Climatic adaptation and ecological divergence between two closely related pine species in Southeast China

Climate is one of the most important drivers for adaptive evolution in forest trees. Climatic selection contributes greatly to local adaptation and intraspecific differentiation, but this kind of selection could also have promoted interspecific divergence through ecological speciation. To test this hypothesis, we examined intra‐ and interspecific genetic variation at 25 climate‐related candidate genes and 12 reference loci in two closely related pine species, Pinus massoniana Lamb. and Pinus hwangshanensis Hisa, using population genetic and landscape genetic approaches. These two species occur in Southeast China but have contrasting ecological preferences in terms of several environmental variables, notably altitude, although hybrids form where their distributions overlap. One or more robust tests detected signals of recent and/or ancient selection at two‐thirds (17) of the 25 candidate genes, at varying evolutionary timescales, but only three of the 12 reference loci. The signals of recent selection were species specific, but signals of ancient selection were mostly shared by the two species likely because of the shared evolutionary history. F_ST outlier analysis identified six SNPs in five climate‐related candidate genes under divergent selection between the two species. In addition, a total of 24 candidate SNPs representing nine candidate genes showed significant correlation with altitudinal divergence in the two species based on the covariance matrix of population history derived from reference SNPs. Genetic differentiation between these two species was higher at the candidate genes than at the reference loci. Moreover, analysis using the isolation‐with‐migration model indicated that gene flow between the species has been more restricted for climate‐related candidate genes than the reference loci, in both directions. Taken together, our results suggest that species‐specific and divergent climatic selection at the candidate genes might have counteracted interspecific gene flow and played a key role in the ecological divergence of these two closely related pine species.     

小叶杨DREB同源基因内SSR的发现及群体结构分析

利用基因特异的PCR引物从小叶杨(Populus simonii)经干旱胁迫后构建的cDNA文库中扩增得到长度为671 bp的PsDREB cDNA克隆。该基因内部含有完整的且大小为543 bp的开放阅读框, 可编码181个氨基酸残基。在此基础上, 对36株小叶杨基因型个体的DREB基因进行了克隆和序列分析, 发现其内部存在以CAC为基本单位的4次(A)、5次(B)、7次(C)、8次(D)、9次(E)、10次(F)和11次(G)7种类型的简单重复序列(SSR)。以该重复序列为扩增对象设计引物, 对我国11个省16个群体528株小叶杨进行了群体遗传结构分析。结果表明, 在检测群体中各位点等位基因频率大小顺序依次为: D＞C＞F＞E＞A＞G＞B; 平均有效等位基因数为3.167 0, 平均观察和期望杂合度分别为0.468 5和0.531 5, 且在多数群体中存在一定程度的近交效应和显著偏离Hardy-Weinberg平衡; 而Ewens-Watterson中立性检验表明, 除山西宁武、辽宁朝阳和河南伊川外, 其它多数群体均属于中立性选择。研究结果将为利用候选基因内SSR标记来评价林木育种资源的遗传多样性以及保护和利用这些资源提供科学的理论依据。     

Application of an integrated physical and functional screening approach to identify inhibitors of the Wnt pathway

Large‐scale proteomic approaches have been used to study signaling pathways. However, identification of biologically relevant hits from a single screen remains challenging due to limitations inherent in each individual approach. To overcome these limitations, we implemented an integrated, multi‐dimensional approach and used it to identify Wnt pathway modulators. The LUMIER protein–protein interaction mapping method was used in conjunction with two functional screens that examined the effect of overexpression and siRNA‐mediated gene knockdown on Wnt signaling. Meta‐analysis of the three data sets yielded a combined pathway score (CPS) for each tested component, a value reflecting the likelihood that an individual protein is a Wnt pathway regulator. We characterized the role of two proteins with high CPSs, Ube2m and Nkd1. We show that Ube2m interacts with and modulates β‐catenin stability, and that the antagonistic effect of Nkd1 on Wnt signaling requires interaction with Axin, itself a negative pathway regulator. Thus, integrated physical and functional mapping in mammalian cells can identify signaling components with high confidence and provides unanticipated insights into pathway regulators.     

Characterization of Enterobacteria Producing the Low-Molecular-Weight Antibiotics Microcins

A comparative study of the morphological, cultural, physiological, and biochemical properties of the microcinogenic strains EcS 5/98, EcS 6/98, and EcB 214/99 and the known microcin C51 producer Escherichia coli M17(p74) showed that these strains belong to the species E. coli. The strains produced microcins with molecular masses lower than 10 kDa. Microcin biosynthesis was stimulated by a deficiency of nutrients in the cultivation media. The microcins were found to be resistant to thermolysin but were degraded by pronase, protolichetrem, and the Bacillus mesentericus metalloproteinase. This indicated that the microcins are peptides or contain peptides in their molecules. The study of cross immunity to the microcins and the sequencing of their genetic determinants showed that the microcins of strains EcS 5/98 and EcS 6/98 are of B type, whereas the microcin of strain EcB 214/99 presumably belongs to another type, since it suppresses the growth of the producers of C and B-type microcins. The new microcin producers possess antibacterial activity against natural isolates belonging to the genera Escherichia and Salmonella, against a wide range of colicinogenic Escherichia strains, and against collection Salmonella cultures.     

Metapopulation dynamics and foraging plasticity in a highly vagile seabird,the southern rockhopper penguin

Population connectivity is driven by individual dispersal potential and modulated by natal philopatry. In seabirds, high vagility facilitates dispersal yet philopatry is also common, with foraging area overlap often correlated with population connectivity. We assess the interplay between these processes by studying past and current connectivity and foraging niche overlap among southern rockhopper penguin colonies of the coast of southern South America using genomic and stable isotope analyses. We found two distinct genetic clusters and detected low admixture between northern and southern colonies. Stable isotope analysis indicated niche variability between colonies, with Malvinas/Falklands colonies encompassing the species entire isotopic foraging niche, while the remaining colonies had smaller, nonoverlapping niches. A recently founded colony in continental Patagonia differed in isotopic niche width and position with Malvinas/Falklands colonies, its genetically identified founder population, suggesting the exploitation of novel foraging areas and/or prey items. Additionally, dispersing individuals found dead across the Patagonian shore in an unusual mortality event were also assigned to the northern cluster, suggesting northern individuals reach southern localities, but do not breed in these colonies. Facilitated by variability in foraging strategies, and especially during unfavorable conditions, the number of dispersing individuals may increase and enhance the probability of founding new colonies. Metapopulation demographic dynamics in seabirds should account for interannual variability in dispersal behavior and pay special attention to extreme climatic events, classically related to negative effects on population trends.     

Using multiple landscape genetic approaches to test the validity of genetic clusters in a species characterized by an isolation‐by‐distance pattern

Bayesian clustering methods are typically used to identify barriers to gene flow, but they are prone to deduce artificial subdivisions in a study population characterized by an isolation‐by‐distance pattern (IbD). Here we analysed the landscape genetic structure of a population of wild boars (Sus scrofa) from south‐western Germany. Two clustering methods inferred the presence of the same genetic discontinuity. However, the population in question was characterized by a strong IbD pattern. While landscape‐resistance modelling failed to identify landscape features that influenced wild boar movement, partial Mantel tests and multiple regression of distance matrices (MRDMs) suggested that the empirically inferred clusters were separated by a genuine barrier. When simulating random lines bisecting the study area, 60% of the unique barriers represented, according to partial Mantel tests and MRDMs, significant obstacles to gene flow. By contrast, the random‐lines simulation showed that the boundaries of the inferred empirical clusters corresponded to the most important genetic discontinuity in the study area. Given the degree of habitat fragmentation separating the two empirical partitions, it is likely that the clustering programs correctly identified a barrier to gene flow. The differing results between the work published here and other studies suggest that it will be very difficult to draw general conclusions about habitat permeability in wild boar from individual studies.     

Small-Scale Fragmentation Effects on Local Genetic Diversity in Two Phyllostomid Bats with Different Dispersal Abilities in Panama

Habitat fragmentation is one of the greatest threats to biodiversity. Despite their importance for conservation, the genetic consequences of small-scale habitat fragmentation for bat populations are largely unknown. In this study, we linked genetic with ecological and demographic data to assess the effects of habitat fragmentation on two species of phyllostomid bats ( Uroderma bilobatum and Carollia perspicillata ) that differ in their dispersal abilities and demographic response to fragmentation. We hypothesized that population differentiation and the effect of habitat fragmentation on levels of genetic diversity will be a function of the species' mobility. We sequenced mtDNA from 232 bats caught on 11 islands in Gatún Lake, Panamá, isolated from the mainland for ca 90 yr, and in adjacent, continuous forest on the mainland. Populations of both species showed significant genetic differentiation ( F _ST). Consistent with our prediction, population subdivision was lower in the highly mobile U. bilobatum ( F _ST= 0.01) compared to the less vagile C. perspicillata ( F _ST= 0.06), and only the latter species showed a pattern indicative of isolation by distance and, in addition, an effect of fragmentation. Genetic erosion as a result of fragmentation was also only detectable in the less mobile species, C. perspicillata , where haplotype diversity was lower in island compared to mainland populations. Our results suggest that some Neotropical bat species are prone to loss of genetic variation in response to anthropogenic small-scale habitat fragmentation. In this context, our findings point toward mobility as a good predictor of a species' vulnerability to fragmentation and altered population genetic structure.     

Island–mainland difference in <Emphasis Type="Italic">Nicotiana glauca</Emphasis> (Solanaceae) corolla length: a product of pollinator-mediated selection?

A match between floral and pollinator traits, such as that between unique island plants and pollinators, is often thought to be the product of pollinator-mediated selection. I examined whether the floral morphology of an introduced hummingbird-pollinated plant, Nicotiana glauca (tree tobacco, Solanaceae), is under selection by pollinators on the California Channel Islands where it is a recent colonist. I first determined differences in floral morphology and pollinator composition between island and mainland populations of N. glauca. I found that island plants have detectably longer corollas (on average 1 mm) and are visited by hummingbird species with on average 1–2 mm longer bills than common mainland visitors. Corolla length differences were not found to be associated with site abiotic differences. Flower size does not vary consistently with season and corolla width is very consistent across sites. I tested whether island–mainland corolla length differences are the product of pollinator-mediated selection by measuring phenotypic selection and per visit effectiveness. Contrary to expectations, a longer corolla was not consistently associated with higher pollen transfer or seed count on the islands. Per visit effectiveness of longer and shorter-billed hummingbirds did differ; however, effectiveness did not depend on corolla length. Although I failed to detect expected patterns of selection for longer corollas on islands, I cannot rule out weak or past pollinator-mediated selection. It is also possible that despite the apparent match between pollinator and floral traits, island–mainland differences in corolla length are instead due to other environmental effects, selection unrelated to pollinators, or stochastic processes such as drift.