Hawkmoth and bee pollinators impact pollen dispersal at the landscape but not local scales in two species of Oenothera

Premise

Animal pollinators play an important role in pollen dispersal. Here, we assessed differences in pollen and seed dispersal and the role of pollinator functional groups with different foraging behaviors in generating patterns of genetic diversity over similar geographic ranges for two closely related taxa. We focused on two members of Oenothera section Calylophus (Onagraceae) that co-occur on gypsum outcrops throughout the northern Chihuahuan Desert but differ in floral phenotype and primary pollinator: Oenothera gayleana (bee) and O. hartwegii subsp. filifolia (hawkmoth).

Methods

We measured breeding system and floral traits and studied gene flow and population differentiation at the local (<13 km; four populations) and landscape (60–440 km; five populations) scales using 10–11 nuclear (pollen dispersal) and three plastid (seed dispersal) microsatellite markers.

Results

Both taxa were self-incompatible and floral traits were consistent with expectations for different pollinators. Seed and pollen dispersal patterns were distinctly different for both species. We found no evidence of genetic structure at the local scale but did at the landscape scale; O. gayleana showed greater differentiation and significant isolation by distance than in O. hartwegii subsp. filifolia. The plastid data were consistent with gravity dispersal of seeds and suggest that pollen dispersal is the principal driver of genetic structure in both species.

Conclusions

We demonstrated that pollinator functional groups can impact genetic differentiation in different and predictable ways. Hawkmoths, with larger foraging distances, can maintain gene flow across greater spatial scales than bees.

     

Genetic structure of the northwestern Russian wolf populations and gene flow between Russia and Finland

We examined the genetic diversity and structure of wolf populations in northwestern Russia. Populations in Republic of Karelia and Arkhangelsk Oblast were sampled during 1995–2000, and 43 individuals were genotyped with 10 microsatellite markers. Moreover, 118 previously genotyped wolves from the neighbouring Finnish population were used as a reference population. A relatively large amount of genetic variation was found in the Russian populations, and the Karelian wolf population tended to be slightly more polymorphic than the Arkhangelsk population. We found significant inbreeding (F = 0.094) in the Karelian, but not in the Arkhangelsk population. The effective size estimates of the Karelian wolf population based on the approximate Bayesian computation and linkage disequilibrium methods were 39.9 and 46.7 individuals, respectively. AMOVA-analysis and exact test of population differentiation suggested clear differentiation between the Karelian, Arkhangelsk and Finnish wolf populations. Indirect estimates of gene flow based on the level of population differentiation (ϕ _ST  = 0.152) and frequency of private alleles (0.029) both suggested a low level of gene flow between the populations (Nm = 1.4 and Nm = 3.7, respectively). Assignment analysis of Karelian and Finnish populations suggested an even lower number of recent migrants (less than 0.03) between populations, with a larger amount of migration from Finland to Karelia than vice versa. Our findings emphasise the role of physical obstacles and territorial behaviour in creating barriers to gene flow between populations in relatively limited geographical areas, even in large-bodied mammalian species with long-distance dispersal capabilities and an apparently continuous population structure.     

How river structure and biological traits influence gene flow: a population genetic study of two stream invertebrates with differing dispersal abilities

1. Determined by landscape structure as well as dispersal‐related traits of species, connectivity influences various key aspects of population biology, ranging from population persistence to genetic structure and diversity. Here, we investigated differences in small‐scale connectivity in terms of gene flow between populations of two ecologically important invertebrates with contrasting dispersal‐related traits: an amphipod (Gammarus fossarum) with a purely aquatic life cycle and a mayfly (Baetis rhodani) with a terrestrial adult stage. 2. We used highly polymorphic markers to estimate genetic differentiation between populations of both species within a Swiss pre‐alpine catchment and compared these results to the broader‐scale genetic structure within the Rhine drainage. Landscape genetic approaches were used to test for correlations of genetic and geographical structures and in‐stream barrier effects. 3. We found overall very weak genetic structure in populations of B. rhodani. In contrast, G. fossarum showed strong genetic differentiation, even at spatial scales of a few kilometres, and a clear pattern of isolation by distance. Genetic diversity decreased from downstream towards upstream populations of G. fossarum, suggesting asymmetric gene flow. Correlation of genetic structure with landscape topography was more pronounced in the amphipod. Our study also indicates that G. fossarum might be capable of dispersing overland in headwater regions and of crossing small in‐stream barriers. 4. We speculate that differences in dispersal capacity but also habitat specialisation and potentially the extent of local adaptation could be responsible for the differences in genetic differentiation found between the two species. These results highlight the importance of taking into account dispersal‐related traits when planning management and conservation strategies.     

Population genetic structure of Bellamya aeruginosa (Mollusca: Gastropoda: Viviparidae) in China: weak divergence across large geographic distances

Bellamya aeruginosa is a widely distributed Chinese freshwater snail that is heavily harvested, and its natural habitats are under severe threat due to fragmentation and loss. We were interested whether the large geographic distances between populations and habitat fragmentation have led to population differentiation and reduced genetic diversity in the species. To estimate the genetic diversity and population structure of B. aeruginosa, 277 individuals from 12 populations throughout its distribution range across China were sampled: two populations were sampled from the Yellow River system, eight populations from the Yangtze River system, and two populations from isolated plateau lakes. We used seven microsatellite loci and mitochondrial cytochrome oxidase I sequences to estimate population genetic parameters and test for demographic fluctuations. Our results showed that (1) the genetic diversity of B. aeruginosa was high for both markers in most of the studied populations and effective population sizes appear to be large, (2) only very low and mostly nonsignificant levels of genetic differentiation existed among the 12 populations, gene flow was generally high, and (3) relatively weak geographic structure was detected despite large geographic distances between populations. Further, no isolation by linear or stream distance was found among populations within the Yangtze River system and no signs of population bottlenecks were detected. Gene flow occurred even between far distant populations, possibly as a result of passive dispersal during flooding events, zoochoric dispersal, and/or anthropogenic translocations explaining the lack of stronger differentiation across large geographic distances. The high genetic diversity of B. aeruginosa and the weak population differentiation are likely the results of strong gene flow facilitated by passive dispersal and large population sizes suggesting that the species currently is not of conservation concern.     

Spatial genetic structure of aquatic bryophytes in a connected lake system

Using genetic markers, we investigated the genetic structure of three clonal aquatic moss species, Calliergon megalophyllum Mikut., Fontinalis antipyretica Hedw. and F. hypnoides Hartm. on two scales: among populations in a connected lake system (large‐scale spatial genetic structure) and among individuals within populations (fine‐scale spatial genetic structure). Mean genetic diversities per population were 0.138, 0.247 and 0.271, respectively, and total diversities equalled 0.223, 0.385 and 0.421, respectively. Relative differentiation levels (F_ST values of 0.173, 0.280 and 0.142, respectively) were significant but showed that there is a moderate amount of gene flow taking place within the lake system connected with narrow streams. Bayesian STRUCTURE analysis provided some indication that the direction of water flow influences population genetic structuring in the studied aquatic mosses. We propose that dispersal leading to gene flow in C. megalophyllum, F. antipyretica and F. hypnoides takes place both along water via connecting streams and by animal vectors, such as waterfowl. Nevertheless, the slight genetic structuring pattern along the direction of water flow suggests that dispersal of shoots or their fragments along water is a means of dispersal in these mosses. The absence of sexual reproduction and spores may have caused the observed spatial genetic structure within populations, including aggregations of similar genotypes (clones or closely related genotypes) at short distances in populations otherwise showing an isolation by distance effect. Regardless of the results pointing to the dominance of vegetative propagation, it is impossible to completely rule out the potential role of rare long‐distance spore dispersal from areas where the species are fertile.     

Identification of conservation units in the European Mergus merganser based on nuclear and mitochondrial DNA markers

The conservation status of small breeding areas of the Goosander (Mergus merganser merganser) in Central Europe is unclear. Geographic isolation of these areas suggests restricted gene flow to and from large North-European populations. On the other hand, migrating Goosanders from northern Europe join the Central European breeding population for wintering. To evaluate the conservation status of the small breeding areas we assessed the genetic structure of M. merganser populations in Europe by examining two nuclear marker systems (microsatellites and Single Nucleotide Polymorphisms, SNP) and mitochondrial (mtDNA) control region sequence variation for Goosanders in 11 sampling areas representing three of five distinct breeding areas and two subspecies (M. m. merganser and M. m. americanus). Overall population differentiation estimates including both subspecies were high, both based on mtDNA () and nuclear markers (θ _ST = 0.219; 95% CI 0.088–0.398, SNP and microsatellites combined). Within Europe, mtDNA revealed a strong overall () and significant pairwise population differentiation between almost all comparisons. In contrast, both nuclear marker systems combined revealed only a small overall genetic differentiation (θ _ST = 0.022; 95% CI 0.003–0.041). The strong genetic differentiation based on female-inherited mtDNA but not on biparentally inherited nuclear markers can be explained by sex-biased dispersal and strong female philopatry. Therefore, small breeding areas in Europe are endangered despite large male-mediated gene-flow, because when these populations decline, only males—but due to strong philopatry not females—can be efficiently supplemented by migration from the large North European populations. We therefore propose to manage the small breeding areas independently and to strengthen conservation efforts for this species in Central Europe.     

Speciation in a keystone plant genus is driven by elevation: a case study in New Guinean Ficus

Much of the world's insect and plant biodiversity is found in tropical and subtropical ‘hotspots’, which often include long elevational gradients. These gradients may function as ‘diversity pumps’ and contribute to both regional and local species richness. Climactic conditions on such gradients often change rapidly along short vertical distances and may result in local adaptation and high levels of population genetic structure in plants and insects. We investigated the population genetic structure of two species of Ficus (Moraceae) along a continuously forested elevational gradient in Papua New Guinea. This speciose plant genus is pollinated by tiny, species‐specific and highly coevolved chalcid wasps (Agaonidae) and represented by at least 73 species at our study gradient. We present results from two species of Ficus sampled from six elevations between 200 m and 2700 m a.s.l. (almost the entire elevational range of the genus) and 10 polymorphic microsatellite loci. These results show that strong barriers to gene flow exist between 1200 m and 1700 m a.s.l. Whereas lowland populations are panmictic across distances over 70 km, montane populations can be disjunct over 4 km, despite continuous forest cover. We suggest that the limited gene flow between populations of these two species of montane Ficus may be driven by environmental limitations on pollinator or seed dispersal in combination with local adaptation of Ficus populations. Such a mechanism may have wider implications for plant and pollinator speciation across long and continuously forested elevational gradients if generalist insect pollinators and vertebrate seed dispersers also form populations based on elevation.     

Gene flow among native bush rat,Rattus fuscipes (Rodentia: Muridae), populations in the fragmented subtropical forests of south‐east Queensland

Abstract Many natural populations in areas of continuous habitat exhibit some form of local genetic structure. Anthropogenic habitat fragmentation can also strongly influence the dynamics of gene flow between populations. We used eight microsatellite markers to investigate the population genetic structure of an abundant forest species, the Australian bush rat (Rattus fuscipes), in the subtropical forests of south‐east Queensland. Five sites were sampled, allowing pairwise comparisons within continuous habitat and across clearings. Weak, but significant population differentiation and a significant pattern of isolation by distance was detected over the small scale (<10 km) of this study. Fine‐scale analysis at a single site (<1 km) showed a significant correlation between individual female genetic distance and geographical distance, but no similar pattern among male individuals. There was no evidence of increased population differentiation across clearings relative to comparisons within continuous forest. This was attributed to dispersal within corridors of remnant and revegetated habitat between the forested areas. We concluded that an inherently restricted dispersal ability, female philopatry and natural habitat heterogeneity play an important part in the development of genetic structure among populations of R. fuscipes. It is important to understand the relationship between landscape features and the pattern of gene flow among continuous populations, as this allows us to predict the impact of fragmentation on natural populations.     

Genetic diversity in fragmented populations of the critically endangered spider orchid Caladenia huegelii: implications for conservation

The Orchidaceae is characterised by a diverse range of life histories, reproductive strategies and geographic distribution, reflected in a variety of patterns in the population genetic structure of different species. In this study, the genetic diversity and structure was assessed within and among remnant populations of the critically endangered sexually deceptive orchid, Caladenia huegelii. This species has experienced severe recent habitat loss in a landscape marked by ancient patterns of population fragmentation within the Southwest Australian Floristic Region, a global biodiversity hotspot. Using seven polymorphic microsatellite loci, high levels of within-population diversity (mean alleles/locus = 6.73; mean H _E = 0.690), weak genetic structuring among 13 remnant populations (F _ST = 0.047) and a consistent deficit of heterozygotes from Hardy–Weinberg expectation were found across all populations (mean F _IS = 0.22). Positive inbreeding coefficients are most likely due to Wahlund effects and/or inbreeding effects from highly correlated paternity and typically low fruit set. Indirect estimates of gene flow (Nm = 5.09 using F _ST; Nm = 3.12 using the private alleles method) among populations reflects a historical capacity for gene flow through long distance pollen dispersal by sexually deceived wasp pollinators and/or long range dispersal of dust-like orchid seed. However, current levels of gene flow may be impacted by habitat destruction, fragmentation and reduced population size. A genetically divergent population was identified, which should be a high priority for conservation managers. Very weak genetic differentiation indicates that the movement and mixing of seeds from different populations for reintroduction programs should result in minimal negative genetic effects.     

Does local adaptation to resources explain genetic differentiation among Daphnia populations?

Substantial genetic differentiation is frequently observed among populations of cyclically parthenogenetic zooplankton despite their high dispersal capabilities and potential for gene flow. Local adaptation has been invoked to explain population genetic differentiation despite high dispersal, but several neutral models that account for basic life history features also predict high genetic differentiation. Here, we study genetic differentiation among four populations of Daphnia pulex in east central Illinois. As with other studies of Daphnia, we demonstrate substantial population genetic differentiation despite close geographic proximity (<50 km; mean θ = 0.22). However, we explicitly tested and failed to find evidence for, the hypothesis that local adaptation to food resources occurs in these populations. Recognizing that local adaptation can occur in traits unrelated to resources, we estimated contemporary migration rates (m) and tested for admixture to evaluate the hypothesis that observed genetic differentiation is consistent with local adaptation to other untested ecological factors. Using Bayesian assignment methods, we detected migrants in three of the four study populations including substantial evidence for successful reproduction by immigrants in one pond, allowing us to reject the hypothesis that local adaptation limits gene flow for at least this population. Thus, we suggest that local adaptation does not explain genetic differentiation among these Daphnia populations and that other factors related to extinction/colonization dynamics, a long approach to equilibrium F_ST or substantial genetic drift due to a low number of individuals hatching from the egg bank each season may explain genetic differentiation.     

Genetic structure and seed-mediated dispersal rates of an endangered shrub in a fragmented landscape: a case study for Juniperus communis in northwestern Europe

Background

Population extinction risk in a fragmented landscape is related to the differential ability of the species to spread its genes across the landscape. The impact of landscape fragmentation on plant population dynamics will therefore vary across different spatial scales. We quantified successful seed-mediated dispersal of the dioecious shrub Juniperus communis in a fragmented landscape across northwestern Europe by using amplified fragment length polymorphism (AFLP) markers. Furthermore we investigated the genetic diversity and structure on two spatial scales: across northwestern Europe and across Flanders (northern Belgium). We also studied whether seed viability and populations size were correlated with genetic diversity.

Results

Unexpectedly, estimated seed-mediated dispersal rates were quite high and ranged between 3% and 14%. No population differentiation and no spatial genetic structure were detected on the local, Flemish scale. A significant low to moderate genetic differentiation between populations was detected at the regional, northwest European scale (PhiPT = 0.10). In general, geographically nearby populations were also genetically related. High levels of within-population genetic diversity were detected but no correlation was found between any genetic diversity parameter and population size or seed viability.

Conclusions

In northwestern Europe, landscape fragmentation has lead to a weak isolation-by-distance pattern but not to genetic impoverishment of common juniper. Substantial rates of successful migration by seed-mediated gene flow indicate a high dispersal ability which could enable Juniperus communis to naturally colonize suitable habitats. However, it is not clear whether the observed levels of migration will suffice to counterbalance the effects of genetic drift in small populations on the long run.     

Distribution,movement, and microhabitat use of the introduced predatory snail Euglandina rosea in Hawaii: implications for management

The purposeful introduction of the land snail Euglandina rosea, which feeds exclusively on snails and slugs, has been implicated as a major factor in the decline of diverse Pacific island land snail faunas. We report on the distribution, movement patterns, and microhabitat preferences of E. rosea in a gulch in the Waianae Mountains, Oahu, Hawaii, because such data will help focus management actions at a local scale to protect native snail populations in areas where E. rosea is established. The Waianae Mountains harbor many endangered or threatened snails, most currently found in isolated habitat patches near the ridges. Conversely, most living individuals (28/29) and shells (46/56) of E. rosea were collected within the gulch, which supported higher densities of other native and non‐native snails, and was cooler and more moist than the ridges. Thirteen individuals of E. rosea were tracked (eight directly using a bobbin and thread method, and five indirectly by mark–recapture); most (10/13) moved on average <2.5 m per week (range 0.1–25.21 m), and all stayed within the gulch. Members of E. rosea preferred leaf litter over open, fern/shrub, or wood microhabitats. There were large differences in the population density of E. rosea over small spatial scales, indicating that there may be places where native snail populations could persist even in areas where populations of E. rosea are established. Identifying areas with differing population densities of E. rosea is critical for not only understanding why some native snail species may be more vulnerable to extinction, but also to locate areas where predation pressure is low and conservation efforts will be most likely to succeed.     

Dispersal via stream corridors structures populations of the endangered St. Francis’ satyr butterfly (Neonympha mitchellii francisci)

Habitat fragmentation may reduce gene flow and population viability of rare species. We tested whether riparian corridors enhanced gene flow and if human habitat modification between riparian corridors subsequently reduced dispersal and gene flow of a wetland butterfly, the US federally endangered St. Francis’ satyr butterfly (Neonympha mitchellii francisci). We surveyed nine populations throughout the taxon’s range using five polymorphic microsatellite loci. We found that genetic diversity of N. m. francisci was relatively high despite its restricted distribution, and that there is little evidence of population bottlenecks or extensive inbreeding within populations. We found substantial gene flow and detectable first generation migration, suggesting that N. m. francisci is unlikely to be currently endangered by genetic factors. Pairwise population differentiation and clustering indicate some structuring between populations on different drainages and suggest that dispersal probably occurs mainly via a stepping stone from the closest riparian corridors. However, genetic differentiation between geographically close populations suggests that isolation by distance is not solely responsible for population structure, and that management actions should be targeted at maintaining connectivity of riparian and upland habitats.     

Genetic evidence for recent range fragmentation and severely restricted dispersal in the critically endangered Sierra Madre Sparrow, Xenospiza baileyi

Assessing patterns of genetic structure and diversity of threatened species has become an essential tool for determining conservation status and designing management strategies. We examine the genetic structure of the Sierra Madre sparrow (Xenospiza baileyi), a species restricted to fragmented patches of subalpine bunchgrass in three small isolated areas of northwestern and central Mexico. Coding and non-coding regions of mtDNA (1,878 bp) from individuals of the only three known populations revealed the existence of a single major lineage, with closely related haplotypes being shared between populations across the range. The sharing of haplotypes between the distant northwest and central populations (~800 km) suggests a recent fragmentation of a formerly contiguous population. Despite a lack of large-scale phylogeographic structure, haplotype frequencies at local scales revealed significant genetic differentiation and high F _ST values between all three remaining populations, even between localities separated by less than 12 km. These results suggest restricted gene flow and limited dispersal, likely due to the species’ inability to cross areas of unsuitable habitat. On the basis of genetic interchange and ecological equivalence criteria, we recommend that the species be managed as a single unit, permitting the strengthening of the small population in the northwest with individuals from central Mexico, and/or the translocation of individuals to new areas of suitable habitat.     

Pollinator shifts between Ophrys sphegodes populations: might adaptation to different pollinators drive population divergence?

Local adaptation to different pollinators is considered one of the possible initial stages of ecological speciation as reproductive isolation is a by‐product of the divergence in pollination systems. However, pollinator‐mediated divergent selection will not necessarily result in complete reproductive isolation, because incipient speciation is often overcome by gene flow. We investigated the potential of pollinator shift in the sexually deceptive orchids Ophrys sphegodes and Ophrys exaltata and compared the levels of floral isolation vs. genetic distance among populations with contrasting predominant pollinators. We analysed floral hydrocarbons as a proxy for floral divergence between populations. Floral adoption of pollinators and their fidelity was tested using pollinator choice experiments. Interpopulation gene flow and population differentiation levels were estimated using AFLP markers. The Tyrrhenian O. sphegodes population preferentially attracted the pollinator bee Andrena bimaculata, whereas the Adriatic O. sphegodes population exclusively attracted A. nigroaenea. Significant differences in scent component proportions were identified in O. sphegodes populations that attracted different preferred pollinators. High interpopulation gene flow was detected, but populations were genetically structured at species level. The high interpopulation gene flow levels independent of preferred pollinators suggest that local adaptation to different pollinators has not (yet) generated detectable genome‐wide separation. Alternatively, despite extensive gene flow, few genes underlying floral isolation remain differentiated as a consequence of divergent selection. Different pollination ecotypes in O. sphegodes might represent a local selective response imposed by temporal variation in a geographical mosaic of pollinators as a consequence of the frequent disturbance regimes typical of Ophrys habitats.     

Distinct migratory and non-migratory ecotypes of an endemic New Zealand eleotrid (<Emphasis Type="Italic">Gobiomorphus cotidianus</Emphasis>) – implications for incipient speciation in island freshwater fish species

Background  

Many postglacial lakes contain fish species with distinct ecomorphs. Similar evolutionary scenarios might be acting on evolutionarily young fish communities in lakes of remote islands. One process that drives diversification in island freshwater fish species is the colonization of depauperate freshwater environments by diadromous (migratory) taxa, which secondarily lose their migratory behaviour. The loss of migration limits dispersal and gene flow between distant populations, and, therefore, is expected to facilitate local morphological and genetic differentiation. To date, most studies have focused on interspecific relationships among migratory species and their non-migratory sister taxa. We hypothesize that the loss of migration facilitates intraspecific morphological, behavioural, and genetic differentiation between migratory and non-migratory populations of facultatively diadromous taxa, and, hence, incipient speciation of island freshwater fish species.     

Significance of habitat type for the genetic population structure of Panonychus citri (Acari: Tetranychidae)

Restricted migration and habitat fragmentation promote genetic differentiation between populations: Because most of the hosts of Panonychus citri are woody plants, mainly citrus trees that are usually planted at intervals of several metres, this mite likely faces more risks (e.g., starvation) by dispersing between host plants, compared to other spider mite species that infest both herbaceous and woody plants, such as Tetranychus urticae. Such a limited gene flow between patches (host plants) can lead to differentiation of populations even within a small area. Therefore, we hypothesize that P. citri populations are genetically differentiated not only between distant populations but also within small areas, such as within a grove. To test this hypothesis, we investigated the divergence of P. citri populations in Japanese citrus groves according to a hierarchical arrangement of geographical distance, ranging from distant populations (10 groves distributed throughout different areas in two major Japanese islands; this level of analysis is referred to as ‘geographic’) to local populations (different trees in a specific grove; ‘local’). Three molecular markers were used an esterase locus, one microsatellite and a point mutation in the mitochondrial cytochrome oxidase subunit I. At a local level acaricide susceptibility tests were also performed using two acaricides: fenpyroximate (25 ppm) and etoxazole (3.33 ppm). At a broad geographic level the gene diversity decreased with decreasing area size and distance between populations. By contrast, at the local level, populations maintained a significant level of variation between trees within groves, and the divergence within groves was higher than between groves. Whereas no statistical difference of the mortalities was detected among groves for the two acaricides tested, the difference was statistically significant among trees within groves in fenpyroximate (ANOVA, p < 0.025) and=" marginal=" in=" etoxazole="><>p < 0.05). we=" concluded=" that=">P. citri populations maintain a higher level of variation between trees (or patches of trees) within groves than between groves at the local level, though the gene diversity tended to be smaller with decreasing distance between populations at the geographical level. Results are discussed in relation to the dispersal behaviour of spider mites.     

The fine-scale genetic structure of the two-spotted spider mite in a commercial greenhouse

The fine-scale genetic structure of Tetranychus urticae Koch was studied to estimate local gene flow within a rose tree habitat in a commercial greenhouse using seven microsatellite markers. Two beds of rose trees with different population densities were selected and 18 consecutive quadrats of 1.2 m length were sequentially established in each bed. Heterozygote deficiency was positive within quadrats, which was most likely a result of the Wahlund effect because the mites usually form small breeding colonies. Low population density and frequent inbreeding could also accelerate genetic differentiation among the breeding colonies. A short-range (2.4–3.6 m) positive autocorrelation and clear genetic cline among quadrat populations was detected within a bed. This suggests that gene flow was limited to a short range even if population density was substantially increased. Therefore, large-scale dispersal such as aerial dispersal contributed very little to gene flow in the greenhouse.