Genetic and phenotypic variation in central and northern European populations of Aedes (Aedimorphus) vexans (Meigen, 1830) (Diptera,Culicidae)

The floodwater mosquito Aedes vexans can be a massive nuisance in the flood plain areas of mainland Europe, and is the vector of Tahyna virus and a potential vector of Dirofilaria immitis. This epidemiologically important species forms three subspecies worldwide, of which Aedes vexans arabiensis has a wide distribution in Europe and Africa. We quantified the genetic and phenotypic variation in Ae. vexans arabiensis in populations from Sweden (northern Europe), Hungary, and Serbia (central Europe). A landscape genetics approach (F_ST, STRUCTURE, BAPS, GENELAND) revealed significant differentiation between northern and southern populations. Similar to genetic data, wing geometric morphometrics revealed two different clusters, one made by Swedish populations, while another included Hungarian and Serbian populations. Moreover, integrated genetic and morphometric data from the spatial analysis suggested groupings of populations into three clusters, one of which was from Swedish and Hungarian populations. Data on spatial analysis regarding an intermediate status of the Hungarian population was supported by observed Isolation‐by‐Distance patterns. Furthermore, a low proportion of interpopulation vs intrapopulation variance revealed by AMOVA and low‐to‐moderate F_ST values on a broader geographical scale indicate a continuous between‐population exchange of individuals, including considerable gene flow on the regional scale, are likely to be responsible for the maintenance of the observed population similarity in Aе. vexans. We discussed data considering population structure in the light of vector control strategies of the mosquito from public health importance.     

Microsatellites reveal a high population structure in Triatoma infestans from Chuquisaca, Bolivia

Background

For Chagas disease, the most serious infectious disease in the Americas, effective disease control depends on elimination of vectors through spraying with insecticides. Molecular genetic research can help vector control programs by identifying and characterizing vector populations and then developing effective intervention strategies.

Methods and Findings

The population genetic structure of Triatoma infestans (Hemiptera: Reduviidae), the main vector of Chagas disease in Bolivia, was investigated using a hierarchical sampling strategy. A total of 230 adults and nymphs from 23 localities throughout the department of Chuquisaca in Southern Bolivia were analyzed at ten microsatellite loci. Population structure, estimated using analysis of molecular variance (AMOVA) to estimate F_ST (infinite alleles model) and R_ST (stepwise mutation model), was significant between western and eastern regions within Chuquisaca and between insects collected in domestic and peri-domestic habitats. Genetic differentiation at three different hierarchical geographic levels was significant, even in the case of adjacent households within a single locality (R _ST = 0.14, F _ST = 0.07). On the largest geographic scale, among five communities up to 100 km apart, R _ST = 0.12 and F _ST = 0.06. Cluster analysis combined with assignment tests identified five clusters within the five communities.

Conclusions

Some houses are colonized by insects from several genetic clusters after spraying, whereas other households are colonized predominately by insects from a single cluster. Significant population structure, measured by both R _ST and F _ST, supports the hypothesis of poor dispersal ability and/or reduced migration of T. infestans. The high degree of genetic structure at small geographic scales, inferences from cluster analysis and assignment tests, and demographic data suggest reinfesting vectors are coming from nearby and from recrudescence (hatching of eggs that were laid before insecticide spraying). Suggestions for using these results in vector control strategies are made.     

Genetic Structure and Wolbachia Genotyping in Naturally Occurring Populations of Aedes albopictus across Contiguous Landscapes of Orissa,India

Background

Aedes albopictus has recently been implicated as a major vector in the emergence of dengue and chikungunya in several parts of India, like Orissa, which is gradually gaining endemicity for arboviral diseases. Ae. albopictus is further known to be naturally infected with Wolbachia (maternally inherited bacterium), which causes cytoplasmic incompatibility (CI) in mosquitoes leading to sperm-egg incompatibility inducing the death of embryo. Knowledge of genetic diversity of Ae. albopictus, along with revealing the type of Wolbachia infection in Ae. albopictus is important to explore the genetic and biological characteristics of Ae. albopictus, prior to exploring the uses of CI-based vector control strategies. In this study, we assessed the population genetic structure and the pattern of Wolbachia infection in Ae. albopictus mosquitoes of Orissa.

Methods and Results

Ae. albopictus mosquitoes were collected from 15 districts representing the four physiographical regions of Orissa from 2010–2012, analyzed for genetic variability at seven microsatellite loci and genotyped for Wolbachia strain detection using wsp gene primers. Most microsatellite markers were successfully amplified and were polymorphic, showing moderate genetic structure among all geographic populations (F_ST = 0.088). Genetic diversity was high (F_ST = 0.168) in Coastal Plains populations when compared with other populations, which was also evident from cluster analyses that showed most Coastal Plains populations consisted of a separate genetic cluster. Genotyping analyses revealed that Wolbachia-infected Ae. albopictus field populations of Orissa were mostly superinfected with wAlbA and wAlbB strains. Wolbachia superinfection was more pronounced in the Coastal Plain populations.

Conclusion

High genetic structure and Wolbachia superinfection, observed in the Coastal Plain populations of Orissa suggested it to be genetically and biologically more unique than other populations, and hence could influence their vectorial attributes. Such high genetic diversity observed among Coastal Plains populations could be attributed to multiple introductions of Ae. albopictus in this region.     

Relative performance of Bayesian clustering software for inferring population substructure and individual assignment at low levels of population differentiation

Traditional methods for characterizing genetic differentiation among populations rely on a priori grouping of individuals. Bayesian clustering methods avoid this limitation by using linkage and Hardy–Weinberg disequilibrium to decompose a sample of individuals into genetically distinct groups. There are several software programs available for Bayesian clustering analyses, all of which describe a decrease in the ability to detect distinct clusters as levels of genetic differentiation among populations decrease. However, no study has yet compared the performance of such methods at low levels of population differentiation, which may be common in species where populations have experienced recent separation or high levels of gene flow. We used simulated data to evaluate the performance of three Bayesian clustering software programs, PARTITION, STRUCTURE, and BAPS, at levels of population differentiation below F _ST=0.1. PARTITION was unable to correctly identify the number of subpopulations until levels of F _ST reached around 0.09. Both STRUCTURE and BAPS performed very well at low levels of population differentiation, and were able to correctly identify the number of subpopulations at F _ST around 0.03. The average proportion of an individual’s genome assigned to its true population of origin increased with increasing F _ST for both programs, reaching over 92% at an F _ST of 0.05. The average number of misassignments (assignments to the incorrect subpopulation) continued to decrease as F _ST increased, and when F _ST was 0.05, fewer than 3% of individuals were misassigned using either program. Both STRUCTURE and BAPS worked extremely well for inferring the number of clusters when clusters were not well-differentiated (F _ST=0.02–0.03), but our results suggest that F _ST must be at least 0.05 to reach an assignment accuracy of greater than 97%.     

Evidence of population structuring following population genetic analyses of Fasciola hepatica from Argentina

Fasciola hepatica, the liver fluke, is a trematode parasite that causes disease of economic importance in livestock. As a zoonosis this parasite also poses a risk to human health in areas where it is endemic. Population genetic studies can reveal the mechanisms responsible for genetic structuring (non-panmixia) within parasite populations and provide valuable insights into population dynamics, which in turn enables theoretical predictions of evolutionary dynamics such as the evolution of drug resistance. Here we genotyped 320 F. hepatica collected from 14 definitive hosts from four provinces in Argentina. STRUCTURE analysis indicated three population clusters, and principal coordinate analysis confirmed this, showing population clustering across provinces. Similarly, pairwise F_ST values amongst all four provinces were significant, with standardised pairwise F_ST (F′_ST) ranging from 0.0754 to 0.6327. Therefore, population genetic structure was evident across these four provinces in Argentina. However, there was no evidence of deviation from Hardy–Weinberg equilibrium, so it appears that within these sub-populations there is largely random mating. We identified 263 unique genotypes, which gave a clonal diversity of 82%. Parasites with identical genotypes, clones, accounted for 26.6% of the parasites studied and were found in 12 of the 14 hosts studied, suggesting some clonemate transmission.     

Population structure of the malaria vector Anopheles sinensis (Diptera: Culicidae) in China: two gene pools inferred by microsatellites

Background

Anopheles sinensis is a competent malaria vector in China. An understanding of vector population structure is important to the vector-based malaria control programs. However, there is no adequate data of A. sinensis population genetics available yet.

Methodology/Principal Findings

This study used 5 microsatellite loci to estimate population genetic diversity, genetic differentiation and demographic history of A. sinensis from 14 representative localities in China. All 5 microsatellite loci were highly polymorphic across populations, with high allelic richness and heterozygosity. Hardy–Weinberg disequilibrium was found in 12 populations associated with heterozygote deficits, which was likely caused by the presence of null allele and the Wahlund effect. Bayesian clustering analysis revealed two gene pools, grouping samples into two population clusters; one includes six and the other includes eight populations. Out of 14 samples, six samples were mixed with individuals from both gene pools, indicating the coexistence of two genetic units in the areas sampled. The overall differentiation between two genetic pools was moderate (F _ST = 0.156). Pairwise differentiation between populations were lower within clusters (F _ST = 0.008–0.028 in cluster I and F _ST = 0.004–0.048 in cluster II) than between clusters (F _ST = 0.120–0.201). A reduced gene flow (Nm = 1–1.7) was detected between clusters. No evidence of isolation by distance was detected among populations neither within nor between the two clusters. There are differences in effective population size (Ne = 14.3-infinite) across sampled populations.

Conclusions/Significance

Two genetic pools with moderate genetic differentiation were identified in the A. sinensis populations in China. The population divergence was not correlated with geographic distance or barrier in the range. Variable effective population size and other demographic effects of historical population perturbations could be the factors affecting the population differentiation. The structured populations may limit the migration of genes under pressures/selections, such as insecticides and immune genes against malaria.     

Scale‐dependent post‐establishment spread and genetic diversity in an invading mollusc in South America

Aims Our study aimed to characterize the dispersal dynamics and population genetic structure of the introduced golden mussel Limnoperna fortunei throughout its invaded range in South America and to determine how different dispersal methods, that is, human‐mediated dispersal and downstream natural dispersal, contribute to genetic variation among populations. Location Paraná–Uruguay–Río de la Plata watershed in Argentina, Brazil, Paraguay and Uruguay. Methods We performed genetic analyses based on a comprehensive sampling strategy encompassing 22 populations (N = 712) throughout the invaded range in South America, using the mitochondrial cytochrome c oxidase subunit I (COI) gene and eight polymorphic nuclear microsatellites. We employed both population genetics and phylogenetic analyses to clarify the dispersal dynamics and population genetic structure. Results We detected relatively high genetic differentiation between populations (F_ST = ?0.041 to 0.111 for COI, ?0.060 to 0.108 for microsatellites) at both fine and large geographical scales. Bayesian clustering and three‐dimensional factorial correspondence analyses consistently revealed two genetically distinct clusters, highlighting genetic discontinuities in the invaded range. Results of all genetic analyses suggest ship‐mediated ‘jump’ dispersal as the dominant mode of spread of golden mussels in South America, while downstream natural dispersal has had limited effects on contemporary genetic patterns. Main conclusions Our study provides new evidence that post‐establishment dispersal dynamics and genetic patterns vary across geographical scales. While ship‐mediated ‘jump’ dispersal dominates post‐establishment spread of golden mussels in South America, once colonies become established in upstream locations, larvae produced may be advected downstream to infill patchy distributions. Moreover, genetic structuring at fine geographical scales, especially within the same drainages, suggests a further detailed understanding of dynamics of larval dispersal and settlement in different water systems. Knowledge of the mechanisms by which post‐establishment spread occurs can, in some cases, be used to limit dispersal of golden mussels and other introduced species.     

Skeeter Buster: A Stochastic, Spatially Explicit Modeling Tool for Studying Aedes aegypti Population Replacement and Population Suppression Strategies

Background

Dengue is the most important mosquito-borne viral disease affecting humans. The only prevention measure currently available is the control of its vectors, primarily Aedes aegypti. Recent advances in genetic engineering have opened the possibility for a new range of control strategies based on genetically modified mosquitoes. Assessing the potential efficacy of genetic (and conventional) strategies requires the availability of modeling tools that accurately describe the dynamics and genetics of Ae. aegypti populations.

Methodology/Principal findings

We describe in this paper a new modeling tool of Ae. aegypti population dynamics and genetics named Skeeter Buster. This model operates at the scale of individual water-filled containers for immature stages and individual properties (houses) for adults. The biology of cohorts of mosquitoes is modeled based on the algorithms used in the non-spatial Container Inhabiting Mosquitoes Simulation Model (CIMSiM). Additional features incorporated into Skeeter Buster include stochasticity, spatial structure and detailed population genetics. We observe that the stochastic modeling of individual containers in Skeeter Buster is associated with a strongly reduced temporal variation in stage-specific population densities. We show that heterogeneity in container composition of individual properties has a major impact on spatial heterogeneity in population density between properties. We detail how adult dispersal reduces this spatial heterogeneity. Finally, we present the predicted genetic structure of the population by calculating F_ST values and isolation by distance patterns, and examine the effects of adult dispersal and container movement between properties.

Conclusions/Significance

We demonstrate that the incorporated stochasticity and level of spatial detail have major impacts on the simulated population dynamics, which could potentially impact predictions in terms of control measures. The capacity to describe population genetics confers the ability to model the outcome of genetic control methods. Skeeter Buster is therefore an important tool to model Ae. aegypti populations and the outcome of vector control measures.     

Population genetic inferences using immune gene SNPs mirror patterns inferred by microsatellites

Single nucleotide polymorphisms (SNPs) are replacing microsatellites for population genetic analyses, but it is not apparent how many SNPs are needed or how well SNPs correlate with microsatellites. We used data from the gopher tortoise, Gopherus polyphemus—a species with small populations, to compare SNPs and microsatellites to estimate population genetic parameters. Specifically, we compared one SNP data set (16 tortoises from four populations sequenced at 17 901 SNPs) to two microsatellite data sets, a full data set of 101 tortoises and a partial data set of 16 tortoises previously genotyped at 10 microsatellites. For the full microsatellite data set, observed heterozygosity, expected heterozygosity and F_ST were correlated between SNPs and microsatellites; however, allelic richness was not. The same was true for the partial microsatellite data set, except that allelic richness, but not observed heterozygosity, was correlated. The number of clusters estimated by structure differed for each data set (SNPs = 2; partial microsatellite = 3; full microsatellite = 4). Principle component analyses (PCA) showed four clusters for all data sets. More than 800 SNPs were needed to correlate with allelic richness, observed heterozygosity and expected heterozygosity, but only 100 were needed for F_ST. The number of SNPs typically obtained from next‐generation sequencing (NGS) far exceeds the number needed to correlate with microsatellite parameter estimates. Our study illustrates that diversity, F_ST and PCA results from microsatellites can mirror those obtained with SNPs. These results may be generally applicable to small populations, a defining feature of endangered and threatened species, because theory predicts that genetic drift will tend to outweigh selection in small populations.     

Remarkably low genetic diversity and strong population structure in common bottlenose dolphins (Tursiops truncatus) from coastal waters of the Southwestern Atlantic Ocean

Knowledge about the ecology of bottlenose dolphins in the Southwestern Atlantic Ocean is scarce. Increased by-catch rates over the last decade in coastal waters of southern Brazil have raised concerns about the decline in abundance of local dolphin communities. Lack of relevant data, including information on population structure and connectivity, have hampered an assessment of the conservation status of bottlenose dolphin communities in this region. Here we combined analyses of 16 microsatellite loci and mitochondrial DNA (mtDNA) control region sequences to investigate genetic diversity, structure and connectivity in 124 biopsy samples collected over six communities of photographically identified coastal bottlenose dolphins in southern Brazil, Uruguay and central Argentina. Levels of nuclear genetic diversity were remarkably low (mean values of allelic diversity and heterozygosity across all loci were 3.6 and 0.21, respectively), a result that possibly reflects the small size of local dolphin communities. On a broad geographical scale, strong and significant genetic differentiation was found between bottlenose dolphins from southern Brazil–Uruguay (SB–U) and Bahía San Antonio (BSA), Argentina (AMOVA mtDNA Φ_ST = 0.43; nuclear F_ST = 0.46), with negligible contemporary gene flow detected based on Bayesian estimates. On a finer scale, moderate but significant differentiation (AMOVA mtDNA Φ_ST = 0.29; nuclear F_ST = 0.13) and asymmetric gene flow was detected between five neighbouring communities in SB–U. Based on the results we propose that BSA and SB–U represent two distinct evolutionarily significant units, and that communities from SB–U comprise five distinct Management Units (MUs). Under this scenario, conservation efforts should prioritize the areas in southern Brazil where dolphins from three MUs overlap in their home ranges and where by-catch rates are reportedly higher.     

Genetic structure of Cydia pomonella populations in Argentina and Chile implies isolating barriers exist between populations

The codling moth (Cydia pomonella (L.)) is an invasive pest of pome fruits introduced to the Americas in the 19–20^th centuries. This pest is widespread on both sides of the Andes range separating Argentina and Chile. We performed an analysis of the population genetic variability and structure of C. pomonella in Argentina and Chile using 13 microsatellite markers and sampled C. pomonella from apple as the main host plant along its distribution area (approx. 1,800 km). A total of 22 locations (11 from Chile and 11 from Argentina) were sampled. Significant genetic differentiation was observed among samples from Argentina and Chile (F_SC = 0.045) and between all localities (F_ST = 0.085). Significant isolation by distance (IBD) was found for each country and when samples from both sides of the Andes range were pooled, although a lower correlation coefficient was observed. The Mantel test showed that the geographic distance and highest altitude of the mountains between locations were significantly associated with the pairwise F_ST when samples from both sides of the Andes range were pooled. According to a Bayesian assignment test (STRUCTURE), samples from Argentina and Chile conformed to two distinct genetic clusters. Our results also suggest that the recent invasion of C. pomonella in the southernmost localities (Aysén Region in Chile and Santa Cruz Province in Argentina) originated in populations from the respective sides of the Andes range. Our results indicate a genetic exchange of C. pomonella within each country and significant genetic differentiation between countries, which could be explained by dispersal mediated by human activities related to fruit production within each country with little exchange between them. A possible explanation is that the Andes range could be a significant barrier for dispersal by flight, and quarantine barriers could prevent the movement of plant material or infested fruit between countries.     

A comparative genetic study of two groups of chukar partridges (<Emphasis Type="Italic">Alectoris chukar</Emphasis>) from Cyprus and Argentina,using microsatellite analysis

The aim of the present work is to estimate the usefulness of microsatellite genetic markers analysis to characterize and analyze the possible differences between a captive reared population and a wild one from the same species. The first sample consists of 27 chukar partridges (Alectoris chukar) bred in one farm in Argentina. The second one is composed of 31 chukar partridges coming from a wild Cyprus population (A. chukar cypriotes). We analyzed seven microsatellite loci: MCW135, MCW225, MCW276, MCW280, MCW295, LEI31, and ADL0142. The Argentina group showed higher genetic variation than the Cyprus did. Significant global F _IS value was found in the Argentina sample. Significant genetic differentiation exists between both groups (F _ST=0.394; p<0.01). The Argentina group did not show any signs of bottleneck. Results from Factorial Correspondence Analysis (FCA) suggest that the 58 partridges could be split into two distinct genetic clusters (Cyprus and Argentina). Nevertheless, in the light of PARTITION results, three Argentina individuals might be related to Cyprus. STRUCTURE is unable to assign these three animals to any of the two groups. This could be due to a single or repeated introduction of external individuals into the original Argentina group, so that these results would point to more than one origin for this population. This admixture of individuals could explain the high genetic variation observed in the Argentina farm. Global F _IS value would probably be higher without these immigrations; on the other hand, these admixtures could have prevented bottlenecks.     

Detecting a hierarchical genetic population structure: the case study of the Fire Salamander (Salamandra salamandra) in Northern Italy

The multistep method here applied in studying the genetic structure of a low dispersal and philopatric species, such as the Fire Salamander Salamandra salamandra, was proved to be effective in identifying the hierarchical structure of populations living in broad‐leaved forest ecosystems in Northern Italy. In this study, 477 salamander larvae, collected in 28 sampling populations (SPs) in the Prealpine and in the foothill areas of Northern Italy, were genotyped at 16 specie‐specific microsatellites. SPs showed a significant overall genetic variation (Global F_ST = 0.032, P < 0.001). The genetic population structure was assessed by using STRUCTURE 2.3.4. We found two main genetic groups, one represented by SPs inhabiting the Prealpine belt, which maintain connections with those of the Eastern foothill lowland (PEF), and a second group with the SPs of the Western foothill lowland (WF). The two groups were significantly distinct with a Global F_ST of 0.010 (P < 0.001). While the first group showed a moderate structure, with only one divergent SP (Global F_ST = 0.006, P < 0.001), the second group proved more structured being divided in four clusters (Global F_ST = 0.017, P = 0.058). This genetic population structure should be due to the large conurbations and main roads that separate the WF group from the Prealpine belt and the Eastern foothill lowland. The adopted methods allowed the analysis of the genetic population structure of Fire Salamander from wide to local scale, identifying different degrees of genetic divergence of their populations derived from forest fragmentation induced by urban and infrastructure sprawl.     

The Neovolcanic Axis Is a Barrier to Gene Flow among Aedes aegypti Populations in Mexico That Differ in Vector Competence for Dengue 2 Virus

Background

Aedes aegypti is the main mosquito vector of the four serotypes of dengue virus (DENV). Previous population genetic and vector competence studies have demonstrated substantial genetic structure and major differences in the ability to transmit dengue viruses in Ae. aegypti populations in Mexico.

Methodology/Principal Findings

Population genetic studies revealed that the intersection of the Neovolcanic axis (NVA) with the Gulf of Mexico coast in the state of Veracruz acts as a discrete barrier to gene flow among Ae. aegypti populations north and south of the NVA. The mosquito populations north and south of the NVA also differed in their vector competence (VC) for dengue serotype 2 virus (DENV2). The average VC rate for Ae. aegypti mosquitoes from populations from north of the NVA was 0.55; in contrast the average VC rate for mosquitoes from populations from south of the NVA was 0.20. Most of this variation was attributable to a midgut infection and escape barriers. In Ae. aegypti north of the NVA 21.5% failed to develop midgut infections and 30.3% of those with an infected midgut failed to develop a disseminated infection. In contrast, south of the NVA 45.2% failed to develop midgut infections and 62.8% of those with an infected midgut failed to develop a disseminated infection.

Conclusions

Barriers to gene flow in vector populations may also impact the frequency of genes that condition continuous and epidemiologically relevant traits such as vector competence. Further studies are warranted to determine why the NVA is a barrier to gene flow and to determine whether the differences in vector competence seen north and south of the NVA are stable and epidemiologically significant.     

Divergence at neutral and non-neutral loci in Drosophila buzzatii populations and their hybrids

The impact of intraspecific hybridisation on fitness and morphological traits depends on the history of natural selection and genetic drift, which may have led to differently coadapted gene-complexes in the parental populations. The divergence at neutral and non-neutral loci between populations can be evaluated by estimating F_ST and Q_ST respectively, and hence give an estimate of drift and selection in the populations. Here we investigate (1) whether divergence between populations in quantitative traits (wing size and shape) can be attributed to selection or drift alone, (2) The impact of intraspecific hybridisation on estimators for divergence at neutral (F_ST) and non-neutral loci (Q_ST) in hybrids, (3) If measurement of shape is more informative than size in order to detect divergence in quantitative traits between populations. The aims were addressed by performing two hybridisations between three populations of Drosophila buzzatii, one between populations from Argentina and the Canary Islands (separated for 200 years), and the other between populations from Argentina and Australia (separated for 80 years). We observed the highest divergence at neutral loci between the Argentinean and Canary Island populations, but highest morphological divergence between the Argentinean and Australian populations, indicating that natural selection is acting on the wings. Divergence based on Q_ST measures in the hybrids was sensitive towards increased phenotypic variance (σ²p) within groups and should be used with care when σ²p of populations differ. Our results indicate that measures of shape give a better estimate of divergence at the underlying quantitative traits loci than measures of size.     

Genetic diversity of oil palm (<Emphasis Type="Italic">Elaeis guineensis</Emphasis> Jacq.) germplasm collections from Africa: implications for improvement and conservation of genetic resources

A total of 723 accessions of oil palm (Elaeis guineensis Jacq.) from 26 populations representing ten countries in Africa and one Deli dura family were screened for allelic variation at seven enzyme loci from six enzyme systems using starch gel electrophoresis. On average, 54.5% of the loci were polymorphic (0.99 criterion). The average and effective number of alleles per locus was 1.80 and 1.35, respectively. Mean expected heterozygosity was 0.184, with values ranging from 0.109 (population 8, Senegal) to 0.261 (population 29, Cameroon). The genetic differentiation among populations was high (F_ST=0.301), indicating high genetic divergence. The calculation of F_ST by geographic zones revealed that the high F_ST was largely due to F_ST among populations in West Africa, suggesting diversifying selection in this region. The mean genetic distance across populations was 0.113. The lowest genetic distance (D) was observed between population 5 from Tanzania and population 7 from the Democratic Republic of the Congo (0.000) and the highest was found between population 4 from Madagascar and population 13 from Sierra Leone (0.568). The total gene flow across oil palm populations was low, with an Nm of 0.576, enhancing genetic structuring, as evident from the high F_ST values. UPGMA cluster analysis revealed three main clusters; the western outlying populations from Senegal and Sierra Leone were in one cluster but separated into two distinct sub-clusters; the eastern outlying populations from Madagascar were in one cluster; the populations from Angola, Cameroon, The Democratic Republic of the Congo, Ghana, Tanzania, Nigeria and Guinea were in one cluster. The Deli dura family seems to be closely related to population 6 from Guinea. Oil palm populations with high genetic diversity—i.e. all of the populations from Nigeria, Cameroon and Sierra Leone, population 6 of Guinea, population 1 of Madagascar and population 2 of Senegal should be used in improvement programmes, whereas for conservation purposes, oil palm populations with high allelic diversity (A_e), which include populations 22 and 29 from Cameroon, populations 39 and 45 from Nigeria, population 6 from Guinea, populations 5 and 13 from Sierra Leone and population 1 from Madagascar should be selected for capturing as much genetic variation as possible.Communicated by D.B. Neale     

Temperature and photoperiod effects on dormancy status and life cycle parameters in Aedes albopictus and Aedes aegypti from subtropical Argentina

Aedes albopictus (Diptera: Culicidae) distribution is bounded to a subtropical area in Argentina, while Aedes aegypti (Diptera: Culicidae) covers both temperate and subtropical regions. We assessed thermal and photoperiod conditions on dormancy status, development time and mortality for these species from subtropical Argentina. Short days (8 light : 16 dark) significantly increased larval development time for both species, an effect previously linked to diapause incidence. Aedes albopictus showed higher mortality than Ae. aegypti at 16 °C under long day treatments (16 light : 8 dark), which could indicate a lower tolerance to a sudden temperature decrease during the summer season. Aedes albopictus showed a slightly higher percentage of dormant eggs from females exposed to a short day, relative to previous research in Brazilian populations. Since we employed more hours of darkness, this could suggest a relationship between day‐length and dormancy intensity. Interestingly, local Ae. aegypti presented dormancy similar to Ae. albopictus, in accordance with temperate populations. The minimum dormancy in Ae. albopictus would not be sufficient to extend its bounded distribution. We believe that these findings represent a novel contribution to current knowledge about the ecophysiology of Ae. albopictus and Ae. aegypti, two species with great epidemiological relevance in this subtropical region.     

Global genetic diversity of Aedes aegypti

Mosquitoes, especially Aedes aegypti, are becoming important models for studying invasion biology. We characterized genetic variation at 12 microsatellite loci in 79 populations of Ae. aegypti from 30 countries in six continents, and used them to infer historical and modern patterns of invasion. Our results support the two subspecies Ae. aegypti formosus and Ae. aegypti aegypti as genetically distinct units. Ae. aegypti aegypti populations outside Africa are derived from ancestral African populations and are monophyletic. The two subspecies co‐occur in both East Africa (Kenya) and West Africa (Senegal). In rural/forest settings (Rabai District of Kenya), the two subspecies remain genetically distinct, whereas in urban settings, they introgress freely. Populations outside Africa are highly genetically structured likely due to a combination of recent founder effects, discrete discontinuous habitats and low migration rates. Ancestral populations in sub‐Saharan Africa are less genetically structured, as are the populations in Asia. Introduction of Ae. aegypti to the New World coinciding with trans‐Atlantic shipping in the 16th to 18th centuries was followed by its introduction to Asia in the late 19th century from the New World or from now extinct populations in the Mediterranean Basin. Aedes mascarensis is a genetically distinct sister species to Ae. aegypti s.l. This study provides a reference database of genetic diversity that can be used to determine the likely origin of new introductions that occur regularly for this invasive species. The genetic uniqueness of many populations and regions has important implications for attempts to control Ae. aegypti, especially for the methods using genetic modification of populations.     

On the Apportionment of Population Structure

Measures of population differentiation, such as F_ST, are traditionally derived from the partition of diversity within and between populations. However, the emergence of population clusters from multilocus analysis is a function of genetic structure (departures from panmixia) rather than of diversity. If the populations are close to panmixia, slight differences between the mean pairwise distance within and between populations (low F_ST) can manifest as strong separation between the populations, thus population clusters are often evident even when the vast majority of diversity is partitioned within populations rather than between them. For any given F_ST value, clusters can be tighter (more panmictic) or looser (more stratified), and in this respect higher F_ST does not always imply stronger differentiation. In this study we propose a measure for the partition of structure, denoted E_ST, which is more consistent with results from clustering schemes. Crucially, our measure is based on a statistic of the data that is a good measure of internal structure, mimicking the information extracted by unsupervised clustering or dimensionality reduction schemes. To assess the utility of our metric, we ranked various human (HGDP) population pairs based on F_ST and E_ST and found substantial differences in ranking order. E_ST ranking seems more consistent with population clustering and classification and possibly with geographic distance between populations. Thus, E_ST may at times outperform F_ST in identifying evolutionary significant differentiation.