Chloroplast DNA phylogeography of Alnus glutinosa (L.) Gaertn.

Traditionally, information on the postglacial history of plant species has been gained from the analysis of fossil pollen data. More recently, surveys of present patterns of genetic variation have given valuable insights into species phylogeography. The genus Alnus , based on fossil data, is known to have had at least four glacial refugia. A survey of chloroplast DNA (cpDNA) diversity in populations of black alder ( A. glutinosa ) was undertaken in order to gain more insight into its postglacial history. This revealed a high degree of structuring of 13 cpDNA haplotypes on a European scale which indicated that most of northern and central Europe was colonized from a refuge in the Carpathian Mountains. Based on the distribution of two common cpDNA haplotypes, colonization routes from this refuge can be determined. The locations of other previously identified refugia are confirmed and two formerly unconfirmed refugial areas for alder (southern Spain and Turkey) are proposed.     

Recombination and introgression of nuclear and chloroplast genomes between the peat mosses, Sphagnum capillifolium and Sphagnum quinquefarium

Haploid hybrid gametophytes are often present at low frequencies in sympatric populations of Sphagnum capillifolium and Sphagnum quinquefarium. We used intersimple sequence repeat (ISSR) markers and polymerase chain reaction-restriction fragment length polymorphism of the trnL(UAA) intron of the chloroplast genome to reveal the nuclear and chloroplast composition of mature hybrid gametophytes from natural populations and of gametophytes derived from spores of hybrid sporophytes collected in nature. Asymmetrical nuclear inheritance was found in the progeny of the hybrid sporophytes, indicating that only spores with a low level of recombination of parental genomes were viable. A similarly skewed nuclear composition was found among the naturally occurring hybrid gametophytes. All hybrid genomes contained a larger proportion of S. capillifolium ISSR markers, combined with only two to five S. quinquefarium markers together with a chloroplast haplotype derived from S. quinquefarium. In this way, a pattern resembling introgression is created within a single generation. Some individuals possessed nuclear genomes typical for S. capillifolium in combination with the chloroplast haplotype of S. quinquefarium, possibly indicating backcrossing. Our results indicate that hybridization between S. capillifolium and S. quinquefarium is relatively common, but the resistance of large parts of the genome against heterospecific genes maintains the genetic distinctness of the species. Further evolutionary and phylogenetic consequences of restricted interspecific gene exchange are discussed.     

A multivariate approach to host plant associated morphological variation in the polyphagous leafhopper, Alnetoidia alneti (Dahlbom)

Canonical variate analysis (CVA) on morphological distance measurements shows that differences exist among adult samples of A. alneti taken from a number of host plant species in South Wales. This variation is also correlated with variation in the degree of yellow pigmentation. Adults taken from alder and hazel form extremes in a continuum of variation, those from alder being larger and more pigmented. The variation between these two populations is greater than host-independent variation among samples of each population taken from a number of individual trees at different localities in Britain in different years. Ordination shows that the variation between the alder and hazel populations is along different axes to that among samples in these populations. Different axes of variation are also found among adults from different pairs of host plant species. Multiple-group principal component analysis (MGPCA) suggests that much of the variation between adults from alder and hazel may be interpreted as allometry-free 'shape' that is uncorrelated with variation in overall size within each population. Transfer experiments showed that the differences in both size and shape may have little genetic basis and are probably host plant induced> The taxonomic and ecological implications of these results are discussed.     

Chloroplast DNA variation and postglacial recolonization of common ash (Fraxinus excelsior L.) in Europe

We used chloroplast polymerase chain reaction-restriction-fragment length polymorphism (PCR-RFLP) and chloroplast microsatellites to assess the structure of genetic variation and postglacial history across the entire natural range of the common ash (Fraxinus excelsior L.), a broad-leaved wind-pollinated and wind-dispersed European forest tree. A low level of polymorphism was observed, with only 12 haplotypes at four polymorphic microsatellites in 201 populations, and two PCR-RFLP haplotypes in a subset of 62 populations. The clear geographical pattern displayed by the five most common haplotypes was in agreement with glacial refugia for ash being located in Iberia, Italy, the eastern Alps and the Balkan Peninsula, as had been suggested from fossil pollen data. A low chloroplast DNA mutation rate, a low effective population size in glacial refugia related to ash's life history traits, as well as features of postglacial expansion were put forward to explain the low level of polymorphism. Differentiation among populations was high (GST= 0.89), reflecting poor mixing among recolonizing lineages. Therefore, the responsible factor for the highly homogeneous genetic pattern previously identified at nuclear microsatellites throughout western and central Europe (Heuertz et al. 2004) must have been efficient postglacial pollen flow. Further comparison of variation patterns at both marker systems revealed that nuclear microsatellites identified complex differentiation patterns in south-eastern Europe which remained undetected with chloroplast microsatellites. The results suggest that data from different markers should be combined in order to capture the most important genetic patterns in a species.     

Chloroplast and nuclear DNA studies in a few members of the <Emphasis Type="Italic">Brassica oleracea</Emphasis> L. group using PCR-RFLP and ISSR-PCR markers: a population genetic analysis

A population genetic analysis of chloroplast and nuclear DNA was performed covering nine wild populations of Brassica oleracea. Three members of the n = 9 group, all close to B. oleracea, Brassica alboglabra Bailey, Brassica bourgeaui (Webb) O. Kuntze and Brassica montana Pourret, were also studied to better understand their relationship with B. oleracea. Chloroplast DNA was analysed using the PCR-RFLP (polymerase chain reaction - restriction fragment length polymorphism) method. The ISSR-PCR (inter-simple sequence repeat - polymerase chain reaction) technique was adopted to study nuclear DNA. Twelve primer pairs of chloroplast DNA showed very good amplification. The amplified product of each primer pair, digested by three restriction enzymes, revealed no variation of cpDNA among the taxa studied. This indicates they may have the same chloroplast genotype. Seven selected ISSR primers have detected genetic variation, both within and among the populations/taxa surveyed. The information obtained on the intra- and inter-populational genetic diversity of wild populations of B. oleracea neatly defined the individual plants. It could provide important guidelines for backing management and conservation strategies in this species. The study confirms a close relationship between B. alboglabra, B. bourgeaui and B. montana, which is parallel to their morphological similitude.     

Genetic diversity and phylogenetic relationships of the genus Lycopersicon (Tourn.) Mill. as revealed by inter-simple sequence repeat (ISSR) analysis

Inter-simple sequence repeat (ISSR) analysis was for the first time used to study the genetic diversity and phylogenetic relationships in 54 wild accessions and cultivars of the genus Lycopersicon. Analysis involved 14 ISSR primers homologous to microsatellite repeats and containing additional selective anchor nucleotides. In total, 318 ISSR fragments were amplified for the wild and cultivated tomato genomes. The interspecific polymorphism revealed with the ISSR primers was 95.6%. Species-specific ISSR fragments were detected for each tomato species. The highest number (more than 20) of species-specific fragments were obtained for L. esculentum sensu lato, although the intraspecific variation of ISSR patterns was low. UPGMA cluster analysis was used to construct a dendrogram and to estimate the genetic distances between the species of the genus Lycopersicon; between populations of L. peruvianum, L. pimpinellifolium, and L. esculentum; and between tomato cultivars. The ISSR-based phylogeny was generally consistent with Lycopersicon taxonomy based on morphological and molecular evidence, suggesting the applicability of ISSR analysis for genotyping and phylogenetic studies in tomato.     

Pollination Flow in Hybrid Formation between Orchis morio and Orchis papilionacea (Orchidaceae) in Two Different Habitats

Two geographically separated natural populations of Orchis xgennarii, a hybrid between Orchis morio and Orchis papilionacea, were examined to establish the parental lineages using nuclear ribosomal DNA and chloroplast DNA length polymorphisms. Results indicate that O. morio more frequently provides the maternal lineage in the population from the volcano Mount Vesuvius (central Campania, Italy) than in the one from Cilento (southern Campania, Italy); in the latter locality maternal genomes are preferentially provided by O. papilionacea. The possible causes of this difference in reproductive behavior are discussed in the light of the pollination biology of parental species and of environmental influences.     

Sequencing and phylogenetic analysis of the chloroplast genome of Pseudosasa japonica f. Akebonosuji

Pseudosasa japonica f. Akebonosuji H. Okamura is a bamboo species with variable leaf colors, including albino, green, and green-white stripes. To determine whether variation in leaf color is due to mutations in the chloroplast genome, we sequenced the chloroplast genomes of green and albino leaves of P. japonica f. Akebonosuji. The results indicated that the chloroplast genome included 86 protein-coding genes, seven ribosomal RNA genes, and 31 tRNA genes. The similarity of chloroplast genomes for the two leaf types was 99.98%, with variation between genes encoding for trnfM and trnT. We observed that the relative expression patterns of trnfM and trnT were reversed in green and albino leaves. Whether the differential expression of trnfM and trnT is involved in leaf color variation among P. japonica f. Akebonosuji remains unclear.With many bamboo chloroplast genomes available, we aligned the chloroplast genomes of 28 bamboo species, including P. japonica f. Akebonosuji, to analyze polymorphisms. This comparison revealed that noncoding regions possessed more nucleotide polymorphisms than coding regions. Chloroplast genomes and the nuclear gene “granule-bound starch synthase I” (GBSSI) of 28 bamboo species were used to construct evolutionary trees. Both evolutionary trees indicated that P. japonica f. Akebonosuji was clustered into Subtrib. Arundinariinae.     

Chloroplast DNA Diversity among Trees, Populations and Species in the California Closed-Cone Pines (Pinus Radiata, Pinus Muricata and Pinus Attenuata)

The amount, distribution and mutational nature of chloroplast DNA polymorphisms were studied via analysis of restriction fragment length polymorphisms in three closely related species of conifers, the California closed-cone pines-knobcone pine: Pinus attenuata Lemm.; bishop pine: Pinus muricata D. Don; and Monterey pine: Pinus radiata D. Don. Genomic DNA from 384 trees representing 19 populations were digested with 9-20 restriction enzymes and probed with cloned cpDNA fragments from Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] that comprise 82% of the chloroplast genome. Up to 313 restriction sites were surveyed, and 25 of these were observed to be polymorphic among or within species. Differences among species accounted for the majority of genetic (haplotypic) diversity observed [G(st) = 84(+/-13)%]; nucleotide diversity among species was estimated to be 0.3(+/-0.1)%. Knobcone pine and Monterey pine displayed almost no genetic variation within or among populations. Bishop pine also showed little variability within populations, but did display strong population differences [G(st) = 87(+/-8)%] that were a result of three distinct geographic groups. Mean nucleotide diversity within populations was 0.003(+/-0.002)%; intrapopulation polymorphisms were found in only five populations. This pattern of genetic variation contrasts strongly with findings from study of nuclear genes (allozymes) in the group, where most genetic diversity resides within populations rather than among populations or species. Regions of the genome subject to frequent length mutations were identified; estimates of subdivision based on length variant frequencies in one region differed strikingly from those based on site mutations or allozymes. Two trees were identified with a major chloroplast DNA inversion that closely resembled one documented between Pinus and Pseudotsuga.     

Genetic Diversity and Phylogenetic Relationships in the Genus Lycopersicon (Tourn.) Mill. as Revealed by Inter-Simple Sequence Repeat (ISSR) Analysis

Inter-simple sequence repeat (ISSR) analysis was for the first time used to study the genetic diversity and phylogenetic relationships in 54 wild accessions and cultivars of the genus Lycopersicon. Analysis involved 14 ISSR primers homologous to microsatellite repeats and containing additional selective anchor nucleotides. In total, 318 ISSR fragments were amplified for the wild and cultivated tomato genomes. The interspecific polymorphism revealed with the ISSR primers was 95.6%. Species-specific ISSR fragments were detected for each tomato species. The highest number (more than 20) of species-specific fragments were obtained for L. esculentum sensu lato, although the intraspecific variation of ISSR patterns was low. UPGMA cluster analysis was used to construct a dendrogram and to estimate the genetic distances between the species of the genus Lycopersicon; between populations ofL. peruvianum, L. pimpinellifolium, and L. esculentum; and between tomato cultivars. The ISSR-based phylogeny was generally consistent with Lycopersicon taxonomy based on morphological and molecular evidence, suggesting the applicability of ISSR analysis for genotyping and phylogenetic studies in tomato.     

Frequent chloroplast capture among Isodon (Lamiaceae) species in Japan revealed by phylogenies based on variation in chloroplast and nuclear DNA

A recent phylogenetic study based only on chloroplast DNA (cpDNA) variation revealed that populations of an Isodon species are frequently embedded paraphyletically among other Isodon species. This phylogenetic discrepancy between species taxonomy and molecular phylogeny was considered to have resulted from chloroplast DNA captures and/or incomplete lineage sorting. To elucidate which of these factors was mainly responsible for the observed phylogenetic pattern, we performed phylogenetic analyses of multiple populations of Isodon species in Japan using cpDNA variation, three single-copy nuclear genes, and double-digest restriction-site-associated DNA sequencing (ddRAD-seq). Although a species often shared chlorotypes with other species, our phylogenetical analyses based on variation in the three single-copy nuclear genes and the ddRAD-seq data showed that most populations belonging to the same species were monophyletic at the species level, suggesting that chloroplast capture may have frequently occurred between Isodon species. Some populations of an intraspecific taxon were embedded paraphyletically within the species, regardless of the large amount of phylogenetic information in nuclear DNA; this incongruity may have resulted from incomplete lineage sorting.     

Uniformity of the nuclear and chloroplast genomes of Spartina maritima (Poaceae), a salt-marsh species in decline along the Western European Coast

Spartina maritima is a salt-marsh species from European and African Atlantic coasts. In the northern range of the species (including north-west France), a rapid decline of the populations has been observed during the 20th century. In this paper, the molecular diversity of 10 populations of S. maritima from France has been investigated using nuclear and chloroplast DNA markers: inter-simple sequence polymorphism (ISSR), randomly amplified polymorphic DNA (RAPD), inter-retrotransposon amplified polymorphism (IRAP), and PCR-RFLP of a 5 kb long portion of chloroplast DNA. The results reveal an extremely low level of genetic variation in this species: only one nuclear marker (out of 98) was polymorphic, with the presence of two genotypes randomly distributed among the populations. The lack of genetic diversity is interpreted in light of the almost exclusive vegetative propagation of the species in its northern range, the colonization history of the populations, and the origin of S. maritima (2n = 60) in the hexaploid lineage of the genus and in the context of the management of S. maritima populations.     

Chloroplast DNA supports a hypothesis of glacial refugia over postglacial recolonization in disjunct populations of black pine (Pinus nigra) in western Europe

European black pine (Pinus nigra Arn.) is a widely distributed Mediterranean conifer. To test the hypothesis that fragmented populations in western Europe survived in situ during the last glacial rather than having been re-colonized in the postglacial period, genetic variation was assessed using a suite of 10 chloroplast DNA microsatellites. Among 311 individuals analysed, 235 haplotypes were detected revealing high levels of chloroplast haplotype diversity in most populations. Bayesian analysis using a model of linked loci, with no prior assumption of population structure, assigned individuals to 10 clusters that corresponded well with the six predefined sampling regions, while an analysis carried out at the population level and assuming unlinked loci, recovered the original six sampling regions. This regional structure was supported by a biogeographical analysis that detected five barriers, with the two most significant separating Alps from Corsica and southern Italy, and southern Spain from the Pyrenees. No signals of demographic expansion were detected, and comparisons of R(ST) with pR(ST) suggested that a stepwise mutational model was important in regional differentiation, but not in population-within-region differentiation. These tests support long-term persistence of the species within the six regions. The temporal depth estimate, assuming a high mutation rate in coalescent modelling, placed the deepest split between the Alps and the other regions at about 150 000 years ago, and the most recent split of Pyrenees from southern France at about 30 000 years ago. Taken together, the data suggest that chloroplast DNA is structured in black pine and disjunct populations in western Europe are likely to have been present during the Last Glacial Maximum.     

Genetic variation at chloroplast microsatellites (cpSSRs) in Abies nebrodensis (Lojac.) Mattei and three neighboring Abies species

Abies nebrodensis (Lojac.) Mattei (Sicilian fir) is an endangered species represented by only one population of 29 adult individuals occurring in a limited area of the Madonie Range in northern Sicily (Italy). Taxonomic boundaries between this taxon and the neighboring Abies species are not clear. In this study, we used six chloroplast simple-sequence repeats (cpSSRs) to investigate the population genetic structure and the distribution of chloroplast haplotypic variation in A. nebrodensis and three of the neighboring Abies species: Abies alba (Mill.), Abies numidica (De Lann) and Abies cepha-lonica (Loud.). Our aims were to quantify the level of cpDNA differentiation within the Abies populations and to shed light on the history of A. nebrodensis. Diversity levels based on the haplotype frequency at six cpSSRs were high, especially in A. alba and A. cephalonica. In all, we found 122 haplotypes among the 169 individuals analyzed, and the four species were distinguished from each other by their haplotype composition. The majority of the haplotypes (76%) were detected only once, but in A. nebrodensis seven individuals (41% of the sample population) shared the same haplotype. Moreover, the seven A. nebrodensis individuals with an identical haplotype showed a tendency to be geographically grouped within the population"s limited range. The analysis of molecular variance (AMOVA) showed a significant difference in the level of apportionment of gene diversity between the species A. alba and A. cephalonica (F_ST=0.191 and 0.012, respectively). AMOVA analysis conducted over all populations from the four species showed that 19% of the total cpSSR variation was attributable to differences among species, 6% was due to differences among populations within species, and 74% to differences within populations. The high percentage of unique haplotypes identified confirms the power of cpSSR haplotype analysis for identifying individual trees in individual Abies populations. Our results indicate that A. nebrodensis differs from the other three Abies species investigated and support its classification as an independent taxon. The results also showed a decreased level of variation in A. nebrodensis and suggested that the species has experienced a genetic bottleneck during the last two centuries. Received: 10 April 2000 / Accepted: 13 July 2000     

Outcrossing rates and organelle inheritance estimated from two natural populations of the Japanese endemic conifer Sciadopitys verticillata

The Japanese endemic conifer Sciadopitys verticillata is one of the most phylogenetically isolated species of all plants. Occurring in small and scattered populations, the species is currently classified as Near Threatened by the International Union for Conservation of Nature and Natural Resources (IUCN) and as Vulnerable in three prefectures of Japan. This study investigated two major factors that should impact the genetic structure of the species at both the nuclear and organelle DNA level, the mating system and the inheritance of both the chloroplast and mitochondrial genomes. The mating system is crucial to determining the degree of outcrossing of plant species and thus should have a key role in shaping the species’ population level genetic diversity and gene flow between populations but as yet has not been studied in S. verticillata. Nine mother trees and their seedling progeny from two natural populations were genotyped using genetic markers from three plant genomes (eight nuclear microsatellites and DNA sequence for the chloroplast and mitochondria). Using a maximum likelihood method implemented in the software MLTR, the study found an outcrossing rate in the seedling stage of 0.49 and 0.79 for Aburazaka and Mount Shirotori populations, respectively, and an average of 0.66 at the species level. These outcrossing rates were low for conifers and therefore may have potential deleterious implications for the conservation of the species. The test of organelle inheritance supported paternal transmission of both the chloroplast and mitochondria consistent with previous microscopic evidence.     

Leaf water relations of black alder [Alnus glutinosa (L.) Gaertn.] growing at neighbouring sites with different water regimes

 The tree species black alder [Alnus glutinosa (L.) Gaertn.] typically inhabits wet sites in central Europe but is also successful on well drained soils. To test the physiological adjustment of the species in situ, conductances, transpiration rates and water potentials (Scholander pressure chamber) of black alder leaves were investigated at two neighbouring sites with different water regimes: alder trees at an occasionally water logged alder forest and alder shrubs in a nearby, much drier hedgerow. Additional experiments with alder cuttings in nutrient culture showed that leaf conductances and gas exchange were both strongly influenced by the substrate water potential. In situ however, there was little spatial variability within the different parts of a crown and we found that physiological regulation at leaf level was hardly influenced by different site water regimes or different tree sizes. Diurnal courses of leaf water relations as well as their regulation at the leaf level (e.g. the hyperbolic relationship between conductances and ΔW) were strikingly similar at both sites. Leaf water potential in black alder was shown to be a consequence of immediate transpiration rates, which were high in comparison to other tree species (up to 4 mmol H₂O m^–2 s^–1), rather than the water potentials being a factor that influenced conductance and, therefore, transpiration. The always high leaf conductances and consequent high transpiration rates are interpreted as a strategy to maximise productivity through low stomatal limitation at sites where water supply is usually not limited. However, at the same time this behaviour restricts black alder to sites where at least the deep-going roots can exploit water. Received: 10 September 1998 / Accepted: 12 January 1999     

Chloroplast diversity in the genus Malus: new insights into the relationship between the European wild apple (Malus sylvestris (L.) Mill.) and the domesticated apple (Malus domestica Borkh.)

To unravel the relationship between the European wild apple, Malus sylvestris (L.) Mill., and its domesticated relative M. domestica Borkh., we studied chloroplast DNA variation in 634 wild and 422 domesticated accessions originating from different regions. Hybridization between M. sylvestris and M. domestica was checked using 10 nuclear microsatellites and a Bayesian assignment approach. This allowed us to identify hybrids and feral plants escaped from cultivation. Sixty-eight genotypes belonging to 12 other wild Malus species, including 20 M. sieversii (Ledeb.) Roem. accessions were also included in the analysis of chloroplast diversity. Marker techniques were developed to type a formerly described duplication and a newly detected transversion in the matK gene. Chloroplast DNA variation was further investigated using PCR-RFLP (Polymerase Chain Reaction-Random Fragment Length Polymorphism), and haplotypes were constructed based on all mutational combinations. A closer relationship than presently accepted between M. sylvestris and M. domestica was established at the cytoplasmic level, with the detection of eight chloroplast haplotypes shared by both species. Hybridization between M. sylvestris and M. domestica was also apparent at the local level with sharing of rare haplotypes among local cultivars and sympatric wild trees. Indications of the use of wild Malus genotypes in the (local) cultivation process of M. domestica and cytoplasmic introgression of chloroplast haplotypes into M. sylvestris from the domesticated apple were found. Only one of the M. sieversii trees studied displayed one of the three main chloroplast haplotypes shared by M. sylvestris and M. domestica. This is surprising as M. sieversii has formerly been described as the main maternal progenitor of the domesticated apple. This study hereby reopens the exciting discussion on the origin of M. domestica.     

Tracking a genetic signal of extinction-recolonization events in a neotropical tree species: Vouacapoua americana Aublet in French Guiana

Drier periods from the late Pleistocene and early Holocene have been hypothesized to have caused the disappearance of various rainforest species over large geographical areas in South America and restricted the extant populations to mesic sites. Subsequent improvement in climatic conditions has been associated with recolonization. Changes in population size associated with these extinction-recolonization events should have affected genetic diversity within species. However, these historical hypotheses and their genetic consequences have rarely been tested in South America. Here, we examine the diversity of the chloroplast and nuclear genomes in a Neotropical rainforest tree species, Vouacapoua americana (Leguminosae, Caesalpinioideae) in French Guiana. The chloroplast diversity was analyzed using a polymerase chain reaction-restriction fragment length polymorphism method (six pairs of primers) in 29 populations distributed over most of French Guiana, and a subset of 17 populations was also analyzed at nine polymorphic microsatellite loci. To determine whether this species has experienced extinction-recolonization, we sampled populations in areas supposedly not or only slightly affected by climatic changes, where the populations would not have experienced frequent extinction, and in areas that appear to have been recently recolonized. In the putatively recolonized areas, we found patches of several thousands of hectares homogeneous for chloroplast variation that can be interpreted as the effect of recolonization processes from several geographical origins. In addition, we observed that, for both chloroplast and nuclear genomes, the populations in newly recolonized areas exhibited a significantly smaller allelic richness than others. Controlling for geographic distance, we also detected a significant correlation between chloroplast and nuclear population differentiation. This result indicates a cytonuclear disequilibrium that can be interpreted as a historical signal of a genetic divergence between fragmented populations. In conclusion, the spatial genetic structure of contemporary V. americana populations shows evidence that this species has experienced large extinction-recolonization events, which were possibly caused by past climatic change.     

Genetic Diversity and Population Structure of Acacia senegal (L) Willd. in Kenya

The level of genetic diversity and population structure of Acacia senegal variety kerensis in Kenya was examined using seven polymorphic nuclear microsatellite loci and two chloroplast microsatellite loci. In both chloroplast and nuclear datasets, high levels of genetic diversity were found within all populations and genetic differentiation among populations was low, indicating extensive gene flow. Analysis of population structure provided support for the presence of two groups of populations, although all individuals had mixed ancestry. Groups reflected the influence of geography on gene flow, with one representing Rift Valley populations whilst the other represented populations from Eastern Kenya. The similarities between estimates derived from nuclear and chloroplast data suggest highly effective gene dispersal by both pollen and seed in this species, although population structure appears to have been influenced by distributional changes in the past. The few contrasts between the spatial patterns for nuclear and chloroplast data provided additional support for the idea that, having fragmented in the past, groups are now thoroughly mixed as a result of extensive gene flow. For the purposes of conservation and in situ management of genetic resources, sampling could target a few, large populations ideally distributed among the spatial groups identified. This should ensure the majority of extant variation is preserved, and facilitate the investigation of variation in important phenotypic traits and development of breeding populations.     

Ecology and genetics of interspecific hybridization in the swallowtails, Papilio hospiton Gene and P. machaon L., in Corsica (Lepidoptera: Papiliomdae)

The Corsican swallowtail butterfly, Papilio hospiton , is endemic to Corsica and Sardinia (France and Italy) and included in the list of endangered species by the Washington Convention, It is spread all over Corsica in scattered populations linked to diverse habitats. A study by enzyme electrophoresis showed that the genetic diversity of the species is of the same order of magnitude as that of Papilio machaon from continental France and Corsica. The differentiation between populations is rather low, which is consistent with the high vagility of the adults. Natural hybridization between P. hospiton and P. machaon is frequent, and laboratory crosses show that the hybrids are not sterile. However, developmental perturbations impair the viability of further hybrid progenies. Although limited introgression between the two species is likely to take place, enzyme electrophoresis and PCR-RFLP analysis of mitochondrial DNA show that their gene pools remain distincfTtienetic assimilation by P. machaon therefore does not seem to be a threat for P. hospiton.