Indirect Estimates Of Gene Flow Research Articles

GENETICS AND DEMOGRAPHY OF KELP GULLS IN PATAGONIA

The Kelp Gull (Larus dominicanus), a common seabird in coastal Patagonia, has recently increased in overall abundance and distribution, creating some concerns for the protection and conservation of other native, threatened species. We combined genetic and demographic data of four large Kelp Gull colonies distributed along 1800 km of the northern Patagonian coast of Argentina to further understand patterns of population growth and migration of the species. DNA analysis of variable intron sequences of two separate genes (myelin proteolipid protein, β-fibrinogen) revealed similar intra-colony levels of DNA sequence diversity. Pairwise FST comparisons revealed significant differentiation of the northernmost colony, Islote La Pastosa, from the two southern colonies, Punta Tombo and Isla Vernaci Sudoeste (p < 0.05). Indirect estimates of gene flow suggest significant mixing among colonies (Nm > 6). Demographic estimates revealed that Islote La Pastosa showed an increase in the number of breeding individuals over time (λ = 1.075), representing an area of potential population expansion. This is consistent with previous studies that have suggested that the demographic connectivity among Kelp Gull colonies in Patagonia may follow a source-sink dynamics, where growth rates of growing colonies are fuelled by the immigration of individuals from nearby colonies. The observed pattern also reflects the overall expansion of the species in the Patagonian region. This study suggests that proper management strategies for the Kelp Gull should take into account the genetic and demographic dynamics of this species.

Using parentage analysis to estimate rates of straying and homing in Chinook salmon (Oncorhynchus tshawytscha).

We used parentage analysis based on microsatellite genotypes to measure rates of homing and straying of Chinook salmon (Oncorhynchus tshawytscha) among five major spawning tributaries within the Wenatchee River, Washington. On the basis of analysis of 2248 natural-origin and 11594 hatchery-origin fish, we estimated that the rate of homing to natal tributaries by natural-origin fish ranged from 0% to 99% depending on the tributary. Hatchery-origin fish released in one of the five tributaries homed to that tributary at a far lower rate than the natural-origin fish (71% compared to 96%). For hatchery-released fish, stray rates based on parentage analysis were consistent with rates estimated using physical tag recoveries. Stray rates among major spawning tributaries were generally higher than stray rates of tagged fish to areas outside of the Wenatchee River watershed. Within the Wenatchee watershed, rates of straying by natural-origin fish were significantly affected by spawning tributary and by parental origin: progeny of naturally spawning hatchery-produced fish strayed at significantly higher rates than progeny whose parents were themselves of natural origin. Notably, none of the 170 offspring that were products of mating by two natural-origin fish strayed from their natal tributary. Indirect estimates of gene flow based on FST statistics were correlated with but higher than the estimates from the parentage data. Tributary-specific estimates of effective population size were also correlated with the number of spawners in each tributary.

Coevolution between Contracaecum (Nematoda, Anisakidae) and Austrolebias (Cyprinodontiformes, Rivulidae) host-parasite complex from SW Atlantic coastal basins.

In recent years, molecular studies in host-parasite interactions in terms of coevolution have become important. Larvae (L3) of two species of Contracaecum were found parasitizing species of Rivulidae in the Atlantic coastal basins from Uruguay. The aim of this study is to determine the patterns of differentiation of this host-parasite complex in order to clarify possible coevolutionary events in such interaction throughout phylogeographic approach using both nuclear and mitochondrial molecular markers (internal transcribed spacers (ITS) and cytochrome oxidase subunit 1 (cox-1)). Based on both markers, intraspecific variation in Contracaecum species was lower than 2 %, while interspecific variation was greater than 10 %. Both species of Contracaecum constitute monophyletic groups. Contracaecum resulted in a paraphyletic genus when incorporating other Contracaecum species and closely related nematode sequences from GenBank. ITS regions showed that Contracaecum sp. 1 is more closely related to other species of the same genus than with their counterparts from Atlantic coastal basins in Uruguay. Haplotype network for both markers corroborate the existence of two distinct taxa. While ITS pairwise FST comparisons and the indirect estimate of gene flow confirm the existence of two distinct Contracaecum species, mitochondrial gene detected low levels of migrants between some of the populations from both species. Our results suggest that coevolution in this host-parasite complex species is plausible. Parasite cladogenetic events occur almost simultaneously with the separation of the hypothetical ancestors of each species complex of Austrolebias during Pliocene. Additionally, the two lineages of Contracaecum colonize differently the species within each of the Austrolebias complexes.

Genetic diversity of Oreopanax xalapensis (Araliaceae) in the Highlands of Chiapas

The genetic diversity of a species determines its ability to respond to environmental changes, thus their knowledge can be important for designing strategies for forest restoration. This study analyzes the diversity and genetic structure of five populations of Oreopanax xalapensis in the Highlands of Chiapas. This species is being used for restoration of the montane cloud forests into the region, but unknown levels of genetic variation in natural populations where seeds are obtained. We used 18 enzymatic loci screened by electrophoresis in cellulose acetate. Genotype frequencies were used to calculate the allelic frequency and obtained the following estimates of genetic diversity: proportion of polymorphism, observed (HO) and expected heterocigosity (HE); and average number of alleles. The FST statistic was used to estimate the level of genetic differentiation among subpopulations. The average number of alleles per locus was between 1.8 and 2.0; the proportion of loci polymorphic ranged from 66 to 100%. Average HO was 0.362, and HE = 0.379. The degree of structure was significantly high (FST = 0.214), the indirect estimate of gene flow among subpopulations was Nm = 5.0 individuals per generation. Subpopulations of O. xalapensis are genetically diverse and are structured; this implies that for an effective restoration practice should be considered the collection of seeds of all populations for a better representation of genetic diversity.

Conservation Genetics of the Endemic Mexican Heliconia uxpanapensis in the Los Tuxtlas Tropical Rain Forest

ABSTRACT Heliconia uxpanapensis (Heliconiaceae) is an outcrossing endemic herb that grows within continuous and fragmented areas of the tropical rain forest of southeastVeracru ´z (Mexico). The genetic diversity, population differentiation, and genetic structure of seven populations of the studied species were assessed using inter-simplesequence repeat) markers. Population differentiation was moderately high (F ST range: 0.18–0.22) and indirect estimates of gene flow were rather low(Nm=0.65–0.83). Analysis of molecular variance indicated that the populations explained 22.2 percent of the variation, while individuals within the populationsaccounted for 77.8 percent. The similar and high level of genetic diversity found within populations of the continuous and fragmented forest suggests that H. uxp-anapensis has not suffered yet the expected negative effect of fragmentation. Genetic structure analyses indicated the presence of fewer genetic clusters (K=4) thanpopulations (N=7). Three of the four fragmented forest populations were assigned each to one of the clusters found within the continuous forest, suggesting theabsence of a negative fragmentation effect on the amount and distribution of genetic variation. Given the significant genetic structure combined with high geneticdiversity and low levels of gene flow, theoretical simulations indicated that H. uxpanapensis might be highly susceptible to changes in the mating system, whichpromotes inbreeding within fragmented populations. Thus, future conservation efforts in this species should be directed to ensure that levels of gene flow amongpopulations are sufficient to prevent an increment in the magnitude of inbreeding within fragments.Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp.Key words: fragmentation; F-statistics; ISSR.

Population genetics and breeding system ofTupistra pingbianensis(Liliaceae), a naturally rare plant endemic to SW China

Abstract The levels and partitioning of genetic diversity and inbreeding depression were investigated inTupistra pingbianensis, a narrow endemic of southeast Yunnan, China, characterized by a naturally fragmented distribution due to extreme specialization on a rare habitat type. Here genetic diversity and patterns of genetic variation within and among 11 populations were analyzed using amplified fragment length polymorphism markers with 97 individuals across its whole geographical range. High levels of genetic variation were revealed both at the species level (P99= 96.012%;Ht= 0.302) and at the population level (P99= 51.41%;Hs= 0.224). Strong genetic differentiation among populations was also detected (FST= 0.2961; θII= 0.281), which corresponded to results reported for typical animal‐pollinated, mixed selfing, and outcrossing plant species. This result was consistent with mating patterns detected by our pollination experiments. The indirect estimate of gene flow based on θIIwas low (Nm= 0.64). Special habitat and its life history traits might play an important role in shaping the genetic diversity and the genetic structure of this species. A pollination experiment also failed to detect significant inbreeding depression upon F1fruit set, seed weight, and germinate rate fitness‐traits. As a naturally rare species,T. pingbianensisis not seriously genetically impoverished and likely to have adapted to tolerating a high level of inbreeding early in its history, we propose this species need only periodic monitoring to ensure their continued persistence, but not intervention to remain viable.

A landscape genetics approach for quantifying the relative influence of historic and contemporary habitat heterogeneity on the genetic connectivity of a rainforest bird

Landscape genetics is an important framework for investigating the influence of spatial pattern on ecological process. Nevertheless, the standard analytic frameworks in landscape genetics have difficulty evaluating hypotheses about spatial processes in dynamic landscapes. We use a predictive hypothesis-driven approach to quantify the relative contribution of historic and contemporary processes to genetic connectivity. By confronting genetic data with models of historic and contemporary landscapes, we identify dispersal processes operating in naturally heterogeneous and human-altered systems. We demonstrate the approach using a case study of microsatellite polymorphism and indirect estimates of gene flow for a rainforest bird, the logrunner (Orthonyx temminckii). Of particular interest was how much information in the genetic data was attributable to processes occurring in the reconstructed historic landscape and contemporary human-modified landscape. A linear mixed model was used to estimate appropriate sampling variance from nonindependent data and information-theoretic model selection provided strength of evidence for alternative hypotheses. The contemporary landscape explained slightly more information in the genetic differentiation data than the historic landscape, and there was considerable evidence for a temporal shift in dispersal pattern. In contrast, migration rates estimated from genealogical information were primarily influenced by contemporary landscape change. We discovered that landscape heterogeneity facilitated gene flow before European settlement, but contemporary deforestation is rapidly becoming the most important barrier to logrunner dispersal.

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 HE = 0.690), weak genetic structuring among 13 remnant populations (FST = 0.047) and a consistent deficit of heterozygotes from Hardy–Weinberg expectation were found across all populations (mean FIS = 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 FST; 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.

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 (ϕST = 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.

Chloroplast DNA Phylogeography of the Chinese Endemic Alpine QuillwortIsoetes hypsophilaHand.‐Mazz. (Isoetaceae)

We examined chloroplast trnL intron sequence variation within Isoetes hypsophila, a Chinese endemic alpine quillwort species. Sequence data were obtained from 46 individuals in six populations throughout the natural distribution of the species. Sequences appeared to have neutral evolution (Tajima’s criterion $$D=-1.66453$$, $$0.1> P> 0.05$$; Fu and Li’s test $$D^{*}=-1.92897$$, $$0.1> P> 0.05$$; $$F^{*}=-2.17823$$, $$0.1> P> 0.05$$). Eleven haplotypes were identified in I. hypsophila. A relatively high level of haplotype diversity ($$h=0.817$$) and a low level of nucleotide diversity ($$\pi =0.0045$$) were detected in I. hypsophila. Indirect estimates of gene flow based on cpDNA variation revealed significant genetic differentiation between the ZD1 population in Yunnan Province and the populations from Sichuan Province. High genetic differentiation between Yunnan and Sichuan populations was consistently indicated by both hierarchical analyses of molecular variance (AMOVA; $$G_{\mathrm{ST}\,}=0.5011$$) and the structure of a neighbor‐joining tree. From nested clade analysis, restricted gene flow with isolation by distance was inferred to be responsible for the current spatial genetic structure of I. hypsophila.

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

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

낙동강에 분포하는 동자개 집단의 유전적 다양성과 집단구조

전분 젤 전기영동을 사용하여 한국내 분포하는 동자개 여섯 집단에서 유전적 다양성과 집단구조를 평가하였다. 14개 대립유전자좌위에서 9좌위가 다형현상을 나타내었다(64.3%). 종수준과 집단수준에서 유전적 다양성은 각각 0.286과 0.277이였다. Wright의 고정지수에서 Hardy-Weinberg 평형에 비해 전반적인 이형접합체 결핍이 나타났다. 이 결핍은 집단내 유효한 개체수의 부족을 시사한다. 집단간 유전적 분화 정도는 0.064로 대부분의 유전적 변이(93.6%)가 집단내에 있음을 의미한다. 간접적으로 평가된 집단간 이주하는 개체수는 3.67로 나타났다. 제한된 유전자 유동과 유효집단의 감소는 유전적 부동을 유발하고, 주기적인 포획으로 인한 개체수의 감소는 유전자 상실로 이어지고 있다. 대부분의 집단이 겨울철 가뭄과 여름철 홍수로 심한 병목을 겪고 있었다. Enzyme electrophoresis was used to estimate genetic diversity and population genetic structure of Pseudobagrus fulvidraco in Korea. Nine of the 14 loci (64.3%) showed detectable polymorphism. Genetic diversity at the population and species levels were 0.286 and 0.277, respectively. Analysis of fixation indices, calculated for all polymorphic loci in each population, showed a substantial deficit of hetero-zygotes relative to Hardy-Weinberg expectations. This deficit is expected that it is due to a limited effective number of individuals per population. The average <TEX>$G_{ST}$</TEX> for polymorphic loci was 0.064, indicating that most (93.6%) of the genetic diversity occurred within populations. The indirect estimate of gene flow based on mean <TEX>$G_{ST}$</TEX> was 3.67. Given limited gene flow is expected to diverge genetically due to drift and reduced populations. Most populations in our study experience annual, severe demo-graphic bottlenecks due to drought and floods.

Genetic diversity and the reproductive system in related species of antirrhinum.

Seven related species of Antirrhinum (A. siculum, A. majus, A. latifolium, A. linkianum, A. litigiosum, A. cirrhigherum and A. tortuosum) were studied in order to compare levels of genetic variation and its partitioning in them, and to check relationships between genetic patterns and the reproductive system. Eight hundred and fifty-one plants were screened for variability at 13 allozyme loci by means of horizontal starch gel electrophoresis. Parameters of genetic diversity and its partitioning, the inbreeding coefficient as well as an indirect estimate of gene flow based on the equation: Nm = (1 - G(ST))/4G(ST), were calculated. Genetic variability in A. siculum was found to be the lowest known in the genus. Mean values of F(IT) and F(IS) were mostly positive and not significantly different from zero. Population differentiation (F(ST)) ranged between 6.1 in A. tortuosum and 17.6 in A. linkianum. The inbreeding coefficient within populations ranged between F(IS) = -0.5 in A. tortuosum and F(IS) = 1 in A. siculum. Estimates of gene flow ranged between Nm = 15 in A. majus (considered as very high) to Nm = 0.42 in A. siculum (considered as low). Correlation was found between levels of diversity and differentiation on one hand, and the reproductive system of the studied taxa on the other. Striking differences among species in the inbreeding coefficient (F(IS)) show different reproductive systems, which mostly support previous reports. Strategies for the conservation of A. siculum are recommended, such as preservation of natural populations as well as ex situ preservation of seeds from different populations.

Direct and indirect estimates of gene flow among wild and managed populations of Polaskia chichipe, an endemic columnar cactus in Central Mexico

Microsatellite markers were used to obtain direct and indirect estimates of gene flow in populations of Polaskia chichipe under different management regimes, in order to understand the genetic consequences of gene flow in the evolutionary process of domestication. P. chichipe is a columnar cactus endemic to the Tehuacan Valley, Central Mexico, and has come under domestication for its edible fruit. Morphological, phenological, physiological, and reproductive differences, apparently attributable to artificial selection, exist between wild and managed populations, which grow sympatrically. However, strong gene flow may counteract the effects of this selection. In this study, we used paternity analysis to demonstrate that although most of the pollinations occur among individuals within the same population at distances < 40 m, pollen flow from other populations is considerable (27 +/- 5%). Heterogeneity in pollen clouds sampled by mother plants (FST = 0.12) indicated nonrandom mating, which is probably due to temporal heterogeneity in pollen movement. Spatial structure on local and regional scales is consistent with an isolation-by-distance model. The similarity of indirect, direct and demographic estimates of neighbourhood size (74-250 individuals) suggests that this genetic structure is representative of an equilibrium state. These results suggest that traditional management practices have conserved the genetic resources of this species in situ, but also that gene flow is counteracting the effect of domestication to some degree. We discuss our results in the general context of genetic exchange between cultivated and wild populations during the domestication process.

Gene flow among established Puerto Rican populations of the exotic tree species, Albizia lebbeck

We estimate gene flow and patterns of genetic diversity in Albizia lebbeck, an invasive leguminous tree in the dry forest of southwestern Puerto Rico. Genetic diversity estimates calculated for 10 populations of 24 trees each indicated that these populations may have been formed from multiple introductions. The presence of unique genotypes in the northernmost populations suggests that novel genotypes are still immigrating into the area. This combination of individuals from disparate locations led to high estimates of genetic diversity (He = 0.266, P = 0.67). Indirect estimates of gene flow indicate that only 0.69 migrants per generation move between populations, suggesting that genetic diversity within populations should decrease due to genetic drift. Since migration-drift equilibrium was not found, however, this estimate needs to be viewed with caution. The regular production of pods in this outcrossing species (tm = 0.979) indicates that sufficient outcross pollen is received to insure successful reproduction. Direct estimates of gene flow indicate that between 44 and 100% of pollen received by trees in four small stands of trees (n < 11) was foreign. The role of gene flow in facilitating the spread of this invasive plant species is discussed.

Genetic variation in the endemic plant Cycas debaoensis on the basis of ISSR analysis

Cycas debaoensis Y.C.Zhong et C.J.Chen is a rare and endangered cycad species that is endemic to South China. It has divided pinnae. Genetic variation in the species was investigated by using an intersimple sequence repeat (ISSR) marker. The species exhibits a moderate level of genetic diversity (at population level P = 34.7%, H = 0.141, I = 0.204; at species level P = 57.4%, H = 0.215, I = 0.315) and a high level of genetic differentiation among populations (Gst = 0.342). Thus, the indirect estimate of gene flow on the basis of Gst was low (Nm = 0.481). The narrow colonisation area and island pattern of distribution, combined with limited gene flow among populations and genetic drift, may play an important role in shaping the genetic structure of C. debaoensis. On the basis of these findings, strategies are suggested for the conservation and management of the species.

Low levels of allozyme variability in the threatened species Antirrhinum subbaeticum and A. pertegasii (Scrophulariaceae): implications for conservation of the species.

This study was designed to compare levels of genetic variation and its partitioning in three related species of Antirrhinum, A. subbaeticum, A. pertegasii and A. pulverulentum, and to check the hypothesis that species with small total population size have lower levels of genetic variability than those with bigger ones. This information should contribute to the development of conservation strategies of rare endemic species of Antirrhinum. One hundred and seventy-seven plants were screened for variability at 14 allozyme loci by means of horizontal starch gel. Parameters of genetic diversity, and its partitioning, were calculated. An indirect estimate of gene flow was based on the equation: Nm = (1 - GST)/4GST. Genetic variabilities in A. subbaeticum and A. pertegasii were found to be the lowest known for the genus, the within-population genetic diversity being correlated with population size in both species. The distribution of genetic diversity is strikingly different among species, with 85 % of the total variation distributed among populations in A. subbaeticum, 6 % in A. pertegasii and 23 % in A. pulverulentum. Estimated levels of gene flow were negligible for A. subbaeticum (0.04), high for A. pertegasii (3.92), and substantial for A. pulverulentum (0.83). Genetic and geographic distances were negatively correlated in A. pertegasii, whereas no significant correlation was found in the other two species. Levels of total genetic diversity agree with the hypothesis that species with small total population size have lower levels of genetic variability than those with bigger ones. Strategies for the conservation of the species are recommended, such as preservation of natural populations and avoidance of possible causes of threat, as well as ex situ preservation of seeds, reinforcement of small populations of A. subbaeticum with plants or seeds from the same population, and avoidance of translocations among populations.

Gene Flow in European Beech (Fagus sylvatica L.)

Three relatively isolated stands were used to study gene flow in European beech (Fagus sylvatica L.) in Northern Germany. Nine allozyme loci (Got-B, Idh-A, Lap-A, Mdh-B, Mdh-C, Mnr-A, 6-pgdh-A, Pgi-B and Pgm-A) were utilized for multilocus-genotyping adult trees and seeds. Expected heterozygosity (He) ranged from 0.325 to 0.351 for the three stands. F(ST) revealed that there was small differentiation among stands (mean F(ST) = 0.013). The indirect estimates of gene flow (Nm) based on the mean F(ST) were high and the average Nm was 19.14. External gene flow by pollen ranged from 0.7 to 1.2% inferred from new alleles in seed samples. Moreover, paternity analysis was used to assess effective pollen dispersal by inferring paternity of offspring. The weighted mean distances of pollen dispersal for these three stands were 36.8 and 37.1 m based on simple exclusion procedure and most-likely method, respectively. Two of the trees in one stand had rare allozyme alleles (Lap-A1 and Idh-A4, respectively), which were used to directly measure pollen movement away from those trees. The frequency of the rare Lap and Idh alleles in seeds declines as the distance from the source tree increases. The weighted mean distance of pollen dispersal with rare allele Lap-A1 or Idh-A4 was 26.3 m.

Patterns of variation within and between Greek populations of Ceratitis capitata suggest extensive gene flow and latitudinal clines.

Four natural Greek populations of Mediterranean fruit fly, Ceratitis capitata (Wiedemann), was studied for genetic variability at 25 enzyme loci. The comparison of polymorphism within and between populations shows two loci with high between-population heterozygosity (HT) and very high fixation index (F(ST)) values, suggesting the presence of balancing selection. The gradual decline of common allele frequency of the polymorphic loci tested indicated that latitudinal clines are present in Greece. Indirect estimates of gene flow based both on Wright's method (Nm*) and on the Slatkin's method (Nm*), which depends on the frequencies of rare alleles found in only one population, revealed a substantial amount of gene flow (Nm = 3.493 and Nm* = 3.197). These estimates of gene flow may well explain why the "introduced" Greek populations of C. capitata, in spite of their low genetic variability, display the same polymorphic loci. Gene flow in combination with natural selection and genetic drift may have played an important role to genetic differentiation in this species in Greece.

Patterns of Variation Within and Between Greek Populations of &lt;I&gt;Ceratitis capitata&lt;/I&gt; Suggest Extensive Gene Flow and Latitudinal Clines

Four natural Greek populations of Mediterranean fruit fly, Ceratitis capitata (Wiedemann), was studied for genetic variability at 25 enzyme loci. The comparison of polymorphism within and between populations shows two loci with high between-population heterozygosity (HT) and very high fixation index (F(ST)) values, suggesting the presence of balancing selection. The gradual decline of common allele frequency of the polymorphic loci tested indicated that latitudinal clines are present in Greece. Indirect estimates of gene flow based both on Wright's method (Nm*) and on the Slatkin's method (Nm*), which depends on the frequencies of rare alleles found in only one population, revealed a substantial amount of gene flow (Nm = 3.493 and Nm* = 3.197). These estimates of gene flow may well explain why the "introduced" Greek populations of C. capitata, in spite of their low genetic variability, display the same polymorphic loci. Gene flow in combination with natural selection and genetic drift may have played an important role to genetic differentiation in this species in Greece.