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1.
Background and Aims Quercus petraea colonized Irelandafter the last glaciation from refugia on mainland Europe. Deforestation,however, beginning in Neolithic times, has resulted in small,scattered forest fragments, now covering less than 12 000 ha. • Methods Plastid (three fragments) and microsatellitevariation (13 loci) were characterized in seven Irish populationssampled along a north–south gradient. Using Bayesian approachesand Wright’s F-statistics, the effects of colonizationand fragmentation on the genetic structure and mating patternsof extant oak populations were investigated. • Key Results All populations possessed cytotypes commonto the Iberian Peninsula. Despite the distance from the refugialcore and the extensive deforestation in Ireland, nuclear geneticvariation was high and comparable to mainland Europe. Low populationdifferentiation was observed within Ireland and populationsshowed no evidence for isolation by distance. As expected ofa marker with an effective population size of one-quarter relativeto the nuclear genome, plastid variation indicated higher differentiation.Individual inbreeding coefficients indicated high levels ofoutcrossing. • Conclusions Consistent with a large effective populationsize in the historical migrant gene pool and/or with high geneflow among populations, high within-population diversity andlow population differentiation was observed within Ireland.It is proposed that native Q. petraea populations in Irelandshare a common phylogeographic history and that the presentgenetic structure does not reflect founder effects.  相似文献   

2.
The western fanshell, Cyprogenia aberti, occurs in the CentralHighlands region of North America and is the only congener ofthe federally endangered fanshell, C. stegaria. Due to a reductionin range size and local extirpations, extant populations ofC. aberti have become increasingly isolated. Consequently, C.aberti has been the focus of numerous conservation efforts,yet no work has examined the degree of genetic variation amongthe species' disjunct populations. Phylogenetic analyses ofnucleotide sequences from two mitochondrial gene portions (CO1and ND1) revealed results important to the conservation managementof C. aberti. First, phylogenetic analyses do not support amonophyletic C. aberti. Second, C. aberti is comprised of asmany as five independent lineages, one of which includes thefederally endangered C. stegaria. Third, analysis recoveredtwo genetically distinct sympatric lineages of C. aberti inthe Ouachita River Drainage. These phylogenetic results suggestthat the five distinct evolutionary lineages of C. aberti shouldbe managed as separate conservation units. This study illustrateswhy it is critical to evaluate genetic variability in endangeredand threatened ‘species’ prior to implementing arecovery program. These data also reveal the value of assessingbiological diversity of nonimperiled taxa before populationsare extirpated and valuable genetic data necessary for reconstructionof evolutionary relationships is lost. (Received 24 October 2005; accepted 8 June 2006)  相似文献   

3.
Background and Aims: Bromeliads (Bromeliaceae) adapted to rock outcrops or ‘inselbergs’in neotropical rain forests have been identified as suitableplant models for studying population divergence and speciationduring continental plant radiations. Little is known about geneticrelationships and variation in reproductive strategies withinand among inselberg-adapted species, yet knowledge of theseparameters is important for understanding divergence processesand for conservation planning. Methods: Nuclear microsatellites were used to assess the role of clonalreproduction, estimate genetic diversity and explore geneticrelationships and variation in reproductive strategies for atotal of 15 populations of four closely related Alcantarea inselbergspecies in south-eastern Brazil: A. glaziouana, A. regina, A.geniculata and A. imperialis. Key Results: Clonal propagation is frequent in coastal populations of A.glaziouana and A. regina, but absent in the high-altitude speciesA. geniculata and A. imperialis. Considerable variation in clonaldiversity, gene diversity (He), allelic richness, and Wright'sinbreeding coefficient (FIS) exists within and between speciesof Alcantarea. A Bayesian analysis of coastal inselberg speciesindicated pronounced genetic structure. A neighbor-joining analysisgrouped populations of each species together with moderate bootstrapsupport, except for the high altitude species A. imperialis. Conclusions: The coastal inselberg species A. glaziouana and A. regina tendto propagate asexually via vegetative clonal growth, and bothreproductive strategies and breeding systems vary greatly betweenpopulations and species of Alcantarea. The microsatellite dataindicate a history of hybridization and reticulation involvingthe high-altitude species A. geniculata and A. imperialis inareas of co-occurrence. The results highlight the need to understandsimilarities and differences in reproductive strategies bothwithin and between related species for conservation planningand as a basis for understanding evolutionary processes in tropicalradiations.  相似文献   

4.
Variations in the chloroplast and mitochondrial DNA of Cycas revoluta Thunb. (Cycadaceae) were examined in 22 populations distributed across the Ryukyu Islands and southern Kyushu. Among the 14,130 bp of sequence examined, only one site mutation and one indel were polymorphic. The identified polymorphisms were located in the spacers between trnS (UGA) and trnfM (CAU) of the chloroplast DNA and between nad1 exon B and exon C of the mitochondrial DNA, respectively. Three haplotypes were identified from the Ryukyu Islands and southern Kyushu. The areas of distribution of the three haplotypes were highly geographically structured. The boundaries of two of the three haplotypes were demarcated by Okinoerabujima Island in the middle Ryukyus. The northern type and southern types lay north and south of the island, respectively. The third haplotype was almost sympatrically distributed with the southern type. The genetic variation within C. revoluta was estimated to be very low (h = 0.641, π = 0.00071) in comparison to its relative in Taiwan, C. taitungensis, which possesses 97 cpDNA haplotypes and 55 mtDNA haplotypes from two relic populations. A reasonable explanation for the low genetic diversity of the cycad on the Ryukyu Islands could be severe bottleneck effects, resulting from the submersion of low islands and the diminished landmass of islands in the interglacial age in the Quaternary period. The geographically restricted nature of the haplotypes could be attributed to vicariance resulting from the land configuration of the Ryukyu Islands, including changes in geography during the interglacial age in the Quaternary.  相似文献   

5.
Ge XJ  Yu Y  Yuan YM  Huang HW  Yan C 《Annals of botany》2005,95(5):843-851
Background and Aims The desert legume genus Ammopiptanthuscomprises two currently endangered species, A. mongolicus andA. nanus. Genetic variability and genetic differentiation betweenthe two species and within each species were examined. • Methods Inter-simple sequence repeat (ISSR) marker datawere obtained and analysed with respect to genetic diversity,structure and gene flow. • Key Results Despite the morphological similarity betweenA. mongolicus and A. nanus, the two species are geneticallydistinct from each other, indicated by 63 % species-specificbands. Low genetic variability was detected for both populationlevel (Shannon indices of diversity Hpop = 0·106, percentageof polymorphic loci P = 18·55 % for A. mongolicus; Hpop= 0·070, P = 12·24 % for A. nanus) and specieslevel (Hsp = 0·1832, P = 39·39 % for A. mongolicus;Hsp = 0·1026, P = 25·89 % for A. nanus). Moderategenetic differentiation was found based on different measures(AMOVA ST and Hickory B) in both A. mongolicus (0·3743–0·3744)and A. nanus (0·2162–0·2369). • Conclusions The significant genetic difference betweenthe two species might be due to a possible vicariant evolutionaryevent from a single common ancestor through the fragmentationof their common ancestor's range. Conservation strategies forthese two endangered species are proposed.  相似文献   

6.
Curcuma zedoaria (Christm.) Roscoe, a member of the family Zingiberaceae, is one of the most widely distributed Curcuma species in Bangladesh. It is a well-known and important species because of its medicinal and horticultural values. However, some plant populations are predicted to be depleted due to habitat destruction and due to extensive collection by local inhabitants. In order to estimate the level of genetic diversity within and between natural populations, RAPD analyses were performed using individual plants from different populations. We used Shannon’s index to partition genetic diversity which clearly demonstrated that hilly populations of Srimangal, Chittagong and Sitakundu maintain rather higher genetic diversity than that of plain land and plateau land populations of Savar and Birganj, respectively. We found a high intrapopulational (Hpop/Hsp) genetic diversity of 0.717 that was higher than the interpopulation diversity G ST[(HspHpop)/Hsp] value of 0.283. Principal Coordinates Analysis (PCoA) showed that individuals of the hilly populations were combined in one group, separated from the plain land and plateau land populations. From a conservation point of view, our results suggest that special attention should be kept on the small populations of plain and plateau lands that are critically threatened due to high anthropogenic activities.  相似文献   

7.
The endangered Cook’s petrel (Pterodroma cookii) is restricted to two separated populations at the extremes of its former range across New Zealand. Prior work revealed morphological, foraging, and reproductive isolation between these two remnant populations. To aid the conservation management of the species, additional information is required on the genetic structure of Cook’s petrel. We used mitochondrial DNA sequences (Cytochrome Oxidase subunit 1 gene), collected from 26 and 19 Cook’s petrel breeding on Little Barrier Island (LBI) and Codfish Island (CDF), respectively, for this preliminary study. We uncovered distinct population genetic structure with analysis of molecular variance suggesting genetic isolation of the populations. Levels of genetic variation were higher in the LBI population (four haplotypes present; h = 0.34 and π = 0.10) whereas the CDF population had only one haplotype that was distinct from the LBI population. Our results indicate that Cook’s petrel constitute two distinct management units for which conservation of genetic as well as behavioural and morphological diversity should be a priority. Further genetic studies using nuclear markers are recommended.  相似文献   

8.
Inter-simple sequence repeats (ISSR) markers were used to assess the genetic diversity and population structure in eight populations of Elymus sibiricus L. from the southeast of Qinghai-Tibet Plateau of China. Of the 100 primers screened, 13 produced highly reproducible ISSR bands. Using these primers, 193 discernible DNA fragments were generated with 149 (77.2%) being polymorphic, indicating considerable genetic variation at the species level. In contrast, there were relatively low levels of polymorphism at the population level with the percentage of polymorphic bands (PPB) ranging from 44.04 to 54.92%. The mean gene diversity (HE) was estimated to be 0.181 within populations (range 0.164–0.200), and 0.274 at the species level. A high level of genetic differentiation among populations was detected based on Nei's genetic diversity analysis (33.1%), Shannon's index analysis (34.5%), Bayesian method (33.2%) and AMOVA analysis (42.5%). No significant statistical differences (analysis of molecular variance [AMOVA], P = 0.08) in ISSR variation were found between the sample collection regions. However, among populations (42.5% of the variance) and within populations (57.5% of the variance), there were significant differences (P < 0.001). Populations shared high levels of genetic identity. This pattern of genetic variation was different from that for most of inbreeding Triticeae species reported. In addition, a geographical pattern of population differentiation, where the populations from south and north of sampling sites were clearly separated from each other, was revealed by both the cluster and principal coordinates analyses. Generally, the result of this study indicates that E. sibiricus contains high molecular variation in its populations. The implications of these results for the conservation of the species are discussed.  相似文献   

9.
Background and Aims For rare endemics or endangered plantspecies that reproduce both sexually and vegetatively it iscritical to understand the extent of clonality because assessmentof clonal extent and distribution has important ecological andevolutionary consequences with conservation implications. Asurvey was undertaken to understand clonal effects on fine-scalegenetic structure (FSGS) in two populations (one from a disturbedand the other from an undisturbed locality) of Echinosophorakoreensis, an endangered small shrub belonging to a monotypicgenus in central Korea that reproduces both sexually and vegetativelyvia rhizomes. • Methods Using inter-simple sequence repeats (ISSRs) asgenetic markers, the spatial distribution of individuals wasevaluated using Ripley's L(d)-statistics and quantified thespatial scale of clonal spread and spatial distribution of ISSRgenotypes using spatial autocorrelation analysis techniques(join-count statistics and kinship coefficient, Fij) for totalsamples and samples excluding clones. • Key Results A high degree of differentiation betweenpopulations was observed (ST(g) = 0·184, P < 0·001).Ripley's L(d)-statistics revealed a near random distributionof individuals in a disturbed population, whereas significantaggregation of individuals was found in an undisturbed site.The join-count statistics revealed that most clones significantlyaggregate at 6-m interplant distance. The Sp statistic reflectingpatterns of correlograms revealed a strong pattern of FSGS forall four data sets (Sp = 0·072–0·154), butthese patterns were not significantly different from each other.At small interplant distances (2 m), however, jackknifed 95% CIs revealed that the total samples exhibited significantlyhigher Fij values than the same samples excluding clones. • Conclusion The strong FSGS from genets is consistentwith two biological and ecological traits of E. koreensis: bee-pollinationand limited seed dispersal. Furthermore, potential clone matesover repeated generations would contribute to the observed highFij values among genets at short distance. To ensure long-termex situ genetic variability of the endangered E. koreensis,individuals located at distances of 10–12 m should becollected across entire populations of E. koreensis.  相似文献   

10.
Aim Our goals were: (1) to assess the population genetic structure and demographic divergence history of a bird‐dispersed tree, Neolitsea sericea, endemic to East Asian land‐bridge islands; and (2) to interpret the results in the light of controversies over the dating and configurations of land bridges through the Japanese Ryukyu Island Arc. Location Japan–Ryukyu–Taiwan Island Arc and Chinese/Korean offshore islands. Methods We applied 10 nuclear microsatellites (nSSRs) and one chloroplast (cp) DNA sequence marker (psbA–trnH intergenic spacer) to 31 populations (397 and 326 individuals, respectively) from throughout the species’ range to infer current patterns of genetic diversity and structure, and pollen‐to‐seed migration ratios (r). A coalescent‐based isolation‐with‐migration (IM) model was applied to the combined nSSR/cpDNA data set to estimate lineage divergence times and population demographic parameters. Results The geographic structure of nSSRs and the distribution of most cpDNA haplotypes revealed two distinct lineages located in areas north and south of the ‘Tokara Gap’, a narrow (c. 37 km wide) but deep (> 1000 m) sea‐strait between the northern and central Ryukyus. Based on the IM analyses, we (1) dated the divergence of these northern and southern lineages to c. 0.07 Ma (90% highest posterior density interval: 0.02–0.38 Ma); (2) estimated a slightly smaller effective population size for the northern compared to the southern lineage; and (3) recovered only trivial signals of post‐divergence gene flow between them. Main conclusions The estimated divergence time for northern and southern lineages is consistent with geological evidence for the existence of land connections in the Tokara region during cold stages of the latest Pleistocene; it is thus incompatible with an ‘ancient sea‐barrier hypothesis’ for the Ryukyu Arc, where we would have expected much older divergences related to the initial formation of the Tokara and Kerama tectonic straits during the Pliocene. Multiple factors are likely to have had a role in the divergence of N. sericea, including not only land‐bridge submergence, but also island configuration, and/or constraints on adaptation along a latitudinal temperature gradient.  相似文献   

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