GENETIC VARIATION IN CACTOPHILIC DROSOPHILA FOR OVIPOSITION ON NATURAL YEAST SUBSTRATES

Theory predicts that environmental heterogeneity in space or in time can maintain genetic polymorphism. Stable polymorphisms are expected to be more readily maintained if there are genotype specific habitat preferences. Genotype specific preferences for oviposition sites in Drosophila could be a major factor promoting habitat selection, and thus the maintenance of genetic variation. This hypothesis is being tested using the cactophilic species, D. buzzatii and D. aldrichi, where available evidence indicates a potential for such habitat selection, the habitats (oviposition sites) being yeast species found in the natural environment of these flies (cactus rots). Genetic variation for oviposition preferences was tested using isofemale lines—for D. buzzatii, a total of 60 lines from seven localities widely distributed through the species range in Australia, and for D. aldrichi, 21 lines from three of these localities. Females were given a choice of five yeast species as oviposition sites. Genetic variation for oviposition preferences on these natural substrates was demonstrated. There was significant variation among isofemale lines within populations in their patterns of preferences for oviposition on the five yeast species. However, analyses of preferences for each yeast species separately showed that the genetic variation for preferences relates to only three of the five species. Heritabilities of individual female preferences for these three species were low, ranging up to 9%. Little geographic differentiation was apparent among populations, most likely due to similar selection regimes within each population. Within populations, this kind of habitat selection could act to maintain polymorphisms, both at loci determining the habitat preferences and at other loci in linkage disequilibrium with them.     

POPULATION GENETIC STRUCTURE IN DIPLOID BLUEBERRY VACCINIUM SECTION CYANOCOCCUS (ERICACEAE)

Vaccinium section Cyanococcus comprises diploid, tetraploid, and hexaploid species (x = 12) all of which are highly self-sterile. In order to assess the distribution of genetic variation within and among the diploids, population genetic analyses of allozyme data were conducted on three species: V. elliottii, V. myrtilloides, and V. tenellum. Populations were located throughout the range of these taxa in eastern North America. Data were collected at 20 loci, 12 of which are mendelian based on formal genetic analyses. Consistent with expectations for out-crossing taxa, these species exhibited high levels of variation within populations. Eighteen loci were polymorphic with the number and frequency of alleles varying among taxa. Mean values for the number of alleles per polymorphic locus, proportion of polymorphic loci, and expected heterozygosity were 2.8, 48.2, and 0.148, respectively. High infraspecific genetic identities exceeding 0.9 indicated that these taxa are homogeneous. All populations were in Hardy-Weinberg equilibrium with slight heterozygote excess observed in V. myrtilloides and V. tenellum. Although total genetic diversity was lower than that observed for other predominantly out-crossing species, it was apportioned similarly. The majority could be attributed to differences among individuals within populations. Conspecific populations were relatively undifferentiated with genetic differentiation similar to other self-incompatible species.     

Isozyme evidence for host races of the fungus Atkinsonella hypoxylon (Clavicipitaceae) infecting the Danthonia (Poaceae) complex in the southern Appalachians

On granite outcrops around Highlands, North Carolina four sympatric Danthonia grass species are infected by the fungus Atkinsonella hypoxylon (Clavicipitaceae). Danthonia epilis and D. sericea (rare hosts) are infected only in this small region, although they range more widely, while D. compressa and D. spicata (widespread hosts) are infected throughout their ranges in eastern North America. To test the hypothesis that infection of the rare hosts has recently spread from the widespread hosts, the genetic structure of fungal populations on different Danthonia hosts was investigated by isozyme electrophoresis. Two hundred isolates were collected from 46 sites and analyzed for ten polymorphic isozyme loci to examine levels of variation, genetic differentiation, and gene flow among fungal populations infecting different hosts. Genetic identities (I) indicated that isolates from within each of the widespread and rare host species pairs were homogeneous (I > 0.99), but the pairs were highly differentiated (0.66 < I < 0.69). With one exception there was no overlap in fungal genotypes isolated from the widespread hosts (12 genotypes) vs. the rare hosts (seven genotypes). Two plants of D. compressa growing sympatrically with infected D. epilis at one site were infected with a genotype characteristic of the latter species. Estimates of gene flow suggest a high degree of host-mediated reproductive isolation in A. hypoxylon, indicating that the fungus forms distinct, long-standing host races or sibling species in the southern Appalachians.     

Predation on reef-building corals: multiscale variation in the density of three corallivorous gastropods, Drupella spp.

 Feeding aggregations of three corallivorous gastropods, Drupella cornus, D. fragum and D. rugosa, have caused considerable coral damage on reefs across the Indo-West Pacific. Distribution and abundance of these three species were explored at Lizard Island, Great Barrier Reef, to determine within-reef variations in density, and spatial relationships between Drupella and their prey corals. The scales of greatest variation were between reef habitats (combinations of exposure and depth) and individual coral colonies. Density varied 12-fold among four habitats: exposed crests (2.55/m²), exposed slopes (0.22/m²), sheltered crests (0.34/m²) and sheltered slopes (2.07/m²). Species composition also varied markedly between habitats. Individuals were highly aggregated, usually forming small clusters (<10 individuals) on live coral colonies and other substrata, and occasional large aggregations of=200 to>2000. Five basic tenets for sampling Drupella are established, based on patterns of variation in density and species composition, and small-scale habitat use. Accepted: 8 February 1999     

Genetic differentiation of theErigeron species (Asteraceae) in the Alps: A case of unusual allozymic uniformity

Allozyme variation was studied in all nine diploidErigeron species known from the Alps:E. alpinus, E. neglectus, E. polymorphus, E. candidus, E. uniflorus, E. atticus, E. gaudinii, E. acer, andE. angulosus. A total of 248 individuals from 24 natural populations was investigated using starch gel electrophoresis. Seven enzymes and 13 loci were assessed. Genetic variation within populations was low with the proportion of polymorphic loci ranging from 0.0–0.385, and average number of alleles per polymorphic locus from 2.0–2.5. In general, 70–100% of the genetic variation was attributed to between population differences. Mean genetic identities for pair-wise comparisons of populations averaged 0.893 within species, and 0.890 among species. Interspecific genetic variation of populations usually did not exceed intraspecific variation. It was concluded that theErigeron species from the Alps may have arisen by recent speciation probably during the epoches of glaciation. Morphological and ecological differences between species seem to be based on few gene loci.     

Genetic variation and hybridization in SwedishSchoenus (Cyperaceae)

Schoenus ferrugineus andS. nigricans have restricted distributions in Sweden and are almost exclusively confined to calcareous fen habitats. AtS. nigricans sites,S. ferrugineus is usually also present, and hybrids are frequently found. In this report, I used allozymes to estimate the amount of gene flow between the two species, and to compare the partitioning of genetic diversity in each of them. Thirteen loci were analysed at eight different enzyme systems. Seven loci were variable between or within the species. The two species had completely different alleles at two of the seven variable loci, whereas there was overlap at five loci. In all, 22 different alleles were found. Six of these alleles were confined toS. nigricans, and five alleles were confined toS. ferrugineus. Nei's genetic identity was 0.55.—InS. ferrugineus, three loci (23%) were polymorphic, and the average number of alleles per polymorphic locus was 2.0 (each polymorphic locus had two alleles). InS. nigricans, three loci (23%) were polymorphic, and the average number of alleles per polymorphic locus was 2.3.—The proportion of genetic diversity due to variation among sites (G _ST) was fairly similar in the two species, mean over loci = 0.12 inS. ferrugineus and 0.15 inS. nigricans. However, the proportion of genetic diversity due to variation among individuals within sites (G _IS) differed markedly between the two species, mean over loci = 0.54 inS. ferrugineus and 0.17 inS. nigricans. Accordingly, there was a much higher individual heterozygosity inS. nigricans than inS. ferrugineus. — Most hybrids were interpreted as F₁ hybrids. However, a small proportion, 0.5–1.6 %, were F_n hybrids or back-crosses.—On the Swedish mainland, all former occurrences ofS. nigricans are extinct, but viable hybrids are still present at a few sites in southernmost Sweden.     

Temporal genetic structuring of a specialist parasitoid,Lysiphlebus hirticornis Mackauer (Hymenoptera: Braconidae) attacking a specialist aphid on tansy

In insect species characterized by inbreeding, limited dispersal, and a metapopulation structure, high genetic differentiation and reduced genetic diversity within local populations are expected. Using the model system Lysiphlebus hirticornis Mackauer, a specialist parasitoid of the tansy aphid, Metopeurum fuscoviride Stroyan (Hemiptera: Aphididae), we examined within‐site temporal population dynamics and genetics, including molecular variation at the tansy plant level. Aphid‐parasitoid dynamics were surveyed and parasitoids sampled from 72 tansy plants at 11 sites in and around Jena, Germany, over one growing season. Thereafter, parasitoid samples were genotyped at 11 polymorphic microsatellite loci. Colonization, extinction, and recolonization events occurred during the season. Allele numbers and identities were highly variable over time. When samples from all sites were pooled, allele number over all loci showed a decreasing trend with time. At the level of sites, temporal changes in genetic diversity were more variable. Analysis of molecular variance revealed that samples at the plant level explained the highest variance compared to at site level. We conclude that the genetic structuring of this insect is very fine grained (i.e. at the tansy plant level) and the temporal genetic diversity is explained by a combination of extinction and recolonization events, as well as inbreeding. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 737–749.     

Population genetic analysis of Elliottiaracemosa (Ericaceae), a rare Georgia shrub

Genetic and genotypic diversity found within populations of threatened plant species can have important implications for their conservation and management. In this study we describe genetic and genotypic diversity found within 10 populations of the endemic shrub Elliottiaracemosa (Ericaceae), the Georgia plume. E. racemosa is a threatened species known from fewer than 50 locations, all within the state of Georgia, USA. Seedset is limited to nonexistent in some E. racemosa populations and sexual recruitment has not been documented. However, the species is known to spread vegetatively via root-sprouts. Twenty-one allozyme loci were resolved for E. racemosa, nine of which were polymorphic. Compared with other woody taxa, E. racemosa has low genetic (i.e. allelic) diversity within populations (H_ep = 0.063) and at the species level (H_es = 0.091). Most of the genetic variation (82%) was found within populations, and genetic identities between populations were high (mean I = 0.96). However, genotypic diversity (i.e. the number of multilocus genotypes) differed markedly among populations. Two of the 10 populations consisted almost entirely of single multilocus genotypes, whereas more than 20 multilocus genotypes (in samples of 48 stems) were detected at three sites. Sites in which few multilocus genotypes were detected have low seedset, suggesting that the lack of clonal diversity limits reproduction in some populations of this reportedly self-incompatible species.     

Genetic diversity of Typha latifolia (Typhaceae) and the impact of pollutants examined with tandem-repetitive DNA probes

Genetic diversity at variable-number-tandem-repeat (VNTR) loci was examined in the common cattail, Typha latifolia (Typhaceae), using three synthetic DNA probes composed of tandemly repeated “core” sequences (GACA, GATA, and GCAC). The principal objectives of this investigation were to determine whether: (1) the previously reported almost complete lack of polymorphism at allozyme loci in this species was indicative of a reduced amount of genetic diversity at VNTR loci as well; (2) VNTR markers were informative about possible clonal propagation; and (3) significant differences in genetic structure of sampling sites were associated with differences in environmental levels of pollutants at those sites. Previously, widespread sampling across the eastern United States, surveying across ten allozyme loci, has detected only two genotypes, involving a difference at a single locus, among 104 populations. In this study, the amount of genetic diversity detected at VNTR loci: (1) among ramets (N = 40; 40 genotypes detected) collected at ∼8-km intervals along a 320-km transect; (2) among ramets (N = 220; 117 genotypes detected) from five study sites separated by 50–3000 m; and (3) even among ramets within each study site [N = 44 per site; from 13 to 34 genotypes detected per site (270 m²)] exceeds that previously found in those more geographically widespread allozyme surveys. Among the 260 ramets analyzed here, the mean number of bands scored per individual was 48.61 (SD = 2.80). Mean genetic similarity among ramets collected along the 320-km transect was 0.91, which was within the range of mean genetic similarity within the five study sites (range: 0.89–0.95). Among the five study sites, 61% of the samples analyzed appeared to be clonal ramets, with up to 12 clones detected for 44 ramets sampled within a site. Clones grew intermingled and ranged up to 39 m in extent. Permutation tests of genetic similarity revealed significant genetic differentiation between each of the five study sites. Consistent with the previous allozyme studies, T. latifolia was characterized by extremely low genetic variation relative to levels of polymorphism detected at VNTR loci in other plant species. Estimated heterozygosity among ramets along the 320-km transect ranged from 0.11 to 0.13, while that within the five study sites ranged from 0.05 to 0.12. Estimates of F_st (0.32–0.41) also indicated considerable genetic subdivision among these stands. Significantly higher genetic diversity was detected at the two study sites that chemistry and toxicity data indicate to be the most severely impacted by pollutants. Although this correlation does not establish cause and effect, the results of this study indicate that the analysis of genetic diversity at VNTR loci may be a useful tool for monitoring anthropogenic-induced changes in the genetic structure of natural populations of plants.     

Genetic diversity in an ant-dispersed chenopod Sclerolaena diacantha

Abstract Sclerolaena diacantha is a common and widespread, short-lived chenopod of arid Australia. The diaspore contains a food mass attractive to ants and, at sites where the ant Rhytidoponera sp B is common, thousands of diaspores accumulate on the nest mounds. Bagged plants set seed, showing that it is self-compatible. Population genetic variation was investigated at two levels: within and between sites, and within and between seed banks accumulated on the ant nests. Electrophoretic analysis of adult plants for 17 loci at 12 sites revealed nine polymorphic loci, but within sites only 6–18% of the loci were polymorphic. The values for mean gene diversity (He = 0.042) and total genetic diversity, (H_T= 0.088) were lower than those recorded for most other plant species. The mean fixation index of 0.52 indicated a mixed mating system with about 70% selfing. Most of the genetic diversity was distributed within sites (Dst = 0.008) and the mean value of 0.094 for GST indicated low levels of genetic differentiation. Electrophoretic analysis of seeds from 12 ant mounds at two sites showed that genetic differentiation was three times greater between seed banks than between the sites. However, collectively the genetic diversity stored within ant mounds was similar to the total diversity within the sites. It appears that restricted ant-dispersal and moderate inbreeding may create a local population structure that is undetected when sampling at a larger scale. Since investigations of genetic patterns on a very local scale are just beginning, there is much to learn about the evolutionary and genetic consequences of different seed flow patterns.     

Allozyme variation and population differentiation of the Aconitum delavayi complex (Ranunculaceae) in the Hengduan Mountains of China

The Aconitum delavayi complex is a group of four climbing species with trisect-leaves occurring in the Hengduan Mountains. The species of this complex are highly localized on very narrow regions with quite small population sizes. Because of rapid environmental changes recently in the Hengduan Mountains, this complex shows complicated morphological variability, which makes it difficult to delimit species. In the present study, 10 enzyme systems coding for 14 putative loci were employed to detect the interspecific and intraspecific genetic variation of the complex. In addition to low genetic diversity within all eight populations surveyed, the results indicate that A. episcopale is a distinct species because of high genetic identities among its three populations. Very low genetic divergence among populations of A. stapfianum and A. delavayi suggests that the two species should be treated as a single one.     

Microsatellite allele sequencing in population analyses of the South American cactophilic species Drosophila antonietae (Diptera: Drosophilidae)

Drosophila antonietae belongs to the Drosophila buzzatii cluster, a cactophilic group of species naturally endemic to South America. Morphological and genetic analyses indicate that its populations are the most homogenous in the cluster and that the diversity observed is mainly a result of variation within populations. Seven polymorphic microsatellite loci were described for this species and used in the present study to investigate the genetic diversity of natural populations of D. antonietae by both length and sequence variation. The study aimed to understand how homoplasy and null alleles affect inferences about the population history of this species and to obtain an accurate interpretation of population inferences where these loci could be applied. The results provide useful information on the interpretation of genetic data derived from the microsatellite loci described for D. antonietae and on evolutionary aspects of cactophilic Drosophila. Importantly, the results indicate that size homoplasy and null alleles do not represent significant problems for the population genetics analyses because the large amount of variability at microsatellite loci compensate the low frequency of these problems in the populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 573–584.     

Evolution of corallivory in the gastropod genus Drupella

Although muricid gastropods in the genus Drupella are well-known consumers of Indo-Pacific corals, their evolutionary and ecological history is unclear, as is their relationship to the apparently facultative coral-feeder Ergalatax margariticola, which has been reported to feed upon corals in Hong Kong. We use a well resolved molecular phylogeny (reconstructed from one nuclear and two mitochondrial genes) to show that the monophyletic genus Drupella falls into the muricid subfamily Ergalataxinae and that the genus includes ‘E. margariticola’, which is composed of two cryptic species. We show that genetic structure within the here reassigned ‘Drupella margariticola’ species complex does not relate to feeding mode, but instead seems to correspond to broad patterns of habitat ecology found in other gastropod taxa. Our analyses suggest that Drupella originated in the late Miocene (approximately 9.6 Ma) and diversified approximately 5.0 Ma, much later than the appearance of modern coral reefs in the early Cenozoic. Thus, it is possible that corallivory in Drupella evolved in response to the major expansion and reorganization of reefs that took place in the early Miocene.     

Analysis of genetic structure in soil populations of Rhizobium leguminosarum recovered from the USA and the UK

Although many studies have shown that animal-associated bacterial species exhibit linkage disequilibrium at chromosomal loci, recent studies indicate that both animal-associated and soil-borne bacterial species can display a nonclonal genetic structure in which alleles at chromosomal loci are in linkage equilibrium. To examine the situation in soil-borne species further, we compared genetic structure in two soil populations of Rhizobium leguminosarum bv. trifolii and two populations of R. leguminosarum bv. viciae from two sites in Oregon, with genetic structure in R. leguminosarum bv. viciae populations recovered from peas grown at a site in Washington, USA, and at a site in Norfolk, UK. A total of 234 chromosomal types (ET) were identified among 682 strains analysed for allelic variation at 13 enzyme-encoding chromosomal loci by multilocus enzyme electrophoresis (MLEE). Chi-square tests for heterogeneity of allele frequencies showed that the populations were not genetically uniform. A comparison of the genetic diversity within combined and individual populations confirmed that the Washington population was the primary cause of genetic differentiation between the populations. Each individual population exhibited linkage disequilibrium, with the magnitude of the disequilibrium being greatest in the Washington population and least in the UK population of R. leguminosarum bv. viciae. Linkage disequilibrium in the UK population was created between two clusters of 9 and 23 ETs, which, individually, were in linkage equilibrium. Strong linkage disequilibrium between the two major clusters of 8 and 12 ETs in the Washington population was caused by the low genetic diversity of the ETs within each cluster relative to the inter-cluster genetic distance. Because neither the magnitude of genetic diversity nor of linkage disequilibrium increased as hierarchical combinations of the six local populations were analysed, we conclude that the populations have not been isolated from each other for sufficient time, nor have they been exposed to enough selective pressure to develop unique multilocus genetic structure.     

GEOGRAPHICAL VARIATION IN ASIMINA TRILOBA DUNAL (ANNONACEAE) REVEALED BY THE M13 “DNA FINGERPRINTING” PROBE

Genetic variation for variable DNA loci was investigated in Asimina triloba using the M13 “fingerprinting” probe. A survey of plants from widely separated sites across portions of the geographical range of the species showed that each site possessed a distinct set of DNA fragments. The probability of two individuals having identical fragment patterns was approximately 1/1,700 at this geographical range. Levels of variation at local sites were quite different than at a wide geographic scale. Within-population variation ranged from moderate levels to none. The fragment profile of a fruit-bearing tree was compared with those of nine of its offspring; all progeny were identical with the maternal parent, indicating that both the staminate and carpellate sources were homozygous at all detected loci. These results suggest that while genetic variation is detectable both among distant individuals and within some very local populations, clonal propagation and/or inbreeding have led to a lack of genetic variation in some populations of A. tribola.     

Patterns of Genetic Population Differentiation in Four Species of Amazonian Frogs: A Test of the Riverine Barrier Hypothesis1

Patterns and levels of allozyme variation among populations of Amazonian frogs were used to test the riverine barrier hypothesis of species differentiation. Two frog species were sampled from each of the two main forest habitats on both banks of the Juruá River in the southwestern Brazilian Amazon Basin at various points along its course to contrast different barrier strengths. Scarthyla ostinodactyla and Scinax rubra were sampled from flooded forest (varzea), and Physalaemus petersi and Epipedobates femoralis from non-flooded forest (terra firme). All species showed high levels of within-population genetic variation. Average Nei's (1978) and Rogers’ (1972) genetic distances between sampled sites for all species were high indicating substantial among-population differentiation. The observation of low gene flow between sampled sites within species was further substantiated with Slatkin's (1993) M? analyses. Randomization tests suggested that there was some population structure at a few assayed polymorphic loci that was consistent with the riverine barrier hypothesis. However, it was apparent from the raw allozyme frequency data that these results were largely driven by substantial differentiation at one or a few collecting localities rather than by basin-wide patterns of riverine differentiation. Phenograms using genetic distance matrices supported this interpretation. Patterns of geographic variation are probably more consistent with the idea of this region being a zone of secondary contact.     

Capturing Genetic Variation during Ecological Restorations: An Example from Kankakee Sands in Indiana

Genetic variation in populations, both natural and restored, is usually considered crucial for response to short‐term environmental stresses and for long‐term evolutionary change. To have the best chance of successful long‐term survival, restored populations should reflect the extant variation found in remnants, but restored sites may suffer from genetic bottlenecks as a result of founder effects. Kankakee Sands is a large‐scale restoration being conducted by The Nature Conservancy (TNC) in northwestern Indiana. Our goal was to test for loss of genetic variation in restored plant populations by comparing them with TNC’s seed source nursery and with local remnant populations that were the source of nursery seed and of the first few restored sites. Allozyme analysis of Baptisia leucantha, Asclepias incarnata, Coreopsis tripteris, and Zizia aurea showed low levels of allozyme diversity within all species and reductions in polymorphism, alleles per locus, and expected heterozygosity between remnants and restorations for all species except A. incarnata. Almost all lost alleles were rare; restored populations contained almost 90% of alleles at polymorphic loci that occurred in remnants at frequencies greater than 1%. Allele frequencies for most loci did not differ between remnants and restored sites. Most species showed significant allele frequency differentiation among remnant populations and among restored sites. Our results indicate that seed collection techniques used at Kankakee Sands captured the great majority of allozyme variation present in seed source remnant populations.     

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.     

A comparison of the genetic diversity in Dipteronia sinensis Oliv. and Dipteronia dyeriana Henry

Dipteronia is an endemic genus to China and includes only two species, Dipteronia sinensis and D. dyeriana. Based on random amplified polymorphic DNA (RAPD) markers, a comparative study of the genetic diversity and genetic structure of Dipteronia was performed. In total, 128 and 103 loci were detected in 17 D. sinensis populations and 4 D. dyeriana populations, respectively, using 18 random primers. These results showed that the proportions of polymorphic loci for the two species were 92.97% and 81.55%, respectively, indicating that the genetic diversity of D. sinensis was higher than that of D. dyeriana. Analysis, based on similarity coefficients, Shannon diversity index and Nei gene diversity index, also confirmed this result. AMOVA analysis demonstrated that the genetic variation of D. sinensis within and among populations accounted for 56.89% and 43.11% of the total variation, respectively, and that of D. dyeriana was 57.86% and 42.14%, respectively. The Shannon diversity index and Nei gene diversity index showed similar results. The abovementioned characteristics indicated that the genetic diversity levels of these two species were extremely similar and that the interpopulational genetic differentiation within both species was relatively high. Analysis of the genetic distance among populations also supported this conclusion. Low levels of interpopulational gene flow within both species were believed to be among the leading causes for the above-mentioned phenomenon. The correlation analysis between genetic and geographical distances showed the existence of a remarkably significant correlation between the genetic distance and the longitudinal difference among populations of D. sinensis (p < 0.01), while no significant correlation was found between genetic and geographical distances among populations of D. dyeriana. This indicated that genetic distance was correlated with geographical distances on a large scale rather than on a small scale. This result may be related to differences in the selection pressure on species by their habitats with different distribution ranges. We suggest that in situ conservation efforts should focus on establishing more sites to protect the natural populations and their habitats. Ex situ conservation efforts should focus on enhancing the exchange of seeds and seedlings among populations to facilitate gene exchange and recombination, and to help conserve genetic diversity. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(5): 785–792 [译自: 植物生态学报, 2005, 29(5): 785–792]     

ALLOZYME VARIATION WITHIN AND BETWEEN LASTHENIA MINOR AND ITS DERIVATIVE SPECIES,L. MARITIMA (ASTERACEAE)

Enzyme electrophoresis was employed to examine genetic variation at 20 loci in 16 populations of Lasthenia minor and 18 populations of its presumed derivative species L. maritima. The purposes of the study were to ascertain levels of genetic variation in each species, to assess how the variation at enzyme-coding genes is apportioned within and among populations of each species, and to determine the level of divergence between the two species. The two species are both diploid annuals, similar morphologically, and produce fertile F₁ hybrids when crossed. Lasthenia minor is self-incompatible and restricted to mainland California, whereas L. maritima is self-compatible and probably largely autogamous; it occurs on seabird rocks from central California to British Columbia. Mean genetic identities for pair-wise comparisons of populations of the two species are similar to values for populations of the same species, indicating they have not diverged at the 20 genes coding for soluble enzymes. Despite its more extensive geographical range, L. maritima exhibits only 50% of the genetic diversity of L. minor. The latter species apportions a greater amount of its diversity within populations, whereas the former harbors more diversity among populations than within them. This is probably a reflection of the different breeding systems of the two species. Six unique alleles were detected in L. minor, whereas only one novel allele was found in a single individual of L. maritima. The electrophoretic data are concordant with the suggestion that L. maritima is relatively recently derived from L. minor. The switch from outcrossing to selfing and selection of genotypes adapted to the chemically and physically unusual substrate on the seabird rocks are considered the critical steps in the evolution of L. maritima.