Population genetic structure of the common warthog (Phacochoerus africanus) in Uganda: evidence for a strong philopatry among warthogs and social structure breakdown in a disturbed population

Fine‐scale genetic structure of large mammals is rarely analysed. Yet it is potentially important in estimating gene flow between the now fragmented wildlife habitats and in predicting re‐colonization following local extinction events. In this study, we examined the extent to which warthog populations from five localities in Uganda are genetically structured using both mitochondrial control region sequence and microsatellite allele length variation. Four of the localities (Queen Elizabeth, Murchison Falls, Lake Mburo and Kidepo Valley) are national parks with relatively good wildlife protection practices and the other (Luwero), not a protected area, is characterized by a great deal of hunting. In the total sample, significant genetic differentiation was observed at both the mtDNA locus (F_ST = 0.68; P < 0.001) and the microsatellite loci (F_ST = 0.14; P < 0.001). Despite the relatively short geographical distances between populations, significant genetic differentiation was observed in all pair‐wise population comparisons at the two marker sets (mtDNA F_ST = 0.21–0.79, P < 0.001; microsatellite F_ST = 0.074–0.191, P < 0.001). Significant heterozygote deficiency was observed at most loci within protected areas while no significant deviation from Hardy–Weinberg expectation was observed in the unprotected Luwero population. We explain these results in terms of: (i) a strong philopatry among warthogs, (ii) a Wahlund effect resulting from the sampling regime and (iii) break down of social structure in the disturbed Luwero population.     

Evaluation of genetic diversity and population structure of west‐central Indian cattle breeds

Evaluations of genetic diversity in domestic livestock populations are necessary to implement region‐specific conservation measures. We determined the genetic diversity and evolutionary relationships among eight geographically and phenotypically diverse cattle breeds indigenous to west‐central India by genotyping these animals for 22 microsatellite loci. A total of 326 alleles were detected, and the expected heterozygosity ranged from 0.614 (Kenkatha) to 0.701 (Dangi). The mean number of alleles among the cattle breeds ranged from 7.182 (Khillar) to 9.409 (Gaolao). There were abundant genetic variations displayed within breeds, and the genetic differentiation was also high between the Indian cattle breeds, which displayed 15.9% of the total genetic differentiation among the different breeds. The genetic differentiation (pairwise F_ST) among the eight Indian breeds varied from 0.0126 for the Kankrej–Malvi pair to 0.2667 for Khillar–Kenkatha pair. The phylogeny, principal components analysis, and structure analysis further supported close grouping of Kankrej, Malvi, Nimari and Gir; Gaolao and Kenkatha, whereas Dangi and Khillar remained at distance from other breeds.     

ESTIMATES OF INTRAGAMETOPHYTIC SELFING AND INTERPOPULATIONAL GENE FLOW IN HOMOSPOROUS FERNS

Relatively little information is available on mating systems and interpopulational gene flow in species of homosporous pteridophytes. Because of the proximity of antheridia and archegonia on the same thallus, it has long been maintained that intragametophytic selling is the predominant mode of reproduction in natural populations of homosporous ferns and other homosporous plants. Furthermore, quantitative estimates of interpopulational gene flow via spore dispersal are lacking. In this paper, we examine five species of homosporous ferns (Botrychium virginianum, Polystichum munitum, P. imbricans, Blechnum spicant, and Dryopteris expansa) and present estimates of 1) rates of intragametophytic selling, 2) levels of interpopulational gene flow, and 3) interpopulational genetic differentiation (F_ST). Our data demonstrate that mating systems vary among species of ferns, just as they do among species of seed plants. The data also suggest that levels of interpopulational gene flow are generally high. The F_ST values indicate little genetic divergence among populations for all species except Dryopteris expansa, which exhibits significant levels of interpopulational genetic differentiation. Patterns of genetic diversity in the five species examined are related to the mating system and rate of interpopulational gene flow in each species. The F_ST values for all species except Botrychium virginianum are in close agreement with those predicted for an island model of population structure.     

Genetic diversity and population structure in multiple Chinese goat populations using a SNP panel

Information about genetic diversity and population structure among goat breeds is essential for genetic improvement, understanding of environmental adaptation as well as utilization and conservation of goat breeds. Here, we measured genetic diversity and population structure in multiple Chinese goat populations, namely, Nanjiang, Qinggeda, Arbas Cashmere, Jining Grey, Luoping Yellow and Guangfeng goats. A total of 193 individuals were genotyped for about 47 401 autosomal single nucleotide polymorphisms (SNPs). We found a high proportion of informative SNPs, ranging from 69.5% in the Luoping Yellow to 93.9% in the Jining Grey goat breeds with an average mean of 84.7%. Diversity, as measured by expected heterozygosity, ranged from 0.371 in Luoping Yellow to 0.405 in Jining Grey goat populations. The average estimated pair‐wise genetic differentiation (F_ST) among the populations was 8.6%, ranging from 0.2% to 16% and indicating low to moderate genetic differentiation. Principal component analysis, genetic structure and phylogenetic tree analysis revealed a clustering of six Chinese goat populations according to geographic distribution. The results from this study can contribute valuable genetic information and can properly assist with within‐breed diversity, which provides a good opportunity for sustainable utilization of and maintenance of genetic resource improvements in the Chinese goat populations.     

Strong genetic impoverishment from the centre of distribution in southern Europe to peripheral Baltic and isolated Scandinavian populations of the pearly heath butterfly

Aim Climatic changes and fluctuations in the past have strongly influenced the distribution of animal and plant species. Such fluctuations are also reflected in the patterns of genetic diversity on both local and global scales. The genetic pattern of the pearly heath butterfly, Coenonympha arcania, was used to evaluate the genetic differentiation of isolated (in north‐western Europe), peripheral (in north‐eastern Europe) and central (in southern Europe) populations in the context of post‐glacial distributional changes of the species. Location Europe (Sweden, Germany, the Baltic states, Italy, Slovenia, Hungary, Romania, Bulgaria). Thus, samples were collected from large parts of the species’ distribution representing the three categories mentioned above. Methods We analysed 18 loci of 569 individuals from 28 populations by allozyme electrophoresis. We used both individual‐based and population‐based analyses, including F‐statistics, various clustering methods and Markov chain Monte Carlo simulations. Results All loci, except Fum, were polymorphic. The mean F_ST for all samples was 0.18. The mean genetic distance among populations was 0.046. Two major genetic lineages were distinguished. Populations from the centre of the distributional range in southern Europe and the northern periphery of the distributional range differed significantly in their level of genetic variability. The central populations of south‐eastern Europe showed high levels of genetic diversity and no differentiation among populations. Main conclusions Most probably the two major genetic lineages evolved during glacial isolation in two disjunct Mediterranean refugia. The lack of genetic differentiation across south‐eastern Europe implies a continuous Würm ice age distribution in this area, thus supporting the functional existence of steppe forests throughout this region. The peripheral‐isolated populations in Sweden seem to have suffered from one or more severe bottlenecks, resulting in substantial genetic impoverishment. The peripheral‐connected eastern Baltic populations, on the other hand, are affected by post‐glacial and possibly recurrent gene flow from more central parts of the distribution.     

Genetic variability and individual assignment of Chinese indigenous sheep populations (Ovis aries) using microsatellites

The purpose of this study was to assess the genetic characteristics of six breeds of Chinese local sheep using 19 microsatellite loci and to effectively validate statistical methods for individual assignment based on informative microsatellites. All the six breeds deviated from Hardy–Weinberg equilibrium expectations, while the majority of markers complied. The polymorphism information content (PIC) of overall loci for the six populations ranged from 0.283 (SRCRSP5) to 0.852 (OarVH72). Tibetan sheep were the most diverse population with the highest mean allelic richness (6.895), while Ujmuqin (UQ) harboured the lowest allelic richness (6.000). The F‐statistics for the six populations were F_IS = ?0.172, F_IT = ?0.082 and F_ST = 0.077, respectively. Furthermore, the pair‐wise F_IS revealed a moderate genetic differentiation among populations (P < 0.01), indicating that all breeds can be considered genetically independent entities. The lowest genetic differentiation was between Tengchong (TC) and UQ (F_ST = 0.041), and the highest one was between TC and Fat‐tailed Han (F_ST = 0.111). In comparing the three statistical models, we note that the seven microsatellite loci (MAF65, OarJMP58, SRCRSP9, MCM140, OarAE129, BM8125 and SRCRSP5) commonly used for individual assignment will ensure a powerful detection of individual origin, with accuracy up to 91.87%, when the likelihood‐based method is used. Overall, these findings shed light onto the genetic characteristics of Chinese indigenous sheep and offer a set of microsatellite loci that is simple, economic and highly informative for individual assignment of Chinese sheep.     

Development of genetic diversity,differentiation and structure over 500 years in four ponderosa pine populations

Population history plays an important role in shaping contemporary levels of genetic variation and geographic structure. This is especially true in small, isolated range‐margin populations, where effects of inbreeding, genetic drift and gene flow may be more pronounced than in large continuous populations. Effects of landscape fragmentation and isolation distance may have implications for persistence of range‐margin populations if they are demographic sinks. We studied four small, disjunct populations of ponderosa pine over a 500‐year period. We coupled demographic data obtained through dendroecological methods with microsatellite data to discern how and when contemporary levels of allelic diversity, among and within‐population levels of differentiation, and geographic structure, arose. Alleles accumulated rapidly following initial colonization, demonstrating proportionally high levels of gene flow into the populations. At population sizes of approximately 100 individuals, allele accumulation saturated. Levels of genetic differentiation among populations (F_ST and Jost's D_est) and diversity within populations (F_IS) remained stable through time. There was no evidence of geographic genetic structure at any time in the populations' history. Proportionally, high gene flow in the early stages of population growth resulted in rapid accumulation of alleles and quickly created relatively homogenous genetic patterns among populations. Our study demonstrates that contemporary levels of genetic diversity were formed quickly and early in population development. How contemporary genetic diversity accumulates over time is a key facet of understanding population growth and development. This is especially relevant given the extent and speed at which species ranges are predicted to shift in the coming century.     

GENETIC STRUCTURE OF NATURAL POPULATIONS IN THE RED ALGAE GELIDIUM CANARIENSE (GELIDIALES,RHODOPHYTA) INVESTIGATED BY RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) MARKERS1

Random amplified polymorphic DNA (RAPD) marker variation was analyzed in female gametophytes in natural populations of Gelidium canariense (Grunow) Seoane‐Camba ex Haroun, Gil‐Rodríguez, Diaz de Castro et Prud'Homme van Reine from the Canary Islands to estimate the degree and distribution of genetic variability and differentiation. A total of 190 haploid individuals were analyzed with 60 polymorphic RAPDs bands which produced 190 distinct multilocus genotypes. A high level of polymorphism was detected in all populations analyzed. Within‐population gene diversity ranged from 0.156 to 0.264. The populations on the island of Gran Canaria showed higher genetic variation than the other populations analyzed. The partitioning of molecular variance by analysis of molecular variance showed that most genetic variation resides within populations (68.85%). These results suggest that sexual reproduction is the predominant mode of reproduction for G. canariense gametophytic populations, and the main determinant in reaching high levels of genetic diversity. The Neighbor‐Joining tree and FCA analysis displayed two subclusters that correspond to the populations from the western islands (Tenerife, La Palma, Gomera) and the eastern island (Gran Canaria). In addition, we have detected a significant relationship between F_ST/(1?F_ST) and geographical distance consistent with data on water circulation and age of islands. The results obtained agree with an isolation by distance model, with gene flow from eastern to the western islands, and a high level of genetic differentiation between populations (F_ST=0.311, P<0.001).     

Population structure and colonization of Bactrocera dorsalis (Diptera: Tephritidae) in China,inferred from mtDNA COI sequences

The oriental fruit fly, Bactrocera dorsalis, is a serious pest of fruits and vegetables in South‐east Asia, and, because of quarantine restrictions, impedes international trade and economic development in the region. Revealing genetic variation in oriental fruit fly populations will provide a better understanding of the colonization process and facilitate the quarantine and management of this species. The genetic structure in 15 populations of oriental fruit fly from southern China, Laos and Myanmar in South‐east Asia was examined with a 640‐bp sequence of the mitochondrial cytochrome oxidase subunit I (COI) gene. The highest levels of genetic diversity were found in Laos and Myanmar. Low to medium levels of genetic differentiation (F_ST ≤ 0.134) were observed among populations. Pooled populations from mainland China differed from those in Laos and Myanmar (F_ST = 0.024). Genetic structure across the region did not follow the isolation‐by‐distance model. The high genetic diversity observed in Laos and Myanmar supports the South‐east Asian origin of B. dorsalis. High genetic diversity and significant differentiation between some populations within mainland China indicate B. dorsalis populations have been established in the region for an extended period of time. High levels of genetic diversity observed among the five populations from Hainan Island and similarity between the Island and Chinese mainland populations indicate that B. dorsalis was introduced to Hainan from the mainland and has been on the island for many years. High genetic diversity in the recently established population in Shanghai (Pudong) suggests multiple introductions or a larger number of founders.     

Signatures of diversifying selection at EST‐SSR loci and association with climate in natural Eucalyptus populations

Understanding the environmental parameters that drive adaptation among populations is important in predicting how species may respond to global climatic changes and how gene pools might be managed to conserve adaptive genetic diversity. Here, we used Bayesian F_ST outlier tests and allele–climate association analyses to reveal two Eucalyptus EST‐SSR loci as strong candidates for diversifying selection in natural populations of a southwestern Australian forest tree, Eucalyptus gomphocephala (Myrtaceae). The Eucalyptus homolog of a CONSTANS‐like gene was an F_ST outlier, and allelic variation showed significant latitudinal clinal associations with annual and winter solar radiation, potential evaporation, summer precipitation and aridity. A second F_ST outlier locus, homologous to quinone oxidoreductase, was significantly associated with measures of temperature range, high summer temperature and summer solar radiation, with important implications for predicting the effect of temperature on natural populations in the context of climate change. We complemented these data with investigations into neutral population genetic structure and diversity throughout the species range. This study provides an investigation into selection signatures at gene‐homologous EST‐SSRs in natural Eucalyptus populations, and contributes to our understanding of the relationship between climate and adaptive genetic variation, informing the conservation of both putatively neutral and adaptive components of genetic diversity.     

PATTERNS OF REPRODUCTION,GENETIC DIVERSITY,AND GENETIC DIFFERENTIATION IN CALIFORNIA POPULATIONS OF THE GENICULATE CORALLINE ALGA LITHOTHRIX ASPERGILLUM (RHODOPHYTA)1

The reproductive composition and genetic diversity of populations of the red seaweed Lithothrix aspergillum Gray (O. Corallinales) were studied at three southern California sites (Shaw's Cove and Treasure Island, Laguna Beach; Indian Rock, Santa Catalina Island) and at a fourth site (Bodega Bay) located in northern California. Sexually reproducing populations were confined to southern California. Diploid individuals were numerically dominant over haploid (gametophytic) individuals at all sites. Intertidal and subtidal subpopulations from Shaw's Cove differed in their reproductive profiles. Most intertidal specimens found on emersed surfaces were densely branched, turf-forming, and bore tetrasporangial (68.6%), carposporangial (11.4%), or spermatangial (5.7%) conceptacles, reflecting a sexual life history; none produced asexual bispores. In contrast, 74.3% of the larger, loosely branched subtidal specimens bore bisporangial conceptacles indicative of asexual reproduction. Nearly 70% of the Indian Rock thalli showed no evidence of conceptacle formation. Only asexual, diploid bispore-producing thalli were obtained from the Bodega Bay site. Genetic diversity (mean number of alleles per locus, percent of polymorphic loci, and average expected heterozygosity) of diploid L. aspergillum populations varied with life-history characteristics and geographic location. A total of 30 alleles was inferred from zymograms of 16 loci examined by starch-gel electrophoresis; of these loci, 11 were polymorphic. The genetic diversity of sexual, diploid populations of L. aspergillum (alleles per locus [A/L] = 1.4-1.5; percent polymorphic loci [%P] = 37.5-50.0) was relatively high compared with other red seaweeds. Lowest diversity (A/L = 1.0; %P = 0.0) occurred in the exclusively asexual Bodega Bay population which consisted of genetic clones. All sexual L. aspergillum populations deviated significantly from Hardy-Wein-berg expectations due to lower than expected heterozygosity. Genetic differentiation (Wright's F_statistic [F_ST]; Nei's Genetic Distance [D]) among sexually reproducing southern California populations was low (F_ST= 0.030) on a local scale (ca. 5 km), suggesting high levels of gene flow, but high genetic differention (F_ST= 0.390 and 0.406) occurred among southern California populations separated by ca. 70 km. Very high genetic differentiation (F_ST= 0.583–0.683) was obtained between northern and southern California populations separated by 700–760 km. Our genetic and reproductive data suggest that the L. aspergillum population from Bodega Bay is sustained by perennation, vegetative propagation, or asexual reproduction by bispores and may represent an isolated remnant or a population established by a founder event.     

Low population genetic differentiation in the Orchidaceae: implications for the diversification of the family

A leading hypothesis for the immense diversity of the Orchidaceae is that skewed mating success and small, disjunct populations lead to strong genetic drift and switches between adaptive peaks. This mechanism is only possible under conditions of low gene flow that lead to high genetic differentiation among populations. We tested whether orchids typically exhibit high levels of population genetic differentiation by conducting a meta‐analysis to compare mean levels of population genetic differentiation (F_ST) between orchids and other diverse families and between rare and common orchids. Compared with other families, the Orchidaceae is typically characterized by relatively low genetic differentiation among populations (mean F_ST = 0.146) at allozyme loci. Rare terrestrial orchids showed higher population genetic differentiation than common orchids, although this value was still lower than the mean for most plant families. All lines of evidence suggest that orchids are typically characterized by low levels of population genetic differentiation, even in species with naturally disjunct populations. As such, we found no strong evidence that genetic drift in isolated populations has played a major role in the diversification of the Orchidaceae. Further research into the diversification of the family needs to unravel the relative roles of biotic and environmental selective pressures in the speciation of orchids.     

VOCAL DIALECTS AND THE STRUCTURE OF GEOGRAPHIC VARIATION IN MORPHOLOGICAL AND ALLOZYMIC CHARACTERS IN THE RUFOUS-COLLARED SPARROW,ZONOTRICHIA CAPENSIS

The geographical patterns of variation shown at 20 allozyme and non-enzymatic protein-coding loci, in 8 external, and in 12 skeletal morphological characters in the rufous-collared sparrow, Zonotrichia capensis, were analyzed in order to test the local (genetic) adaptation hypothesis regarding the origin and maintenance of vocal dialects in birds. Approximately 20 males were collected from each of four sites within each of six different dialect zones. There was significant variability in both external and skeletal morphology among all 24 sites and among dialect groups. Average Wright's corrected fixation coefficient (F_ST) was 0.118, indicating significant genetic differentiation among all sites, regardless of dialect. Hierarchical F statistics indicated that only 50% of among site variability was due to a dialect effect. Puna dialect sites were highly differentiated from all other sites with respect to both morphology (external and skeletal measures) and allozyme frequencies. Heterogeneity at the PGM-1 locus among puna scrub sites was the major cause of the high average F_ST across all sites, and within the puna scrub dialect. Average genetic differentiation among non-puna sites (F_ST = 0.018) was similar to differentiation among sites within each of the five non-puna dialect groups (mean F_ST = 0.0132 ± 0.0069). Hierarchical F statistics indicated that none of the among-site differentiation in this subset of samples was due to a dialect effect. These observations are not consistent with the local adaptation hypothesis. All significant genetic heterogeneity occurred among sites in mountainous habitats, and we suggest that topography and patchiness of habitat may have been major factors involved in population differentiation, rather than vocal dialects.     

Selection on life‐history traits and genetic population divergence in rotifers

A combination of founder effects and local adaptation – the Monopolization hypothesis – has been proposed to reconcile the strong population differentiation of zooplankton dwelling in ponds and lakes and their high dispersal abilities. The role genetic drift plays in genetic differentiation of zooplankton is well documented, but the impact of natural selection has received less attention. Here, we compare differentiation in neutral genetic markers (F_ST) and in quantitative traits (Q_ST) in six natural populations of the rotifer Brachionus plicatilis to assess the importance of natural selection in explaining genetic differentiation of life‐history traits. Five life‐history traits were measured in four temperature × salinity combinations in common‐garden experiments. Population differentiation for neutral genetic markers – 11 microsatellite loci – was very high (F_ST = 0.482). Differentiation in life‐history traits was higher in traits related to sexual reproduction than in those related to asexual reproduction. Q_ST values for diapausing egg production (a trait related to sexual reproduction) were higher than their corresponding F_ST in some pairs of populations. Our results indicate the importance of divergent natural selection in these populations and suggest local adaptation to the unpredictability of B. plicatilis habitats.     

GENETIC DIFFERENTIATION AMONG CHEWING LOUSE POPULATIONS (MALLOPHAGA: TRICHODECTIDAE) IN A POCKET GOPHER CONTACT ZONE (RODENTIA: GEOMYIDAE)

Genetic variation among populations of chewing lice (Geomydoecus actuosi) was examined in relation to chromosomal and electrophoretic variation among populations of their hosts (Thomomys bottae) at a contact zone. Louse demes were characterized by low levels of genetic heterozygosity (H? = 0.039) that may result from founder effects during primary infestation of hosts, compounded by seasonal reductions in louse population size. Louse populations sampled from different hosts showed high levels of genetic structuring both within and among host localities. Microgeographic differentiation of louse populations is high (mean F_ST = 0.092) suggesting that properties of this host–parasite system promote differentiation of louse populations living on different individual hosts. Among-population differentiation in lice (F_ST = 0.240) was similar to that measured among host populations (F_ST = 0.236), suggesting a close association between gene flow in pocket gophers and gene flow in their lice.     

Molecular diversity and genetic relationships among Sri Lankan pomegranate Punica granatum landraces assessed with inter simple sequence repeat (ISSR) regions

Pomegranate Punica granatum was first introduced to Sri Lanka, possibly through ancient trade routes, thousands of years ago. However, there is no information about the diversity of the pomegranate germplasm in the country, which is important both for breeding new varieties and for conservation efforts. We used inter‐simple sequence repeat (ISSR) regions to investigate the genetic diversity and population structure of pomegranate on the island of Sri Lanka. Hundred and twenty accessions representing seven populations from all pomegranate growing regions of the country were analyzed using 20 ISSR primers. A total of 107 loci were amplified with an average polymorphism information content of 0.3. While the average inter‐population genetic distance was 0.141, it was 0.149 between populations, indicating moderate genetic diversity both within and among populations. Analysis of molecular variance and Nei's genetic diversity revealed higher genetic variation within populations than among populations, and low genetic differentiation (G_ST) in pair‐wise comparison of populations also suggested limited population differentiation. A considerable level of among‐population gene flow (Nm) was indicated, irrespective of geographical structure and distances. The results of cluster analysis was also in agreement with above analysis and suggest human mediated gene flow and migration patterns. Cluster analysis revealed two main population clusters with several sub‐clusters. While these clusters did not show any correlation with geography, all red peeled accessions clustered into a small sub‐cluster. The results indicate that analysis of ISSR variability is sufficiently informative and powerful to assess the genetic diversity of P. granatum landraces in Sri Lanka.     

Contrasting patterns of morphological and neutral genetic divergence among geographically proximate populations of sockeye salmon Oncorhynchus nerka in Lake Aleknagik,Alaska

Levels of differentiation in morphological traits (age at maturity, body length at age, egg mass and body depth) and spawning time were examined in sockeye salmon Oncorhynchus nerka from three geographically proximate but physically distinct creeks in Lake Aleknagik, Alaska. Happy Creek fish had significantly greater values for most measured morphological traits, and Eagle Creek fish spawned significantly later than fish in the other creeks. Phenotypic differentiation between creeks, measured as P_ST, was then compared with microsatellite marker differentiation between creeks, measured as F_ST. No correlations were apparent between P_ST and F_ST values, and P_ST values were generally significantly larger than zero (P_ST= 0·0018–0·31) whereas F_ST values were not (F_ST=?0·0004 to 0·0016). The insignificant pair‐wise F_ST values between creek samples indicated that gene flow occurs between creeks, assuming the creek populations have reached migration–drift equilibrium. However, the strong homing behaviour of sockeye salmon precludes a scenario in which fish from the three creeks constitute a single population that segregates by body size. Rather, significant phenotypic differentiation suggests that strong divergent selection occurs on the phenotypic traits despite the homogenizing effects of gene flow.     

MICROSATELLITE MARKERS REVEAL POPULATION GENETIC STRUCTURE OF THE TOXIC DINOFLAGELLATE ALEXANDRIUM TAMARENSE (DINOPHYCEAE) IN JAPANESE COASTAL WATERS1

This is the first report to explore the fine‐scale diversity, population genetic structure, and biogeography of a typical planktonic microbe in Japanese and Korean coastal waters and also to try to detect the impact of natural and human‐assisted dispersals on the genetic structure and gene flow in a toxic dinoflagellate species. Here we present the genetic analysis of Alexandrium tamarense (Lebour) Balech populations from 10 sites along the Japanese and Korean coasts. We used nine microsatellite loci, which varied widely in number of alleles and gene diversity across populations. The analysis revealed that Nei's genetic distance correlated significantly with geographic distance in pair‐wise comparisons, and that there was genetic differentiation in about half of 45 pair‐wise populations. These results clearly indicate genetic isolation among populations according to geographic distance and restricted gene flow via natural dispersal through tidal currents among the populations. On the other hand, high P‐values in Fisher's combined test were detected in five pair‐wise populations, suggesting similar genetic structure and a close genetic relationship between the populations. These findings suggest that the genetic structure of Japanese A. tamarense populations has been disturbed, possibly by human‐assisted dispersal, which has resulted in gene flow between geographically separated populations.     

Comparison of genetic differentiation at marker loci and quantitative traits

The comparison of the degree of differentiation in neutral marker loci and genes coding quantitative traits with standardized and equivalent measures of genetic differentiation (F_ST and Q_ST, respectively) can provide insights into two important but seldom explored questions in evolutionary genetics: (i) what is the relative importance of random genetic drift and directional natural selection as causes of population differentiation in quantitative traits, and (ii) does the degree of divergence in neutral marker loci predict the degree of divergence in genes coding quantitative traits? Examination of data from 18 independent studies of plants and animals using both standard statistical and meta‐analytical methods revealed a number of interesting points. First, the degree of differentiation in quantitative traits (Q_ST) typically exceeds that observed in neutral marker genes (F_ST), suggesting a prominent role for natural selection in accounting for patterns of quantitative trait differentiation among contemporary populations. Second, the F_ST – Q_ST difference is more pronounced for allozyme markers and morphological traits, than for other kinds of molecular markers and life‐history traits. Third, very few studies reveal situations were Q_ST < F_ST, suggesting that selection pressures, and hence optimal phenotypes, in different populations of the same species are unlikely to be often similar. Fourth, there is a strong correlation between Q_ST and F_ST indices across the different studies for allozyme (r=0.81), microsatellite (r=0.87) and combined (r=0.75) marker data, suggesting that the degree of genetic differentiation in neutral marker loci is closely predictive of the degree of differentiation in loci coding quantitative traits. However, these interpretations are subject to a number of assumptions about the data and methods used to derive the estimates of population differentiation in the two sets of traits.     

Peripheral genetic structure of Helicoverpa zea indicates asymmetrical panmixia

Seasonal climatic shifts create peripheral habitats that alternate between habitable and uninhabitable for migratory species. Such dynamic peripheral habitats are potential sites where migratory species could evolve high genetic diversity resulting from convergence of immigrants from multiple regionally distant areas. Migrant populations of Helicoverpa zea (Boddie) captured during two different seasons were assessed for genetic structure using microsatellite markers and for host plant type using stable carbon isotope analysis. Individuals (N = 568) were genotyped and divided into 13 putative populations based on collection site and time. Fixation indices (F‐statistics), analysis of molecular variance (AMOVA), and discriminant analysis of principal components (DAPC) were used to examine within and among population genetic variation. Mean number of alleles per locus was 10.25 (± 3.2 SD), and allelic richness ranged from 2.38 to 5.13 (± 3.2 SD). The observed and expected heterozygosity ranged from 0.07 to 0.48 and 0.08 to 0.62, respectively. Low F_ST (0.01 to 0.02) and high F_IS (0.08 to 0.33) values suggest captured migrants originated from breeding populations with different allele frequencies. We postulate that high genetic diversity within migrant populations and low genetic differentiation among migrant populations of H. zea are the result of asymmetrical immigration due to the high dispersal and reproductive behavior of H. zea, which may hinder the adaptation and establishment of H. zea to peripheral habitat. These findings highlight the importance of assessing peripheral population structure in relation to ecological and evolutionary dynamics of this and other highly reproductive and dispersive species.