Higher genetic variation estimated by microsatellites compared to isoenzyme markers in Aedes aegypti from Rio de Janeiro

Aedes aegypti populations from five districts in Rio de Janeiro were analyzed using five microsatellites and six isoenzyme markers, to assess the amount of variation and patterns of gene flow at local levels. Microsatellite loci were polymorphic enough to detect genetic differentiation of populations collected at small geographic scales (e.g. within a city). Ae. aegypti populations were highly differentiated as well in the city center as in the outskirt. Thus, dengue virus propagation by mosquitoes could be as efficient in the urban area as in the outskirt of Rio de Janeiro, the main entry point of dengue in Brazil.

A population genetics study of Anopheles darlingi (Diptera: Culicidae) from Colombia based on random amplified polymorphic DNA-polymerase chain reaction and amplified fragment lenght polymorphism markers

The genetic variation and population structure of three populations of Anopheles darlingi from Colombia were studied using random amplified polymorphic markers (RAPDs) and amplified fragment length polymorphism markers (AFLPs). Six RAPD primers produced 46 polymorphic fragments, while two AFLP primer combinations produced 197 polymorphic fragments from 71 DNA samples. Both of the evaluated genetic markers showed the presence of gene flow, suggesting that Colombian An. darlingi populations are in panmixia. Average genetic diversity, estimated from observed heterozygosity, was 0.374 (RAPD) and 0.309 (AFLP). RAPD and AFLP markers showed little evidence of geographic separation between eastern and western populations; however, the F ST values showed high gene flow between the two western populations (RAPD: F ST = 0.029; Nm: 8.5; AFLP: F ST = 0.051; Nm: 4.7). According to molecular variance analysis (AMOVA), the genetic distance between populations was significant (RAPD:phiST = 0.084; AFLP:phiST = 0.229, P < 0.001). The F ST distances and AMOVAs using AFLP loci support the differentiation of the Guyana biogeographic province population from those of the Chocó-Magdalena. In this last region, Chocó and Córdoba populations showed the highest genetic flow.

Population genetic structure of the major malaria vector Anopheles darlingi (Diptera: Culicidae) from the Brazilian Amazon, using microsatellite markers

The population genetic structure of Anopheles darlingi, the major human malaria vector in the Neotropics, was examined using seven microsatellite loci from nine localities in central and western Amazonian Brazil. High levels of genetic variability were detected (5-25 alleles per locus; H E = 0.519-0.949). There was deviation from Hardy-Weinberg Equilibrium for 59.79% of the tests due to heterozygote deficits, while the analysis of linkage disequilibrium was significant for only two of 189 (1.05%) tests, most likely caused by null alleles. Genetic differentiation (F ST = 0.001-0.095; Nm = 4.7-363.8) indicates that gene flow is extensive among locations < 152 km apart (with two exceptions) and reduced, but not absent, at a larger geographic scale. Genetic and geographic distances were significantly correlated (R² = 0.893, P < 0.0002), supporting the isolation by distance (IBD) model. The overall estimate of Ne was 202.4 individuals under the linkage disequilibrium model, and 8 under the heterozygote excess model. Analysis of molecular variance showed that nearly all variation (~ 94%) was within sample locations. The UPGMA phenogram clustered the samples geographically, with one branch including 5/6 of the state of Amazonas localities and the other branch the Acre, Rondônia, and remaining Amazonas localities. Taken together, these data suggest little genetic structure for An. darlingi from central and western Amazonian Brazil. These findings also imply that the IBD model explains nearly all of the differentiation detected. In practical terms, populations of An. darlingi at distances < 152 km should respond similarly to vector control measures, because of high gene flow.

A preliminary analysis of the population genetics and molecular phylogenetics of Onchocerca volvulus (Nematoda: Filarioidea) using nuclear ribosomal second internal transcribed spacer sequences

Nuclear internal transcribed spacer 2 (ITS2) rDNA sequences were used for a molecular phylogenetics analysis of five Onchocerca species. The sister species of the human parasite O. volvulus was found to be the cattle parasite O. ochengi and not O. gibsoni, contrary to chromosomal evidence. The genetic differentiation of two African populations (representing the two African strains) and a Brazilian population of O. volvulus was also studied. Phylogenetic and network reconstruction did not show any clustering of ITS2 alleles on geographic or strain grounds. Furthermore, population genetics tests showed no indication of population differentiation but suggested gene flow among the three populations.

Population structure of the malaria vector Anopheles darlingi in Rondônia, Brazilian Amazon, based on mitochondrial DNA

Anopheles darlingi is the most important Brazilian malaria vector, with a widespread distribution in the Amazon forest. Effective strategies for vector control could be better developed through knowledge of its genetic structure and gene flow among populations, to assess the vector diversity and competence in transmitting Plasmodium. The aim of this study was to assess the genetic diversity of An. darlingi collected at four locations in Porto Velho, by sequencing a fragment of the ND4 mitochondrial gene. From 218 individual mosquitoes, we obtained 20 different haplotypes with a diversity index of 0.756, equivalent to that found in other neotropical anophelines. The analysis did not demonstrate significant population structure. However, haplotype diversity within some populations seems to be over-represented, suggesting the presence of sub-populations, but the presence of highly represented haplotypes complicates this analysis. There was no clear correlation among genetic and geographical distance and there were differences in relation to seasonality, which is important for malarial epidemiology.

Population dynamics of Triatoma vitticeps (Stål, 1859) in Itanhomi, Minas Gerais, Brazil

Taxonomic markers (head structure morphometry, isoenzymes and randon amplified polymorphism of DNA - RAPD) were used to understand the population dynamics of Triatoma vitticeps, predominant triatomine species in Itanhomi district, using samples obtained from domestic, peridomiciliary and sylvatic habitats. Morphometric analysis revealed sexual dimorphism within the three samples although specimens could not be separated according to the habitat in which they were captured. Forty-two bands were analyzed from RAPD profiles generated using four primers. A dendrogram constructed from Dice's similarity coefficient values showed that migration of the insects between the habitats has occurred, without structuring of populations. Moreover, the dendrogram obtained from the genetic distance values showed an important gene flow between the sylvatic and domestic habitats. No polymorphism was found in the electrophoretic mobility of proteins for the ten enzymes studied. Our results revealed movement of triatomines between the three habitats, suggesting that the presence of T. vitticeps in houses should not be ignored. As invasion of houses by sylvatic insects is frequent and the natural infection indices of this species are among the highest known, epidemiological vigilance studies may reveal possible changes in T. vitticeps behaviour which could present future risks to public health.

Genetic structure of Aedes aegypti in the city of Córdoba (Argentina), a recently reinfested area

To understand the transmission of a vector-borne disease, knowledge of the magnitude of dispersal among vector populations is essential because of its influence on pathogen transfer. The principal vector of dengue, the most common arboviral disease in the world, is the mosquito Aedes aegypti (L.). This tropical and subtropical species is native to Africa but has dispersed worldwide since the XV century. In Argentina, the species was declared eradicated in 1963, but has reinfested the country in recent years. In the present work, we used RAPD-PCR markers to assess the levels of genetic variability and differentiation among populations of Ae. aegypti (the vector of dengue and yellow fever) in Córdoba, the second largest city in Argentina. We detected similar levels of genetic variability (He between 0.351-0.404) across samples and significant genetic differentiation between most population pairs within the city (F ST between 0.0013-0.0253). Genetic distances indicate that there are three distinct groups, formed predominantly by populations that are connected by, or near, main roads. This suggests that, in addition to other factors such as availability of oviposition sites or step-by-step migration, passive transport plays an important role in gene flow within the city.

Influence of anti-filarial chemotherapy strategies on the genetic structure of Wuchereria bancrofti populations

Lymphatic filarial (LF) parasites have been under anti-filarial drug pressure for more than half a century. Currently, annual mass drug administration (MDA) of diethylcarbamazine (DEC) or ivermectin in combination with albendazole (ALB) have been used globally to eliminate LF. Long-term chemotherapies exert significant pressure on the genetic structure of parasitic populations. We investigated the genetic variation among 210 Wuchereria bancrofti populations that were under three different chemotherapy strategies, namely MDA with DEC alone (group I, n = 74), MDA with DEC and ALB (group II, n = 60) and selective therapy (ST) with DEC (group III, n = 34) to understand the impact of these three drug regimens on the parasite genetic structure. Randomly amplified polymorphic DNA profiles were generated for the three groups of parasite populations; the gene diversity, gene flow and genetic distance values were determined and phylogenetic trees were constructed. Analysis of these parameters indicated that parasite populations under ST with a standard dose of DEC (group III) were genetically more diverse (0.2660) than parasite populations under MDA with DEC alone (group I, H = 0.2197) or with DEC + ALB (group II, H = 0.2317). These results indicate that the MDA may reduce the genetic diversity of W. bancrofti populations when compared to the genetic diversity of parasite populations under ST.

Molecular evidence for a single taxon, Anopheles nuneztovari s.l., from two endemic malaria regions in Colombia

To elucidate the Anopheles nuneztovari s.l. taxonomic status at a microgeographic level in four malaria endemic localities from Antioquia and Córdoba, Colombia, fragments of the cytochrome oxidase subunit I (COI) and the white gene were used. The COI analysis showed low genetic differentiation with fixation index (F ST) levels between -0.02-0.137 and Nm values between 3-∞, indicating the presence of high gene flow among An. nuneztovari s.l. populations from the four localities. The COI network showed a single most common haplotype, type 1 (n = 55), present in all localities, as the likely ancestral haplotype. Analysis of the white gene showed that An. nuneztovari s.l. populations from both departments grouped with haplotypes 19 and 20, which are part of lineage 3 reported previously. The results of the present study suggest that An. nuneztovari s.l. is a single taxon in the area of the present study.

PCR-RAPD and PCR-RFLP polymorphisms detected in Anopheles cruzii (Diptera, Culicidae)

The aim of the present study was to examine genetic variability in populations of An. cruzii by employing PCR-RAPD and PCR-RFLP markers. All analyses were carried out using individuals of the F1 generation of wild caught females obtained in Santa Catarina State (Florianópolis and São Francisco do Sul), Paraná State (Morretes, Paranaguá and Guaratuba) and São Paulo State (Cananéia). In the PCR-RAPD experiments, seven primers were used for comparisons within and among populations. The restriction profile of the ITS2 including a fragment of both 5.8S and 28S regions of the rDNA was obtained with the enzymes BstUI, HaeIII, TaqI, HhaI, Sau96I, HinfI, HincII and NruI. The PCR-RAPD method detected a large number of polymorphic bands. Genetic distance among populations of An. cruzii varied from 0,0214 to 0,0673, suggesting that all individuals used in the analyses belong to a single species. The number of migrants per generation (Nm) was 4.3, showing the existence of gene flow among populations. The restriction profile of the ITS2, 5.8S and 28S gene regions was similar in all An. cruzii samples, whereas the results obtained by using HhaI and NruI are indicative that the individuals analyzed have nucleotide sequences distinct from those of An. cruzii samples from Peruíbe and Juquiazinho deposited in GenBank.

Genetic structure of populations of Pissodes castaneus (De Geer) (Coleoptera, Curculionidae) using amplified fragment length polymorphism

Genetic structure of populations of Pissodes castaneus (De Geer) (Coleoptera, Curculionidae) using amplified fragment length polymorphism. The objective of this study was to determine the genetic structure of populations of Pissodes castaneus from different areas and on different species of Pinus using the PCR-AFLP technique. Twenty samples were analyzed, representing 19 populations from Brazil and one from Florence, Italy, which is the region of origin of P. castaneus. The four combinations of primers generated a total of 367 fragments of DNA, and 100% of polymorphic loci, indicating high degree of molecular polymorphism. The dendrogram did not reveal trends for grouping the populations in relation to origin. The low genetic similarity (0.11 between the most distant groups) and genetic distances of 0.13 and 0.44 for 10 out of the 20 samples may indicate several founding events or multiple introductions of heterogeneous strains into Brazil. The allelic fixation index (Fst) was 0.3851, considered high, and the number of migrants (Nm) was 0.3991, indicating low gene flow among populations. The highest genetic distances were between the population from Irani, SC and Cambará do Sul, RS and Bituruna, PR, indicating an independent founding event or a particular allelic fixation in the former location. The high genetic diversity among populations points out that the populations are genetically heterogeneous with a diverse gene pool in the surveyed areas, what makes them to respond differently to control measures.

Diversity and genetic struture in cajá tree (spondias mombin l.) populations in northeastern Brazil

Spondias mombin L. is a fruit tree from the American continent from the Anacardiaceae family. In Brazil it is common in different vegetation types but is more frequent in the Atlantic and Amazonian rainforests. It is economically important because of its fruits, which are widely consumed raw or processed as fruit jellies, juices and ice creams. The leaves have great importance in the pharmaceutical industry because of their antibacterial properties. In the state of Pernambuco, cajá tree is widely distributed in the Zona da Mata region and less frequently in the Agreste and Sertão areas. In this work diversity and genetic structure were studied in four populations of cajá tree from Pernambuco's Zona da Mata, Northeast Brazil, using isozymes polymorphism analyses from electrophoreses. The result showed 100% of polymorphism (P) for nine alleles and the average of alleles per locus s was 2.4. The expected heterozygosity ranged from 0.530 to 0.574 and the observed heterozygosity , from 0.572 to 0.735. It was not observed inbreeding and the average F IT was -0.175, whereas within population inbreeding (f) varied from -0.08 to- 0.37. The genetic divergence among the populations (F ST) ranged from 0.006 to 0.028 and the average was 0.026. The average of estimated gene flow (Nm) was high (5.27). The CG-IPA population, corresponding to the germplasm collection of IPA, showed more than 96% of genetic similarity with other populations; therefore, it is a good representative of the existent genetic diversity in the Zona da Mata region.

Diversity and genetic structure in natural populations of Hancornia speciosa var. speciosa Gomes in northeastern Brazil

Hancornia speciosa Gomes is a fruit tree native from Brazil that belongs to Apocinaceae family, and is popularly known as Mangabeira. Its fruits are widely consumed raw or processed as fruit jam, juices and ice creams, which have made it a target of intense exploitation. The extractive activities and intense human activity on the environment of natural occurrence of H. speciosa has caused genetic erosion in the species and little is known about the ecology or genetic structure of natural populations. The objective of this research was the evaluation of the genetic diversity and genetic structure of H. speciosa var. speciosa. The genetic variability was assessed using 11 allozyme loci with a sample of 164 individuals distributed in six natural populations located in the States of Pernambuco and Alagoas, Northeastern Brazil. The results showed a high level of genetic diversity within the species (e= 0.36) seeing that the most of the genetic variability of H. speciosa var. speciosa is within its natural populations with low difference among populations ( or = 0.081). The inbreeding values within ( = -0.555) and among populations ( =-0.428) were low showing lacking of endogamy and a surplus of heterozygotes. The estimated gene flow ( m ) was high, ranging from 2.20 to 13.18, indicating to be enough to prevent the effects of genetic drift and genetic differentiation among populations. The multivariate analyses indicated that there is a relationship between genetic and geographical distances, which was confirmed by a spatial pattern analysis using Mantel test (r = 0.3598; p = 0.0920) with 1000 random permutations. The high genetic diversity index in these populations indicates potential for in situ genetic conservation.

Genetic structure and diversity of Copaifera langsdorffii Desf. in Cerrado fragments of the São Paulo State, Brazil

The loss of large areas of Cerrado (Brazilian savanna) in Brazil can lead to reduced biodiversity and to the extinction of species. Therefore, the present study aimed to investigate the genetic fragility of populations of Copaifera langsdorffii Desf exposed to different anthropic conditions in fragments of Cerrado in the state of São Paulo. The study was carried out in two Experimental Stations operated by the Forest Institute (Assis and Itirapina), in one fully protected conservation unit (Pedregulho) and in one private property (Brotas). Analyses were conducted using leaf samples from 353 adult specimens and eight pairs of microsatellite loci. The number of alleles per locus ranged from 13 to 15 in all populations, but the mean number of effective alleles was approximately half this value (7.2 to 9-1). Observed heterozygosity was significant and lower than the expected in all populations. Consequently, all populations deviated from Hardy-Weinberg expected frequencies. Fixation indexes were significant for all populations, with the Pedregulho population having the lowest value (0.189) and Itirapina having the highest (0.283). The analysis of spatial genetic structure detected family structures at distance classes of 20 to 65 m in the populations studied. No clones were detected in the populations. Estimates of effective population size were low, but the area occupied by each population studied was large enough for conservation, medium and long term. Recent reductions or bottlenecks were detected in all four populations. Mean Gst’ (genetic divergence) indicated that most of the variation was within populations. Cluster structure analysis based on the genotypes detected K= 4 clusters with distinct allele frequencies patterns. The genetic differentiation observed among populations is consistent with the hypothesis of genetic and geographic isolation. Therefore, it is essential to adopt conservation strategies that raise the gene flow between fragments.

Vegetative and reproductive development of Costa Rican weedy rice compared with commercial rice (Oryza sativa)

The variability in the chronology of the vegetative and reproductive development of weedy rice complex has been little studied. However, a field trial was established to study the timing of growth stages of sixteen weedy rice morphotypes and five rice varieties of Costa Rica. Weedy rice presented a wide range of variation for all descriptors among and within morphotypes. Weedy rice was taller than the rice varieties during vegetative phase and showed a growth increase of 14-23 cm every two weeks. Six morphotypes emerged earlier than commercial rice varieties, but no differences where found between samples for the time required for starting tillering. Early emergence of weedy rice morphotypes was not associated with early flowering, thus no correlation was detected between the vegetative and reproductive phases. All weedy rice morphotypes reached anthesis and maturity earlier than the rice varieties. Nevertheless, varieties Setesa-9 and CR-5272 overlapped anthesis with eleven morphotypes and variety CR-4338 overlapped flowering with eight weedy rice morphotypes. In contrast, none of the morphotypes overlapped anthesis with varieties CR-1821 and CR-1113. The results obtained showed the competitive capacity of weedy rice and provided valuable information about flowering overlap between weedy rice morphotypes and rice varieties which will be useful in the design of gene flow studies among them.