Population biology of Avena

Summary Surveys for polymorphisms in natural populations of A. barbata sampled in California grasslands had provided evidence for widespread monomorphism and rather localized polymorphic areas in the north coastal and San Francisco regions, based on a set of morphological and isoenzymatic marker loci. Since this species, like many other annuals, was introduced from the Mediterranean region during the Spanish mission period, a comparative study of the Canadian-Welsh collections of Avena species from the Mediterranean region was undertaken using various plant characters and starch gel electrophoresis to analyze variants for esterase, phosphatase and peroxidase systems. A total of 96 samples including 73 of A. barbata and 23 of A. hirtula were studied and the results were scored to compute the polymorphism indices. In both species, only 10 to 15 percent sites showed any significant degree of polymorphism of which a majority seemed to originate from localized regions in Italy and Turkey; a part of this observed lack of within-sample variation might be the result of small sample size. In general, the patterns of variation in A. barbata from the California surveys and the present analyses seemed to be very similar and raised some interesting questions on (a) the colonizing history of introduced materials (b) the factors underlying such marked patterns of geographical variation, and (c) the current evolutionary changes occurring in these two broad, disjunct areas of species distribution.

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Zusammenfassung Untersuchungen der Polymorphismen in natürlichen Populationen von A. barbata im kalifornischen Weideland hatten einerseits zum Nachweis eines weit verbreiteten Monomorphismus und andererseits streng lokalisierter polymorpher Bereiche in der nördlichen Küsten- und San Francisco-Region geführt, wobei eine Anzahl morphologischer und isoenzymatischer Markerloci zugrunde gelegt wurde. Da diese Art, wie viele andere Annuelle auch, während der spanischen Missionsperiode aus der Mittelmeerregion eingeführt wurde, wurde eine vergleichende Untersuchung der Canadian-Welsh-Sammlungen von Avena-Arten aus der Mittelmeerregion anhand verschiedener Merkmale der Pflanzen und der Stärkegelelektrophorese-Untersuchung auf Esterase-, Phosphatase- und Peroxydase-Systeme durchgeführt. Es wurde eine Gesamtheit von 96 Stichproben, bestehend aus 73 A. barbata und 23 A. hirtula, untersucht und die Ergebnisse zur Berechnung von Polymorphismus-Indices verwendet. In beiden Arten zeigten nur 10 bis 15% der Herkünfte einen signifikanten Polymorphismusgrad. Von ihnen scheint die Mehrzahl von lokalisierten Regionen in Italien und Griechenland abzustammen. Ein Teil des beobachteten Fehlens einer Variation innerhalb der Stichproben könnte eine Folge des geringen Stichprobenumfangs sein. Im allgemeinen scheinen die Variationsmuster der kalifornischen Untersuchungen und die der vorliegenden Analysen von A. barbata sehr ähnlich zu sein. Das führt zu einigen interessanten Fragen nach a) der Besiedelungsgeschichte des eingeführten Materials, b) den Faktoren, die derart auffallenden Mustern der geographischen Variation unterliegen und c) den laufenden evolutionären Änderungen, die in diesen beiden großen, voneinander getrennten Gebieten der Artverteilung auftreten.

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This work was supported in part by a grant from the National Science Foundation (GB 8627).     

Population biology of Avena

Summary Pollen and seed dispersal patterns were analyzed in both natural and experimental populations of Avena barbata. Localized estimates of gene flow rates and plant densities gave estimates of neighborhood size in the range of 40 to 400 plants; the estimates of mean rate and distance of gene flow seemed to vary widely due to variable wind direction, rodent activity, microsite heterogeneity, etc. The relative sizes of neighborhoods in several populations were correlated with the patchy distribution of different genotypes (scored for lemma color and leaf sheath hairiness) within short distances, but patch sizes had a wide range among different sites. Highly localized gene flow patterns seemed to account for the observed pattern of highly patchy variation even when the dispersal curves for both pollen and seed were platykurtic in many cases. Measures of the stability of patches in terms of their size, dispersion in space and genetic structure in time are needed in order to sort out the relative roles of founder effects, random drift (due to small neighborhood size), and highly localized selection. However, our observations suggest that many variables and stochastic processes are involved in such studies so as to allow only weak inference about the underlying role of natural selection, drift and factors of population regulatien.     

Within-family selection in Avena fatua and A. barbata

Summary Twenty families each of Avena fatua and A. barbata drawn from a natural population were used for measuring the response to within-family selection for the two extremes in heading date and seed size. The estimates of the relative amounts of between- and within-family variation were interpreted in relation to the realized responses to show that A. fatua has greater genetic variability than A. barbata which, on the other hand, has more phenotypic plasticity. These results support our model on the alternative adaptive strategies in the two species discussed earlier.

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Zusammenfassung Je 20 Familien von Avena fatua und A. barbata, die aus natürlichen Populationen entnommen worden waren, wurden zur Messung der Reaktion auf intrafamiliäre Selektion auf die beiden Extreme des Schoß-Termins und der Samengröße verwendet. Die Schätzungen der relativen Beiträge der Variation zwischen und innerhalb der Familien wurden in Beziehung zu der erzielten Reaktion interpretiert, um zu zeigen, daß A. fatua eine größere genetische Variabilität und A. barbata eine größere phänotypische Plastizität als die jeweils andere Art besitzt. Die vorliegenden Ergebnisse stützen unser früher diskutiertes Modell der alternativen adaptiven Strategien in diesen beiden Spezies.

     

Testing for local adaptation in Avena barbata: a classic example of ecotypic divergence

Forty years ago, Robert Allard and colleagues documented that the slender wild oat, Avena barbata , occurred in California as two multi-locus allozyme genotypes, associated with mesic and xeric habitats. This is arguably the first example of ecotypes identified by molecular techniques. Despite widespread citation, however, the inference of local adaptation of these ecotypes rested primarily on the allozyme pattern. This study tests for local adaptation of these ecotypes using reciprocal transplant and quantitative trait locus (QTL) mapping techniques. Both ecotypes and 188 recombinant inbred lines (RILs) derived from a cross between them were grown in common garden plots established at two sites representative of the environments in which the ecotypes were first described. Across four growing seasons at each site, three observations consistently emerged. First, despite significant genotype by environment interaction, the mesic ecotype consistently showed higher lifetime reproductive success across all years and sites. Second, the RILs showed no evidence of a trade-off in performance across sites or years, and fitness was positively correlated across environments. Third, at QTL affecting lifetime reproductive success, selection favoured the same allele in all environments. None of these observations are consistent with local adaptation but suggest that a single genotype is selectively favoured at both moist and dry sites. I propose an alternative hypothesis that A. barbata may be an example of contemporary evolution – whereby the favoured genotype is spreading and increasing in frequency – rather than local adaptation.     

Restoration of Stipa pulchra Grasslands: Effects of Mycorrhizae and Competition from Avena barbata

Experiments were conducted in the field and the greenhouse to determine whether vesicular-arbus-cular mycorrhizae affect growth and competition between the native perennial Stipa pulchra and the introduced annual Avena barbata. Soils in the greenhouse were steam-sterilized, and in the field they were treated with the fungicide benomyl. Stipa pulchra showed decreased shoot dry mass and increased root mass when inoculated, while A. barbata showed the opposite response, increased shoot mass and decreased root mass. Mycorrhizal A. barbata also produced more seeds. Mycorrhizae did not alleviate the negative effects of competition of A. barbata on S. pulchra, as has been demonstrated for other pairs of weedy and nonweedy species. The same three species of mycorrhizal fungi were present in annual and perennial grasslands, but their relative composition was different. When inoculum from the two grassland types were tested in the field, the fungal species began to revert within five months to the species composition found in grasslands of the host plant. This indicates that, once annual grassland has been revegetated with the native S. pulchra, the original fungal species composition may return relatively quickly. Where A. barbata dominates, inoculation with mycorrhizal fungi alone will not suffice for establishing S. pulchra, and the usual practices for control of weed competition need to be employed.     

Population biology of human onchocerciasis.

Human onchocerciasis (river blindness) is the filarial infection caused by Onchocerca volvulus and transmitted among people through the bites of the Simulium vector. Some 86 million people around the world are at risk of acquiring the nematode, with 18 million people infected and 600,000 visually impaired, half of them partially or totally blind. 99% of cases occur in tropical Africa; scattered foci exist in Latin America. Until recently control programmes, in operation since 1975, have consisted of antivectorial measures. With the introduction of ivermectin in 1988, safe and effective chemotherapy is now available. With the original Onchocerciasis Control Programme of West Africa coming to an end, both the new African Programme for Onchocerciasis Control and the Onchocerciasis Elimination Programme for the Americas, rely heavily on ivermectin self-sustained mass delivery. In consequence, the need for understanding the processes regulating parasite abundance in human and simuliid populations is of utmost importance. We present a simple mathematical framework built around recent analyses of exposure- and density-dependent processes operating, respectively, within the human and vector hosts. An expression for the basic reproductive ratio, R0, is derived and related to the minimum vector density required for parasite persistence in localities of West Africa in general and northern Cameroon in particular. Model outputs suggest that constraints acting against parasite establishment in both humans and vectors are necessary to reproduce field observations, but those in humans may not fully protect against reinfection. Analyses of host age-profiles of infection prevalence, intensity, and aggregation for increasing levels of endemicity and intensity of transmission in the Vina valley of northern Cameroon are in agreement with these results and discussed in light of novel work on onchocerciasis immunology.     

Identifying loci under selection across contrasting environments in Avena barbata using quantitative trait locus mapping

We constructed recombinant inbred lines of a cross between naturally occurring ecotypes of Avena barbata (Pott ex Link), Poaceae, associated with contrasting moisture environments. These lines were assessed for fitness in common garden reciprocal transplant experiments in two contrasting field sites in each of two years, as well as a novel, benign greenhouse environment. An AFLP (amplified fragment length polymorphism) linkage map of 129 markers spanned 644 cM in 19 linkage groups, which is smaller, with more linkage groups, than expected. Therefore parts of the A. barbata genome remain unmapped, possibly because they lack variation between the ecotypes. Nevertheless, we identified QTL (quantitative trait loci) under selection in both native environments and in the greenhouse. Across years at the same site, the same loci remain under selection, for the same alleles. Across sites, an overlapping set of loci are under selection with either (i) the same alleles favoured at both sites or (ii) loci under selection at one site and neutral at the other. QTL under selection in the greenhouse were generally unlinked to those under selection in the field because selection acted on a different trait. We found little evidence that selection favours alternate alleles in alternate environments, which would be necessary if genotype by environment interaction were to maintain genetic variation in A. barbata. Additive effect QTL were best able to explain the genetic variation among recombinant inbred lines for the greenhouse environment where heritability was highest, and past selection had not eliminated variation.     

Heritable variation and genetic correlation of quantitative traits within and between ecotypes of Avena barbata

We examined heritable variation for quantitative traits within and between naturally occurring mesic and xeric ecotypes of the slender wild oat (Avena barbata), and in 188 recombinant inbred lines derived from a cross between the ecotypes. We measured a suite of seedling and adult traits in the greenhouse, as well as performance-related traits in field sites native to the two ecotypes. Although the ecotypes were genetically diverged for most traits, few traits showed significant heritable variation within either ecotype. In contrast, considerable heritable variation was released in the recombinant progeny of the cross, and transgressive segregation was apparent in all traits. Heritabilities were substantially greater in the greenhouse than in the field, and this was associated with an increase in environmental variance in the field, rather than a decrease in genetic variance. Strong genetic correlations were evident among the recombinants, such that 22 measured traits could be well represented by only seven underlying factors, which accounted for 80% of the total variation. The primary axis of variation in the greenhouse described a trade-off between vegetative and reproductive allocation, mediated by the date of first flowering, and fitness was strongly correlated with this trade-off. Other factors in the greenhouse described variation in size and in seedling traits. Lack of correlation among these factors represents the release of multivariate trait variation through recombination. In the field, a separate axis of variation in overall performance was found for each year/site combination. Performance was significantly correlated across field environments, but not significantly correlated between greenhouse and field.     

Variation in polygalacturonase production among Aspergillus flavus isolates.

Pectinase production by Aspergillus flavus was determined by measuring clear zones formed around colonies stained with ruthenium red. Several isolates produced red zones instead of clear zones. Red zones were reproduced with pectinesterase and correlated with absence of specific polygalacturonases. Of 87 isolates tested, 15 produced red zones.     

Variation of Population Type in Phragmites communis Trin.

The four main categories of mature populations of Phragmitescommunis Trin. are the dense tall stand, the sub-optimal one,the depauperate sparse stand and the restricted sparse stand.The depauperate represents the first and the suboptimal thesecond stage in the development of a dense stand. Sub-optimalstands occur where one or more habitat factors are unfavourable;restricted ones where competition or shortage of nutrients,water, and so on, severely restrict the formation of lateralshoots; and depauperate ones are typical of grazed areas. An advancing margin in an unsatisfactory habitat is indistinguishablefrom a restricted stand, except for the orientation of proximalgrowth. At the other extreme, in an open, optimum habitat, theannual advance, commonly of 1–2 m, is of very dense shoots,showing various characters rare in established populations.There is no set ‘advancing behaviour’, merely theresponse of rhizomes to the conditions for bud stimulation ineach place, which may be less or more favourable than in thehinterland, depending on the habitat.     

Population biology and biological control of nematodes.

We studied the population biology of the nematophagous fungus Hirsutella rhossiliensis to understand its potential as a biological control agent. Because the fungus is an infectious and transmissible parasite, we framed our study within an epidemiological context. Field observations, theory, and experiments demonstrated that (i) parasitism of nematodes by H. rhossiliensis is dependent on nematode density, (ii) local populations of the fungus will go extinct unless supplied with some minimum number of nematodes (the host threshold density), and (iii) natural epidemics of this fungus in populations of nematodes develop slowly and only after long periods of high host density. Additional in-depth research on population biology is needed to explain other biological control systems and to guide future research. The most effective research will combine field observation, theory, and experimentation.     

Variation inSclerotium rolfsii isolates in Japan

Sixty-seven isolates of the southern blight fungus from Japan were divided into five groups based on ITS-RFLP analysis of nuclear rDNA. Morphological characters of sclerotia varied between groups. Three groups were reidentified asSclerotium rolfsii, and two resembledS. delphinii in RFLP patterns and/or in having large sclerotia and relatively low optimal growth temperature (28°C). Sclerotia of the latter, however, varied in size according to temperature and became indistinguishable from those ofS. rolfsii at high temperatures. Hyphal anastomosis (imperfect fusion) was observed between different ITS-RFLP groups, as well as between different isolates belonging to the same groups. These results indicate that populations of this fungus in Japan consists of several different subgroups, although morphological differences are not always evident.     

Variation in pathogenicity of isolates of Cercospora spp. attacking Heliotropium spp.

The pathogenicity of a set of 13 Cercospora samples collected in France, Turkey and Australia from four Heliotropium species has been evaluated with a detached leaf technique. All of five Euro-Asian Heliotropium species tested were susceptible to all Cercospora species isolates. However, variation in the degree of partial resistance to different isolates was observed and showed some similarity for isolates from the same region of origin. Further studies are required to clarify the taxonomy of Cercospora blight strains, but the consequences of the noted differences in pathogenicity are discussed in relation to the biological control ofH. europaeum L. in Australia.     

短尾猴的种群生物学

短尾猴是高等灵长类动物,中国特有物种。是多雄多雌群体,猴群中性成熟雌雄性比接近于1：1,雌性略多于雄性。虽然雌性定居、雄性移民,但大多数雄性的迁出发生在成年以后,而不是成年之前。社会和生态因素在调节猴群的数量中都有重要作用。雄性个体之间具有复杂的行为,雄猴之间频繁交往,以减少群体的紧张。猴群内具有严格的社会等级关系,年轻雄猴是群体的最高统治者。