白背叶(大戟科)性系统和传粉生物学研究

为探讨野桐属(Mallotus)雌雄异株的进化和传粉机制,对白背叶(Mallotus apelta)野生居群的性系统和传粉生物学进行了研究。结果表明,所调查的白背叶居群均由雌性(F)、雄性(M)和少数两性(B)个体组成,平均性比为1：0.66：0.18(F：M：B);3种性别植株的基径大小差异不显著;雌株与两性植株的单花胚珠数、单果结籽数和自然结实率无显著差异;雄株与两性植株的花粉萌发率、花粉组织化学和花粉微形态特征也无显著差异,但雄株的单花花粉量是两性植株的1.26~1.63倍,且差异显著;雌株的异交结实率为96.67%,两性植株的异交结实率为76.00%,两者差异显著,说明居群内雌株的潜在种子生产力明显高于两性植株;野外观察到雄株和两性植株上的雄花具有访花者而雌株没有;雌株经套网处理后结实率超过30%而套袋处理不结实。这些表明白背叶具典型的亚雌雄异株性系统,雌株和雄株的适合度均高于两性植株;雌株以风媒传粉结实,两性植株可能兼有风媒和虫媒传粉特征。     

Genetic Load and Viability Distribution in Central and Marginal Populations of DROSOPHILA SUBOBSCURA

Relative viabilities of individuals homozygous or randomly heterozygous for wild O chromosomes derived from a marginal (Norwegian) and a central (Greek) population of D. subobscura were obtained by means of a newly prepared marker strain. In the central and marginal populations 20.8 and 28.8 percent of all chromosomes proved lethal or semilethal in homozygous condition. Mean viability was higher for +/+ random heterozygotes than for +/+ homozygotes. This remained the case for the marginal, but not for the central populations, after exclusion of the detrimental chromosomes from the calculations. The variances of viabilities were higher for homozygotes than for heterozygotes, but the test crosses with chromosomes from the marginal population had generally higher variances than those with chromosomes from the central population. No correlation was found in either populations between the action of a chromosome in homozygous condition with its action in heterozygous condition. This is interpreted as complete recessiveness of genetic load. The results are discussed in terms of the observed reduction of the inversion polymorphism which is not paralleled by a reduction in enzyme and, as shown here, by reduction in viability variation. It is thought that the heterotic effect of inversions is due to their homeostatic action, which depends less on structural genes than on higher orders of organization due to gene interaction or regulation. Whatever the causes, it is very likely that marginal populations differ from central populations with respect to their genetic system.     

Androgyny of individuals and polygamy in populations of Salix myrsinifolia Salisb. in the south-western part of its geographical range (NE-Poland)

The aims of the study were to describe the phenomenon of androgyny (a change in the sexual behaviour of individuals) in Salix myrsinifolia, and to consider the implications of androgyny for the sex structure of local populations and for the sex structure of the species across a larger geographical range. Field surveys of the sexual behaviour of individuals and populations of Salix myrsinifolia were carried out over nine years (1989–1997) in an area of 40,000 km² of NE-Poland. More detailed studies were performed on populations in Polana Białowieska (the Białowieża Clearing) in the Białowieża Primeval Forest, in the Białystok area, in the Biebrza Valley and in the experimental garden and laboratory of the Białowieża Geobotanical Station.

The bisexuality of Salix myrsinifolia is basically expressed through the development of a number of different forms of catkin that are intermediate between those that are entirely male and those that are entirely female. Flowers on bisexual catkins are fully developed, as on monosexual ones, but the male segment usually develops prior to the female one. With the exception of one form, a clear partitioning between the male and female parts of the catkin remains. This partitioning of the genders mainly takes place transversely, but in one case longitudinally. It is thus usually possible to speak of the division of a bisexual catkin into male and female sectors.

In all three populations studied in detail, marked shrubs, on which bisexuality had been noted at the beginning, retained this trait throughout the 9-year observation period. However, there were changes in both the expression of bisexuality, i.e. the frequency of bisexual and monosexual catkins, and in the frequency of different patterns of bisexual catkin. Only bisexual individuals with a clear prevalence of female features retained their character. In the two larger populations studied, many originally monosexual individuals became bisexual during the study period.

In the south-western part of the range of S. myrsinifolia in NE-Poland all local populations were characterized by the presence of bisexual individuals and are thus polygamous. There was a close association between the presence of S. myrsinifolia and the degree of ruderalization of habitats. The degree of polygamy in a population was also significantly correlated with ruderalization. It is concluded that androgyny and polygamy may be favoured not only by changes in environmental conditions, but also by the particular pressures to which individuals and populations of a species may be subject at the edge of its geographical range.     

Osservazioni sul comportamento sessuale del Populus tremula L. in Italia

Abstract

OBSERVATIONS ON SEXUAL BEHAVIOUR OF POPULUS TREMULA L. IN ITALY. — A research has been carried on sex distribution of Populus tremula in Italy. On 101 observed populations the sexual ratio resulted of 2:1 in favour of male sex. The analysis of results referred to the two geographycal sectors of the peninsula, North and MiddleSouth, is however showing some discordant data in the sexual composition of several populations. In North-Italy the ratio results of 2,5:1 in favour of male sex, in MiddleSouth 1:1.

These discordant results would show that male sex can be adapted whether in continental or in mountain climate.

The Author deems that the geographycal position of populations and corresponding climatic characteristics can be responsible for the sexual selection, so that the several deviations wich are found in natural populations of P. tremula can get an explanation in an possible correlation between habitat and sex.

The Author dwells particulary upon population discovered at Campiglione, near Pozzuoli (Naples). Stamens, varying in number from 2 to 4, were observed on almost all the pistillate flowers of every single catkin of these individuals and especially from the base to a little over halfway up the catkin.

The high proportion of bisexual catkins found on every individual examined leads to the conclusion that P. tremula is « polygamo-dioecious » in character, that is, it produces bisexual and unisexual character in the case of P. tremuloides, where, however, in the majority of the bisexual individuals, the percentage of hermaphrodite flowers on one catkin was very small (1–2%).

These cases of bisexuality lead one to thing that dioecism is an acquired character in the genus Populus. This condition (wich, at least in the case of P. tremula, is perhaps to be connected with the poor fertility of the species) could in time have lead to the present geographycal distribution in colonies of isolated and sexually anbalanced individuals.

These cold have survived to our times due to their aptitude vegetative propagation by means of suckers, giving rise to scattered clumps of unisexual individuals of the same clone. The finding of these bisexual individuals is of considerable importance for applied genetics, and could initiate new researches in Italy to obtain genotypic and polyploid descendants.     

Gametogenesis in Amphimictic and Parthenogenetic Populations of Aphelenchus avenae

The fetnale reproductive system of Aphelenchus avenae, studied in orcein-stained material, showed a peculiar structural pattern not yet reported in other nematodes. Chromosome morphology and behavior during gametogenesis could be studied in more detail than in other tylenchid or aphelenchid species investigated to date. In a bisexual population from Australia, gametogenesis was by normal meiosis and reproduction by amphimixis. The haploid chromosome number was n=8 in both males and females, and no sex chromosomes were detected. Three monosexual populations from Australia, California, and North Carolina underwent oogenesis by meiosis but reproduced hy parthenogenesis. The haploid chromosome number was n=8 in the Australia and the North Carolina populations, but n=9 in the California population. Spermatogenesis in temperature-induced males of the California population was by normal meiosis, and sperm had n=9 chromosomes. Most chronmsomes consisted of a central euchromatic section and two characteristic heterochromatic ends. No centromere was observed in any chronmsome. The relationship hetween the California population with n=9 and all the other populations with n=8 chromosomes is not well understood.     

Suppressor Systems of Segregation Distorter (SD) Chromosomes in Natural Populations of DROSOPHILA MELANOGASTER

Several natural populations of D. melanogaster were investigated for the presence (or absence) of the Segregation Distorter ( SD) chromosomes and their suppressor systems. The SD chromosomes were found, at frequencies of a few percent, in two independent samples taken in different years from a Raleigh, North Carolina, population, whereas no SD chromosomes were found in samples collected from several populations in Texas. The populations in these localities were found to contain suppressor X chromosomes in high frequencies (75% or higher). They also contained relatively low frequencies of partial suppressor or insensitive second chromosomes of varying degrees, but completely insensitive second chromosomes were practically absent in all populations examined. The frequencies of suppressor X chromosomes, as well as those of the partially insensitive or suppressor second chromosomes, were the same among the populations investigated. This suggests the possibility that the development of a suppressor system of SD in a population could be independent of the presence of an SD chromosome. Segregation distortion appeared to be occurring in natural genetic backgrounds, but the degree of distortion varied among males of different genotypes. There were many instances in which the SD chromosomes showed transmission frequencies from their heterozygous male parents that were smaller than 0.6 and, in several cases, even smaller than 0.5. The presence of a recessive suppressor, or suppressors, of SD in natural populations was suggested.     

Genetic Basis of Self-Incompatibility in the Lichen-Forming Fungus Lobaria pulmonaria and Skewed Frequency Distribution of Mating-Type Idiomorphs: Implications for Conservation

Fungal populations that reproduce sexually are likely to be genetically more diverse and have a higher adaptive potential than asexually reproducing populations. Mating systems of fungal species can be self-incompatible, requiring the presence of isolates of different mating-type genes for sexual reproduction to occur, or self-compatible, requiring only one. Understanding the distribution of mating-type genes in populations can help to assess the potential of self-incompatible species to reproduce sexually. In the locally threatened epiphytic lichen-forming fungus Lobaria pulmonaria (L.) Hoffm., low frequency of sexual reproduction is likely to limit the potential of populations to adapt to changing environmental conditions. Our study provides direct evidence of self-incompatibility (heterothallism) in L. pulmonaria. It can thus be hypothesized that sexual reproduction in small populations might be limited by an unbalanced distribution of mating-type genes. We therefore assessed neutral genetic diversity (using microsatellites) and mating-type ratio in 27 lichen populations (933 individuals). We found significant differences in the frequency of the two mating types in 13 populations, indicating a lower likelihood of sexual reproduction in these populations. This suggests that conservation translocation activities aiming at maximizing genetic heterogeneity in threatened and declining populations should take into account not only presence of fruiting bodies in transplanted individuals, but also the identity and balanced representation of mating-type genes.     

The Persistence of Facultative Parthenogenesis in Drosophila albomicans

Parthenogenesis has evolved independently in more than 10 Drosophila species. Most cases are tychoparthenogenesis, which is occasional or accidental parthenogenesis in normally bisexual species with a low hatching rate of eggs produced by virgin females; this form is presumed to be an early stage of parthenogenesis. To address how parthenogenesis and sexual reproduction coexist in Drosophila populations, we investigated several reproductive traits, including the fertility, parthenogenetic capability, diploidization mechanisms, and mating propensity of parthenogenetic D. albomicans. The fertility of mated parthenogenetic females was significantly higher than that of virgin females. The mated females could still produce parthenogenetic offspring but predominantly produced offspring by sexual reproduction. Both mated parthenogenetic females and their parthenogenetic-sexual descendants were capable of parthenogenesis. The alleles responsible for parthenogenesis can be propagated through both parthenogenesis and sexual reproduction. As diploidy is restored predominantly by gamete duplication, heterozygosity would be very low in parthenogenetic individuals. Hence, genetic variation in parthenogenetic genomes would result from sexual reproduction. The mating propensity of females after more than 20 years of isolation from males was decreased. If mutations reducing mating propensities could occur under male-limited conditions in natural populations, decreased mating propensity might accelerate tychoparthenogenesis through a positive feedback mechanism. This process provides an opportunity for the evolution of obligate parthenogenesis. Therefore, the persistence of facultative parthenogenesis may be an adaptive reproductive strategy in Drosophila when a few founders colonize a new niche or when small populations are distributed at the edge of a species'' range, consistent with models of geographical parthenogenesis.     

Population genetics of bisexual and unisexual populations of the scaly-winged bark louse Echmepteryx hageni (Insecta: Psocoptera)

The scaly-winged bark louse, Echmepteryx hageni, exhibits a unique pattern of co-existence of apparently differnt reproductive modes. Unisexuality is widespread in eastern North America, while sexual populations are restricted to isolated rock out-croppings in southern Illinois and eastern Kentucky. Three of the four nuclear loci examined show greater genetic diversity in the unisexual form compared to the sexual form of E. hageni, in accordance with the pattern previously shown in mitochondrial genetic data. Neutrality tests of the nuclear loci indicate a consistent signal of demographic expansion in asexual populations, but not in sexual populations. There was evidence of inbreeding in the isolated sexual populations at three of the nuclear loci, and one locus had signs of gene specific balancing selection. However, there is no significant genetic differentiation between bisexual and unisexual populations, possibly due to the greater effective population size of nuclear loci relative to mitochondrial loci. The mitochondrial differentiation of E. hageni populations in the northwestern part of their range (Minnesota and Wisconsin) was also not reflected in the nuclear data. We present three hypotheses that may explain the disparity in observed nuclear and mitochondrial genetic diversity between the reproductive forms of E. hageni.     

Sexual reproduction and recombination in the aflatoxin-producing fungus Aspergillus parasiticus

The fungal phylum Ascomycota comprises a large proportion of species with no known sexual stage, despite high genetic variability in field populations. One such asexual species, Aspergillus parasiticus, is a potent producer of carcinogenic and hepatotoxic aflatoxins, polyketide-derived secondary metabolites that contaminate a wide variety of agricultural crops. In this study, individuals of A. parasiticus from a population showing an evolutionary history of recombination were examined for sexual reproduction. Crosses between strains with opposite mating-type genes MAT1-1 and MAT1-2 resulted in the development of ascospore-bearing ascocarps embedded within stromata. Sexually compatible strains belonged to different vegetative compatibility groups. Recombination through the independent assortment of chromosomes 3 and 6 was detected using loci for mating type, aflatoxin gene cluster, and a protein-encoding gene. Our discovery of the sexual stage in A. parasiticus has important implications for current biological control strategies using nontoxigenic strains to reduce aflatoxin contamination in crops.     

A De Novo Case of Floating Chromosomal Polymorphisms by Translocation in Quasipaa boulengeri (Anura,Dicroglossidae)

Very few natural polymorphisms involving interchromosomal reciprocal translocations are known in amphibians even in vertebrates. In this study, thirty three populations, including 471 individuals of the spiny frog Quasipaa boulengeri, were karyotypically examined using Giemsa stain or FISH. Five different karyomorphs were observed. The observed heteromorphism was autosomal but not sex-related, as the same heteromorphic chromosomes were found both in males and females. Our results indicated that the variant karyotypes resulted from a mutual interchange occurring between chromosomes 1 and 6. The occurrence of a nearly whole-arm translocation between chromosome no. 1 and no. 6 gave rise to a high frequency of alternate segregation and probably resulted in the maintenance of the translocation polymorphisms in a few populations. The translocation polymorphism is explained by different frequencies of segregation modes of the translocation heterozygote during meiosis. Theoretically, nine karyomorphs should be investigated, however, four expected karyotypes were not found. The absent karyomorphs may result from recessive lethal mutations, position effects, duplications and deficiencies. The phylogenetic inference proved that all populations of Q. boulengeri grouped into a monophyletic clade. The mutual translocation likely evolved just once in this species and the dispersal of the one karyomorph (type IV) can explain the chromosomal variations among populations.     

Postzygotic isolation involves strong mitochondrial and sex-specific effects in Tigriopus californicus,a species lacking heteromorphic sex chromosomes

Detailed studies of the genetics of speciation have focused on a few model systems, particularly Drosophila. The copepod Tigriopus californicus offers an alternative that differs from standard animal models in that it lacks heteromorphic chromosomes (instead, sex determination is polygenic) and has reduced opportunities for sexual conflict, because females mate only once. Quantitative trait loci (QTL) mapping was conducted on reciprocal F₂ hybrids between two strongly differentiated populations, using a saturated linkage map spanning all 12 autosomes and the mitochondrion. By comparing sexes, a possible sex ratio distorter was found but no sex chromosomes. Although studies of standard models often find an excess of hybrid male sterility factors, we found no QTL for sterility and multiple QTL for hybrid viability (indicated by non-Mendelian adult ratios) and other characters. Viability problems were found to be stronger in males, but the usual explanations for weaker hybrid males (sex chromosomes, sensitivity of spermatogenesis, sexual selection) cannot fully account for these male viability problems. Instead, higher metabolic rates may amplify deleterious effects in males. Although many studies of standard speciation models find the strongest genetic incompatibilities to be nuclear–nuclear (specifically X chromosome–autosome), we found the strongest deleterious interaction in this system was mito–nuclear. Consistent with the snowball theory of incompatibility accumulation, we found that trigenic interactions in this highly divergent cross were substantially more frequent (>6 × ) than digenic interactions. This alternative system thus allows important comparisons to studies of the genetics of reproductive isolation in more standard model systems.     

Parallel polymorphism for supernumerary segments inChorthippus parallelus (zetterstedt)

A complex and parallel pattern of polymorphism for heterochromatic supernumerary segments in the M₇ and S₈ chromosomes has been found in 14 populations of the meadow grasshopperChorthippus parallelus. Nine distinct karyotype classes for these two chromosome pairs occur though they are not equally represented in different populations. Populations differ also with respect to the frequency of supernumerary segments they contain. In all populations the presence of supernumerary segments leads to a significant elevation of mean cell chiasma frequency compared to individuals from the same population lacking such segments. The extent of the effect appears to differ in different populations. The observed frequencies of S₈ karyotypes conform to the expectations of a Hardy-Weinberg distribution. Those of the M₇, however, do not, and in all but one of the 14 populations there is a significant excess of homokaryotypes. In the Ashurst population 26% of the individuals sampled were characterised by germ-line polysomy for the M₄ chromosome, either in the form of entire tetrasomics or more usually as mosaics ranging from tri- to hepta-somics. In all these polysomics the M₄ chromosomes in excess of two were regularly heteropycnotic at first meiotic prophase from zygotene to diakinesis. As a consequence of this multivalents are rare. Extra M₄ chromosomes do not modify the chiasma characteristics of the other chromosomes in the complement. Nor do they modify the action of the supernumerary segments in any way.     

Across-population variation in sex ratio in invasive Japanese Potamopyrgus antipodarum (Caenogastropoda: Rissooidea: Hydrobiidae)

Potamopyrgus antipodarum, a well-known invasive species, has both sexual and asexual forms in its native area, and is generally asexual in exotic areas. Potamopyrgus antipodarum was sampled from ten locations in central and western Japan, and the sex distribution was analyzed. Males were found in two of the ten localities; the percentages of males in these localities were 7.2 and 7.3 %, which is within the range of that observed in asexual populations in native and introduced areas. A flow cytometry analysis showed that populations with a low percentage of males (Kanro) and populations consisting only of females (Banyu Park, Hadano and Yugawara) and perhaps the population reported as having a high male percentage in a previous study (Chiba; 29.8 %) were triploid. Males from Chiba and Kanro produced sperm. Most of the females from Chiba stored sperm in their seminal receptacle, showing that they had copulated, but no females from Kanro stored sperm. Fertilization by males, normal development of fertilized eggs, and the fecundity of juveniles should be evaluated in further studies to demonstrate the sexual reproduction of P. antipodarum in Japan. The risk of introduction of sexual P. antipodarum individuals is further discussed in the article.     

The Chromosomal Basis of Sexual Isolation in Two Sibling Species of Drosophila: D. ARIZONENSIS and D. MOJAVENSIS

The chromosomal determination of interspecific differences in mating behavior was studied in the interfertile pair, Drosophila arizonensis and Drosophila mojavensis, by means of chromosomal substitutions. Interspecific crossing over was avoided by crossing hybrid males to parental females, and identification of the origin of each chromosome in backcrossed hybrids was possible by means of allozyme markers. It was found that male mating behavior is controlled by factors located in the PGM-marked chromosome (which, in other Drosophila species, is part of the X chromosome) and in the Y chromosome. The other chromosomes influence male sexual behavior through their interactions with each other and with the PGM-marked chromosome, but their overall effect is minor. Female mating behavior is controlled by factors located in the ODH-marked and AMY-marked chromosomes, with the other chromosomes exercising a small additive effect. Hence, the two sex-specific behaviors are under different genetic control. Cytoplasmic origin has no effect on the mating behavior of either sex. There appears to be no correlation between a chromosome's structural diversity (i.e., amounts of inversion polymorphism within a species or numbers of fixed inversions across species) and its contribution to sexual isolation. These findings are in general agreement with those from similar Drosophila studies and may not be specific to the species studied here.     

Oogenesis and the Chromosomes of Twelve Bisexual Species of Heterodera (Nematoda: Heteroderidae)

Twelve bisexual species of Heterodera reproduced by amphimixis and had the same number of n=9 (2n=18) chromosomes in maturing oocytes. H. schachtii had slightly larger chromosomes than all other species. Only sperm nuclei with n=9 chromosomes were observed inside maturing oocytes and no specialized sex chromosomes were detected in any case. A "supernumerary" chromosome was observed occasionally in oocytes of H. schachtii and H. weissi and was transmitted regularly to one-half of the progeny of the nematodes that possessed it. Cytological characteristics were not very instructive in differentiating amphimictic tleterodera species. Such karyotypic uniformity indicates cytogenetic stability of the genus and close interrelationship among its members.     

Chromosomal variation in social voles: a Robertsonian fusion in Günther’s vole

The study reports on chromosomes in several populations of social voles from south-eastern Europe and the Middle East. The standard karyotypes of individuals of Microtus hartingi and Microtus guentheri originating from both south-eastern Europe and Asia Minor comprised 54 mostly acrocentric chromosomes. However, variation between populations was found in the amount and distribution of C-heterochromatin in certain autosomes and the sex chromosomes. Furthermore, a specific pattern of argyrophilic nucleolar organizer region distribution was recorded in different geographic populations. In a population from Asia Minor, a heterozygous centric fusion of two autosomes was found. The G-banded karyotypes of M. guentheri and Microtus socialis were compared, and tandem fusions of autosomes were suggested as possible mechanism of the divergence. The karyotypes of the nine currently recognized species of social voles are reviewed, and implications of chromosomal data for systematics are evaluated.     

Observations of meiotic chromosomes in Gaura (Onagraceae)

Observations of meiotic chromosomes are reported for all 21 species and 3 additional sub species ofGaura (Onagraceae), based upon a study of 647 individuals from 509 naturally occurring populations throughout the range of the genus. The basic chromosome number for the genus isx = 7, and 18 species are diploid withn = 7. Among these, the self-incompatible ones are often highly chromosomally heterozygous, with no homozygous individuals having been found in nature in the perenrennialsGaura lindheimeri andG. villosa, and two-thirds or more of the individuals apparently heterozygous in the following well-sampled species:G. calcicola, G. longiflora, andG. suffulta subsp.suffulta. In contrast, the autogamous species are entirely chromosomally homozygous or nearly so. Two species ofGaura are reported as chromosomal structural heterozygotes, with about 50% pollen abortion:G. biennis andG. triangulata; the translocation systems originated independently of one another. Two of the three polyploid species,G. sinuata andG. drummondii (G. odorata of many authors), are consistently tetraploid (n = 14) and, despite their cytological autotetraploidy, are thought to have originated following interspecific hybridization. They are the only rhizomatous species in the genus and may have had one ancestor in common. The remaining polyploid,G. coccinea, includes populations withn = 7, 14, 21, and 28, as well as evident interploid hybrids and, frequently, supernumerary chromosomes. The relationship among these populations is close and is maintained by frequent hybridization and exchange of genetic material. No other species seems to have participated in their origin, and the association of their chromosomes is consistently that characteristic of autopolyploidy in plants with tetraploid and higher chromosome numbers.     

GENETIC VARIATION IN THE HOMOSPOROUS FERN PELLAEA ANDROMEDIFOLIA

Genetic variability was examined in nine sexual and three apogamous natural populations of the homosporous fern Pellaea andromedifolia by electrophoretic analysis of enzymes specified by eight loci. Genetic interpretations of heterozygous banding patterns were determined by segregational analysis of gametophytes. High levels of segregating heterozygosity characterized the sexually reproducing populations, and genotype frequencies at the five polymorphic loci were consistent with those expected under conditions of random intergametophytic mating. Multiple-banded patterns in the apogamously reproducing populations resembled those of heterozygous sexual individuals, but did not segregate. The results suggest that genetic variation in sexual homosporous vascular plants is produced by cross fertilization of genetically different gametes and may not result from pairing between homoeologous chromosomes carrying duplicated loci as previously thought.     

Population Genetic Structure of the Grasshopper Eyprepocnemis plorans in the South and East of the Iberian Peninsula

The grasshopper Eyprepocnemis plorans subsp. plorans harbors a very widespread polymorphism for supernumerary (B) chromosomes which appear to have arisen recently. These chromosomes behave as genomic parasites because they are harmful for the individuals carrying them and show meiotic drive in the initial stages of population invasion. The rapid increase in B chromosome frequency at intrapopulation level is thus granted by meiotic drive, but its spread among populations most likely depends on interpopulation gene flow. We analyze here the population genetic structure in 10 natural populations from two regions (in the south and east) of the Iberian Peninsula. The southern populations were coastal whereas the eastern ones were inland populations located at 260–655 m altitude. The analysis of 97 ISSR markers revealed significant genetic differentiation among populations (average G_ST =  0.129), and the Structure software and AMOVA indicated a significant genetic differentiation between southern and eastern populations. There was also significant isolation by distance (IBD) between populations. Remarkably, these results were roughly similar to those found when only the markers showing low or no dropout were included, suggesting that allelic dropout had negligible effects on population genetic analysis. We conclude that high gene flow helped this parasitic B chromosome to spread through most of the geographical range of the subspecies E. plorans plorans.