Genetic differentiation between sun and shade habitats in populations of Lindera benzoin L.

Differences in selection patterns among habitats can alter the distribution of genetic diversity even when this is estimated with neutral markers. For plants, light is an essential resource that can influence both abiotic and biotic components of habitat. We examined genetic differentiation between sun and shade habitats in Lindera benzoin L. (Spicebush), a perennial understory shrub. Genetic diversity of 127 plants from sun and shade habitats in two populations of L. benzoin was determined using 12 polymorphic microsatellite markers. We analyzed patterns of genetic diversity using analysis of molecular variance (AMOVA), and we assessed correlation between genetic and geographic distance using Mantel tests. We found (1) low levels of differentiation among populations (F _ST = 0.028), (2) little evidence of genetic structure within populations due to isolation-by-distance, and (3) some evidence of habitat-based genetic differentiation. Specifically, the AMOVA showed a small (0.5%) but significant portion of overall variation could be explained by differences between habitats. The overall low levels of differentiation we saw were likely a result of extensive gene flow in this dioecious, bird-dispersed species.     

Genetic differentiation within and between two habitats.

We investigate the usefulness of analyses of population differentiation between different ecological types, such as host races of parasites or sources and sink habitats. To that aim, we formulate a model of population structure involving two classes of subpopulations found in sympatry. Extensions of previous results for Wright''s F-statistics in island and isolation-by-distance models of dispersal are given. It is then shown that source and sinks cannot in general be distinguished by F-statistics nor by their gene diversities. The excess differentiation between two partially isolated classes with respect to differentiation within classes is shown to decrease with distance, and for a wide range of parameter values it should be difficult to detect. In the same circumstances little differentiation will be observed in "hierarchical" analyses between pools of samples from each habitat, and differences between levels of differentiation within each habitat will only reflect differences between levels of gene diversity within each habitat. Exceptions will indicate strong isolation between the different classes or habitat-related divergent selection.     

Genetic and epigenetic differentiation between natural Betula ermanii (Betulaceae) populations inhabiting contrasting habitats

Disentangling the molecular mechanisms of adaptation in natural plant populations in response to different environmental conditions is a central topic in evolutionary biology. In the present study, we investigated a wind-pollinated woody species of Changbai Mountain of northeastern China, namely, Betula ermanii Cham. This woody species B. ermanii is not only a dominant species in subalpine forest (SF), but it also occurs in the alpine tundra (AT) regions. This attribute indicates that it may play important roles in the two contrast habitats. In order to evaluate the influences of different habitats on differentiation in B. ermanii, we assessed the genetic and epigenetic population structure in selected populations from two contrasting habitats by using amplified fragment length polymorphism (AFLP) and methylation-sensitive AFLP techniques. According to our results, the AT group not only exhibits higher genetic and epigenetic diversity than the SF group but also shows greater population genetic and epigenetic differentiation. In addition, the analysis of cytosine methylation levels also revealed that the AT group exhibits higher degrees of genome methylation than the SF group. Taken together, our results indicate that populations from two contrasting habitats show significantly different genetic and epigenetic population structures. Along with other potential explanations, these findings suggest that environmental conditions could play an important role in facilitating adaptive evolution in B. ermanii.     

Phenotypic and genetic differentiation between native and introduced plant populations

Plant invasions often involve rapid evolutionary change. Founder effects, hybridization, and adaptation to novel environments cause genetic differentiation between native and introduced populations and may contribute to the success of invaders. An influential idea in this context has been the Evolution of Increased Competitive Ability (EICA) hypothesis. It proposes that after enemy release plants rapidly evolve to be less defended but more competitive, thereby increasing plant vigour in introduced populations. To detect evolutionary change in invaders, comparative studies of native versus introduced populations are needed. Here, we review the current empirical evidence from: (1) comparisons of phenotypic variation in natural populations; (2) comparisons of molecular variation with neutral genetic markers; (3) comparisons of quantitative genetic variation in a common environment; and (4) comparisons of phenotypic plasticity across different environments. Field data suggest that increased vigour and reduced herbivory are common in introduced plant populations. In molecular studies, the genetic diversity of introduced populations was not consistently different from that of native populations. Multiple introductions of invasive plants appear to be the rule rather than the exception. In tests of the EICA hypothesis in a common environment, several found increased growth or decreased resistance in introduced populations. However, few provided a full test of the EICA hypothesis by addressing growth and defence in the same species. Overall, there is reasonable empirical evidence to suggest that genetic differentiation through rapid evolutionary change is important in plant invasions. We discuss conceptual and methodological issues associated with cross-continental comparisons and make recommendations for future research. When testing for EICA, greater emphasis should be put on competitive ability and plant tolerance. Moreover, it is important to address evolutionary change in characteristics other than defence and growth that could play a role in plant invasions.     

入侵植物粗毛牛膝菊种群遗传多样性及遗传分化

利用ISSR分子标记技术,分析粗毛牛膝菊(Galinsoga quadriradiata)在中国分布的18个地理种群遗传多样性和遗传结构特点,为粗毛牛膝菊的防控奠定基础。结果表明:筛选的10条引物共扩增出349个位点,经Popgene软件分析,粗毛牛膝菊种群多态位点百分比(P)为8.88%~29.51%,Nei基因多样性指数(H)为0.0248~0.1023;种群遗传分化系数(Gst)为0.4663,种群间基因流(Nm)为0.5723;遗传相似度平均为0.9404,遗传距离平均为0.0621,UPGMA聚类分析将18个粗毛牛膝菊地理种群分为5大类;经Mantel检验,不同地理种群遗传距离与地理距离相关性不显著。研究表明,粗毛牛膝菊种群的遗传多样性较低;各地理种群间产生了一定程度的遗传分化;粗毛牛膝菊的入侵及扩散途径以人为多次反复传播为主。     

Genetic differentiation between sympatric populations of Bacillus cereus and Bacillus thuringiensis

Little is known about genetic exchanges in natural populations of bacteria of the spore-forming Bacillus cereus group, because no population genetics studies have been performed with local sympatric populations. We isolated strains of Bacillus thuringiensis and B. cereus from small samples of soil collected at the same time from two separate geographical sites, one within the forest and the other at the edge of the forest. A total of 100 B. cereus and 98 B. thuringiensis strains were isolated and characterized by electrophoresis to determine allelic composition at nine enzymatic loci. We observed genetic differentiation between populations of B. cereus and B. thuringiensis. Populations of a given Bacillus species--B. thuringiensis or B. cereus--were genetically more similar to each other than to populations of the other Bacillus species. Hemolytic activity provided further evidence of this genetic divergence, which remained evident even if putative clones were removed from the data set. Our results suggest that the rate of gene flow was higher between strains of the same species, but that exchanges between B. cereus and B. thuringiensis were nonetheless possible. Linkage disequilibrium analysis revealed sufficient recombination for B. cereus populations to be considered panmictic units. In B. thuringiensis, the balance between clonal proliferation and recombination seemed to depend on location. Overall, our data indicate that it is not important for risk assessment purposes to determine whether B. cereus and B. thuringiensis belong to a single or two species. Assessment of the biosafety of pest control based on B. thuringiensis requires evaluation of the extent of genetic exchange between strains in realistic natural conditions.     

Genetic comparisons between seed bank and Stipa krylovii plant populations

The soil seed bank represents the potential plant population since it is the source for population replacement. The genetic structure of a Stipa krylovii (Roshev.) plant population and its soil seed bank was investigated in the Xilinguole Steppe of Inner Mongolia using random amplified polymorphic DNA (RAPD) analyses. The population was sampled at two sites that were in close proximity to each other (0.5 km apart). Thirty plants and 18 seed bank samples were taken from each site to determine the genetic diversity between sites and between sources (plant or seed). The material was analyzed using 13 primers to produce 92 loci. Eighty-six were multi-loci, of which 23 loci (26.74%) of allele frequencies showed significant differences (P < or = 0.05). The genetic similarity between two seed bank sites was 0.9843 while the genetic similarity between two plant sites was 0.9619. Their similarities were all greater than that between the seed bank and plant populations. An analysis of their genetic structure showed that 87.86% of total variation was derived by two-loci. Genetic structures between plant and soil seed bank populations in S. krylovii were different due to the variance of mean gametic disequilibria and mean gene diversity. AMOVA results showed that the majority of variance (88.62%) occurred within sites, 12.75% was from between-groups. Further research is needed to investigate the selective function in maintaining the genetic diversity of Stipa krylovii plant populations.     

Genetic differentiation within and between populations of a hermaphroditic freshwater planarian

Dispersal of individuals is an important factor that can influence genetic differentiation between populations. The hermaphroditic freshwater planarian Schmidtea polychroainhabits shallow regions of lakes and streams, in which they appear to be continuously distributed. In the present study we used three highly polymorphic markers for analysing small-scale and large-scale genetic structure within one, and between four natural lake populations. Genetic differentiation could already be observed between samples collected at least 13 m apart, but not between neighbouring samples, and was most pronounced between samples from different lakes. Probably due to the high variance in F(ST)values, a significant correlation between genetic differentiation and geographic distance could not be observed. These results show that individual dispersal of S. polychroa is limited, but that there is gene flow between subpopulations from the same lake. They further suggest that long-distance dispersal and gene flow between lakes, if present, is not a common process in S. polychroa.     

Genetic differences between populations and habitats in Lamium purpureum plastic response to conspecific density

Plants from Open and Shade habitats in two natural populations (Vrsac and Avala) were grown in two densities (High and Low). As expected, density had significant effect on most of measured traits and that effect was concordant with Shade avoidance syndrome predictions. Genetic differences between populations both in mean trait values and in plastic responses to density were also detected. Number of leaves and flowers showed plasticity in Avala population only, while shoot weight was plastic in both populations but with greater plasticity in Avala population. Differences between habitats for plant height and number of internodes were present in Vrsac population only. Habitat difference in response to density was revealed for seed weight and it was due to lack of response in plants originated from Shade habitat in Vrsac population. This study showed that not only populations, but also subpopulations occupying different habitats can differ genetically in their plastic response to density, and that between habitat differences can be population-specific.     

Genetic differences between populations and habitats in Lamium purpureum plastic response to conspecific density

Plants from Open and Shade habitats in two natural populations (Vršac and Avala) were grown in two densities (High and Low). As expected, density had significant effect on most of measured traits and that effect was concordant with Shade avoidance syndrome predictions. Genetic differences between populations both in mean trait values and in plastic responses to density were also detected. Number of leaves and flowers showed plasticity in Avala population only, while shoot weight was plastic in both populations but with greater plasticity in Avala population. Differences between habitats for plant height and number of internodes were present in Vršac population only. Habitat difference in response to density was revealed for seed weight and it was due to lack of response in plants originated from Shade habitat in Vršac population. This study showed that not only populations, but also subpopulations occupying different habitats can differ genetically in their plastic response to density, and that between-habitat differences can be population-specific. The text was submitted by the author in English.     

Genetic differentiation among local populations of the European hedgehog (Erinaceus europaeus) in mosaic habitats

Tissue samples from 160 European hedgehogs, Erinaceus europaeus , representing eight small populations from a highly fragmented landscape in Oxfordshire, UK, were screened for polymorphism at six microsatellite loci. Permutation analysis of allelic compositions revealed no evidence for linkage disequilibrium among loci. Genotype proportions within populations and at five loci did not differ from those expected at Hardy–Weinberg equilibrium. However, significant heterozygote deficit and amplification failure of several samples necessitated removal of one locus from the analysis. Mean observed heterozygosity was 0.70. Average Rho _ST was 0.079 and differed significantly from zero, suggesting restricted gene flow among local populations. Pairwise Nm values and geographical distance were not correlated, indicating that factors other than distance affected dispersal.     

Genetic and morphometric differentiation between island and mainland southern elephant seal populations

We compare genetic (both nuclear and mitochondrial) and morphometric measures between two putative populations of southern elephant seal (Mirounga leonina), and interpret the results in the context of data from mark-recapture and satellite-telemetric studies. One population is on the Argentine mainland, while the other is 2,400 km away on South Georgia island. We found pronounced differentiation at the mitochondrial DNA (mtDNA) control region that was distinct from the pattern of variation seen among island rookeries. Some morphometric characters and seven out of ten nuclear-DNA markers also showed differentiation between the island and mainland sites. Diversity at nuclear markers was high in both populations but mtDNA diversity was low in the mainland population, suggesting a founder event and little subsequent immigration of females. Morphological differences may suggest different selective environments at the two sites.     

Genetic differentiation between parapatric 'nearshore' and 'offshore' populations of the bottlenose dolphin.

The existence of nearshore and offshore populations of the bottlenose dolphin has been documented throughout its range. In several cases the two regional forms have been shown to be morphologically distinct, although there is considerable overlap for most characters. The populations off the eastern coast of North America have been the subject of a long-term programme of research on their distribution and movements. In this study, we compare mitochondrial and nuclear genetic markers between dolphins classified as either nearshore or offshore type. These putative populations were found to be distinct at both nuclear and mitochondrial genetic markers. Further, the level of variation among the nearshore dolphins was reduced compared with the offshore population. A broader geographical comparison suggests a shared lineage between offshore dolphins from the western North Atlantic and both offshore and nearshore dolphins from the eastern Atlantic. These results are consistent with local differentiation based on habitat or resource specialization in the western North Atlantic, and suggest differences in the character of the nearshore/offshore distinction in different parts of the world.     

Genetic distance and electrophoretic identity of proteins between taxa

Summary The relationship between amino acid substitution and charge change of proteins in the evolutionary process is studied by using a stochastic model. A mathematical formula is developed for the electrophoretic identity of proteins between two different taxa for a given number of average codon differences per protein locus. Using this formula, a reference figure is constructed for estimating the average number of codon differences per locus between taxa.     

Ecological differentiation of Central EuropeanBolboschoenus taxa and their relationship to plant communities

The taxa of theBolboschoenus maritimus group occurring in Central Europe were studied with respect to morphological differentiation, plant communities and soil conditions. Four morphological types ofBolboschoenus were distinguished, differing in habitat conditions, dispersal and distribution: type 1 —Bolboschoenus maritimus subsp.maritimus with narrow triangular fruits; type 2 —B. maritimus subsp.maritimus with wider triangular fruits, type 3 —B. maritimus subsp.compactus with round convex fruits; and type 4 —B. planiculmis auct. with concave fruits. Strong ecological differentiation of these types was found compared with relatively weak morphological diagnostic features. High discriminant efficiency appeared in the relationship to soil chemistry. Differences were also found in habitat-type spectra of individualBolboschoenus morphological types, which was reflected in their affinities to plant communities. Nomenclature, taxonomic classification, and distribution of these taxa in Europe need thorough revision.     

天然片断生境中山姜(Alpinia japonica)种群遗传结构

理论和实验研究表明片断化是导致生物多样性丧失的主要因素之一,但有关研究基本上集中在人类活动引发的片断化生境体系中.由于长期气候变化以及地形等因素的影响,一些物种的种群之间天然情况下就存在隔离,对这些种群进行研究可以弥补人类活动引起的片断化体系经历时间较短的不足.山姜是一个喜湿耐荫的多年生植物,分布在热带亚热带地区,由于气候和地形原因,该物种在浙江东部呈现天然片断化状态,如在浙江天童森林公园及其周边地区,仅分布在少数几个沟谷中.以这些种群为对象,采用RAPD标记分析经历长期天然片断化山姜种群遗传多样性程度和遗传分化格局.7条RAPD引物获得了69个位点,其中多态位点68个.种群水平遗传多样性较高,多态位点百分比、期望杂合度和Shannon多样性指数分别为78.81%～85.51%、0.3170～0.3430、0.4560～0.4914,这与其异交的繁殖方式有关,同时与山姜克隆生长,每个世代维持的时间长,种群更新降低也有关系.遗传变异大多分配在种群内,但种群间遗传分化达到显著程度,ΦST为0.297,计算的基因流中等,为0.592,不足以克服长期遗传漂变导致的种群分化,Mantel检验表明遗传距离与空间距离不存在相关关系,显示了长期片断化状态下遗传漂变的作用.     

Genetic differentiation between populations of the European rose hip fly Rhagoletis alternata

We tested for genetic differentiation between populations of Rhagoletis alternata Fall. (Diptera: Tephritidae) on three different host species. We collected larvae from three rose species of the section Caninae ( Rosa canina L., Rosa corymbifera Borkh . , and Rosa rubiginosa L.) from 15 sites across Germany, where the three roses occurred together. Additionally, we sampled three sites in Switzerland. Roses differ in morphology (e.g. leaf glands) as well as phenology. We were able to score nine allozyme loci (five polymorphic). Populations from the three hosts did not differ in genetic variability. We found significant genetic differentiation between populations from different host species. However, the differentiation was very low (0.9%). Hence, we found no indication for host races. Furthermore, surprisingly little geographical structure of genetic differentiation was found between populations of this fruit fly across central Europe. We offer three mutually non-exclusive explanations for these findings. First, gene flow between populations of Rh. alternata is high. Second, the pattern of genetic differentiation is based on a recent expansion of the distributional range . Third, the ongoing gene flow between roses of the section Caninae acts as a hybrid bridge.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 619–625.     

Genetic diversity and differentiation of Kermode bear populations

The Kermode bear is a white phase of the North American black bear that occurs in low to moderate frequency on British Columbia's mid-coast. To investigate the genetic uniqueness of populations containing the white phase, and to ascertain levels of gene flow among populations, we surveyed 10 highly polymorphic microsatellite loci, assayed from trapped bear hairs. A total of 216 unique bear genotypes, 18 of which were white, was sampled among 12 localities. Island populations, where Kermodes are most frequent, show approximately 4% less diversity than mainland populations, and the island richest in white bears (Gribbell) exhibited substantial genetic isolation, with a mean pairwise FST of 0.14 with other localities. Among all localities, FST for the molecular variant underlying the coat-colour difference (A893G) was 0.223, which falls into the 95th percentile of the distribution of FST values among microsatellite alleles, suggestive of greater differentiation for coat colour than expected under neutrality. Control-region sequences confirm that Kermode bears are part of a coastal or western lineage of black bears whose existence predates the Wisconsin glaciation, but microsatellite variation gave no evidence of past population expansion. We conclude that Kermodism was established and is maintained in populations by a combination of genetic isolation and somewhat reduced population sizes in insular habitat, with the possible contribution of selective pressure and/or nonrandom mating.