Spatiotemporal heterogeneity of plankton communities in Lake Donghu, China, as revealed by PCR–denaturing gradient gel electrophoresis and its relation to biotic and abiotic factors

The 16S and 18S rRNA genes of planktonic organisms derived from five stations with nutrient gradients in Lake Donghu, China, were studied by PCR–denaturing gradient gel electrophoresis (DGGE) fingerprinting, and the relationships between the genetic diversity of the plankton community and biotic/abiotic factors are discussed. The concentrations of total nitrogen (TN), total phosphorus (TP), NH₄-N and As were found to be significantly related ( P <0.05) to morphological composition of the plankton community. Both chemical and morphological analyses suggested that temporal heterogeneity was comparatively higher than spatial heterogeneity in Lake Donghu. Although the morphological composition was not identical to the DGGE fingerprints in characterizing habitat similarity, the two strongest eutrophic stations (I and II) were always initially grouped into one cluster. Canonical correspondence analysis suggested that the factors strongly correlated with the first two ordination axes were seasonally different. The concentrations of TN and TP and the densities of rotifers and crustaceans were generally the main factors related to the DGGE patterns of the plankton communities. The study suggested that genetic diversity as depicted by metagenomic techniques (such as PCR-DGGE fingerprinting) is a promising tool for ecological study of plankton communities and that such techniques are likely to play an increasingly important role in assessing the environmental conditions of aquatic habitats.     

THE CELLULAR IMMUNE RESPONSE OF DAPHNIA MAGNA UNDER HOST–PARASITE GENETIC VARIATION AND VARIATION IN INITIAL DOSE

In invertebrate–parasite systems, the likelihood of infection following parasite exposure is often dependent on the specific combination of host and parasite genotypes (termed genetic specificity). Genetic specificity can maintain diversity in host and parasite populations and is a major component of the Red Queen hypothesis. However, invertebrate immune systems are thought to only distinguish between broad classes of parasite. Using a natural host–parasite system with a well‐established pattern of genetic specificity, the crustacean Daphnia magna and its bacterial parasite Pasteuria ramosa, we found that only hosts from susceptible host–parasite genetic combinations mounted a cellular response following exposure to the parasite. These data are compatible with the hypothesis that genetic specificity is attributable to barrier defenses at the site of infection (the gut), and that the systemic immune response is general, reporting the number of parasite spores entering the hemocoel. Further supporting this, we found that larger cellular responses occurred at higher initial parasite doses. By studying the natural infection route, where parasites must pass barrier defenses before interacting with systemic immune responses, these data shed light on which components of invertebrate defense underlie genetic specificity.     

最大信息熵原理与群体遗传平衡

建立了用最大信息熵原理推导群体遗传平衡定律的统一数学模型,并给出了模型的统一解,此解正是Hardy-Weinberg定律所给出的平衡群体的基因型频率,说明当群体信息熵达到最大时,群体基因型频率不再变化,即达到“平衡”。这证明了最大熵分布就是Hardy-Weinberg平衡分布。Hardy-Weinberg平衡定律与最大信息熵原理的内在一致性说明,杂交和随机交配是一个不可逆过程,使群体基因型信息熵增大,无序性增,是选择和近亲交配使群体的信息熵降低,有序性增加,育种过程实际就是调节群体信息熵的过程。过程信息熵的含义是表示一个概率分布的不确定性,最大熵原理意味着在一定的约束条件,选择具有最大不确定性的分布,从而其分布是最为随机的。最大熵原理在信息,工程,天文,地理,图像处理,模式识别等自然科学和社会科学领域都有广泛的成功应用,本文从群体遗传学角度证明了这一原理具有普遍适用性。熵是描述系统状态的函数,而最大熵原理则表明了系统发展变化的趋势,系统的最终状态必然是熵增加至最大值的状态,对于任何系统都是如此。因此,群体遗传系统的平衡定律可以统一用最大熵原理进行判定和描述;任意群体的基因型信息熵在随机交配世代传递时有不断增加的趋势;在一定约束条件下基因型信息熵达到最大值时,就称之为达到遗传平衡。本文将信息论原理应用于群体遗传学研究,揭示了基因信息熵的生物学意义,并表明可以用信息学和控制论的原理和方法来研究群体遗传学问题。     

Non-invasive genetic identification of small mammal species using real-time polymerase chain reaction

DNA identification of non-invasive samples is a potentially useful tool for monitoring small mammal species. Here we describe a novel method for identifying five small mammal species: wood mouse, bank vole, common shrew, pygmy shrew and water shrew. Species-specific real-time polymerase chain reaction primers were designed to amplify fragments of the mitochondrial cytochrome b gene from hair and scat samples. We also amplified nuclear DNA from scats, demonstrating their potential as a source of DNA for population genetic studies.     

Development of nuclear microsatellite markers for the threatened wetland plant Geranium soboliferum var. kiusianum (Geraniaceae)

Nuclear microsatellite markers were developed for the threatened plant Geranium soboliferum var. kiusianum, which has decreased its population size as a result of loss of its wetland habitat in Kyushu, Japan. Utilizing RNA‐seq data obtained by next‐generation sequencing techniques, 10 polymorphic microsatellite markers with 3–16 alleles in a nuclear genome were developed and characterized. Two to 15 alleles were observed in G. soboliferum. These markers will be used to investigate the genetic circumstance of remnant populations of G. soboliferum var. kiusianum and their phylogenetic relationship with G. soboliferum.     

结缕草属植物种间关系的SSR分析

以结缕草属的9种1变种共58份种源为材料,利用SSR标记技术进行了多样性分析和种间关系研究。结果表明:结缕草属植物具有很高的遗传多样性;14对SSR引物中,共扩增出267条带,Nei’s基因多样性指数为0.376 0,Shannon多样性指数为0.552 6;属内总基因多样性为0.382 3,种内基因多样性为0.219 6,57.44%的遗传变异存在于种内,基因流为0.674 8,不同的种之间有遗传分化,遗传漂变对该遗传分化有一定的贡献。UPGMA遗传距离聚类分析结果表明,结缕草、中华结缕草、朝鲜结缕草和大穗结缕草聚为一类;沟叶结缕草、小结缕草和细叶结缕草聚为一类;大花结缕草、长花结缕草和太平洋结缕草各自为一类。研究表明,生态地理条件相似的种优先聚集。     

Role ofDrosophila TRP in inositide-mediated Ca2+ entry

Inositol lipid signaling relies on an InsP₃-induced Ca²⁺ release from intracellular stores and on extracellular Ca²⁺ entry, which takes place when the Ca²⁺ stores become depleted of Ca²⁺. This interplay between Ca²⁺ release and Ca²⁺ entry has been termed capacitative Ca²⁺ entry and the inward current calcium release activated current (CRAC) to indicate gating of Ca²⁺ entry by Ca²⁺-store depletion. The signaling pathway and the gating mechanism of capacitative Ca²⁺ entry, however, are largely unknown and the molecular participants in this process have not been identified. In this article we review genetic, molecular, and functional studies of wild-type and mutantDrosophila photoreceptors, suggesting that thetransient receptor potential mutant (trp) is the first putative capacitative Ca²⁺ entry mutant. Furthermore, several lines of evidence suggest that thetrp gene product TRP is a candidate subunit of the plasma membrane channel that is activated by Ca²⁺ store depletion.     

THE PONTIA DAPLIDICE-ED USA HYBRID ZONE IN NORTHWESTERN ITALY

The pierid butterflies Pontia daplidice and P. edusa, parapatrically distributed in southern Europe, have very similar morphologies and life histories, but show fixed differences at four allozyme markers. We sampled these allozymes in a 28-population transect north of Genoa in Italy, through the hybrid zone where these taxa meet. We used the numerical techniques developed for hybrid zone analysis to study the patterns of genetic differentiation and their underlying evolutionary causes. The hybrid zone is characterized by a very short and steep central region, flanked by broad tails of introgression extended up to 100 km in either direction. From mean two-locus disequilibium of D = 0.148 (maximum-likelihood two-unit support limits 0.139-0.153), and after accounting for minor differences in the center locations of the single-locus clines, which act to bias the dispersal estimate, we estimated a dispersal rate of σ = 4.4 (3.7-5.5) km/gen^1/2. The effective selection needed to maintain the steep central portion is strong, 0.47 < s? < 0.64, when combined over potential intrinsic (genetic background) and extrinsic (ecological) sources of selection. The clines in allozyme loci showed variation that was significantly different between the most divergent shapes, and the differences are attributable to different degrees of introgression on the edusa side of the zone. The average selection acting on individual allozyme loci was high at s_???e  1.5%, but because of the narrowness of the central region of the cline, we suspect that this estimate is somewhat biased by selection on loci closely linked to the allozyme markers. A common question for taxa that show fixed allozyme differences in parapatry is whether or not they are genetically isolated. A fairly general measure of genetic isolation across hybrid zones is the time, T, that it takes a neutral allele to cross the hybrid zone and recombine into the opposite genetic background, given by T = (β/σ)², where β is the barrier strength of the hybrid zone. Genetic isolation in the Pontia zone is weak, with T  25 generations for most allozyme markers. By this measure, populations of daplidice and edusa on opposite sides of the hybrid zone share more identical-by-descent alleles than do populations of phenotypically pure daplidice in, say, France and Morocco. Accordingly, we think it best for systematists to consider edusa as a well-marked subspecies of P. daplidice.     

Molecular tests of the proposed diploid hybrid originof Gilia achilleifolia (Polemoniaceae)

Gilia achilleifolia is a putative diploid hybrid species. Hybrid origin was hypothesized based on traditional biosystematicevidence (i.e., morphological, cytological, and crossability data),which may be insufficient to establish genealogical history. Here,phylogenetic analysis of sequence data from the internal transcribedspacer (ITS) regions is used to examine the relationship between theputative hybrid species and its proposed parents. Isozyme variation isassayed to test for genetic additivity in the putative hybrid taxon andmorphological data are analyzed cladistically to evaluate the charactersthat led to the original hypothesis of hybrid origin. The ITS-basedgene tree placed G. achilleifolia in two divergent clades, eachsister to one of the putative parental lineages. Little isozymeadditivity was observed and G. achilleifolia possessed sixunique alleles among 42 alleles observed. However, ITS and isozymetrees differed in their placement of the two lineages of G.achilleifolia; both lineages are closer to a third putative parentin the isozyme tree. Also, G. achilleifolia is intermediate orpolymorphic for all nine morphological characteristics differentiatingthe parental species. Sorting of ancestral polymorphisms cannot easilyaccount for expression patterns of seven of these characters. In ourview, these results fail to distinguish between alternative hypothesesof ancient hybrid origin and divergent evolution, belying the difficultyof detecting ancient hybrids.