Mating patterns and contemporary gene flow by pollen in a large continuous and a small isolated population of the scattered forest tree Sorbus torminalis

The influence of population size and spatial isolation on contemporary gene flow by pollen and mating patterns in temperate forest trees are not well documented, although they are crucial factors in the life history of plant species. We analysed a small, isolated population and a large, continuous population of the insect-pollinated tree species Sorbus torminalis in two consecutive years. The species recently experienced increased habitat fragmentation due to altered forest management leading to forests with closed canopies. We estimated individual plant size, percentage of flowering trees, intensity of flowering, degree of fruiting and seed set per fruit, and we determined mating patterns, pollen flow distances and external gene flow in a genetic paternity analysis based on microsatellite markers. We found clear effects of small population size and spatial isolation in S. torminalis. Compared with the large, continuous population, the small and isolated population harboured a lower percentage of flowering trees, showed less intense flowering, lower fruiting, less developed seeds per fruit, increased selfing and received less immigrant pollen. However, the negative inbreeding coefficients (F(IS)) of offspring indicated that this did not result in inbred seed at the population level. We also show that flowering, fruiting and pollen flow patterns varied among years, the latter being affected by the size of individuals. Though our study was unreplicated at the factor level (i.e. isolated vs non-isolated populations), it shows that small and spatially isolated populations of S. torminalis may also be genetically isolated, but that their progeny is not necessarily more inbred.     

Contrasting patterns of pollen and seed flow influence the spatial genetic structure of sweet vernal grass (Anthoxanthum odoratum) populations

The spatial genetic structure of plant populations is determined by a combination of gene flow, genetic drift, and natural selection. Gene flow in most plants can result from either seed or pollen dispersal, but detailed investigations of pollen and seed flow among populations that have diverged following local adaptation are lacking. In this study, we compared pollen and seed flow among 10 populations of sweet vernal grass (Anthoxanthum odoratum) on the Park Grass Experiment. Overall, estimates of genetic differentiation that were based on chloroplast DNA (cpDNA) and, which therefore resulted primarily from seed flow, were lower (average F(ST) = 0.058) than previously published estimates that were based on nuclear DNA (average F(ST) = 0.095). Unlike nuclear DNA, cpDNA showed no pattern of isolation by adaptation; cpDNA differentiation was, however, inversely correlated with the number of additions (nutrients and lime) that each plot had received. We suggest that natural selection is restricting pollen flow among plots, whereas nutrient additions are increasing seed flow and genetic diversity by facilitating the successful germination and growth of immigrant seeds. This study highlights the importance of considering all potential gene flow mechanisms when investigating determinants of spatial genetic structure, and cautions against the widespread assumption that pollen flow is more important than seed flow for population connectivity in wind-pollinated species.     

Spatial genetic structure among and within populations of Primula sieboldii growing beside separate streams

We investigated the hierarchical genetic structure of SSR (simple sequence repeats) and cpDNA (chloroplast DNA) polymorphisms among and within populations of Primula sieboldii, a heterostylous clonal herb. Seven out of eight populations at the study site, located in a mountainous region of Nagano Prefecture, had each developed alongside a different stream, and the other occurred on a flat area 70 m from the nearest stream. The magnitude of genetic differentiation among streamside populations in maternally inherited cpDNA (Phi = 0.341) was much higher than that in biparentally inherited SSRs (Phi = 0.011). This result suggests that seed dispersal among streams was restricted, and pollen was the primary agent of gene flow among streamside populations. In contrast, genetic differentiation among subpopulations within streams were low at both markers (Phi = 0.053 for cpDNA, Phi = 0.025 for SSR). This low differentiation among subpopulations in cpDNA compared with that among streamside populations suggest that seed dispersal occur along the stream probably during flooding. This hypothesis was supported by the fact that in cpDNA haplotypes, no clear genetic structure was detected within the streamside population, while a significant genetic structure was found within 20 m in the nonstreamside population. Furthermore, within the streamside populations, two pairs of ramets with identical multilocus genotypes for eight SSR loci were distantly (> 50 m) distributed along the same streamside, suggesting dispersal of clonal propagule. Our study showed that the heterogeneity of the landscape can influence gene flow and hence spatial genetic structure.     

Genetic effects of chronic habitat fragmentation on tree species: the case of Sorbus aucuparia in a deforested Scottish landscape

Sustainable forest restoration and management practices require a thorough understanding of the influence that habitat fragmentation has on the processes shaping genetic variation and its distribution in tree populations. We quantified genetic variation at isozyme markers and chloroplast DNA (cpDNA), analysed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in severely fragmented populations of Sorbus aucuparia (Rosaceae) in a single catchment (Moffat) in southern Scotland. Remnants maintain surprisingly high levels of gene diversity (HE) for isozymes (HE = 0.195) and cpDNA markers (HE = 0.490). Estimates are very similar to those from non-fragmented populations in continental Europe, even though the latter were sampled over a much larger spatial scale. Overall, no genetic bottleneck or departures from random mating were detected in the Moffat fragments. However, genetic differentiation among remnants was detected for both types of marker (isozymes Theta n = 0.043, cpDNA Theta c = 0.131; G-test, P-value < 0.001). In this self-incompatible, insect-pollinated, bird-dispersed tree species, the estimated ratio of pollen flow to seed flow between fragments is close to 1 (r = 1.36). Reduced pollen-mediated gene flow is a likely consequence of habitat fragmentation, but effective seed dispersal by birds is probably helping to maintain high levels of genetic diversity within remnants and reduce genetic differentiation between them.     

DNA from bird-dispersed seed and wind-disseminated pollen provides insights into postglacial colonization and population genetic structure of whitebark pine (Pinus albicaulis)

Uniparentally inherited mitochondrial (mt)DNA and chloroplast (cp)DNA microsatellites (cpSSRs) were used to examine population genetic structure and biogeographic patterns of bird-dispersed seed and wind-disseminated pollen of whitebark pine (Pinus albicaulis Engelm.). Sampling was conducted from 41 populations throughout the range of the species. Analyses provide evidence for an ancestral haplotype and two derived mtDNA haplotypes with distinct regional distributions. An abrupt contact zone between mtDNA haplotypes in the Cascade Range suggests postglacial biogeographic movements. Among three cpSSR loci, 42 haplotypes were detected within 28 cpSSR sample populations that were aggregated into six regions. Analysis of molecular variance (amova) was used to determine the hierarchical genetic structure of cpSSRs. amova and population pairwise comparisons (FST ) of cpSSR, and geographical distribution of mtDNA haplotypes provide insights into historical changes in biogeography. The genetic data suggest that whitebark pine has been intimately tied to climatic change and associated glaciation, which has led to range movements facilitated by seed dispersal by Clark's nutcracker (Nucifraga columbiana Wilson). The two hypotheses proposed to explain the genetic structure are: (i) a northward expansion into Canada and the northern Cascades in the early Holocene; and (ii) historical gene flow between Idaho and the Oregon Cascades when more continuous habitat existed in Central Oregon during the late Pleistocene. Genetic structure and insights gained from historical seed movements provide a basis on which to develop recovery plans for a species that is at risk from multiple threats.     

Estimation of gene flow into fragmented populations of Bursera simaruba (Burseraceae) in the dry-forest life zone of Puerto Rico

We examined the impact of habitat fragmentation on gene flow in populations of the neotropical tree Bursera simaruba. In particular, we compared the effectiveness of three common techniques to estimate gene flow in the context of a highly disturbed system. Paternity analysis on emerging seedlings from eight small (N = 3 to 9) stands of trees showed that between 45% and 100% of seedlings were sired from outside their stand, indicating pollen moved readily over the isolation distances examined. Based on six populations of 21-24 trees each, estimates of allozyme genetic diversity (P(s) = 73.3%; H(e) = 0.244) were higher than those reported for species with similar life history traits. Indirect, F(ST)-based gene flow estimates for these six populations yielded an estimate of 3.57 migrants per generation, although possible violations of model assumptions limit the reliability of the estimate. A twogener analysis showed pollen moved either 320 m or 361 m and that there were only 2.46 effective pollen donors per maternal tree. Despite the potential for long-distance pollen movement, seed abortion was high, especially in stands with fewer than four trees. Population size, rather than isolation distance, appears to limit reproduction in the populations examined.     

Population structure of the large Japanese field mouse, Apodemus speciosus (Rodentia: Muridae), in suburban landscape, based on mitochondrial D-loop sequences

Genetic structure of the large Japanese field mouse populations in suburban landscape of West Tokyo, Japan was determined using mitochondrial DNA control region sequence. Samples were collected from six habitats linked by forests and green tract along the Tama River, and from two forests segregated by urban areas from those continuous habitats. Thirty-five haplotypes were detected in 221 animals. Four to eight haplotypes were found within each local population belonging to the continuous landscape. Some haplotypes were shared by two or three adjacent local populations. On the other hand, two isolated habitats were occupied by one or two indigenous haplotypes. Significant genetic differentiation between all pairs of local populations, except for one pair in the continuous habitats, was found by analysis of molecular variance (amova). The geographical distance between habitats did not explain the large variance of pairwise F(ST)-values among local populations. F(ST)-values between local populations segregated by urban areas were higher than those between local populations in the continuous habitat, regardless of geographical distance. The results of this study demonstrated quantitatively that urban areas inhibit the migration of Apodemus speciosus, whereas a linear green tract along a river functions as a corridor. Moreover, it preserves the metapopulation structure of A. speciosus as well as the corridors in suburban landscape.     

Habitat loss other than fragmentation per se decreased nuclear and chloroplast genetic diversity in a monoecious tree

Generally, effect of fragmentation per se on biodiversity has not been separated from the effect of habitat loss. In this paper, using nDNA and cpDNA SSRs, we studied genetic diversity of Castanopsis sclerophylla (Lindl. & Paxton) Schotty populations and decoupled the effects of habitat loss and fragmentation per se. We selected seven nuclear and six cpDNA microsatellite loci and genotyped 460 individuals from mainland and island populations, which were located in the impoundment created in 1959. Number of alleles per locus of populations in larger habitats was significantly higher than that in smaller habitats. There was a significant relationship between the number of alleles per locus and habitat size. Based on this relationship, the predicted genetic diversity of an imaginary population of size equaling the total area of the islands was lower than that of the global population on the islands. Re-sampling demonstrated that low genetic diversity of populations in small habitats was caused by unevenness in sample size. Fisher's α index was similar among habitat types. These results indicate that the decreased nuclear and chloroplast genetic diversity of populations in smaller habitats was mainly caused by habitat loss. For nuclear and chloroplast microsatellite loci, values of F(ST) were 0.066 and 0.893, respectively, and the calculated pollen/seed dispersal ratio was 162.2. When separated into pre-and post-fragmentation cohorts, pollen/seed ratios were 121.2 and 189.5, respectively. Our results suggest that habitat loss explains the early decrease in genetic diversity, while fragmentation per se may play a major role in inbreeding and differentiation among fragmented populations and later loss of genetic diversity.     

THE RELATIVE IMPORTANCE OF HISTORICAL EVENTS AND GENE FLOW ON THE POPULATION STRUCTURE OF A MEDITERRANEAN RAGWORT,SENECIO GALLICUS (ASTERACEAE)

Comparisons of cytoplasmic and nuclear diversity within and among natural plant populations have the potential to distinguish the relative influences of seed and pollen dispersal on contemporary gene flow, or alternatively, may permit inferences of the colonization history of a species via seed. We examined patterns of cpDNA and allozyme variation in Senecio gallicus, a diploid, annual plant that occurs in both coastal and ruderal inland areas of the Iberian Peninsula and southern France. The species appears to have a strong propensity for long-distance seed dispersal. Five cpDNA haplotypes were found by RFLP analysis among a sample of 111 individuals derived from 11 populations. Differences in haplotype frequencies across populations were most evident with respect to a dramatic increase in the frequency of a derived haplotype from coastal to inland localities. The level of cpDNA differentiation among populations within the inland group (θ₀ = 0.07) was significantly less than that seen within the coastal group (θ₀ = 0.41). In contrast, for allozymes, no significant difference in population structure was evident between collections from coastal and inland habitats. At the rangewide geographic scale, there was only a very weak association between inferred levels of gene flow and geographic distance for cpDNA, and no such association was found for allozymes. It appears that while seed movement in the species might be sufficiently great to disturb the pattern of isolation by distance for cpDNA, it cannot fully account for the nearly randomized spatial structure at polymorphic allozyme loci. It is suggested that isolation of populations in Atlantic-Mediterranean coastal refugia during previous glacial maxima, and the effects of subsequent colonization events in inland areas, have had an important effect on molding the present genetic structure of the species.     

Genetic variation and population differentiation of Michelia formosana (Magnoliaceae) based on cpDNA variation and RAPD fingerprints: relevance to post-Pleistocene recolonization

We used sequence variation of the atpB- rbcL intergenic spacer of cpDNA and nested clade analysis to assess the phylogeographic pattern of Michelia formosana, a species restricted to Taiwan and the Ryukyus. In total, 31 haplotypes were identified and clustered into four major chlorotypes. Genetic composition of nearly all populations was heterogeneous and paraphyletic phylogenetically. Although the apportionment of cpDNA variation hardly revealed a geographic pattern due to the coancestry of dominant sequences, some chlorotypes were restrictedly distributed. According to the patterns of clade dispersion and displacement, a reconstructed minimum spanning network revealed that historical events of past fragmentation and range expansion, associated with glaciation, may have shaped the phylogeographic patterns of M. formosana. Four possible refugia were identified: the Iriomote and Ishigaki Islands (the southern Ryukyus), Wulai (northern Taiwan), and Nanjen (southern Taiwan), on the basis of the interior positions of their haplotypes in the network and the high level of nucleotide diversity. Given insufficient time for coalescence at the cpDNA locus since the late Pleistocene recolonization, lineage sorting led to low levels of genetic differentiation among populations. In contrast, hierarchical examination of the random amplified polymorphic DNA (RAPD) data scored from six populations across three geographical regions, using an analysis of molecular variance (AMOVA), indicated high genetic differentiation both among populations (Phi(ST) = 0.471) and among regions (Phi(CT) = 0.368). An unweighted pair group method with arithmetic mean (UPGMA) tree of the RAPD fingerprints revealed that populations of two offshore islands of eastern Taiwan ( M. formosana var. kotoensis) were clustered with geographically remote populations of the Ryukyus instead of those in southern Taiwan, suggesting some historical division due to geographic barriers of the central mountain range. In contrast to the paraphyly of the nearly neutral cpDNA alleles, differentiated RAPDs may have experienced diversifying selection.     

Inheritance of chloroplast DNA is not strictly maternal in Silene vulgaris (Caryophyllaceae): evidence from experimental crosses and natural populations

Chloroplast DNA (cpDNA) is maternally inherited in the majority, but not all, of angiosperm species. The mode of inheritance of cpDNA is a critical determinant of its molecular evolution and of its population genetic structure. Here, we present the results of investigations of the inheritance of cpDNA in Silene vulgaris, a plant used in a variety of studies in which cpDNA is an important component. PCR/RFLP markers were used to compare mother and offspring cpDNA genotypes sampled from two natural populations, and mother, father, and offspring genotypes obtained from controlled greenhouse crosses. Ten of 215 offspring cpDNA genotypes studied in the controlled crosses and three of 156 offspring from natural populations did not match that of the mother, demonstrating rare nonmaternal inheritance. That the chloroplast genome is occasionally transmitted through pollen is discussed in the context of using S. vulgaris cpDNA as a marker in studies of seed dispersal and when considering the joint evolution of the chloroplast and mitochondrial genomes.     

Distribution of chloroplast DNA diversity within and among populations in gynodioecious Beta vulgaris ssp. maritima (Chenopodiaceae)

With the recent technical advances in molecular biology, chloroplast DNA (cpDNA) has become a marker used for the study of cytoplasmic differentiation of natural populations of plants. As chloroplasts are maternally inherited in most plant species, the seed component of gene flow is thus made accessible. We present here a study of cpDNA polymorphism within the maritima subspecies of the gynodioecious Beta vulgaris in which we try to assess the impact of such a reproductive system on seed flow. One hundred and eighty-eight wild beets were sampled from 20 hermaphroditic and 20 gynodioecious (i.e. containing both hermaphroditic and female plants) populations from the Atlantic coast of Europe. cpDNA variability in these populations was characterized with a rapid restriction fragment length polymorphism (RFLP) method. Eight cpDNA haplotypes were found. Strong differentiation among populations was observed ( F _ST = 0.43) and was consistent with isolation by distance, although most of the cpDNA haplotypes were ubiquitous. Gynodioecy seems to affect the distribution of cpDNA diversity: gynodioecious populations of Beta vulgaris ssp. maritima contained a greater number of cpDNA types but were less differentiated among themselves than hermaphroditic ones.     

Genetic variation and population differentiation in the lichen-forming ascomycete Xanthoria parietina on the island Storfosna, central Norway

Genetic diversity and fine-scale population structure in the lichen-forming ascomycete Xanthoria parietina was investigated using sequence variation in part of the intergenic spacer (IGS) and the complete internal transcribed spacer (ITS) regions of the nuclear ribosomal DNA. Sampling included 213 and 225 individuals, respectively, from seven populations in two different habitats, bark and rock, on the island Storfosna off the central west coast of Norway. Both markers revealed significant variation and a total of 10 IGS and 16 ITS haplotypes were found. There were no signs of significant positive spatial autocorrelation at any spatial size class down to 10% of transect length, nor did we find significant deviations from neutrality or signs of historical population expansion. Analysis of molecular variance (amova) indicated that most of the genetic variance observed was within populations, but when populations were grouped according to habitat, more than a quarter of the variance was explained among groups. Pairwise comparisons of populations (F(ST), exact tests of population differentiation) revealed significant differentiation between populations in different habitats (on bark or rock), but not between populations in the same habitat. Haplotype networks show that internal and presumably old haplotypes are shared between habitats, whereas terminal haplotypes tend to be unique to a habitat, mostly bark. We interpret the observed pattern to mean that there is no evidence of restricted gene flow between populations in the same habitat at the present spatial scale (interpopulation distances one or a few kilometres). On the other hand, differentiation between habitats is considerable, which we attribute to restricted gene flow between habitats (habitat isolation). Evidence suggests that the observed differentiation did not evolve locally. Estimates of divergence time between populations in the respective habitats indicate that an ancestral population started to diverge at least 34,000 years ago but probably much further back in time.     

Phylogeography of the Qinghai-Tibetan Plateau endemic Juniperus przewalskii (Cupressaceae) inferred from chloroplast DNA sequence variation

The vegetation of the northeast Qinghai-Tibetan Plateau is dominated by alpine meadow and desert-steppe with sparse forests scattered within it. To obtain a better understanding of the phylogeography of one constituent species of the forests in this region, we examined chloroplast trnT-trnF and trnS-trnG sequence variation within Juniperus przewalskii, a key endemic tree species. Sequence data were obtained from 392 trees in 20 populations covering the entire distribution range of the species. Six cpDNA haplotypes were identified. Significant population subdivision was detected (G(ST) = 0.772, N(ST) = 0.834), suggesting low levels of recurrent gene flow among populations and significant phylogeographic structure (N(ST) > G(ST), P < 0.05). Eight of the nine disjunct populations surveyed on the high-elevation northeast plateau were fixed for a single haplotype (A), while the remaining, more westerly population, contained the same haplotype at high frequency together with two low frequency haplotypes (C and F). In contrast, most populations that occurred at lower altitudes at the plateau edge were fixed or nearly fixed for one of two haplotypes, A or E. However, two plateau edge populations had haplotype compositions different from the rest. In one, four haplotypes (A, B, D and E) were present at approximately equivalent frequencies, which might reflect a larger refugium in the area of this population during the last glacial period. Phylogenetic analysis indicated that the most widely distributed haplotype A is not ancestral to other haplotypes. The contrasting phylogeographic structures of the haplotype-rich plateau edge area and the almost haplotype-uniform plateau platform region indicate that the plateau platform was recolonized by J. przewalskii during the most recent postglacial period. This is supported by the findings of a nested clade analysis, which inferred that postglacial range expansion from the plateau edge followed by recent fragmentation is largely responsible for the present-day spatial distribution of cpDNA haplotypes within the species.     

Population genetic analysis of European Prunus spinosa (Rosaceae) using chloroplast DNA markers

Chloroplast DNA diversity in Prunus spinosa, a common shrub of European deciduous forests, was assessed using the polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) technique. Thirty-two haplotypes were detected in 25 populations spread across the European continent. Ten haplotypes were shared by two or more populations, and 22 were private. The major proportion of the total cpDNA diversity (H(T) = 0.73) was located within the populations (H(S) = 0.49), and differentiation between populations was low (G(ST) = 0.33) compared with other forest species. Haplotype diversity was higher in southern Europe than in northern Europe, indicating probable localization of glacial refugia in southern Europe. The minimum-length spanning tree of haplotypes showed incongruency between the phylogeny of haplotypes and their geographic locations. This might be the result of intensive seed movements following recolonization, which thereby erased the phylogeographic structure in P. spinosa.     

Pollen- versus seed-mediated gene flow in a scattered forest tree species

We examined the spatial distribution of maternally inherited chloroplast DNA markers over the French part of the range of Sorbus torminalis, a scattered temperate forest tree native to most of Europe. The survey by restriction analysis of polymerase-chain-reaction amplified fragments for 880 individuals distributed among 55 populations allowed the detection of 25 haplotypes. The coefficient of differentiation among populations computed on the basis of haplotype frequency (G(STc) = 0.34) was one of the lowest found in forest trees so far, and the mean within-population diversity was relatively high, indicating multiple-mother foundation events. A significant but slight geographical pattern was observed, up to distances of about 100 km. This pattern of differentiation was compared to the genetic structure of the same populations revealed by biparentally inherited markers (isoenzymes), and a new method to quantify the relative importance of seed and pollen dispersal was derived, based on isolation-by-distance models. Neither pollen- nor seed-mediated gene flow was predominant in S. torminalis, a finding that differs from those for the majority of tree species studied so far. This result was most likely due to an extinction-recolonization dynamics based on efficient seed dispersal strategies. The joint screening of 31 individuals of the related Sorbus aria and of 163 hybrid individuals shows that hybridization occurs predominantly in one direction and is rarely followed by cytoplasmic introgression. As a consequence, interspecific gene flow should not significantly affect the diversity dynamics within S. torminalis.     

Microsatellite variation and structure of 28 populations of the common wetland plant, Lychnis flos-cuculi L., in a fragmented landscape

Habitat fragmentation is known to cause genetic differentiation between small populations of rare species and decrease genetic variation within such populations. However, common species with recently fragmented populations have rarely been studied in this context. We investigated genetic variation and its relationship to population size and geographical isolation of populations of the common plant species, Lychnis flos-cuculi L., in fragmented fen grasslands. We analysed 467 plants from 28 L. flos-cuculi populations of different sizes (60 000-54 000 flowering individuals) in northeastern Switzerland using seven polymorphic microsatellite loci. Genetic differentiation between populations is small (F(ST) = 0.022; amova; P < 0.001), suggesting that gene flow among populations is still high or that habitat fragmentation is too recent to result in pronounced differentiation. Observed heterozygosity (H(O) = 0.44) significantly deviates from Hardy-Weinberg equilibrium, and within-population inbreeding coefficient F(IS) is high (0.30-0.59), indicating a mixed mating breeding system with substantial inbreeding in L. flos-cuculi. Gene diversity is the only measure of genetic variation which decreased with decreasing population size (R = 0.42; P < 0.05). While our results do not indicate pronounced effects of habitat fragmentation on genetic variation in the still common L. flos-cuculi, the lower gene diversity of smaller populations suggests that the species is not entirely unaffected.     

Real-time patterns of pollen flow in the wild-service tree, Sorbus torminalis (Rosaceae). III. Mating patterns and the ecological maternal neighborhood

Understanding the role of mother plants as pollen recipients in shaping mating patterns is essential for understanding the evolution of populations and in particular to predict the consequence of habitat fragmentation. Here, we investigated variation in mating patterns due to maternal phenotypic traits, phenological variance, and landscape features in Sorbus torminalis, a hermaphroditic, insect-pollinated and low-density, European temperate forest tree. The diversity and composition of pollen clouds received by maternal trees in S. torminalis were mainly determined by their conspecific neighborhood: isolated individuals sample more diversity through more even paternal contributions, low relatedness among paternal genes, and high rates of long-distance pollen dispersal within their progenies. Maternal phenotypic traits related to pollinator attractiveness also had an effect, but only when competition was strong: in this case, larger mother trees with more flowers sampled more diversity. The floral architecture of S. torminalis, with multiple-seeded fruit, strongly shaped mating patterns, with higher levels of correlated paternity among seeds belonging to the same fruit (30% full sibs) than among seeds belonging to different fruits (14% full sibs). Finally, flowering phenology affected the distribution of diversity among maternal pollen clouds, but the earliest and latest mother trees did not receive less diversity of pollen than the others.     

Genetic variation of Trigonobalanus verticillata,a primitive species of Fagaceae,in Malaysia revealed by chloroplast sequences and AFLP markers

The genetic variation of Trigonobalanus verticillata, the most recently described genus of Fagaceae, was studied using chloroplast DNA sequences and AFLP fingerprinting. This species has a restricted distribution that is known to include seven localities in tropical lower montane forests in Malaysia and Indonesia. A total of 75 individuals were collected from Bario, Kinabalu, and Fraser's Hill in Malaysia. The sequences of rbcL, matK, and three non-coding regions (atpB-rbcL spacer, trnL intron, and trnL-trnF spacer) were determined for 19 individuals from these populations. We found a total of 30 nucleotide substitutions and four length variations, which allowed identification of three haplotypes characterizing each population. No substitutions were detected within populations, while the tandem repeats in the trnL -trnF spacer had a variable repeat number of a 20-bp motif only in Kinabalu. The differentiation of the populations inferred from the cpDNA molecular clock calibrated with paleontological data was estimated to be 8.3 MYA between Bario and Kinabalu, and 16.7 MYA between Fraser's Hill and the other populations. In AFLP analysis, four selective primer pairs yielded a total of 431 loci, of which 340 (78.9%) were polymorphic. The results showed relatively high gene diversity (H(S) = 0.153 and H(T) = 0.198) and nucleotide diversity (pi(S) = 0.0132 and pi(T) = 0.0168) both within and among the populations. Although the cpDNA data suggest that little or no gene flow occurred between the populations via seeds, the fixation index estimated from AFLP data (F(ST) = 0.153 and N(ST) = 0.214) implies that some gene flow occurs between populations, possibly through pollen transfer.     

Contrasting phylogeography in three endemic Hawaiian limpets (Cellana spp.) with similar life histories

The marine environment offers few obvious barriers to dispersal for broadcast-spawning species, yet population genetic structure can occur on a scale much smaller than the theoretical limits of larval dispersal. Comparative phylogeographical studies of sympatric sister species can illuminate how differences in life history, behaviour, and habitat affinity influence population partitioning. Here we use a mitochondrial DNA marker (612 bp of cytochrome c oxidase subunit I) to investigate population structure of three endemic Hawaiian broadcast-spawning limpets (Cellana spp.) with planktonic larvae that are competent to settle within 4 days. All three species exhibit significant population structure and isolation by distance, but the spatial scales of partitioning differ among the species. Cellana talcosa (n = 105) exhibits strong population structure between Kauai and the other main Hawaiian Islands (MHI) where the maximum channel width is 117 km, and no shared haplotypes were observed (Phi(CT) = 0.30, P < 0.001). In contrast, populations of Cellana exarata (n = 149) and Cellana sandwicensis (n = 109) exhibit weaker population structure within the MHI (Phi(ST) = 0.03-0.04, P < 0.05), and between the MHI and the Northwestern Hawaiian Islands (Phi(ST) = 0.03-0.09, P < 0.01), where the maximum channel width is 260 km. Biogeographical range and microhabitat use were correlated with estimates of dispersal, while phylogenetic affiliation and minimum pelagic larval duration were poor predictors of population partitioning. Despite similar life histories, these closely related limpets have contrasting patterns of population structure, illustrating the danger of relying on model species in management initiatives to predict population structure and dispersal in the context of marine protected area delineation.