genotype, nor did they lose virulence on the novel host genotype. Our results indicate that host heterogeneity can maintain broader host ranges in parasite populations. Individual host genotypes, however, vary in the degree to which they select for specialization in parasite populations.     

Observations on the ultrastructure, mode of infectivity and host range of xenosomes

Xenosomes are infectious bacterial-like symbionts that reside in the cytoplasm of certain strains of the marine hymenostome ciliate, Parauronema acutum. Ultrastructural studies of xenosomes of one such strain, P. acutum, 110/3, reveal that the particles possess a cell envelope whose outer membrane resembles that of Gramnegative bacteria. Unlike typical Gram-negative bacteria, however, xenosomes possess a much reduced ‘murein’ layer. The DNA is not located in a ‘nucleosome’ or ‘nuclear body’ as it is in most bacteria, but may be found dispersed throughout the internal contents of the particle. Xenosomes are capable of infecting several strains of Parauronema spp. and at least one other ciliate of marine origin, Miamiensis avidus, Ma. They are also capable of inhibiting the growth of certain marine ciliate strains, particularly those of the genus Uronema. Infectivity may be related to the fact that the particles are motile. When released from the host protozoan, they may be seen spinning or darting rapidly, suggesting the presence of a motile apparatus. Phosphotungstic acid staining of the released particles show that they do, indeed, possess bacterial-like flagella. The average number of flagella per particle observed was two, although some particles were seen with as many as five. A flagellum may occur at almost any point on the surface of the particle and is characteristically wider near its point of insertion into the cell envelope than it is near its tip. During normal growth in axenic culture, xenosomes are actively released into the ambient medium. Particles, thus released, rapidly lose their capacity to infect susceptible hosts, and this capacity parallels their ability to remain motile.     

Genetic variation of geminiviruses: comparison between sexual and asexual host plant populations

One of the most promising hypotheses for the evolution of sex is that sexual reproduction is advantageous because it increases the rate of adaptive evolution in response to parasites. To investigate this advantage of sex, we compared genetic variation of geminiviruses infecting sexual and asexual populations of Eupatorium (Asteraceae). The infection frequency was 37.5% in the sexual population and 87.8% in the asexual population. The lower infection frequency in the sexual population might be the result of higher genetic diversity of host plants. If geminiviruses have diverged to counter defence systems of genetically variable hosts, genetic diversity of viruses is expected to be higher in sexual host populations than in asexual host populations. To test this expectation, we used single-strand conformation polymorphism (SSCP) analysis to examine genetic diversity of the geminiviruses in a DNA region containing the open-reading frame (ORF) C4 gene, which is known to function as a host range determinant. As predicted, higher genetic diversity of viruses was observed in the sexual population: three SSCP types were found in the asexual population while six types were found in the sexual population. Sequencing of the polymerase chain reaction (PCR) products revealed further genetic diversity. Phylogenetic analysis of the sequences showed that the SSCP types belonged to four different clades. Several SSCP types from the same clade were found in the sexual population, whereas the asexual population included only one SSCP type from each clade. Amino acid replacements of ORF C4 are suggested to be accelerated in the sexual population. This evidence supports the hypothesis that sexual reproduction is advantageous as a defence against epidemic disease.     

蒙古沙拐枣种群形态和同工酶变异的比较研究

调查和测定了中国西北荒漠地区的蒙古沙拐枣(Calligomum mongolicum Turcz)5个种群的形态学指标,应用方差分析(MANOVA)、主成分分析(PCA)和聚类分析,对种群间及种群内的形态性状进行研究。结果表明,种群间的形态变异差异显著。植株高度、种子刺毛长度和种子重量指标具有较强的形态差异性分析意义。形态差异(欧氏距离)与种群间基因流动(地理距离)间没有发现相关关系。聚类分析结果表明,种群M1与M2亲缘关系最近,种群M5与其他种群的亲缘关系相对较远;采用垂直板聚丙烯酰胺电泳技术对5个种群的3个酶系统进行了遗传多样性分析,结果表明,种群M5与其他种群的遗传一致度稍低(0．8197～0．8902)以外,其余各种群遗传一致度较高(0．8480～0．9505),体现其亲缘关系较近。依据Nei的遗传距离进行聚类,结果与形态聚类结果有一定的相似性。     

Geographic variation of host use in the leaf beetle Agelasa nigriceps suggests host range expansion

Host range expansion is an important event in the evolution of host use in phytophagous insects. Herein, we report geographic variation of host use in the chrysomelid leaf beetle, Agelasa nigriceps Motschulsky (Coleoptera: Chrysomelidae), and suggest that this beetle is expanding its host range. This beetle has been recently recorded on Pterostyrax hispidus Sieb. et Zucc. (Styracaceae) in addition to its common host plant Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq. (Actinidiaceae). The A. arguta‐associated populations were widely found in Japan, whereas the P. hispidus‐associated populations were found only in central and southwestern Japan. In the present study, we examined adult feeding behavior and larval performance of 12 A. nigriceps populations collected from eight localities, four localities where beetles occurred only on A. arguta (allopatric localities) and four localities where A. arguta‐ and P. hispidus‐associated populations occurred sympatrically (sympatric localities). Beetles of all populations, irrespective of their host plants and localities, showed high acceptance of and high larval performance on A. arguta leaves. In contrast, we found considerable variation in the beetle response to P. hispidus leaves. The A. arguta‐associated populations of allopatric localities scarcely accepted P. hispidus leaves, whereas those of sympatric localities, particularly those of P. hispidus‐associated populations, accepted and grew on P. hispidus leaves, although the degree of acceptance and larval performance varied among localities. These results strongly suggest that A. arguta is the ancestral host for A. nigriceps, and host range expansion to the P. hispidus has occurred in this beetle.     

The genetics of naturalization: A comparison of morphological variation within and between populations of

Previous work in New Zealand has shewn that genetic variation within populations of Agrostis capillaris can be comparable to that between populations, even between populations over a very wide environmental range. To determine whether this reflects the recent advent of A. capillaris in New Zealand, with a small founding gene pool and a short time for ecotypic differentiation, populations from a comparable range of environments were sampled randomly in the same way in Britain. Populations were grown in comparable conditions in the two countries, but to ensure comparability only proportional variation was examined. Characters used in the assessment of within- and between-population variation were step+sheath length, lamina length, lamina width and relative growth rate. Within populations, there were highly significant genotypic differences, especially in the British populations. Differences between populations were rather greater than those within- populations, and for lamina length this was significant in both countries. For both Britain and New Zealand, there were cases where the two genotypes sampled from a population were similar in a particular character. In some cases, populations from comparable habitats in the two countries were similar to each other. For the three morphological characters, total genotypic variation over all populations sampled was greater in Britain than in New Zealand. For some characters this was due to between-site variation, and for some to within-site variation. It is concluded that some of the evidence for non-adaptation in A. capillaris in New Zealand is caused by a more limited gene pool, and insufficient time for sorting of genotypes into habitats.     

安氏白腹鼠的形态分化与分布范围修订

安氏白腹鼠（Niviventer andersoni） (Thomas, 1911) 是中国特有种,也是白腹鼠属体型最大的种类。这一物种的基础研究较为薄弱,形态分化也缺乏系统分析。化石记录显示这一物种在第四纪晚期曾广泛分布于中国川黔地区中低海拔环境,然而国内外主要的数据库和专著均显示安氏白腹鼠现生种群分布区较为狭窄,主要在中国西南地区。本文通过检视国内外主要动物博物馆馆藏标本,结合课题组近十年来的野外采集,对安氏白腹鼠不同地理种群的形态分化进行研究,综合利用采集记录和博物馆馆藏数据对这一物种的分布范围进行修订。基于线粒体细胞色素b（Cyt b）的系统发育分析显示这一物种具有3个遗传支系。安氏白腹鼠指名亚种包含于四川盆地周边山脉与华中、华南支系,安氏白腹鼠哀牢山亚种分布于云南西南及藏东南支系。基于头骨测量数据的分析显示安氏白腹鼠不同地理种群已产生显著的分化。安氏白腹鼠现生种群从中国西藏东南地区到秦岭,甚至武陵山地区中高海拔森林环境均有分布,但与第四纪晚期这一物种的化石分布记录相比,现生种群分布海拔已明显上升。     

Predation risk influences adaptive morphological variation in fish populations

Predators can cause a shift in both density and frequency of a prey phenotype that may lead to phenotypic divergence through natural selection. What is less investigated is that predators have a variety of indirect effects on prey that could potentially have large evolutionary responses. We conducted a pond experiment to test whether differences in predation risk in different habitats caused shifts in behavior of prey that, in turn, would affect their morphology. We also tested whether the experimental data could explain the morphological variation of perch in the natural environment. In the experiment, predators caused the prey fish to shift to the habitat with the lower predation risk. The prey specialized on habitat-specific resources, and there was a strong correlation between diet of the prey fish and morphological variation, suggesting that resource specialization ultimately affected the morphology. The lack of differences in competition and mortality suggest that the morphological variation among prey was induced by differences in predation risk among habitats. The field study demonstrated that there are differences in growth related to morphology of perch in two different habitats. Thus, a trade-off between foraging and predator avoidance could be responsible for adaptive morphological variation of young perch.     

Barley segregates resistant and susceptible to the cereal cyst-nematode (Heterodera avenae Woll.)

In the first year of this experiment both nematode-resistant and susceptible segregates of spring barley were equally invaded by Heterodera avenae larvae, but few females developed in the roots of the resistant plants and numbers of eggs in the soil were fewer after the resistant crop. In the second year, a commercial, nematode-susceptible barley crop yielded significantly more grain following the resistant segregate. The resistant segregate, derived from Hordeum pallidum var 191, suppresses the development of Heterodera avenae pathotypes 1 and 2 [British nomenclature] and should be useful in areas where these pathotypes predominate.     

Molecular basis of host range variation in avian retroviruses.

Previous genetic analysis has localized the region of the Rous sarcoma virus (RSV) env gene responsible for host range specificity to that encoding the middle one-third of gp85. To better understand the host range determinants, the relevant regions of the genomes of infectious molecular clones of the transformation-defective Prague strain of RSV, subgroup B (Pr-RSV-B) and Rous-associated virus 0 (RAV-0) (subgroup E) were sequenced and compared with the sequence of Pr-RSV-C. This comparative analysis identified two variable regions of low amino acid sequence homology flanked by highly conserved amino acid sequences. The first variable region (hr1) begins at base 5654 in the Pr-RSV-C sequence and encodes 32 amino acids. The second variable region (hr2) begins at base 5846 and encodes 27 amino acids. To test the role of the variable regions in host range specificity, we determined the sequence of this region of the env gene of NTRE-4, a recombinant virus between Pr-RSV-B and RAV-0 which exhibits an extended host range. This analysis revealed that the recombinant subgroup-encoding region of NTRE-4 is composed of 200 bases of RAV-0 sequence, including hr2, flanked by sequences which are otherwise of Pr-RSV-B origin. This study indicates that hr1 and hr2 are the domains of gp85 responsible for host range determination in avian retroviruses.     

枕骨三维形态在现生人群间的变异

与面颅、脑颅和颅底不同,枕骨与人群间遗传信息的关系不明确且研究较少。传统形态测量方法对枕骨的研究难以全面反映枕骨的形态信息。为更加精细地探究枕骨形态与人群的关系,本文以亚洲、非洲和欧洲地区的103例现生男性头骨为研究对象,通过三维几何形态测量和多元统计分析的方法对枕骨三维形态和异速生长模式在人群间的差异进行了研究。研究结果表明,枕骨的大小和形状在现生人群中具有显著差异,然而这种差异并不足以区分不同人群。现代人枕骨的三维形态具有较大的变异,主要表现在枕外隆凸点的突出程度、上下相对位置以及枕平面与项平面的比例,其次表现在星点位置在前后、内外以及上下方向上的变化,斜坡的倾角变化等方面。异速生长的分析表明,不同人群中存在不同的异速生长模式,但是非洲和欧洲人群也存在相似的趋势。本研究认为枕骨三维形态在反映人群间遗传关系上作用较小,支持枕骨形态可能更多受到功能和环境等因素的影响。     

The invasion and development of the cereal cyst-nematode, Heterodera avenae in the roots of autumn-and spring-sown cereals

Observations were made at 2 or 4 wk intervals from December to harvest on all stages of Heterodera avenae in winter oats growing on infested land. Second-stage larvae were present in all soil samples except on 5 and 20 July. Invasion and development of larvae was slow during winter. The nodal and seminal roots of winter oats were both heavily invaded by the nematode; larvae which invaded seminal roots tended to become male whereas those in nodal roots tended to become female. There was a small second invasion in August. Females were first observed on the roots of winter oats on 17 May, 214 days after the crop was sown and 62 days after the first fourth-stage larva was observed. The nodal roots of spring barley contained few H. avenae larvae whereas these roots were heavily invaded in winter wheat and oats. In spring barley the nodal roots were developing in June and July when few second-stage larvae were in the soil whereas in winter oats and wheat the nodal roots were growing rapidly in April when larvae were most numerous, and so were heavily invaded.     

Seasonal variation of morphological characters and growth in contrasting white clover populations

The seasonal growth potential of contrasting white clover populations differing in leaf size and geographical origin was studied during the year in a cool glasshouse in the absence of freeze damage. A Mediterranean population showed superior growth to all other populations during the cooler months of late autumn, winter and spring when it also had longer leaflets, petioles and internodes. In contrast, large leaf types of north European origin grew faster and had longer leaflets, petioles and internodes than the Mediterranean type during summer. A hybrid between these contrasting types showed an intermediate response with more uniform growth and expression of these morphological characters throughout the year. The exploitation of this out-of-season growth potential by hybridisation of Mediterranean and north European genotypes followed by selection is discussed in the context of recent introductions of ecotypes from the Swiss Alps in which desirable combinations of good spring growth and winter hardiness have been identified.     

On the relationship between morphological and semantic markedness

This paper explores two possible connections between the diagnostics for morphological and semantic markedness. One possibility, a positive correlation, predicts that if a grammatical feature is diagnosed as being morphologically marked then it should also be semantically marked. This possibility follows from the assumption that features are interpreted as restrictions on denotations. The second possibility, a negative correlation, predicts that if a grammatical feature is diagnosed as being morphologically marked then it should be semantically unmarked. This systematic inconsistency follows from the assumption that features are interpreted as augmenting functions. In our exploration of number marking, we find that the negative correlation is not only theoretically consistent with the semantic literature (in particular Link, in: Bartsch et al. (eds.) Semantics and contextual expressions, 1983), but it is also more consistent with the empirical landscape (as noted by Sauerland, in: Young and Zhou (eds.) Proceedings of Semantics and linguistic theory SALT XIII 2008). As a result, the morphological diagnostics lend support to the view that plural features are interpreted as augmenting functions.     

The evolutionary relationship between adult oviposition preferences and larval host plant range in Papilio machaon L.

Summary In Papilio machaon host plant utilization is argued to be proximally guided by adult and larval preferences, both of which are genetically determined. To decide whether these preferences are controlled by one or two gene complexes, oviposition preferences and larval survival of a Scandinavian population were investigated with regard to all potential host plants in the region. The experiments revealed a substantial difference between the potential host plant ranges of the adults and the larvae, indicating that adult and larval host plant preferences are determined by separate gene complexes.Based on this inference, a theoretical model is developed for the co-evolutionary relationship between adult oviposition preferences and larval feeding preferences for species in which the host plant choice is exercised by the adults.     

Field estimation of variation in host plant use between local populations of pea aphids from two crops

Abstract. 1. In a reciprocal transplant experiment on pea aphids (Acyrthosiphon pisum (Harris)), the relative performance of clones collected from nearby alfalfa and red clover fields was tested by allowing clonal replicates to develop on both crops under field conditions.
2. Populations from alfalfa and red clover differed in relative survivorship and probabilities of reproduction on the two crops. Clones had significantly higher performance on the crop from which they were collected (the 'home' crop) than they did on the other crop.
3. Evidence is presented that previous experience on these host plants cannot account for the increased probability of reproduction observed on the 'home' crop. Thus, the differences between these two populations in their relative performance on alfalfa and clover are likely to be genetically based.
4. These results illustrate that local adaptation to different host plants can occur within small geographical areas, despite the high probability that migrants are exchanged between nearby fields of the two crops.
5. Experimental designs of the type described here permit estimation of patterns of genetic variation within and between insect populations. When applied to pest species, such designs will facilitate the study of evolution in agricultural systems.