A palynological study of the genus Mentha L. (Lamiaceae)

The pollen morphology and exine structure of 10 Mentha L . species were investigated using light microscopy and scanning electron microscopy. The pollen grains of all 11 species were hexazonocolpate with granular membranes and a circular amb, varying in shape from prolate-spheroidal to suboblate. Different colpus shapes were recognized in M . ×  dumetorum . The exine was bireticulate in section Pulegium , and reticulate in section Menthae . A correlation was found between pollen size and chromosome number. The results indicate that the pollen characters of the genus Mentha are valuable for taxonomic applications and may be useful for classification.  © 2008 Uludag University. Journal compilation © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 141–154.     

Genetic structure and population differentiation of the Mediterranean pioneer spiny broom Calicotome villosa across the Strait of Gibraltar

The region around the Strait of Gibraltar is considered to be one of the most relevant 'hot spots' of biodiversity in the Mediterranean Basin due to its historical, biogeographical, and ecological features. Prominent among these is its role as a land bridge for the migration and differentiation of species during the Pleistocene, as a consequence of the lowering of sea level and climate changes associated with the Ice Ages. In the present study, we report a multilevel hierarchical investigation of the genetic diversity of Calicotome villosa , a common pioneer legume shrub, at the regional scale. The results of genetic analysis of progeny arrays are consistent with a predominantly outcrossing mating system in all the populations analysed. Geographically, a pattern of population isolation by distance was found, but the Strait accounted for only approximately 2% of the among-population genetic differentiation. Consequently, extensive historical gene flow appears to be the rule for this species in this area. According to the natural history traits of C. villosa (pollination, dispersal, and colonization ability), we hypothesize that gene flow must be strongly influenced by seed dispersal because pollen flow is very limited. Based on the history of trade and land use, cattle and human movements across the Strait must have strongly favoured seed dispersal. We review and discuss these results and compare them with those of other reported studies of genetic and phylogenetic differentiation across the Strait of Gibraltar. It is stressed that colonization ability, which depends upon seed dispersal and life form, can be a more critical factor in gene flow than pollination.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 39–51.     

Comparing direct vs. indirect estimates of gene flow within a population of a scattered tree species

The comparison between historical estimates of gene flow, using variance in allelic frequencies, and contemporary estimates of gene flow, using parentage assignment, is expected to provide insights into ecological and evolutionary processes at work within and among populations. Genetic variation at six microsatellite loci was used to quantify genetic structure in the insect-pollinated, animal-dispersed, low-density tree Sorbus torminalis L. Crantz, and to derive historical estimates of gene flow. The neighbourhood size and root-mean-squared dispersal distance inferred from seedling genotypes ( N _b  = 70 individuals, σ _e  = 417 m) were similar to those inferred from adult genotypes ( N _b  = 114 individuals, σ _e  = 472 m). We also used parentage analyses and a neighbourhood model approach after an evaluation of the statistical properties of this method on simulated data. From our data, we estimated even contributions of seed- and pollen-mediated dispersal to the genetic composition of established seedlings, with both fat-tailed pollen and seed dispersal kernels, and slightly higher mean distance of pollen dispersal (248 m) as compared to seed dispersal (135 m). The resulting contemporary estimate of gene dispersal distance (σ _c  = 211 m) was ∼twofold smaller than the historical estimates. Besides different assumptions and statistical nuances of both approaches, this discrepancy is likely to reflect a recent restriction in the scale of gene flow which requires manager's attention in a context of increasing forest fragmentation.     

Microscale variation in alpine grasslands: AFLPs reveal a high level of genotypic diversity in Primula minima (Primulaceae)

The microscale variation and spatial genetic structure of the alpine plant species Primula minima L. was analysed using AFLPs. AFLP analysis based on three primer combinations and 123 fragments revealed no identical genotypes among the 86 studied samples from a 300 × 300 cm plot. Variation within the study plot was high: Nei's gene diversity was 0.22, Shannon's information index 0.33 and the percentage of polymorphic bands was 60.9. Cluster analysis revealed four main groups of genetically similar individuals and mapping these individuals resulted in a clear spatial pattern, with samples from the same group often located close together. The observed microscale structure was corroborated using a Mantel test, which revealed significant correlation of genetic and spatial distances, and by the results of a spatial autocorrelation analysis that indicated a high level of similarity between adjacent samples. An analysis of molecular variance revealed clear differentiation (18%) between the spatial groups. Overall gene flow within the plot was 1.11 and ranged from 0.33 between the spatially most distant groups to 2.33 between directly neighbouring groups. The extraordinary level of diversity detected in this study indicates an unexpectedly strong relevance of reproduction by seed for the species P. minima in alpine grasslands. The strong microscale variation suggests, however, that there is limited dispersal of seeds. Clonal reproduction is of subsidiary importance to sexual reproduction and seems to occur only over very small distances.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 549–556.     

Increased inbreeding and strong kinship structure in Taxus baccata estimated from both AFLP and SSR data

Habitat fragmentation can have severe genetic consequences for trees, such as increased inbreeding and decreased effective population size. In effect, local populations suffer from reduction of genetic variation, and thus loss of adaptive capacity, which consequently increases their risk of extinction. In Europe, Taxus baccata is among a number of tree species experiencing strong habitat fragmentation. However, there is little empirical data on the population genetic consequences of fragmentation for this species. This study aimed to characterize local genetic structure in two natural remnants of English yew in Poland based on both amplified fragment length polymorphism (AFLP) and microsatellite (SSR) markers. We introduced a Bayesian approach that estimates the average inbreeding coefficient using AFLP (dominant) markers. Results showed that, in spite of high dispersal potential (bird-mediated seed dispersal and wind-mediated pollen dispersal), English yew populations show strong kinship structure, with a spatial extent of 50–100 m, depending on the population. The estimated inbreeding levels ranged from 0.016 to 0.063, depending on the population and marker used. Several patterns were evident: (1) AFLP markers showed stronger kinship structure than SSRs; (2) AFLP markers provided higher inbreeding estimates than SSRs; and (3) kinship structure and inbreeding were more pronounced in denser populations regardless of the marker used. Our results suggest that, because both kinship structure and (bi-parental) inbreeding exist in populations of English yew, gene dispersal can be fairly limited in this species. Furthermore, at a local scale, gene dispersal intensity can be more limited in a dense population.     

Small-scale spatial genetic structure in an ant species with sex-biased dispersal

In a population of the monogynous, polyandrous ant Cataglyphis cursor , we analysed the spatial genetic structure of queens, colony fathers and workers at a microgeographical scale to infer the extent of sex-biased dispersal and to assess the impact of limited dispersal on the patterns of relatedness within the colony. To this end, four microsatellite markers were scored for the queen and an average of 26 workers from each of 35 mapped colonies. We used pair-wise kinship coefficients between all pairs of genotypes, including the reconstructed colony father genotypes (1) to test and quantify isolation by distance patterns within each sex or caste through the analysis of kinship–distance curves, and (2) to compute the average relatedness between categories of colony members. The kinship–distance curve was much steeper for colony queens than colony fathers, indicating male-biased dispersal. However, colony fathers also displayed a non-random spatial genetic structure, so that even males show some dispersal limitation at the scale of the population, which extends over less than 250 m. The degree of relatedness between the different sexes and castes of colonies was well predicted from the number of mates per queen and the inbreeding of queens, and the impact of limited dispersal was very weak at this scale of observation. We discuss the interest of kinship–distance curves to assess sex-biased dispersal on a local scale and we compare our results with large-scale analyses of genetic structure in Cataglyphis cursor and other monogynous ant species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 465–473.     

Long‐distance dispersal in a fire‐ and livestock‐protected savanna

Savannas are highly diverse and dynamic environments that can shift to forest formations due to protection policies. Long‐distance dispersal may shape the genetic structure of these new closed forest formations. We analyzed eight microsatellite loci using a single‐time approach to understand contemporary pollen and effective seed dispersal of the tropical tree, Copaifera langsdorffii Desf. (Fabaceae), occurring in a Brazilian fire‐ and livestock‐protected savanna. We sampled all adult trees found within a 10.24 ha permanent plot, young trees within a subplot of 1.44 ha and open‐pollinated seeds. We detected a very high level of genetic diversity among the three generations in the studied plot. Parentage analysis revealed high pollen immigration rate (0.64) and a mean contemporary pollen dispersal distance of 74 m. In addition, half‐sib production was 1.8 times higher than full‐sibs in significant higher distances, indicating foraging activity preference for different trees at long distances. There was a significant and negative correlation between diameter at breast height (DBH) of the pollen donor with the number of seeds (r = ?0.640, P‐value = 0.032), suggesting that pollen donor trees with a higher DBH produce less seeds. The mean distance of realized seed dispersal (recruitment kernel) was 135 m due to the large home range dispersers (birds and mammals) in the area. The small magnitude of spatial genetic structure found in young trees may be a consequence of overlapping seed shadows and increased tree density. Our results show the positive side of closed canopy expansion, where animal activities regarding pollination and seed dispersal are extremely high.     

Contrasting levels of genetic diversity between the common, self-compatible Liparis kumokiri and rare, self-incompatible Liparis makinoana (Orchidaceae) in South Korea

Levels of allozyme variation and intrapopulation spatial genetic structure of the two terrestrial clonal orchids Liparis kumokiri , a self-compatible relatively common species, and L. makinoana , a self-incompatible rare species, were examined for 17 ( N  = 1875) and four ( N  = 425) populations, respectively, in South Korea. Populations of L. makinoana harboured high levels of genetic variation ( H _e = 0.319) across 15 loci. In contrast, L. kumokiri exhibited a complete lack of allozyme variation ( H _e = 0.000). Considering the lack of genetic variability, it is suggested that current populations of L. kumokiri in South Korea originated from a genetically depauperate ancestral population. For L. makinoana , a significant deficit of heterozygosity (mean F _IS = 0.198) was found in population samples excluding clonal ramets, suggesting that pollen dispersal is localized, generating biparental inbreeding. The significant fine-scale genetic structuring (≤ 2 m) found in a previous study, in addition to the moderate levels of population differentiation ( F _ST = 0.107) and the significant relationship between genetic and geographical distances ( r  = 0.680) found here, suggests a leptokurtic distribution of seed dispersal for L. makinoana . Although populations of L. makinoana harbour high levels of genetic variation, they are affected by a recent genetic bottleneck. This information suggests that genetic drift and limited gene flow could be the main evolutionary forces for speciation of a species-rich genus such as Liparis .  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 41–48.     

Gynoecium, fruit and seed structure of Paullinieae (Sapindaceae)

Despite an emphasis on fruit characters in Paullinieae taxonomy, few detailed morphological and anatomical studies of the gynoecia, fruits and seeds exist. The aims of the present study were (1) to provide a detailed documentation of gynoecium, fruit and seed structure and ontogeny in selected Paullinieae taxa; (2) to determine whether the gynoecium, seed and seedling provide additional characters of systematic value within the tribe; and (3) to relate the structural findings to mechanisms of fruit dehiscence and dispersal within these taxa. Newly described characters of systematic value within Paullinieae are shape and surface of the obturator, type of pollen tube transmitting tract, indumentum of the inner and outer surface of the carpels, ovary wall anatomy, aril anatomy, pseudo-hilum form, seedling germination mode and structure of first leaves. The fruits of Paullinia are septifragal, and conspicuous colour contrasts between the pericarp, aril and seed in most species of this genus are suggestive of a bird dispersal syndrome. Interestingly, it appears that relatively minor structural changes are associated with switches to rodent dispersal in Paullinia sphaerocarpa and water dispersal in P. clathrata and P. hystrix. Anemochorous fruits are septifragal ( Cardiospermum and Urvillea ) or schizocarpic ( Houssayanthus , Lophostigma , Serjania ). They are structurally similar and Cardiospermum with septifragal capsules may also show septicidal dehiscence.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 159–189.     

Socio-genetic structure of mound-building mice, Mus spicilegus, in autumn and early spring

Mus spicilegus has become a popular biological model species in the last decade because of the evolutionary interest of its behavioural particularities (the building of mounds, bi-parental care and monogamous mating system). The genetic structure of M. spicilegus populations should reflect those life-history traits. Although many studies have reported on mound-building mouse populations in the field or in a semi-natural enclosure, only one used hyper variable genetic markers to assess parentage and social structure. In the present study conducted in Hungary, we analysed individuals from seven highly populous mounds in autumn with the set of loci used in a previous study. Our results confirmed that mounds are inhabited by juveniles from several parental units, but revealed population differences. In a capture–recapture field session in spring, we assessed genetic relationships between individuals after dispersal from the mounds, the other key moment of the life cycle of this species. The results indicate that the social structure at this moment reflects a transition phase between the large over-wintering groups and the monogamous pairs described later in the year. Social bounds forged during the long winter cohabitation may have lasting effects on social and genetic structure of this species. This scenario is discussed in respect of the available literature on this species as well as other species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 689–699.     

Dispersal and population structure of two sympatric species of the mediterranean land snail genus Mastus (Gastropoda, Pulmonata, Enidae)

We studied the population dynamics of Mastus by investigating the effects of population structure, spatial ecology and biology of reproduction on the genetic diversity of two sympatric Mastus species endemic to the island of Crete. Over a period of 27 months, we carried out both mark–recapture and random quadrat sampling techniques in order to assess the dispersal trends, the aggregation patterns, the neighbourhood size and the habitat preferences of these species. There were 154 recorded movements for M. butoti and 114 for M. cretensis . Mean monthly dispersal was estimated at d  = 0.5 m for M. butoti and d  = 1 m for M. cretensis . Both species showed a random dispersal pattern but tended to aggregate in the field. Their populations were found to be highly structured owing to their highly parsimonious dispersal behaviour and the very low population densities, estimated at D  = 2.07 ± 0.16 and D  = 0.73 ± 0.16 individuals m⁻² for M. butoti and M. cretensis , respectively. The neighbourhood size did not exceed 150 individuals for either species. The habitat occupied by each species changed during the active season, but both the immature and the adult individuals of each species seemed to prefer the same habitats throughout the active season. Partial population activation during the active season was observed in both species. We conclude that the population structure, the partial population activation and the species-specific reproductive strategies have a profound effect on maintaining the genetic diversity of the genus' populations.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 131–144.     

Limited seed dispersal and microspatial population structure of an agamospermous grass of West African savannahs, Hyparrhenia diplandra (Poaceae)

We studied the microspatial population structure of the perennial tussock grass, Hyparrhenia diplandra (Poaceae), a facultative agamospermous species of West African savannahs. The microspatial population structure of H. diplandra was investigated by choosing two 100-m(2); quadrats at random from which all individuals were mapped. The genotype of every individual was determined using two highly polymorphic microsatellite loci. A chloroplast locus was also used to investigate the role of seed dispersal on the genetic structure of populations. The genetic diversity index (0.85) was high for a clonal species. Significant genetic differentiation over short distances was detected by F statistics, and spatial autocorrelation analyses within both quadrats showed significant isolation-by-distance patterns, both with the cytoplasmic locus and the nuclear loci. Some clones formed large patches (up to 5 m in diameter) whereas others were more scattered. However, the genetic differentiation between quadrats was much higher when studied with the cytoplasmic locus than with the nuclear loci, indicating that gene flow via pollen, but not seeds, may frequently occur between quadrats. The maintenance of genetic diversity in this facultative agamospermous species most likely results from several factors, such as low seed dispersal ability, nonnegligible gene flow through pollen, and selective pressures induced by regularly occurring fires in this ecosystem.     

Fragmentation can increase spatial genetic structure without decreasing pollen-mediated gene flow in a wind-pollinated tree

Fragmentation reduces population sizes, increases isolation between habitats and can result in restricted dispersal of pollen and seeds. Given that diploid seed dispersal contributes more to shaping fine-scale spatial genetic structure (SGS) than haploid pollen flow, we tested whether fine-scale SGS can be sensitive to fragmentation even if extensive pollen dispersal is maintained. Castanopsis sclerophylla (Lindley & Paxton) Schottky (Fagaceae), a wind-pollinated and gravity seed-dispersed tree, was studied in an area of southeast China where its populations have been fragmented to varying extents by human activity. Using different age classes of trees in areas subject to varying extents of fragmentation, we found no significant difference in genetic diversity between prefragmentation vs. postfragmentation C. sclerophylla subpopulations. Genetic differentiation among postfragmentation subpopulations was also only slightly lower than among prefragmentation subpopulations. In the most fragmented habitat, selfing rates were significantly higher than zero in prefragmentation, but not postfragmentation, cohorts. These results suggest that fragmentation had not decreased gene flow among these populations and that pollen flow remains extensive. However, significantly greater fine-scale SGS was found in postfragmentation subpopulations in the most fragmented habitat, but not in less fragmented habitats. This alteration in SGS reflected more restricted seed dispersal, induced by changes in the physical environments and the prevention of secondary seed dispersal by rodents. An increase in SGS can therefore result from more restricted seed dispersal, even in the face of extensive pollen flow, making it a sensitive indicator of the negative consequences of population fragmentation.     

Seed survival and dispersal of an endemic Atlantic forest palm: the combined effects of defaunation and forest fragmentation

About 45 palm species occur in the Atlantic forest of Brazil, and most of them are affected by loss of seed dispersers resulting from forest fragmentation and hunting. Here we report the effects of habitat loss and defaunation on the seed dispersal system of an endemic palm, Astrocaryum aculeatissimum . We evaluated seed removal, insect and rodent seed predation, and scatter-hoarding in nine sites, ranging from 19 ha to 79 000 ha. We report the seedling, juvenile and adult palm densities in this range of sites. Endocarps remaining beneath the parent palm had a higher probability of being preyed upon by insects in small, mostly fragmented and more defaunated sites. The frequency of successful seed removal, scatter-hoarding and consumption by rodents increased in the larger, less defaunated sites. Successful removal and dispersal collapsed in small (< 1000 ha), highly defaunated sites and frequently resulted in low densities of both seedlings and juveniles. Our results indicate that a large fraction of Atlantic forest palms that rely on scatter-hoarding rodents may become regionally extinct due to forest fragmentation and defaunation. Current management practices including palm extraction and hunting pressure have a lasting effect on Atlantic forest palm regeneration by severely limiting successful recruitment of prereproductive individuals. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 141–149.     

Does provenance matter? Fitness is not determined by genetic distance or the scale of pollen dispersal in Grevillea sphacelata (Proteaceae)

Understanding how the scale of pollen transfer determines the outcome of matings is important evolutionarily and a key issue in restoration ecology. We tested the effects of pollen transfer distance for the self‐incompatible shrub Grevillea sphacelata using (1) open pollination and transfer among (2) near neighbours, (3) neighbouring subpopulations and (4) populations separated by c. 4 km. We used AFLP markers to test for evidence of genetic differentiation within and among populations. Patterns of seed initiation suggest that open pollinated flowers were pollen limited, although in one subpopulation open seed set was greater than that achieved with pollen from near neighbours or other subpopulations. We detected no other effects of pollen source on seed initiation or seed and seedling development. In contrast, our genetic survey revealed significant spatial autocorrelation to 5 m, moderate differentiation of populations separated by up to 4 km and significant isolation by distance > 16 km. Our data suggest that, although dispersal of pollen may typically be localized, gene flow prevents localized adaptation or co‐adaptation and we detected no effects of inbreeding depression. In a restoration context, our results imply that movement of seed between populations separated by 4 km will not have detrimental consequences, despite significant differentiation at neutral genetic markers, and may be beneficial in maintaining genetic diversity and evolutionary potential. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 290–302.     

Fragmentation reduces regional‐scale spatial genetic structure in a wind‐pollinated tree because genetic barriers are removed

Gene flow strongly influences the regional genetic structuring of plant populations. Seed and pollen dispersal patterns can respond differently to the increased isolation resulting from habitat fragmentation, with unpredictable consequences for gene flow and population structuring. In a recently fragmented landscape we compared the pre‐ and post‐fragmentation genetic structure of populations of a tree species where pollen and seed dispersal respond differentially to forest fragmentation generated by flooding. Castanopsis sclerophylla is wind‐pollinated, with seeds that are dispersed by gravity and rodents. Using microsatellites, we found no significant difference in genetic diversity between pre‐ and post‐fragmentation cohorts. Significant genetic structure was observed in pre‐fragmentation cohorts, due to an unknown genetic barrier that had isolated one small population. Among post‐fragmentation cohorts this genetic barrier had disappeared and genetic structure was significantly weakened. The strengths of genetic structuring were at a similar level in both cohorts, suggesting that overall gene flow of C. sclerophylla has been unchanged by fragmentation at the regional scale. Fragmentation has blocked seed dispersal among habitats, but this appears to have been compensated for by enhanced pollen dispersal, as indicated by the disappearance of a genetic barrier, probably as a result of increased wind speeds and easier pollen movement over water. Extensive pollen flow can counteract some negative effects of fragmentation and assist the long‐term persistence of small remnant populations.     

Microspatial population genetic structure of the Mediterranean shrub Fumana thymifolia

Fumana thymifolia (Cistaceae) is an insect-pollinated, gravity-dispersed evergreen shrub, which is a common component of fire-prone Mediterranean shrubland ecosystems. Despite the availability of basic knowledge on its ecology, little is known of its breeding system and no information is available on its population genetic structure. We explored the within-population genetic structure of this species using amplified fragment length polymorphism (AFLP) molecular markers and related this to predictions based on its breeding system, pollen and seed dispersal. Existing information on the reproductive ecology of F. thymifolia was supplemented by artificial pollination experiments. We determined that self-fertilisation can occur in F. thymifolia but results in reduced fruit set. Significant genetic structuring was detected within the population, a likely consequence of localised seed dispersal in combination with a mixed mating system. In a study site covering approximately 0.5 ha, amova revealed that approximately 9% of genetic variability was distributed among population subsamples. Significant spatial genetic structure was detected, with kinship coefficients being significantly elevated above the null expectation in the first six distance classes (maximum 5 m), and a value of Sp of up to 0.0342, comparable with species having similar ecological characteristics. Weak isolation by distance at the plot scale was detected, suggesting that insect-mediated pollen flow is non-random, despite being more extensive than seed dispersal. Fumana thymifolia provides a promising model for the investigation of both short- and long-term population dynamics in relation to fire frequency within this plant community.     

A new species of Begonia (Begoniaceae) from Guangxi, China

Begonia gigabracteata H.Z. Li & H. Ma sp. nov. ( Begonia section Diploclinium , Begoniaceae) is described and illustrated from North Guangxi Zhuang Autonomous Region, south-west China. Its chromosome number (2 n  = 30) and pollen and seed micromorphology are reported. This species grows in ravines on damp or slightly moist limestone. It is morphologically similar to B. summoglabra T.T. Yü (section Reichenheimia ) and B. labordei H. Lél. (section Diploclinium ). However, it differs by its sparse glandular hairs, number of perianth segments, colour of venation on the abaxial blade, and unique heteromorphous bracts. A line drawing and plate of B. gigabracteata and a photograph of the type of B. summoglabra are presented as an aid to identification.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 83–90.     

Habitat loss and fragmentation reduce effective gene flow by disrupting seed dispersal in a neotropical palm

Habitat loss and fragmentation often reduce gene flow and genetic diversity in plants by disrupting the movement of pollen and seed. However, direct comparisons of the contributions of pollen vs. seed dispersal to genetic variation in fragmented landscapes are lacking. To address this knowledge gap, we partitioned the genetic diversity contributed by male gametes from pollen sources and female gametes from seed sources within established seedlings of the palm Oenocarpus bataua in forest fragments and continuous forest in northwest Ecuador. This approach allowed us to quantify the separate contributions of each of these two dispersal processes to genetic variation. Compared to continuous forest, fragments had stronger spatial genetic structure, especially among female gametes, and reduced effective population sizes. We found that within and among fragments, allelic diversity was lower and genetic structure higher for female gametes than for male gametes. Moreover, female gametic allelic diversity in fragments decreased with decreasing surrounding forest cover, while male gametic allelic diversity did not. These results indicate that limited seed dispersal within and among fragments restricts genetic diversity and strengthens genetic structure in this system. Although pollen movement may also be impacted by habitat loss and fragmentation, it nonetheless serves to promote gene flow and diversity within and among fragments. Pollen and seed dispersal play distinctive roles in determining patterns of genetic variation in fragmented landscapes, and maintaining the integrity of both dispersal processes will be critical to managing and conserving genetic variation in the face of continuing habitat loss and fragmentation in tropical landscapes.     

High genetic variability in Neotropical myophilous orchids

The patterns of genetic variability of seven Bulbophyllum Thouars species were investigated using 14 enzymatic loci, and compared with those of other Neotropical myophilous orchid species. The genetic variability estimated was very high ( H _e = 0.39–0.61, P  = 86–100%, A  = 2.6–3.8), despite the small population sizes, which may be explained by the vegetative reproduction. Of the three species with multiple populations, only B. epiphytum showed moderate values of genetic structuring. Environmental characteristics and seed dispersal mechanisms are important in understanding the differences in the population structure observed. Almost all pairs of species showed low genetic similarity, indicating a long period of divergence. Our results suggest that B. adiamantinum and B. insectiferum , species currently classified in different sections of the genus, are more closely related than previously thought.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 33–40.