Patterns of hybridization and population genetic structure in the terrestrial orchids Liparis kumokiri and Liparis makinoana (Orchidaceae) in sympatric populations

We investigated the potential for gene flow and genetic assimilation via hybridization between common and rare species of the terrestrial orchid genus Liparis, focusing specifically on sympatric and allopatric populations of the common Liparis kumokiri and the rare Liparis makinoana. We utilized analyses of genetic diversity, morphology, and the spatial distributions of individuals and genotypes to quantify the dynamics of interspecific gene flow at within- and among-population scales. High levels of allozyme genetic diversity (HE) were found in populations of the rare L. makinoana (0.317), whereas the common L. kumokiri (N = 1744 from 14 populations) revealed a complete lack of variation. This contrast may reflect different breeding systems and associated rates of genetic drift (L. makinoana is self-incompatible, whereas L. kumokiri is self-compatible). At the two known sympatric sites, individuals were found that recombined parental phenotypes, possessing floral characteristics of L. kumokiri and vegetative characteristics of L. makinoana. These putative hybrids were the only individuals found segregating alleles diagnostic of both parental species. Analysis of these individuals indicated that hybrid genotypes were skewed towards L. kumokiri and later generation recombinants of L. kumokiri at both sympatric sites. Furthermore, Ripley's bivariate L(r) statistics revealed that at one site these hybrids are strongly spatially clustered with L. kumokiri. Nonetheless, the relatively low frequency of hybrids, absence of ongoing hybridization (no F1s or first generation backcrossess), and strong genetic differentiation between morphologically 'pure' parental populations at sympatric sites (FST = 0.708-0.816) indicates that hybridization was not an important bridge for gene flow. The results from these two species suggest that natural hybridization has not played an important role in the diversification of Liparis, but instead support the view that genetic drift and limited gene flow are primarily responsible for speciation in Liparis. Based on genetic data and current status of the species, implications of the research for conservation are considered to provide guidelines for appropriate conservation and management strategies.     

Genetic diversity in the endangered dysploid larkspur Delphinium bolosii and its close diploid relatives in the series Fissa of the Western Mediterranean area

Allozyme diversity was evaluated in four closely-related taxa of the Delphinium series Fissa distributed throughout the Western Mediterranean area. All are considered threatened plants. Delphinium bolosii and Delphinium mansanetianum are narrowly endemic to the Eastern Iberian Peninsula, whereas Delphinium fissum ssp. sordidum is found in a few populations across the Peninsula. Delphinium fissum ssp. fissum is more widely distributed but often in small and isolated populations. In this group, Delphinium bolosii is dysploid (2 n  = 18) whereas the other taxa are diploid (2 n  = 16). A total of 12 populations were surveyed, including all known locations for D. bolosii , D. mansanetianum , and D. fissum ssp. sordidum . Eleven enzyme systems were assayed and 15 loci were resolved. Markedly depauperate values for genetic diversity were obtained for D. mansanetianum ( H _e = 0.013) and D. fissum ssp. sordidum ( H _e = 0.044). The estimates for D. fissum ssp. fissum ( H _e = 0.071) were below the values expected for widespread species. Small population size and marginal distribution have probably contributed to the low variability observed in this group. By contrast, D. bolosii exhibited comparatively larger populations and greater genetic diversity ( H _e = 0.138). We suggest that, apart from population size and local adaptation, genetic diversity during speciation may have been promoted by dysploidy through genomic recombination.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 773–784.     

High genetic variability in Neotropical myophilous orchids

The patterns of genetic variability of seven Bulbophyllum Thouars species were investigated using 14 enzymatic loci, and compared with those of other Neotropical myophilous orchid species. The genetic variability estimated was very high ( H _e = 0.39–0.61, P  = 86–100%, A  = 2.6–3.8), despite the small population sizes, which may be explained by the vegetative reproduction. Of the three species with multiple populations, only B. epiphytum showed moderate values of genetic structuring. Environmental characteristics and seed dispersal mechanisms are important in understanding the differences in the population structure observed. Almost all pairs of species showed low genetic similarity, indicating a long period of divergence. Our results suggest that B. adiamantinum and B. insectiferum , species currently classified in different sections of the genus, are more closely related than previously thought.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 33–40.     

Relative contribution of contemporary pollen and seed dispersal to the effective parental size of seedling population of California valley oak (Quercus lobata, Née)

For plant populations, gene movement through pollen and seed dispersal governs the size of local genetic neighbourhoods and shapes the opportunities for natural selection and genetic drift. A critical question is how together these two processes influence the evolutionary dynamics of local populations. To assess the respective contributions of pollen and seed flow, we propose a novel indirect assessment of the separate male and female gametic contributions to total effective parental size ( N _e), based on parental correlations estimated via kinship coefficients, that can be applied to data sets that include unambiguous genotypes for male and female gametic contributions. Using the endemic Californian valley oak ( Quercus lobata ) as our study species, we apply this method to a set of microsatellite genotypes for two distinct ecological sets of naturally recruiting seedlings with acorns attached. We found that the effective numbers of contributing male parents ( N _ep) exceed effective numbers of female parents ( N _em) for seedlings established beneath adult trees ( N _ep = 8.1 and N _em = 1.1), as well as for seedlings established away from adult trees ( N _ep = 15.4 and N _em = 2.7), illustrating that seed dispersal enhances pollen dispersal and increases the effective number of seed sources in open seedling patches. The resulting effective parental size of seedling populations translates into smaller effective numbers of parents for undispersed vs. dispersed seedlings ( N _e = 3.6 and N _e = 6.7, respectively). This study introduces a novel statistic method and provides important new evidence that, on a short-term temporal scale, seed dispersal shapes the local neighbourhood size of new recruits.     

Genetic and morphological variability of the endangered Syngonanthus mucugensis Giul. (Eriocaulaceae) from the Chapada Diamantina, Brazil: implications for conservation and taxonomy

Allozymic and morphometric studies were carried out on ten populations of Syngonanthus mucugensis (Eriocaulaceae), a species from north-eastern Brazil threatened by extinction. Genetic and morphological variability was low or moderately low in all populations, being lower in populations from Rio de Contas/Catolés ( P _L = 14.3–21.4, A  = 1.1–1.2, H _e = 0.026–0.059, D2M = 26.893–33.157) than in those from Mucugê ( P _L = 28.6–35.7, A  = 1.3–1.5, H _e = 0.078–0.164, D2M = 28.999–45.077). A high coefficient of endogamy ( F _is = 0.257) was found, which can be explained by the reproductive characteristics and distribution of the species. The values for genetic and morphological structuring ( F _st = 0.512 and A _MRPP = 0.175, respectively) were high as a result of the differentiation between populations from the two areas. The mean genetic identity between populations from the two areas (0.812) was much lower than between populations from the same area (Mucugê, 0.980; Rio de Contas/Catolés, 0.997). These results indicate that we are dealing with two distinct taxa and, as a result of the nature of the morphological differences found, a new subspecies is described for the populations of the region of Rio de Contas and Catolés, Syngonanthus mucugensis ssp. riocontensis . Such conclusions raise important implications for the conservation of Syngonanthus mucugensis , and will be used in the drawing up of management plans for its conservation.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 401–416.     

Extremely low levels of genetic diversity in the terrestrial orchid Epipactis thunbergii (Orchidaceae) in South Korea: implications for conservation

Levels of allozyme variation, population genetic structure, and fine-scale genetic structure (FSGS) of the rare, both sexually and clonally reproducing terrestrial orchid Epipactis thunbergii were examined for eight ( N  = 734) populations in a 20 × 20-km area in South Korea. Twenty-three putative allozyme loci resolved from 15 enzyme systems were used. Extremely low levels of allozyme variation were found within populations: the mean frequency of polymorphic loci was 3.8% [isocitrate dehydrogenase ( Idh-2 ) with two alleles was polymorphic across populations], the mean number of alleles per locus was 1.04, and the mean expected heterozygosity was 0.013. The overall fixation index was not significantly different from zero ( F _IS = 0.069), although the species is self-compatible. However, a significantly high degree of population differentiation was found between populations at Idh-2 ( F _ST = 0.388) in the studied area. Furthermore, spatial autocorrelation analyses revealed a significant FSGS (up to 3 m) within populations. These observations suggest that the main explanatory factors for the extremely low levels of genetic diversity and the shaping of the population genetic structure of E. thunbergii are genetic drift as a result of a small effective population size, a restricted gene flow, and the isolation of populations. Considering the current genetic structure of E. thunbergii , three guidelines are suggested for the development of conservation strategies for the species in South Korea: (1) protection of habitats of standing populations; (2) prohibition by law of any collection of E. thunbergii ; and (3) protection of nearby pollinator populations, given the fact that fruit set in natural habitats is very low.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 161–169.     

Stability of genetic structure and effective population size inferred from temporal changes of microsatellite DNA polymorphisms in the land snail Helix aspersa (Gastropoda: Helicidae)

Temporal evolution of genetic variability may have far-reaching consequences for a diverse array of evolutionary processes. Within the polders of the Bay of Mont-Saint-Michel (France), populations of the land snail Helix aspersa are characterized by a metapopulation structure with occasional extinction processes resulting from farming practices. A temporal survey of genetic structure in H . aspersa was carried out using variability at four microsatellite loci, in ten populations sampled two years apart. Levels of within-population genetic variation, as measured by allelic richness, H _e or F _is , did not change over time and similar levels of population differentiation were demonstrated for both sampling years. The extent of genetic differentiation between temporal samples of the same population established (i) a stable structure for six populations, and (ii) substantial genetic changes for four populations. Using classical F -statistics and a maximum likelihood method, estimates of the effective population size ( N _e) illustrated a mixture of stable populations with high N _e, and unstable populations characterized by very small N _e estimates (of 5–11 individuals). Owing to human disturbances, intermittent gene flow and genetic drift are likely to be the predominant evolutionary processes shaping the observed genetic structure. However, the practice of multiple matings and sperm storage is likely to provide a reservoir of variability, minimizing the eroding genetic effects of population size reduction and increasing the effective population size.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 89–102.     

Patterns of genetic diversity in related taxa of Antirrhinum L. assessed using allozymes

Allozyme diversity was studied within and among populations of five related taxa of Antirrhinum L. endemic to the Iberian Peninsula ( A. graniticum Rothm. ssp. graniticum , ssp. brachycalyx Sutton and ssp. ambiguum (Lange) Mateu & Segarra, A. boissieri Rothm. and A. onubensis (Fdez. Casas) Fdez. Casas). All of the studied taxa are obligate outcrossing endemic perennial herbs which form isolated populations. However, the taxa vary in range and population sizes, and are found on different soil types. The level and distribution of allozyme diversity differed widely between taxa: A. graniticum ssp. brachycalyx had the lowest level of allozyme diversity (H_T = 0.09), whilst the highest level was detected in A. boissieri (H_T = 0.25). Total variation was partitioned into within- and among-population variation. The proportion attributable to variation within populations varied from about 67% up to 84.3% and 89.5% in A. graniticum ssp. brachycalyx and A. graniticum ssp. ambiguum , respectively. Both these subspecies also showed little population divergence (G_ST = 0.10 and 0.09, respectively) and had high levels of estimated gene flow (Nm = 2.18 and 2.62, respectively). These results are discussed in relation to geographical proximity of populations and habitat continuity. Isolation by distance was not detected in any of the studied taxa. This result suggests that divergence among populations is due to random genetic drift.  © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 79 , 299–307.     

Chloroplast DNA variation in the shrub Justicia areysiana (Acanthaceae) endemic to the monsoon affected coastal mountains of the southern Arabian Peninsula

The monsoon affected mountains of the southern Arabian Peninsula harbour in climatically favoured refugia vegetation elements of palaeo-African origin. To understand better the temporal and spatial differentiation of these refugia, chloroplast variation in Justicia areysiana Deflers (Acanthaceae), a shrub species endemic to the Yemeni and Omani mountains close to the Arabian Sea, was studied using PCR-RFLP and chloroplast microsatellite diversity. Eleven haplotypes were characterized and show a distinct geographical distribution pattern with a deep split between populations from south Yemeni fog oases and those from Hawf Mountains/Dhofar region in east Yemen and south Oman. Very limited haplotype diversity within populations (h_S = 0.15) and a high level of population differentiation (G_ST = 0.81) demonstrate the strong genetic isolation of populations from each other. Past oscillations between humid and arid periods connected with glacial and interglacial episodes in the Pleistocene and Holocene are considered responsible for the observed patterns of genetic variation.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 437–444.     

Microsatellite DNA analysis of northern pike (Esox lucius L.) populations: insights into the genetic structure and demographic history of a genetically depauperate species

The northern pike Esox lucius L. is a freshwater fish exhibiting pronounced population subdivision and low genetic variability. However, there is limited knowledge on phylogeographical patterns within the species, and it is not known whether the low genetic variability reflects primarily current low effective population sizes or historical bottlenecks. We analysed six microsatellite loci in ten populations from Europe and North America. Genetic variation was low, with the average number of alleles within populations ranging from 2.3 to 4.0 per locus. Genetic differentiation among populations was high (overall θ_ST = 0.51; overall ρ_ST = 0.50). Multidimensional scaling analysis of genetic distances between populations and spatial analysis of molecular variance suggested a single phylogeographical race within the sampled populations from northern Europe, whereas North American and southern European populations were highly distinct. A population from Ireland was monomorphic at all loci, presumably reflecting founder events associated with introduction of the species to the island in the sixteenth century. Bayesian analysis of demographic parameters showed differences in θ (a product of effective population size and mutation rate) among populations from large and small water bodies, but the relative differences in θ were smaller than expected, which could reflect population subdivision within the larger water bodies. Finally, the analyses showed drastic population declines on a time scale of several thousand years within European populations, which we ascribe to either glacial bottlenecks or postglacial founder events.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 91–101.     

Population divergence in the amphicarpic species Amphicarpaea edgeworthii Benth. (Fabaceae): microsatellite markers and leaf morphology

Comparative analyses of the genetic differentiation in microsatellite markers ( F _ST) and leaf morphology characters ( Q _ST) of Amphicarpaea edgeworthii Benth. were conducted to gain insight into the roles of random processes and natural selection in the population divergence. Simple sequence repeat analyses on 498 individuals of 19 natural populations demonstrate that a significant genetic differentiation occurs among populations (mean F _ST = 0.578), and A. edgeworthii is a highly self-fertilized species (mean selfing rate s  = 0.989). The distribution pattern of genetic diversity in this species shows that central populations possess high genetic diversity (e.g. population WL with H _E = 0.673 and population JG with H _E = 0.663), whereas peripheral ones have a low H _E as in population JD (0.011). The morphological divergence of leaf shape was estimated by the elliptical Fourier analysis on the data from 11 natural and four common garden populations. Leaf morphology analyses indicate the morphological divergence does not show strong correlation with the genetic differentiation ( R  = 0.260, P  = 0.069). By comparing the 95% confidence interval of Q _ST with that of F _ST, Q _ST values for five out of 12 quantitative traits are significantly higher than the average F _ST value over eight microsatellite loci. The comparison of F _ST and Q _ST suggests that two kinds of traits can be driven by different evolutionary forces, and the population divergence in leaf morphology is shaped by local selections.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 505–516.     

Comparing direct vs. indirect estimates of gene flow within a population of a scattered tree species

The comparison between historical estimates of gene flow, using variance in allelic frequencies, and contemporary estimates of gene flow, using parentage assignment, is expected to provide insights into ecological and evolutionary processes at work within and among populations. Genetic variation at six microsatellite loci was used to quantify genetic structure in the insect-pollinated, animal-dispersed, low-density tree Sorbus torminalis L. Crantz, and to derive historical estimates of gene flow. The neighbourhood size and root-mean-squared dispersal distance inferred from seedling genotypes ( N _b  = 70 individuals, σ _e  = 417 m) were similar to those inferred from adult genotypes ( N _b  = 114 individuals, σ _e  = 472 m). We also used parentage analyses and a neighbourhood model approach after an evaluation of the statistical properties of this method on simulated data. From our data, we estimated even contributions of seed- and pollen-mediated dispersal to the genetic composition of established seedlings, with both fat-tailed pollen and seed dispersal kernels, and slightly higher mean distance of pollen dispersal (248 m) as compared to seed dispersal (135 m). The resulting contemporary estimate of gene dispersal distance (σ _c  = 211 m) was ∼twofold smaller than the historical estimates. Besides different assumptions and statistical nuances of both approaches, this discrepancy is likely to reflect a recent restriction in the scale of gene flow which requires manager's attention in a context of increasing forest fragmentation.     

Low genetic diversity and allozymic evidence for autopolyploidy in the tetraploid Pyrenean endemic larkspur Delphinium montanum (Ranunculaceae)

Allozyme electrophoresis was conducted to survey the levels and distribution of genetic diversity in the tetraploid perennial larkspur Delphinium montanum (Ranunculaceae), which is endemic to the eastern Pyrenees of Spain and France and considered to be endangered. Seven populations were sampled, resolving 14 putative enzymatic loci belonging to eight enzymes. Banding patterns stained in gels revealed several enzymatic duplications attributable to autotetraploidy, such as the presence of both balanced and unbalanced heterozygotes and the lack of fixed heterozygosity. However, variability in D. montanum ( P  = 23.8%, A  = 1.48, and H _e = 0.082) was lower than that expected for an autotetraploid species. This, in addition to the scarcity of loci showing three or four different alleles, could indicate that this species has suffered genetic erosion through population bottlenecks, or, alternatively, that it is undergoing diploidization.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 211–222.     

Genetic variation and clonal diversity in island Cephalanthera rubra populations from the Biebrza National Park, Poland

Three populations of the orchid species Cephalanthera rubra localized on neighbouring mineral islands in the Biebrza National Park (north-east Poland) were examined using 16 allozyme loci. The percentage of polymorphic loci in these C. rubra populations ranged from 25 to 31.3% and the mean number of alleles per polymorphic locus from 1.25 to 1.31. The levels of observed heterozygosity at polymorphic loci were higher than expected for all populations. The overabundance of heterozygotes was noted in every population. The values of fixation indices were highly negative. The genetic differentiation among the three populations was small ( F _ST = 0.0173), albeit statistically significant ( P  < 0.001). The level of gene flow varied from 13 to 16. Fourteen multilocus genotypes were found among the 401 ramets sampled from the populations. Only four of them were common for all populations. The frequency of genotypes was different in these three populations of C. rubra . Some of the multilocus genotypes dominated in the given populations, others were found sporadically. Genetic variation within C. rubra populations is mainly the result of small population sizes and reflects the influences of breeding system and type of reproduction. On the other hand, these properties are also connected with habitat conditions.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 99–108.     

Genetic structure of fragmented November moth (Lepidoptera: Geometridae) populations in farmland

Habitats are now becoming increasingly fragmented throughout the world due to intense cultivation. As a consequence, populations of some animals with low mobility have become isolated, thus increasing the risk of inbreeding and local extinction. In Britain, weakly flying geometric moths of the genus Epirrita are a good model species with which to test the genetic effects of habitat fragmentation on insect populations. Genetic variation within and between populations of two Epirrita species captured using a network of light traps at two spatial scales (local and national) was assessed using allozyme electrophoresis, with particular reference to the local scale (the 330-ha arable farm estate at Rothamsted, Hertfordshire, in southern Britain). Populations sampled widely in England and Wales displayed low (but statistically significant) levels of genetic differentiation for both species ( F _st  = 0.0051–0.0114 and 0.0226 for E. dilutata and E. christyi , respectively). However, analysis of large samples of E. dilutata from four small woods at Rothamsted revealed low ( F _st  = 0.0046) but significant differentiation, indicating that gene flow was restricted, even at this very small scale. It was concluded that small intervening patches of farmland (often a few fields width) were enough to prevent genetic homogeneity. The close similarity between more distant Epirrita populations was considered to be a result of historical, rather than recurrent gene flow, as genetic equilibrium between drift and gene flow is unlikely over such scales.  © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78 , 467–477.     

Cryptic speciation, genetic diversity and gene flow in the California turret spider Atypoides riversi (Araneae: Antrodiaetidae)

Populations of the turret spider Atypoides riversi from eight central Californian sites were compared based on variation at ten allozyme loci. Multidimensional scaling of interpopulation genetic distances defined four population units (Coast Range, Sierran, Valley, Jenness Camp), corroborating the distinctness of Coast Range and Sierran populations indicated by a prior study. While the species status of these units has yet to be determined, Jenness Camp is the most likely to represent a new species, given its clear genetic uniqueness (two fixed allelic differences). Populations in all units were generally in Hardy–Weinberg equilibrium with no evidence of inbreeding, though variability was minimal (mean H _o = 2.8%, mean P  = 15.4%). Reduced variability in these populations may be the result of repeated bottlenecks, environmental homogeneity, and/or directional selection. Interpopulation differentiation within units was significant in the absence of intervening forest habitat and was substantially less in its presence, indicating that gene flow is likely only when forest corridors exist. To foster preservation of the existing gene pool and enhance participation in it, management of the units of At. riversi should focus on maintaining as many populations in situ as possible and facilitating connections between them, while also creating or restoring habitat for potential colonization.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 27–37.     

Genetic structure and differentiation of Gentiana atuntsiensis W. W. Smith and G. striolata T. N. Ho (Gentianaceae) as revealed by ISSR markers

The Hengduan Mountains are the core region of the Himalaya hotspot, and are renowned for their high levels of endemism. Gentiana atuntsiensis and G. striolata are two closely related and morphologically similar species endemic to this region. In this study, inter-simple sequence repeat (ISSR) markers were used to investigate the genetic structure within these two species, as well as the differentiation between them. An analysis of molecular variance-derived estimate demonstrated only 13.5% of genetic differentiation between the two species. Considering their adjacent distribution patterns, low genetic divergence, and clear clustering into two groups, it is hypothesized that the two species arose from a rapid and recent speciation event induced mainly by geographical isolation. A relatively high level of genetic diversity was revealed in each species (Shannon's index of diversity: H _sp = 0.324 and 0.391; H _pop = 0.225 and 0.274; for G. atuntsiensis and G. striolata , respectively). Most of the genetic variation was partitioned within populations ( Ø _ST = 0.232 and 0.226 in G. atuntsiensis and G. striolata , respectively). The large population sizes, outcrossing breeding system, and small, light seeds that disperse widely may explain the genetic structure in both species.  © 2007 The Linnean Society of London. Botanical Journal of the Linnean Society , 2007, 154 , 225–232.     

Low population differentiation and high genetic diversity in the invasive species Carduus acanthoides L. (Asteraceae) within its native range in the Czech Republic

Colonizing species are predicted to suffer from reductions in genetic diversity during founding events. Although there is no unique mode of reproduction that is characteristic of successful plant colonizers, many of them are predominantly self-fertilizing or apomictic species, and almost all outcrossing colonizers are self-compatible. Carduus acanthoides comprises a species of disturbed habitats with wind-dispersed seeds that colonizes open spaces of various sizes. Population genetic diversity was expressed by assessing patterns of variation at nine putatively neutral allozyme loci within and among 20 natural populations in its native distribution range in the Czech Republic. Overall, C. acanthoides displayed high levels of genetic diversity compared to other herbaceous plants. The percentage of polymorphic loci was 84.5, with values of 2.37, 0.330, and 0.364 for the mean number of alleles per polymorphic locus ( A ), observed heterozygosity ( H _o), and expected heterozygosity ( H _e), respectively. There was only weak evidence of inbreeding within populations ( f  = 0.097) and very low genetic differentiation among populations ( θ  = 0.085). Analyses of the data provide strong evidence for isolation-by-distance for the whole study area. Even the colonizing species, C. acanthoides , currently supports a substantial amount of allozyme variation at both the species and population levels.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 596–607.     

Population genetic structure in Myrtus communis L. in a chronically fragmented landscape in the Mediterranean: can gene flow counteract habitat perturbation?

Ancient managed landscapes provide ideal opportunities to assess the consequences of habitat fragmentation on the patterns of genetic diversity and gene flow in long-lived plant species. Using amplified fragment length polymorphism (AFLP) and allozyme markers, we quantified seed-mediated gene flow and population genetic diversity and structure in 14 populations of Myrtus communis (myrtle), a common endozoochorous shrub species of forest patches in lowland agricultural Mediterranean areas. Overall, allozyme diversity for myrtle was low (P₉₅   =   25%; A   =   1.411; H_e = 0.085) compared to other known populations, and a significant portion of populations (57%) had lower levels of allelic diversity and/or heterozygosity than expected at random, as shown by simulated resampling of the whole diversity of the landscape. We found significant correlations between allozyme variability and population size and patch isolation, but no significant inbreeding in any population. Genetic differentiation among populations for both allozyme and AFLP markers was significant (Φ_ST = 0.144 and Φ_ST = 0.142, respectively) but an isolation-by-distance pattern was not detected. Assignment tests on AFLP data indicated a high immigration rate in the populations ( ca. 20–22%), likely through effective seed dispersal across the landscape by birds and mammals. Our results suggest that genetic isolation is not the automatic outcome of habitat destruction since substantial levels of seed-mediated gene flow are currently detectable. However, even moderate rates of gene flow seem insufficient in this long-lived species to counteract the genetic erosion and differentiation imposed by chronic habitat destruction.     

Genetics of the peripheral populations of the alpine bullhead, Cottus poecilopus (Scorpaeniformes, Cottidae) in Poland

The alpine bullhead ( Cottus poecilopus ) in Poland is highly polymorphic ( P for examined populations in the range of 0.0–0.45, mean P  = 0.11, P for species 0.64) in seven out of 11 loci studied ( Pgd-1, Mdh-1, Ck-1, Gpd-1, Gpd-2, Gpi-1, Gpi-2 ). However, they reveal very low heterozygosity (mean H _o = 0.007, mean H _e = 0.019), which may result from population subdivisions, small genetically effective size ( N _e) of some populations and frequent inbreeding, the latter being probably mediated through polygyny. The index of genetic differentiation ( G _ST) for the Polish metapopulation equals 0.48, which is relatively high. By far, the strongest are genetic differences between the Sudeten-Carpathian group and the Hańcza population. Gene flow between the Sudeten-Carpathian group and the Hańcza population is very limited and their divergence may have started as early as the last (Eemian) interglacial period.