Population Dynamics of the Endangered, Long-Lived Perennial Species, Ligularia sibirica

Ligularia sibirica is a relict wetland perennial plant species of the Czech and Slovak Republic. Explaining variation in population growth rate and identifying the causes of that variation is important for effective protection of such an endangered species. Matrix models based on four years of data of 11 populations were used to identify the pattern of variation in the demographic vital rates of this species, and to examine the causes of the variation such as population size and habitat type. Further, the matrix model was used to determine the population growth rate, longevity and risk of extinction of each population and to identify the specific vital rates that most affect population growth rate. The results showed that population growth rates were significantly different between years and populations. Temporal variation was mostly due to variable survival of adult individuals, while spatial variation was mainly driven by fertility of one small currently expanding population. Further, most studied populations of L. sibirica are performing well and only those growing in nitrogen-rich habitats have a high extinction risk. The results also indicate that all populations have low adult mortality, long-lived individuals (61.3?years on average) and some populations also show features of remnant populations (i.e., the persistence of populations in severe conditions in spite of no reproduction). Our results imply that detailed demographic data are needed to understand the long-term prospects of these populations. These data may serve as an early warning system for this species long before an obvious decline occurs in the populations.     

Very Low Population Structure in a Highly Mobile and Wide-Ranging Endangered Bird Species

The loss of biodiversity following fragmentation and degradation of habitat is a major issue in conservation biology. As competition for resources increases following habitat loss and fragmentation, severe population declines may occur even in common, highly mobile species; such demographic decline may cause changes within the population structure of the species. The regent honeyeater, Anthochaera phrygia, is a highly nomadic woodland bird once common in its native southeast Australia. It has experienced a sharp decline in abundance since the late 1970s, following clearing of large areas of its preferred habitat, box-ironbark woodland, within the last 200 years. A captive breeding program has been established as part of efforts to restore this species. This study used genetic data to examine the range-wide population structure of regent honeyeaters, including spatial structure, its change through time, sex differences in philopatry and mobility, and genetic differences between the captive and wild populations. There was low genetic differentiation between birds captured in different geographic areas. Despite the recent demographic decline, low spatial structure appears to have some temporal consistency. Both sexes appear to be highly mobile, and there does not seem to be significant genetic differentiation between the captive and wild populations. We conclude that management efforts for survival of this species, including habitat protection, restoration, and release of captive-bred birds into the wild, can treat the species as effectively a single genetic population.     

Micropropagation of Endangered Species Daphne cneorum

A new protocol for micropropagation of endangered Daphne cneorum through multiple shoot formation has been developed. Two different types of explants (dormant apical buds and in vitro seed-derived young seedlings) from plants in two different localities were used for the initiation of multiple shoots on agar woody plant medium (WPM) with 0.2 mg dm^–3 benzylaminopurine (BAP), 0.1 mg dm^–3-indolebutyric acid (IBA), 200 mg dm^–3 glutamine, and 200 mg dm^–3 casein hydrolysate. From 10 seeds only one germinated and the multi-apex culture bearing 12 shoots sprouted out from in vitro seed-derived young seedling. After 6-month cultivation 35 multi-apex cultures were achieved from in vitro seed-derived young seedling. On 1/3 strength WPM medium supplemented with 2.83 mg dm^–3 IBA 50 % of cultures (clusters of 3 – 5 shoots) rooted but no rooting occurred in the presence of -naphthaleneacetic acid (NAA). The rooted plantlets were acclimatized for 4 weeks in the greenhouse and then transferred into natural conditions. The plants successfully survived the winter and flowered.     

Recombinational Landscape and Population Genomics of Caenorhabditis elegans

Recombination rate and linkage disequilibrium, the latter a function of population genomic processes, are the critical parameters for mapping by linkage and association, and their patterns in Caenorhabditis elegans are poorly understood. We performed high-density SNP genotyping on a large panel of recombinant inbred advanced intercross lines (RIAILs) of C. elegans to characterize the landscape of recombination and, on a panel of wild strains, to characterize population genomic patterns. We confirmed that C. elegans autosomes exhibit discrete domains of nearly constant recombination rate, and we show, for the first time, that the pattern holds for the X chromosome as well. The terminal domains of each chromosome, spanning about 7% of the genome, exhibit effectively no recombination. The RIAILs exhibit a 5.3-fold expansion of the genetic map. With median marker spacing of 61 kb, they are a powerful resource for mapping quantitative trait loci in C. elegans. Among 125 wild isolates, we identified only 41 distinct haplotypes. The patterns of genotypic similarity suggest that some presumed wild strains are laboratory contaminants. The Hawaiian strain, CB4856, exhibits genetic isolation from the remainder of the global population, whose members exhibit ample evidence of intercrossing and recombining. The population effective recombination rate, estimated from the pattern of linkage disequilibrium, is correlated with the estimated meiotic recombination rate, but its magnitude implies that the effective rate of outcrossing is extremely low, corroborating reports of selection against recombinant genotypes. Despite the low population, effective recombination rate and extensive linkage disequilibrium among chromosomes, which are techniques that account for background levels of genomic similarity, permit association mapping in wild C. elegans strains.     

High Genetic Diversity and Population Differentiation in the Critically Endangered Plant Species Trailliaedoxa gracilis (Rubiaceae)

Trailliaedoxa gracilis W. W. Smith et Forrest (Rubiaceae), a Chinese endemic monotypic genus belonging to the Alberteae (Rubiaceae), exhibits a narrow distribution in the dry valleys of the Jinsha River and Red River drainage area in southwestern China. The few sites at which T. gracilis occurs are fragmented and isolated, and several are highly vulnerable to human disturbance. As T. gracilis is a protected plant with a second-degree national priority, the genetic diversity and structure of the populations of this species should be investigated to determine the most suitable conservation strategy. In this study, two chloroplast regions and one nuclear region were used to investigate the genetic diversity, genetic structure, and demographic history of T. gracilis. We observed a high total genetic diversity (H _T?=?0.952 and 0.966) and low average within-population diversity (H _S?=?0.07 and 0.489) based on cpDNA and nDNA analyses. Thus, a strong genetic structure (F _ST?=?0.98049 and 0.59731) was detected. A phylogeographic structure was detected by nuclear DNA analysis (N _ST?>?G _ST, P?<?0.05); however, the chloroplast data did not show a significant phylogeographic structure (N _ST?<?G _ST, P?>?0.05). The Bayesian skyline plot and isolation with migration analysis were used to estimate the demographic history of T. gracilis. The results indicated that a marked bottleneck effect occurred during the glacial-interglacial of the Pleistocene. Among the extant populations of T. gracilis, the population found in ChunJiang, LuQuan, and YuXi showed the highest haplotype diversity based on cpDNA sequences and should be given priority for protection. According to the nDNA analysis, every population presented a high level of diversity and a high content of private haplotypes. Therefore, every population should be protected.

     

The Population Genomics of Trans-Specific Inversion Polymorphisms in Anopheles gambiae

In the malaria mosquito Anopheles gambiae polymorphic chromosomal inversions may play an important role in adaptation to environmental variation. Recently, we used microarray-based divergence mapping combined with targeted resequencing to map nucleotide differentiation between alternative arrangements of the 2La inversion. Here, we applied the same technique to four different polymorphic inversions on the 2R chromosome of An. gambiae. Surprisingly, divergence was much lower between alternative arrangements for all 2R inversions when compared to the 2La inversion. For one of the rearrangements, 2Ru, we successfully mapped a very small region (∼100 kb) of elevated divergence. For the other three rearrangements, we did not identify any regions of significantly high divergence, despite ample independent evidence from natural populations of geographic clines and seasonal cycling, and stable heterotic polymorphisms in laboratory populations. If these inversions are the targets of selection as hypothesized, we suggest that divergence between rearrangements may have escaped detection due to retained ancestral polymorphism in the case of the youngest 2R rearrangements and to extensive gene flux in the older 2R inversion systems that segregate in both An. gambiae and its sibling species An. arabiensis.MORE than 70 years ago Dobzhansky and Sturtevant (1938) first discovered polymorphic inversion arrangements carried by various Drosophila pseudoobscura populations. After observing correlations between environmental conditions and inversion frequencies, Dobzhansky proposed that inversions are under strong selection due to their role in promoting local adaptation to the heterogeneous conditions a species encounters both spatially and temporally (Dobzhansky 1944, 1948; Powell 1997). More recent studies have implicated chromosomal inversions in the adaptation of a diversity of eukaryotes including humans (Coluzzi et al. 1979; Feder et al. 2003; Hoffmann et al. 2004; Stefansson et al. 2005). Long known to be common in dipteran insects, more recent HapMap data suggest that polymorphic inversions may be numerous in human populations and by extension other mammals (Bansal et al. 2007). Given their potential importance in facilitating adaptation, surprisingly little is known about the mechanism(s) or the genes responsible for maintaining inversion polymorphisms in natural populations.Gene exchange between inverted and standard arrangements, although reduced, can still occur through gene flux: the action of gene conversion and multiple crossovers in inversion heterozygotes (heterokaryotypes) (Chovnick 1973; Navarro et al. 1997; Schaeffer and Anderson 2005). Over time allelic variation unrelated to ecological adaptation should become homogenized between arrangements, while alleles which are under divergent selection pressures should remain in linkage disequilibrium with each other and with the inversion itself, leading to heightened differentiation between standard and inverted arrangements at and near the target loci. In principle, this process allows the identification of specific loci involved in adaptive divergence (Schaeffer et al. 2003; Schaeffer and Anderson 2005; Storz 2005). Consistent with this model, previous low-resolution studies of Drosophila inversions revealed heterogeneous patterns of nucleotide diversity relative to divergence, as well as the interspersion of regions of high and low genetic association potentially due to the interaction of selection and gene flux (Schaeffer et al. 2003; Kennington et al. 2006; but see Munte et al. 2005). The application of high-resolution tools flowing from completely sequenced genomes will facilitate the mapping of genes that are the targets of divergent natural selection within gene arrangements.Although Drosophila has been the favored model, the African malaria vector Anopheles gambiae sensu stricto also provides an excellent system for studying the maintenance of inversion polymorphisms, not only within a species but across speciation events of different ages in the An. gambiae sibling species complex. The nominal species An. gambiae s.s. (hereafter, An. gambiae) is synanthropic: almost exclusively biting humans, resting indoors, and exploiting anthropogenic larval habitats (Coluzzi 1999). This close association with humans, vital to making An. gambiae one of the most proficient vectors of malaria, is likely to have been facilitated by chromosomal inversions thought to confer adaptive benefits in heterogeneous climatic and ecological settings in Africa. Seven common polymorphic inversions exist on the second chromosome. Six of these are located on the right arm (2R): j, b, c, u, d, and k, while 2La is the only inversion on the left arm (Coluzzi et al. 2002). Facilitated by the sequenced reference genome (Holt et al. 2002), some of the breakpoints for these polymorphic inversions have been localized to small genomic regions (Sharakhov et al. 2006; Coulibaly et al. 2007; Sangare 2007). Most of these inversions appear to be the targets of strong selection. Five of the inversions (2La and 2Rb, -c, -d, and -u) are nonrandomly associated with degree of aridity; each cycles seasonally with rainfall, and all except 2Ru form stable geographic clines in frequency from mesic forest to xeric regions bordering the Sahara (Coluzzi et al. 1979; Toure et al. 1994, 1998; Powell et al. 1999). Inversion 2Rj is not clinal, but its distribution in Mali is consistent with adaptation to novel rockpool niches (Coluzzi et al. 1985; Manoukis et al. 2008).In the An. gambiae species complex, inversion polymorphisms can be maintained across the boundaries of emerging and even full species. An. gambiae and its sibling An. arabiensis, strictly sympatric throughout most of their extensive ranges in sub-Saharan Africa, differ by multiple fixed chromosomal rearrangements on the X but share three chromosome 2 inversions: 2La, fixed in An. arabiensis and polymorphic in An. gambiae; and 2Rb and -c, polymorphic in both species (Coluzzi et al. 1979, 2002). Moreover, these same inversions and all other common An. gambiae inversions with the exception of 2Rj are shared and polymorphic in two lineages apparently undergoing ecological speciation within An. gambiae—the assortatively mating M and S molecular forms (della Torre et al. 2002, 2005). Inversion frequencies are correlated with climatic and ecological conditions in parallel in both lineages (Costantini et al. 2009; Simard et al. 2009). Unlike the full species, the M and S incipient species are not distinguished by any fixed inversion differences. Indeed, genomewide divergence mapping between the M and S forms revealed that significant differentiation was confined to two small low-recombination regions adjacent to the centromeres of 2L and X which are distant from any inversions (Turner et al. 2005). Thus, in distinction to models of speciation invoking inversions as facilitating the persistence of hybridizing species (Noor et al. 2001; Rieseberg 2001; Ortiz-Barrientos et al. 2002; Navarro and Barton 2003), the An. gambiae data suggest that chromosome 2 inversions are not directly responsible for reproductive isolation. Instead, the same chromosome 2 inversion polymorphisms appear to confer similar ecological benefits, within and across species boundaries. A long-term research goal is to identify the mechanisms and the genes controlling these processes.Previously we conducted the first high-density genomic scan of divergence across a chromosomal inversion (2La) in An. gambiae (White et al. 2007). By hybridizing genomic DNA from S form mosquitoes homokaryotypic for alternate gene arrangements on chromosome 2L (2La or 2L+^a) to oligonucleotide microarrays we were able to measure divergence across the 22-Mb inversion at nearly 14,000 markers. Differentiation in the rearranged region was significantly higher than in collinear portions of chromosome 2L. Between breakpoints the pattern of differentiation was heterogeneous: two genomic clusters of significantly higher divergence were identified near but not adjacent to the breakpoints. Directed resequencing within the S form confirmed these results and suggested that both clusters contained genes targeted by selection. Observed levels of linkage disequilibrium between the 2La breakpoints and markers in the clusters are highly unlikely under a neutral scenario, in light of known recombination rates and plausible estimates of the age of the inversion.The present study characterizes the patterns of genetic variation in polymorphic rearrangements on the opposite (right) arm of chromosome 2: 2Rj, -b, -c, and -u. With the goal of identifying candidate genes maintaining these inversions in natural populations, we applied microarray-based divergence mapping to measure differentiation between alternative 2R arrangements. Because three of four inversions have taxonomic distributions that span incipient and/or completed speciation events, we validated the microarray findings by targeted sequencing in multiple taxa: sympatric Malian populations of An. gambiae M and S forms, and the sibling species An. arabiensis.     

木莲属濒危植物致濒原因及繁殖生物学研究进展

物种濒危的本质是在自然状况下,种群难以更新和维持。而导致濒危的内在原因就是由于物种的生物学、遗传学因素影响了种群的丰富度。繁殖是种群构建、更新和维持的关键环节,而繁殖成功的标准是能产生成熟个体。从繁殖生物学角度总结木莲属濒危种产生成熟个体的关键环节的研究状况,从其生殖发育异常、交配系统研究、物种自然繁殖特性及个体生存力角度探讨物种致濒的原因。     

Using Species Distribution Model to Estimate the Wintering Population Size of the Endangered Scaly-Sided Merganser in China

Scaly-sided Merganser is a globally endangered species restricted to eastern Asia. Estimating its population is difficult and considerable gap exists between populations at its breeding grounds and wintering sites. In this study, we built a species distribution model (SDM) using Maxent with presence-only data to predict the potential wintering habitat for Scaly-sided Merganser in China. Area under the receiver operating characteristic curve (AUC) method suggests high predictive power of the model (training and testing AUC were 0.97 and 0.96 respectively). The most significant environmental variables included annual mean temperature, mean temperature of coldest quarter, minimum temperature of coldest month and precipitation of driest quarter. Suitable conditions for Scaly-sided Merganser are predicted in the middle and lower reaches of the Yangtze River, especially in Jiangxi, Hunan and Hubei Provinces. The predicted suitable habitat embraces 6,984 km of river. Based on survey results from three consecutive winters (2010–2012) and previous studies, we estimated that the entire wintering population of Scaly-sided Merganser in China to be 3,561 ± 478 individuals, which is consistent with estimate in its breeding ground.     

功能基因组研究进展

基因组研究已经进入了以功能基因组研究为标志的后基因组时代,功能基因组研究不仅是21世纪整体细胞生物学最重要的内容,而且将为医药,农业和工业的革新提供崭新的思路。主要探讨功能基因组的研究方法和模式生物的功能基因组研究进展。     

Comparative Genomics of Wolbachia and the Bacterial Species Concept

The importance of host-specialization to speciation processes in obligate host-associated bacteria is well known, as is also the ability of recombination to generate cohesion in bacterial populations. However, whether divergent strains of highly recombining intracellular bacteria, such as Wolbachia, can maintain their genetic distinctness when infecting the same host is not known. We first developed a protocol for the genome sequencing of uncultivable endosymbionts. Using this method, we have sequenced the complete genomes of the Wolbachia strains wHa and wNo, which occur as natural double infections in Drosophila simulans populations on the Seychelles and in New Caledonia. Taxonomically, wHa belong to supergroup A and wNo to supergroup B. A comparative genomics study including additional strains supported the supergroup classification scheme and revealed 24 and 33 group-specific genes, putatively involved in host-adaptation processes. Recombination frequencies were high for strains of the same supergroup despite different host-preference patterns, leading to genomic cohesion. The inferred recombination fragments for strains of different supergroups were of short sizes, and the genomes of the co-infecting Wolbachia strains wHa and wNo were not more similar to each other and did not share more genes than other A- and B-group strains that infect different hosts. We conclude that Wolbachia strains of supergroup A and B represent genetically distinct clades, and that strains of different supergroups can co-exist in the same arthropod host without converging into the same species. This suggests that the supergroups are irreversibly separated and that barriers other than host-specialization are able to maintain distinct clades in recombining endosymbiont populations. Acquiring a good knowledge of the barriers to genetic exchange in Wolbachia will advance our understanding of how endosymbiont communities are constructed from vertically and horizontally transmitted genes.     

物种濒危的机制与保护对策

本文以生物多样性和保护生物学的若干基础理论为依据,分析了物种濒危的现状,论述了濒危物种的概念和特征、易于濒危和灭绝的类型,阐明了物种濒危的机制,并由此提出了濒危物种种质资源的保护对策。     

Aphid Species and Population Dynamics Associated with Strawberry

Aphids are among the major pests associated with strawberries in Southern Brasil. In this study, we identified the main species that occur in strawberry fields in the states of Paraná and Rio Grande do Sul, Brasil. We also compared the effectiveness of different sampling methods and studied the population dynamics of aphid species during two strawberry crop cycles in the municipality of Pinhais, state of Paraná, Brasil. Chaetosiphon fragaefolii (Cockerell) and Aphis forbesi Weed were the main species associated with strawberry. The method of hit plant and the Möericke trap showed equal effectiveness to capture wingless and winged insects. The peak population of aphids in the state of Paraná occurred from September to November. This information can help producers to implement strategies to monitor and control the major aphid species that occur in strawberry culture.     

Limited Population Structure,Genetic Drift and Bottlenecks Characterise an Endangered Bird Species in a Dynamic,Fire-Prone Ecosystem

Fire is a major disturbance process in many ecosystems world-wide, resulting in spatially and temporally dynamic landscapes. For populations occupying such environments, fire-induced landscape change is likely to influence population processes, and genetic patterns and structure among populations. The Mallee Emu-wren Stipiturus mallee is an endangered passerine whose global distribution is confined to fire-prone, semi-arid mallee shrublands in south-eastern Australia. This species, with poor capacity for dispersal, has undergone a precipitous reduction in distribution and numbers in recent decades. We used genetic analyses of 11 length-variable, nuclear loci to examine population structure and processes within this species, across its global range. Populations of the Mallee Emu-wren exhibited a low to moderate level of genetic diversity, and evidence of bottlenecks and genetic drift. Bayesian clustering methods revealed weak genetic population structure across the species'' range. The direct effects of large fires, together with associated changes in the spatial and temporal patterns of suitable habitat, have the potential to cause population bottlenecks, serial local extinctions and subsequent recolonisation, all of which may interact to erode and homogenise genetic diversity in this species. Movement among temporally and spatially shifting habitat, appears to maintain long-term genetic connectivity. A plausible explanation for the observed genetic patterns is that, following extensive fires, recolonisation exceeds in-situ survival as the primary driver of population recovery in this species. These findings suggest that dynamic, fire-dominated landscapes can drive genetic homogenisation of populations of species with low-mobility and specialised habitat that otherwise would be expected to show strongly structured populations. Such effects must be considered when formulating management actions to conserve species in fire-prone systems.     

Comparative Population Genomics of the Borrelia burgdorferi Species Complex Reveals High Degree of Genetic Isolation among Species and Underscores Benefits and Constraints to Studying Intra-Specific Epidemiological Processes

Lyme borreliosis, one of the most frequently contracted zoonotic diseases in the Northern Hemisphere, is caused by bacteria belonging to different genetic groups within the Borrelia burgdorferi species complex, which are transmitted by ticks among various wildlife reservoirs, such as small mammals and birds. These features make the Borrelia burgdorferi species complex an attractive biological model that can be used to study the diversification and the epidemiology of endemic bacterial pathogens. We investigated the potential of population genomic approaches to study these processes. Sixty-three strains belonging to three species within the Borrelia burgdorferi complex were isolated from questing ticks in Alsace (France), a region where Lyme disease is highly endemic. We first aimed to characterize the degree of genetic isolation among the species sampled. Phylogenetic and coalescent-based analyses revealed clear delineations: there was a ∼50 fold difference between intra-specific and inter-specific recombination rates. We then investigated whether the population genomic data contained information of epidemiological relevance. In phylogenies inferred using most of the genome, conspecific strains did not cluster in clades. These results raise questions about the relevance of different strategies when investigating pathogen epidemiology. For instance, here, both classical analytic approaches and phylodynamic simulations suggested that population sizes and migration rates were higher in B. garinii populations, which are normally associated with birds, than in B. burgdorferi s.s. populations. The phylogenetic analyses of the infection-related ospC gene and its flanking region provided additional support for this finding. Traces of recombination among the B. burgdorferi s.s. lineages and lineages associated with small mammals were found, suggesting that they shared the same hosts. Altogether, these results provide baseline evidence that can be used to formulate hypotheses regarding the host range of B. burgdorferi lineages based on population genomic data.     

濒危物种灰叶胡杨的大孢子发生和雌配子体发育

用石蜡切片法对濒危物种灰叶胡杨的大孢子发生和雌配子体发育过程进行观察研究.结果显示,灰叶胡杨雌蕊由三心皮构成,侧膜胎座,胚珠为倒生型,有18～21列;发育早期的胚珠为双珠被,厚珠心;当外珠被发育至与内珠被处于同一水平时,内珠被便开始退化,故成熟胚珠为单珠被;孢原细胞1个,并且自表皮下2层处分化;大孢子母细胞由孢原细胞分裂后形成的造孢细胞直接发育而来;大孢子四分体直线形排列,合点端的大孢子为功能大孢子,蓼型胚囊;在胚囊发育过程中珠孔端的珠心组织退化.根据开花物候不同阶段花的形态特征,可以初步判断灰叶胡杨大孢子发生和雌配子体的发育进程.     

Females Lead Population Collapse of the Endangered Hawaii Creeper

Population collapses result from drastic environmental changes, but the sexes may differ in vulnerability. Collapse of the endangered Hawaii creeper (Oreomystis mana) at Hakalau Forest National Wildlife Refuge resulted from food limitation associated with increased numbers of an introduced bird (Japanese white-eye, Zosterops japonicus), which competes with the creeper for food. Both creeper sexes had stunted bill growth and the greatest change in molt of native species in the community. With a surge in numbers of white-eyes, a recent cohort of adult females had very low survival after breeding, while adult males from the same cohort, and older females and males, continued to have high survival. Lower female survival resulted in a significantly more male-biased adult sex ratio. Recent low female survival was based on a great cost of reproduction, indicated by molt-breeding overlap that was previously avoided, and lower fat during the lengthy fledgling period. The difference in female survival between cohorts was associated with stunted bills from being reared in and then breeding in an increasingly poor food environment. Trend analysis of survey data indicate that the bird is declining throughout the refuge, with males being 72–80% of adults left six years after the white-eye increased. Competition over time was consistent with that previously documented over space on the Island of Hawaii. Adaptive management to recover the bird in this protected area needs to focus on improving both adult female survival and the adult sex ratio.