Geographic Distance Matrices Research Articles

Genetic diversity and population structure of Hypericum humifusum L. (Hypericacae) in Tunisia: Implications for conservation

Sixteen Tunisian natural populations of Hypericum humifusum from different bioclimates (sub‐humid, upper semi‐arid and lower semi‐arid) were assessed for their genetic diversity using nine isozymes. For all populations and all enzymes, 11 polymorphic loci were detected. The allelic frequencies varied according to the populations. A high genetic diversity and an excess of heterozygosity were observed within populations (A p = 2.02; P% = 64.29; H o = 0.321). The outbreeding mating system and the high number of individuals in the starting populations may contribute to this high variation. A relatively high level of differentiation (F ST = 0.142) and a restricted gene flow among populations (N m =1.34) were revealed. The lower semi‐arid populations showed the highest differentiation (F ST = 0.205). The relationship between F ST and geographic distance matrices was not significant, indicating that the genetic structure among populations is more closely linked to habitat fragmentation and probably to founder events. Nei’s unbiased genetic distances among pairs of populations were low (0.012–0.119). The unweighted pair group method with arithmetic averaging algorithm cluster based on these distances showed four sub‐clusters. Population groupings had no evident relationship with bioclimates or geographic regions. The substantial differentiation between populations and their high genetic similarity suggest their recent divergence as a result of habitat fragmentation. Most of the total variation was found within populations, thus ex‐situ conservation should be based on sampling seeds within, rather than among, populations. Populations harbouring rare alleles and a high genetic diversity level should be collected first.

Population structures ofAstragalus filipescollections from western North America

The majority of species used for revegetation in semi-arid western rangelands of North America are grasses, with few forbs and nearly no legumes. Astragalus filipes (Torr. Ex A. Gray) is a western North American legume and a promising candidate for use in rangeland revegetation, but assessments of plant species diversity and structure are necessary to determine which collections should be used to constitute a conservation unit or regional seed source. To address this issue, we characterized within-collection genetic diversity, identified genetically differentiated groups, and tested genetic correlations with environmental variables on 67 collections of A. filipes. Within-population genetic diversity was greatest for collections in Oregon and lowest for collections in British Columbia and central Nevada. Five genetically differentiated groups were detected: one with strong support from central Nevada, one with strong support from British Columbia, and three with weak support comprising all other collections throughout Oregon, Washington, California, Idaho, and Nevada. Although there was significant correlation between genetic and linear geographic distance matrices, there was no correlation between genetic and phenotypic, elevation, temperature, or precipitation distance matrices. These results show that geographic distance contributes to genetic differentiation, and that structured populations have occurred in northernmost and southernmost groups of collections of A. filipes.

Genetic Variation of Spartina alterniflora in the New York Metropolitan Area and Its Relevance for Marsh Restoration

We examined the genetic population structure of Spartina alterniflora in Jamaica Bay, Queens, NY and the surrounding area in order to assist the ongoing restoration of Jamaica Bay. AMOVA (Analysis of Molecular Variance) indicated that population differences accounted for 15% of molecular variance (Φ PT = 0.15, p = 0.001). Observed heterozygosity (Ho) ranged from 0.61 to 0.73 among populations. A Mantel test indicated a weak and non-significant correlation between pairwise Φ PT and geographic distance matrices (r = 0.34, p = 0.12). A PCA revealed no obvious grouping pattern for sampled populations. Based on these data, we determined that the studied populations contained similar genetic variability to other populations in the New York vicinity and to those of the entire region. It seems likely that collection of germplasm from within the region will prove sufficient in maintaining overall genetic variation in restoration plantings. Given the small amount of genetic structure among populations within Jamaica Bay, however, it would be prudent to collect widely within the target marsh. We also recommend the practice of propagating plugs of S. alterniflora from wild seed, as opposed to using vegetative cuttings, when creating planting stock, in order to maximize genetic diversity in restored marshes.

Population and family structure of brown trout, Salmo trutta, in a Mediterranean stream

The physical arrangement of closely related individuals is expected to significantly influence the pattern of population genetic structure. For example, if related individuals are non-randomly distributed and included in samples, this may lead to exaggerated conclusions about genetic differentiation. In the present study, we compared population structure v. family relationships of brown trout (Salmo trutta L.) along a Mediterranean stream (Pyrenees) by using eight microsatellite loci. Results showed low levels of genetic (FST) differentiation between collections in a 6.5-km transect along the stream, and a significant correlation between genetic and geographical distance matrices, indicating a weak population structure associated with spatial distribution. Our data also indicated that geographical proximity of related individuals in the youngest (0+, 1+) cohorts probably was associated with limited dispersal of younger brown trout from spawning redds. Family relationships provided evidence, however, for movement of adult trout over distances of a few kilometres that probably contributed to the low observed differentiation. Dispersal of adult Mediterranean trout contrasts with the clustering of related older trout observed for some north European rivers and could be related to the reduced productivity in southern stream basins.

Genetic diversity in Tunisian Crataegus azarolus L. var. aronia L. populations assessed using RAPD markers

• The genetic diversity of nine wild Tunisian Crataegus azarolus var. aronia L. populations from different bioclimates was assessed using RAPD markers.• Eight selected primers generated a total of 105 bands, 81 of which were polymorphic. Shannon’s index (H ′) ranged from 0.222 to 0.278 according to a population with an average of 0.245. The genetic variation within the species (H SP = 0.423) was relatively low. A high differentiation (G ST = 0.421) among populations coupled with a low level of gene flow (N m = 0.472) were observed. The analysis of molecular variance (AMOVA) revealed also significant differentiation among populations (ΦST = 0.371), even at a low scale space. The majority of variation occurred within populations (63.31%). The Mantel test performed on genetic (ΦST ) and geographic distance matrices among population pairs did not reveal an isolation by distance.• Interpretation of Neighbour-joining tree based on Nei’s and Li’s genetic distance among individuals showed distinct population groupings. The UPGMA dendrogram based on ΦST values revealed two population sub-clusters, each including populations from different bioclimates and/or geographic regions.• The low level of genetic diversity and the high genetic structure of populations resulted from genetic drift caused both by habitat fragmentation and the low size of populations.• The high differentiation among populations and the similar low level of diversity within populations suggest that in situ conservation should interest all populations. The ex situ conservation should be based on the collection of seeds rather within than among populations because of the maximum of variation was revealed within populations.

Geographic and Breed Distribution Patterns of an A/G Polymorphism resent in the Mx Gene Suggests Balanced Selection in Village Chickens

An A/G Single Nucleotide Polymorphism (SNP) at position 1,892 of the Mx gene coding sequence has been linked to susceptibility/resistance to avian viral infection in vitro. Using PCR-RFLP and sequencing methods, 1,946 samples from 109 populations from Asia, Africa and Europe; grouped as indigenous village, commercial, fancy chicken as well as wild junglefowl were genotyped for the polymorphism. Allele and genotype frequencies were calculated. Only the G allele was present in Ceylon junglefowl Gallus lafayetti. Using the wild red junglefowl G. gallus population as reference, we assessed if the A/G alleles and genotypes frequencies have been affected by the breeding history and the geographic dispersion of domestic chicken. Within group variation was high but overall there were no significant variation in distribution of alleles and genotypes frequencies between the red junglefowl and indigenous village chickens (p>0.1946), with the exception of the East Asian group (p<0.0001). However, allele and genotype frequencies were significantly different between the red junglefowl and the commercial or fancy groups (p<0.0001). A small but significant negative correlation (r = - 0.166, p<0.0003) was observed between allelic and geographic distance matrices amongst indigenous village chicken populations. Human selection and genetic drift are likely the main factors having shaped today's observed allele and genotype frequencies in commercial and fancy breeds. In indigenous village chicken and red junglefowl, we propose that both A and G alleles have been maintained by natural selection for disease resistance through a balancing selection mechanism.

Climate Signatures in the Morphological Differentiation of Worldwide Modern Human Populations

The ability of cranial morphology to reflect population/phylogenetic history, and the degree to which it might be influenced by environmental factors and selection pressures have been widely discussed. Recent consensus views cranial morphology as largely indicative of population history in humans, with some anatomical cranial regions/measurements being more informative on population history, while others being under selection pressure. We test earlier findings using the largest and most diverse cranial dataset available as yet: 7,423 male specimens from 135 geographic human population samples represented by 33 standard craniometric linear measurements. We calculated Mahalanobis D(2) for three datasets: complete cranial dataset; facial measurement dataset; and neurocranial measurement dataset; these morphological distance matrices were then compared to matrices of geographic distances as well as of several climatic variables. Additionally, we calculated Fst values for our cranial measurements and compared the results to the expected Fst values for neutral genetic loci. Our findings support the hypothesis that cranial, and especially neurocranial morphology, is phylogenetically informative, and that aspects of the face and cranium are subject to selection related to climatic factors. The Fst analysis suggest that selection to climate is largely restricted to groups living in extremely cold environments, including Northeast Asia, North America, and Northern Europe, though each of these regions appears to have arrived at their morphology through distinct adaptive pathways.

Effects of landscape and history on diversification of a montane, stream‐breeding amphibian

AbstractAim The aim of this study was to understand the roles of landscape features in shaping patterns of contemporary and historical genetic diversification among populations of the Andean tree frog (Hypsiboas andinus) across spatial scales.Location Andes mountains, north‐western Argentina, South America.Methods Mitochondrial DNA control region sequences were utilized to assess genetic differentiation among populations and calculate population pair‐wise genetic distances. Three models of movement, namely traditional straight‐line distance and two effective distances based on habitat classification, were examined to determine which of these explained the most variation in pair‐wise population genetic differentiation. The two habitat classifications were based on digital vegetation and hydrology layers that were generated from a 90‐m resolution digital elevation model (DEM) and known relationships between elevation and habitat. Mantel tests were conducted to test for correlations between geographic and genetic distance matrices and to estimate the percentage variation explained by each type of geographic distance. To investigate the location of possible barriers to gene flow, we used Monmonier’s maximum difference algorithm as implemented in barrier 2.2.Results At both geographic scales, effective distances explained more variation in genetic differentiation than did straight‐line distance. The least‐cost distances based on the simple classification performed better than the more detailed habitat classification. We controlled for the effects of historical range fragmentation determined from previous nested clade analyses, and therefore evaluated the effect of different distances on the genetic variation attributable to more recent factors. Effective distances identified populations that were highly divergent as a result of isolation in unsuitable habitats. The proposed locations of barriers to gene flow identified using Monmonier’s maximum difference algorithm corresponded well with earlier analyses and supported findings from our partial Mantel tests.Main conclusions Our results indicate that landscape features have been important in both historical and contemporary genetic structuring of populations of H. andinus at both large and small spatial scales. A landscape genetic perspective offers novel insights not provided by traditional phylogeographic studies: (1) effective distances can better explain patterns of differentiation in populations, especially in heterogeneous landscapes where barriers to dispersal may be common; and (2) least‐cost path analysis can help to identify corridors of movement between populations that are biologically more realistic.

Genetic and linguistic coevolution in Northern Island Melanesia.

Recent studies have detailed a remarkable degree of genetic and linguistic diversity in Northern Island Melanesia. Here we utilize that diversity to examine two models of genetic and linguistic coevolution. The first model predicts that genetic and linguistic correspondences formed following population splits and isolation at the time of early range expansions into the region. The second is analogous to the genetic model of isolation by distance, and it predicts that genetic and linguistic correspondences formed through continuing genetic and linguistic exchange between neighboring populations. We tested the predictions of the two models by comparing observed and simulated patterns of genetic variation, genetic and linguistic trees, and matrices of genetic, linguistic, and geographic distances. The data consist of 751 autosomal microsatellites and 108 structural linguistic features collected from 33 Northern Island Melanesian populations. The results of the tests indicate that linguistic and genetic exchange have erased any evidence of a splitting and isolation process that might have occurred early in the settlement history of the region. The correlation patterns are also inconsistent with the predictions of the isolation by distance coevolutionary process in the larger Northern Island Melanesian region, but there is strong evidence for the process in the rugged interior of the largest island in the region (New Britain). There we found some of the strongest recorded correlations between genetic, linguistic, and geographic distances. We also found that, throughout the region, linguistic features have generally been less likely to diffuse across population boundaries than genes. The results from our study, based on exceptionally fine-grained data, show that local genetic and linguistic exchange are likely to obscure evidence of the early history of a region, and that language barriers do not particularly hinder genetic exchange. In contrast, global patterns may emphasize more ancient demographic events, including population splits associated with the early colonization of major world regions.

Comparative morphology of populations of Monstera Adans. (Araceae) from natural forest fragments in Northeast Brazil using elliptic Fourier Analysis of leaf outlines

A comparative study of the leaf outline morphometrics of Monstera adansonii var. klotzschiana, M. adansonii var. laniata and M. praetermissa was carried out. The study focused on populations in isolated montane humid (brejo) forests of Ceara state in Northeast Brazil and compared them with populations from Amazonia and the Brazilian Atlantic Forest. Digitised outlines were prepared from a total of 1,695 field-collected leaf images from 20 populations, and elliptic Fourier analysis was used to generate matrices of coefficients, from which six shape variables (principal components) were extracted using Principal Components Analysis. Intra-population variability and inter-population differences were analysed with multivariate distance methods. Separate analyses were carried out for each of three leaf size classes (juvenile, submature, mature) because of the strong heteroblasty typical of this genus. Juvenile leaves were the least variable size class within populations of M. adansonii var. klotzschiana. The shape variables expressed very similar types of variation in all three size classes. The Ceara brejo populations of M. adansonii var. klotzschiana showed significant differences between mature leaf outlines in all pairwise comparisons; the Pacatuba population was the most distinct. The Ceara populations did not cluster together exclusively. In all three size classes, populations clustered together into their taxonomic groups, most clearly so in mature leaves. No correlation between morphological and geographic distance matrices was found, nor between morphological and molecular distance. The study showed that leaf outline shape is a practicable and useful quantitative trait for studying morphological variability at species, varietal and population levels.

Genetic variation of the razor clam Ensis siliqua (Jeffreys, 1875) along the European coast based on random amplified polymorphic DNA markers

Ensis siliqua is regarded as an increasingly valuable fishery resource with potential for commercial aquaculture in many European countries. The genetic variation of this razor clam was analysed by randomly amplified polymorphic DNA (RAPD) in six populations from Spain, Portugal and Ireland. Out of the 40 primers tested, five were chosen to assess genetic variation. A total of 61 RAPD loci were developed ranging in size from 400 to 2000 bp. The percentages of polymorphic loci, the allele effective number and the genetic diversity were comparable among populations, and demonstrated a high level of genetic variability. The values of Nei's genetic distance were small among the Spanish and Portuguese populations (0.051–0.065), and high between these and the Irish populations. Cluster and principal coordinate analyses supported these findings. A mantel test performed between geographic and genetic distance matrices showed a significant correlation (r=0.84, P<0.05), suggesting an isolation by distance process.

Comparative population structure of Chinese sumac aphid Schlechtendalia chinensis and its primary host-plant Rhus chinensis

Most of our current understanding of comparative population structure has been come from studies of parasite-host systems, whereas the genetic comparison of gallnut-aphids and their host-plants remain poorly documented. Here, we examined the population genetic structure of the Chinese sumac aphid Schlechtendalia chinensis and its unique primary host-plant Rhus chinensis in a mountainous province in western China using inter-simple sequence repeat (ISSR) markers. Despite being sampled from a mountainous geographic range, analysis of molecular variance (AMOVA) showed that the majority of genetic variation occurred among individuals within populations of both the aphid and its host. The aphid populations were found to be structured similarly to their primary host populations (F (ST) values were 0.239 for the aphid and 0.209 for its host), suggesting that there are similar patterns of gene flow between the populations of the aphid and between populations of its host-plant. The genetic distances (F (ST)/1 - F (ST)) between the aphid populations and between its host-plant populations were uncorrelated, indicating that sites with genetically similar host-plant populations may not always have genetically similar aphid populations. The lack of relationships between genetic and geographical distance matrices suggested that isolation by distance (IBD) played a negligible role at this level. This may be mainly attributed to the founder effect, genetic drift and the relative small spatial scale between populations.

Measuring European Population Stratification with Microarray Genotype Data

A proper understanding of population genetic stratification--differences in individual ancestry within a population--is crucial in attempts to find genes for complex traits through association mapping. We report on genomewide typing of approximately 10,000 single-nucleotide polymorphisms in 297 individuals, to explore population structure in Europeans of known and unknown ancestry. The results reveal the presence of several significant axes of stratification, most prominently in a northern-southeastern trend, but also along an east-west axis. We also demonstrate the selection and application of EuroAIMs (European ancestry informative markers) for ancestry estimation and correction. The Coriell Caucasian and CEPH (Centre d'Etude du Polymorphisme Humain) Utah sample panels, often used as proxies for European populations, are found to reflect different subsets of the continent's ancestry.

Population structure of Eupemphix nattereri (Amphibia, Anura, Leiuperidae) from Central Brazil

This study reports on 156 specimens of the amphibian Eupemphix nattereri, a widely distributed leiuperid, obtained from 11 municipalities of central Brazil. The extent of genetic variation was quantified by determining the mean number of alleles per locus and the proportion of polymorphic loci. An analysis of molecular variance (AMOVA) was performed on the random amplified polymorphic DNA (RAPD) haplotypes. The genetic distances obtained by calculating pairwise phist among local samples were used to determine population relationships using the unweighted pair-group method (UPGMA) and non-metric multidimensional scaling (NMDS). The cophenetic correlation was calculated to confirm agreement between the genetic matrix and the unweighted pair group method with averages (UPGMA) dendrogram. To determine if genetic distances were correlated to geographical distances we constructed pairwise genetic distance and geographical distance matrices and compared them using the Mantel test. The AMOVA results indicated significant genetic differences (p < 0.001) between E. nattereri populations, representing 69.5% of the within population genetic diversity. The Mantel test showed no significant correlation (r = 0.03; p = 0.45) between the genetic and geographical distance matrices. Our findings indicate that the genetic variation of E. nattereri populations was randomly distributed in geographic space and that gene flow for this species is probably structured at spatial scales smaller than those between our samples

Fine scale patterns of migration and gene flow in the endangered mound spring snail, Fonscochlea accepta (Mollusca:Hydrobiidae) in arid Australia

Naturally patchy ecosystems are models for other systems currently undergoing anthropogenic habitat fragmentation. Understanding patterns of gene flow in these model systems can help us manage species and ecosystems threatened by human impacts. The mound springs of central Australia represent such a natural model ecosystem, supporting a unique aquatic fauna distributed within an inhospitable arid landscape. Moreover, these springs are being impacted by over extraction of groundwater, providing a unique opportunity to look at dispersal in a patchy habitat that is changing. The present study represents the first fine scale analysis of gene flow under different scenarios of habitat connectivity for the endangered mound spring snail, Fonscochlea accepta. Within a single spring group pairwise estimates of F ST between springs were very low (ave 0.015) with no association found between genetic distance and a series of geographical distance matrices based on the degree of habitat connectivity among the springs: results implying unstructured dispersal and limited population isolation. However, results from Bayesian assignment tests showed that on average approximately 97% of snails were assigned to their spring of origin. In a preliminary analysis at broader geographic scales (among spring groups) the results from F ST estimates, Mantel correlation analyses and assignment tests all suggest much stronger and geographically correlated population structuring. While varying results from F-statistics and Bayesian analyses stem from the different information they utilise, together they provide data on contemporary and historical estimates of gene flow and the influence of landscape dynamics on the spatial genetic patterning of the springs.

Patterning of geographic variation in Middle Pleistocene Homo frontal bone morphology

A quantitative assessment of the frontal bone morphology of a sample of Middle Pleistocene hominins was undertaken in order to address questions regarding their population structure and evolutionary history. Outline tracings of the frontal bones of forty-seven fossil crania were obtained, and size-standardized measurements were then computed using an Elliptical Fourier analysis of these tracings. Principal component scores of the Fourier harmonic amplitudes were derived and served as a quantitative representation of the morphology of the frontal bone. Morphological, geographical, and temporal distance matrices were then constructed between each pair of fossils. A partial Mantel matrix correlation test was performed between morphological and geographical distance matrices, controlling for temporal distance, in order to determine if the pattern of geographical differentiation in features of the frontal bone of mid-Pleistocene Homo followed that of an isolation-by-distance model of population structure. The results of the partial Mantel tests indicate that the overall patterning of differentiation in the features of the frontal bone cannot best be explained by a population structure shaped by isolation-by-distance. Additionally, various aspects of the frontal bone quantified here follow different patterns of geographical differentiation, suggesting that a mosaic pattern of evolution holds true for characters within one cranial region and not just for those between regions.

RAPD Polymorphism of the White-Flowered Gourd (Lagenaria siceraria (Molina) Standl. Landraces and its Wild Relatives in Kenya

The present study was performed to investigate genetic diversity of Kenyan landraces of the white-flowered gourd (Lagenaria siceraria), which exhibits tremendous morphological variation. RAPD analyses were performed on 53 landraces of the cultivated species L. siceraria and 42 accessions of three wild species (40 L. sphaerica, 1 L. abyssinica, and 1 L. breviflora). A total of 432 polymorphic bands were detected using 54 primers. The four species were clearly differentiated from one another. Intra-specific variations were investigated with L. siceraria and its wild relative L. sphaerica. Landraces of the cultivated species collected from different ethnic communities or regions were differentiated. Morphological variations were not associated with RAPD variations. Bitter landraces collected in Maasai communities showed two specific RAPD bands. In the wild species, accessions collected from the eastern and western sides of the Great Rift Valley were genetically differentiated from each other. In both species, genetic and geographical distance matrices computed among all pairs of accessions were significantly correlated, implying that the observed geographical variation can be explained by the 'Isolation by distance model'. Progeny plants derived from a common mother in L. siceraria showed a low level of segregation in RAPD pattern, suggesting that collected landraces are cultivated, maintaining their inherent traits although they are monoecious and insect-pollinated, whereas the wild relative L. sphaerica showed a higher level of segregation. The morphological diversity observed among landraces of L. siceraria is the result of human selection and their genetic identities are maintained by inbreeding probably resulting from frequent self-pollination.

Genetic diversity in Hordeum chilense Roem. et Schult. germplasm collection as determined by endosperm storage proteins

Hordeum chilense Roem. et Schult. shows interesting characteristics for breeding, such as disease or pest resistance and has high variability for endosperm storage proteins, valuable for the improvement of the breadmaking quality of both tritordeum and wheat. Knowledge of the genetic structure and the level of H. chilense genetic diversity within its distribution zone may be important to decide on breeding strategies as well as management procedures. The pattern of genetic variation within and among different regions of the distribution area of H. chilense, was analysed by endosperm storage proteins (gliadin and low-molecular- weight glutenin subunits). Several analyses were performed including AMOVA, direct correlation between phenotypic and geographic distance matrices and spatial genetics differentiation. Most genetic diversity was caused by differences among individuals within a population, although all the analyses performed suggest the existence of a low degree of differentiation within regions. Correlation values between phenotypic and geographic distances were low but significant. The spatial genetics analysis revealed that the average phenotypic distances of each of the spatial distance class were not lower (or higher) than that expected by chance. These results are explained by their neutral behaviour towards a selection of endosperm storage proteins and could be very useful in optimising future sample collecting strategies.

Contrasting patterns of spatial genetic structure of diploid and triploid populations of the clonal aquatic species,Butomus umbellatus (Butomaceae), in Central Europe

Genetic diversity in a sample of an aquatic plantButomus umbellatus from 37 localities in Czechia and Slovakia was studied by analyzing six polymorphic loci in three enzymatic systems (SKDH, PGD and AAT). Diversity among ramets was low in eight populations with relatively extensive sampling (only one population possessed more than one multilocus genotype), suggesting high clonality of reproduction in these populations. However, among-population diversity was high: G = 0.782 and 0.881 for the samples of diploid and triploid populations, respectively. Heterozygosity of individual plants averaged over variable loci was also high: H = 0.554 for diploids and 0.453 for triploids. Genetic differentiation among populations was additionally studied using cluster analysis. Several populations of diploids clustered separately from all other populations, whereas another group of diploid populations clustered with some triploid populations, indicating the possibility of relatively recent, probably multiple origin of these triploid populations from their diploid progenitors. Association between matrices of Nei’s genetic distances among populations from different localities and matrices of geographic distances among these localities revealed highly significant correlation for the sample of diploid populations (r = 0.60,P < 0.001) but no significant correlation for the sample of triploid populations (r = 0.02,P = 0.593). These results indicate a spatial structure of diploid populations in accordance with the isolation by distance model, and a random distribution of genotypes among triploid populations ofB. umbellatus.

Patterns of genetic variability in Anopheles quadrimaculatis (sensu stricto) (Diptera: Culicidae) populations in eastern Arkansas.

Electrophoretically detectable isozyme differences in 15 populations of Anopheles quadrimaculatus (Say) (sensu stricto) from eastern Arkansas were compared to measure levels of genetic diversity and study the sources of the variation. All of the enzyme loci had 2-7 alleles. Average levels of polymorphism per population were 88.9%. Heterozygotes for alleles of at least 1 of the 9 loci made up an average overall loci of 0.323 +/- 0.078 of the individuals examined. F-statistic analysis suggested a small, but statistically significant interpopulation differentiation of heterozygote frequency. The reduced heterozygote frequency was not attributable to the presence of more than one species in any population nor to the preferential use of oviposition habitats by certain populations within the species. Nei's distance values for pairwise population comparisons were small (<0.06). Correlation between genetic and geographic distance matrices was not significant. Migration among populations in the agricultural areas of the Arkansas delta region is apparently sufficient to homogenize most of the genetic divergence arising because of habitat or geographic isolation between populations in the region.