Molecular genetic variation following a population crash in the endangered Mauna Kea silversword, Argyroxiphium sandwicense ssp. sandwicense (Asteraceae)

The endangered Mauna Kea silversword, Argyroxiphium sandwicense ssp. sandwicense (Asteraceae), has experienced a severe decline in distribution and abundance because of predation by alien ungulates. The small remnant natural population on the Mauna Kea volcano contains only 46 individuals. By contrast, the Haleakala silversword, A. sandwicense ssp. macrocephalum, consists of a large, vigorous population exceeding 60 000 individuals. Molecular genetic variation in the two populations was assessed using random amplified polymorphic DNA (RAPD) loci. Despite its severe crash in size, the Mauna Kea population did not differ significantly from the Haleakala population in the number of detectably polymorphic loci or in heterozygosity. The lack of substantial reduction in genetic variation, at least as measured with RAPD loci, suggests that the Mauna Kea population may not yet have gone through multiple generations at very small size.     

Population genetics of wood-feeding cockroaches in the genus Cryptocercus

Members of the genus Cryptocercus are xylophagous, wingless, subsocial cockroaches that inhabit decaying logs in temperate forests. Given their winglessness, subsocial living, and the patchy distribution of food resources (decomposing logs), it is likely that Cryptocercus populations are substructured. Allozyme variation at eight polymorphic loci was assayed for 10 subpopulations of Cryptocercus darwini and 13 subpopulations of Cryptocercus wrighti, both of which are distributed in the Appalachian Mountains. The mean F(IS) was 0.13 and F(ST) was about 0.25 for both C. darwini and C. wrighti. The relatedness among individuals of a subpopulation of both species was not significantly different from that expected among full sibs. In terms of how genetic variation is partitioned, C. darwini and C. wrighti differed from each other substantially. Most of the genetic variation occurred among subpopulations of C. wrighti in the same region and among subpopulations of C. darwini in different regions. We discuss the factors that may have contributed to the observed similarities and differences in the breeding structure of the two species.     

Genetic variation,population structure and identification of yellow catfish, <Emphasis Type="Italic">Mystus nemurus</Emphasis> (C&;V) in Thailand using RAPD,ISSR and SCAR marker

Random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers were used to investigate the genetic structure of four subpopulations of Mystus nemurus in Thailand. The 7 RAPD and 7 ISSR primers were selected. Of 83 total RAPD fragments, 80 (96.39%) were polymorphic loci, and of 81 total ISSR fragments, 75 (92.59%) were polymorphic loci. Genetic variation and genetic differentiation obtained from RAPD fragments or ISSR fragments showed similar results. Percentage of polymorphic loci (%P), observed number of alleles, effective number of alleles, Nei’s gene diversity (H) and Shannon’s information index revealed moderate to high level of genetic variations within each M. nemurus subpopulation and overall population. High levels of genetic differentiations were received from pairwise unbiased genetic distance (D) and coefficient of differentiation. Mantel test between D or gene flow and geographical distance showed a low to moderate correlation. Analysis of molecular variance indicated that variations among subpopulations were higher than those within subpopulations. The UPGMA dendrograms, based on RAPD and ISSR, showing the genetic relationship among subpopulations are grouped into three clusters; Songkhla (SK) subpopulation was separated from the other subpopulations. The candidate species-specific and subpopulation-specific RAPD fragments were sequenced and used to design sequence-characterized amplified region primers which distinguished M. nemurus from other species and divided SK subpopulation from the other subpopulations. The markers used in this study should be useful for breeding programs and future aquacultural development of this species in Thailand.     

EVIDENCE OF PARTIAL APOMIXIS IN ANTENNARIA MEDIA (ASTERACEAE: INULEAE) DETECTED BY THE SEGREGATION OF GENETIC MARKERS

The interplant variation in sexual and asexual reproduction in an Oregon population of the alpine perennial Antennaria media was investigated. Four polymorphic loci were assayed by enzyme electrophoresis of the progeny of 72 families from two subpopulations of A. media. The population was divided into two spatially distinct subpopulations. A multilocus model, incorporating a mixture of apomixis and random outcrossing, was used to estimate the mating system of pistillate plants both on the population and individual levels with statistical significance of the estimates based on bootstrap methods. The population contained a mixture of sexual individuals, partial apomicts, and obligate apomicts. The first subpopulation contained individuals that were partially apomictic and presumably produced both reduced and unreduced embryo sacs. There was a conspicuous difference in the breeding system composition between the two subpopulations. The first subpopulation had a “female” biased gender ratio and contained mostly obligate apomicts, some partial apomicts, and some outcrossing amphimicts. The second subpopulation, which had a nearly balanced gender ratio, contained mostly amphimicts, some obligate apomicts, but no facultative apomicts. This is the first study to document partial apomixis in individual plants by the use of genetic markers.     

Genetic Variation and Differentiation of Larix decidua Populations in Swiss Alps (in English)

Genetic diversity within and among six subpopulations of Larix decidua Mill. from two altitudinal transects of Swiss Alps was investigated using 6 enzyme systems coding for 8 loci. Globally, the mean proportion of polymorphic loci was 22.9%, the average number of alleles per locus was 1.3, and the mean expected heterozygosity was 0.095. Only 5.8% of the genetic variation resided among populations. The mean genetic distance was 0.006. Several significant differences of gene frequencies were found between different age classes. Positive values of the species mean fixation index observed in this study suggested a considerable deficit of heterozygotes in the populations of L. decidua of Swiss Alps. At one of the sites (Arpette), the highest subpopulation in elevation gave the lowest level of genetic diversity (as evidenced by the lowest proportion of polymorphic loci and the lowest mean expected heterozygosity) and the largest value of genetic distance when compared to other subpopulations. The genetic differences between the highest subpopulation and the other ones suggest that the founder effect may be an important factor influencing genetic differentiation of L. decidua populations at Arpette transect.     

Genetic structure and mating system in the palila, an endangered Hawaiian honeycreeper, as assessed by DNA fingerprinting

We conducted DNA fingerprinting analyses to ascertain the mating system and population genetic structure of the palila, an endangered Hawaiian honeycreeper, which occupies a fragmented range on the Mauna Kea volcano of the island of Hawai'i. DNA fingerprinting of twelve complete families from the Pu'u La'au population revealed no evidence of extrapair fertilization or intraspecific brood parasitism. Band-sharing coefficients from fingerprints produced with two probes revealed that the large Pu'u La'au population on the southwest slope of Mauna Kea, and a smaller, geographically separate population on the east slope (at Kanakaleonui) had relatively high and virtually identical levels of minisatellite variability (mean S of 0.27 for each population based on combined data of M13 and Jeffreys 33.15 probes). The two populations also had nearly identical allele frequencies based on their mean corrected similarity, S_ij, of 0.98. These data suggest that the two populations have not been fragmented long and/or have sufficient current gene flow to ameliorate any affects of genetic drift. We conclude that present levels of inbreeding are low within both populations, and that proposed translocations of individuals from Pu'u La'au to Kanakaleonui appear appropriate from a genetic standpoint.     

瑞士阿尔卑斯山欧洲落叶松居群的遗传变异和分化

应用等位酶分析技术,沿两个海拔梯度在瑞士阿尔卑斯山研究了欧洲落叶松（Larix decidua Mill.)居群内和居群间的遗传多态性,结果表明,多态性位点的比例为22.9%,平均每个位点的等位基因数为1.3,平均期望杂合度为0.095,遗传变异的5.8%存在于居群之间,平均遗传距离为0.006。几个有统计意义的基因频率差别在不同树龄类被发现,正在繁育系数值表明在瑞士阿尔卑斯山欧洲落叶松居群有相当的杂合体缺乏,在阿尔拜特（Ar-pette),海拔最高的亚居群与其他亚居群相比较显示最低的遗传多态性（如显示最低的我态性位点比例和最低的平均期望杂合度）和最大的遗传距离值,在最高亚居群和其他亚居群间的遗传差别暗示奠基效应可能是影响这个定样场所欧洲落叶松居群遗传分化的主要因素。     

Genetic diversity and floral dimorphism in Limonium dendroides (Plumbaginaceae), a woody Canarian species on the way of extinction

We combined reproductive and allozyme data to assess the levels and structuring of genetic variation and propose conservation guidelines in Limonium dendroides, a critically endangered Canarian endemic Plumbaginaceae featuring the floral and pollen pap/cob dimorphisms associated with the heteromorphic diallelic self-incompatibility system described for this family. Although seed germination has been reported in greenhouse conditions, the detection of individuals of only one morph in all wild subpopulations surveyed explains the extremely limited seed production and recruitment in nature. The geographical proximity and genetic closeness between some subpopulations, together with absence of inbreeding depression symptoms, and a higher allozyme variation in the cultured or reintroduced offspring than in their parental wild subpopulations indicate the viability of occasional compatible matings, thereby suggesting that even low levels of gene flow could mitigate the deleterious effects of fragmentation on subpopulation survival. However, our overall results indicate that L. dendroides is in a critical conservation situation where the utter scarcity of compatible mates within the subpopulations, radically low subpopulation sizes, poor inter-subpopulation gene flow, impoverished genetic variation, herbivore grazing, and the extreme habitat topography have overridden the reproductive capabilities of the species. According to our results, once morph types in all wild and cultured specimens can be determined, inducing fertile crosses through mixed reinforcements is advisable only in the most extremely isolated and small subpopulations (Argaga and Guarimiar) using individuals from the nearest ones (Azadoe and Palmarejo), whilst non-mixed reinforcements seem viable in the remaining subpopulations. Only when the subpopulations attain higher seed production and recruitment rates will it be adequate to collect seeds for their storage at a germplasm bank facility.     

极度濒危植物五针白皮松的保护遗传学研究

用随机扩增多态(RAPD)方法对极度濒危植物五针白皮松(Pinus squamata X.W.Li)的遗传多样性和居群遗传结构进行了研究。14个随机引物共获得93条RAPD谱带,其中6条为多态带,多态位点百分率仅为6．45％,遗传多样性极低。Shannon指数I和Nei指数h在种内也只有0．020和0．030,两个亚居群间(半阴坡亚居群与半阳坡亚居群)遗传分化程度不高,遗传分化系数Gst只有0．110,与大多数松科植物近似,居群每代迁移数为4．032。五针白皮松极低的遗传多样性可能是由于它在演化过程中遭受过严重的灾害,造成严重的瓶颈效应,丧失其大部分遗传变异。在随后的演化过程中由于遗传漂变、自交衰退等小种群现象,导致遗传多样性的进一步丧失。另外,阔叶树种对其生存的挤压和人类的干扰也是导致五针白皮松遗传多样性降低的因素之一。本文最后对该结果的保护生物学意义进行了评价。     

Low genetic differentiation among populations ofArabis serrata (Brassicaceae) along an altitudinal gradient

We investigated the extent of genetic differentiation among populations of fujihatazao,Arabis serrata along an altitudinal gradient at Mt. Fuji in Shizuoka Prefecture. This species is a perennial plant, widely distributed in Japan forming small isolated populations. However, at Mt. Fuji, this species constitutes a large population distributed from 1440 to 2400 m altitude. A total of 411 individuals were sampled from ten subpopulations. Eighteen loci were detected on eleven enzyme systems. Eleven loci were monomorphic and seven loci were polymorphic with a mean of 2.11 alleles per loci. Nei's genetic distance (mean 0.01) and genetic identity (mean 0.968) were very similar among populations indicating a low genetic differentiation. The total genetic diversity (H _T ) estimated for the polymorphic loci was, in average, 0.396. The mean gene differentiation (G_ST=0.091) was very low. Gene frequency of seven polymorphic loci was analyzed by spatial autocorrelation methods based on Moran's indexes. Only Pgi-3 exhibited a significant negative autocorrelation (−0.160;P<0.05); other loci values ranged from −0.134 to 0.027. Gene flow estimated by indirect methods varied between genes but most of the values were high (meanNm=20.8) suggesting that subpopulations at different altitudes are probably connected. Despite plants at different altitudes present different ecological traits (e.g., differences in phenology, growth and reproductive traits), subpopulations ofA. serrata are still low differentiated, at least for the loci studied. This may be explained by the recent origin of some habitats (e.g., second crater and surrounded areas) in this locality.     

GENETIC VARIABILITY OF GELIDIUM CANARIENSIS (RHODOPHYTA) DETERMINED BY ISOZYME ELECTROPHORESIS1

The populations of Gelidium canariensis (Grunow) Seoane-Camba from the Canary Islands were analyzed for genetic variability by isozyme electrophoresis in 1989 and 1990. Each population was divided into sporophytic and gametophytic subpopulations. Twenty-three to 27 putative alleles corresponding to 22 gene loci were analyzed. Sev-enteen loci were monomorphic in all six subpopulations, and five were polymorphic in at least one subpopulation. Significant deviations from Hardy-Weinberg equilibrium were found. The amount of genetic variability (percentage of polymorphic loci, mean number of alleles per locus, and average gene diversity) of haploid subpopulations was lower than that of diploid subpopulations. No correlation between genetic distance and geographical distance was found. Low genetic differentiation between sporophytic and gametophytic subpopulations of the same locality was obsewed in two populations. The low genetic diversity and genetic differentiation suggest that the genetic structure of the populations of G. canariensis from the Canary Islands is due to a combination of founder effects and the predominance of asexual reproduction. Initial differences in gene frequencies may have persisted because of insufficient time to reach a higher level of differentiation.     

Genetic structure and differentiation of Psathyrostachys huashanica populations detected with RAPD markers

Psathyrostachys huashanica Keng is a perennial grass and belongs to genus Psathyrostachys under Triticeae.sathyrostachys is found in the center of Middle Asia and the Caucasus Mountain,while P.huashanica,a species endemic to China,is only located in Mt.Hua in the Shaanxi province,China.At present,the population of this species is decreasing,and reaching the edge of extinction.Due to the limitation in distribution and the importance as breeding material for germplasm storage,it has been considered as first class among the national protected rare plants.For this reason,the present study is significant in probing plant flora,origin and evolution of Triticeae,and crop breeding.Randomly amplified polymorphic DNA (RAPD)markers were used to analyze the genetic structure and differentiation of P.huashanica populations sampled in three valleys (Huangpu,Xian,and Huashan Valleys)in Mr.Hua.One hundred and twenty-two RAPDfragments were obtained in all 266 individuals with 20 primers with a mean of 6.1 (2-10)fragments per primer.The percentage of polymorphic loci (PPB)was 60.66%in Huangpu Valley,90.98%in Xian Valley,95.08%in Huashan Valley,and the total PPB was 95.08%,which indicated a highly genetic variability of P.huashanica.The Shannon's Information index and GST were 0.3306 and 0.3263,respectively,indicating that there were more genetic variations within the subpopulations than those among the subpopulations.The gene flow among the subpopulations of P.huashanica (Nm=1.0322)was much less than that of the common anemophytes (Nm=5.24).Mean genetic distance is 0.1571(range:0.0022-0.2901).The highest value of genetic distance was found between the subpopulation (hp1)of Huangpu Valley and the highest altitude subpopulation (h8)of Huashan Valley.Correlation analysis detected significant correlation between genetic distance and vertical distance of altitude.Clustering analysis and principal coordinate analysis revealed the genetic differentiation among the populations of P.huashanica.Differentiation mainly occurred between the higher altitude subpopulations and the lower altitude subpopulations,suggesting that altitude might be the major factor that restricted the gene flow between different altitude subpopulations and resulted in differentiation of subpopulations.     

Inferring population history from fine-scale spatial genetic analysis in Oryza rufipogon (Poaceae)

Determining the genetic structure of an in situ conserved population can provide insight into the dynamics of population genetic processes associated with successful plant conservation. We used 21 microsatellite loci to analyse the genetic relationships among individuals (n = 813) collected from a small Oryza rufipogon population conserved since 1993 in Hunan Province of China. The analysis revealed four distinct genetic subpopulations (F(ST) = 0.145) without geographic isolation. One subpopulation was composed of possible introgressed individuals, two subpopulations were composed of seed recruits and their descendants, and the fourth subpopulation consisted of reintroduced individuals, seed recruits and their descendants. Positive spatial genetic structures were detected by spatial autocorrelation statistics at the population (c. 63 m) and subpopulation levels (11-30 m), but the degree of autocorrelation was stronger at the population level. These results showed that prejudging the cryptic structure is important before autocorrelation analysis for the entire population. Our study suggests that population history can be a significant determinant on population structure for plant restoration projects.     

Mosaic microecological differential stress causes adaptive microsatellite divergence in wild barley, Hordeum spontaneum, at Neve Yaar, Israel.

Genetic diversity at 38 microsatellite (short sequence repeats (SSRs)) loci was studied in a sample of 54 plants representing a natural population of wild barley, Hordeum spontaneum, at the Neve Yaar microsite in Israel. Wild barley at the microsite was organized in a mosaic pattern over an area of 3180 m2 in the open Tabor oak forest, which was subdivided into four microniches: (i) sun-rock (11 genotypes), (ii) sun-soil (18 genotypes), (iii) shade-soil (11 genotypes), and (iv) shade-rock (14 genotypes). Fifty-four genotypes were tested for ecological-genetic microniche correlates. Analysis of 36 loci showed that allele distributions at SSR loci were nonrandom but structured by ecological stresses (climatic and edaphic). Sixteen (45.7%) of 35 polymorphic loci varied significantly (p < 0.05) in allele frequencies among the microniches. Significant genetic divergence and diversity were found among the four subpopulations. The soil and shade subpopulations showed higher genetic diversities at SSR loci than the rock and sun subpopulations, and the lowest genetic diversity was observed in the sun-rock subpopulation, in contrast with the previous allozyme and RAPD studies. On average, of 36 loci, 88.75% of the total genetic diversity exists within the four microniches, while 11.25% exists between the microniches. In a permutation test, G(ST) was lower for 4999 out of 5000 randomized data sets (p < 0.001) when compared with real data (0.1125). The highest genetic distance was between shade-soil and sun-rock (D = 0.222). Our results suggest that diversifying natural selection may act upon some regulatory regions, resulting in adaptive SSR divergence. Fixation of some loci (GMS61, GMS1, and EBMAC824) at a specific microniche seems to suggest directional selection. The pattern of other SSR loci suggests the operation of balancing selection. SSRs may be either direct targets of selection or markers of selected haplotypes (selective sweep).     

Large‐scale population genetic structure in Bonelli's Eagle Aquila fasciata

In bird species that have a high movement capacity, dispersal may connect subpopulations over vast geographical regions, with important consequences for the design of conservation management strategies. Here we used a molecular approach to infer the patterns and rates of dispersal among eight Mediterranean subpopulations of the endangered Bonelli's Eagle, based on 245 individuals screened at 17 microsatellite loci. There was moderate genetic differentiation between subpopulations sampled in the western (Iberia and Morocco) and eastern (Cyprus) Mediterranean, whereas differentiation among subpopulations in the former region was weak to moderate and followed a pattern of isolation by distance. Within the western Mediterranean, the small, peripheral and ecologically unique population of southwest Portugal had the lowest genetic diversity and the highest differentiation. The remaining subpopulations formed two loose clusters, one including Morocco and southwest and eastern Spain, and the other northeast Portugal and western and central Spain. Few recent migrants were detected, and they originated primarily from adjacent subpopulations. Our findings suggest that western Mediterranean Bonelli's Eagles may have a large‐scale metapopulation structure, with subpopulations connected to some extent by distance‐dependent dispersal, probably influenced by natal philopatry and the geographical configuration of subpopulations. The combination of marked ecological and genetic divergence suggests that the peripheral subpopulation of southwest Portugal may be regarded as a distinct management unit.     

POPULATION VARIATION,OUTCROSSING, AND COLONIZATION OF DISTURBED AREAS BY CALAMAGROSTIS CANADENSIS: EVIDENCE FROM ALLOZYME ANALYSIS

Calamagrostis canadensis (a rhizomatous grass) exists in temperate forest sites of different successional age. It can rapidly colonize disturbed sites to form dense swards. We examined allozyme variation in: four populations (mature forest, intermediate aged forest, forest cutblock, wetland); nine small plots (2 m × 4 m) within the cutblock; and progeny of several families from three populations; in order to assess the mode of colonization of disturbed areas and the effect of successional changes on population genetic structure. All four populations showed equal and extensive genetic variation (1.5 to 1.7 alleles per locus [K], 41.7% to 50% polymorphic loci [PPL], H_st = 0.155 to 0.208) and were not genetically differentiated (G_st = 0.0193, 1 = 0.986 to 0.997). The cutblock subpopulations also showed considerable genetic variation (K = 1.6 to 1.8, PPL = 50% to 58.3%, H_st = 0.151 to 0.278) and no microdifferentiation (G_st = 0.034, I = 0.967 to 0.997). We found 14 different genotypes among the 30 individuals sampled from the cutblock as a whole (based on five polymorphic loci). The cutblock subpopulations had from nine to 14 different genotypes each (same five loci, 18 individuals per subpopulation). Seed produced was primarily outcrossed (multilocus estimate 0.888 to 0.900). We concluded that disturbed sites are colonized primarily by sexually produced seedlings. Potential genetic drift and natural selection, which occur during subsequent successional changes, do not result in reduced genetic variation or population differentiation.     

Local differentiation and gene dispersal distances in a Danish population of Armaria maritima

In a continuously distributed population of the self-incompatible species Armeria maritima , nine artificially delimited subpopulations were sampled in a transect with a length of 1300 m. Genetic variation was quantified with enzyme electrophoresis, which revealed five polymorphic loci. The genotypic distribution within subpopulations accorded to Hardy-Weinberg proportions, but revealed a Wahlund effect at one of the loci when the total population was considered. The Wahlund effect was supported by significant differences in allele frequencies among the nine subpopulations. The differentiation was low with a F_ST value of 0.028, which is much smaller than the previously reported value of 0.18 for 17 geographically separated Danish populations of this species. The low differentiation of the subpopulations was also revealed by an assignment test. In this test, the multilocus genotype of an individual is used to assign it to the subpopulation it has the highest likelihood to appear in. With this test, a lower percentage of individuals were assigned to the subpopulation of origin (24) than was seen with assignment of individuals to populations in Denmark (34). No abrupt changes in allele frequencies were observed. A spatial autocorrelation analysis suggested a breeding patch size of 500–700 m in diameter along the transect.     

Relatedness structure in Rhododendron metternichii var. hondoense revealed by microsatellite analysis

The relatedness structure of Rhododendron metternichii Sieb. et Zucc. var. hondoense Nakai was analysed in a 150 x 70-m quadrat in Hiroshima Prefecture, western Japan. The population of R. metternichii occurred as three subpopulations at the study site (A1-A3). Pairwise relatedness based on microsatellite genotypes at eight loci and Mantel tests revealed a hierarchical structure of relatedness within and among subpopulations: (i) relatedness between individuals within 10 m of one another was significantly positive; (ii) relatedness between individuals in the same subpopulation was significantly positive, but negative between individuals in distant subpopulations; and (iii) relatedness was not significantly different from zero among neighbouring subpopulations. In detail, however, relatedness within each subpopulation was significantly positive in subpopulation A1, relatively weak but significantly positive in subpopulation A2, and not significantly different from zero in subpopulation A3. Relatedness within each subpopulation was inversely related to correlations between interindividual distance and relatedness. The aggregation of related individuals at short distances from one another may lead to decreasing relatedness within subpopulations as a whole. Moreover, negative correlations between interindividual distance and relatedness corresponded to high flowering densities at less than 10-m distance, implying that high flowering densities reduce pollinator foraging distance and lead to stronger genetic structure within subpopulations. Small individuals (< 2.0 m in height) showed stronger genetic structure compared with that of large individuals (> or = 2.0 m in height). The different relatedness structure within and among subpopulations may be caused by various degrees of gene flow affected by distribution patterns of individuals and population density.     

大王马先蒿云南五个居群遗传变异研究

采用随机扩增多态DNA(RAPD)分子标记方法,对大王马先蒿(PedicularisrexL.)分布在云南中甸、丽江、大理、武定和昆明的5个居群(其中中甸居群有3个亚居群)的遗传多样性和遗传结构进行了研究。结果表明,大王马先蒿居群具有较高的遗传多样性,多态位点百分率P、Shannon表型多样性指数I和Nei的基因多样性指数h分别为82.0%、0.361和0.240,遗传多样性水平与居群的地理分布范围相关;大王马先蒿居群间的遗传变异较高,遗传变异主要发生在居群之间,而不是居群内部;居群间遗传分化系数Gst为0.747,遗传分化明显,居群间基因交流较少。居群间的遗传距离与居群间的相对地理距离具有一定的相关性。对云南西北部中甸居群的3个亚居群的遗传多样性分析表明,居群的遗传多样性水平与海拔高度有一定的相关性。居群间遗传变异较高可能是由于大王马先蒿为短命多年生植物,繁育系统为混交型,且自交占较大比例等原因造成的。     

Population genetic structure of two rare tree species (Colubrina oppositifolia and Alphitonia ponderosa,Rhamnaceae) from Hawaiian dry and mesic forests using random amplified polymorphic DNA markers

Hawaiian dry and mesic forests contain an increasingly rare assemblage of species due to habitat destruction, invasive alien weeds and exotic pests. Two rare Rhamnaceae species in these ecosystems, Colubrina oppositifolia and Alphitonia ponderosa, were examined using random amplified polymorphic DNA (RAPD) markers to determine the genetic structure of the populations and the amount of variation relative to other native Hawaiian species. Relative variation is lower than with other Hawaiian species, although this is probably not a consequence of genetic bottleneck. Larger populations of both species contain the highest levels of genetic diversity and smaller populations generally the least as determined by number of polymorphic loci, estimated heterozygosity, and Shannon's index of genetic diversity. Populations on separate islands were readily discernible for both species as were two populations of C. oppositifolia on Hawai'i island (North and South Kona populations). Substructure among Kaua'i subpopulations of A. ponderosa that were ecologically separated was also evident. Although population diversity is thought to have remained at predisturbance levels, population size continues to decline as recruitment is either absent or does not keep pace with senescence of mature plants. Recovery efforts must focus on control of alien species if these and other endemic dry and mesic forest species are to persist.