Genetic structure of the genera Psorophora (Diptera: Culicidae) in Columbian and North American populations using isoenzymes and ITS2 sequences

Two, a priori, Psorophora columbiae and one, a priori, Ps. toltecum populations from Colombia were studied by means of eleven isoenzyme loci. The levels of genetic diversity, Hardy-Weinberg equilibrium, gene flow estimates, isolation by distance and genetic relationships among these three populations were studied and the results were as follows: 1. The gene diversity levels were high as well as very similar among the three populations indicating no differences between them. 2. Within each population and from a hierarchical standpoint several loci were not in Hardy-Weinberg equilibrium simultaneously by excess and defect of heterozygous. This could reflect that several natural selection forces are acting upon these mosquito populations. 3. The gene flow estimate for these populations showed the existence of this event between them. This agrees quite well with the fact that the three populations really belong to a single species. In addition, maximum parsimony analyses with 16 isoenzyme for several individuals from four Colombian and two United States Psorophora populations showed that effectively only one species was present in the Colombian area surveyed, and that this species is Ps. columbiae, which hardly contrast with that previously suggested by other authors.     

Comparative Genetic Structure between Tropical Colombian and North American Drosophila pseudoobscura Populations1

Since the discovery of Drosophila pseudoobscura in the tropical highlands of the Colombian Andes during the 1960s, this population has been studied by many evolutionary biologists because of its geographical isolation from the main North American range of this species. We used five highly variable microsatellite loci (DPSX001, DPS2001, DPS3001, DPS3002, and DPS4001) to analyze the genetic structure of three Colombian populations and the genetic relationships with four North American populations. We found that the average heterozygosity was consistent among the three tropical Colombian populations (H = 0.665–0.675), but they had less variability than their North American counterparts. Nonetheless, the genie diversity found in the Colombian populations was higher than that found previously using other genetic markers. The average genie heterogeneity estimate among the Colombian populations (Rjr = 0.042), although statistically significant, was substantially lower than that found among the North American populations (RsT ⁼ 0.088). We identified alleles in the Colombian populations not reported in North American populations, suggesting further divergence between the populations. We estimated that the populations on the two continents diverged ca 80,000 years ago, consistent with independent sequence analyses of these populations but contrary to some suggestions in the literature. Finally, we estimated an average effective population size of the Colombian populations to be on the order of 100,000.     

POPULATION GENETIC STRUCTURE IN DIPLOID BLUEBERRY VACCINIUM SECTION CYANOCOCCUS (ERICACEAE)

Vaccinium section Cyanococcus comprises diploid, tetraploid, and hexaploid species (x = 12) all of which are highly self-sterile. In order to assess the distribution of genetic variation within and among the diploids, population genetic analyses of allozyme data were conducted on three species: V. elliottii, V. myrtilloides, and V. tenellum. Populations were located throughout the range of these taxa in eastern North America. Data were collected at 20 loci, 12 of which are mendelian based on formal genetic analyses. Consistent with expectations for out-crossing taxa, these species exhibited high levels of variation within populations. Eighteen loci were polymorphic with the number and frequency of alleles varying among taxa. Mean values for the number of alleles per polymorphic locus, proportion of polymorphic loci, and expected heterozygosity were 2.8, 48.2, and 0.148, respectively. High infraspecific genetic identities exceeding 0.9 indicated that these taxa are homogeneous. All populations were in Hardy-Weinberg equilibrium with slight heterozygote excess observed in V. myrtilloides and V. tenellum. Although total genetic diversity was lower than that observed for other predominantly out-crossing species, it was apportioned similarly. The majority could be attributed to differences among individuals within populations. Conspecific populations were relatively undifferentiated with genetic differentiation similar to other self-incompatible species.     

Genetic diversity and morphological differentiation in Liatris helleri (Asteraceae), a threatened plant species

Liatris helleri (Asteraceae) is an insect-pollinated herbaceous perennial endemic to several high-elevation sites in the Blue Ridge Mountains of North Carolina. Allozymes were used to describe the genetic diversity and population structure in nine populations of this rare, federally listed species. Differences in leaf morphology were also examined for greenhouse-grown plants representing several populations. The proportion of the total genetic diversity found among populations, as indicated by the allozyme data, was 16%. Higher levels of population differentiation were found for differences in leaf shape; population of origin accounted for 37% of the variation in maximum leaf width, while families within populations accounted for 7%. In contrast to many endemic species, L. helleri maintains fairly high levels of genetic diversity. For the species, the percent polymorphic loci was 87.5, the average number of alleles at variable loci was 3.00 and the gene diversity was 0.276. Mean population values were percent polymorphic loci =58.4, mean number of alleles per polymorphic locus =2.59 and gene diversity =0.219. The estimated gene flow was low (Nm=0.85–1.32) and a relatively high correlation (r=0.55; p<0.005) was found between linear geographic and genetic distance. This suggests that the populations are partially isolated by distance, despite the limited range (<60 km) of the species. We recommend that population distinetiveness be maintained in restoration efforts.     

Development of polymorphic microsatellite loci in the hermaphroditic freshwater snails Drepanotrema surinamense and Drepanotrema depressissimum

We characterized new variable microsatellites in two congeneric species of hermaphroditic freshwater snails (Drepanotrema depressissimum and D. surinamense), as well as conditions for multiplexing and simultaneously genotyping sets of loci. D. depressissimum had high mean gene diversity (> 0.8) and large number of alleles (= 10.9) per population. Most loci and populations were at Hardy–Weinberg equilibrium. The F_ST estimates were low among lesser Antilles populations and larger with a Venezuelan population. Far less diversity was found in D. surinamense with mean number of alleles and gene diversity per population of 2.8 and 0.34, respectively. Very few heterozygous individuals were observed. The most likely explanation is a high selfing rate (> 0.825) in this species. Unsurprisingly, the F_ST estimates among populations were much higher than in D. depressissimum. Cross‐species amplification in three congeneric species was on the whole unsuccessful.     

Hardy-Weinberg equilibria in random mating populations

The structure of multiloci random mating populations is examined. Sufficient conditions for the existence of stable local Hardy-Weinberg equilibria for n loci and an arbitrary number of alleles per locus, are then derived for specified situations under the assumption of multiplicative gene action between loci. It is shown that a stable Hardy-Weinberg equilibrium can not be a local maximum of the mean fitness function with multiplicative gene action between loci. The stability of Hardy-Weinberg type border points and the condition for the increase of newly introduced genes are topics on which some n-loci results are also obtained for an arbitrary number of alleles per locus in systems that allow Hardy-Weinberg equilibria.     

Microsatellite analysis of the spectacled bear (Tremarctos ornatus) across its range distribution

DNA samples of the spectacled bear (Tremarctos ornatus) from five Andean countries, Venezuela, Colombia, Ecuador, Peru and Bolivia, were analyzed for nine microsatellite loci. Seven of them were polymorphic, which led us to investigate several population-genetic parameters. Private alleles and significant differences in gene frequencies were found among the populations studied, which demonstrated the extent of genetic differentiation among the spectacled bear populations. The levels of gene diversity measured with these microsatellites were rather modest in this species. Hardy-Weinberg disequilibrium was especially found for the overall and the Ecuadorian samples, and might be due to the Wahl-und effect or consanguinity. Significant genetic heterogeneity was mainly observed among the Colombian and the Ecuadorian populations. Markov chain Monte Carlo simulations clearly showed that two different gene pools were present, one present in the Venezuelan-Colombian bears and other in the Ecuadorian ones.     

Patterns of allozyme variation and clonal diversity in Carex lasiocarpa and C. pellita (Cyperaceae)

We compared genetic variability and clonal diversity in the closely related sedges Carex lasiocarpa and C. pellita using allozyme markers at 12 loci. Both species produce spreading rhizomes, occur in open habitats, and can form large clones; C. lasiocarpa primarily along lakeshores, or in bogs, fens, or marshes, and C. pellita more commonly along riverbanks and ditches or in wet meadows. Polymorphism was high in both species, similar to that of other rhizomatous Carex and to other species with comparable growth forms and life histories. Total gene diversity was higher for C. lasiocarpa (H_T = 0.266) than for C. pellita (H_T = 0.248), but the coefficient of differentiation among populations was lower. Rare alleles usually occurred as heterozygotes rather than homozygotes, and significant deviations from Hardy-Weinberg equilibrium were found at few loci, suggesting that both species are predominantly outcrossing. Mean clone size, diversity, and evenness were not significantly different between the two species, although populations varied from monoclonal to those where nearly every sampled shoot belonged to a different clone. No significant differences in genetic variation or clone size of C. pellita were found when comparisons were made between groups based on climate (warmer vs. cooler) or successional stage (pioneer vs. established). However, within C. lasiocarpa, genetic variability decreased and clone size increased in cooler climates and at established sites.     

Genetic diversity and multilocus genetic structure in the relictual endemic herb<Emphasis Type="Italic"> Japonolirion osense</Emphasis> (Petrosaviaceae)

Plant clonality may greatly reduce effective population size and influence management strategies of rare and endangered species. We examined genetic diversity and the extent of clonality in four populations of the monotypic herbaceous perennial Japonolirion osense, which is one of the most rare flowering plants in Japan. Allozyme analysis revealed moderate levels of genetic variation, and the proportion of polymorphic loci (P=66.7%) was higher than the value for species with similar life-history traits. With four polymorphic loci, 19 multilocus genotypes were observed among 433 aerial shoot samples and 10 (52%) were found only in single populations. The proportion of distinguishable genotypes (PD=0.10) and Simpson's index of diversity (D=0.52) also exhibited moderate levels of genotypic diversity compared to other clonal plants, with genotype frequencies at Hardy-Weinberg equilibrium. The distributions of genotypes were often localized and they were mostly found within a radius of 5 m. Spatial autocorrelation analysis showed that shoot samples located 4 m apart were expected to be genetically independent. The results suggest that the spatial extent of genets was relatively narrow and thus the clonality was not extensive.     

New microsatellite loci for estimating genetic diversity and structure in Octopus hubbsorum from Nayarit,México

Background

Octopus hubbsorum Berry, 1953 is the most important species for commercial fishing in the Mexican Pacific. However, there is a lack of information regarding population structure that could have important management implications. We tested 44 microsatellite loci in O. hubbsorum by cross-amplification from O. bimaculatus.

Methods and results

Genetic diversity and structure was tested over 30 octopus sampled from Santa Cruz de Miramar (Nayarit, México). A total of 11 loci were successfully amplified. All loci were polymorphic with the number of effective alleles ranging from 2.13 to 23.14, while three loci significantly deviated from Hardy-Weinberg equilibrium. No significant LD was observed between pairs of loci (P?≥?0.05). The application of the new markers in a O. hubbsorum population from Santa Cruz de Miramar Nayarit, México, did not showed Wahlund or isolate breaking effects due to the mixing of distinct populations.

Conclusions

The loci were useful to estimate levels of pairwise relatedness and to discard the presence of recent demographic bottlenecks in the population. We consider that eight microsatellites are adequate from the 11 amplified loci

     

GENETIC CONSEQUENCES OF RARITY IN ASTER FURCATUS (ASTERACEAE), A THREATENED,SELF-INCOMPATIBLE PLANT

Aster furcatus is a rare, self-incompatible plant with fewer than 50 known populations throughout its range. We verified self-incompatibility in A. furcatus by conducting experimental self- and cross-pollinations and by examining seed set in a small population comprised of a single clonal genet. We examined variation at 22 electrophoretic loci in 23 populations of A. furcatus from across its range in Wisconsin, Illinois, Indiana, and Missouri. Except for two rare alleles found in single individuals in three populations, all loci but one of those examined were fixed for single alleles. The only variable locus (triosephosphate isomerase, TPI-1) tended to exhibit genotype frequencies in Hardy-Weinberg equilibrium or with a slight excess of heterozygotes. Although overall gene diversity was extremely low, TPI genotype frequencies were indicative of an outcrossing plant. We examined the subpopulation genetic structure among clonal plants within one Wisconsin population in greater detail. F statistics indicated that much of the genetic variation at the polymorphic TPI locus was due to differentiation among populations. We discuss the implications of self-incompatibility and low levels of genetic variation for the evolution and conservation of Aster furcatus and other rare plants with similar breeding systems.     

Development and characterization of the first microsatellite markers in the mangrove species Pelliciera rhizophorae Triana & Planchon

Pelliciera rhizophorae is a unique Neotropical mangrove species belonging to Pelliciera genus. We isolated eight microsatellite loci from this species. All loci were polymorphic and showed three to nine alleles per locus in Colombian Pacific and Caribbean populations. Polymorphic information content ranged from 0.46 to 0.69. Two loci (PeRh‐14 and PeRh‐19) showed null alleles on the Caribbean coast, which suggest genetic differentiation between Pacific and Caribbean populations of P. rhizophorae. Development of these microsatellite loci constitutes a new molecular tool to carry out studies in the genome of the species and to evaluate its population dynamics.     

Genetic diversity of the black mangrove (Avicennia germinans L.) in Colombia

This study analyzed the genetic diversity and patterns of genetic structure in Colombian populations of Avicennia germinans L. using microsatellite loci. A lower genetic diversity was found on both the Caribbean (Ho = 0.439) and the Pacific coasts (Ho = 0.277) than reported for the same species in other locations of Central American Pacific, suggesting the deterioration of genetic diversity. All the populations showed high inbreeding coefficients (0.131–0.462) indicating heterozygotes deficience. The genetic structure between the Colombian coasts separated by Central American Isthmus was high (F_RT = 0.39) and the analyses of the genetic patterns of A. germinans revealed a clear differentiation of populations and no-recent gene flow evidence between coasts. Genetic structure was found within each coast (F_ST = 0.10 for the Caribbean coast and F_ST = 0.22 for the Pacific coast). The genetic patterns along the two coasts appear to reflect a forcing by local geomorphology and marine currents. Both coasts constitute a different Evolutionary Significant Unit, so we suggest for future transplantations plans that propagules or saplings of the populations of the Caribbean coast should not be mixed with those of the Pacific Colombian coast. Besides, we suggest that reforestation efforts should carefully distinguish propagules sources within each coast.     

Genetic Diversity and Population Structure of Alnus hirsuta (Betulaceae) in Korea

Alnus hirsuta in Korea was measured to estimate the amount and pattern of genetic diversity and population structure. The mean genetic diversity within populations was 0.166. Korean alder populations have slightly high levels of genetic diversity compared to those of two Canadian alder species. The genetic differentiation among populations accounted for 9% of the total variation. The rate of gene flow was estimated high (Nm=2.63). Analysis of inbreeding coefficient, calculated for all polymorphic loci in each population, showed a substantial heterozygote deficiency relative to Hardy-Weinberg expectations. The mean G _ST value of A. hirsuta in Korea was 0.087. The low value of G _ST in this species, reflecting little spatial genetic differentiation, may indicate extensive gene flow. A relationship between the mean heterozygosity and annual rainfall showed a positive relationship (r ²=0.54, F=4.67). Received 8 August 1998/ Accepted in revised form 7 July 1999     

Allozyme variation in the sympatric ferns Culcita macrocarpa and Woodwardia radicans at the northern extreme of their ranges

Isozymes were used to study genetic variation in the clonal ferns Culcita macrocarpa and Woodwardia radicans in the northwestern Iberian Peninsula, their northern distributional limit. Despite their high chromosome numbers, both species were isozymic diploids. In C. macrocarpa all 18 resolved loci were monomorphic, with the same allele in all ramets from all populations. In W. radicans only two of the 16 interpreted loci were polymorphic, with two alleles per locus; ramet-level genotypes showed Hardy-Weinberg equilibrium, indicating an intergametophytic mating system; the number of genets distinguished was 1–3 per population; and among-population variation was low (F _ST = 0.231), suggesting effective gene flow (i.e. spore exchange). More generally, the very low (W. radicans, H _T = 0.012) or zero (C. macrocarpa) genetic diversity detected in the present study may be due to genetic drift associated with the reduction of populations in the last glaciation, and to founder effects in the subsequent Holocene expansion.     

ALLOZYME VARIATION WITHIN AND AMONG MATURE POPULATIONS OF SPECKLED ALDER (ALNUS RUGOSA) AND RELATIONSHIPS WITH GREEN ALDER (A. CRISPA)

Vegetative tissues from 14 sexually mature populations of speckled alder (Alnus rugosa (Du Roi) Sprengel) in Québec have been analyzed for electrophoretically demonstrable variation in 9 enzymes encoding a total of 15 loci. Speckled alder demonstrated a diploid-like expression for all polymorphic loci investigated. Populations were in Hardy-Weinberg equilibrium for the 9 polymorphic loci observed. The total expected heterozygosity was 0.173. Analysis of fixation indices indicated a slight deficiency of heterozygotes, relative to panmictic expectations. This was likely due to weak population differentiation, which did not follow any particular geographical trend. Qualitative estimates of interpopulation rates of gene flow were high, and in good agreement with the small pair-wise population genetic distances and among-population fixation index. Levels of genetic diversity and partition of this diversity were similar to previous observations obtained with the sympatric species A. crispa (Ait.) Pursh. However, no phenomena of interspecific hybridization were noted. The average genetic distance between these two alder species was large, with a value of 0.4, emphasizing the different ecological niches colonized by each of the two species. The estimate of divergence time between these two taxa was two million years. It is in agreement with the hypothesis of repetitive spatial isolation of each species in ice-free refugia during the Pleistocene, thus promoting their reproductive isolation. The interspecific divergence noted at the enzyme level allowed for the easy electrophoretic identification of each taxon.     

Microsatellite polymorphism and genetic differentiation in three Norwegian populations of Elymus alaskanus (Poaceae)

 Variation at seven microsatellite loci was investigated in three local E. alaskanus populations from Norway and microsatellite variation was compared with allozyme variation. The percentage of polymorphic loci was 81%, the mean number of alleles per polymorphic locus was 5.7 and expected heterozygosity was 0.37. An F-statistic analysis revealed an overall 48% deficit of heterozygotes over Hardy-Weinberg expectations. Gene diversity is mainly explained by the within population component. The averaged between population differentiation coefficient, F _st , over 7 loci is only 0.13, which accounts for only 13% of the whole diversity and was contrary to allozyme analysis. The mean genetic distance between populations was 0.12. However, a χ² -test showed that allele frequencies were different (p < 0.05) among the populations at 5 of the 7 loci. In comparison with the genetic variation detected by allozymes, microsatellite loci showed higher levels of genetic variation. Microsatellite analysis revealed that population H10576 possesses the lowest genetic variation among the tested three populations, which concur with allozyme analysis. The dendrogram generated by microsatellites agreed very well with allozymic data. Our results suggest that natural selection may be an important factor in shaping the genetic diversity in these three local E. alaskanus populations. Possible explanations for deficit heterozygosity and incongruence between microsatellites and allozymes are discussed. Received November 6, 2001; accepted April 24, 2002 Published online: November 14, 2002 Addresses of the authors: Genlou Sun (e-mail: Genlou.sun@STMARYS.CA), Biology Department, Saint Mary's University, Halifax. Nova Scotia, B3H 3C3, Canada. B. Salomon, R. von Bothmer, Department of Crop Science, The Swedish University of Agricultural Sciences, P.O. Box 44, SE-230 53, Alnarp, Sweden.     

Psorophora columbiae and Psorophora toltecum (Diptera: Culicidae) Colombian populations cannot be differentiated by isoenzymes

Two populations of the mosquito Psorophora columbiae from the central Andean area of Colombia and one population of Ps. toltecum from the Atlantic coast of Colombia were analyzed for 11 isoenzyme markers. Psorophora columbiae and Ps. toltecum are two of the main vectors of Venezuelan equine encephalitis. We found no conspicuous genetic differences between the two species. The relatively high gene flow levels among these populations indicate that these are not two different species or that there has been recent divergence between these taxa. In addition, no global differential selection among the loci was detected, although the alpha-GDH locus showed significantly less genetic heterogeneity than the remaining loci, which could mean that homogenizing natural selection acts at this locus. No isolation by distance was detected among the populations, and a spatial population analysis showed opposite spatial trends among the 31 alleles analyzed. Multiregression analyses showed that both expected heterozygosity and the average number of alleles per locus were totally determined by three variables: altitude, temperature and size of the human population at the locality. Individually, the expected heterozygosity is more related to these three variables than to the average number of alleles.     

Isolation and characterization of 15 nuclear microsatellite markers for Baillonella toxisperma Pierre (Sapotaceae), a low-density tree species of Central Africa

Baillonella toxisperma is a scattered endemic species of the Guineo-Congolian forest. We developed 15 nuclear microsatellite markers specifically for B. toxisperma to analyse the genetic diversity of 188 individuals distributed in two natural populations in Gabon. On average, 8.3 alleles per locus were identified; observed heterozygosity ranged from 0.056 to 0.872 and expected heterozygosity from 0.282 to 0.823 among populations. Only three loci showed a significant departure to Hardy-Weinberg equilibrium, but no linkage disequilibrium was observed for any pair of loci.     

Genetic structure of the red mangrove (<Emphasis Type="Italic">Rhizophora mangle</Emphasis> L.) on the Colombian Pacific detected by microsatellite molecular markers

Rhizophora mangle, one of the five species of the genus Rhizophora, is found widely distributed along the American and West African coasts. This species is one of the principal constituents of the mangrove ecosystem in Colombia and is also found within the most important economic activities for the communities that inhabit the littoral. In order to assess the degree of genetic diversity of R. mangle in five populations of the Colombian Pacific, nuclear microsatellite molecular markers were used. In 92 individuals sampled, it was found that 100% of the loci were polymorphic , and no private alleles were detected. The population structure of R. mangle in the Colombian Pacific, was highly significant (P < 0.001); however, the greatest differentiation was detected at the within-population level (94.62%). For the populations of La Plata, Virudó and Charambirá, the tendency toward panmixia could be the cause of the low differentiation among these three locations. Within populations, the genetic diversity revealed a deviation from Hardy–Weinberg equilibrium with high significance in Virudó and Tumaco, where it appears the intense anthropogenic activity has exercised strong pressure on the red mangrove, resulting in the possible fragmentation of the local landscape and therefore an increase in the rate of endogamy within these populations. Despite this situation, our study―one of the first developed in genetics of the red mangrove in Colombia―did not show evidence of recent bottleneck effects or deterioration in its genetic composition, which could be exploited to propose management and restoration programs for the zones where the forests of this species are degraded. Handling editor: K. Martens