More introgression with less gene flow: chloroplast vs. mitochondrial DNA in the Picea asperata complex in China, and comparison with other Conifers

Recent work has suggested that rates of introgression should be inversely related to levels of gene flow because introgressed populations cannot be 'rescued' by intraspecific gene flow if it is too low. Mitochondrial and chloroplast DNA (mtDNA and cpDNA) experience very different levels of gene flow in conifers due to their contrasted maternal and paternal modes of transmission, hence the prediction that mtDNA should introgress more readily than cpDNA in this group. Here, we use sequence data from both mtDNA and cpDNA to test this hypothesis in a group of closely related spruces species, the Picea asperata complex from China. Nine mitochondrial and nine chloroplast haplotypes were recovered from 459 individuals in 46 natural populations belonging to five species of the Picea asperata complex. Low variation was found in the two mtDNA introns along with a high level of differentiation among populations ( G _ST = 0.90). In contrast, we detected higher variation and lower differentiation among populations at cpDNA markers ( G _ST = 0.56), a trend shared by most conifer species studied so far. We found that cpDNA variation, although far from being fully diagnostic, is more species-specific than mtDNA variation: four groups of populations were identified using cpDNA markers, all of them related to species or groups of species, whereas for mtDNA, geographical variation prevails over species differentiation. The literature suggests that mtDNA haplotypes are often shared among related conifer species, whereas cpDNA haplotypes are more species-specific. Hence, increased intraspecific gene flow appears to decrease differentiation within species but not among species.     

Distribution of chloroplast DNA diversity within and among populations in gynodioecious Beta vulgaris ssp. maritima (Chenopodiaceae)

With the recent technical advances in molecular biology, chloroplast DNA (cpDNA) has become a marker used for the study of cytoplasmic differentiation of natural populations of plants. As chloroplasts are maternally inherited in most plant species, the seed component of gene flow is thus made accessible. We present here a study of cpDNA polymorphism within the maritima subspecies of the gynodioecious Beta vulgaris in which we try to assess the impact of such a reproductive system on seed flow. One hundred and eighty-eight wild beets were sampled from 20 hermaphroditic and 20 gynodioecious (i.e. containing both hermaphroditic and female plants) populations from the Atlantic coast of Europe. cpDNA variability in these populations was characterized with a rapid restriction fragment length polymorphism (RFLP) method. Eight cpDNA haplotypes were found. Strong differentiation among populations was observed ( F _ST = 0.43) and was consistent with isolation by distance, although most of the cpDNA haplotypes were ubiquitous. Gynodioecy seems to affect the distribution of cpDNA diversity: gynodioecious populations of Beta vulgaris ssp. maritima contained a greater number of cpDNA types but were less differentiated among themselves than hermaphroditic ones.     

Geographic distribution of chloroplast variation in Italian populations of beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.)

The distribution of chloroplast DNA (cpDNA) variation in Italian beech (Fagus sylvatica L.) populations was studied using PCR-RFLP and microsatellite markers. In total, 67 populations were analysed, and 14 haplotypes were identified by combining the two marker types. A remarkable subdivision of cpDNA diversity in Italian beech was found, as indicated by a high level of genetic differentiation (G_st=0.855). The highest level of total haplotype diversity (h_t=0.822) was estimated for southern Italian populations. The highest number of haplotypes was found in the central-southern region of the peninsula. The nested clade analysis provided evidence for past fragmentation events that may have been occurred during the Quaternary glaciations and had a major role in defining the genetic structure of the central-southern Italian beech populations. Only one haplotype apparently spread towards the north of Italy along the Apennine chain and reached the Italian slope of the western part of the Alps (Maritime Alps, Liguria). All haplotypes found along the Apennines remained trapped in the Italian peninsula. Southern and central Italy represent hotspots of haplotype diversity for Italian beech.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by O. Savolainen     

药食同源植物薤白的谱系地理学研究

对我国14个地区的药食同源植物薤白（Allium macrostemon）的叶绿体基因片段（psbA-trnH、rps16和trnL-F）与核基因片段（ITS）进行测序分析,揭示薤白的遗传变异分布式样、单倍型地理分布格局,并推断其在第四纪冰期的避难所。结果表明：薤白叶绿体基因（cpDNA）遗传多样性低于核基因（nrDNA）遗传多样性（cpDNA：H_T=0.868;nrDNA：H_T=0.890）。cpDNA和nrDNA的分子变异分析（AMOVA）结果显示：薤白遗传变异主要发生在居群间（cpDNA：92.84%;nrDNA：98.40%）,存在遗传分化（cpDNA：N_st=0.918,G_st=0.866,F_st=0.928;nrDNA：N_st=0.984,G_st=0.855,F_st=0.984）,且N_st均大于G_st,表明该物种具有明显的谱系地理结构。在薤白居群中,共检测到11个叶绿体单倍型和14个nrDNA基因型;单倍型网络图及地理分布图表明,叶绿体单倍型H3、核DNA基因型H1频率最高,位于网络结构图的中心位置,可能为古老单倍型。此外,冰期避难所假说认为遗传多样性高、拥有古老单倍型和较多特有单倍型的区域可能是该物种的冰期避难所,因此推测薤白在第四纪冰期时可能在大盘山、天水和通化地区存在多个冰期避难所。这些分析可为类似草本植物的进化提供参考,丰富对东亚草本植物分子系统与生物地理学的认识。     

Distinct geographical structure across species units evidenced by chloroplast DNA haplotypes and nuclear ribosomal ITS genotypes of Corylopsis (Hamamelidaceae) in the Japanese islands

The geographical distribution of chloroplast DNA (cpDNA) haplotypes and nuclear ribosomal internal transcribed spacer (nrITS) genotypes of Japanese Corylopsis (Hamamelidaceae), which consists of four species, was investigated. Two hundred and five individuals belonging to four species from 30 populations, covering the entire geographical range, were studied. Based on approximately 1108 bp of the three non-coding regions of cpDNA, nine haplotypes were detected, and each was distinguished from adjacent haplotypes by one substitution. Based on approximately 507-bp nrITS sequences, 47 genotypes were detected, for which three clades were identified in the phylogenetic analysis. There was inconsistency between the cpDNA haplotypes, nrITS genotypes, and classification of Corylopsis taxa, possibly because of incomplete lineage sorting or introgressive hybridization. The distribution of the haplotypes was highly structured geographically, and N _ST (0.893) was significantly greater than G _ST (0.819), implying that the current distribution of Corylopsis species was structured phylogeographically during Quaternary climatic oscillations. The haplotype composition and results of analysis of molecular variance showed that the populations in Hokuriku were highly divergent, suggesting that they are long-term persistent populations arising from refugia during the Quaternary climatic oscillations. Refugial populations in Chugoku and Shikoku may have lost genetic diversity because of a bottleneck resulting from a small population size, followed by post-glacial range expansion. Pre-existing refugia may have been so small that the subsequent range expansion replaced the pre-existing genetic structure.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 501–518.     

Chloroplast DNA phylogeography of the argan tree of Morocco

Polymorphisms in the chloroplast genome of the argan tree (Sapotaceae), an endemic species of south-western Morocco, have been detected by restriction site studies of PCR-amplified fragments. A total of 12 chloroplast DNA (cpDNA) and two mitochondrial DNA (mtDNA) fragments were amplified and digested with a single restriction enzyme ( Hin fI). Polymorphisms were identified in six of the cpDNA fragments, whereas no mtDNA polymorphisms were detected in a survey of 95 individuals from 19 populations encompassing most of the natural range of the species. The cpDNA polymorphisms allowed the identification of 11 haplotypes. Two lineages, one in the south-east and the other in the north-west, divide the range of the argan tree into two distinct areas. The level of genetic differentiation measured at the haplotype level ( G _STc= 0.60) (i.e. with unordered haplotypes) was smaller than when phylogenetic relationships were taken into account ( N _STc= 0.71–0.74) (ordered haplotypes), indicating that population history must be considered in the study of the geographical distribution of cpDNA lineages in this species. If contrasted with the level of nuclear genetic differentiation measured in a previous study with isozymes ( G _STn= 0.25), the results indicate a relatively high level of gene flow by seeds, or conversely a relatively low level of gene flow by pollen, as compared with other tree species. Goats and camels could have played an important role in disseminating the fruits of this tree.     

基于cpDNA和ITS序列对庭藤复合群的居群遗传学研究

采用2个叶绿体基因组片段(ndh J-trn F和trn D-trn T)和核基因组ITS序列对分布于中国东部和相邻地区的庭藤复合群(Indigofera decora complex)的24个居群进行分析,探讨该复合群的遗传多样性、单倍型分布、遗传结构和居群历史动态。cp DNA和ITS序列分析表明,庭藤复合群的单倍型多样性较高,而总体遗传多样性偏低(cp DNA片段:Hd=0.778,π=0.00123;ITS:Hd=0.909,π=0.01290);皖浙地区居群的遗传多样性相对较高,推测其可能是该复合群遗传多样性的分布中心。遗传变异主要存在于复合群居群间,种内居群间遗传分化较大(cp DNA片段:FST=0.848;ITS:FST=0.787);基因流较小(cp DNA片段:Nm=0.228;ITS:Nm=0.241),主要是地理隔离(遗传漂变)或生境片段化促进了物种形成;复合群的不同物种间存在由基因渐渗引起的单倍型共享现象,可能是种间不完全的生殖隔离所致。花木蓝的居群单独聚为一枝,且与其他种无共享单倍型,因此应保留花木蓝种的分类地位,而其他种的分类地位有待进一步研究。     

Comparison between mitochondrial and chloroplast DNA variation in the native range of Silene vulgaris

A detailed survey of mitochondrial and chloroplast diversity in eight populations of Silene vulgaris from Central Europe was conducted for comparison with previously published data on diversity from S. vulgaris populations in the introduced range. Mitochondrial DNA (mtDNA) variation around the coxI gene was assessed with Southern blotting/restriction fragment length polymorphism methods. Chloroplast variation was assessed by sequencing the intergenic spacer separating the trnH and psbA genes. Thirty mtDNA haplotypes and 24 chloroplast DNA (cpDNA) haplotypes were found within 86 individuals. The overall genetic diversity h (0.941 for mitochondrial, and 0.893 for chloroplast markers) and within-population diversity were higher than reported in previous population studies of S. vulgaris in the USA and Europe. The frequency of private alleles was surprisingly high - more than 90% for both kinds of markers. Most of our populations were large and located in relatively undisturbed meadows, whereas surveys in Virginia consisted of smaller roadside populations. The slow rate of population turnover in European populations is discussed as a factor responsible for the relatively high diversity of S. vulgaris in undisturbed areas of its native range. Association between mtDNA and cpDNA haplotypes was also demonstrated. Finally, gender and mtDNA haplotype were associated in the Alps populations, where females were very rare.     

Decoupled mitochondrial and chloroplast DNA population structure reveals Holocene collapse and population isolation in a threatened Mexican-endemic conifer

Chihuahua spruce (Picea chihuahuana Martínez) is a montane subtropical conifer endemic to the Sierra Madre Occidental in northwestern México. Range-wide variation was investigated using maternally inherited mitochondrial (mtDNA) and paternally inherited chloroplast (cpDNA) DNA markers. Among the 16 mtDNA regions analysed, only two mitotypes were detected, while the study of six cpDNA microsatellite markers revealed eight different chlorotypes. The average cpDNA diversity (H = 0.415) was low but much higher than that for mtDNA (H = 0). The distribution of mitotypes revealed two clear nonoverlapping areas (G(ST) = N(ST) = 1), one including northern populations and the second one including the southern and central stands, suggesting that these two regions may represent different ancestral populations. The cpDNA markers showed lower population differentiation (G(ST) = 0.362; R(ST) = 0.230), implying that the two ancestral populations continued to exchange pollen after their initial geographic separation. A lack of a phylogeographic structure was revealed by different spatial analyses of cpDNA (G(ST) > R(ST); and samova), and reduced cpDNA gene flow was noted among populations (Nm = 0.873). Some stands deviated significantly from the mutation-drift equilibrium, suggesting recent bottlenecks. Altogether, these various trends are consistent with the hypothesis of a population collapse during the Holocene warming and suggest that most of the modern P. chihuahuana populations are now effectively isolated with their genetic diversity essentially modelled by genetic drift. The conservation efforts should focus on most southern populations and on the northern and central stands exhibiting high levels of genetic diversity. Additional mtDNA sequence analysis confirmed that P. martinezii (Patterson) is not conspecific with P. chihuahuana, and thus deserves separate conservation efforts.     

Potential refugium on the Qinghai–Tibet Plateau revealed by the chloroplast DNA phylogeography of the alpine species Metagentiana striata (Gentianaceae)

Metagentiana striata is an alpine annual herbaceous plant endemic to the east of the Qinghai–Tibet (Q–T) Plateau and adjacent areas. The phylogeography of M. striata was studied by sequencing the chloroplast DNA (cpDNA) trn S– trn G intergenic spacer. Ten haplotypes were identified from an investigation of 232 individuals of M. striata from 14 populations covering the entire geographical range of this species. The level of differentiation amongst populations was very high ( G _ST = 0.746; N _ST = 0.774) and a significant phylogeographical structure was observed ( P  < 0.05). An analysis of molecular variance found a high variation amongst populations (76%), with F _ST = 0.762 (highly significant, P  < 0.001), indicating that little gene flow occurred amongst the different regions; this was explained by the isolation of populations by high mountains along the Q–T Plateau and adjacent areas ( N _m = 0.156). Only one ancestral haplotype (A) was common and widespread throughout the distributional range of M. striata. The populations of the Hengduan Mountains region of the south-eastern Q–T Plateau showed high diversity and uniqueness of haplotypes. It is suggested that this region was the potential refugium of M. striata during the Quaternary glaciation, and that interglacial and postglacial range expansion occurred from this refugium. This scenario was in good agreement with the results of nested clade analysis, which inferred that the current spatial distribution of cpDNA haplotypes and populations resulted from range expansion, together with past allopatric fragmentation events.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 125–140.     

Genetic variation at allozyme and RAPD loci in sessile oak Quercus petraea (Matt.) Liebl.: the role of history and geography

The nuclear genetic variation within and among 21 populations of sessile oak was estimated at 31 RAPD loci in conjunction with previous estimates of variation at eight allozyme loci. The aim of the study was to assess the relative role of isolation-by-distance and postglacial history on patterns of nuclear variation. Because of its small effective population size and maternal transmission, the chloroplast genome is a good marker of population history. Both kinds of nuclear variation (RAPD and allozyme) were therefore compared, first, to the geographical distances among populations and, secondly, to chloroplast DNA restriction polymorphism in the same populations. Multiple Mantel tests were used for this purpose. Although RAPDs revealed less genetic diversity than allozymes, levels of genetic differentiation ( G _ST) were identical. The standard genetic distance calculated at all RAPD loci was correlated with geographical distances but not with the genetic distance calculated from chloroplast DNA data. Conversely, allozyme variation was correlated with chloroplast DNA variation, but not with geography. Possibly, divergent selection at two allozyme loci during the glacial period could explain this pattern. Because of its greater number of loci assayed, RAPDs probably provided a less biased picture of the relative role of geography and history.     

Chloroplast DNA variation within prairie cordgrass (Spartina pectinata Link) populations in the U.S.

Chloroplast DNA (cpDNA) is most often maternally inherited and highly conserved leading to previous observation of little to no sequence variation. Comparing cpDNA haplotypes have provided valuable insight into the establishment and migration of polyploid populations. However, to use chloroplast haplotypes to their full potential intrapopulational variation needs to be addressed. In this study, cpDNA haplotype variation was surveyed within 16 natural populations of prairie cordgrass (Spartina pectinata Link) located east of the 100th west meridian and north of the 35th north parallel in the U.S.A. using two non-coding, polymorphic chloroplast regions. Two main clades were defined with subclades as follows: haplotype 1 and haplotype 2A and 2B. It was discovered that seven populations showed intrapopulational chloroplast genome variation. Of the total amount of variation, 95.5% occurred within the octoploid populations and 4.5% occurred within the tetraploid populations. Both variant haplotypes, 2A and 2B, were found in a larger sampling of one of the natural populations, but no variation was found in a mixed ploidy population. The intrapopulational cpDNA variation we found in this study cannot directly be related to mechanisms of introduction of the non-native populations into native populations. Therefore, this cpDNA variation could be novel natural variation that has been fixed as the octoploid populations were established and moved northwest. This analysis provides insight into determining the usefulness of indels and single nucleotide polymorphisms for population identification and may provide information in regards to the origin of chloroplast variation and its subsequent fixation and establishment in natural prairie cordgrass populations.     

The hierarchical spatial distribution of chloroplast DNA polymorphism across the introduced range of Silene vulgaris

Silene vulgaris was introduced into North America sometime prior to 1800. In order to document the population structure that has developed since that time, collections were made from 56 local populations distributed among 9 geographical regions in eastern North America. Individual plants were characterized for chloroplast DNA (cpDNA) haplotype by restriction fragment size analysis of four noncoding regions of cpDNA amplified by polymerase chain reaction. A total of 19 cpDNA haplotypes were detected using this method. The overall gene diversity of 0.85 is quite similar to the diversity detected in these same regions of cpDNA in a previously published sample of S. vulgaris taken from across much of Europe. The spatial distribution of the North American cpDNA diversity was quantified by hierarchical F-statistics that partitioned the genetic variance into variation among local populations within regions, and variation among regions. The average FST among populations within regions was 0.66 and the FST among regions was 0.09. The among-region variation was due to both differences among regions in the frequency of two most common haplotypes, and to the presence of a number of region-specific haplotypes. In order to test for isolation by distance at the regional level, FST values were calculated for all possible pairs of regions, and regressed against the geographical distance between those regions. There was no evidence for isolation by distance. It is suggested that the local population structure is generated by recent extinction/colonization dynamics, and that the among-region structure reflects demographic events associated with range expansion following introduction to North America.     

Genetic Variation and Clonal Diversity of the Two Divergent Types of Clonal Populations of Leymus chinensis Tzvel on the Song Liao Steppe in the West of Northeastern China

The genetic variation and clonal diversity of two divergent types (grey-green and yellow-green) of clonal populations of Leymus chinensis Tzvel at 14 loci were compared. Total gene diversity (HT) and the coefficient of genetic differentiation (GST) were all higher for the yellow-green type (HT = 0.270; GST =0.186) than for the grey-green type (HT = 0.250; GST = 0.157) of L. chinensis. Rare alleles usually occurred as heterozygotes rather than homozygotes and significant deviations from Hardy-Weinberg equilibrium were found only at a few loci. This indicated that these two types of populations were mainly out-crossing. Clonal diversity, evenness of clones, and mean clone size were not significantly different between the two types. We found that differences between the clone size and genetic variation of the yellow-green type of populations occurred with different climate and habitat population groups. However, for the grey-green type of populations, these genetic variations decreased under conditions of different climate and habitat population groups.     

Carbon dioxide-induced changes in beech foliage cause female beech weevil larvae to feed in a compensatory manner

The phenology of Fagus sylvatica was unaffected by exposure to an atmosphere of elevated CO₂ (600 μL L^-1) after two years of fumigation. Non-significant changes in nitrogen and phenolic content of the leaves decreased the nutritional status of beech for female larvae in elevated CO₂ such that they responded by eating in a compensatory manner; males were unaffected. Rates of development, mortality and adult biomass of Rhynchaenus fagi were no different from those in ambient CO₂ concentrations (355 μL L ^-1). It is possible that, with the changes in leaf chemistry affecting the females, fecundity will be altered, with important consequences for populations of beech weevil.     

基于叶绿体基因组SNP的天台鹅耳枥谱系结构与分化分析

天台鹅耳枥为中国特有的濒危植物,仅间断分布于浙江省境内,种群数量稀少,已处于极危状态。该文通过对6个自然居群(包含所有居群的母株)叶绿体基因组(cpDNA)单核苷酸多态性(SNP)研究,探讨天台鹅耳枥谱系结构与系统分化,以评估濒危状况,并提出相应的保护策略。使用TIANGEN试剂盒法提取基因组DNA,用Illumina NovaSeq 6000进行高通量测序,对获得叶绿体全基因组序列,使用在线程序OGDRAW制作cpDNA图谱,用DnaSP分析核苷酸多样性,用PopART软件进行单倍型网络构建,使用RAxML软件构建极大似然树(ML tree),用MrBayes构建Bayes tree。结果表明：(1)通过天台鹅耳枥叶绿体全基因组序列分析,发现大多数蛋白质编码基因和氨基酸序列显示出明显的密码子偏好,检测到cpLTR正向重复32个、回文重复25个、反转重复22个;SSR重复序列不同类型87个,其中大多数富含A/T,单核苷酸的数量最多。(2)在cpDNA中鉴定了314条SNPs,单核苷酸取代显示天台鹅耳枥群体属单系,分为天台县居群(THS)和景宁县居群(JST),居群单倍型之间演化关系呈现...     

Allozyme Diversity in Populations of Cymbidium goeringii (Orchidaceae)

Abstract: Using 14 allozyme loci, we investigated levels of genetic diversity within populations, and degree of genetic divergence among 24 populations of Cymbidium goeringii (Orchidaceae) in Korea and Japan. Cymbidium goeringii maintains high levels of genetic diversity both at population (mean expected heterozygosity, H _e = 0.238) and species levels (0.260). Means of H _e found in 24 populations were not significantly different from each other. About 90 % of the total variation in the species is common to all populations (mean G _ST = 0.108). No unique allele was found in any population. The indirect estimate of gene flow based on the mean G _ST was high ( Nm = 2.06). Nei's genetic identities for pairs of populations had high values (mean = 0.974 [SD = 0.013]). The Mantel-Z test showed a significant correlation between genetic distance and geographic distance. However, the mean G _ST value between 17 populations in Korea and seven Japanese populations was relatively low (0.029), even though the land connection between the southern Korean peninsula and southern Japanese archipelagos has not existed since the middle Pleistocene. Large numbers of small seeds of C. goeringii might travel long distances by wind from populations to populations both in Korea and Japan, increasing genetic diversity within populations and maintaining low genetic differentiation among populations.     

Cryptic speciation in liverworts – a case study in the Aneura pinguis complex

Bryophytes are amongst the most ancestral terrestrial plants and often have large distribution ranges across continents. Recent biochemical and molecular studies have suggested that many worldwide morphological species of bryophyte may represent genetically divergent and reproductively isolated cryptic species. We tested the cryptic species hypothesis in the thalloid liverwort Aneura pinguis complex. We applied analyses of chloroplast DNA (cpDNA) sequence variation and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methods to discriminate between specimens of A. pinguis derived from various habitats in five distant geographical regions in Poland. Of the 19 specimens sequence characterized for the cpDNA tRNA^Leu region, seven haplotypes were identified divided into three nonmonophyletic clusters. The application of developed PCR-RFLP markers confirmed the existence of three tRNA^Leu types of A. pinguis (A–C) within the specimens derived from 21 populations. Sympatric populations of different tRNA^Leu types were found in lowland and mountain regions. No clear correlation between stand type and the presence of two tRNA^Leu types (A, B) was observed, as both were growing on soil, humus, and rocks. The tRNA^Leu type C was found only on humus and its distribution was restricted to low-lying northern populations. The above results indicate that the A. pinguis complex is highly differentiated at the molecular level and may represent three cryptic species.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 273–282.     

Hotspots of diversity in a clonal world--the Mediterranean moss Pleurochaete squarrosa in Central Europe

Diversity patterns of the dioecious haploid Mediterranean moss Pleurochaete squarrosa were analysed from Central and Northwest Europe using nuclear and chloroplast DNA sequencing and enzyme electrophoresis. Across 69 populations, 38 distinct haploid multilocus genotypes (MLGs) were detected, but nearly all populations were clonal. Only five MLGs occurred in more than two regions, and two diversity hotspots were detected. The Kaiserstuhl mountains in Southwest Germany harboured 34 MLGs, 25 being endemic within Central Europe. Levels of linkage disequilibrium and population structure in Kaiserstuhl populations were similar to levels and structure in sexually reproducing populations in the Mediterranean Basin. In the Moselle-Nahe area, some 250 km north, a comparably high allelic diversity, but no evidence of recombination, was detected. Genetic diversity measures were significantly lower than estimates obtained in the Mediterranean Basin and a G _ST of 0.89 signified extreme population differentiation. Mantel tests identified a positive correlation on genetic and geographical distance for distances up to 50 km. Seven nrITS and three cpDNA haplotypes were detected, their geographical structure mirroring enzyme data set results. Comparative analysis with Mediterranean data demonstrated multiple recolonization of Central Europe from both the Iberian Peninsula and the Balkans. A suture zone of genotypes was detected along the border of Belgium/France and Germany. Despite P. squarrosa having haploid spore and/or vegetative propagules dispersal, we found patterns of postglacial recolonization of Central Europe comparable with those reported in flowering plants and animals. This study demonstrates the importance of comparative research on population genetics and phylogeography of a diverse range of organisms.     

Genetic effects of chronic habitat fragmentation on tree species: the case of Sorbus aucuparia in a deforested Scottish landscape

Sustainable forest restoration and management practices require a thorough understanding of the influence that habitat fragmentation has on the processes shaping genetic variation and its distribution in tree populations. We quantified genetic variation at isozyme markers and chloroplast DNA (cpDNA), analysed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in severely fragmented populations of Sorbus aucuparia (Rosaceae) in a single catchment (Moffat) in southern Scotland. Remnants maintain surprisingly high levels of gene diversity (HE) for isozymes (HE = 0.195) and cpDNA markers (HE = 0.490). Estimates are very similar to those from non-fragmented populations in continental Europe, even though the latter were sampled over a much larger spatial scale. Overall, no genetic bottleneck or departures from random mating were detected in the Moffat fragments. However, genetic differentiation among remnants was detected for both types of marker (isozymes Theta n = 0.043, cpDNA Theta c = 0.131; G-test, P-value < 0.001). In this self-incompatible, insect-pollinated, bird-dispersed tree species, the estimated ratio of pollen flow to seed flow between fragments is close to 1 (r = 1.36). Reduced pollen-mediated gene flow is a likely consequence of habitat fragmentation, but effective seed dispersal by birds is probably helping to maintain high levels of genetic diversity within remnants and reduce genetic differentiation between them.