Characterization of microsatellite markers in cassava based on microsatellite-AFLP technique

We developed molecular markers for cassava based on the microsatellite-amplified fragment length polymorphism (M-AFLP) technique. Twenty primer pairs were developed and used for the analysis of 48 samples of Manihot species, consisting of M. esculenta (33), M. esculenta ssp flabellifolia (3), M. chlorosticta (3), M. carthaginensis (3), M. filamentosa (3), and M. tristis (3). Nine microsatellite loci that were polymorphic among these Manihot species were identified, giving 32 polymorphic alleles and from two to seven alleles per locus. Unbiased and direct count heterozygosity varied from 0.0233 to 0.7924 and 0.0000 to 0.7083, respectively. There was significant deviation (P < 0.05) from Hardy-Weinberg equilibrium at five loci. Genotypic data from the Manihot species were subjected to genetic diversity analysis. We found that M. chlorosticta and M. esculenta ssp flabellifolia were the closest populations, while M. filamentosa and M. esculenta ssp flabellifolia were the most divergent. Considering within M. esculenta, the samples from Nigeria and Fiji were the most closely related, while those from Venezuela and of unknown origin were the most divergent. We conclude that the M-AFLP technique is an effective method for generating microsatellite markers that are useful for genetic diversity analysis in Manihot species.     

Population history of Manihot esculenta (Euphorbiaceae) inferred from nuclear DNA sequences

The nature of gene flow in plants -- including the propensity for interspecific introgression -- makes them interesting candidates for phylogeographical analysis. Plant phylogeography studies have been limited, however, by the availability of suitable intraspecific variation. In this study, DNA sequence variation from a nuclear gene [Glyceraldehyde 3-phosphate dehydrogenase; (G3pdh)] was used to examine the population history of Manihot esculenta ssp. flabellifolia and a potentially hybridizing species, M. pruinosa. These species occur in the rainforest-savanna ecotone adjoining the Amazon basin, a region believed to have undergone major habitat shifts since the Pleistocene. Geographical distributions of the G3pdh haplotypes indicate genetic isolation-by-distance across the range of M. esculenta ssp. flabellifolia. However, there is greater genetic similarity between northeastern and western populations than would be expected given the present species distribution. A nested clade analysis suggests that northeastern and western populations were connected by gene flow until relatively recently, when they became fragmented. This inferred fragmentation event is consistent with post-Pleistocene habitat shifts proposed for the Amazon basin. At the interspecific level, haplotype sharing with M. pruinosa may reflect either recent interspecific introgression or incomplete lineage sorting between these closely related species.     

Evolution under domestication: contrasting functional morphology of seedlings in domesticated cassava and its closest wild relatives

Although cassava (Manihot esculenta ssp. esculenta) is asexually propagated, farmers incorporate plants from seedlings into planting stocks. These products of sex are exposed to selection, which in agricultural environments should favour rapid growth. To examine whether seedling morphology has evolved under domestication, we compared domesticated cassava, its wild progenitor (M. esculenta ssp. flabellifolia) and their sister species (M. pruinosa) under controlled conditions. Field observations complemented laboratory study. In both wild taxa, the hypocotyl did not elongate (hypogeal germination) and cotyledons remained enclosed in the testa. In domesticated cassava, the hypocotyl elongated (epigeal germination), and cotyledons emerged and became foliaceous. The difference in hypocotyl elongation was fixed, whereas cotyledon morphology varied with environmental conditions in M. pruinosa. Comparative analysis suggests that epigeal germination is primitive in Manihot, that the lineage including wild ancestors of cassava evolved hypogeal germination--which confers greater tolerance to risks in their savanna environment--and that with domestication, there was a reversion to epigeal germination and photosynthetic cotyledons, traits conferring high initial growth rates in agricultural habitats.     

Microsatellite variation in cassava (Manihot esculenta, Euphorbiaceae) and its wild relatives: further evidence for a southern Amazonian origin of domestication

Genetic variation at five microsatellite loci was used to investigate the evolutionary and geographical origins of cassava (Manihot esculenta subsp. esculenta) and the population structure of cassava's wild relatives. Two hundred and twelve individuals were sampled, representing 20 crop accessions, 27 populations of cassava's closest wild relative (M. esculenta subsp. flabellifolia), and six populations of a potentially hybridizing species (M. pruinosa). Seventy-three alleles were observed across all loci and populations. These data indicate the following on cassava's origin: (1) genetic variation in the crop is a subset of that found in the wild M. esculenta subspecies, suggesting that cassava is derived solely from its conspecific wild relative. (2) Phenetic analyses group cassava with wild populations from the southern border of the Amazon basin, indicating this region as the likely site of domestication. (3) Manihot pruinosa, while closely related to M. esculenta (and possibly hybridizing with it where sympatric), is probably not a progenitor of the crop. Genetic differentiation among the wild populations is moderately high (F:(ST) = 0.42, rho(ST) = 0.54). This differentiation has probably arisen primarily through random genetic drift (rather than mutation) following recent population divergence.     

Development of polymorphic markers from expressed sequence tags of Manihot esculenta Crantz

In this study, 49 primers were designed from sequences containing di-, tri-, tetra-, penta- and hexanucleotide motifs with a minimum of four repeats and presence of motif size polymorphisms (insertion/deletion) from cassava (Manihot esculenta Crantz) expressed sequence tags deposited in public sequence database. Each locus was subsequently screened on 29 M. esculenta Crantz obtained from 15 different countries. Cross-amplification was tested with M. esculenta Crantz (ssp. flabellifolia) and four different Manihot species, M. chlorosticta, M. carthaginensis, M. filamentosa and M. tristis. Of these, nine loci showed polymorphic profiles within M. esculenta Crantz, which revealed two to four alleles per locus. The average unbiased and direct count heterozygosities were 0.4901 and 0.5674, respectively.     

Insights on the evolution of a vegetatively propagated crop species

The opportunity for gene flow between a vegetatively propagated crop and its wild relatives is expected to be much lower than for seed-propagated crops, since sexual reproduction in the crop occurs only infrequently. A study by Duputié and colleagues now demonstrates evidence of sexual reproduction between a vegetatively propagated crop and a closely related wild congener. Working in French Guiana, these workers have documented a hybrid zone arising from introgression between cassava (Manihot esculenta ssp. esculenta, Euphorbiaceae), which is propagated by stem cuttings, and wild Manihot populations growing in close proximity. Patterns of heterozygosity suggest that there are little-to-no barriers to reproduction between the crop and these wild populations. Previous work by these researchers has documented the importance of occasional sexual reproduction for the development of cassava varieties in traditional Amerindian farming systems. Taken together with their previous work, these new findings suggest that gene flow between wild Manihot populations and cassava plants could potentially play a much greater role in the crop's evolution than previously thought.     

Landscape genetic connectivity in European wildcat (Felis silvestris silvestris): a matter of food,shelters and demographic status of populations

Understanding landscape impacts on gene flow is necessary to plan comprehensive management and conservation strategies of both the species of interest and its habitat. Nevertheless, only a few studies have focused on the landscape genetic connectivity of the European wildcat, an umbrella species whose conservation allows the preservation of numerous other species and habitat types. We applied population and landscape genetics approaches, using genotypes at 30 microsatellites from 232 genetically-identified wildcats to determine if, and how, landscape impacted gene flow throughout France. Analyses were performed independently within two population patches: the historical north-eastern patch and the central patch considered as the colonization front. Our results showed that gene flow occurred at large spatial scales but also revealed significant spatial genetic structures within population patches. In both population patches, arable areas, pastures and permanent grasslands and lowly fragmented forested areas were permeable to gene flow, suggesting that shelters and dietary resources are among the most important parameters for French wildcat landscape connectivity, while distance to forest had no detectable effect. Anthropized areas appeared highly resistant in the north-eastern patch but highly permeable in the central patch, suggesting that different behaviours can be observed according to the demographic context in which populations are found. In line with this hypothesis, spatial distribution of genetic variability seemed uneven in the north-eastern patch and more clinal in the central patch. Overall, our results highlighted that European wildcat might be a habitat generalist species and also the importance of performing spatial replication in landscape genetics studies.

     

Biological parameters of Bemisia tabaci (Gennadius) biotype B (Hemiptera: Aleyrodidae) on Jatropha gossypiifolia, commercial (Manihot esculenta) and wild cassava (Manihot flabellifolia and M. carthaginensis) (Euphorbiaceae)

Bemisia tabaci (Gennadius) is one of the most important pests of cassava in Africa and several countries of Asia due to the damage caused by direct feeding, the excretion of honeydew, and its capacity as a vector of cassava mosaic geminivirus. There is a general consensus that B. tabaci is a complex of morphologically indistinguishable populations with different biotypes. In the Americas, the polyphagous biotype B does not appear to feed on cassava. Recent studies indicate that it is possible, however, for biotype B to gradually adapt to cassava using phylogenetically related hosts. Therefore, the possibility that some wild species of cassava constitute intermediate hosts in the adaptation process may lead to the establishment of biotype B on commercial varieties of Manihot esculenta. In here, we evaluated Jatropha gossypiifolia, two wild species of cassava (Manihot flabellifolia and M. carthaginensis) and a commercial cassava variety (MCol 2063) as hosts of biotype B. The highest oviposition rate (2.7 eggs /two days) occurred on M. esculenta, although the development time (44 d) was the longest when compared to M. carthaginensis and J. gossypiifolia. About 60% of the population could reproduce on the wild cassava species vs. 55% on J. gossypiifolia and 27.5% on the commercial variety. Our data suggest that J. gossypiifolia is a suitable host and the wild species M. carthaginensis can constitute a potential intermediate host in the adaptation of biotype B to commercial varieties of cassava.     

Pleistocene expansion and connectivity of mesic forests inside the South American Dry Diagonal supported by the phylogeography of a small lizard*

Traditionally focused on Amazonian and Atlantic rainforests, studies on the origins of high Neotropical biodiversity have recently shifted to also investigate biodiversity processes in the South American dry diagonal, encompassing Chaco, Cerrado savannas, and Caatinga seasonally dry tropical forests. The plateau/depression hypothesis states that riparian forests in the Brazilian Shield in central Brazil are inhabited by Pleistocene lineages, with shallow divergences and signatures of population expansion. Moreover, riparian forests may have acted as a vegetation network in the Pleistocene, allowing gene/species flow across the South American dry diagonal. We tested these hypotheses using Colobosaura modesta, a small gymnophthalmid lizard from forested habitats in the Cerrado savannas and montane/submontane forests in the Caatinga. We conducted phylogeographic analyses using a multi-locus dataset, tested alternative demographic scenarios with Approximate Bayesian Computation, and also employed species delimitation tests. We recovered a history of recent colonization and expansion along riparian forests, associated with Pleistocene climate shifts, and the existence of a new species of Colobosaura restricted to the Serra do Cachimbo region. We also present evidence that riparian forests have provided an interconnected network for forest organisms within the South American dry diagonal and that Pleistocene events played an important role in their evolutionary history.     

Cross-species amplification of cassava (Manihot esculenta) (Euphorbiaceae) microsatellites: allelic polymorphism and degree of relationship

Microsatellite amplification was performed on cassava (Manihot esculenta) and six other different species (all wild) of the Manihot genus. We used ten pairs of microsatellite primers previously developed from cassava, detecting 124 alleles in a sample of 121 accessions of the seven species. The number of alleles per locus ranged from four to 21 alleles, and allelic diversity was greater in the wild species than in cassava. Seventy-nine alleles, including unique ones, were detected in the wild species but were not found in the crop. The lower level of heterozygosity in some wild species probably resulted from a combination of fine-scale differentiation within the species and the presence of null alleles. Overall, microsatellite primers worked across the genus, but, with increasing genetic distance, success in amplifying loci tended to decrease. No accession of M. aesculifolia, M. carthaginensis, and M. brachyloba presented a banding pattern at locus Ga-140; neither did one appear for M. aesculifolia at locus Ga-13. Previous work with amplified fragment length polymorphism (AFLP) markers and this microsatellite analysis show that these three wild taxa are the most distant relatives of the crop, whereas the wild forms M. esculenta subsp. flabellifolia and M. esculenta subsp. peruviana appear to be the closest.     

New insights into the genetic structure of Araucaria araucana forests based on molecular and historic evidences

The conservation of genetic resources is a prerequisite for the maintenance of long-lived forest species. Araucaria araucana (Mol.) K. Koch is one of the oldest conifers in South America and a representative symbol of Chilean forest due to its endemicity and longevity. The aim of this study was to evaluate the genetic structure of the current A. araucana populations in Chile, to verify the possible genetic divergence between Coastal and Andean populations and to assess whether bottleneck events have influenced habitat fragmentation and threaten the genetic resources and evolutionary potential of the species. Twelve natural populations, nine from the Andes Cordillera and three from the Coast Cordillera were analysed by means of eight genomic microsatellite markers developed in A. araucana. Results of analysis of molecular variance (AMOVA) highlighted significant differentiation between Coastal and Andean populations (16 %; P?=?0.004), detecting one significant barrier that separated populations from both Cordilleras as maximally differentiated areas. At local scale, both ranges revealed significant inter-population differentiation, with higher values for Coastal populations compared with Andean populations. These results suggested the presence of four gene pools (three in the Andes and one in the Coast Cordilleras) and one population (VIL) in the Coast Cordillera that differed to the rest. The differentiation between the Andean and Coastal populations may provide important baseline data that should allow further studies of landscape genetics in the species and that can contribute to develop conservation strategies for its genetic resources.     

Size asymmetry in intraspecific competition and the density-dependence of inbreeding depression in a natural plant population: a case study in cassava (Manihot esculenta Crantz, Euphorbiaceae)

The effects of competition on the genetic composition of natural populations are not well understood. We combined demography and molecular genetics to study how intraspecific competition affects microevolution in cohorts of volunteer plants of cassava (Manihot esculenta) originating from seeds in slash-and-burn fields of Palikur Amerindians in French Guiana. In this clonally propagated crop, genotypic diversity is enhanced by the incorporation of volunteer plants into farmers' stocks of clonal propagules. Mortality of volunteer plants was density-dependent. Furthermore, the size asymmetry of intraspecific competition increased with local clustering of plants. Size of plants was correlated with their multilocus heterozygosity, and stronger size-dependence of survival in clusters of plants, compared with solitary plants, increased the magnitude of inbreeding depression when competition was severe. The density-dependence of inbreeding depression of volunteer plants helps explain the high heterozygosity of volunteers that survive to harvest time and thus become candidates for clonal propagation. This effect could help favour the maintenance of sex in this 'vegetatively' propagated crop plant.     

Genetic structure of the xerophilous bromeliad Pitcairnia geyskesii on inselbergs in French Guiana – a test of the forest refuge hypothesis

Inselbergs are isolated granitic rock outcrops that provide distinctive ecological conditions. In northern South America they rise above the surrounding rainforest. Among inselberg specialists, Pitcairnia geyskesii (Bromeliaceae) is restricted to these habitats in French Guiana. We studied populations from 12 inselbergs using 7 microsatellite loci to give a "reverse image" of the reduction-expansion of the rainforest in the context of the refuge hypothesis. Our analyses showed that populations are fragmented with dispersal occurring only over very short distances. Genetic diversity was higher in northern French Guiana, whereas specific alleles were observed in the south. The results point to the occurrence of a dry corridor in the north, as hypothesized by Tardy (1998) based on charcoal analyses, whereas de Granville's (1982) hypothesis of a unique past refuge is not confirmed. Moreover, our data suggests the importance of Oyapock River as a pathway for range expansion, arguing against the potential role of the Inini-Camopi Mountains as a physical barrier. Finally, in spite of a strongly argued scenario in favour of a north-to-south migration history, a clear genetic isolation of P. geyskesii populations living on inselbergs of the Mitaraka archipelago suggests a distinct ancestry of the most southern populations.     

Ecology and Distribution of Melastomataceae in African Rain Forest Inselbergs1

The ecology and distribution of thirty‐seven Melastomataceae species found on 29 inselbergs in the rain forest of Equatorial Guinea, Gabon, and Cameroon are described. The relative contributions of climatic determinism, and stochastic and historical processes to the present distribution of the species amongst the study sites are investigated. Inselbergs are rock outcrops enduring very harsh edaphic and microclimatic conditions, forming “xeric islands” in the rain forest, where natural grasslands develop. For each Melastomataceae species, the habitats where they were collected on the inselbergs and in other biotopes were listed, and their phytogeographical distribution was established. Three species are restricted to rock outcrops. Most species are distributed inside the Guineo‐Congolian Region. Three species have disjunct distributions on rain forest inselbergs and have their main distribution area outside the forested zone. The distribution of the species amongst the inselbergs is correlated to the altitude and the annual rainfall of the sites, and to inselberg geographical location. This correlation of the species distribution with the geographical location of the inselberg is attributed to the spatial autocorrelation of environmental variables and to the combined effects of the history of past vegetation changes due to climatic fluctuations and dispersal limitation.     

Switchgrass (Panicum virgatum L.) Genotypes Differ between Coastal Sites and Inland Road Corridors in the Northeastern US

Switchgrass (Panicum virgatum L.) is a North American grass that exhibits vast genetic diversity across its geographic range. In the Northeastern US, local switchgrass populations were restricted to a narrow coastal zone before European settlement, but current populations inhabit inland road verges raising questions about their origin and genetics. These questions are important because switchgrass lines with novel traits are being cultivated as a biofuel feedstock, and gene flow could impact the genetic integrity and distribution of local populations. This study was designed to determine if: 1) switchgrass plants collected in the Long Island Sound Coastal Lowland coastal Level IV ecoregion represented local populations, and 2) switchgrass plants collected from road verges in the adjacent inland regions were most closely related to local coastal populations or switchgrass from other geographic regions. The study used 18 microsatellite markers to infer the genetic relationships between 122 collected switchgrass plants and a reference dataset consisting of 28 cultivars representing ecotypes, ploidy levels, and lineages from North America. Results showed that 84% of 88 plants collected in the coastal plants were most closely aligned with the Lowland tetraploid genetic pool. Among this group, 61 coastal plants were similar to, but distinct from, all Lowland tetraploid cultivars in the reference dataset leading to the designation of a genetic sub-population called the Southern New England Lowland Tetraploids. In contrast, 67% of 34 plants collected in road verges in the inland ecoregions were most similar to two Upland octoploid cultivars; only 24% of roadside plants were Lowland tetraploid. These results suggest that cryptic, non-local genotypes exist in road verges and that gene flow from biofuels plantations could contribute to further changes in switchgrass population genetics in the Northeast.     

Historical diversification of a terra-firme forest bird superspecies: a phylogeographic perspective on the role of different hypotheses of Amazonian diversification

Among those few hypotheses of Amazonian diversification amenable to falsification by phylogenetic and population genetics methods, three can be singled out because of their general application to vertebrates: the riverine barrier, the refuge, and the Miocene marine incursion hypotheses. I used phylogenetic and population genetics methods to reconstruct the diversification history of the upland (terra-firme) forest superspecies Xiphorhynchus spixii/elegans (Aves: Dendrocolaptidae) in Amazonia, and to evaluate predictions of the riverine barrier, refuge, and Miocene marine incursion hypotheses. Phylogeographic and population genetics analyses of the X. spixiilelegans superspecies indicated that the main prediction of the riverine barrier hypothesis (that sister lineages occur across major rivers) hold only for populations separated by "clear-water" rivers located on the Brazilian shield, in central and eastern Amazonia; in contrast, "white-water" rivers located in western Amazonia did not represent areas of primary divergence for populations of this superspecies. The main prediction derived from the refuge hypothesis (that populations of the X. spixii/elegans superspecies would show signs of past population bottlenecks and recent demographic expansions) was supported only for populations found in western Amazonia, where paleoecological data have failed to support past rainforest fragmentation and expansion of open vegetation types; conversely, populations from the eastern and central parts of Amazonia, where paleoecological data are consistent with an historical interplay between rainforest and open vegetation types, did not show population genetics attributes expected under the refuge hypothesis. Phylogeographic and population genetics data were consistent with the prediction made by the Miocene marine incursion hypothesis that populations of the X. spixii/elegans superspecies found on the Brazilian shield were older than populations from other parts of Amazonia. In contrast, the phylogeny obtained for lineages of this superspecies falsified the predicted monophyly of Brazilian shield populations, as postulated by the Miocene marine incursion hypothesis. In general, important predictions of both riverine barrier and Miocene marine incursion hypotheses were supported, indicating that they are not mutually exclusive; in fact, the data presented herein suggest that an interaction among geology, sea level changes, and hydrography created opportunities for cladogenesis in the X. spixii/elegans superspecies at different temporal and geographical scales.     

Population genetic structure in the dioecious pioneer plant species Hippophae rhamnoides investigated by random amplified polymorphic DNA (RAPD) markers

Hippophae rhamnoides is an outcrossing pioneer plant species with a severely fragmented distribution. Random amplified polymorphic DNA (RAPD) marker variation was analysed in 10 populations of ssp. rhamnoides and in one population of ssp. mongolica to estimate the amount and distribution of genetic variability. No less than 89.7% of the scorable markers were polymorphic, but few of these were fixed and populations consequently differed mainly by frequency variation of individual markers. Within-population gene diversity was somewhat low for an outcrossing plant species: 0.192 or 0.159 for ssp. rhamnoides , depending on whether it was based on all 156 polymorphic RAPDs or on only those 63 RAPDs that fulfilled the 3/ N criterion. Analysis of molecular variance applied to the ssp. rhamnoides showed only 15% between-population variability, indicating a relatively restricted population differentiation as expected in outcrossing species and shown in several other AMOVA studies. The tendency for island populations to be somewhat more differentiated, and to have less within-population diversity than mainland populations, may indicate an effect of population fragmentation. Genetic distance estimates among populations, obtained with and without pruning of RAPD loci on the basis of the 3/ N criterion, were generally in very good agreement. Cluster analyses and principal coordinate analyses showed populations of ssp. rhamnoides to be rather close, but quite isolated from the single ssp. mongolica population. Genetic and geographical distances between the ssp. rhamnoides populations were not associated, indicating that large-scale geographical and ecotypic differentiation was not reflected in the RAPD profiles.     

Immigration and in situ glacial survival of the low-alpine Erinus alpinus (Scrophulariaceae)

It has been hypothesized that the subalpine Erinus alpinus survived the Pleistocene glaciation in southern French refugia peripheral to the Alps and postglacially immigrated to its northern Alpine distribution (tabula rasa hypothesis). However, E. alpinus is also known from nunataks in the northern Prealps. PCR–RFLP of the cpDNA revealed no variation, whereas AFLPs identified three phylogeographical groups among the 22 populations: (1) a central Swiss group, (2) a single central Swiss population on Mount Rigi, and (3) all other populations located to the west and east of the central Swiss group (west-eastern populations). The population representing the putative French refugium was not distinct from the west-eastern populations but was different from the populations of central Switzerland. We consider this support for locally restricted in situ survival of E. alpinus in the northern Prealps or nearby Jura mountains (dating back to 60–28 ky BP). However, the west-eastern gene-pool probably immigrated postglacially from southern France through the prealpine lowlands (not before 14.6 kyr BP), skirting central Switzerland. The near-absence of gene flow among the central Swiss and the west-eastern populations may be the reason why these historical genetic patterns are still detectable.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77, 87–103.     

Reproduction and hybrid load in all-hybrid populations of Rana esculenta water frogs in Denmark

All-hybrid populations of the water frog, Rana esculenta, are exceptional in consisting of independently and to some extent sexually reproducing interspecific hybrids. In most of its range R. esculenta reproduces hemiclonally with one of the parental species, R. lessonae or R. ridibunda, but viable populations of diploid and triploid hybrids, in which no individuals of the parental species have been found, exist in the northern part of the range. We test the hypothesis that nonhybrids arise every year in these all-hybrid populations, but die during larval development. Microsatellite markers were used to determine the genotypes of adults and abnormal and healthy offspring in three all-hybrid populations of R. esculenta in Denmark. Of all eggs and larvae, 63% developed abnormally or died, with some being nonhybrid (genomes matching one of the parental species), many being aneuploid (with noninteger chromosome sets), a few being tetraploid, and many eggs possibly being unfertilized. The 37% surviving and apparently healthy froglets were all diploid or triploid hybrids. In all three populations, gametogenesis matched the pattern previously described for all-hybrid R. esculenta populations in which most triploid adults have two R. lessonae genomes. This pattern was surprising for the one population in which triploid adults had two R. ridibunda genomes, because here it leads to a deficiency of gametes with an R. lessonae genome and should compromise the stability of this population. We conclude that faulty gametogenesis and mating between frogs with incompatible gametes induce a significant hybrid load in all-hybrid populations of R. esculenta, and we discuss compensating advantages and potential evolutionary trajectories to reduce this hybrid load.     

Genetic structure of the saxicole Pitcairnia geyskesii (Bromeliaceae) on inselbergs in French Guiana

South American inselbergs constitute singular and fragmented habitats in the tropical rain forest. Pitcairnia geyskesii is restricted to these habitats and exhibits both sexual and asexual reproduction. The genetic structure of populations on three inselbergs in French Guiana is examined by analysis of ten isozyme loci. All analyzed populations show high levels of genetic variation. On average, 63.3% of loci per population were polymorphic, with a mean number of 2.21 alleles per polymorphic locus, and mean observed and expected heterozygosities of 0.185 and 0.183, respectively. The analyses of genetic variability displayed at different levels (inselbergs, subpopulations, and mats) give different but complementary information. A significant multilocus disequilibrium was detected in one subpopulation, whereas none was observed within the whole populations sampled on the three inselbergs. Tests on spatial genetic structure indicate a patchy distribution of genotypes on two inselbergs. The data give some insights on the reproductive behavior of P. geyskesii. (1) Efficient sexual reproduction leads to seed recruitment at the level of the inselberg. (2) Both clonality and seed recruitment occur within mats. (3) Vegetative spread by fragmentation is involved in the establishment of new mats. There is substantial differentiation (F(ST) = 0.322) and low gene flow among inselbergs (Nm = 0.234). High genetic diversity within inselbergs appears as a consequence of the association of genet longevity induced by clonal replication and recruitment of new genets produced by sexual reproduction.