Variation in chloroplast single-sequence repeats in Portuguese maritime pine (Pinus pinaster Ait.)

Genetic variation in 12 Pinus pinaster (maritime pine) populations spanning most of the distribution range of the species in Portugal was evaluated using six polymorphic chloroplast microsatellite (cpSSR) loci. Thirty-two haplotypes were found. There were indications of very weak differentiation among populations (Weir’s θcoefficient, 0.023), and the R _ST value, derived from the stepwise mutation model (SMM), was not significantly different from zero. The pattern, in which similarities in allele size, in base pairs, do not contribute to the genetic structure, may be due to the recent mixing of genetic material from different stands through plantations. Overall, a high level of haplotypic variation within populations was detected. Using the SMM estimator (mean genetic distance of individuals within populations, D ² _sh –––) we divided the populations into two groups, with above and below average values. The first group contained 5 populations, mainly from the central part of the country, which possess, in general, high levels of haplotypic diversity. Among them, 2 populations were divergent from the others based on the pair-wise Nei’s distance. The results indicate that there is no discernible geographic genetic pattern for the Portuguese populations of P. pinaster investigated. The history of expansion of the species range in Portugal during the twentieth century (mainly due to human activity) and extensive gene flow among populations associated with the expansion could explain this finding. Received: 15 February 2000 / Accepted: 14 April 2000     

Haplotype richness in refugial areas: phylogeographical structure of <Emphasis Type="Italic">Saxifraga callosa</Emphasis>

This paper illustrates the phylogeographical structure of Saxifraga callosa in order to describe its genetic richness in refugial areas and to reconstruct its glacial history. S. callosa is a species spread throughout south-east France and Italy with a high distribution in the Maritime Alps. Four chloroplast microsatellite and AFLP markers were analyzed in populations of S. callosa. The size variants of all tested loci amount to 11 different haplotypes. Intrapopulational haplotype variation was found in two of the populations analyzed: on the Mt. Toraggio in the Maritime Alps, and in the Apuan Alps. On the other hand, no intrapopulational variation was found in 25 populations, most of which were sampled from isolated areas. Analysis of the haplotype distribution showed that population subdivision across all populations was high (G _ST = 0.899). Moreover, its genetic structure was studied using AMOVA and STRUCTURE analysis. The study legitimated inferred conclusions about the phylogeographical structure of the species and identified centers of diversity. Considerations concerning genetic structure and divergence among three major clades (Maritime Alps, Apuan Alps and Apennines), the patchy distribution of haplotypes, and the high number of private haplotypes support the proposal that S. callosa survived in some refugia within the Italian Peninsula refugium, and that mainly northern populations of refugia were involved in postglacial recolonization.     

Variation in the chloroplast DNA of Swiss stone pine (Pinus cembra L.) reflects contrasting post-glacial history of populations from the Carpathians and the Alps

Aim To characterize the genetic structure and diversity of Pinus cembra L. populations native to two disjunct geographical areas, the Alps and the Carpathians, and to evaluate the rate of genetic differentiation among populations. Location The Swiss Alps and the Carpathians. Methods We screened 28 populations at three paternally inherited chloroplast simple sequence repeats (cpSSRs) for length variation in their mononucleotide repeats. Statistical analysis assessed haplotypic variation and fixation indices. Hierarchical analysis of molecular variance (AMOVA), Mantel test, spatial analysis of molecular variance (SAMOVA) and barrier analyses were applied to evaluate the geographical partitioning of genetic diversity across the species’ range. Results Haplotypic diversity was generally high throughout the natural range of P. cembra, with the mean value substantially higher in the Carpathians (H = 0.53) than in the Alps (H = 0.35). The isolated Carpathian populations showed the highest haplotype diversity among the populations originating from the High Tatras (Velka Studena Dolina) and South Carpathians (Retezat Mountains). AMOVA revealed that only 3% of the total genetic variation derived from genetic differentiation between the two mountain ranges. Differentiation among Carpathian populations was higher (F_ST = 0.19) than among Alpine populations (F_ST = 0.04). Low, but significant, correlation was found between the geographical and genetic distances among pairs of populations (r = 0.286, P < 0.001). SAMOVA results revealed no evident geographical structure of populations. barrier analysis showed the strongest differentiation in the eastern part of the species’ range, i.e. in the Carpathians. Main conclusions The populations of P. cembra within the two parts of the species’ range still share many cpDNA haplotypes, suggesting a common gene pool conserved from a previously large, continuous distribution range. Carpathian populations have maintained high haplotypic variation, even higher than Alpine populations, despite their small population sizes and spatial isolation. Based on our results, we emphasize the importance of the Carpathian populations of Swiss stone pine for conservation. These populations comprise private haplotypes and they may represent a particular legacy of the species’ evolutionary history.     

Genetic variation and population differentiation of Michelia formosana (Magnoliaceae) based on cpDNA variation and RAPD fingerprints: relevance to post-Pleistocene recolonization

 We used sequence variation of the atpB-rbcL intergenic spacer of cpDNA and nested clade analysis to assess the phylogeographic pattern of Michelia formosana, a species restricted to Taiwan and the Ryukyus. In total, 31 haplotypes were identified and clustered into four major chlorotypes. Genetic composition of nearly all populations was heterogeneous and paraphyletic phylogenetically. Although the apportionment of cpDNA variation hardly revealed a geographic pattern due to the coancestry of dominant sequences, some chlorotypes were restrictedly distributed. According to the patterns of clade dispersion and displacement, a reconstructed minimum spanning network revealed that historical events of past fragmentation and range expansion, associated with glaciation, may have shaped the phylogeographic patterns of M. formosana. Four possible refugia were identified: the Iriomote and Ishigaki Islands (the southern Ryukyus), Wulai (northern Taiwan), and Nanjen (southern Taiwan), on the basis of the interior positions of their haplotypes in the network and the high level of nucleotide diversity. Given insufficient time for coalescence at the cpDNA locus since the late Pleistocene recolonization, lineage sorting led to low levels of genetic differentiation among populations. In contrast, hierarchical examination of the random amplified polymorphic DNA (RAPD) data scored from six populations across three geographical regions, using an analysis of molecular variance (AMOVA), indicated high genetic differentiation both among populations (Φ_ST = 0.471) and among regions (Φ_CT = 0.368). An unweighted pair group method with arithmetic mean (UPGMA) tree of the RAPD fingerprints revealed that populations of two offshore islands of eastern Taiwan (M. formosana var. kotoensis) were clustered with geographically remote populations of the Ryukyus instead of those in southern Taiwan, suggesting some historical division due to geographic barriers of the central mountain range. In contrast to the paraphyly of the nearly neutral cpDNA alleles, differentiated RAPDs may have experienced diversifying selection. Received: July 2, 2001 / Accepted: February 20, 2002     

Protecting evolutionary significant units for the remnant populations of <Emphasis Type="Italic">Berchemiella wilsonii</Emphasis> var. <Emphasis Type="Italic">pubipetiolata</Emphasis> (Rhamnaceae)

Berchemiella wilsonii var. pubipetiolata (Rhamnaceae) is an endangered tree in eastern China. Habitat destruction has resulted in fragmentation of remnant populations and extinction of local populations. AFLP and cpDNA markers were used to determine the population structure of remnant populations of B. wilsonii var. pubipetiolata. Moderate nuclear genomic diversity was found within each of the four remnant populations (H _S = 0.141–0.172), while the cpDNA haplotype diversity in each population ranged from 0.356 to 0.681. Six haplotypes were identified by a combined cpRFLP and cpSSR analysis in a total of 89 individuals. AMOVA revealed significantly AFLP genetic differentiation within and between regions (Φ_SC = 0.196, Φ_CT = 0.396, respectively), and a high cpDNA haplotype differentiation between regions (Φ_CT = 0.849). The results suggest low gene flow between populations of B. wilsonii var. pubipetiolata. Strong genetic divergence between two regional populations as revealed by both AFLP and cpDNA markers provided convincing evidence that two distinct evolutionary lineages existed, and should be recognized as ‘evolutionary significant units’ (ESUs) for conservation concerns.     

Distribution and population genetic structure of the Mediterranean pine shoot beetle Tomicus destruens in the Iberian Peninsula and Southern France

1 The Mediterranean pine shoot beetle Tomicus destruens has long been indistinguishable from its congeneric Tomicus piniperda. Both species attack pines, and can be found in sympatry. The geographical distribution of T. destruens is still unclear in most of the Mediterranean Basin. 2 We aimed to describe the geographical distribution and zones of sympatry of both species in the Iberian Peninsula and France, and to study the molecular phylogeographical pattern of T. destruens. 3 Tomicus spp. adults were sampled in Portugal, Spain and France, and a portion of the mitochondrial genes COI and COII was sequenced for 84 individuals. Sequences were aligned to a data set previously obtained from French localities. 4 Tomicus destruens was found in all populations, except for one locality in Portugal and in the Landes (France). It was in sympatry with T. piniperda in two locations on Pinus pinaster and one location on Pinus radiata. 5 Within‐population genetic diversity was high, but we found a significant pattern of spatial distribution of genetic variation, as well as a significant effect of the host tree. 6 The data suggest the existence of two glacial refugia, from which T. destruens recolonized its current range. One refugium was located in Portugal where the beetle probably evolved on P. pinaster. The corresponding haplotypes show a West–East frequency gradient. The other refugium was probably in the eastern range, where the beetles evolved on Pinus halepensis and P. pinea. The corresponding haplotypes show an East–West frequency gradient.     

Distribution and genetic structure of the Japanese wood pigeon (Columba janthina) endemic to the islands of East Asia

The Japanese wood pigeon (Columba janthina) is endemic to the islands of East Asia and it is included in the Japanese and Asian Red Lists because of its narrow habitat range that is restricted to mature forests on small islands and because of the destruction of these habitats. We examined the genetic structure of Columba janthina by studying 463 base pairs of the mitochondrial control region sequences. We analyzed 154 samples from eight populations and identified 27 haplotypes. Three population groups were identified based on the pairwise Φ_ST values. A substantial gene flow, as reflected by the low and non-significant Φ_ST values, is maintained among the northern group that includes six populations found on the Okinawa, Tokara, Goto, Setouchi, Oki, and Izu islands. In contrast, the southeastern group found on the Ogasawara Islands had large Φ_ST values with every population from other regions (0.910 < Φ_ST < 0.962). The southwestern group found on the Sakishima Islands also had significant but small Φ_ST values with every population from the northern group (0.081 < Φ_ST < 0.205). The Mantel test showed a highly significant correlation between the Φ_ST values and the route length of the habitat network, as well as the linear distance with correction of the habitat gap effect, indicating the importance of the closely connected structure of the habitats. The three groups mentioned above could be considered as independent management units, and the southeastern group has the highest conservation priority due to its narrow distribution range and small population size. Electronic Supplementary Material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Genetic analysis of two Portuguese populations of <Emphasis Type="Italic">Ruditapes decussatus</Emphasis> by RAPD profiling

The clam Ruditapes decussatus is commercially important in the south of Portugal. The random amplified polymorphic DNA (RAPD) technique was applied to assess the genetic diversity and population structure of two Portuguese populations occurring in the Ria Formosa (Faro) and the Ria de Alvor, respectively. Twenty-five individuals of each population were investigated by RAPD profiles. Genetic diversity within populations, measured by the percentage of polymorphic loci (%P), varied between 68.57% (Alvor) and 73.88% (Faro). Shannon’s information index (H) and Nei’s gene diversity (h) were 0.281 and 0.176, respectively, for the Alvor population and 0.356 and 0.234 for the Faro population. Overall, genetic variation within R. decussatus populations was high. The total genetic diversity (H _T) was explained by a low variation between populations (G _ST = 0.145), which is consistent with high gene flow (N _m = 2.9). The analysis of molecular variance (AMOVA) showed that 65% of variability is within populations and 35% between populations (Φ_PT = 0.345; P ≥ 0.001). The value of Nei’s genetic distance was 0.0881, showing a low degree of population genetic distance, despite the different geographic origin. This is the first study on the population genetics of R. decussatus by RAPD technique. The results may be useful for restocking programs and aquaculture.     

The influence of spatial scale on the genetic structure of a widespread tropical wetland tree, Pterocarpus officinalis (Fabaceae)

Identifying factors that cause genetic differentiation in plant populations and the spatial scale at which genetic structuring can be detected will help to understand plant population dynamics and identify conservation units. In this study, we determined the genetic structure and diversity of Pterocarpus officinalis, a widespread tropical wetland tree, at three spatial scales: (1) drainage basin “watershed” (<10 km), (2) within Puerto Rico (<100 km), and (3) Caribbean-wide (>1000 km) using AFLP. At all three spatial scales, most of the genetic variation occurred within populations, but as the spatial scale increased from the watershed to the Caribbean region, there was an increase in the among population variation (Φ_ST=0.19 to Φ_ST=0.53). At the watershed scale, there was no significant differentiation (P=0.77) among populations in the different watersheds, although there was some evidence that montane and coastal populations differed (P<0.01). At the island scale, there was significant differentiation (P<0.001) among four populations in Puerto Rico. At the regional scale (>1000 km), we found significant differentiation (P<0.001) between island and continental populations in the Caribbean region, which we attributed to factors associated with the colonization history of P. officinalis in the Neotropics. Given that genetic structure can occur from local to regional spatial scales, it is critical that conservation recommendations be based on genetic information collected at the appropriate spatial scale.     

Genetic structure of montane isolates of Pinus sylvestris L. in a Mediterranean refugial area

Aim This work investigates the population genetic effects of periodic altitudinal migrations and interstadial fragmentation episodes in long‐term Scots pine (Pinus sylvestris L.) populations at a regional scale. Location The study focuses on Scots pine populations in the northern Meseta and peripheral mountain chains, central and north‐western Iberian Peninsula. The ample macrofossil record in the area shows that this 60,000‐km² region represent a glacial refugium for Scots pine. The species occupied large areas on the Meseta plains during glacial cold stages, but it has periodically sheltered at high elevation in the surrounding mountain chains during warm episodes, conforming to a fragmented pattern similar to its present‐day distribution. Methods We perform a fine‐scale chloroplast microsatellite (cpSSR) survey to assess the genetic structure of 13 montane Scots pine isolates in the northern Meseta (total N = 322 individuals). Using a hierarchical analysis of molecular variance (amova ), we test the hypothesis of genetic isolation among disjunct mountain areas. We use a standard coalescence model to estimate genealogical relationship among populations, investigating the potential role of the regional relief as a factor influencing historic gene exchange among Scots pine populations. Results Population haplotypic diversity was high among Scots pine populations (H_e = 0.978), greater than values reported for other more thermophilic pine species in the Iberian Peninsula. The amova revealed low (but significant) differentiation among populations (Φ_ST = 0.031, P = 0.010), showed that the disjoint montane distribution could not account for the genetic divergence among areas (Φ_CT = 0.012, P = 0.253), and that there was non‐trivial subdivision among populations within the same mountain region (Φ_SC = 0.021, P = 0.012). The genealogical relationships among populations showed that Scots pine isolates growing on disjoint mountain blocks, but on slopes flowing to the same basin, were genetically closer than populations growing on different slopes of the same mountain chain, flowing to different basins. Main conclusions The observed genetic structure for Scots pine is consistent with its population history, inferred from the palaeobotanical record, with vertical migrations throughout climatic pulses and with the drainage basins and large long‐term population sizes connecting different mountain blocks during the cooler glacial periods. Overall, the results suggest that, despite periodic interstadial fragmentation episodes, Scots pine biology provides for the long‐term maintenance of high within‐population and low among‐population genetic diversity at neutral genetic markers.     

Genetic structure of Heliofungia actiniformis (Scleractinia: Fungiidae) populations in the Indo-Malay Archipelago: implications for live coral trade management efforts

The fungiid Heliofungia actiniformis is one of the most popular scleractinian coral species in the growing live aquarium trade, with the majority of specimens originating in Indonesia. Details on population connectivity may potentially provide important information with regards to harvest management efforts. Genetic structure was examined, using ribosomal ITS1, 5.8S and partial ITS2 sequences on a small scale among populations in the Spermonde Archipelago, South Sulawesi (up to 65 km distance, Φ_st = 0.09), and on a large scale throughout the Indo-Malay Archipelago (up to 2,900 km distance, Φ_st = 0.26). Significant genetic structuring was found at both scales. Within the Spermonde Archipelago isolation by distance as well as local oceanographic features shaped patterns of genetic connectivity. On the large scale, the data revealed genetically distinct populations in Tomini Bay, New Guinea and the Thousand Islands near Jakarta, and a lack of genetic differentiation among populations lying close to or directly in the path of the Indonesian throughflow: from the central Visayas to the Flores Sea (Φ_ct = 0.32). Whilst the influence of both historical and present day processes on genetic structuring of H. actiniformis populations was revealed, large scale results further emphasised the importance of oceanographic dynamics on larval dispersal patterns in this species. Potential for larval input from surrounding populations, and the increased vulnerability of upstream as well as isolated populations should be taken into consideration when setting future harvest quotas.     

Genetic Diversity and Geographical Differentiation of <Emphasis Type="Italic">Desmodium triflorum</Emphasis> (L.) DC. in South China Revealed by AFLP Markers

High levels of genetic variation enable species to adapt to changing environments and provide plant breeders with the raw materials necessary for artificial selection. In the present study, six AFLP primer pairs were used to assess the genetic diversity of Desmodium triflorum (L.) DC. from 12 populations in South China. A high percentage of polymorphic loci (P = 76.16%) and high total gene diversity (H _T = 0.310) were found, indicating that the genetic diversity of D. triflorum is high at the species level. Genetic diversity was also relatively high at the population level (P = 55.85%, H _e = 0.230). The coefficient of gene differentiation among populations (G _ST) was 0.255, indicating that while most genetic diversity resided within populations, there was also considerable differentiation among populations. AMOVA also indicated 24.29% of the total variation to be partitioned among populations (Φ_ST = 0.243). UPGMA clustering analysis based on genetic distances showed that the 12 populations could be separated into three subgroups: an eastern, a western, and a central-southern subgroup. However, a Mantel test revealed no significant correlation (r = 0.286, p = 0.983) between the geographical distances and genetic distances separating these populations; mountain barriers to gene flow and human disturbance may have confounded these correlations. The present study has provided some fundamental genetic data that will be of use in the exploitation of D. triflorum.     

Cold Tolerance of the Photosynthetic Apparatus: Pleiotropic Relationship between Photosynthetic Performance and Specific Leaf Area of Maize Seedlings

The objective of this study was to elucidate the genetic relationship between the specific leaf area (SLA) and the photosynthetic performance of maize (Zea mays L.) as dependent on growth temperature. Three sets of genotypes: (i) 19 S₅ inbred lines, divergently selected for high or low operating efficiency of photosystem II (Φ_PSII) at low temperature, (ii) a population of 226 F_2:3 families from the cross of ETH-DL3 × ETH-DH7, and (iii) a population of 168 F_2:4 families from the cross of Lo964 × Lo1016 were tested at low (15/13 °C day/night) or at optimal (25/22 °C day/night) temperature. The latter cross was originally developed to study QTLs for root traits. At 15/13 °C the groups of S₅ inbred lines selected for high or low Φ_PSII differed significantly for all the measured traits, while at optimal temperature the groups differed only with regard to leaf greenness (SPAD). At low temperature, the SLA of these inbred lines was negatively correlated with Φ_PSII (r = − 0.56, p < 0.05) and SPAD (r = − 0.80, p < 0.001). This negative relationship was confirmed by mapping quantitative trait loci (QTL) in the two mapping populations. A co-location of three QTLs for SLA with QTLs for photosynthesis-related traits was detected in both populations at 15/13 °C, while co-location was not detected at 25/22 °C. The co-selection of SLA and Φ_PSII in the inbred lines and the co-location of QTL for SLA, SPAD, and Φ_PSII at 15/13 °C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high Φ_PSII at low temperature leads to a constitutively altered SLA.     

HISTORICAL DEMOGRAPHY AND PRESENT DAY POPULATION STRUCTURE OF THE GREENFINCH,CARDUEUS CHLORIS—AN ANALYSIS OF mtDNA CONTROL-REGION SEQUENCES

Genetic variability within and among 10 geographically distinct populations of Greenfinches (Carduelis chloris) was assayed by directly sequencing a 637 BP part of the mtDNA control region from 194 individuals. Thirteen variable positions defined 18 haplotypes with a maximum sequence divergence of 0.8%. Haplotype (h = 0.28–0.77) and nucleotide (π = 0.058–0.17%) diversities within populations were low, and decreased with increasing latitude (h:r_s = –0.81; π: r_s = –0.89). The distribution of pairwise nucleotide differences fit better with expectations of a “sudden expansion” than of an “equilibrium” model, and the estimates of long term effective population sizes were considerably lower than current census estimates, especially in northern European samples. Selection is an unlikely cause of observed patterns because the distribution of variability conformed to expectations of neutral infinite alleles model and haplotype diversity across populations was positively correlated with heterozygosity (H_E) in nuclear genes (r_s = 0.74, P < 0.05). Hence, a recent bottleneck, followed by serial bottlenecking during the process of post-Pleistocene recolonization of northern Europe, together with recent population expansion provide a plausible explanation for the low genetic diversity in the north. Genetic distances among populations showed a clear pattern of isolation-by-distance, and 14% of the haplotypic variation was among populations, the rest being distributed among individuals within populations. In accordance with allozyme and morphological data, a hierarchical analysis of nucleotide diversity recognized southern European populations as distinct from northern European ones. However, the magnitude of divergence in mtDNA, allozymes and morphology were highly dissimilar (morphology > mtDNA > allozymes).     

Morphological and molecular characterization of the Landes honey bee (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.) ecotype for genetic conservation

A population of honey bees (Apis mellifera mellifera L.) with an annual colony brood cycle adapted to a locally abundant floral source in the Landes region of Southwest France is the subject of genetic conservation efforts. This population is maintained by local beekeepers in an area that experiences both an annual seasonal influx of non-local colonies and the permanent culture of imported stock. However, some colonies native to the Landes do not have the adapted brood cycle and their status as ecotypic are in question. The present study used morphology, mitochondrial DNA and microsatellites to characterize the endemic population and suggests further genetic conservation strategies. These methods yielded different degrees of discrimination of native and imported colonies and provided a powerful suite of tools for local resource managers. Colonies from the Landes could be differentiated from non-local French A. m. mellifera populations using morphometric analysis, and from non-native and reference populations using mtDNA and microsatellites. Seven morphological characters were identified by discriminant analysis as informative for delineating the Landes ecotype from other A. m. mellifera populations. Mitochondrial haplotypes for the population were characterized and five microsatellite loci were found to be informative in characterizing the Landes population. Asymmetric gene flow detected with microsatellite alleles was observed to be 5.5–5.9% from imported to native stocks of honey bees while introgression of native microsatellite alleles into imported colonies was 21.6%.     

Population Genetic Structure of the Yangtze Finless Porpoise (Neophocaena phocaenoides asiaeorientalis): Implications for Management and Conservation

Understanding the population genetic structure is a prerequisite for conservation of a species. The degree of genetic variability characteristic of the mitochondrial DNA control region has been widely exploited in studies of population genetic structure and can be useful in identifying meaningful population subdivisions. To estimate the genetic profile of the Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis), an endangered freshwater population endemic to China, the complete mtDNA control region was examined in 39 individuals belonging to seven different stocks inhabiting the middle and lower reaches of the Yangtze River. Very low genetic diversity was found (nucleotide diversity 0.0011± 0.0002 and haplotypic diversity 0.65± 0.05). The mtDNA genetic pattern of the Yangtze population appears to indicate a founder event in its evolutionary history and to support the marine origin for this population. Analyses by F_st and Φ_st yielded statistically significant population genetic structure (F_st = 0.44, P < 0.05; Φ_st = 0.36, P < 0.05). These results may have significant implications for the management and conservation of the Yangtze finless porpoise in the future.     

Maintenance of genetic diversity in Cordia africana Lam., a declining forest tree species in Ethiopia

We assessed genetic variation in a total of 22 populations of the tree species Cordia africana Lam. in Ethiopia and analyzed the country-wide impact of population history, forest disturbance and alteration of land use on extant intraspecific diversity. Amplified Fragment Length Polymorphisms (AFLPs) and chloroplast microsatellite markers were investigated. The analyses of the AFLP data revealed high diversity in all investigated populations: the percentage of polymorphic loci (PPL) ranged from 62.2% to 92.2% and Nei's gene diversity from 0.220 to 0.320 within the populations. The mean PPL and the mean diversity within populations were 85.7% and 0.287, respectively. The analysis of molecular variance revealed a moderate level of differentiation (Φ_ST = 0.07, p < 0.001) among the populations. The Mantel test proved a significant but low correlation (r = 0.31, p < 0.001) between the geographic distance and the genetic differentiation matrices. Only three different cpDNA haplotypes were observed; no more than two haplotypes were found in any population. The dominant haplotype with an overall frequency of 81% was observed in all populations. The level of differentiation among the populations was comparatively low at chloroplast DNA (G _ST = 0.18, R _ST, N _ST = 0.22). The observed patterns and levels of genetic variation within and among the populations indicate that efficient gene flow via pollen and seed is likely to be the main factor contributing to the maintenance of genetic diversity in natural and disturbed conditions.     

Genetic Diversity and Geographic Differentiation in the Threatened Species Dysosma pleiantha in China as Revealed by ISSR Analysis

Dysosma pleiantha, an important threatened medicinal plant species, is restricted in distribution to southeastern China. The species is capable of reproducing both sexually and asexually. In this study, inter-simple sequence repeat marker data were obtained and analyzed with respect to genetic variation and genetic structure. The extent of clonality, together with the clonal and sexual reproductive strategies, varied among sites, and the populations under harsh ecological conditions tended to have large clones with relatively low clonal diversity caused by vegetative reproduction. The ramets sharing the same genotype show a clumped distribution. Across all populations surveyed, average within-population diversity was remarkably low (e.g., 0.111 for Nei’s gene diversity), with populations from the nature reserves maintaining relatively high amounts of genetic diversity. Among all populations, high genetic differentiation (AMOVA: Φ_ST = 0.500; Nei’s genetic diversity: G _ST = 0.465, Bayesian analysis: Φ_B = 0.436) was detected, together with an isolation-by-distance pattern. Low seedling recruitment due to inbreeding, restricted gene flow, and genetic drift are proposed as determinant factors responsible for the low genetic diversity and high genetic differentiation observed.     

Stocking may increase mitochondrial DNA diversity but fails to halt the decline of endangered Atlantic salmon populations

Over the last 50 years, Spanish Atlantic salmon (Salmo salar) populations have been in decline. In order to bolster these populations, rivers were stocked with fish of northern European origin during the period 1974–1996, probably also introducing the furunculosis-inducing pathogen, Aeromonas salmonicida. Here we assess the relative importance of processes influencing mitochondrial (mt)DNA variability in these populations from 1948 to 2002. Genetic material collected over this period from four rivers in northern Spain (Cantabria) was used to detect variability at the mtDNA ND1 gene. Before stocking, a single haplotype was found at high frequency (0.980). Following stocking, haplotype diversity (h) increased in all rivers (mean h before stocking was 0.041, and 0.245 afterwards). These increases were due principally to the dramatic increase in frequency of a previously very low frequency haplotype, reported at higher frequencies in northern European populations proximate to those used to stock Cantabrian rivers. Genetic structuring increased after stocking: among-river differentiation was low before stocking (1950s/1960s Φ _ST = –0.00296–0.00284), increasing considerably at the height of stocking (1980s Φ _ST = 0.18932) and decreasing post-stocking (1990s/2002 Φ _ST = 0.04934–0.03852). Gene flow from stocked fish therefore seems to have had a substantial role in increasing mtDNA variability. Additionally, we found significant differentiation between individuals that had probably died from infectious disease and apparently healthy, angled fish, suggesting a possible role for pathogen-driven selection of mtDNA variation. Our results suggest that stocking with non-native fish may increase genetic diversity in the short term, but may not reverse population declines.     

Relationship between δ13C and photosynthetic parameters and their responses to leaf nitrogen content in six broadleaf tree species

Stable carbon isotope composition (δ¹³C), net photosynthetic rate (P _N), actual quantum yield of photosystem 2 (PS2) electron transport (ΦPS2), nitrogen content (N_c), and photosynthetic nitrogen use efficiency (PNUE) in the leaves of six broadleaf tree species were determined under field environmental conditions. The six tree species were Magnolia liliflora Desr., M. grandiflora Linn., M. denudata Desr., Prunus mume (Sieb.) Sieb. et Zucc. cv. Meiren Men, P. mume (Sieb.) Sieb. et Zucc. f. alphandii (Carr.) Rehd., and P. persica (L.) Batsch. var. rubro-plena. The relationships among δ¹³C, Φ_PS2, P _N, and PNUE, as well as their responses to N_c in the six species were also studied. Both P _N and δ¹³C negatively correlated with N_c, but Φ_PS2 positively correlated with N_c. This indicated that with N_c increase, P _N and δ¹³C decreased, while Φ_PS2 increased. There were weak negative correlations between δ¹³C and PNUE, and strong negative correlations (p<0.01) between Φ_PS2 and PNUE. According to the variance analysis of parameters, there existed significant interspecific differences (p<0.001) of δ¹³C, P _N, Φ_PS2, PNUE, and N_c among the tree seedlings of the six tree species, which suggests that the potential photosynthetic capacities depend on plant species, irradiance, and water use capacity under field conditions.