Patterns of genetic differentiation in two annual bromegrasses,Bromus lanceolatus andB. hordeaceus (Poaceae)

Infraspecific genetic differentiation was analysed in two tetraploid annual bromegrasses,Bromus lanceolatus (from N Africa) andB. hordeaceus (from N Africa and France). Genetic analysis of populations was based on allozyme polymorphisms at 17 loci. Different fixed heterozygous phenotypes were scored in both species, according to their allopolyploid origin. In N Africa, more variation occurred among populations ofB. lanceolatus than ofB. hordeaceus. The variation was not randomly distributed among populations of both species. InB. lanceolatus, differentiation was correlated with climatic variables rather than with geographic distance between populations. Higher correlation of genetic differentiation with geographic distance occurred inB. hordeaceus, particularly at large geographic scale, between French and N African populations. Within each region, the populations appeared weakly genetically differentiated, even when belonging to different subspecies.     

Patterns of genetic diversity and differentiation in the tsetse fly <Emphasis Type="Italic">Glossina morsitans morsitans</Emphasis> Westwood populations in East and southern Africa

Genetic diversity and differentiation within and among nine G. morsitans morsitans populations from East and southern Africa was assessed by examining variation at seven microsatellite loci and a mitochondrial locus, cytochrome oxidase (COI). Mean COI diversity within populations was 0.63 ± 0.33 and 0.81 taken over all populations. Diversities averaged over microsatellite loci were high (mean number of alleles/locus ≥7.4; mean H _E ≥ 65%) in all populations. Diversities averaged across populations were greater in East Africa (mean number of alleles = 22 ± 2.6; mean h _e = 0.773 ± 0.033) than in southern Africa (mean number of alleles = 18.7 ± 4.0; mean h _e = 0.713 ± 0.072). Differentiation among all populations was highly significant (R _ST = 0.25, F _ST = 0.132). Nei’s G _ij statistics were 0.09 and 0.19 within regions for microsatellites and mitochondria, respectively; between regions, G _ij was 0.14 for microsatellites and 0.23 for mitochondria. G _ST among populations was 0.23 for microsatellite loci and 0.40 for mitochondria. The F, G and R statistics indicate highly restricted gene flow among G. m. morsitans populations separated over geographic scales of 12–917 km.     

Allozyme variation in 16 natural populations of Faidherbia albida (Del.) A. Chev

The objectives of this study were (1) to investigate the genetic variability; and (2) to determine the phylogenetic relationship in the leguminous tree Faidherbia albida through out its range of distribution in East, West and Southern Africa. A total of 16 populations were subjected to enzyme electrophoresis and 6 enzyme systems (Adh, Mdh, G6pdh, Idh, 6Pgdh, and alpha-Est) encoded by 12 loci were scored. A total of fifty one different alleles were detected, with an average of 2.5 alleles per locus. Forty three percent of the loci were polymorphic at a 95% criterion. The average expected heterozygosity (gene diversity index H(e)) was 0.141. All provenances showed significant deviation from Hardy-Weinberg expectation. The UPGMA cluster analysis, based on Modified Rogers distance revealed close similarities between Eastern and Southern African provenances, except Debre zeit from Ethiopia, which was closest to West African populations than to the East African populations. Also, Bignona from West Africa was peculiarly closer to East African provenances. Differentiation of West African populations from Eastern and Southern African provenances was quite evident, emphasising the clinical pattern of variation in these two major geographical races of F. albida in Africa. Wright's F-statistics showed an overall significant deficit of heterozygotes, a common feature in mixed mating, entomophilous, widespread species such as F. albida. The dendrogram analysis showed wide separation among the three Ethiopian provenances indicating a high level of genetic differentiation and diversity among them.     

Genetic variation and population structure in Korean endemic species: III.Hosta minor (Liliaceae)

Hosta minor, an insect-pollinated and rhizomatous herbaceous perennial, occurs in eastern and southern Korean Peninsula. AlthoughH. minor is a Korean endemic species and most populations of the species are scattered, the species maintains considerably high levels of genetic variation within the species, with a moderate level of variation (14%) found among populations. Nineteen of the 29 putative loci resolved (66%) were polymorphic within the species, the mean number of alleles per locus was 2.10 across all populations and averaged 1.68 within populations. In addition, genetic diversity was a considerably higher (for species and population level, mean estimates of genetic diversity were 0.275 and 0.230, respectively) than the average for other long-lived herbaceous perennials. Indirect estimate of the number of migrants per generation (Nm=1.03, calculated from mean G_ST) was moderate. Factors contributing to the high levels of genetic diversity found within populations ofH. minor include population maintenance via sexual and asexual modes of reproduction, primarily outcrossing breeding system, long generation time, probable ancient polyploid origin of the species, and moderate levels of seed dispersal by wind. Human disturbance in South Korea such as road and apartment constructions appears to be the major threat to this genetically diverse species.     

A cline of allozyme variation inAbies mariesii

Genetic variation at 22 allozyme loci was examined for 1,003 trees from 11 isolated natural populations ofAbies mariesii covering all except the southernmost region of its geographic range. Genetic diversity within species (H _es=0.063) was low compared to many other long-lived woody species. Most of the genetic variation is found within populations (G _ST=0.144) despite their isolated distribution. Genetic distance between populations was positively correlated with geographic distance. Genetic diversity within populations was generally low (meanH _ep=0.054), but varied across populations in a clinal fashion such that genetic variation decreased with increasing latitude. These genetic characteristics may reflect the distribution history of this species.     

Gene variation and gene flow inOrchis morio (Orchidaceae) from Italy

Data are presented on genetic variation at 27 enzyme loci of the Green-Winged orchid,Orchis morio, in 18 population samples from Italy. The existence in Italy of two subspecies, i.e. subspp.morio andpicta, is not supported by allozyme data. No genetic heterogeneity was found betweenmorio-like andpicta-like samples and specimens. Moreover, morphological transition between the two forms was observed in different Italian populations. The parameters of genetic variability estimated forO. morio populations are consistent with those found among monocotyledon plants, and among those outcrossing, animal-pollinated and with wind-dispersed seeds. Genetic diversity of ItalianO. morio is mostly within populations. Correspondingly, low values of interpopulational genetic distance were found. This appears to be due to high levels of gene flow, which were estimated with different methods. The lack ofO. longicornu from Italian samples, as well as of any hybrid withO. morio (F₁, backcrossed or recombinant individuals) is demonstrated on the basis of genetic data. It is concluded that recurrent reports ofO. longicornu from Italy are due to confusion withO. morio or with otherOrchis species.     

Low genetic differentiation betweenAdiantum capillusveneris L. andA. ogasawarense Tagawa (Adiantaceae), an endemic pteriodophyte of the bonin (ogasawara) islands

Genetic differentiation was examined betweenAdiantum capillus-veneris L. andA. ogasawarense Tagawa. A total of 136 individuals from two populations ofA. ogasawarense and three populations ofA. capillus-veneris were sampled. Allozymes encoded by 19 putative loci for nine enzyme systems were observed. The populations ofA. ogasawarense are genetically differentiated from those ofA. capillus-veneris; conspecific populations cluster together. However, genetic identity between two species was estimated to be 0.815, and indicates that the degree of allozyme differentiation is lower than those between endemic flowering plants and their progenitors. It is possible that the low genetic differentiation observed betweenA. ogasawarense andA. capillus-veneris results from a recent origin of the endemic species,A. ogasawarense.     

Genetic diversity in the threatened insular endemic plantAster asa-grayi (Asteraceae)

Genetic diversity in an insular endemic plantAster asa-grayi was examined using enzyme electrophoresis. Distribution ofA. asa-grayi is restricted to only four subtropical islands of Japan, and this species is listed as vulnerable to extinction in the Red Data Book of Japanese wild plants. A total of 161 individuals were sampled from five populations on four islands. Genetic diversity values at the population level were very low, compared to other plant species with a similar life history. Genetic variability at the species level is comparable to the mean value of endemic species. Genetic differentiation among populations is extremely high (G_ST= 0.71), indicating that the gene flow among populations is highly impeded, and pollen and seed dispersal is limited due to the pollinators and the seed morphology. This is because the four islands are geographically isolated. Fixation indices suggested that most populations do not randomly cross. To conserve the genetic diversity of the species, artificial crossings among different island populations are necessary.     

Genetic characterisation of a domestic dog<Emphasis Type="Italic">Canis familiaris</Emphasis> breed endemic to South African rural areas

Allozyme electrophoresis (horizontal starch gel and PAGE) and histochemical staining techniques were used to study the genetic composition of an endemic southern African domestic dogCanis familiaris Linnaeus, 1758, the Africanis breed. Genetic differentiation was analysed at 21 protein-coding loci. The results were compared to those for three other populations/breeds: representatives of established Western breeds, crossbred dogs of Western descent from rural areas in South Africa, and indigenous Saluki dogs from the Middle East. Nine polymorphic loci were found (Ak-1,-2, Ck, Per, Hb, Po-A-1 to-3 andPo-Tf). Two unique alleles at theCk andPo-A-2 loci separated the Africanis breed from the other groups. There were also significant differences between Africanis and the other breeds in pair-wise comparisons of allelic frequencies at polymorphic loci. An assignment test, fixation index values, gene flow and genetic distance values indicated a closer genetic association between the Africanis and Saluki breeds than with dogs of Western origin. This finding supports archaeological evidence that the endemic Africanis breed was introduced from the Middle East into Africa thousands of years ago, and not through later western influences. The average heterozygosity ranged from 0.106–0.15, with least heterozygosity in the Africanis and most in the rural crossbred group. The percentage of polymorphic loci, the mean number of alleles per locus (biologically more significant than heterozygosity), and conformation of genotypes to Hardy-Weinberg proportions showed no evidence of recent loss of genetic diversity in Africanis. Genetic differentiation and support of archaeological evidence by genetics indicate that the endemic southern African domestic dog breed is unique.     

Population Genetic structure ofPotentilla fragariodes var.major (Rosaceae) in Korea

The genetic diversity and population structure of eighteenPotentilla fragariodes var.major (Rosaceae) populations in Korea were determined using genetic variations at 22 allozyme loci. The percent of polymorphic loci within the enzymes was 66.7%. Genetic diversity at the species level and at the population level was high (Hes = 0.203; Hep = 0.185, respectively), whereas the extent of the population divergence was relatively low (G_ST = 0.069). F_IS, a measure of the deviation from random mating within the 18 populations, was 0.075. An indirect estimate of the number of migrants per generation (Nm = 3.36) indicated that gene flow was high among Korean populations of the species. In addition, analysis of fixation indices revealed a slight heterozygote deficiency in some populations and at some loci. Wide geographic ranges, perennial herbaceous nature and the persistence of multiple generations are associated with the high level of genetic variation. AlthoughP. fragariodes var.major usually propagated by asexually-produced ramets, we could not rule out the possibility that sexual reproduction occurred at a low rate because each ramet may produce terminal flowers. Mean genetic identity between populations was 0.983. It is highly probable that directional movement toward genetic uniformity in a relatively homogeneous habitat operates among Korean populations ofP. fragariodes var.major.     

Genetic diversity and population differentiation of chestnut blight fungus, Cryphonectria parasitica, in China as revealed by RAPD

Seventeen Cryphonectria parasitica populations sampled from six regions in China were investigated using RAPD. Across all 169 isolates from the 17 populations evaluated, 52 of the 71 markers (73%) were polymorphic, total genetic diversity (h) was 0.1463, and Shannon’s index was 0.2312. Diversity within populations accounted for 74% of total genetic diversity, and genetic differentiation among populations was 0.26 (G _ST = 0.26). Gene flow was 1.4 among the populations; higher gene flow was found among populations within regions and among regions [N _m (G _SR) = 2.8 and N _m (G _RT) = 3.5]. The unweighted pair group mean analysis (UPGMA) dendrogram revealed two distinct clusters: the northern China group and the southern China group. The spatial autocorrelation analysis revealed that the variation at most loci was randomly distributed and lacked spatial structure, but several loci and closer distances were spatially structured. Human activity and habitat could also be important factors affecting genetic structure among C. parasitica populations in China. Genetic diversity was highest in Southwest China, descending in an orderly fashion to Northeast China. This pattern indicated that Southwest China might be the center of origin of C. parasitica in China. The present study provides useful information for understanding the origin and spread of chestnut blight fungus in China and valuable data for formulating relevant strategies for controlling the disease in China.     

Patterns of genetic variation of the genusCapsicum (Solanaceae) in Mexico

The evolutionary relationships of 186 accessions ofCapsicum from Mexico were studied through enzyme electrophoresis. A total of 76 alleles representing 20 genetic loci coding for nine enzyme systems were observed and the allelic variations of enzymes were studied for geographical distribution. Allele frequencies were used to estimate the apportionment of gene diversity within and between populations and to construct a dendrogram based on a similarity matrix containingNei genetic distances. — The gene diversity estimates suggest that the structure ofCapsicum populations in Mexico consists of predominantly homozygous genotypes presumably due to a self-pollinated breeding system and population bottlenecks. Significant genetic differentiation was found mainly between populations of differing geographical regions.—Based on the results of this study, three species of domesticatedCapsicum can be identified in Mexico,C. annuum var.annuum, C. chinense, andC. pubescens. Semidomesticated and wild forms include two species,C. frutescens andC. annuum var.glabriusculum. A sharp geographical division results between the latter species;C. frutescens was collected exclusively in the southeastern states of Oaxaca, Chiapas, and Tabasco; whereas wild and semidomesticated forms from the rest of the country areC. annuum. Based upon the similarity of enzyme genotypes of semidomesticated and wild forms, the primary center of domestication of cultivatedC. annuum was estimated to be the region comprising the states of Tamaulipas, Nuevo Leon, San Luis Potosi, Veracruz, and Hidalgo in eastern Mexico. A possible second center of domestication is suggested to be localized in the state of Nayarit, western Mexico.     

Latitudinal variability of Drosophila melanogaster: Allozyme frequencies divergence between European and Afrotropical populations

Allelic frequencies at five polymorphic loci were determined in seven European and six Afrotropical populations of Drosophila melanogaster. African populations, which may be considered as ancestral for the species, showed a greater genetic diversity as measured by the number of alleles found. Within each geographic group (Europe or tropical Africa) genetic distances between local populations were very small (D=0.027). By contrast, the average distance between European and African populations (D=0.389) was more than 12 times bigger. It was previously known that various morphological or physiological differences, which probably reflect genetic adaptations to different environments, exist between these temperate and tropical populations. Data presented here suggest that the divergence in allozyme frequencies also reflects some selective mechanisms.     

Adaptive radiation and genetic differentiation in the woodySonchus alliance (Asteraceae:Sonchinae) in the Canary Islands

The woodySonchus alliance consists of 19 species ofSonchus subg.Dendrosonchus, one species ofSonchus subg.Sonchus and species of five genera (i.e.Babcockia, Sventenia, Taeckholmia, Lactucosonchus, Prenanthes), and is restricted primarily to the archipelago of the Canaries in the Macaronesian phytogeographical region. An enzyme electrophoretic study, including 13 loci, was conducted to assess genetic diversity within and divergence among species of the alliance. Nei's genetic identities (distances) between genera and/or subgenera range from 0.490 (0.714) to 0.980 (0.013), and pairwise comparisons of all populations show relatively high genetic identities, with a mean of 0.804. The high identities further support the genetic cohesiveness of the alliance and its single origin on the Macaronesian islands. Species in the alliance also show about 50%; higher total genetic diversity (H_T) than the mean for other oceanic endemics. There is greater divergence between endemics or species on older islands compared to those on younger islands, which suggests that time is a factor for divergence at allozyme loci. Furthermore, populations on older islands have higher total genetic diversities and lower identities than conspecific populations on younger islands. These results imply early colonization, radiation, and divergence of the woodySonchus alliance on older islands followed by subsequent colonization to younger islands. The taxonomic distribution of alleles in the alliance indicates lineage sorting also played a role in divergence among species. Lineage sorting may also produce nonconcordance with either taxonomic designation or the pattern of variation obtained from other molecular markers such as ITS sequences of nrDNA. Timing for the origin and radiation of the alliance agrees with the estimate based on ITS sequences, and suggests that the early divergence and rapid radiation took place during the Late Tertiary on either Gran Canaria or Tenerife.     

Genetic structure and dispersal in a small South African rodent. Is dispersal female-biased?

Dispersal greatly determines genetic structure of populations, although it is influenced by landscape heterogeneity, quality of the matrix, resource distribution and local population densities and dynamics. To get insights into some of those processes we analysed the genetic structure of the hairy-footed gerbil Gerbillurus paeba (Rodentia, Murinae, Gerbillinae) in the southern Kalahari (South Africa). Samples were taken from 20 populations covering an area of about 2200 km². Genetic data were related to landscape characters and population dynamics. We used newly developed microsatellites and found at all loci some indication for the presence of null alleles. However, null alleles seem to have little influence on the general results of our analyses. Altogether we found even nearby populations of G. paeba to be significantly differentiated, although assignment tests revealed 24% of individuals as immigrants. Genetic structure was independent of landscape heterogeneities at all spatial scales. Autocorrelation analyses (range 50–90 km) revealed significant genetic structure within populations on distances <3 km. We found some indication for female-biased dispersal. Our study suggests that dispersing individuals have little influence on the long-term genetic structure and that drift is the major cause of genetic diversity. The observed genetic pattern likely derives from strong population fluctuations of G. paeba. The landscape structure has little influence on the genetic differentiation between populations.     

Biosystematic studies onCapsella bursa-pastoris (Brassicaceae): Enzyme polymorphism in natural populations

The genetic variability of natural populations ofCapsella bursapastoris in North- and Middle-Europe has been estimated by means of enzyme assays. Zymograms of 81 populations have been developed. 17 loci could be identified, and 8 of them can be heterozygous. Genetic variability is greater between populations than within. No correlation between actual population sizes and genetic heterogeneity could be detected. Some electromorphs shift their frequencies proportionally to increasing adversity of climatic conditions, some appear to be constant over the whole area, and others are characterized by an apparently irregular variation pattern. Marginal populations comprise a significantly higher proportion of heterozygous plants than central ones. Apart from this clinal variation pattern, a mosaic pattern, strongly related to habitat conditions, was observed: genetic heterogeneity is greater in more intensively disturbed sites. The pattern of genetic variation in natural populations ofCapsella bursa-pastoris is rather highly influenced by the breeding system.     

Phenetic investigation of non-nodulating African species ofAcacia (Leguminosae) using morphological and molecular markers

Morphological and RAPD markers were used to assess the relationships among nodulating and non-nodulating species of AfricanAcacia. Non-nodulating species of AfricanAcacia are only found within subg.Aculeiferum sect.Monacanthea. African species of sect.Monacanthea examined were found to form a group distinct from the other African species examined on a morphological and molecular basis. All lack the ability to nodulate, suggesting that non-nodulation may be used as a taxonomic tool. The species of sect.Aculeiferum were separated by RAPD and morphological analysis into two groups depending on whether they were armed with prickles in pairs and/or prickles in threes, or solitary. A third group of species was identified within sect.Acacia: further subdivision of this group was achieved into subsectt.Pluriseriae andUniseriae. The position ofA. albida relative to other AfricanAcacia species was found to be distinct but not totally independent of the genus. The partitioning and distribution of the genetic variability within the genus is further elucidated by the RAPD analysis of populations ofAcacia species. A population analysis ofA. polyacantha demonstrated geographical and site-specific variation.     

Allozyme diversity in Chinese,Seguin and American chestnut (Castanea spp.)

Allozyme genetic variability in three chestnut (Castanea) species was investigated using 19 loci from ten enzyme systems. G-tests of heterogeneity of isozymic allele distribution showed significant differences between the three species at 15 of the 19 loci, and between the 13 C. mollissima populations at 13 of the 19 loci examined. C. mollissima was found to possess a significantly-higher value of mean gene heterozygosity (H=0.3050±0.0419), the percentage of polymorphic loci (P=84.21%) and the average number of alleles per locus (A=2.05), than any other species in the Castanea section Eucastanon. When the genetic variability of populations of C. mollissima from four regions in China was investigated, the population from the Changjiang river region showed a markedly higher mean gene heterozygosity (H=0.3480±0.0436) than populations from the other regions. Genetic relationships among the four regions were assessed by Nei's genetic identity I and standard genetic distance D. An approximately-identical distance between the population from the Changjiang river region and populations from the three other regions was observed, while populations from the latter regions showed almost the same genetic distance from each other. These data, when considered with information existing prior to this study, contribute to an understanding of the possible origin and progenitor of the chestnut species.     

Genetic differentiation among populations ofArabis serrata (Brassicaceae) along its geographic distribution

Levels and distribution of genetic variation were investigated in ten populations of the perennialArabis serrata distributed along a latitudinal gradient throughout Japan. Populations of this endemic species occupy predominantly three types of habitats: limestone and derived soils, volcanic and disturbed sites. Previous studies showed that plants ofA. serrata are differentiated in morphological and ecological traits under both natural conditions and common garden experiments suggesting genetic differentiation among populations. To assess the degree of genetic differentiation under different habitats ofA. serrata populations, we analyzed the isozyme genetic structure. Ten populations, located in mountains of central and northern Honshu and Hokkaido, were analyzed by starch gel enzyme electrophoresis. Fourteen loci of eight enzymes were resolved and six loci were monomorphic for all the populations. Populations sampled maintain low levels of genetic variation (P=0.16;H=0.05;A=1.16) compared to that maintained by other outcrossing seed plants. In some cases, few or no heterozygous individuals were detected, and consequently, mean observed heterozygosity was zero or near zero. Six (29%) of the fixation indices,F, estimated deviated significantly from Hardy Weinberg genotypic expectations indicating a deficiency of heterozygotes in most of the cases. The mean genetic identity (Nei'sI) between population pairs was 0.852 and indicates a moderate level of genetic differentiation among populations.Arabis serrata has most of its genetic variation distributed among rather than within populations. The among-population component of the total genetic diversity (G _ST mean value) was 0.416, indicating genetic differentiation between populations. There groups of populations were recognized in an unrooted tree generated by the Neighbor-Joining method. These results suggest groups of populations differentiated regionally. Estimates of interpopulational gene flow (Nm) were very variable (range 0.049–3.718) with a meanNm=1.203 for all populations.     

From Scilla to Charybdis – is our voyage safer now?

The genus Charybdis Speta (previously Urginea maritima agg.) was investigated karyologically and genetically throughout its geographic range in the Mediterranean. The different ploidy levels show a strong geographic pattern. Diploid populations are mainly found along the northern coast of Africa with C. pancration extending northwards from Tunisia to southern Italy. Tetraploid populations are most densely distributed in the eastern Mediterranean but are also found in North Africa, on the Balearic and Canary Islands. Hexaploid populations are restricted to the Iberian Peninsula and adjacent Morocco and Algeria. Chloroplast microsatellite data suggest that determination of ploidy levels alone is insufficient to adequately describe the existing populations. Especially the tetraploid and hexaploid populations exhibit additional genetic differentiation and geographic structuring. AFLP data indicate that tetraploid populations from southern Italy are of hybrid origin. Phylogenetic analysis further revealed that the genera Urginea Steinh. and Charybdis are not directly related to each other but have strong ties to genera from southern Africa. A possible colonization scenario of the Mediterranean via NW Africa and Iberia is discussed.