Q型烟粉虱东地中海种群遗传多样性的mtCOI与SSR分析

前期研究表明入侵我国山东的Q型烟粉虱Bemisia tabaci（Genn.）种群来源于西地中海地区而非来源于东地中海地区。为了揭示Q型烟粉虱的入侵遗传机制, 本研究进一步利用线粒体COI（mtCOI）基因与6个具有多态性的微卫星位点（SSR）分析了东地中海Q型烟粉虱（Q1支系与Q2支系）种群的遗传多样性, 并与西地中海种群遗传多样性的前期研究结果进行了比较分析。基于mtCOI基因与微卫星标记分析结果表明, 东地中海种群与西地中海种群一样也具有较高的遗传多样性, 然而两个地区种群存在着遗传异质性。不同入侵性种群遗传结构的比较研究将为进一步解析外来种群的入侵生理生态机制奠定基础。     

基于微卫星标记对中国Q型烟粉虱早期入侵种群与B型烟粉虱种群的遗传结构分析（英文）

2003年首次在云南昆明发现Q型烟粉虱Bemisia tabaci (Gennadius)传入中国。随后几年时间内, 它在许多省份逐年取代了B型烟粉虱种群。2008年后,Q型烟粉虱基本上成为了中国多数省份农区的优势生物型。为了进一步揭示Q型烟粉虱在中国快速扩散以及取代B型烟粉虱的遗传学基础, 本研究利用11个微卫星位点分析并比较了2003年中国云南昆明Q型烟粉虱入侵种群及其他地点的11个B型入侵种群, 西班牙2个Q型土著种群, 以色列1个Q型入侵种群, 以色列1个B型土著种群, 以及西班牙、 美国与澳大利亚的5个B型入侵种群的遗传结构。结果表明, 中国Q型烟粉虱早期种群（云南昆明种群）可能来自于西部地中海地区。中国B型烟粉虱种群遗传多样性高于西班牙、 澳大利亚、 美国B型种群, 中国B型可能存在多次传入或某个混合种群的再次传入。相对于原产地种群, 中国Q型烟粉虱早期入侵种群与B型烟粉虱种群遗传多样性并没有明显降低, 表明Q型与B型烟粉虱种群可能经历了较小的瓶颈效应或奠基者效应。中国Q型烟粉虱早期入侵种群遗传多样性高于B型烟粉虱种群, Q型烟粉虱这种较高的遗传多样性可能为其较强的生态适应性提供了遗传基础, 有利于Q型烟粉虱在新的环境下快速扩散并取代B型烟粉虱。     

Invasion success and genetic diversity of introduced populations of guppies Poecilia reticulata in Australia

High genetic diversity is thought to characterize successful invasive species, as the potential to adapt to new environments is enhanced and inbreeding is reduced. In the last century, guppies, Poecilia reticulata, repeatedly invaded streams in Australia and elsewhere. Quantitative genetic studies of one Australian guppy population have demonstrated high additive genetic variation for autosomal and Y-linked morphological traits. The combination of colonization success, high heritability of morphological traits, and the possibility of multiple introductions to Australia raised the prediction that neutral genetic diversity is high in introduced populations of guppies. In this study we examine genetic diversity at nine microsatellite and one mitochondrial locus for seven Australian populations. We used mtDNA haplotypes from the natural range of guppies and from domesticated varieties to identify source populations. There were a minimum of two introductions, but there was no haplotype diversity within Australian populations, suggesting a founder effect. This was supported by microsatellite markers, as allelic diversity and heterozygosity were severely reduced compared to one wild source population, and evidence of recent bottlenecks was found. Between Australian populations little differentiation of microsatellite allele frequencies was detected, suggesting that population admixture has occurred historically, perhaps due to male-biased gene flow followed by bottlenecks. Thus success of invasion of Australia and high additive genetic variance in Australian guppies are not associated with high levels of diversity at molecular loci. This finding is consistent with the release of additive genetic variation by dominance and epistasis following inbreeding, and with disruptive and negative frequency-dependent selection on fitness traits.     

High genetic differentiation of red gorgonian populations from the Atlantic Ocean and the Mediterranean Sea

Patterns of genetic variation within a species may be used to infer past events in the evolutionary history of marine species. In the present study we aimed to compare the genetic diversity of the red gorgonian Paramuricea clavata in the Atlantic Ocean and the Mediterranean Sea. For genetic markers we used microsatellites and a mitochondrial gene fragment. Our results revealed a distinct genetic composition and diversity between the Mediterranean and the Atlantic. The Mediterranean samples had higher microsatellite heterozygosity, allelic richness and private allelic richness. The hypotheses that can explain these patterns are the isolation of Atlantic populations and/or a founder effect. Additionally, a clear difference was obtained from the mitochondrial locus, since sequences from Atlantic and Mediterranean samples diverged by 1%, which is high for soft corals.     

Genetic Variation of the Siberian Sturgeon (<Emphasis Type="Italic">Acipenser baerii</Emphasis> Brandt, 1869) in Aquaculture

Genetic variation of aquaculture broodstocks of the Siberian sturgeon of different origin from 13 farms across the Russian Federation was assessed at five tetraploid microsatellite loci and the mitochondrial DNA control region. At present, in aquaculture stocks of Siberian sturgeon originating from the Lena and Ob rivers, a sharp decline of haplotype diversity is observed. The most part of aquaculture individuals carry two major haplotypes characteristic of the European part of Russia (the Lena aquaculture) and two haplotypes characteristic of the western part of Siberia (the Ob aquaculture). According to the results of the microsatellite analysis, in sturgeon aquaculture stock originating from the Lena River, two genetic clusters can be distinguished. One of these clusters is represented by the stocks composed of inbred individuals and, because of this, is characterized by depleted allelic variation and the loss of rare alleles.     

Genetic management of the red squirrel,Sciurus vulgaris: a practical approach to regional conservation

The progressive decline in red squirrel (Sciurus vulgaris) numbers in Wales has led to conservation and reintroduction projects being established on the island of Anglesey. The recovery of the island’s remnant wild population was initially successful, however concern remained over potential loss of genetic diversity resulting from an observed demographic bottleneck. We used mitochondrial DNA (mtDNA) control region sequences and six microsatellite loci to assess current levels of genetic variation in the population. Samples were monomorphic for control region sequences and a historic specimen from the same area carrying a different haplotype demonstrated a loss of mtDNA diversity during the last 20 years. Inclusion of other Welsh haplotypes indicated phylogeographic structure in the region, in contrast to previous UK studies. Genotyping results showed allelic diversity and heterozygosity to be less than 50% of that recorded in other UK populations, with strong evidence for a recent genetic bottleneck. A parallel reintroduction programme on Anglesey included genetic analysis of individuals during the selection of captive breeding pairs. We present analysis of sequence and microsatellite data, and subsequent management decisions taken to maximise diversity in the founder and F1 generations. Population and Habitat Viability Analysis applied to both populations modelled future levels of heterozygosity and allelic diversity. Supplementation of the remnant and reintroduced populations with translocated squirrels was simulated as a potential management tool; results support use of this strategy to reduce loss of diversity and increase survival. The limitations of applying conservation genetic theory within small-scale management projects are discussed.     

Genetic diversity of a successful colonizer: isolated populations of Metrioptera roeselii regain variation at an unusually rapid rate

Newly founded isolated populations need to overcome detrimental effects of low genetic diversity. The establishment success of a population may therefore depend on various mechanisms such as assortative mating, purging of deleterious alleles, creation of new mutations and/or repeated inflow of new genotypes to reduce the effects of inbreeding and further loss of genetic variation. We compared the level of genetic variation in introduced populations of an insect species (Metrioptera roeselii) far beyond its natural distribution with levels found in their respective founder populations and coupled the data with timing since establishment. This allowed us to analyze if the introduced populations showed signs of temporal changes in genetic variation and have made it possible to evaluate underlying mechanisms. For this, we used neutral genetic markers, seven microsatellite loci and a 676–bp‐long sequence of the mtDNA COI gene. All tested indices (allelic richness, unbiased expected heterozygosity, effective size, haplotype diversity, and nucleotide diversity) except inbreeding coefficient had significantly higher values in populations within the founding populations inside the continuous area of the species distribution compared with the introduced populations. A logarithmic model showed a significant correlation of both allelic richness and unbiased expected heterozygosity with age of the isolated populations. Considering the species' inferred colonization history and likely introduction pathways, we suggest that multiple introductions are the main mechanism behind the temporal pattern observed. However, we argue that influences of assortative mating, directional selection, and effects of an exceptional high intrapopulation mutation rate may have impacts. The ability to regain genetic diversity at this level may be one of the main reasons why M. roeselii successfully continue to colonize northern Europe.     

Reconciling molecular signatures across markers: mitochondrial DNA confirms founder effect in invasive North American house finches (<Emphasis Type="Italic">Carpodacus mexicanus</Emphasis>)

Well-characterized species introductions provide opportunities to compare the genetic signatures of known founder effects across classes of molecular markers. The release of small numbers of house finches (Carpodacus mexicanus) into the eastern United States in the 1940s led to substantial interest in the effects of this introduction on genetic diversity in this now abundant species, an issue that has been highlighted by a recent Mycoplasma disease epidemic that most intensively affects the introduced and potentially genetically depauperate house finch populations. Previous studies comparing genetic diversity levels in native and introduced house finch populations produced seemingly disparate results: comparisons based on amplified fragment length polymorphism, RFLP mtDNA, and allozyme markers found essentially equivalent levels of diversity in eastern and western populations, whereas microsatellite markers showed clear reductions in diversity in the introduced populations. Here we employ sequence variation at the ND2 mtDNA locus to further compare levels of diversity between the four native and five introduced house finch populations that were previously examined in the microsatellite study. We found substantially lower ND2 haplotype richness and diversity across all introduced populations of house finches. The majority of sequence variation (78%) was detected within subpopulations, with the remainder (22%) explained by the historical status of each population (native or introduced). Our results are consistent with previous microsatellite evidence for a founder effect during the introduction of eastern house finches, and suggest that the mtDNA founder effect was particularly severe, likely owing to a male-biased sex ratio at the time of introduction coupled with the lower effective population size of clonally inherited markers. We discuss how the inconsistencies between past studies of house finch diversity can inform the usefulness of distinct marker sets for detecting molecular signatures of founder events.     

Genetics of the early stages of invasion of the Lessepsian rabbitfish Siganus luridus

Information on the initial stages of dispersal and settlement are of great interest in understanding the dynamics of biological invasions and in designing management responses. A newly settled population of the Lessepsian rabbitfish migrant Siganus luridus, that arrived in Linosa Island (Sicily Strait) in 2000, offered a unique opportunity to examine the genetic variability of the early phase of invasion and the starting point to test genetic variation within and between colonist and source populations.Demographics and dynamic aspects of S. luridus in the Mediterranean were evaluated by using phylogeographic and demographic (coalescent) methods based on DNA sequences of the mitochondrial control region. Sequences from 95 S. luridus, 25 Siganus rivulatus, and one of Siganus (Lo) vulpinus and S. doliatus were used. Samples were collected in one locality in the Red Sea (Eilat) and three localities in the Mediterranean (Israel, Greece and Linosa, Italy). Data showed (for the first time in a Lessepsian migrant) a lowering of the genetic diversity of the invading population (Mediterranean) (haplotype diversity 0.879, nucleotide diversity 0.592) compared to the parental one (Red Sea) (haplotype diversity 0.978, nucleotide diversity 0.958).Within the Mediterranean populations, there was no pattern of regional separation and mitochondrial diversity appeared to be preserved during the Linosa colonization, with no traces of founder events. Such evidence agrees with the idea that Lessepsian migration involves many individuals from its earliest stages.     

Genetic variation and structure in the expanding moss Pogonatum dentatum (Polytrichaceae) in its area of origin and in a recently colonized area

Genetic variation in the expanding moss species Pogonatum dentatum was studied using intersimple sequence repeat (ISSR) markers. The genetic consequences of range expansion were studied by comparing source populations in a mountain area with populations from a recently colonized lowland area in Sweden. Indices of genetic variation show slightly lower number of alleles per locus in the lowlands and a similar gene diversity in both areas. Three of four lowland populations had evidence of a recently passed bottleneck. Considerably higher haplotype diversity was found in the recently colonized lowlands compared to source populations in the mountains. Patterns of allelic diversity suggest that P. dentatum experiences loss of genetic variation through founder effects and genetic drift when expanding its distribution range. Higher haplotypic diversity, less linkage disequilibrium, and fewer compatible loci indicate that sexual recombination is relatively more important in the lowlands compared to the mountains. A likely explanation is higher success of establishment from spores in the lowlands, while clonal propagation predominates in the mountains. Less genetic differentiation among lowland populations indicates more gene flow in the lowland area, involving more spores and/or fragments moving among populations.     

Molecular evidence for a founder effect in invasive house finch (Carpodacus mexicanus) populations experiencing an emergent disease epidemic

The impact of founder events on levels of genetic variation in natural populations remains a topic of significant interest. Well-documented introductions provide a valuable opportunity to examine how founder events influence genetic diversity in invasive species. House finches (Carpodacus mexicanus) are passerine birds native to western North America, with the large eastern North American population derived from a small number of captive individuals released in the 1940s. Previous comparisons using amplified fragment length polymorphism (AFLP) markers found equivalent levels of diversity in eastern and western populations, suggesting that any genetic effects of the founder event were ameliorated by the rapid growth of the newly established population. We used an alternative marker system, 10 highly polymorphic microsatellites, to compare levels of genetic diversity between four native and five introduced house finch populations. In contrast to the AFLP comparisons, we found significantly lower allelic richness and heterozygosity in introduced populations across all loci. Three out of five introduced populations showed significant reductions in the ratio of the number of alleles to the allele size range, a within-population characteristic of recent bottlenecks. Finally, native and introduced populations showed significant pairwise differences in allele frequencies in every case, with stronger isolation by distance within the introduced than native range. Overall, our results provide compelling molecular evidence for a founder effect during the introduction of eastern house finches that reduced diversity levels at polymorphic microsatellite loci and may have contributed to the emergence of the Mycoplasma epidemic which recently swept the eastern range of this species.     

A peculiar relationship between genetic diversity and adaptability in invasive exotic species: bluegill sunfish as a model species

A peculiar relationship exists between population genetics and invasion biology. Introduced populations often suffer a depletion of genetic variation, but they can persist and adapt to new environments. Here, we show that this relationship is observed in bluegill sunfish (Lepomis macrochirus), an invasive exotic fish in Japan. Genetic analysis using selectively neutral genetic markers reconfirmed that the bluegill introduced into Japan from the United States in 1960 had a single origin with only 15 founders. The analysis also shows that in the process of range expansion, the introduced bluegills experienced severe depletion of genetic diversity due to the founder effect and/or genetic drift. Despite such a decline in genetic diversity, the bluegill populations exhibited a divergent feeding morphology in response to the colonized environments. Such a morphological divergence can facilitate prey exploitation, thereby causing a greater negative impact on native prey resources. Further, in a trophically polymorphic bluegill population in Lake Biwa, physiological characteristics and genetic structures of the intestinal bacterial communities were associated with the difference in diet among the trophic morphs in the host bluegill population. This empirical evidence suggests that despite the severe decline in genetic diversity, the introduced bluegill populations rapidly adapted to the new environment and formed diverse functional relationships with the native bacterial community. Thus, these findings suggest that genetic variation at selectively neutral markers does not always predict adaptability and invasiveness in introduced populations.     

Adaptive gradients and isolation-by-distance with postglacial migration in Picea sitchensis

Fossil pollen records suggest rapid migration of tree species in response to Quaternary climate warming. Long-distance dispersal and high gene flow would facilitate rapid migration, but would initially homogenize variation among populations. However, contemporary clinal variation in adaptive traits along environmental gradients shown in many tree species suggests that local adaptation can occur during rapid migration over just a few generations in interglacial periods. In this study, we compared growth performance and pollen genetic structure among populations to investigate how populations of Sitka spruce (Picea sitchensis) have responded to local selection along the historical migration route. The results suggest strong adaptive divergence among populations (average Q(ST)=0.61), corresponding to climatic gradients. The population genetic structure, determined by microsatellite markers (R(ST)=0.09; F(ST)=0.11), was higher than previous estimates from less polymorphic genetic markers. The significant correlation between geographic and pollen haplotype genetic (R(ST)) distances (r=0.73, P<0.01) indicates that the current genetic structure has been shaped by isolation-by-distance, and has developed in relatively few generations. This suggests relatively limited gene flow among populations on a recent timescale. Gene flow from neighboring populations may have provided genetic diversity to founder populations during rapid migration in the early stages of range expansion. Increased genetic diversity subsequently enhanced the efficiency of local selection, limiting gene flow primarily to among similar environments and facilitating the evolution of adaptive clinal variation along environmental gradients.     

How do reproductive skew and founder group size affect genetic diversity in reintroduced populations?

Reduced genetic diversity can result in short-term decreases in fitness and reduced adaptive potential, which may lead to an increased extinction risk. Therefore, maintaining genetic variation is important for the short- and long-term success of reintroduced populations. Here, we evaluate how founder group size and variance in male reproductive success influence the long-term maintenance of genetic diversity after reintroduction. We used microsatellite data to quantify the loss of heterozygosity and allelic diversity in the founder groups from three reintroductions of tuatara ( Sphenodon ), the sole living representatives of the reptilian order Rhynchocephalia. We then estimated the maintenance of genetic diversity over 400 years (∼10 generations) using population viability analyses. Reproduction of tuatara is highly skewed, with as few as 30% of males mating across years. Predicted losses of heterozygosity over 10 generations were low (1–14%), and populations founded with more animals retained a greater proportion of the heterozygosity and allelic diversity of their source populations and founder groups. Greater male reproductive skew led to greater predicted losses of genetic diversity over 10 generations, but only accelerated the loss of genetic diversity at small population size (<250 animals). A reduction in reproductive skew at low density may facilitate the maintenance of genetic diversity in small reintroduced populations. If reproductive skew is high and density-independent, larger founder groups could be released to achieve genetic goals for management.     

Polymorphic microsatellite loci for the cardinal fish (<Emphasis Type="Italic">Apogon imberbis</Emphasis>)

Eight polymorphic microsatellite loci were isolated and characterized for the Cardinal fish (Apogon imberbis), a coastal-reef fish endemic to the Mediterranean Sea. Characterization of 30 Cardinal fish individuals form the western Mediterranean showed moderate to high allelic diversity ranging from 6 to 19 alleles per locus. Two loci showed significant departures from Hardy-Weinberg equilibrium presumably due to null alleles. No evidence of linkage disequilibrium was found for any locus pairwise comparasions. This microsatellite set could be useful for any basic population genetic studies of this species.     

Invasion genetics of the Eurasian round goby in North America: tracing sources and spread patterns

The Eurasian round goby Neogobius melanostomus ( Apollonia melanostoma ) invaded the North American Great Lakes in 1990 through ballast water, spread rapidly, and now is widely distributed and moving through adjacent tributaries. We analyse its genetic diversity and divergence patterns among 25 North American ( N  = 744) and 22 Eurasian ( N  = 414) locations using mitochondrial DNA cytochrome b gene sequences and seven nuclear microsatellite loci in order to: (i) identify the invasion's founding source(s), (ii) test for founder effects, (iii) evaluate whether the invasive range is genetically heterogeneous, and (iv) determine whether fringe and central areas differ in genetic diversity. Tests include F _ST analogues, neighbour-joining trees, haplotype networks, Bayesian assignment, Monmonier barrier analysis, and three-dimensional factorial correspondence analysis. We recovered 13 cytochrome b haplotypes and 232 microsatellite alleles in North America and compared these to variation we previously described across Eurasia. Results show: (i) the southern Dnieper River population was the primary Eurasian donor source for the round goby's invasion of North America, likely supplemented by some alleles from the Dniester and Southern Bug rivers, (ii) the overall invasion has high genetic diversity and experienced no founder effect, (iii) there is significant genetic structuring across North America, and (iv) some expansion areas show reduced numbers of alleles, whereas others appear to reflect secondary colonization. Sampling sites in Lake Huron's Saginaw Bay and Lake Ontario significantly differ from all others, having unique alleles that apparently originated from separate introductions. Substantial genetic variation, multiple founding sources, large number of propagules, and population structure thus likely aided the goby's ecological success.     

Invasion Pathway of the Ctenophore Mnemiopsis leidyi in the Mediterranean Sea

Gelatinous zooplankton outbreaks have increased globally owing to a number of human-mediated factors, including food web alterations and species introductions. The invasive ctenophore Mnemiopsis leidyi entered the Black Sea in the early 1980s. The invasion was followed by the Azov, Caspian, Baltic and North Seas, and, most recently, the Mediterranean Sea. Previous studies identified two distinct invasion pathways of M. leidyi from its native range in the western Atlantic Ocean to Eurasia. However, the source of newly established populations in the Mediterranean Sea remains unclear. Here we build upon our previous study and investigate sequence variation in both mitochondrial (Cytochrome c Oxidase subunit I) and nuclear (Internal Transcribed Spacer) markers in M. leidyi, encompassing five native and 11 introduced populations, including four from the Mediterranean Sea. Extant genetic diversity in Mediterranean populations (n = 8, N _a = 10) preclude the occurrence of a severe genetic bottleneck or founder effects in the initial colonizing population. Our mitochondrial and nuclear marker surveys revealed two possible pathways of introduction into Mediterranean Sea. In total, 17 haplotypes and 18 alleles were recovered from all surveyed populations. Haplotype and allelic diversity of Mediterranean populations were comparable to populations from which they were likely drawn. The distribution of genetic diversity and pattern of genetic differentiation suggest initial colonization of the Mediterranean from the Black-Azov Seas (pairwise F _ST = 0.001–0.028). However, some haplotypes and alleles from the Mediterranean Sea were not detected from the well-sampled Black Sea, although they were found in Gulf of Mexico populations that were also genetically similar to those in the Mediterranean Sea (pairwise F _ST = 0.010–0.032), raising the possibility of multiple invasion sources. Multiple introductions from a combination of Black Sea and native region sources could be facilitated by intense local and transcontinental shipping activity, respectively.     

Microsatellite variation among divergent populations of stalk-eyed flies, genus Cyrtodiopsis

Microsatellite primers are often developed in one species and used to assess neutral variability in related species. Such analyses may be confounded by ascertainment bias (i.e. a decline in amplification success and allelic variability with increasing genetic distance from the source of the microsatellites). In addition, other factors, such as the size of the microsatellite, whether it consists of perfect or interrupted tandem repeats, and whether it is autosomal or X-linked, can affect variation. To test the relative importance of these factors on microsatellite variation, we examine patterns of amplification and allelic diversity in 52 microsatellite loci amplified from five individuals in each of six populations of Cyrtodiopsis stalk-eyed flies that range from 2.2 % to 11.2% mitochondrial DNA sequence divergence from the population used for microsatellite development. We find that amplification success and most measures of allelic diversity declined with genetic distance from the source population, in some cases an order of magnitude faster than in birds or mammals. The median and range of the repeat array length did not decline with genetic distance. In addition, for loci on the X chromosome, we find evidence of lower observed heterozygosity compared with loci on autosomes. The differences in variability between X-linked and autosomal loci are not adequately explained by differences in effective population sizes of the chromosomes. We suggest, instead, that periodic selection events associated with X-chromosome meiotic drive, which is present in many of these populations, reduces X-linked variation.     

Haplotype variation in a mitochondrial tandem repeat of Norway spruce (Picea abies) populations suggests a serious founder effect during postglacial re-colonization of the western Alps

Populations from 13 elevational transects of Norway spruce [Picea abies (L.) Karst] across the Alpine range were sampled to elucidate the geographical pattern of genetic variation in relation to postglacial re-colonization and to study elevational effects on haplotypic diversity. We assessed fragment length variation in a tandem repeat region of the mitochondrial (mt) nad1 intron 2. This maternally inherited genetic marker is suited to infer migration as it is dispersed by seed only. A total of 10 haplotypes was found, most of which were due to repeat copy number variation. An analysis of molecular variance (amova) showed that overall population differentiation was high (F(ST)=0.41), and it revealed a significant differentiation between monomorphic western and moderately to highly variable eastern Alpine populations. This phylogeographic pattern may be explained by a founder effect during postglacial re-colonization. An early arriving haplotype, assumed to originate from a western Carpathian refugium, could expand into suitable habitats, reducing the chances for establishment of subsequently arriving haplotypes. On the other hand, the high variation in populations within an Italian transect of the south-eastern Alps may be the consequence of merging migration pathways from and close distance to putative glacial refugia, most likely those assumed in the Carpathian mountains and on the Balkan peninsula or possibly in the central plains of Italy. An effect of elevation on haplotypic diversity was not evident, though a low, but significant, partition of total genetic variation was attributed to among-population variation in one Italian transect. Various factors, such as vertical seed dispersal and forest management, may account for blurring an otherwise established pattern of genetic variation on a small geographical scale.