华北地区小丛红景天种群的AFLP遗传多样性

利用扩增片段长度多态性(AFLP)标记, 对分布于华北地区5个山脉的25个小丛红景天(Rhodiola dumulosa)自然种群的776个样品进行了遗传多样性和遗传结构的研究。结果表明: 华北地区小丛红景天种群具有较高的遗传多样性, 4对选择扩增引物共扩增出398条清晰的条带, 其中多态带312条, 种群的平均多态位点百分率为78.46%, 种群总的Nei’s基因多样性为0.364 9, 总Shannon多态性信息指数为0.542 2。华北地区小丛红景天种群间的遗传分化系数G_st = 0.150 7, 基因流Nm = 2.817 9, 表明种群间遗传分化较低, 有一定的基因交流。AMOVA分析结果也表明: 华北地区小丛红景天的遗传变异主要存在于种群内, 地理单元间有一定的遗传分化, 而种群间的遗传分化较低。STRUCTURE的分析和UPGMA聚类分析结果一致, 结果显示地理分布距离相近的种群优先聚在一起。Mantel检验也进一步证实, 华北地区小丛红景天种群的遗传距离与地理距离间呈显著的正相关关系(r = 0.512 9, p < 0.001)。种群的遗传多样性与海拔呈显著的负相关关系(p < 0.05), 而与坡向没有显著相关性。用Dfdist软件分析海拔对遗传多样性的影响, 结果表明没有显著的受选择位点。     

PHENOTYPIC DIFFERENTIATION AT SOUTHERN LIMIT BORDERS: THE CASE STUDY OF TWO FUCOID MACROALGAL SPECIES WITH DIFFERENT LIFE‐HISTORY TRAITS1

Marginal populations are often geographically isolated, smaller, and more fragmented than central populations and may frequently have to face suboptimal local environmental conditions. Persistence of these populations frequently involves the development of adaptive traits at phenotypic and genetic levels. We compared population structure and demographic variables in two fucoid macroalgal species contrasting in patterns of genetic diversity and phenotypic plasticity at their southern distribution limit with a more central location. Models were Ascophyllum nodosum (L.) Le Jol. (whose extreme longevity and generation overlap may buffer genetic loss by drift) and Fucus serratus L. (with low genetic diversity at southern margins). At edge locations, both species exhibited trends in life‐history traits compatible with population persistence but by using different mechanisms. Marginal populations of A. nodosum had higher reproductive output in spite of similar mortality rates at all life stages, making edge populations denser and with smaller individuals. In F. serratus, rather than demographic changes, marginal populations differed in habitat, occurring restricted to a narrower vertical habitat range. We conclude that persistence of both A. nodosum and F. serratus at the southern‐edge locations depends on different strategies. Marginal population persistence in A. nodosum relies on a differentiation in life‐history traits, whereas F. serratus, putatively poorer in evolvability potential, is restricted to a narrower vertical range at border locations. These results contribute to the general understanding of mechanisms that lead to population persistence at distributional limits and to predict population resilience under a scenario of environmental change.     

Genetic variation of Eryngium campestre L. (Apiaceae) in Central Europe

In Germany, Eryngium campestre is restricted to dry habitats along the rivers Rhine and Elbe and to a few areas in Central Germany. This distribution pattern is usually regarded as a typical pattern of postglacial immigration. In the present study, we investigated whether these two geographically distinct distribution areas are genetically differentiated and whether conclusions can be drawn regarding colonization history. To analyse the phylogeographic structure of E. campestre in Central Europe, 278 individuals from 29 populations within Germany and from further reference populations within Europe were analysed. We applied amplified fragment length polymorphisms to examine their genetic relatedness. Our analyses revealed three groups: a Mediterranean group additionally including two Rhine populations; a Rhine–Main group which further includes the westernmost population from the central German dry area; and one group which includes all eastern populations. Our results show that the two geographically distinct areas are genetically differentiated. As genetic diversity within the Elbe populations is very low, we conclude that this area, which was strongly affected through the late glacial maximum, was colonized relatively recently. High genetic diversity in the Rhine populations indicates a contact zone where lineages of different origin met. This would imply that today's patterns of genetic variation were caused through glacial range contractions and expansions. The present study is one of the first studies that deal with the postglacial distribution pattern of a dry grassland plant species in Central Europe and the results suggest that a survival of E. campestre at least during the Dryas cold stage might be possible.     

Genetic position of Andalusians from Huelva in relation to other European and North African populations: a study based on GM and KM allotypes

An understanding of population relationships in the Mediterranean region is crucial to the reconstruction of recent human evolution. Andalusia, the most southern region of Spain, has been continuously and densely occupied since ancient times and has a rich history of contacts with many different Mediterranean populations. Thus, to understand the Mediterranean peopling process, investigators should analyze the population relationships between the Iberian peninsula and northern Africa based on an assessment of genetic diversity that takes Andalusia into consideration. The aim of this study was to address the extent of genetic variation in the Iberian peninsula between its geographic extremes (Huelva and the Basque area) and to explain the intensity of the phylogenetic relationships between Andalusians and other neighboring populations, such as those from North Africa. We present, for the first time, results on allotype markers (GM and KM) of human immunoglobulins in the Andalusian population from Huelva. The most frequent GM haplotypes in Andalusia correspond to those that are also the most common in Europe. A sub-Saharan haplotype was found at a relatively high frequency compared to other Iberian samples, and a North Asian marker did not reach polymorphic frequencies in the study sample. A hierarchical cluster analysis based on the first two principal components (94.1% of the total genetic variance) revealed an interesting geographic structure for the 49 populations selected from the literature. The Huelva sample showed a central position in the multivariate space--despite being geographically located at one of the extremes of the Mediterranean basin--and clustered with most Western European populations. Western Europe and Eastern Europe (the latter group paradoxically including Italy and the major islands of the western Mediterranean) were differentiated. North African populations were grouped in two clusters that did not separate either Arabs and Berbers or their present-day countries. Analysis of immunoglobulin allotype markers shows that gene flow among human populations should generally be interpreted in terms of complex patterns, with the observed frequencies being the consequence of the entire genetic and demographic history of the population. Single historical events rarely determine gene frequencies in large human populations. Analysis of the GM system has shown that the Andalusian population from Huelva, as a result of its complex history, is not simply an outstanding part of the Mediterranean world but rather the genetic center of gravity of that world.     

Traditional home-garden conserving genetic diversity: a case study of Acacia pennata in southwest China

Conserving biodiversity in human-dominated systems requires research into mechanisms that can maintain biodiversity in fragmented landscapes. Home-garden as traditional agroforestry system in many regions has shown great value in maintaining a wide range of species. Here we show that home-garden populations are also capable of maintaining high level of genetic variation. Using six polymorphic microsatellite DNA markers, we have genotyped 260 individuals of Acacia pennata, a popular wild vegetable in the tropical region of southeast Asia. Samples were collected from home-gardens and wild populations in Xishuangbanna, southwest China. Microsatellite DNA diversity in planted populations were compared with that in geographically nearby wild populations with similar population size. Over 90?% of microsatellite genetic variation in wild populations was also present in planted populations. Pairwise comparison of planted and adjacent wild population showed no significant difference in allelic diversity and heterozygosity. Analysis revealed no significant genetic differences between wild and planted populations, while four home-garden populations showed sign of bottleneck. We conclude that home-gardens show great promise in maintaining genetic diversity, and that these managed patches could be of significant conservation value in tropical regions.     

High regional genetic differentiation of an endangered relict plant Craigia yunnanensis and implications for its conservation

Of the genus Craigia, widespread in the Tertiary, only two relict species survived to modern times. One species is now possibly extinct and the other one, Craigia yunnanensis, is severely endangered. Extensive surveys have located six C. yunnanensis populations in Yunnan province, southwest China. Using fluorescent amplified fragment length polymorphism (AFLP), the genetic diversity and population structure of these populations were examined. It was found that genetic diversity of C. yunnanensis was moderate at the species level, but low at regional and population levels. Analysis of population structure showed significant genetic differentiation between Wenshan and Dehong regions, apparently representing two geographically isolated for long time refuges. There are also clear indications of isolation between populations, which, together with anthropogenically caused decline of population size, will lead to general loss of the species genetic variation with subsequent loss of adaptive potential. To conserve the genetic integrity of C. yunnanensis, we recommend that ex-situ conservation should include representative samples from every population of the two differentiated regions (e.g. Wenshan and Dehong). The crosses between individuals originated from different regions should be avoided because of a high risk of outbreeding depression. As all the extant populations of C. yunnanensis are in unprotected areas with strong anthropogenic impact, there is no alternative to reintroduction of C. yunnanensis into suitable protected locations.     

The effect of migratory behaviour on genetic diversity and population divergence: a comparison of anadromous and freshwater Atlantic salmon Salmo salar

The genetic diversity of anadromous and freshwater Atlantic salmon ( Salmo salar ) populations from north-west Russia and other north European locations was compared using microsatellite variation to evaluate the importance of anadromous migration, population size and population glacial history in determining population genetic diversity and divergence. In anadromous Atlantic salmon populations, the level of genetic diversity was significantly higher and the level of population divergence was significantly lower than among the freshwater Atlantic salmon populations, even after correcting for differences in stock size. The phylogeographic origin of the populations also had a significant effect on the genetic diversity characteristics of populations: anadromous populations from the basins of the Atlantic Ocean, White Sea and Barents Sea possessed higher levels of genetic diversity than anadromous populations from the Baltic Sea basin. Among the freshwater populations, the result was the opposite: the Baltic freshwater populations were more variable. The results of this study imply that differences in the level of long-term gene flow between freshwater populations and anadromous populations have led to different levels of genetic diversity, which was also evidenced by the hierarchical analysis of molecular variance. Furthermore, the results emphasize the importance of taking the life history of a population into consideration when developing conservation strategies: due to the limited possibilities for new genetic diversity to be generated via gene flow, it is expected that freshwater Atlantic salmon populations would be more vulnerable to extinction following a population crash. Hence, high conservation status is warranted in order to ensure the long-term survival of the limited number of European populations with this life-history strategy.     

Population diversity in salmon: linkages among response,genetic and life history diversity

Response diversity and asynchrony are important for stability and resilience of meta‐populations, however little is known about the mechanisms that might drive such processes. In salmon populations, response diversity and asynchrony have been linked to the stability of their meta‐populations and the fisheries that integrate across them. We examined how population diversity influenced response diversity and asynchrony in 42 populations of Chinook salmon from the Fraser River, British Columbia. We examined diversity in the survival responses to large‐scale ocean climate variables for populations that differed in life history. Different life‐histories responded differently to ocean environmental conditions. For instance, an increase of offshore temperature was associated with decreased survival for a population with ocean rearing juveniles but increased survival for a population with stream rearing juveniles. In a second analysis, we examined asynchrony in abundance between populations, which we then correlated with life history, spatial, and genetic diversity. Populations that were more genetically distant had the most different population dynamics. Collectively, these results suggest that fine‐scale population diversity can contribute to the asynchrony and response diversity that underpins the stability of fisheries or metapopulation dynamics, and emphasize the need to manage and conserve this scale of population diversity.     

Comparison of genetic diversity of the invasive weed Rubus alceifolius poir. (Rosaceae) in its native range and in areas of introduction, using amplified fragment length polymorphism (AFLP) markers

Theory predicts that colonization of new areas will be associated with population bottlenecks that reduce within-population genetic diversity and increase genetic differentiation among populations. This should be especially true for weedy plant species, which are often characterized by self-compatible breeding systems and vegetative propagation. To test this prediction, and to evaluate alternative scenarios for the history of introduction, the genetic diversity of Rubus alceifolius was studied with amplified fragment length polymorphism (AFLP) markers in its native range in southeast Asia and in several areas where this plant has been introduced and is now a serious weed (Indian Ocean islands, Australia). In its native range, R. alceifolius showed great genetic variability within populations and among geographically close populations (populations sampled ranging from northern Vietnam to Java). In Madagascar, genetic variability was somewhat lower than in its native range, but still considerable. Each population sampled in the other Indian Ocean islands (Mayotte, La Réunion, Mauritius) was characterized by a single different genotype of R. alceifolius for the markers studied, and closely related to individuals from Madagascar. Queensland populations also included only a single genotype, identical to that found in Mauritius. These results suggest that R. alceifolius was first introduced into Madagascar, perhaps on multiple occasions, and that Madagascan individuals were the immediate source of plants that colonized other areas of introduction. Successive nested founder events appear to have resulted in cumulative reduction in genetic diversity. Possible explanations for the monoclonality of R. alceifolius in many areas of introduction are discussed.     

Extremely low genetic variability and highly structured local populations of Arabidopsis thaliana at higher latitudes

The genetic diversity and population structure of Arabidopsis thaliana populations from Norway were studied and compared to a worldwide sample of A. thaliana to investigate the demographic history and elucidate possible colonization routes of populations at the northernmost species limit. We genotyped 282 individuals from 31 local populations using 149 single nucleotide polymorphism markers. A high level of population subdivision (F(ST) = 0.85 ± 0.007) was found indicating that A. thaliana is highly structured at the regional level. Significant relationships between genetic and geographical distances were found, suggesting an isolation by distance mode of evolution. Genetic diversity was much lower, and the level of linkage disequilibrium was higher in populations from the north (65-68°N) compared to populations from the south (59-62°N); this is consistent with a northward expansion pattern. A neighbour-joining tree showed that populations from northern Norway form a separate cluster, while the remaining populations are distributed over a few minor clusters. Minimal gene flow seems to have occurred between populations in different regions, especially between the geographically distant northern and southern populations. Our data suggest that northern populations represent a homogenous group that may have been established from a few founders during northward expansions, while populations in the central part of Norway constitute an admixed group established by founders of different origins, most probably as a result of human-mediated gene flow. Moreover, Norwegian populations appeared to be homogenous and isolated compared to a worldwide sample of A. thaliana, but they are still grouped with Swedish populations, which may indicate common colonization histories.     

Unconstrained gene flow between populations of a widespread epiphytic lichen Usnea subfloridana (Parmeliaceae,Ascomycota) in Estonia

Few studies have investigated the genetic diversity of populations of common and widespread lichenized fungi using microsatellite markers, especially the relationships between different measures of genetic diversity and environmental heterogeneity. The main aim of our study was to investigate the population genetics of a widespread and mainly clonally reproducing Usnea subfloridana at the landscape scale, focusing on the comparison of lichen populations within hemiboreal forest stands. Particular attention has been paid to the genetic differentiation of lichen populations in two geographically distinct regions in Estonia and the relationships between forest characteristics and measures of genetic diversity. We genotyped 578 Usnea thalli from eleven lichen populations using seven specific fungal microsatellite markers. Measures of genetic diversity (allelic richness, Shannon's information index, Nei's unbiased genetic diversity, clonal diversity, the number of multilocus genotypes, the number of private alleles, and the minimum number of colonization events) were calculated and compared between Usnea populations. Shared haplotypes, gene flow and AMOVA analyses suggest that unconstrained gene flow and exchange of multilocus genotypes exist between the two geographically remote regions in Estonia. Stand age, mean circumference of the host tree, size of forest site and tree species composition did not show any significant influence on allelic richness, Shannon's information index, Nei's unbiased genetic diversity, clonal diversity, the number of private alleles, and the minimum number of colonization events of U. subfloridana populations. Therefore it was concluded that other factors of habitat heterogeneity could probably have a more significant effect on population genetics of U. subfloridana populations.     

Patterns of population subdivision, gene flow and genetic variability in the African wild dog (Lycaon pictus)

African wild dogs are large, highly mobile carnivores that are known to disperse over considerable distances and are rare throughout much of their geographical range. Consequently, genetic variation within and differentiation between geographically separated populations is predicted to be minimal. We determined the genetic diversity of mitochondrial DNA (mtDNA) control region sequences and microsatellite loci in seven populations of African wild dogs. Analysis of mtDNA nucleotide diversity suggests that, historically, wild dog populations have been small relative to other large carnivores. However, population declines due to recent habitat loss have not caused a dramatic reduction in genetic diversity. We found one historical and eight recent mtDNA genotypes in 280 individuals that defined two highly divergent clades. In contrast to a previous, more limited, mtDNA analysis, sequences from these clades are not geographically restricted to eastern or southern African populations. Rather, we found a large admixture zone spanning populations from Botswana, Zimbabwe and south-eastern Tanzania. Mitochondrial and microsatellite differentiation between populations was significant and unique mtDNA genotypes and alleles characterized the populations. However, gene flow estimates (Nm) based on microsatellite data were generally greater than one migrant per generation. In contrast, gene flow estimates based on the mtDNA control region were lower than expected given differences in the mode of inheritance of mitochondrial and nuclear markers which suggests a male bias in long-distance dispersal.     

Lack of genetic structure among ecologically adapted populations of an Australian rainforest Drosophila species as indicated by microsatellite markers and mitochondrial DNA sequences

Although fragmented rainforest environments represent hotspots for invertebrate biodiversity, few genetic studies have been conducted on rainforest invertebrates. Thus, it is not known if invertebrate species in rainforests are highly genetically fragmented, with the potential for populations to show divergent selection responses, or if there are low levels of gene flow sufficient to maintain genetic homogeneity among fragmented populations. Here we use microsatellite markers and DNA sequences from the mitochondrial ND5 locus to investigate genetic differences among Drosophila birchii populations from tropical rainforests in Queensland, Australia. As found in a previous study, mitochondrial DNA diversity was low with no evidence for population differentiation among rainforest fragments. The pattern of mitochondrial haplotype variation was consistent with D. birchii having undergone substantial past population growth. Levels of nuclear genetic variation were high in all populations while F(ST) values were very low, even for flies from geographically isolated areas of rainforest. No significant differentiation was observed between populations on either side of the Burdekin Gap (a long-term dry corridor), although there was evidence for higher gene diversity in low-latitude populations. Spatial autocorrelation coefficients were low and did not differ significantly from random, except for one locus which revealed a clinal-like pattern. Comparisons of microsatellite differentiation contrasted with previously established clinal patterns in quantitative traits in D. birchii, and indicate that the patterns in quantitative traits are likely to be due to selection. These results suggest moderate gene flow in D. birchii over large distances. Limited population structure in this species appears to be due to recent range expansions or cycles of local extinctions followed by recolonizations/expansions. Nevertheless, patterns of local adaptation have developed in D. birchii that may result in populations showing different selection responses when faced with environmental change.     

Genetic structure of Araucaria angustifolia (Araucariaceae) populations in Brazil: implications for the in situ conservation of genetic resources

The distribution of the genetic variation within and among natural populations of A. ANGUSTIFOLIA growing in different regions in Brazil was assessed at microsatellite and AFLP markers. Both markers revealed high gene diversity ( H = 0.65; AR = 9.1 for microsatellites and H = 0.27; P = 77.8 % for AFLPs), moderate overall differentiation ( RST = 0.13 for microsatellites and FST = 0.10 for AFLPs), but high divergence of the northernmost, geographically isolated population. In a Bayesian analysis, microsatellite data suggested population structure at two levels: at K = 2 and at K = 3 in agreement to the geographical distribution of populations. This result was confirmed by the UPGMA dendrogram based on microsatellite data (bootstrap support > 95 %). Non-hierarchical AMOVA revealed high variation among populations from different A POSTERIORI defined geographical groups. The genetic distance between sample locations increased with geographical distance for microsatellites ( R = 0.62; P = 0.003) and AFLPs ( R = 0.32; P = 0.09). This pattern of population differentiation may be correlated with population history such as geographical isolation and postglacial colonization of highlands. Implications of the population genetic structure for the conservation of genetic resources are discussed.     

Gene Flow and Genetic Diversity of a Broadcast-Spawning Coral in Northern Peripheral Populations

Recently, reef-building coral populations have been decreasing worldwide due to various disturbances. Population genetic studies are helpful for estimating the genetic connectivity among populations of marine sessile organisms with metapopulation structures such as corals. Moreover, the relationship between latitude and genetic diversity is informative when evaluating the fragility of populations. In this study, using highly variable markers, we examined the population genetics of the broadcast-spawning coral Acropora digitifera at 19 sites in seven regions along the 1,000 km long island chain of Nansei Islands, Japan. This area includes both subtropical and temperate habitats. Thus, the coral populations around the Nansei Islands in Japan are northern peripheral populations that would be subjected to environmental stresses different from those in tropical areas. The existence of high genetic connectivity across this large geographic area was suggested for all sites (F _ST≤0.033) although small but significant genetic differentiation was detected among populations in geographically close sites and regions. In addition, A. digitifera appears to be distributed throughout the Nansei Islands without losing genetic diversity. Therefore, A. digitifera populations in the Nansei Islands may be able to recover relatively rapidly even when high disturbances of coral communities occur locally if populations on other reefs are properly maintained.     

A tale of two genomes: contrasting patterns of phylogeographic structure in a widely distributed bat

One of the most widely distributed bats in the New World, the big brown bat (Eptesicus fuscus) exhibits well-documented geographic variation in morphology and life history traits, suggesting the potential for significant phylogeographic structure as well as adaptive differentiation among populations. In a pattern broadly consistent with morphologically defined subspecies, we found deeply divergent mitochondrial lineages restricted to different geographic regions. In contrast, sequence data from two nuclear loci suggest a general lack of regional genetic structure except for peripheral populations in the Caribbean and Mexico/South America. Coalescent analyses suggest that the striking difference in population structure between genomes cannot be attributed solely to different rates of lineage sorting, but is likely due to male-mediated gene flow homogenizing nuclear genetic diversity across most of the continental range. Despite this ongoing gene flow, selection has apparently been effective in producing and maintaining adaptive differentiation among populations, while strong female site fidelity, maintained over the course of millions of years, has produced remarkably deep divergence among geographically isolated matrilines. Our results highlight the importance of evaluating multiple genetic markers for a more complete understanding of population structure and history.     

Genetic diversity in fragmented populations of Berchemiella wilsonii var. pubipetiolata (Rhamnaceae)

BACKGROUD AND AIMS: Berchemiella wilsonii var. pubipetiolata (Rhamnaceae) is distributed in fragmented habitat patches in eastern China. It is highly endangered because of severe disturbance by anthropogenic activities. Information on genetic variation and structure is critical for developing successful conservation strategies for this species. METHODS: Allozyme variation of population genetic diversity and structure was investigated for a total of 98 individuals sampled from four extant populations using isoelectric focusing in thin-layer polyacrylamide slab gels. KEY RESULTS: Based on 20 loci scored from the nine enzymes examined, a high genetic diversity was detected at both the species and population level, while there was a loss of low frequency alleles (<0.1) in all populations. Most loci showed deviation from Hardy-Weinberg equilibrium due to excess of heterozygotes in all populations, suggesting that selection for heterozygotes has occurred in this species. The genetic diversity was mainly found within populations with a moderate genetic differentiation (F(ST) = 0.13), but the two geographically discontinuous population groups showed significant differences, with F-statistic values of 0.078 for the Zhejiang populations and 0.014 for the Anhui populations, respectively. CONCLUSIONS: It appears most likely that this species has experienced a recent decrease in population size, and genetic drift in small populations has resulted in a loss of alleles occurring at low frequency. The differentiation into two population groups reflects a population genetic consequence that has been influenced by the different land-use in the two regions. Some conservation concerns are discussed together with possible strategies for implementing in situ and ex situ conservation.     

Population structure and genetic diversity of red deer (<Emphasis Type="Italic">Cervus elaphus</Emphasis>) in forest fragments in north-western France

Red deer have been subjected to anthropogenic interference for many centuries. Most populations are managed according to hunting schedules, some have been kept long-term in enclosures and other populations have been restocked with foreign deer. The red deer in the Brittany region of north-western France only occupy the largest forests in the region, reaching quite high densities in restricted areas. Here, we aimed to assess the extent of the genetic variability of the populations in four forest fragments and investigate their population genetic structure. We show that, despite relatively large expected heterozygosity values, these geographically isolated populations are genetically impoverished relative to individuals from large continuous forests in other parts of Western Europe. We provide evidence for population genetic structure with large genetic differentiation between geographically close populations, suggesting the absence of effective exchange between the forests. Using samples from the most likely source population, we show that at least two populations were non-indigenous. In order to limit further loss of genetic diversity, it should be a management objective to reduce isolation of the different forests, rather than further increase it by fences and hunting practices that could limit free movement of red deer.     

Microbial diversity--insights from population genetics

Although many environmental microbial populations are large and genetically diverse, both the level of diversity and the extent to which it is ecologically relevant remain enigmatic. Because the effective (or long-term) population size, N_e, is one of the parameters that determines population genetic diversity, tests and simulations that assume selectively neutral mutations may help to identify the processes that have shaped microbial diversity. Using ecologically important genes, tests of selective neutrality suggest that adaptive as well as non-adaptive types of selection act and that departure from neutrality may be widespread or restricted to small groups of genotypes. Population genetic simulations using population sizes between 10³ and 10⁷ suggest extremely high levels of microbial diversity in environments that sustain large populations. However, census and effective population sizes may differ considerably, and because we know nothing of the evolutionary history of environmental microbial populations, we also have no idea what N_e of environmental populations is. On the one hand, this reflects our ignorance of the microbial world. On the other hand, the tests and simulations illustrate interactions between microbial diversity and microbial population genetics that should inform our thinking in microbial ecology. Because of the different views on microbial diversity across these disciplines, such interactions are crucial if we are to understand the role of genes in microbial communities.     

The Austroasiatic Munda population from India and Its enigmatic origin: a HLA diversity study

The Austroasiatic linguistic family disputes its origin between two geographically distant regions of Asia, India, and Southeast Asia, respectively. As genetic studies based on classical and gender-specific genetic markers provided contradictory results to this debate thus far, we investigated the HLA diversity (HLA-A, -B, and -DRB1 loci) of an Austroasiatic Munda population from Northeast India and its relationships with other populations from India and Southeast Asia. Because molecular methods currently used to test HLA markers often provide ambiguous results due to the high complexity of this polymorphism, we applied two different techniques (reverse PCR-SSO typing on microbeads arrays based on Luminex technology, and PCR-SSP typing) to type the samples. After validating the resulting frequency distributions through the original statistical method described in our companion article ( Nunes et al. 2011 ), we compared the HLA genetic profile of the sampled Munda to those of other Asiatic populations, among which Dravidian and Indo-European-speakers from India and populations from East and Southeast Asia speaking languages belonging to different linguistic families. We showed that the Munda from Northeast India exhibit a peculiar genetic profile with a reduced level of HLA diversity compared to surrounding Indian populations. They also exhibit less diversity than Southeast Asian populations except at locus DRB1. Several analyses using genetic distances indicate that the Munda are much more closely related to populations from the Indian subcontinent than to Southeast Asian populations speaking languages of the same Austroasiatic linguistic family. On the other hand, they do not share a closer relationship with Dravidians compared with Indo-Europeans, thus arguing against the idea that the Munda share a common and ancient Indian origin with Dravidians. Our results do not favor either a scenario where the Munda would be representative of an ancestral Austroasiatic population giving rise to an eastward Austroasiatic expansion to Southeast Asia. Rather, their peculiar genetic profile is better explained by a decrease in genetic diversity through genetic drift from an ancestral population having a genetic profile similar to present-day Austroasiatic populations from Southeast Asia (thus suggesting a possible southeastern origin), followed by intensive gene flow with neighboring Indian populations. This conclusion is in agreement with archaeological and linguistic information. The history of the Austroasiatic family represents a fascinating example where complex interactions among culturally distinct human populations occurred in the past.