A preliminary study on population genetic structure and phylogeography of the wild and cultivated Zizania latifolia (Poaceae) based on Adh1a sequences

Recent decades have witnessed growing interests in exploring the population genetics and phylogeography of crop plants and their wild relatives because of their important value as genetic resources. In this study, sequence variation of the nuclear Adh1a gene was used to investigate the genetic diversity and phylogeographic pattern of the wild and cultivated Zizania latifolia Turcz. Sequence data were obtained from 126 individuals representing 21 wild populations in China and 65 varieties of the cultivated Zizania latifolia. Low to medium level nucleotide diversity was found in the wild populations, with northeastern populations being the most variable. We detected significant population subdivision (F _ST = 0.481) but no significant phylogeogaphical structure, suggesting limited gene flow and dispersal among populations. The current pattern of genetic variation in the wild populations might be explained by a fragmentation of ancient populations due to habitat destruction and degradation during recent decades. The heterogeneous levels and spatial apportionment of genetic diversity among wild populations also suggested a history of gradual colonization of Zizania latifolia populations from the northeast to the south of China. Interestingly, all 65 varieties of the cultivated Zizania latifolia possessed a single identical genotype, implying a single domestication associated with very few initial individuals. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Range-wide genetic structure in a north-east Asian spruce (Picea jezoensis) determined using nuclear microsatellite markers

Aim We used microsatellite markers to determine the range‐wide genetic structure of Picea jezoensis and to test the hypothesis that the past population history of this widespread cold‐temperate spruce has resulted in a low level of genetic variation and in imprints of inbreeding and bottlenecks in isolated marginal populations. Location The natural range of the three infraspecific taxa of P. jezoensis throughout north‐east Asia, including isolated marginal populations. Methods We analysed a total of 990 individuals across 33 natural populations using four nuclear microsatellite loci. Population genetic structure was assessed by analysing genetic diversity indices for each population, examining clustering (model‐based and distance‐based) among populations, evaluating signals of recent bottlenecks, and testing for isolation by distance (IBD). Results The 33 populations were clustered into five groups. The isolated marginal groups of populations (in Kamchatka, Kii in Japan and South Korea) exhibited low levels of allelic richness and gene diversity and a complete or almost complete loss of rare alleles. A recent bottleneck was detected in the populations in Hokkaido across to mid‐Sakhalin. The IBD analysis revealed that genetic divergence between populations was higher for populations separated by straits. Main conclusions Picea jezoensis showed a higher level of genetic differentiation among populations (F_ST = 0.101) than that observed in the genus Picea in general. This might be attributable to the fact that historically the straits around Japan acted as barriers to the movement of seeds and pollen. The low levels of genetic diversity in the isolated marginal population groups may reflect genetic drift that has occurred after isolation. Evidence of a significant bottleneck between the Hokkaido and mid‐Sakhalin populations implies that the cold, dry climate in the late Pleistocene resulted in the decline and contraction of populations, and that there was a subsequent expansion followed by a founder effect when conditions improved. The high polymorphism observed in P. jezoensis nuclear microsatellites revealed cryptic genetic structure that organellar DNA markers failed to identify in a previous study.     

Species‐level view of population structure and gene flow for a critically endangered primate (Varecia variegata)

Lemurs are among the world's most threatened mammals. The critically endangered black‐and‐white ruffed lemur (Varecia variegata), in particular, has recently experienced rapid population declines due to habitat loss, ecological sensitivities to habitat degradation, and extensive human hunting pressure. Despite this, a recent study indicates that ruffed lemurs retain among the highest levels of genetic diversity for primates. Identifying how this diversity is apportioned and whether gene flow is maintained among remnant populations will help to diagnose and target conservation priorities. We sampled 209 individuals from 19 sites throughout the remaining V. variegata range. We used 10 polymorphic microsatellite loci and ~550 bp of mtDNA sequence data to evaluate genetic structure and population dynamics, including dispersal patterns and recent population declines. Bayesian cluster analyses identified two distinct genetic clusters, which optimally partitioned data into populations occurring on either side of the Mangoro River. Localities north of the Mangoro were characterized by greater genetic diversity, greater gene flow (lower genetic differentiation) and higher mtDNA haplotype and nucleotide diversity than those in the south. Despite this, genetic differentiation across all sites was high, as indicated by high average F_ST (0.247) and Φ_ST (0.544), and followed a pattern of isolation‐by‐distance. We use these results to suggest future conservation strategies that include an effort to maintain genetic diversity in the north and restore connectivity in the south. We also note the discordance between patterns of genetic differentiation and current subspecies taxonomy, and encourage a re‐evaluation of conservation management units moving forward.     

Sequential loss of genetic variation in flea beetle Agasicles hygrophila (Coleoptera: Chrysomelidae) following introduction into China

The flea beetle (Agasicles hygrophila) was imported to Florida, USA and then introduced from Florida into China in 1987 as a biological control agent for the invasive plant alligator weed (Alternanthera philoxeroides). The initial beetle population was subsequently used for sequential introductions in other areas of China, but little is known about the genetic consequences of the introductions. In this study, the genetic diversity and population structure of five beetle populations, the source Florida population, three intentionally introduced China populations and one accidentally dispersed China population, were examined using amplified fragment length polymorphisms. The results showed a clear pattern of decreasing genetic diversity with the sequential introductions. The diversity was highest in the Florida population followed by the first introduction to Chongqing and then in Kunming and Fuzhou. The lowest diversity was found in the accidentally dispersed Guangzhou population that was first recorded in 1996. Both loci parameters and Nei's genetic diversity showed a high variation among these populations. Genetic differentiation among populations was further verified by the G_ST statistic (0.136–0.432). Beetles in Kunming had the highest gene flow with those in Guangzhou, and therefore lowest differentiation and closest genetic distance. These data show that sequential introduction influenced the genetic diversity of populations in China. Genetic diversity should be considered in planning introduction and long‐term maintenance of populations.     

Consequences of multiple mating‐system shifts for population and range‐wide genetic structure in a coastal dune plant

Evolutionary transitions from outcrossing to selfing can strongly affect the genetic diversity and structure of species at multiple spatial scales. We investigated the genetic consequences of mating‐system shifts in the North American, Pacific coast dune endemic plant Camissoniopsis cheiranthifolia (Onagraceae) by assaying variation at 13 nuclear (n) and six chloroplast (cp) microsatellite (SSR) loci for 38 populations across the species range. As predicted from the expected reduction in effective population size (N_e) caused by selfing, small‐flowered, predominantly selfing (SF) populations had much lower nSSR diversity (but not cpSSR) than large‐flowered, predominantly outcrossing (LF) populations. The reduction in nSSR diversity was greater than expected from the effects of selfing on N_e alone, but could not be accounted for by indirect effects of selfing on population density. Although selfing should reduce gene flow, SF populations were not more genetically differentiated than LF populations. We detected five clusters of nSSR genotypes and three groups of cpSSR haplotypes across the species range consisting of parapatric groups of populations that usually (but not always) differed in mating system, suggesting that selfing may often initiate ecogeographic isolation. However, lineage‐wide genetic variation was not lower for selfing clusters, failing to support the hypothesis that selection for reproductive assurance spurred the evolution of selfing in this species. Within three populations where LF and SF plants coexist, we detected genetic differentiation among diverged floral phenotypes suggesting that reproductive isolation (probably postzygotic) may help maintain the striking mating‐system differentiation observed across the range of this species.     

Population structure and colonization of Bactrocera dorsalis (Diptera: Tephritidae) in China,inferred from mtDNA COI sequences

The oriental fruit fly, Bactrocera dorsalis, is a serious pest of fruits and vegetables in South‐east Asia, and, because of quarantine restrictions, impedes international trade and economic development in the region. Revealing genetic variation in oriental fruit fly populations will provide a better understanding of the colonization process and facilitate the quarantine and management of this species. The genetic structure in 15 populations of oriental fruit fly from southern China, Laos and Myanmar in South‐east Asia was examined with a 640‐bp sequence of the mitochondrial cytochrome oxidase subunit I (COI) gene. The highest levels of genetic diversity were found in Laos and Myanmar. Low to medium levels of genetic differentiation (F_ST ≤ 0.134) were observed among populations. Pooled populations from mainland China differed from those in Laos and Myanmar (F_ST = 0.024). Genetic structure across the region did not follow the isolation‐by‐distance model. The high genetic diversity observed in Laos and Myanmar supports the South‐east Asian origin of B. dorsalis. High genetic diversity and significant differentiation between some populations within mainland China indicate B. dorsalis populations have been established in the region for an extended period of time. High levels of genetic diversity observed among the five populations from Hainan Island and similarity between the Island and Chinese mainland populations indicate that B. dorsalis was introduced to Hainan from the mainland and has been on the island for many years. High genetic diversity in the recently established population in Shanghai (Pudong) suggests multiple introductions or a larger number of founders.     

Identification and characterization of nuclear microsatellite loci in the aquatic moss Platyhypnidium riparioides (Brachytheciaceae)

Eight microsatellite loci from the aquatic moss Platyhypnidium riparioides were identified using the method of microsatellite‐enriched libraries. Polymorphism was assessed in a sample of four populations of 20 individuals each from four streams of the Meuse hydrographic basin in southern Belgium. The markers amplified three to seven alleles per locus. Comparison of observed and expected heterozygosities as well as F‐statistics (F_ST = 0.62) reveals a significant genetic differentiation among populations. These markers will be useful for further investigation of population genetic structure and diversity at different nested spatial scales.     

Microsatellite genetic variation in the Chinese endemic Eucommia ulmoides (Eucommiaceae): implications for conservation

Eucommia ulmoides, a traditional Chinese medicinal plant, is endangered as a consequence of long‐term and widespread harvest in the late 20th century. It has been widely cultivated as a source of herbal medicine and for use in the organic chemical industry in China. In this study, eight microsatellite markers were applied to investigate genetic diversity in E. ulmoides. Three hundred individuals from one semi‐wild population and nine cultivated populations across its main production area were collected. A high level of genetic diversity at population levels (H_E = 0.716) was observed. The highly outcrossed mating system, high longevity of E. ulmoides and seed admixture may be responsible for high genetic variation within populations. A genetic bottleneck was observed in one population. Populations were only slightly differentiated from one another (F_ST = 0.063); this was also supported by AMOVA, which revealed that 94.05% of the total variation resided within populations. This is probably attributable to long‐distance gene flow mediated by the exchange of seeds by local farmers. Implications of these results for the conservation of genetic resources of E. ulmoides are discussed. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 775–785.     

Genomewide patterns of variation in genetic diversity are shared among populations,species and higher‐order taxa

Genomewide screens of genetic variation within and between populations can reveal signatures of selection implicated in adaptation and speciation. Genomic regions with low genetic diversity and elevated differentiation reflective of locally reduced effective population sizes (N_e) are candidates for barrier loci contributing to population divergence. Yet, such candidate genomic regions need not arise as a result of selection promoting adaptation or advancing reproductive isolation. Linked selection unrelated to lineage‐specific adaptation or population divergence can generate comparable signatures. It is challenging to distinguish between these processes, particularly when diverging populations share ancestral genetic variation. In this study, we took a comparative approach using population assemblages from distant clades assessing genomic parallelism of variation in N_e. Utilizing population‐level polymorphism data from 444 resequenced genomes of three avian clades spanning 50 million years of evolution, we tested whether population genetic summary statistics reflecting genomewide variation in N_e would covary among populations within clades, and importantly, also among clades where lineage sorting has been completed. All statistics including population‐scaled recombination rate (ρ), nucleotide diversity (π) and measures of genetic differentiation between populations (F_ST, PBS, d_xy) were significantly correlated across all phylogenetic distances. Moreover, genomic regions with elevated levels of genetic differentiation were associated with inferred pericentromeric and subtelomeric regions. The phylogenetic stability of diversity landscapes and stable association with genomic features support a role of linked selection not necessarily associated with adaptation and speciation in shaping patterns of genomewide heterogeneity in genetic diversity.     

Population size,center–periphery,and seed dispersers’ effects on the genetic diversity and population structure of the Mediterranean relict shrub Cneorum tricoccon

The effect of population size on population genetic diversity and structure has rarely been studied jointly with other factors such as the position of a population within the species’ distribution range or the presence of mutualistic partners influencing dispersal. Understanding these determining factors for genetic variation is critical for conservation of relict plants that are generally suffering from genetic deterioration. Working with 16 populations of the vulnerable relict shrub Cneorum tricoccon throughout the majority of its western Mediterranean distribution range, and using nine polymorphic microsatellite markers, we examined the effects of periphery (peripheral vs. central), population size (large vs. small), and seed disperser (introduced carnivores vs. endemic lizards) on the genetic diversity and population structure of the species. Contrasting genetic variation (H_E: 0.04–0.476) was found across populations. Peripheral populations showed lower genetic diversity, but this was dependent on population size. Large peripheral populations showed high levels of genetic diversity, whereas small central populations were less diverse. Significant isolation by distance was detected, indicating that the effect of long‐distance gene flow is limited relative to that of genetic drift, probably due to high selfing rates (F_IS = 0.155–0.887), restricted pollen flow, and ineffective seed dispersal. Bayesian clustering also supported the strong population differentiation and highly fragmented structure. Contrary to expectations, the type of disperser showed no significant effect on either population genetic diversity or structure. Our results challenge the idea of an effect of periphery per se that can be mainly explained by population size, drawing attention to the need of integrative approaches considering different determinants of genetic variation. Furthermore, the very low genetic diversity observed in several small populations and the strong among‐population differentiation highlight the conservation value of large populations throughout the species’ range, particularly in light of climate change and direct human threats.     

Mitochondrial DNA phylogeography of Spodoptera exigua across a broad geographic area in China

The beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), is an important agriculture pest in China that causes serious economic losses in some of the main crop‐producing areas. To monitor and manage this pest effectively, it is necessary to investigate its phylogeographic patterns in China. In this study, we used a partial sequence of mitochondrial DNA Cytb gene consisting of 724 bps to investigate the genetic diversity of the beet armyworm. A total of 765 individuals from 47 populations across the main distribution range of the species were collected, and 112 haplotypes were identified. Moderate‐to‐high levels of genetic diversity (Hd = 0.672 ± 0.017, Pi = 0.00268 ± 0.00021) for the total populations were obtained. Phylogenetic and median‐joining network analyses indicated there was no distinct geographic distribution pattern among haplotypes. Overall, the study also revealed significant differentiation among some populations (P < 0.05). The F_ST values of Shenyang population (SY2012–SY 2014), as well as Baoding (BD), Taian (TA), Lucheng (LC), Zhengzhou (ZZ) and Wuhan (WH), were significantly different from those of the populations in most other locations. Hierarchical AMOVA showed there was no significantly genetic structure between populations located in seven geographic regions and four main bioclimatic zones. Finally, unimodal mismatch distribution combined with negative Tajima's D (D = ?2.696, P < 0.001) and Fu's F_S (F_S = ?207.228, P > 0.05) indicated recent population expansion of S. exigua at large spatial scales in China.     

Genetic diversity of the endangered Chinese endemic herb Primulina tabacum (Gesneriaceae) revealed by amplified fragment length polymorphism (AFLP)

Primulina tabacum Hance, is a critically endangered perennial endemic to limestone area in South China. Genetic variability within and among four extant populations of this species was assessed using AFLP markers. We expected a low genetic diversity level of this narrowly distributed species, but our results revealed that a high level of genetic diversity remains, both at population level (55.5% of markers polymorphic, H _E = 0.220, I _S = 0.321), and at species level (P = 85.6% of markers polymorphic, H _E = 0.339, I _S = 0.495), probably resulting from its refugial history and/or breeding system. High levels of genetic differentiation among populations was apparent based on Nei’s genetic diversity analysis (G _st=0.350). The restricted gene flow between populations is a potential reason for the high genetic differentiation. The population genetic diversity of P. tabacum revealed here has clear implications for conservation and management. To maintain present levels of genetic diversity, in situ conservation of all populations is necessary.     

Population genetic structure and larval dispersal potential of spottedtail goby Synechogobius ommaturus in the north‐west Pacific

Larval dispersal may have an important effect on genetic structure of benthic fishes. To examine the population genetic structure of spottedtail goby Synechogobius ommaturus, a 478 base pair (bp) fragment of the hypervariable portion of the mtDNA control region was sequenced and used to interpret life‐history characteristics and larval dispersal strategy. Individuals (n = 186) from 10 locations on the coasts of China and Korea were analysed and 44 haplotypes were obtained. The levels of haplotype and nucleotide diversity were higher in East China Sea populations than in other populations. Both the phylogenetic tree and the minimum spanning tree showed that no significant genealogical structures corresponding to sampling locations existed. AMOVA and pair‐wise F_ST revealed significant genetic differentiation between populations from Korea and China. A significant isolation by distance pattern was observed in this species (r = 0·53, P < 0·001). Both mismatch distribution analysis and neutrality tests showed S. ommaturus to have experienced a recent population expansion. These results suggest that the Pleistocene ice ages had a major effect on the phylogeographic pattern of S. ommaturus, that larvae might avoid offshore dispersal and that dispersal of larvae may maintain a migration–drift equilibrium.     

The phylogeography of Fagus hayatae (Fagaceae): genetic isolation among populations

The beech species Fagus hayatae is an important relict tree species in subtropical China, whose biogeographical patterns may reflect floral responses to climate change in this region during the Quaternary. Previous studies have revealed phylogeography for three of the four Fagus species in China, but study on F. hayatae, the most sparsely distributed of these species, is still lacking. Here, molecular methods based on eight simple sequence repeat (SSR) loci of nuclear DNA (nDNA) and three chloroplast DNA (cpDNA) sequences were applied for analyses of genetic diversity and structure in 375 samples from 14 F. hayatae populations across its whole range. Both nDNA and cpDNA indicated a high level of genetic diversity in this species. Significant fixation indexes and departures from the Hardy–Weinberg equilibrium, with a genetic differentiation parameter of R_st of 0.233, were detected in nDNA SSR loci among populations, especially those on Taiwan Island, indicating strong geographic partitioning. The populations were classified into two clusters, without a prominent signal of isolation‐by‐distance. For the 15 haplotypes detected in the cpDNA sequence fragments, there was a high genetic differentiation parameter (G_st = 0.712) among populations. A high G_st of 0.829 was also detected outside but not within the Sichuan Basin. Consistent with other Fagus species in China, no recent population expansion was detected from tests of neutrality and mismatch distribution analysis. Overall, genetic isolation with limited gene flow was prominent for this species and significant phylogeographic structures existed across its range except for those inside the Sichuan Basin. Our study suggested long‐term geographic isolation in F. hayatae with limited population admixture and the existence of multiple refugia in the mountainous regions of the Sichuan Basin and southeast China during the Quaternary. These results may provide useful information critical for the conservation of F. hayatae and other Chinese beech species.     

Genetic variation and population genetic structure of Laodelphax striatellus via genome‐wide single nucleotide polymorphisms from specific‐locus amplified fragment‐sequencing

The small brown planthopper (SBPH), Laodelphax striatellus, is one of the most destructive agricultural pests that causes serious economic loss in the main rice‐producing areas of China. To clarify issues such as the genetic differentiation, gene flow and population genetic structure of SBPH populations, we investigated the genetic diversity, genetic structure and phylogeography of 27 SBPH populations at 23 sampling sites from three climatic zones of China using specific‐locus amplified fragment sequencing (SLAF‐seq) for large‐scale single nucleotide polymorphism (SNP) detection. In total, 115.95 M reads, 56,355 polymorphic specific‐locus amplified fragments were developed, and 32,556 reliable single nucleotides (SNPs) were detected. The results indicated that the genotypes of many polymorphism sites had low heterozygosity in every population. Overall, the pairwise F_ST values between the populations varied from 0.056 to 0.092; it suggested the lack of strong differentiation among three climatic zone groups, respectively. It also suggested a strong level of gene flow (Nm) among populations in different climate zones, ranging from 28.864 to 35.197. Phylogenetic analyses, principal component analysis (PCA), Bayesian clustering method and AMOVA revealed that there was no evidence genetic clustering in three main bioclimatic zones. Neutrality testing provided strong evidence for a recent rapid expansion without any recent genetic bottleneck in these populations. Accordingly, the results of the present study should be beneficial for SBPH management and provide insight into the genetics of SBPH.     

大叶藻居群微卫星遗传多样性研究

采用4对微卫星引物对大叶藻的7个地理居群进行了遗传多样性与遗传结构分析。扩增148株大叶藻得到57个等位基因, 每个位点平均等位基因数为6, 大叶藻居群的平均期望杂合度(He)为0.687, 平均观测杂合度(Ho)为0.417。青岛湾居群的遗传多样性最高(A=7.750, AR=7.043), 俚岛居群最低(A=4.750, AR=4.543)。从F_st值来看, 7个大叶藻居群间属于中度分化。UPGMA系统发育树显示, 中国4个大叶藻居群聚类到一起, 其遗传分化可能是由于历史大海草场的遗留小片段居群产生, 而中国、韩国、日本和爱尔兰居群间的遗传分化则主要是由于地理隔离造成的。自由交配估计结果支持海草的东亚起源说。青岛湾居群遗传多样性较高, 可优先作为大叶藻移植修复的材料和基因库, 并进行重点保护。     

Contrasting levels of genetic diversity between the historically rare orchid Cypripedium japonicum and the historically common orchid Cypripedium macranthos in South Korea

Many terrestrial orchids are historically rare and occur in small, spatially isolated populations. Theory predicts that such species will harbour low levels of genetic variation within populations and will exhibit a high degree of population genetic divergence, primarily as a result of genetic drift. If the origin of the present‐day populations is relatively recent from the same genetically depauperate source population, a complete lack of genetic differentiation between conspecific populations is expected. If a terrestrial orchid was historically common with moderate or high levels of genetic diversity, but has experienced more recent anthropogenic disturbance as a result of over‐collection, it would still exhibit initial levels of genetic variation within populations and a low degree of genetic divergence between populations. To test these predictions, we examined the genetic diversity in six populations (N = 131) of the historically and currently rare Cypripedium japonicum and in four populations (N = 94) of the historically common but now rare C. macranthos from South Korea. Fourteen putative allozyme loci resolved from eight enzyme systems revealed no variation either within or among populations of C. japonicum, which supports the first prediction. In contrast, populations of C. macranthos harboured high levels of genetic variation (mean percentage of polymorphic loci %P = 46.7; mean expected heterozygosity H_e = 0.185) and exhibited a low degree of population genetic divergence (G_ST = 0.059), supporting the second prediction. The lack of genetic variation both within and among conspecific populations of C. japonicum may suggest that populations originated from the same genetically depauperate ancestral population. The high levels of genetic diversity maintained in populations of C. macranthos suggest that the collection‐mediated decrease in the number of individuals is still too recent for long‐term effects on genetic variation. Based on current demographic and genetic data, in situ and ex situ conservation strategies should be provided to preserve genetic variation and to ensure the long‐term survival of the two species in the Korean Peninsula. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 119–129.     

Population genetics and breeding system of Tupistra pingbianensis (Liliaceae), a naturally rare plant endemic to SW China

The levels and partitioning of genetic diversity and inbreeding depression were investigated in Tupistra pingbianensis, a narrow endemic of South-east Yunnan, China, characterized by a naturally fragmented distribution due to extreme specialization on a rare habitat type. Here genetic diversity and patterns of genetic variation within and among 11 populations were analyzed using AFLP markers with 97 individuals across its whole geographical range. High levels of genetic variation were revealed both at the species level (P₉₉ = 96.012%; H_t = 0.302) and at the population level (P₉₉ = 51.41%; H_s = 0.224). Strong genetic differentiation among populations was also detected (F_ST = 0.2961; ⍬^嘦= 0.281), which corresponded to results reported for typical animal-pollinated, mixed selfing and outcrossing plant species. This result was consistent with mating patterns detected by our pollination experiments. The indirect estimate of gene flow based on ⍬^嘦 was low (N_m = 0.64). Special habitat and its life history traits may play an important role in shaping the genetic diversity and the genetic structure of this species. A pollination experiment also fail to detect significant inbreeding depression upon F₁ fruit set, seed weight and germinate rate fitness-traits. Since naturally rare species T. pingbianensis is not seriously genetically impoverished and likely to have adapted to tolerating a high level of inbreeding early in its history, we propose this species need only periodic monitoring to ensure their continued persistence but not intervention to remain viable.     

Strong intraspecific variation in genetic diversity and genetic differentiation in Daphnia magna: the effects of population turnover and population size

Theory predicts that genetic diversity and genetic differentiation may strongly vary among populations of the same species depending on population turnover and local population sizes. Yet, despite the importance of these predictions for evolutionary and conservation issues, empirical studies comparing high‐turnover and low‐turnover populations of the same species are scarce. In this study, we used Daphnia magna, a freshwater crustacean, as a model organism for such a comparison. In the southern/central part of its range, D. magna inhabits medium‐sized, stable ponds, whereas in the north, it occurs in small rock pools with strong population turnover. We found that these northern populations have a significantly lower genetic diversity and higher genetic differentiation compared to the southern/central populations. Total genetic diversity across populations was only about half and average within‐population diversity only about a third of that in southern/central populations. Moreover, an average southern population contains more genetic diversity than the whole metapopulation system in the north. We based our analyses both on silent sites and microsatellites. The similarity of our results despite the contrasting mutation rates of these markers suggests that the differences are caused by contemporary rather than by historical processes. Our findings show that variation in population turnover and population size may have a major impact on the genetic diversity and differentiation of populations, and hence may lead to differences in evolutionary processes like local adaptation, hybrid vigour and breeding system evolution in different parts of a species range.     

Microsatellite‐based analysis of genetic structure and gene flow of Mythimna separata (Walker) (Lepidoptera: Noctuidae) in China

The oriental armyworm, Mythimna separata, is a serious agricultural pest in China. Seasonal and roundtrip migration has recently led to sudden, localized outbreaks and crop losses. To evaluate genetic differentiation between populations in eastern and western China and elucidate gene flow, the genetic structure of 20 natural populations from nine provinces was examined using seven microsatellite markers. The results indicated high genetic diversity. However, little to moderate (0 < F_ST < 0.15) genetic differentiation was detected, and there was no correlation between genetic distance and geographical distance. Bayesian clustering analysis identified three groups whereas discriminant analysis of principal components identified ten clusters that were considered as two clear‐cut clusters and one admixed group. Gene flow occurred frequently in most population pairs, and an asymmetrical migration rate was detected in several pairwise population comparisons. The bottleneck test showed that few populations had experienced recent bottlenecks. Correspondingly, large‐scale and long‐distance migration of M. separata has caused low genetic differentiation and frequent gene exchange. Our findings are important for studying genetic evolution and help to improve predictions of M. separata outbreaks in China.