The effect of developmental variation on hybridization and rarity in Stipoid grasses

Developmental variation in some Achnatherum species was evaluated for two kinds of groups, (1) species pairs that do or do not hybridize and (2) rare and common species. Variation was assessed in two different ways, one that captures developmental events expressed in an individual and one reflecting developmental events that are part of the information systems of a species. The former captures the effect of the environment on development; the latter expresses developmental variation without the information controlling ontogenetic events being filtered through the environment. Development variation is lower for species pair that hybridizes when the effect of development in an individual is expressed. When that variation is of the species information system, the non-hybridizing species pair shows a lower level of developmental variation, likely the effect of greater similarity between those species. It is lower for rare species when variation in development is that of the information system of a species. The lower level of developmental variation seen in species pairs that hybridize likely reflects the necessity of compatible developmental programs in order for a hybrid to appear. Lower variation in development in rare species is expected. Here, though, the lower variation is a property of the species and not of the environment.     

Conservation of taxonomic and biological trait diversity of European stream macroinvertebrate communities: a case for a collective public database

The use of databases for the conservation of biodiversity is increasing. During the last decade, such a database has been created for European stream macroinvertebrates. Today, it includes 527 sites that are the least human-impacted representatives of many stream types across many European regions. It includes data on the abundance of 312 invertebrate genera, several environmental site characteristics, collection methods, bibliographic data sources, and 11 biological traits of the genera (e.g. size, life cycle, food and feeding habits, described in 61 categories). The database will be useful in addressing many topics that are potentially relevant to biodiversity conservation. To illustrate this potential, we provide examples of how the data could be exploited. First, we describe the frequency of some taxonomic and biological characteristics (e.g. richness and diversity of genera and traits) of the macroinvertebrate communities and assess how these characteristics are related (e.g. how trait richness increases with genus richness). Second, we describe the frequency of some characteristics of the genera and traits (e.g. occurrence frequency, abundance, dispersion index) and again assess how these characteristics are related (e.g. how occurrence increases with abundance). Finally, we suggest how the database could be developed into a collective, publicly accessible database that covers stream types and regions of Europe more comprehensively.     

Timescales of population rarity and commonness in random environments

This is a mathematical study of the interactions between non-linear feedback (density dependence) and uncorrelated random noise in the dynamics of unstructured populations. The stochastic non-linear dynamics are generally complex, even when the deterministic skeleton possesses a stable equilibrium. There are three critical factors of the stochastic non-linear dynamics; whether the intrinsic population growth rate (lambda) is smaller than, equal to, or greater than 1; the pattern of density dependence at very low and very high densities; and whether the noise distribution has exponential moments or not. If lambda < 1, the population process is generally transient with escape towards extinction. When lambda > or = 1, our quantitative analysis of stochastic non-linear dynamics focuses on characterizing the time spent by the population at very low density (rarity), or at high abundance (commonness), or in extreme states (rarity or commonness). When lambda >1 and density dependence is strong at high density, the population process is recurrent: any range of density is reached (almost surely) in finite time. The law of time to escape from extremes has a heavy, polynomial tail that we compute precisely, which contrasts with the thin tail of the laws of rarity and commonness. Thus, even when lambda is close to one, the population will persistently experience wide fluctuations between states of rarity and commonness. When lambda = 1 and density dependence is weak at low density, rarity follows a universal power law with exponent -3/2. We provide some mathematical support for the numerical conjecture [Ferriere, R., Cazelles, B., 1999. Universal power laws govern intermittent rarity in communities of interacting species. Ecology 80, 1505-1521.] that the -3/2 power law generally approximates the law of rarity of 'weakly invading' species with lambda values close to one. Some preliminary results for the dynamics of multispecific systems are presented.     

Rare plants at the extremes of distribution: broadly and narrowly distributed rare species

The flora of North America north of Mexico was used to study rare species at the two extremes of geographic distribution: endemic species, those with large local populations but small geographic ranges, and suffusively rare species, those with small local populations but large geographic ranges. The taxonomic distribution, geographic distribution, and life history characteristics of the two groups were compared. Only 2% of North American species are suffusively rare, while 22.6% of species are endemic to one state or province. Suffusively rare species are significantly more likely to be seedless vascular plants and monocots than expected, and are less likely to be eudicots. Conversely, endemic species are more likely to be eudicots, and less likely to be monocots. Suffusively rare species are most abundant in Canada and the northeastern United States, whereas there are few endemic species in those areas. The highest proportions of endemic species are found in California, Florida, and Texas. Wetland habitats support many suffusively rare species, but few endemic species. Neither are common in alpine habitats. Suffusively rare and endemic species also differ in the dominant growth form. Suffusively rare species are most likely to be herbaceous eudicots, and less likely to be shrubs or shrub-herbs. Endemic species are also likely to be herbaceous, but are also frequently shrubs. A high proportion of endemic species exhibit plasticity in growth form, whereas few suffusively rare species have plastic growth forms. While both groups contain rare species, they differ considerably in geographic distribution and life history traits.     

Diversity and geographical distribution of members of the Streptomyces violaceusniger 16S rRNA gene clade detected by clade-specific PCR primers

The Streptomyces violaceusniger 16S rRNA gene clade contains organisms that are of ecological interest and a rich source of novel bioactive metabolites. Improvements in the classification of members of the S. violaceusniger clade made it possible to design, evaluate and use an oligonucleotide primer set to gain an insight into the presence, distribution and taxonomic diversity of members of this taxon in environmental samples. In silico testing showed that the primers had a perfect match with representatives of the S. violaceusniger clade. The primers, designated S-S-Svio-66-a-S-20 and S-S-Svio-1274-a-A-20, amplified an approximately 1190-bp stretch of 16S rRNA gene from authenticated members of the S. violaceusniger clade, but not from representatives of other actinomycete taxa. Following amplification of DNA extracted from sediment and soil samples, the sequences of cloned PCR products confirmed the specific amplification of target sequences in 87% of the clones; the use of 16S rRNA gene fragment similarity correlations indicated that the clones represented new species. The primers can be used to facilitate the isolation of novel members of the S. violaceusniger 16S rRNA gene clade by allowing prescreening of environmental samples and the subsequent detection and retrieval of targetted strains through the use of selective isolation procedures.     

Genetic diversity analysis of Rhodothermus reflects geographical origin of the isolates

The genetic diversity and relationships of 81 Rhodothermus isolates from different geothermal environments in Iceland were examined by analysis of electrophoretically demonstrable allelic variation of 13 genes encoding enzymes. All the enzymes were polymorphic. A total of 71 distinctive multilocus genotypes (electrophoretic types, ETs) were identified. The mean genetic diversity per locus (H _t ) was 0.586. The relatively high genetic variance observed within Rhodothermus isolates from different locations is most likely the result of genetic changes occurring independently in the locations studied. A high G _st value (0.284) indicates that a considerable part of the variance observed is due to differences between locations. Cluster analysis revealed two major groups of ET clusters diverging at a genetic distance of 0.75, reflecting strongly the geographic origin of isolates. Estimation of the association index (I _A) indicates that Rhodothermus marinus is a clonal species in which recombination events occur rarely. Partial or whole sequencing of the 16S rRNA genes of Rhodothermus isolates grouping at genetic distance of 0.40 confirmed that all the isolates belonged to the species Rhodothermus marinus. The results of this study confirm that, despite phylogenetic and phenotypic similarity, genetic diversity within Rhodothermus marinus is quite high. Received: January 21, 2000 / Accepted: April 27, 2000     

The rarity concept and the commonness of rarity in freshwater zooplankton

1. Regional distribution, frequency of occurrence and relative abundance were scored in 2467 Norwegian lakes for all the recorded 130 species of crustacean zooplankton. The majority of species were rare in the sense that 65% of species were recorded in fewer than 10% of localities. Only six species were recorded in more than 50% of localities, and the median number of species in a given locality was 14 (i.e. 10% of the total species pool). 2. Abundances of all species were scored according to the fraction of lakes in which they were recorded, their geographical range of distribution, and their numerical abundance. Typically the most rare species were rare by all three criteria, and vice versa for the common species, pointing to rarity as an inherent property of some species. For some species this rarity reflects being on the edge of their distributional range, while for others rarity seems to be a consequence of their life cycle strategies. 3. Some of the truly rare species have high dispersal rates and high colonization abilities, but are rapidly replaced by other species. Others are confined to specific habitats, often highly eutrophic, pointing to highly specialized niche adaptations. 4. A major cause for the few truly common species seems to be the limited number of species that are able to coexist within a given locality, reflecting ‘the ghost of competition past’ and predation pressure. 5. While species composition and species richness may reflect colonization abilities and stochastic events, the presence or absence of species is not only a random lottery but also a consequence of species‐specific attributes.     

The geographical distribution of lymphatic filariasis infection in Malawi

Background

Papua New Guinea is the only endemic country in the Western Pacific Region that has not yet introduced a countrywide programme to eliminate lymphatic filariasis. However, on Misima Island in Milne Bay Province, government and private sectors have collaborated to implement a pilot elimination programme. Although interim evaluation indicated that the programme has been parasitologically successful, an appreciation that sustainable health gains depend on understanding and accommodating local beliefs prompted this qualitative study.

Methods

We investigated Misima community members knowledge and attitudes about lymphatic filariasis and the elimination programme. A combination of focus groups and key informant interviews were used to explore participants perceptions of health; knowledge of the aetiology and symptoms of filariasis, elephantiasis and hydrocele; attitudes towards the disease and mass drug distribution; and the social structure and decision-making protocols within the villages.

Results

Focus group discussions proved inferior to key informant interviews for gathering rich data. Study participants did not consider lymphatic filariasis ("pom") a major health problem but were generally positive about mass drug administration campaigns. A variety of conditions were frequently and incorrectly attributed to filariasis. Participants expressed the belief that individuals infected with filariasis always had visible manifestations of disease. A common misconception was that taking drugs during campaigns provided long-term immunity against disease. The role of mosquito vectors in transmission was not generally appreciated and certain clinical presentations, particularly hydrocele, were associated with supernatural forces. Multiple adverse events were associated with mass drug administration campaigns and most study participants mentioned community members who did not participate in campaigns.

Conclusion

Important issues requiring educational intervention and elimination activity modification in the Misima region were identified during this study. Research outcomes should assist Papua New Guinea in developing and implementing a national elimination strategy and inform discussions regarding the appropriateness of current elimination strategies.     

转基因鸡的制备方法探讨

由于鸡本身的众多优点,转基因鸡的研究逐渐受到了研究者的重视,简要介绍了转基因鸡的发展史,对各种转基因技术方法进行了比较和分析,提出了每种方法的优缺点,尤其在精子介导法上作了较为详细的论述,并展望了转基因鸡的应用前景。     

中国凤蝶科昆虫地理分布的聚类分析

在对中国凤蝶科昆虫多样性分布统计的基础上,用特有性简约性方法构建中国凤蝶科昆虫的分布区分支图。结果表明,中国凤蝶在8大生物地理分布区中可分成6个聚类群,至少有5次大的隔离分化事件造成了目前我国凤蝶科昆虫的分布格局。分支图显示出东北区与蒙新区比其他分布区形成要早,华南区和西南区的凤蝶多样性最为丰富,推测其原因可能与生态环境等因素有关。     

Latitudinal gradients in abundance, and the causes of rarity in the tropics: a test using Australian honeyeaters (Aves: Meliphagidae)

Several studies have uncovered interspecific latitudinal gradients in abundance (population density) such that tropical species tend to be, on average, less abundant than species at higher latitudes. The causes of this relationship remain poorly studied, in contrast to the relative wealth of literature examining the relationship to latitude of other variables such as range size and body mass. We used a cross-species phylogenetic comparative approach and a spatial approach to examine three potential determining factors (distribution, reproductive output and climate) that might explain why abundance correlates with latitude, using data from 54 species of honeyeaters (Meliphagidae) in woodland environments in eastern Australia. There is a strong positive correlation between mean abundance and latitude in these birds. Reproductive output (clutch size) was positively linked to both abundance and latitude, but partial correlation analysis revealed that clutch size is not related to abundance once the effects of latitude are removed. A subsequent multiple regression model that also considered range size, clutch size and body mass showed that latitude is the only strong predictor of abundance in honeyeaters. In the separate spatial analysis, the climatic variables that we considered (temperature, rainfall and seasonality) were all strongly linked to latitude, but none served as a better predictor of abundance than latitude per se, either individually or collectively. The most intriguing result of our analyses was that the cross-species latitudinal pattern in abundance was not evident within species. This suggests an intrinsic cause of the pattern of ‘rarity in the tropics’ in Australian honeyeaters. We suggest that evolutionary age may provide a key to understanding patterns of abundance in these birds.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

The age and geographical distribution of fossil cercopithecids in China

Cercopithecids did not arrive in China until the latest Tertiary, relatively late in their evolutionary history. Cercopithecines are represented in the Chinese fossil record by two genera,Procynocephalus andMacaca, both of which made their appearance in the Late Pliocene or Early Pleistocene, but only one of which,Macaca, was widely distributed throughout the Quaternary and remains in the country today. The much less well known genusProcynocephalus disappeared from China in the late Early Pleistocene, but is of considerable interest because it appears to have been part of a radiation of large terrestrial cercopithecines that extended throughout portions of southern and eastern Asia. Colobines are poorly represented in the fossil record of China. Aside from a few scattered occurrences ofRhinopithecus in the Middle and Late Pleistocene records of southern China, the subfamily is represented by only one other intriguing specimen. This is the large and nearly complete mandible now classified as «Megamacaca lantianensis» from the Gongwangling locality of Lantian, Shaanxi Province. The specimen was retrieved from sediments of late Early Pleistocene age and was associated with elements of a typical southern,Ailuropoda — Stegodon fauna. The distribution of cercopithecids, especiallyMacaca, in China followed the southern and eastern retreat of subtropical habitats during the course of the Pleistocene.     

The geographical distribution of Naididae (Oligochaeta) in Britain

A compilation of records of the geographical location of naidid species in Britain is presented. Many species previously considered rare are shown to be widely distributed.     

湖北地区蝇科物种多样性及地理分布

研究湖北地区蝇科已知种类及区系组成资料,并与邻近的江西、湖南和河南3地区蝇科区系进行比较,分析湖北地区蝇科物种多样性及地理分布。湖北地区已知蝇科物种150种,其中东洋界为主的种类69种,占46.0%;古北界为主的种类57种,占38.0%;广布两界的种类24种,占16.0%。结论认为,湖北地区蝇科区系应划归东洋界。