Inheritance Of Chloroplast DNA Research Articles

Natural hybridization of Yezo and Sakhalin spruce in central Hokkaido, revealed by DNA markers with contrasting modes of inheritance

AbstractYezo spruce (Picea jezoensis var. jezoensis) and Sakhalin spruce (Picea glehnii) occur across Hokkaido and co‐occur in some forest habitats. This leads to the potential for natural hybridization between these two species, which has been shown to occur at low frequencies. The purpose of this study was to identify these hybrids and their possible mating patterns, using various Pinaceae DNA markers with different modes of inheritance. The markers used were maternally inherited mitochondrial DNA (mtDNA), paternally inherited chloroplast DNA (cpDNA) and biparentally inherited nuclear microsatellites (nSSRs). Seven putative natural hybrids, four artificially‐crossed F1 hybrids, four parent plants from each species, and two artificially‐backcrossed hybrids of putative natural hybrids and their parents were analyzed using the diagnostic DNA markers developed in this study. We found Yezo spruce and Sakhalin spruce to be distinct (J and G types, respectively), and the modes of inheritance held true for the two species, as was previously reported to be the case in Pinaceae. Four of the seven putative natural hybrids harbored J‐type cpDNA, G‐type mtDNA and J/G‐type nSSRs, indicating that natural F1 hybrids are likely to arise from a G (female) × J (male) crossing. One natural hybrid harbored G‐type cpDNA, J‐type mtDNA and J/G‐type nSSRs, which implies that hybrids produced by J (female) × G (male) crossings occur at low frequencies. The two remaining hybrids harbored J‐type cpDNA and mtDNA with either J/G or J/J‐type nSSRs, suggesting that they may be F2 hybrids resulting from backcrossing between an F1 hybrid and a Yezo spruce.

Evolutionary history of Orinus thoroldii (Poaceae), endemic to the western Qinghai-Tibetan Plateau in China

To explore the responses of arid-tolerant alpine plants to Pleistocene climatic oscillations, we examined the evolutionary history of Orinus thoroldii, a grass species endemic to the western Qinghai-Tibetan Plateau (QTP) in China. Three maternally inherited chloroplast DNA (cpDNA) markers (matK, rbcL, and trnH-psbA) and the bi-parentally inherited nuclear ribosomal internal transcribed spacer (nrITS) were sequenced for 243 individuals from 28 populations. In all, seven chloroplast haplotypes (H1–H7) and seven nrITS types (S1–S7) were detected. Whereas two haplotypes were widespread, each of the remaining five was restricted to single populations or shared with only its adjacent population. Phylogenetic analyses of the cpDNA haplotypes revealed two distinct lineages distributed in the eastern and western regions of the western QTP. Our analysis of molecular variance (AMOVA) demonstrated the major partitioning (66.56%) of cpDNA variation between the western and eastern groups. A significant phylogeographical structure was detected (NST = 0.81, GST = 0.72; P < 0.05) based on the cpDNA dataset. The distribution of nrITS types also showed a certain geographical pattern. Whereas types S1 and S5 were widely distributed across the region, the others were exclusively restricted to specific populations. However, the two lineages discerned by the cpDNA sequence variations were not supported by phylogenetic and AMOVA analyses of nrITS variation. Based on documented mutation rates for grasses, we estimated that the two cpDNA lineages of this species diverged at 0.64 Ma during the Pleistocene. This divergence was very consistent with the largest glaciation recorded in the QTP. Long-distance pollen migrations probably blurred the divergence boundary at the nrITS sequence variations. These findings imply that O. thoroldii probably experienced a long-term allopatric divergence plus more recent regional expansions that corresponded to Pleistocene climate changes. Our data also suggest that this grass species survived throughout the Pleistocene glacial stage within the extremely adverse habitats of the QTP.

Contrasts between the phylogeographic patterns of chloroplast and nuclear DNA highlight a role for pollen-mediated gene flow in preventing population divergence in an East Asian temperate tree

Plant phylogeographic studies in East Asia have provided support for the biogeographic hypothesis that the complex landforms and climate of this region have provided substantial opportunities for allopatric speciation. However, most of these studies have been based on maternally inherited chloroplast DNA (cpDNA) markers and were therefore unable to reveal the role of pollen-mediated gene flow in preventing population divergence. Here, we investigate the phylogeography of the Chinese walnut Juglans cathayensis, a temperate deciduous tree widely distributed across disjunct montane sites in subtropical China. We genotyped 19 populations using seven cpDNA fragments and ten nuclear microsatellite loci and modeled the ecological niche of J. cathayensis. CpDNA analysis identified a total of nine haplotypes, and each of the 19 sampled populations was fixed for a single haplotype, displaying a prominent phylogeographic structure. The results of ecological niche modeling indicated that J. cathayensis populations survived the last glaciation in situ, although they were probably more fragmented than today. In contrast, we detected a much weaker, but nonetheless clear, genetic structure based on nuclear microsatellite data. Our study demonstrates how extensive pollen flow can erase the genetic imprint of long-term refugial isolation in maternal lineages, effectively preventing population differentiation in temperate, particularly wind-pollinated, forest trees in subtropical China.

Genetic evidence for paternal inheritance of the chloroplast in four Australian Callitris species (Cupressaceae)

The mode of chloroplast inheritance was investigated in the four Australian conifer species; Callitris columellaris, C. intratropica, C. gracilis and C. verrucosa (Callitroideae, Cupressaceae), as a basis for future use of chloroplast genetic markers for the genus. Open-pollinated seeds and the foliage tissue of the mother trees were collected from one population per species, in which two distinct chloroplast haplotypes at the trnL (UAA) 5′ exon–trnF (GAA) region were co-distributed. In total, the DNA sequences of the chloroplast fragments in 255 samples were determined, and the haplotypes of the germinated seedlings and the mother trees were compared. Among the 16 mother trees examined across all species, 12 trees were shown to have produced at least one offspring with a different haplotype from the mother, indicating the occurrence of paternal inheritance of chloroplast in the fertilization processes. In binomial GLMM analyses, the haplotype of mother trees in C. columellaris, C. gracilis, and C. verrucosa did not significantly affect those of their offspring, and the predicted frequency of seedlings' haplotypes was compatible with the observed frequency in adult canopy trees. These findings provide a genetic support that paternal inheritance of chloroplast DNA via pollen dispersal would be dominant in the Callitris species.

Molecular evidence for natural hybridization in the mangrove fern genus Acrostichum

BackgroundNatural hybridization is prevalent in ferns, and plays an important role in fern evolution and speciation. In the Indo West-Pacific region, the mangrove fern genus Acrostichum consists of two largely sympatric species, A. aureum and A. speciosum. Although there has been no report of interspecific hybridization before, we found some individuals morphologically intermediate between them in Guangdong and Hainan, China, for the first time, which were suspected to be hybrids. In this study, we aimed to test the hypothesis of natural hybridization between A. aureum and A. speciosum in Guangdong and Hainan using three low-copy nuclear genes. A chloroplast intergenic spacer was used to infer the hybridization direction once the hybrid status was confirmed. In addition, we examined spore shapes and germination for these taxa.ResultsBoth A. aureum and A. speciosum showed a low level of polymorphism at all three nuclear genes; however, they were well separated at these loci. At both locations, each individual of the putative hybrid showed additivity in chromatograms at all sites where the two species showed fixed differences. Haplotype analysis at all three nuclear genes indicated that each individual of the putative hybrid possessed two haplotypes, matching with those of A. aureum and A. speciosum, respectively. Sequencing of the chloroplast trnV-trnM regions showed that A. aureum differed from A. speciosum by eleven nucleotide substitutions and three indels (insertions/deletions), and all sampled individuals of the putative hybrid had the identical sequences with A. speciosum. Compared with A. aureum and A. speciosum, the putative hybrid had much reduced spore germination rate.ConclusionsSequence data of the three nuclear genes provide compelling evidence for natural hybridization between A. aureum and A. speciosum, and all the hybrid individuals are likely F1s. The hybridization is unidirectional and A. speciosum is the maternal parent of the hybrid based on the assumption of maternal inheritance of chloroplast DNA. Human disturbance on mangrove habitats may facilitate the establishment of hybrids of Acrostichum.

Nymphaea albavar.rubrais a Hybrid ofN. albaandN. odorataas Evidenced by Molecular Analysis

Sequencing signals of the biparentally inherited ITS marker and sequence matching of the chloroplast trnK intron, matK and rbcL gene of an Indian plant identified as Nymphaea alba var. rubra contradict its identity. Additional signals depicted in chromatograms of the ITS region and the exact match of the maternally inherited chloroplast DNA sequences suggest that the Indian material is a hybrid of N. alba and N. odorata. Molecular cloning techniques resulted in the isolation of ITS alleles from the putative hybrid with DNA sequences not exclusive of either of the parental species. Such allelic DNA sequences confirmed that hybridization between N. alba and N. odorata has occurred. Our DNA sequence analyses indicate this plant is an interspecific hybrid involving N. odorata as the maternal parent, and N. alba as the paternal parent.

Uniparental Inheritance of Chloroplast DNA Is Strict in the Isogamous Volvocalean Gonium

BackgroundA problem has remained unresolved regarding the exceptions to the unilateral inheritance of chloroplast DNA (cpDNA) from MT+/female in Chlamydomonas and other volvocaleans demonstrated by the previous genetic analyses. For identification of the parental types of cpDNA, these studies used parents that have differences in restriction fragment length polymorphisms and exhibit partial sexual incompatibility.Methodology/Principal FindingsIn the present study, we used sexually compatible parents of the isogamous colonial volvocalean Gonium maiaprilis that seemed an ideal species to identify the pattern of cpDNA inheritance based on the length difference in the putative group I intron interrupted in the Rubisco large subunit gene and objective identification of mating types by the presence or absence of the minus-dominance (MID) gene. We examined patterns of inheritance of cpDNA and presence/absence of a MID ortholog (GmMID) in 107 F1 progeny of G. maiaprilis that were obtained by inducing germination of separated single zygotes. The results demonstrated no exception of the uniparental inheritance of cpDNA from the MT+ parent (lacking GmMID) in sexually compatible or genetically less divergent strains of G. maiaprilis.Conclusions/SignificanceThe present data suggest that the uniparental inheritance of cpDNA is likely more strict in crossings of less diverged strains or sexually compatible parental volvocaleans, and some genetic inconsistency between the parents may cause exceptional uniparental inheritance of cpDNA.

Phylogeographic structure of jack pine (Pinus banksiana; Pinaceae) supports the existence of a coastal glacial refugium in northeastern North America

The genetic structure of jack pine (Pinus banksiana Lamb.), a North American boreal conifer with large longitudinal distribution, was investigated to test for the possible existence of a genetically distinct lineage in the Maritimes region in northeastern North America, which could be indicative of a mid-latitude coastal refuge during the last glaciation. • One maternally inherited mitochondrial DNA (mtDNA) minisatellite marker and four paternally inherited chloroplast DNA (cpDNA) microsatellite markers were used to assess the range-wide geographical structure of jack pine populations with particular focus on northeastern North America. • The populations from the Maritimes region presented a unique mtDNA background characterized by very low diversity and the preponderance of a distinctive mitotype. The distribution of cpDNA diversity was not spatially structured, though three chlorotypes were restricted to the east. • MtDNA data suggest that populations from the Maritimes region derive from a genetically depauperated north-coastal refugium. Contrastingly, the much higher geographical uniformity observed for cpDNA variation indicates that gene flow by pollen had been much more effective than seed gene flow at homogenizing population structure.

Post-glacial history and introgression in Abies (Pinaceae) species of the Russian Far East inferred from both nuclear and cytoplasmic markers

Aim The main aim of the present study is to infer the post-glacial history of Abies species from north-east Asia and to test the hypotheses that coastal Abies populations suffered less from climatic fluctuations during Pleistocene glacial periods than their more continental counterparts, and that Sakhalin was a major area of introgression. Location Natural ranges of the fir species Abies nephrolepis, Abies sachalinensis and Abies holophylla in the Russian Far East, and of Abies gracilis, which is endemic to the Kamchatka Peninsula. Methods Nineteen populations were sampled for allozyme analysis. Seventeen of these populations were also screened for variation at two paternally inherited chloroplast DNA microsatellite loci (cpSSR) and variation at one maternally inherited mitochondrial marker (nad4-3/4). Finally a subset of 11 populations was analysed with amplified fragment length polymorphism (AFLP). Comparisons were made with already available Abies sibirica data. For all sets of markers, we estimated genetic diversity and differentiation using an analysis of molecular variance (AMOVA). Population clustering was assessed with a Bayesian approach implemented in structure v.2.3. Results Among the three major species, A. sibirica, A. nephrolepis and A. sachalinensis, A. sachalinensis demonstrated the highest cytoplasmic and nuclear diversity and the most continental species, A. sibirica, the lowest. Both nuclear and mitochondrial DNA markers revealed the presence of a transitional zone on Sakhalin Island between A. nephrolepis and A. sachalinensis of south Sakhalin. The structure analysis delivered very clear results confirming the admixed origin of A. sachalinensis, with a genetic contribution from A. nephrolepis. No variation in cytoplasmic markers was found in A. gracilis, suggesting the occurrence of a recent bottleneck. Main conclusions There is a clear reduction of genetic diversity in Abies species from the Pacific coast into the continent. The higher diversity in A. sachalinensis could have two causes: a larger effective population size in the islands due to relatively stable climatic conditions and consequently less pronounced demographic fluctuations in population size and/or hybridization with continental and Japanese populations. Sakhalin Island is a major transitional zone for conifer species. Finally, the fir from Kamchatka, A. gracilis, should be regarded as a separate species closely related to the A. nephrolepis–A. sachalinensis complex.

Variation of selfing rate and inbreeding depression among individuals and across generations within an admixed Cedrus population

We investigated the variation and short-term evolution of the selfing rate and inbreeding depression (ID) across three generations within a cedar forest that was established from admixture ca 1860. The mean selfing rate was 9.5%, ranging from 0 to 48% among 20 seed trees (estimated from paternally inherited chloroplast DNA). We computed the probability of selfing for each seed and we investigated ID by comparing selfed and outcrossed seeds within progenies, thus avoiding maternal effects. In all progenies, the germination rate was high (88-100%) and seedling mortality was low (0-12%). The germination dynamics differed significantly between selfed and outcrossed seeds within progenies in the founder gene pool but not in the following generations. This transient effect of selfing could be attributed to epistatic interactions in the original admixture. Regarding the seedling growth traits, the ID was low but significant: 8 and 6% for height and diameter growth, respectively. These rates did not vary among generations, suggesting minor gene effects. At this early stage, outcrossed seedlings outcompeted their selfed relatives, but not necessarily other selfed seedlings from other progenies. Thus, purging these slightly deleterious genes may only occur through within-family selection. Processes that maintain a high level of genetic diversity for fitness-related traits among progenies also reduce the efficiency of purging this part of the genetic load.

Phylogeography of Douglas-fir based on mitochondrial and chloroplast DNA sequences: testing hypotheses from the fossil record

The integration of fossil and molecular data can provide a synthetic understanding of the ecological and evolutionary history of an organism. We analysed range-wide maternally inherited mitochondrial DNA and paternally inherited chloroplast DNA sequence data with coalescent simulations and traditional population genetic methods to test hypotheses of population divergence generated from the fossil record of Douglas-fir (Pseudotsuga menziesii), an ecologically and economically important western North American conifer. Specifically, we tested (i) the hypothesis that the Pliocene orogeny of the Cascades and Sierra Nevada caused the divergence of coastal and Rocky Mountain Douglas-fir varieties; and (ii) the hypothesis that multiple glacial refugia existed on the coast and in the Rocky Mountains. We found that Douglas-fir varieties diverged about 2.11 Ma (4.37 Ma-755 ka), which could be consistent with a Pliocene divergence. Rocky Mountain Douglas-fir probably resided in three or more glacial refugia. More variable molecular markers would be required to detect the two coastal refugia suggested in the fossil record. Comparison of mitochondrial DNA and chloroplast DNA variation revealed that gene flow via pollen linked populations isolated from seed exchange. Postglacial colonization of Canada from coastal and Rocky Mountain refugia near the ice margin at the Last Glacial Maximum produced a wide hybrid zone among varieties that formed almost exclusively by pollen exchange and chloroplast DNA introgression, not seed exchange. Postglacial migration rates were 50-165 m/year, insufficient to track projected 21st century warming in some regions. Although fossil and genetic data largely agree, each provides unique insights.

Paternal inheritance of mitochondria in Chlamydomonas

To analyze mitochondrial DNA (mtDNA)inheritance, differences in mtDNA between Chlamydomonas reinhardtii and Chlamydomonas smithii, respiration deficiency and antibiotic resistance were used to distinguish mtDNA origins. The analyses indicated paternal inheritance. However, these experiments raised questions regarding whether paternal inheritance occurred normally.Mitochondrial nucleoids were observed in living zygotes from mating until 3 days after mating and then until progeny formation. However, selective disappearance of nucleoids was not observed. Subsequently, experimental serial backcrosses between the two strains demonstrated strict paternal inheritance. The fate of mt+ and mt- mtDNA was followed using the differences in mtDNA between the two strains. The slow elimination of mt+ mtDNA through zygote maturation in darkness was observed, and later the disappearance of mt+ mtDNA was observed at the beginning of meiosis. To explain the different fates of mtDNA, methylation status was investigated; however, no methylation was detected. Variously constructed diploid cells showed biparental inheritance. Thus, when the mating process occurs normally, paternal inheritance occurs. Mutations disrupting mtDNA inheritance have not yet been isolated. Mutations that disrupt maternal inheritance of chloroplast DNA (cpDNA) do not disrupt inheritance of mtDNA. The genes responsible for mtDNA inheritance are different from those of chloroplasts.

Contrasting geographical patterns of ancient and modern genetic lineages in Mediterranean Abies species

The diversification and distribution of Abies species throughout the Mediterranean region has led to a complex of species which are difficult to classify. An open question is whether these mainly allopatric taxa have exchanged genetic information via secondary contact. We studied the variation and geographic distribution of paternally inherited chloroplast DNA markers in nine Mediterranean Abies taxa. Markers with high and low mutation rates were applied in order to differentiate among a scenario of secondary genetic contact and a scenario of complete isolation after speciation. The observed molecular variation was analysed using statistical parsimony, geostatistics, and measures of population genetic differentiation. Ancient paternal lineages, represented by markers with low mutation rates, were shared among species. The central and widespread A. alba retained all ancient lineages whereas other species exhibited fewer, down to a single lineage. In contrast, modern lineages, depicted by markers with high mutation rates, were largely separated among species. The western Mediterranean A. pinsapo and A. numidica were clearly separated from each other and from the remaining Abies species. This indicates the absence of secondary contact. The same scenario applies to the eastern Mediterranean Abies species. An exception is the parapatric complex of A. alba, A. cephalonica, and their supposed hybrid A. borisii regis, which exhibited evidence of secondary contact.

Genetic diversity and phylogeographic analysis of Pinus leiophylla: a post‐glacial range expansion

AbstractAim Mexico is a centre of diversity for species of the genus Pinus, most of which have restricted geographical distributions. An exception is Pinus leiophylla Schiede and Deppe, which is widely distributed throughout most of Mexico’s mountainous regions. We attempt to reconstruct the phylogeographic history of this species, in order to determine if its current broad distribution is associated with major events of environmental change that occurred during the Quaternary.Location Coniferous forests in Sierra Madre Occidental, Eje Volcánico Transversal and Sierra Montañosa del Norte de Oaxaca, Mexico.Methods A total of 323 individuals of both P. leiophylla var. leiophylla and P. leiophylla var. chihuahuana sampled from 22 populations were screened for variation at six paternally inherited chloroplast DNA microsatellite markers (cpSSR). In addition to haplotypic diversity estimates and neutrality tests, the following clustering methods were employed: principal components analysis (PCA), analysis of molecular variance (AMOVA), spatial analysis of molecular variance (SAMOVA), haplotype network and a technique similar to Croizat’s panbiogeographical method of individual and generalized tracks.Results The combination of mutations at the six microsatellites yielded a total of 92 different haplotypes. The percentage of shared haplotypes between varieties (P. leiophylla var. leiophylla and P. leiophylla var. chihuahuana) was only 2.2%. The average haplotypic diversity for the species was H = 0.760. PCA and SAMOVA indicate the presence of four main genetic clusters. The estimated divergence time between the two most frequent haplotypes was between 75,000 and 110,000 years. Significantly large negative Fs values suggest that most of the sampled populations are currently expanding. Individual and generalized tracks identified three potential zones that may have harboured ancestral populations of P. leiophylla and from which the expansion of this species started, as well as two secondary contact zones between the two varieties.Main conclusions The results indicate that one of the three potential areas hypothesized to have harboured ancestral populations of P. leiophylla may be related to the origin of P. leiophylla var. chihuahuana, while the other two may be related to the origin of P. leiophylla var. leiophylla. The current broad distribution of P. leiophylla is probably associated with its strong colonization ability.

The Chloroplast DNA Polymorphisms of White Oaks of Section Quercus in The Central Balkans

Abstract A total of 444 oak trees from 110 populations from a previously under-sampled area in the central Balkans were analysed using four primer/enzyme combinations which amplified and restricted four, largely non-coding regions of the maternally inherited chloroplast DNA. Using the nomenclature of PETIT et al. (2002 a) to classify the haplotypes and lineages, the seven haplotypes that were found in Croatia, Bosnia and Herzegovina, Montenegro, Albania, Macedonia and southern Kosovo consisted of haplotypes 2, 4, 5, 6, 7, 17, 31, as well as the subtypes of haplotypes 4 (a), 5 (a, b, c), and 17 (a). Five of these haplotypes belong to lineage A. One of these, haplotype 5, is present throughout the sampled area. The distributions of the other haplotypes from this lineage are more geographically structured. The other two haplotypes, haplotype 2 and haplotype 17, belong to lineages C and E, respectively. The data are combined with previous data by PETIT et al. (2002 b) to provide more detailed information of the postglacial routes of colonisation taken by oaks in south-eastern Europe.

SEXUALITY AND UNIPARENTAL INHERITANCE OF CHLOROPLAST DNA IN THE ISOGAMOUS GREEN ALGA ULVA COMPRESSA (ULVOPHYCEAE)(1).

Ulva compressa L. is a heterothallic macroalga considered to be in the early evolutionary stage between isogamy and anisogamy. Two genetic lines of this species, each consisting of gametophytes with opposite mating types, were collected on the coasts of Ehime and Iwate prefectures: MGEC-1 (mt(+) ) and MGEC-2 (mt(-) ) from Ehime, and MGEC-5 (mt(+) ) and MGEC-6 (mt(-) ) from Iwate. Their relative gamete sizes (i.e., cell volumes) do not correspond to their mating types: MGEC-6 (19.8 μm(3) ) > MGEC-1 (18.6 μm(3) ) > MGEC-5 (17.0 μm(3) ) > MGEC-2 (10.1 μm(3) ). The pattern of organelle inheritance is an important sexual characteristic in many eukaryotes. We therefore investigated the relationship between gamete size and the inheritance of chloroplast DNA (cpDNA). Polymorphisms between the cpDNA of the two lines were used as markers. We found a 24 bp insertion between psbF and psbL, and the substitution of a StyI site (from CCAAGG to TCAAGG) in the intergenic region between petD and accD. Two interline crosses (MGEC-1 × MGEC-6 and MGEC-2 × MGEC-5) produced 42 and 38 zygotes, respectively. PCR and PCR-RFLP analyses showed that the cpDNA of the mt(+) gametes was consistently inherited in both crosses. The cpDNA is inherited from one parent only, and it depends not on gamete size but on being mt(+) . The cpDNA was observed during crossing and in the zygotes 6 h after mating. In 6% of the zygotes, the cpDNA derived from the mt(-) gametes disappeared 3-4 h after mating. Preferential digestion of the cpDNA in the zygote's mt(-) gamete may form the basis for uniparental inheritance of cpDNA.

Molecular characterization of reciprocal crosses of Aerides vandarum and Vanda stangeana (Orchidaceae) at the protocorm stage

Aerides vandarum and Vanda stangeana are two rare and endangered vandaceous orchids with immense floricultural traits. The intergeneric hybrids were synthesized by performing reciprocal crosses between them. In vitro germination response of the immature hybrid embryos was found to be best on half-strength Murashige and Skoog medium supplemented with 20% (v/v) coconut water/liquid endosperm from tender coconut. Determination of hybridity was made as early as the immature seeds or embryos germinated in vitro, using randomly amplified polymorphic DNA (RAPD) markers. Out of 15 arbitrarily chosen decamer RAPD primers, two were found to be useful in amplification of polymorphic bands specific to the parental species and their presence in the reciprocal crosses. However, a decisive profile that can identify the reciprocal crosses could not be provided by RAPD. Amplification of the trnL-F non-coding regions of chloroplast DNA of the parent species and hybrids aided easy identification of the reciprocal crosses from the fact that maternal inheritance of chloroplast DNA held true for these intergeneric hybrids. Subsequent restriction digestion of the polymerase chain reaction (PCR) amplified trnL-F non-coding regions of chloroplast DNA also consolidated the finding. Such PCR-based molecular markers could be used for early determination of hybridity and easy identification of the reciprocal crosses.

Testing a hypothesis of unidirectional hybridization in plants: observations on Sonneratia, Bruguiera and Ligularia.

BackgroundWhen natural hybridization occurs at sites where the hybridizing species differ in abundance, the pollen load delivered to the rare species should be predominantly from the common species. Previous authors have therefore proposed a hypothesis on the direction of hybridization: interspecific hybrids are more likely to have the female parent from the rare species and the male parent from the common species. We wish to test this hypothesis using data of plant hybridizations both from our own experimentation and from the literature.ResultsBy examining the maternally inherited chloroplast DNA of 6 cases of F1 hybridization from four genera of plants, we infer unidirectional hybridization in most cases. In all 5 cases where the relative abundance of the parental species deviates from parity, however, the direction is predominantly in the direction opposite of the prediction based strictly on numerical abundance.ConclusionOur results show that the observed direction of hybridization is almost always opposite of the predicted direction based on the relative abundance of the hybridizing species. Several alternative hypotheses, including unidirectional postmating isolation and reinforcement of premating isolation, were discussed.

Ancestry and divergence of subtropical montane forest isolates: molecular biogeography of the genus Abies (Pinaceae) in southern México and Guatemala

The genus Abies has a complex history in southern México and Guatemala. In this region, four closely related species, Abies flinckii, A. guatemalensis, A. hickelii, and A. religiosa, are distributed in fragmented and isolated montane populations. Range-wide genetic variation was investigated across species using cytoplasmic DNA markers with contrasted inheritance. Variation at two maternally inherited mitochondrial DNA markers was low. All species shared two of the nine mitotypes detected, while the remaining seven mitochondrial DNA types were restricted to a few isolated stands. Mitochondrial genetic differentiation across taxa was high (G(ST) = 0.933), it was not related to the taxonomic identity (amova; P > 0.05) of the populations, and it was not phylogeographically structured (G(ST) approximately N(ST)). In contrast, variation at three paternally inherited chloroplast DNA microsatellites was high. Chloroplast genetic differentiation was lower (G(ST) = 0.402; R(ST) = 0.547) than for mitochondrial DNA, but it was significantly related to taxonomy (amova; P < 0.001), and exhibited a significant phylogeographical structure (G(ST) < R(ST)). Different analyses of population structure indicated that A. flinckii was the most divergent taxon, while the remaining three species formed a relatively homogeneous group. However, a small number of the populations of these three taxa, all located at the limits of their respective ranges or in the Transverse Volcanic Belt, diverged from this main cluster. These trends suggest that the Mesoamerican Abies share a recent common ancestor and that their divergence and speciation is mainly driven by genetic drift and isolation during the warm interglacial periods.

Chloroplast DNA variation in the European herb Silene dioica (red campion): postglacial migration and interspecific introgression

Many recent studies of intraspecific geographic variation in maternally inherited chloroplast DNA (cpDNA) in European trees have revealed haplotype distributions that can be interpreted in terms of scenarios of postglacial migration and range expansion. However, there is still a lack of comparable information from widespread herb species. In the present study, we investigated the geographic distribution of cpDNA variation in 124 populations, covering a large part of the range of the widespread, dioecious, European herb, Silene dioica. PCR-RFLP analysis revealed 24 different cpDNA haplotypes. As in the majority of European tree species, the large-scale geographic distributions of the most common S. dioica haplotypes suggest that the species colonized Europe from more than one geographic source. Material from 16 populations of S. latifolia and five hybrid populations was also included in the study for comparative purposes. Five out of seven haplotypes detected in S. latifolia were shared with S. dioica. The similarity of the geographic distributions of the shared haplotypes in both species is consistent with a history of past and/or recent interspecific hybridization and introgression between these closely related plants. The two haplotypes detected only in S. latifolia were present in populations in the Mediterranean region – on the southern margin of the species’ area of sympatry, or outside the range of S. dioica.