云南松三种同域共存切梢小蠹梢转干期的空间分布格局

分布在我国西南地区的横坑切梢小蠹,云南切梢小蠹和短毛切梢小蠹同域危害寄主云南松,给林业生产带来巨大损失。为探讨同域切梢小蠹种群在共存下对其空间分布格局的影响,采用传统聚集指标法和地统计学方法研究了三者在梢转干期不同受害云南松纯林树冠中的空间分布型。结果表明重度受害样地中云南切梢小蠹种群密度显著高于横坑切梢小蠹,在轻度受害样地则相反;传统聚集指标法结果显示同域共存的3种切梢小蠹种群在不同受害程度云南松中均为聚集分布,横坑切梢小蠹和云南切梢小蠹聚集是由环境因素和昆虫本身的聚集习性引起;地统计学结果表明除重度受害样地中短毛切梢小蠹呈随机分布外,其余切梢小蠹在不同种群密度下均呈聚集分布;除重度受害样地横坑切梢小蠹外,其他小蠹的空间依赖范围为4.01—7.45 m。横坑切梢小蠹和云南切梢小蠹在不同受害林分中拟合的半变异函数模型在球形模型和高斯模型之间转换。同域共存关系不影响不同种群密度下的切梢小蠹种群空间分布类型,但影响其半变异函数模型和理论参数。     

Coexistence of drosophilid flies: Aggregation, patch size diversity and parasitism

We carried out field experiments to investigate the coexistence of Drosophila species in domestic and forest areas on the basis of the aggregation model. Three cosmopolitan species Drosophila simulans Sturtevant, Drosophila melanogaster Meigen and Drosophila immigrans Sturtevant, and a native species, Drosophila auraria Peng, emerged abundantly from banana placed at the domestic station, while Drosophila immigrans and five native species, Drosophila lutescens Okada, Drosophila rufa Kikkawa and Peng, Drosophila bizonata Kikkawa and Peng, Drosophila sternopleuralis Okada and Kurokawa and Scaptodrosophila coracina (Kikkawa and Peng), were abundant at the forest station. The present analysis suggests that their coexistence was facilitated by the aggregation mechanism. In the cosmopolitan species, the density of individuals that emerged from patches increased with the increase of patch size, but the relationship between fly density and patch size was not clear in the native species. This difference in distribution patterns between the cosmopolitan and native species is likely to be due to the difference in the female visiting behavior. In the present analysis, however, it was not clear whether patch size diversity facilitated their coexistence or not. The effect of patch size diversity may have been masked, because the effect of aggregation was more prominent. The rate of parasitism by wasps was high in October at the domestic station, and in May and June at the forest station. The present result suggests that the rate of parasitism was density-dependent, at least at the domestic station, and therefore parasitism facilitates the coexistence of drosophilid species in domestic areas.     

不同林分白蜡树云斑白条天牛种群空间格局地统计学分析

云斑白条天牛是我国重要林业害虫,在黄河三角洲地区对白蜡树造成严重危害。利用地统计学方法,通过调查城市行道绿化林、庭院绿化林、公路林和片林4种不同林分类型的白蜡树林地,以产卵刻槽、排粪孔和羽化孔为调查指标,对危害白蜡云斑白条天牛种群卵、幼虫、成虫(蛹)的空间格局进行了研究。结果表明:除片林样点成虫(蛹)的半变异函数模型为指数模型外,危害白蜡云斑白条天牛种群卵、幼虫、成虫(蛹)在不同林分类型下的半变异函数模型均为球形模型,其指明空间分布均为聚集分布,种群的聚集分布习性与林分类型相关性不强。但不同林分类型云斑白条天牛种群的空间相关性地统计学参数存在差异,片林调查样点的卵、幼虫和成虫(蛹)的变程a、块金值C0和基台值C0+C均小于其他3种林分类型的统计值,片林样点成虫(蛹)的半变异函数模型不同于其他林分类型为指数模型。     

Spatial distributions and clutch sizes of Drosophila species ovipositing on cherry fruits of different stages

In the aggregation theory, aggregation of eggs is one of important conditions for the coexistence of species. However, aggregation of eggs by clutch laying does not always promote coexistence, whereas aggregation of eggs by aggregated distributions of ovipositing females always has a significant contribution to the coexistence. In this study, spatial distributions of three Drosophila species across naturally occurring cherry fruits were studied with relation to their clutch sizes. Drosophila suzukii oviposited eggs mainly on fresh fruits on trees, and its eggs were randomly distributed across cherry fruits. The emergence data also indicated random spatial distributions of this species. Random egg distributions of this species are explained by random visits of females to fruits and the production of clutches of mostly single eggs. On the other hand, D. lutescens and D. rufa oviposited on fallen fruits, showed aggregated distributions in the emergence data, and frequently produced clutches of a few eggs. In these species, the degree of aggregation was usually significantly lower than the expectation based on random visits of females to fruits and their clutch sizes observed in the present experiments, indicating that their aggregation is unlikely to arise from aggregated distributions of ovipositing females. Thus, the spatial aggregation of these species does not necessarily lead to their coexistence.     

The effect of travel time on oviposition behavior and spatial egg aggregation: experiments with Drosophila

A higher degree of spatial egg aggregation is often observed in environments where resource patches are more sparsely distributed. This suggests a higher probability of species coexistence when resource distribution is sparse. However, it is still unclear how the degree of spatial egg aggregation increases. I propose a model to explain this phenomenon, which assumes that (i) egg load (the number of mature eggs in ovaries) increases in the travel period between resource patches and (ii) the retention of eggs in the ovaries is harmful (egg load pressure). With these assumptions, a female would lay accumulated eggs on arrival at a new resource patch, resulting in a higher degree of spatial egg aggregation. Laboratory experiments with three drosophilid species, Drosophila simulans Surtevant, Drosophila auraria Peng, and Drosophila immigrans Sturtevant, support the model. This study provides evidence that host availability affects the spatial egg aggregation via egg load.     

Stabilization effects of spatial aggregation of vectors in plant disease systems

Stabilization effects of spatial aggregation of vectors were examined in insect-borne plant disease systems by constructing a model that describes the yearly dynamics of rice stripe virus disease transmitted by the small brown planthopperLaodelphax striatellus (Fallén). Two transmission paths between vectors were considered: vertical transmission from parents through eggs, and horizontal transmission from infected plants by acquisition feeding. In this model, a paddy field was divided into quadrats and horizontal transmission was assumed to occur within each quadrat. A negative binomial distribution was used to describe the frequency distribution of vectors per quadrat. The parameters of the model were estimated using field data collected in Ibaraki Prefecture, Japan. The model showed that (1) the disease cannot invade into an epidemiological system if the mean crowding of vectors is less than a critical value, (2) the proportion of infected vectors is maintained at about 30% irrespective of the vector density if vectors are highly aggregated, and (3) the proportion of infected plants is maintained at a low level irrespective of the vector density if vectors are highly aggregated. It was also shown that these stabilization effects of aggregation in this epidemiological system come from a mechanism that is common to other systems such as single-species systems and competition systems.     

Parasitoid aggregation and interference in host–parasitoid dynamics

1. Parasitoids do not distribute themselves evenly among available patches, which has an important bearing on the dynamics of host–parasitoid interactions. This study examined the density‐dependent nature of aggregation of the parasitoid Dirhinus giffardii Silvestri on the oriental fruit fly host, Bactrocera dorsalis (Hendel) distributed among discrete patches. 2. Four artificial patches were created in a cage, and the number of hosts in each patch was manipulated. Parasitoids were released into the cage, and whether parasitoid density and host density influence the degree of parasitoid aggregation was examined. 3. Parasitoid aggregation became stronger (e.g. uneven distribution among patches) as the parasitoid density decreased and also as the host density increased. The index of parasitoid aggregation was not influenced by the distribution of hosts among patches. 4. The empirically characterised aggregation pattern was incorporated in a host–parasitoid model that consists of one host and one parasitoid species. The analysis of the model shows that an unstable system (i.e. the coexistence of the host and parasitoid is impossible) can be stabilised (i.e. coexistence is possible) when the parasitoid aggregates in a way that is consistent with the pattern found in the experiment.     

Nonlinear frequency‐dependent selection promotes long‐term coexistence between bacteria species

Negative frequency‐dependent selection (NFDS) is an important mechanism for species coexistence and for the maintenance of genetic polymorphism. Long‐term coexistence nevertheless requires NFDS interactions to be resilient to further evolution of the interacting species or genotypes. For closely related genotypes, NFDS interactions have been shown to be preserved through successive rounds of evolution in coexisting lineages. On the contrary, the evolution of NFDS interactions between distantly related species has received less attention. Here, we tracked the co‐evolution of Escherichia coli and Citrobacter freundii that initially differ in their ecological characteristics. We showed that these two bacterial species engaged in an NFDS interaction particularly resilient to further evolution: despite a very strong asymmetric rate of adaptation, their coexistence was maintained owing to an NFDS pattern where fitness increases steeply as the frequency decreases towards zero. Using a model, we showed how and why such NFDS pattern can emerge. These findings provide a robust explanation for the long‐term maintenance of species at very low frequencies.     

云南兰坪云南红豆杉种群年龄结构与空间分布格局分析

利用点格局分析法对滇西北兰坪县4个云南红豆杉(Taxus yunnanensis)种群的年龄结构、不同生长阶段空间分布格局及其关联性进行分析。结果表明:(1)林窗与人为干扰影响4个云南红豆杉种群的龄级结构,小林窗的种群呈稳定型;较大林窗的种群呈进展型;群落结构完整未出现林窗和有较大人为干扰的种群年龄结构均呈衰退型,幼苗、幼树与小树个体缺乏,种群存在一定程度的更新困难,林窗的大小是种群更新的重要因素。(2)人为干扰、自然生境与本身生物学特性影响4个种群空间分布格局,种群1整体及其不同生长阶段个体均呈聚集分布;种群2和种群4在小尺度呈聚集分布,而在大尺度上呈随机分布;种群3随着空间尺度增大分布格局表现为聚集→随机→聚集趋势。(3)种群2中幼苗、小树和中树在小尺度下表现为聚集分布,其他尺度下表现为随机分布;种群3的小树阶段聚集分布和随机分布皆有出现,中树与大树在不同尺度上表现为聚集分布;种群4聚集分布的强度随生长阶段的增加在减弱。(4)4个种群各发育阶段间皆呈或接近显著正相关,种内竞争弱,有利于种群维持。     

Distribution of Insect Attacks in Biological Control of Weeds: Infestation of Centaurea virgata Flowerheads by a Gall Fly

The success of biological control efforts to reduce weed density through release of insects may depend as much on the distribution of insect attacks among individual plants or plant parts as on the mean level of infestation. We used an index of dispersion to describe the distribution of Urophora quadrifasciata (Diptera: Tephritidae) galls among squarrose knapweed (Centaurea virgata) flowerheads at 18 west central Utah sites in the first 5 years following introduction of the biological control agent. Two thirds of the samples showed a significantly aggregated distribution of galls among flowerheads. Statistical analysis showed that site and year accounted for relatively small proportions of the variance in the index of dispersion. The degree of gall aggregation among flowerheads was positively correlated with the mean flowerhead quality (mean number of seeds per flowerhead; P = 0.013) and tended to be negatively correlated with the mean fly density per flowerhead at a site in a given year (P = 0.097). Our data suggest that higher quality flowerheads, and possibly higher quality plants, are preferentially attacked by U. quadrifasciata and therefore are more heavily subject to reduced reproductive potential through biological control. However, an aggregated distribution of fly attacks may undercut the potential of the fly to reduce seed production by the weed population as a whole. Understanding both the distribution of insect attacks among individual plants and the behavioral mechanisms producing such distribution patterns is important to the biological control of weeds.     

桥山林区麻栎种群不同发育阶段空间格局及关联性

为探究麻栎种群不同发育阶段的空间分布特征及关联性,以黄土高原南部桥山林区麻栎天然次生林为研究对象,用L(r)函数对麻栎种群不同发育阶段空间分布特征及关联性进行分析。结果表明:(1)样地内麻栎种群各发育阶段数量结构均为不规则倒"J"型,种群结构稳定,能实现持续更新。(2)麻栎种群总体的空间分布特征受生境异质性影响较大,纯林样地中,种群在0—10 m尺度上表现为高强度聚集分布,5—35 m尺度表现为低强度聚集;混交林样地中,0—5 m尺度上表现为高强度聚集分布,5—35 m尺度上则表现为低强度聚集分布。(3)随着种群的发育及尺度的增大,麻栎种群空间聚集强度减弱,纯林样地内,麻栎幼苗在0—6 m的小尺度表现为聚集分布,6—12 m尺度上表现为随机分布;幼树在各尺度上均表现为聚集分布;中龄树与成龄树在各尺度上均表现为随机分布。混交林样地中,仅幼苗在0—6 m尺度上表现为聚集分布,其余各阶段在各尺度下均趋于随机分布。(4)种群不同发育阶段不同尺度空间关联性不同,纯林样地中,幼苗与幼树在1—2 m小尺度上呈负相关,幼树与中龄树在8 m尺度呈正相关,其余各生长阶段之间在任意尺度上均无关联性;混交林样地中,幼树与中龄树在2—12 m尺度上表现为正相关,其余各生长阶段之间在各尺度上均无关联。在未来的森林经营中,应对不同发育阶段、不同生境的种群进行不同抚育措施,促进种群良性发育。     

Isolation by distance and a chromosomal cline in the Cayapa cytospecies of <Emphasis Type="Italic">Simulium exiguum</Emphasis>, the vector of human onchocerciasis in Ecuador

The population genetic structure of the Cayapa cytospecies of Simulium exiguum, the vector of onchocerciasis, was analysed using allozyme frequency and chromosomal inversion polymorphism data from 6 and 15 populations respectively, collected in Ecuador. Eight allozyme loci were scored. No unique allozyme markers were found enabling us to identify biting adults of the vector from the non-vector Bucay cytotype. Mannose-phosphate isomerase (Mpi) contributed largely to the significant heterogeneity in gene frequency among populations of the Cayapa cytospecies and also to the overall population structuring (F_ST=0.015 ± 0.014) which fitted the isolation by distance model. However, heterozygote deficits were recorded for Mpi in four of the six populations, which could indicate that selection is acting at this locus but this hypothesis will require further convincing evidence. Furthermore the significant population structuring of allozymes was not evident when Mpi was omitted from the analysis. All inversion polymorphisms (IIS-B, IIS-F, IIL-A and IIL-B) were in Hardy-Weinberg equilibrium, showed significant heterogeneity between populations and revealed the occurrence of an altitudinal cline in inversion IIS-B frequency. The inversion polymorphisms revealed a significant degree of population structuring (F_ST=0.083 ± 0.027), which can be explained by the isolation by distance model. A UPGMA cluster analysis revealed the relatively remote, high altitude Rio Mira populations to be the most genetically distinct.     

Prevalence of the prothrombin G20210A polymorphism in the Lebanese population: use of a reverse hybridization strip assay approach

The factor II (prothrombin) G20210A gene polymorphism is the second most common SNP reported in VTE where it is associated with elevated plasma prothrombin levels and with a 3-fold increased risk. We studied the distribution of the G/G, G/A, and A/A genotypes of the Prothrombin G20210A gene mutation in the general Lebanese population using a novel technique in order to assess their prevalence, compare the results to previously reported data and to describe an available method that will permit easy and fast identification of the mutation. Prothrombin different genotypes were determined using the Cardiovascular Disease (CVD) StripAssay which is based on a Polymerase Chain Reaction-Reverse hybridization technique and DNA from 205 unrelated healthy donors from our HLA-bank was used. The prevalence of G/G, G/A, and A/A genotypes was found to be 98.54, 1.46, and 0%, respectively, with G and A allelic frequency of 99 and 1%, respectively. The sampled Lebanese population showed prothrombin genotypes distribution similar to Caucasians, and our results are comparable to other reports on the Lebanese healthy individuals. However, this is the first report on the prevalence of prothrombin G20210A mutation using this technique. Our results suggest that this approach is reliable and can be used as an assessment for thrombophilia profile. In addition, future investigations should be conducted to assess the contribution of the prothrombin G20210A mutation, on its own and in collaboration with other factors, in various clinical entities notably VTE.     

庐山香果树毛竹混交林空间格局研究

为了解庐山毛竹入侵对香果树的影响,采用Ripley’sK(t)函数分析香果树毛竹混交林群落空间分布格局和种间关联关系。结果表明:香果树幼树在较小的尺度上呈聚集分布,较大尺度上随机分布直至均匀分布;香果树成年树在较小的尺度上呈随机分布,较大尺度上聚集分布;毛竹在所有的研究尺度上为显著聚集分布,且随着尺度的增大,聚集强度增加。毛竹与香果树幼树在较小的尺度上没有明显关联性,在较大的尺度上呈显著负相关;毛竹与香果树成年树在一系列尺度上均表现为显著负相关。根据空间关联性分析结果,应从幼龄起对生长有香果树的森林群落进行必要的管理,伐除毛竹及一些影响较大的其它乔木树种,挖除地下竹鞭,为香果树提供良好的生长环境,进而恢复其种群的天然合理配置。否则,香果树这一珍贵的植物资源在庐山将有灭绝的危险。     

Binomial sequential sampling of adult Saccharicoccus sacchari on sugarcane

The between-stalk dispersion characteristics of adults of the pink sugarcane mealybug Saccharicoccus sacchari (Cockerell) were determined in southern Queensland. Iwao's patchiness regression was inappropriate to describe the relationship between mean and variance. Taylor's power law indicated that adults were aggregated, especially at the beginning and end of the ratoon growth period. Binomial data were modelled by the Nachman model; the model of Grout and two models of Wilson & Room were inappropriate to describe the relationship between proportion of stalks infested and mean numbers of adults per stalk. Relationships to determine sample sizes for fixed levels of precision and binomial fixed-precision-level stop lines are developed for different sampling times using Taylor's power law and Nachman's equation.     

闽东北海域中华管鞭虾种群聚集特性

以负二项参数、平均拥挤度和聚块指数为种群分布格局强度指标,分析了闽东北海域中华管鞭虾(Solenocera crassicornis)种群聚集特性,探讨了种群聚集特性的驱动因子。结果表明,中华管鞭虾种群聚集强度较强,个体平均拥挤度较高,种群主要集中于少数团聚的斑块,不同季节种群聚集特性差异显著,春季,种群聚集强度较强,个体平均拥挤度最低,种群主要由单一团聚的斑块组成;夏季,种群聚集强度较弱,个体平均拥挤度高,种群主要由4个斑块组成;秋季,种群聚集强度最弱,个体平均拥挤度较低,种群主要由7个斑块组成;冬季,种群聚集强度最强,个体平均拥挤度最高,种群主要由单一团聚的大斑块组成。随着个体生长速度的增大,种群呈现扩散的趋势,饵料浮游动物生物量和底层水温是影响种群聚集强度的主要因子。     

Effect of Moniliformis moniliformis density on distribution within the definitive host population (Rattus norvegicus)

The population dynamics of Moniliformis moniliformis was studied in ‘free-ranging’ laboratory rats, Rattus norvegicus, presented with different relative density levels of M. moniliformis in cockroaches, Periplaneta americana. Changes in selected population parameters of the negative binomial distribution were evaluated as indicators of changes in aggregation. A significant increase in the degree of aggregation of parasites occurred as a result of the increase in relative density of infective stages available to the rats. This increase in aggregation was due to the increase in over-dispersion that occurred in female rats only. The degree of aggregation in females was found to be significantly higher than that in males at both treatment levels. The best indicators of the degree of aggregation were found to be the ratio of the variance to the relative density and the ratio of the log-variance to log-relative density. Changes in k were not correlated with changes in over-dispersion or the relative density.     

Development of a simple functional marker for fragrance in rice and its validation in Indian Basmati and non-Basmati fragrant rice varieties

Fragrance development in rice has been reported due to a 8-bp deletion in the exon 7 of badh2 gene located on Chromosome 8S. Multiplex markers targeting the functional InDel polymorphism was earlier reported for genotyping fragrance trait, but the marker was observed to be inconsistent and difficult to use. We have developed a simple, co-dominant, functional marker for fragrance trait, which can be resolved in an agarose gel and validated in Basmati and non-Basmati aromatic rice varieties and in a mapping population segregated for fragrance trait. The marker targets the InDel polymorphism in badh2 gene and amplifies 95 and 103 bp fragments in fragrant and non-fragrant genotypes, respectively. The newly developed marker was highly efficient in discriminating all fragrant and non-fragrant genotypes and showed perfect co-segregation with the trait of fragrance in the mapping population. We recommend the use of this simple, low-cost marker in routine genotyping for fragrance trait in large scale breeding materials and germplasm.     

Aggregation and species coexistence in fleas parasitic on small mammals

The aggregation model of coexistence states that species coexistence is facilitated if interspecific aggregation is reduced relative to intraspecific aggregation. We investigated the relationship between intraspecific and interspecific aggregation in 17 component communities (the flea assemblage of a host population) of fleas parasitic on small mammals and hypothesized that interspecific interactions should be reduced relative to intraspecific interactions, facilitating species coexistence. We predicted that the reduction of the level of interspecific aggregation in relation to the level of intraspecific aggregation would be positively correlated with total flea abundance and species richness of flea assemblages. We also expected that the higher degree of facilitation of flea coexistence would be affected by host parameters such as body mass, basal metabolic rate (BMR) and depth and complexity of burrows. Results of this study supported the aggregation model of coexistence and demonstrated that, in general, a) conspecific fleas were aggregated across their hosts; b) flea assemblages were not dominated by negative interspecific interactions; and c) the level of interspecific aggregation in flea assemblages was reduced in relation to the level of intraspecific aggregation. Intraspecific aggregation tended to be correlated positively to body mass, burrow complexity and mass-independent BMR of a host. Positive interspecific associations of fleas tended to occur more frequently in species-rich flea assemblages and/or in larger hosts possessing deep complex burrows. Intraspecific aggregation increased relative to interspecific aggregation when species richness of flea infracommunities (the flea assemblage of a host individual) and component communities increased. We conclude that the pattern of flea coexistence is related both to the structure of flea communities and affinities of host species.     

Utility of the methylation-sensitive amplified polymorphism (MSAP) marker for detection of DNA methylation polymorphism and epigenetic population structure in a wild barley species (<Emphasis Type="Italic">Hordeum brevisubulatum</Emphasis>)

We report here that by using a modified scoring criterion, the methylation-sensitive amplified polymorphism or MSAP marker can be used effectively to detect polymorphism in DNA methylation patterns within and among populations of a perennial wild barley species, Hordeum brevisubulatum. Twenty-four selected individual genotypes representing four natural populations of H. brevisubulatum distributed in the Songnen Prairie in northeastern China were studied. The utility of MSAP was evidenced by its detection of high levels of polymorphism in DNA methylation patterns between individuals within a given population, and the clear inter-population differentiation in methylation patterns (methylation-based epigenetic population structure) revealed among the four populations. The resolving power of MSAP to detect DNA methylation polymorphism was found to be comparable with that of a retrotransposon-based sequence-specific amplified polymorphism marker, or SSAP, to detect genetic polymorphism in the same set of plants, suggesting that MSAP with a modified scoring criterion can be used efficiently to detect DNA methylation polymorphism and assess epigenetic population structure in natural plant populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.