THE INFLUENCE OF INTRASPECIFIC VARIATION IN DISPERSAL STRATEGIES ON THE GENETIC STRUCTURE OF PLANTHOPPER POPULATIONS

The hypothesis that levels of gene flow among populations are correlated with dispersal ability has typically been tested by comparing gene flow among species that differ in dispersal abilities, an approach that potentially confounds dispersal ability with other species-specific differences. In this study, we take advantage of geographic variation in the dispersal strategies of two wing-dimorphic planthopper species, Prokelisia marginata and P. dolus, to examine for the first time whether levels of gene flow among populations are correlated with intraspecific variation in dispersal ability. We found that in both of these coastal salt marsh–inhabiting species, population-genetic subdivision, as assessed using allozyme electrophoresis, parallels geographic variation in the proportion of flight-capable adults (macropters) in a population; in regions where levels of macroptery are high, population genetic subdivision is less than in regions where levels of macroptery are low. We found no evidence that geographic variation in dispersal capability influences the degree to which gene flow declines with distance in either species. Thus, both species provided evidence that intraspecific variation in dispersal strategies influences the genetic structure of populations, and that this effect is manifested in population-genetic structure at the scale of large, coastal regions, rather than in genetic isolation by distance within a region. This conclusion was supported by interspecific comparisons revealing that: (1) population-genetic structure (G_ST) of the two Prokelisia species correlated negatively with the mean proportion of flight-capable adults within a region; and (2) there was no evidence that the degree of isolation by distance increased with decreasing dispersal capability. Populations of the relatively sedentary P. dolus clustered by geographic region (using Nei's distances), but this was not the case for the more mobile P. marginata. Furthermore, gene flow among the two major regions we surveyed (Atlantic and Gulf Coasts) has been substantial in P. marginata, but relatively less in P. dolus. The results for P. marginata suggest that differences in the dispersal strategies of Atlantic and Gulf Coast populations occur despite extensive gene flow. We argue that gene flow is biased from Atlantic to Gulf Coast populations, indicating that selection favoring a reduction in flight capability must be intense along the Gulf. Together, the results of this study provide the first rigorous evidence of a negative relationship within a species between dispersal ability and the genetic structure of populations. Furthermore, regional variation in dispersal ability is apparently maintained by selective differences that outweigh high levels of gene flow among regions.     

Population structure on breeding grounds of Lake Malawi’s ‘twilight zone’ cichlid fishes

Aim Free‐ranging benthopelagic fishes often have large population sizes and high rates of dispersal. These traits can act to homogenize population structure across the distributional range of a species and to reduce the likelihood of allopatric speciation. The apparent absence of any barriers to gene flow among populations, together with prior molecular evidence for panmixia across the ranges of three species, has resulted in Diplotaxodon, a genus of benthopelagic cichlid fishes of Lake Malawi, being proposed as a candidate case of sympatric speciation. Our aim was to further investigate this possibility by testing for intraspecific genetic subdivision among breeding populations, and intraspecific differences in breeding habitat. Location Lake Malawi, central‐east Africa. Methods We analysed eight microsatellite DNA loci to test for spatial genetic differences among populations on breeding grounds of eight Diplotaxodon species. We also tested for temporal population genetic differences within breeding grounds of three species. Records of ripe Diplotaxodon encountered during sampling were analysed to test if spatial variation in assemblage structure was linked to nearshore water depth and geographic proximity of sampling sites. Results Consistent with previous molecular evidence, within four of the eight species tested we found no evidence of spatial genetic structuring among breeding populations. However, within the other four species we found slight yet significant spatial genetic differences, indicating restricted gene flow among breeding grounds. There was no evidence of temporal genetic differences within sites. Analyses of the distributions of ripe Diplotaxodon revealed differences in assemblage structure linked to nearshore water depth. Main conclusions Together, these results demonstrate both the evolution of fidelity to deep‐water breeding locations in some Diplotaxodon species, and differences in breeding habitat among species. These findings are consistent with a role for divergence of breeding habitat in speciation of these cichlids, possibly promoted by dispersal limitation among geographically segregated spawning aggregations.     

Measures of gene flow in the Columbian ground squirrel

From analyses of published data and a review of the literature, I studied indirect and direct measures of gene flow among populations of Columbian ground squirrels, Spermophilus columbianus. New analyses were used to examine an allozyme data set (seven polymorphic loci) that had been collected by Zammuto and Millar (1985a) from six populations of ground squirrels that were spread over 183 km. G-tests indicated significant variation in allele frequencies among populations, but F-statistics revealed relatively little population differentiation (average F _ST=0.026). F _ST values were used to estimate rates of gene flow indirectly and indicated fairly high rates of gene flow (average N _e m=13.5). Recorded dispersal distances of individual ground squirrels were fairly short (most<4 km, maximum recorded distance was 8.5 km), and the minimum distance between populations used to create the allozyme data set was about 25 km. Thus, direct dispersal among the populations in the allozyme data set was highly unlikely. Small genetically effective populations may have experienced high rates of migration over short distances (about 43% of adults in local populations were immigrants), however, resulting in homogeneous allele frequencies over the geographic range. This explanation provides an alternative to invoking gene flow in the recent past to explain discrepancies between dispersal distances in the field and homogenization of allele frequencies over large ranges, Mammalian species that have virtually complete dispersal of subadult males from the natal area might be expected to exhibit relatively high rates of gene flow, regardless of actual dispersal distances. Genetically effective populations may be much smaller than more extensive ecological populations and experience higher rates of gene flow.     

Population genetic structure of three freshwater mussel (Unionidae) species within a small stream system: significant variation at local spatial scales

1. Unionid mussels are highly threatened, but little is known about genetic structure in populations of these organisms. We used allozyme electrophoresis to examine partitioning of genetic variation in three locally abundant and widely distributed species of mussels from a catchment in Ohio. 2. Within‐population variation was similar to that previously reported for freshwater mussels, but genotype frequencies exhibited heterozygote deficiencies in many instances. All three species exhibited significant among‐population variation. Evidence of isolation‐by‐distance was found in Elliptio dilatata and Ptychobranchus fasciolaris, while Lampsilis siliquoidea showed no geographical pattern of among‐population variation. 3. Our results suggest that the isolating effects of genetic drift were greater in L. siliquoidea than in the other species. Differentiation of populations occurred at a much smaller spatial scale than has previously been found in freshwater mussels. Differences among species may reflect differences in the dispersal abilities of fishes that serve as hosts for the glochidia larvae of mussels. 4. Based on our results, we hypothesise that species of mussels that are common to large rivers exhibit relatively large amounts of within‐population genetic variation and little differentiation over large geographical distances. Conversely, species typical of small streams show lower within‐population genetic variation and populations will be more isolated. If this hypothesis can be supported, it may prove useful in the design of conservation strategies that maintain the genetic structure of target species.     

Genetic structure of giant clam (Tridacna maxima) populations from reefs in the Western Coral Sea

Allozyme variation at six polymorphic loci was examined in 10 populations of Tridacna maxima from reefs in the Western Coral Sea, to test whether patterns of relatedness previously reported for foraminiferan populations reflected a fundamental structuring of the fauna in the region. Genetic distances (Nei's D) among populations of T. maxima ranged from 0–0.065 and increased with increasing geographical separation. No significant differences in gene frequencies were observed among populations within two groups of reefs identified by cluster analysis: the Great Barrier Reef (GBR), and among the offshore reefs excluding Lihou and Osprey. Significant genetic differences among these groups and the outliers Lihou and Osprey were consistent with the greater geographical separation of populations between areas than within areas. There was no evidence of differentiation along a north-south axis as reported for the foraminiferan Marginopora vertebralis, nor did populations from offshore reefs on the Queensland Plateau form a well-defined group that was genetically distinct from the GBR. The patterns observed for M. vertebralis do not appear to reflect a fundamental structuring of biota in the region. The differences in the pattern of genetic variation for M. vertebralis as compared with those for T. maxima may be due to several differences in the biological characteristics of the two species. The time of breeding in particular may influence the extent to which the divergence of the East Australian Current restricts larval dispersal among reefs in the central Queensland Plateau.     

Population structure affected by excess gene flow in self-pollinating Elymus nutans and E. burchan-buddae (Triticeae: Poaceae)

Seed-mediated gene flow can considerably affect population genetic structure of strictly self-pollinating species, but little is known on the extent and nature of such gene flow among pastoral plant populations. Molecular fingerprints provide a powerful tool to address the relevant issues. Genetic structure of 22 populations of two self-pollinating pasture species, Elymus nutans and E. burchan-buddae, collected from various altitudes of the Qinghai–Tibetan Plateau was studied using fluorescence-based amplified fragment length polymorphism technique. Analysis of molecular variance revealed 42.97% and 37.63% among-population variation for the two Elymus species, respectively, indicating that the majority of the total variation presented within populations. This result contradicts the common genetic variation pattern for a selfing plant species: lower genetic variation within populations. Further analysis suggested higher level of gene flow among populations within the same region than among different regions across the sampled area for the two Elymus species. STRUCTURE analyses of the Elymus populations indicated an evident admixture genetic structure, particularly among neighboring populations from the same region, supporting the hypothesis of considerable seed dispersal among populations. The excess within-region gene flow of E. nutans and E. burchan-buddae might be caused by grazing animals that promote seed dispersal when moved around the pastoral lands during foraging. The among-population gene flow promulgated by grazing animals may promote the maintenance of genetic diversity in the pasture species, particularly in small and fragmented populations within a given region.     

Gene flow measured by allozymic analysis in pesticide resistant Typhlodromus pyri occurring within and near apple orchards

Electrophoresis of allozymes was used to estimated gene flow among populations of Typhlodromus puri Scheuten from apple orchards and nearby blackberry plants from two valleys of western Oregon, USA. Four allozyme loci unaffected by pesticides were tested. Wright's coefficient of inbreeding, F _ST, for all populations was 0.115 and the proportion of populations that migrated per generation, Nm, was 2.08. These values were higher than expected for such locally collected mites. No allelic patterns could be discerned for populations among or within valleys: however, more variation was found for mites collected within than between valleys. From other studies of dispersal and pesticide resistance, we concluded that T. pyri had a low dispersal rate, but these data from allozymic analysis indicated there was moderate gene flow among populations. We concluded that the unique features of the population dynamics of T. pyri may account for the differences seen in estimating gene flow when using different types of population assessment (i.e., dispersal distances, resistance rates and allozyme frequency studies).     

Genetic Diversity and the Reintroduction of Meadow Species

Abstract: Restoration of formerly nutrient‐poor and species‐rich grasslands generally leads to an increase in species diversity. However, species without a persistent seed bank and with poor dispersal ability often do not re‐establish spontaneously. Here, reintroduction is an option. If existing populations are comparable in their genetic composition, any population will do. This is not the case if populations have local adaptations. Unfortunately, whether populations are adapted locally is not easily determined, in contrast to assessing differentiation using neutral genetic markers. We used AFLP to study genetic diversity of Cirsium dissectum and Succisa pratensis within and among several Junco‐Molinion plant communities in the Netherlands (up to 200 km apart) that were potential source populations, and followed the reintroduction using seeds from these populations. Also, vegetative growth phase characteristics of three populations of C. dissectum were analyzed under controlled conditions. Most of the genetic variation in these cross‐fertilizing species was found within populations. Small but significant genetic differences in band frequencies were found among populations (F_st 0.100 ‐ 0.135). The first generation of reintroduced plants contained less polymorphic bands than the source populations. The genetic differences caused by reintroduction using a limited number of seeds (founder effects) were significant in all except one case (F_st 0.012 ‐ 0.101 between source and corresponding reintroduced population), but the magnitude was smaller than the source population differentiation. In assignment tests, reintroduced populations resembled their source population more than any other population, but all populations contained sizeable proportions of plants that were assigned to most similar plants from other populations, indicating that the populations are only marginally distinct. Calculations show that reintroduction from more than one source population introduces significantly more polymorphic bands into the new population, capitalizing on the existence of band frequency differences among populations.     

GENETIC STRUCTURE OF GIANT CLAM (TRIDACNA MAXIMA) POPULATIONS IN THE WEST PACIFIC IS NOT CONSISTENT WITH DISPERSAL BY PRESENT-DAY OCEAN CURRENTS

The Pacific marine biota, particularly species with long planktonic larval stages, are thought to disperse widely throughout the Pacific via ocean currents. The little genetic data available to date has supported this view in that little or no significant regional differentiation of populations has been found over large geographical distances. However, recent data from giant clams has demonstrated not only significant regional differentiation of populations, but routes of gene flow that run perpendicular to the main present-day ocean currents. Extensive surveys of genetic variation at eight polymorphic loci in 19 populations of the giant clam Tridacna maxima, sampled throughout the West and Central Pacific, confirmed that the patterns of variation seen so far in T. gigas were not unique to that species, and may reflect a fundamental genetic structuring of shallow-water marine taxa. Populations of T. maxima within highly connected reef systems like the Great Barrier Reef were panmictic (average F_ST < 0.003), but highly significant genetic differences between reef groups on different archipelagos (average F_ST = 0.084) and between West and Central Pacific regions (average F_ST = 0.156) were found. Inferred gene flow was high (N_em usually > 5) between the Philippines and the Great Barrier Reef, between the Philippines and Melanesia (the Solomon Islands and Fiji), and between the Philippines and the Central Pacific island groups (Marshall Islands, Kiribati, Tuvalu and Cook Islands). Gene flow was low between these three sets of island chains (N_em < 2). These routes of gene flow are perpendicular to present-day ocean currents. It is suggested that the spatial patterns of gene frequencies reflect past episodes of dispersal at times of lower sea levels which have not been erased by subsequent dispersal by present-day circulation. The patterns are consistent with extensive dispersal of marine species in the Pacific, and with traditional views of dispersal from the Indo-Malay region. However, they demonstrate that dispersal along present-day ocean surface currents cannot be assumed, that other mechanisms may operate today or that major dispersal events are intermittent (perhaps separated by several thousands of years), and that the nature and timing of dispersal of Pacific marine species is more complex than has been thought.     

Contrasting ecosystem-effects of morphologically similar copepods

Organisms alter the biotic and abiotic conditions of ecosystems. They can modulate the availability of resources to other species (ecosystem engineering) and shape selection pressures on other organisms (niche construction). Very little is known about how the engineering effects of organisms vary among and within species, and, as a result, the ecosystem consequences of species diversification and phenotypic evolution are poorly understood. Here, using a common gardening experiment, we test whether morphologically similar species and populations of Diaptomidae copepods (Leptodiaptomus ashlandi, Hesperodiaptomus franciscanus, Skistodiaptomus oregonensis) have similar or different effects on the structure and function of freshwater ecosystems. We found that copepod species had contrasting effects on algal biomass, ammonium concentrations, and sedimentation rates, and that copepod populations had contrasting effects on prokaryote abundance, sedimentation rates, and gross primary productivity. The average size of ecosystem-effect contrasts between species was similar to those between populations, and was comparable to those between fish species and populations measured in previous common gardening experiments. Our results suggest that subtle morphological variation among and within species can cause multifarious and divergent ecosystem-effects. We conclude that using morphological trait variation to assess the functional similarity of organisms may underestimate the importance of species and population diversity for ecosystem functioning.     

GENETIC STRUCTURE AND EVOLUTION OF SPECIES IN THE MANGROVE GENUS AVICENNIA (AVICENNIACEAE) IN THE INDO-WEST PACIFIC

Allozyme variation in species of the mangrove genus Avicennia was screened in 25 populations collected from 22 locations in the Indo-West Pacific and eastern North America using 11 loci. Several fixed gene differences supported the specific status of Avicennia alba, A. integra, A. marina, and A. rumphiana from the Indo-West Pacific, and A. germinans from the Atlantic-East Pacific. The three varieties of A. marina, var. marina, var. eucalyptifolia, and van australasica, had higher genetic similarities (Nei's I) and no fixed gene differences, confirming their conspecific status. Strong genetic structuring was observed in A. marina, with sharp changes in gene frequencies at the geographical margins of varietal distributions. The occurrence of alleles found otherwise in only one variety, in only immediately adjacent populations of another variety, provided evidence of introgession between varieties. The varieties appear to have diverged recently in the Pleistocene and are apparently not of ancient Cretaceous origin, as suggested earlier. Despite evidence of high degrees of outcrossing, gene flow among populations was relatively low (N_em < 1–2), except where populations were geographically continuous, questioning assumptions that these widespread mangrove species achieve high levels of long-distance dispersal.     

Rangewide phylogeography and landscape genetics of the Western U.S. endemic frog Rana boylii (Ranidae): implications for the conservation of frogs and rivers

Genetic data are increasingly being used in conservation planning for declining species. We sampled both the ecological and distributional limits of the foothill yellow-legged frog, Rana boylii to characterize mitochondrial DNA (mtDNA) variation in this declining, riverine amphibian. We evaluated 1525 base pairs (bp) of cytochrome b and ND2 fragments for 77 individuals from 34 localities using phylogenetic and population genetic analyses. We constructed gene trees using maximum likelihood and Bayesian inference, and quantified genetic variance (using AMOVA and partial Mantel tests) within and among hydrologic regions and river basins. Several moderately supported, geographically-cohesive mtDNA clades were recovered for R. boylii. While genetic variation was low among populations in the largest, most inclusive clade, samples from localities at the edges of the geographic range demonstrated substantial genetic divergence from each other and from more central populations. Hydrologic regions and river basins, which represent likely dispersal corridors for R. boylii, accounted for significant levels of genetic variation. These results suggest that both rivers and larger hydrologic and geographic regions should be used in conservation planning for R. boylii.     

The geographic structure of morphological variation in eight species of fiddler crabs (Ocypodidae: genus Uca) from the eastern United States and Mexico

Species with larger geographic distributions are more likely to encounter a greater variety of environmental conditions and barriers to gene flow than geographically‐restricted species. Thus, even closely‐related species with similar life‐history strategies might vary in degree and geographic structure of variation if they differ in geographic range size. In the present study, we investigated this using samples collected across the geographic ranges of eight species of fiddler crabs (Crustacea: Uca) from the Atlantic and Gulf coasts of North America. Morphological variation in the carapace was assessed using geometric morphometric analysis of 945 specimens. Although the eight Uca species exhibit different degrees of intraspecific variation, widespread species do not necessarily exhibit more intraspecific or geographic variation in carapace morphology. Instead, species with more intraspecific variation show stronger morphological divergence among populations. This morphological divergence is partly a result of allometric growth coupled with differences in maximum body size among populations. On average, 10% of total within‐species variation is attributable to allometry. Possible drivers of the remaining morphological differences among populations include gene flow mediated by ocean currents and plastic responses to various environmental stimuli, with isolation‐by‐distance playing a less important role. The results obtained indicate that morphological divergence among populations can occur over shorter distances than expected based on dispersal potential. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 248–270.     

Unexpected relationships of substructured populations in Chinese Locusta migratoria

Background  

Highly migratory species are usually expected to have minimal population substructure because strong gene flow has the effect of homogenizing genetic variation over geographical populations, counteracting random drift, selection and mutation. The migratory locust Locusta migratoria belongs to a monotypic genus, and is an infamous pest insect with exceptional migratory ability – with dispersal documented over a thousand kilometers. Its distributional area is greater than that of any other locust or grasshopper, occurring in practically all the temperate and tropical regions of the eastern hemisphere. Consequently, minimal population substructuring is expected. However, in marked contrast to its high dispersal ability, three geographical subspecies have been distinguished in China, with more than nine being biologically and morphologically identified in the world. Such subspecies status has been under considerable debate.     

DEPENDENCE OF GENE FLOW ON GEOGRAPHIC DISTANCE IN TWO SOLITARY CORALS WITH DIFFERENT LARVAL DISPERSAL CAPABILITIES

When the level of gene flow among populations depends upon the geographic distance separating them, genetic differentiation is relatively enhanced. Although the larval dispersal capabilities of marine organisms generally correlate with inferred levels of average gene flow, the effect of different modes of larval development on the association between gene flow and geographic distance remains unknown. In this paper, I examined the relationship between gene flow and distance in two co-occurring solitary corals. Balanophyllia elegans broods large, nonfeeding planulae that generally crawl only short distances from their place of birth before settling. In contrast, Paracyathus stearnsii free-spawns and produces small planktonic larvae presumably capable of broad dispersal by oceanic currents. I calculated F-statistics using genetic variation at six (P. stearnsii) or seven (B. elegans) polymorphic allozyme loci revealed by starch gel electrophoresis, and used these F-statistics to infer levels of gene flow. Average levels of gene flow among twelve Californian localities agreed with previous studies: the species with planktonic, feeding larvae was less genetically subdivided than the brooding species. In addition, geographic isolation between populations appeared to affect gene flow between populations in very different ways in the two species. In the brooding B. elegans, gene flow declined with increasing separation, and distance explained 31% of the variation in gene flow. In the planktonically dispersed P. stearnsii distance of separation between populations at the scale studied (10–1000 km) explained only 1% of the variation in gene flow between populations. The mechanisms generating geographic genetic differentiation in species with different modes of larval development should vary fundamentally as a result of these qualitative differences in the dependence of gene flow on distance.     

LONG-DISTANCE GENE FLOW IN THE SEDENTARY BUTTERFLY,EUPHILOTES ENOPTES (LEPIDOPTERA: LYCAENIDAE)

The relationship between gene flow and geographic proximity has been assessed for many insect species, but dispersal distances are poorly known for most of these. Thus, we are able to assess the concordance between vagility and gene flow for only a few species. In this study, I documented variation at six allozyme loci among Washington and Oregon populations of the sedentary, patchily distributed, lycaenid butterfly, Euphilotes enoptes (Boisduval) to assess whether the relationship between gene flow and geographic distance is consistent with the dispersal biology of this species. Both a phenogram based on genetic distances between populations and a regression analysis of gene flow estimates on geographic distances showed a pattern consistent with genetic isolation by distance. Many estimates of gene flow among pairs of populations separated by more than 100 km exceeded the equivalent of 10 individuals exchanged per generation, a value much greater than would be predicted from the limited dispersal ability of this species. However, based on the allozyme data, genetic neighborhood size was estimated to be approximately 39 individuals, a value that is consistent with poor vagility. The results of this study speak to the power of stepping-stone gene flow among populations and are compared to the results of other studies that have examined the relationship between dispersal and gene flow in sedentary insects.     

Associations between physical isolation and geographical variation within three species of Neotropical birds

We studied effects of physical isolation on geographical variation in mtDNA RFLP polymorphisms and a suite of morphological characters within three species of neotropical forest birds; the crimson-backed tanager Ramphocelus dimidiatus, the blue-gray tanager Thraupis episcopus, and the streaked saltator Saltator albicollis. Variation among populations within continuous habitat on the Isthmus of Panama was compared with that among island populations isolated for about 10000 years. Putative barriers to dispersal were influential, but apparent isolation effects varied by species, geographical scale, and whether molecular or morphological traits were being assessed. We found no geographical structuring among the contiguous, mainland sampling sites. Migration rates among the islands appeared sufficient to maintain homogeneity in mtDNA haplotype frequencies. In contrast, variation in external morphology among islands was significant within two of three species. For all species, we found significant variation in genetic and morphological traits between the island (collectively) and mainland populations. Interspecific variation in the effects of isolation was likely related to differential vagility. These data generally corroborate other studies reporting relatively great geographical structuring within tropical birds over short distances. Behaviourally based traits - low vagility and high ‘sensitivity’ to geographical barriers - may underlie extensive diversification within neotropical forest birds, but more extensive ecological and phylogeographic information are needed on a diverse sample of species.     

GENETIC CONSEQUENCES OF SEED DISPERSAL IN THREE SYMPATRIC FOREST HERBS. I. HIERARCHICAL POPULATION-GENETIC STRUCTURE

To examine the effects of seed dispersal on spatial genetic structure, we compare three sympatric species of forest herbs in the family Apiaceae whose fruits differ widely in morphological adaptations for animal-attached dispersal. Cryptotaenia canadensis has smooth fruits that are gravity dispersed, whereas Osmorhiza claytonii and Sanicula odorata fruits have appendages that facilitate their attachment to animals. The relative seed-dispersal ability among species, measured as their ability to remain attached to mammal fur, is ranked Sanicula > Osmorhiza > Cryptotaenia. We use a nested hierarchical sampling design to analyze genetic structure at spatial scales ranging from a few meters to hundreds of kilometers. Genetic differentiation among population subdivisions, estimated by average genetic distance and hierarchical F-statistics, has an inverse relationship with dispersal ability such that Cryptotaenia > Osmorhiza > Sanicula. In each species, genetic differentiation increases with distance among population subdivisions. Stochastic variation in gene flow, arising from seed dispersal by attachment to animals, may partly explain the weak relationship between pairwise spatial and genetic distance among populations and heterogeneity in estimates of single locus F-statistics. A hierarchical island model of gene flow is invoked to describe the effects of seed dispersal on population genetic structure. Seed dispersal is the predominant factor affecting variation in gene flow among these ecologically similar, taxonomically related species.     

Adaptive significance of amylase polymorphism in Drosophila I. The geographical pattern of allozyme polymorphism at the amylase locus in Drosophila subobscura

Allelic variation at the Amy locus was studied in eight natural populations from the central and northern range of D. subobscura, and the geographical pattern of Amy polymorphism over the range of this species was described. Even though regional and local differences in gene frequencies were found, in general the same alleles occur at high, intermediate and low frequencies, in nearly all populations. There are no significant differences in allele frequencies, but there is significant difference in the degree of heterozygosity among groups of populations from the northern, central and southern range. An analysis of population subdivision indicates that heterogeneity within populations is higher than between populations. Genetic distance values indicate that there is a variable degree of geographical differentiation between local populations. Variability within and between continental and insular populations is also discussed.