Oviposition dynamics of Aedes aegypti in Central Argentina.

Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) is the vector of multiple arboviruses. To evaluate the association between environmental factors and the oviposition activity of Ae. aegypti in Argentina, data on the presence and abundance of eggs were collected using ovitraps, between September of 2018 and May of 2019, in the cities of Villa María, Río Cuarto and Salsipuedes (Córdoba province, Argentina). We analysed the relationships between oviposition and five environmental factors: Temperature, precipitation, vegetation cover, human population density and distance to sites with a potential high density of larval habitats, like cemeteries and trash dumps. Environmental factors' data were collected using satellite image products. The oviposition activity was randomly distributed in three cities. Using generalized linear mixed models, we show that the house where each ovitrap was placed was a source of variability in oviposition, suggesting the relevance of microsite factors and the importance of domestic control actions. Ae. aegypti oviposition was positively correlated with night-time temperature of the previous 3 weeks, and in a context-dependent manner, it was positively correlated with human population density, vegetation cover and precipitation. The consistency and magnitude of these relationships varied between cities, indicating that oviposition is related to a complex system of environmental variables.

May captive populations of Greater Rhea (Rhea americana) act as genetic reservoirs in Argentina?

The Greater Rhea (Rhea americana) is a characteristic bird of the Argentine Pampas. Despite the increasing farming interest of this ratite, their natural populations are progressively decreasing in size and range. The object of this study was to evaluate the status of captive populations as potential genetic reservoirs. Using Inter-Simple Sequence Repeats as molecular markers, levels of genetic variability of F1 individuals from two captive populations were estimated and compared with those of wild populations in the same region. The captive populations were polymorphic for 12.22 and 13.33% of the loci, with a genetic diversity of 0.050. Differences with wild populations were not significant (z=1.79; P>0.05). Therefore, captive populations of rheas in Argentina should not be overlooked as genetic reservoir and source of individuals for reinforcement of natural populations, through reintroduction and translocation.

Genetic relationships among populations of Aedes aegypti from Uruguay and northeastern Argentina inferred from ISSR-PCR data.

Aedes aegypti (L.) (Diptera: Culicidae), the main vector of yellow fever and dengue viruses, was eradicated from Argentina between 1955 and 1963, but reinvaded the country in 1986. In Uruguay, the species was reintroduced in 1997. In this study we used highly polymorphic inter-simple sequence repeats (ISSR) markers to analyse the genetic structure of Ae. aegypti populations from Uruguay and northeastern Argentina to identify possible colonization patterns of the vector. Overall genetic differentiation among populations was high (F(ST) = 0.106) and showed no correlation with geographic distance, which is consistent with the short time since the reintroduction of the species in the area. Differentiation between pairs of Argentine populations (F(ST) 0.072 to 0.221) was on average higher than between Uruguayan populations (F(ST)-0.044 to 0.116). Bayesian estimation of population structure defined four genetic clusters and most populations were admixtures of two of them: Mercedes and Treinta y Tres (Uruguay) were mixtures of clusters 1 and 3; Salto (Uruguay) and Paraná (Argentina) of clusters 1 and 4; Fray Bentos (Uruguay) of clusters 2 and 3, and Gualeguaychú (Argentina) of clusters 2 and 3. Posadas and Buenos Aires in Argentina were fairly genetically homogeneous. Our results suggest that Ae. aegypti recolonized Uruguay from bordering cities in Argentina via bridges over the Uruguay River and also from Brazil.

Current resistance status to temephos in Aedes aegypti from different regions of Argentina.

In Argentina, more than 25,000 cases of dengue were reported in the summer of 2009, even in provinces where the disease was formerly absent. We analysed the susceptibility levels to the larvicide temephos in seven populations of Aedes aegypti, the primary vector of dengue, collected during summer 2007/2008, using the susceptible Rockefeller strain as a control. Although no control failures were observed during the experiment, a majority of the lethal concentration and resistance ratio values indicate an incipient resistance. An integrative program to monitor the resistance of Ae. aegypti to insecticides is needed in the country.

Two different routes of colonization of Aedes aegypti in Argentina from neighboring countries.

Aedes aegypti L. (Diptera, Culicidae) is the main vector of dengue and yellow fever. In Argentina, the species was apparently eradicated approximately in 1964; by 1986, it was reintroduced. To identify different gene pools in geographical populations of the species and to ascertain the possible routes of colonization, we analyzed the diversity of mitochondrial DNA haplotypes in 572 specimens from Argentina and neighboring countries. We found that the restriction fragment length polymorphism-polymerase chain reaction screening of a large DNA fragment including the A+T-rich region was the best strategy to reconstruct the colonization pattern ofAe. aegypti in Argentina. Twenty haplotypes were recognized; levels of genetic similarity varied among populations from different geographical locations. The haplotype network constructed on the basis of genetic distances showed three well differentiated groups. Two of them exhibited a well defined spatial distribution and populations in these groups presented an isolation-by-distance pattern. The persistence of relictual populations after the last eradication campaigns would explain the high levels of haplotype diversity and the presence of exclusive haplotypes in urban centers from northwestern Argentina. Eastern Argentine populations showed one prevalent haplotype, also predominant in Brazil and Paraguay. Our results highlight the need for efficient surveys and control campaigns, given the strong effect of land trade on genetic exchange among mosquito populations from Argentina and neighboring countries where dengue is endemic.

Gene flow in Aedes albifasciatus (Diptera:Culicidae) from central Argentina.

To estimate gene flow among populations of the floodwater mosquito Aedes albifasciatus, allozymic frequencies were analyzed at 16 loci in samples from 6 localities in central Argentina. Expected mean heterozygosity ranged from 0.057 to 0.137. FST was significant for 5 of 11 polymorphic loci; mean value was 0.024, which gave an Nm of 50.96. Levels of genetic identity among samples were high (IN between 0.9815 and 0.9988) even between populations 500 km apart. However, there was a significant correlation between genetic and geographic distance, which indicated that although the 6 populations were at approximate equilibrium because of gene flow, this was restricted by distance. The distribution of allele frequencies possibly reflected the present status of a single large population occupying this region in the past. When geological change separated breeding areas, a moderate level of gene flow may have resulted in the current genetic structure of the populations.

Genetic structure of Aedes albifasciatus (Diptera:Culicidae) from a marsh ecosystem in Córdoba, Argentina.

Allozymic variability was analyzed for 8 samples of the floodwater mosquito Aedes albifasciatus (Macquart) obtained in October and November 1993 from marsh and pasture habitats along the Mar Chiquita ecosystem in central Argentina. Expected mean heterozygosity among 17 loci was low. Fls values were negative for all polymorphic loci, and mean FST values were low, indicating high levels of gene exchange and the absence of subpopulations within the 25-km-wide study area. Genetic homogeneity throughout the area suggests that outcrossing occurs frequently as a result of dispersal among sampled sites.

Genetic relationships among Aedes aegypti (Diptera: Culicidae) populations from Argentina using random amplified polymorphic DNA polymerase chain reaction markers.

Random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) polymorphism was analyzed in five Aedes aegypti (L.) populations from Argentina and one from Puerto Rico to estimate levels of intraspecific polymorphism and genetic relatedness. Allele frequencies were estimated assuming that RAPD products segregate as dominants and that genotype frequencies at those loci are in Hardy-Weinberg equilibrium. Mean expected heterozygosity (He) was 0.350; F(ST) values were significant at all loci except one, supporting the usefulness of the fragments used here to discriminate among populations. Rogers' genetic similarity between samples ranged from 0.806 to 0.621. The population from Puerto Rico was the most different from the Argentina populations. Considering that Ae. aegypti eggs, larvae, and pupae can be transported easily, relationships among the Argentinian populations may reflect the routes and intensity of commercial transit.

Culex species (Diptera: Culicidae) from central Argentina: identification by electrophoretic zymograms and genetic relationships.

Starch gel electrophoretic zymograms were used for the taxonomic separation of mosquitoes of the genus Culex, possible vectors of encephalitis in Argentina. Catalase, hexokinase, malic enzyme, isocitrate and malate dehydrogenases, and leucine aminopeptidase were species markers that allowed the clear identification of individual Culex apicinus Philippi, Cx. bidens Dyar, Cx. brethesi Dyar, Cx. declarator Dyar and Knab, Cx. dolosus Arribalzaga, Cx. maxi Dyar, Cx. quinquefasciatus Say, Cx. saltanensis Dyar, and Cx. tatoi Casal & García. Intraspecific polymorphism was revealed but did not preclude species separation. On the basis of allele frequencies, an index of genetic distance between species was calculated. Genetic affinities determined by electrophoretic data agreed with taxonomic affinities ascertained by conventional systematics. Thus, electrophoretic zymograms proved to be a powerful tool for the study of the genus Culex in Argentina.

Genetic structure of Aedes albifasciatus (Diptera: Culicidae) populations in central Argentina determined by random amplified polymorphic DNA-polymerase chain reaction markers.

The floodwater mosquito, Aedes albifasciatus (Macquart), is the main vector of western equine encephalomyelitis virus in Argentina. Previous studies on the genetic structure of this species using allozymes showed low levels of polymorphism, absence of subpopulations at distinct habitats, and moderate differentiation among localities separated up to 500 km. To examine gene flow using other genetic methods, we analyzed random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) polymorphism in 28 presumptive loci of Ae. albifasciatus from 6 populations in central Argentina. Allele frequencies were estimated assuming that RAPD products segregate as dominants and that genotype frequencies at those loci are in Hardy-Weinberg equilibrium. Expected heterozygosity ranged between 0.19 and 0.31, approximately 3 times the value obtained on the basis of the 16 allozymic loci studied previously. Four of the populations formed a single panmictic unit. Allele frequencies in populations occupying different phytogeographic regions gave significant FST values at 5 loci. Effective migration rates among populations estimated from FST ranged from 2.3 to 9.0. The results support the existence of a north-south cline.

Allozymic polymorphism in Aedes aegypti populations from Argentina.

In Argentina, reinfestation with Aedes aegypti was registered in 1986. At present, the mosquito is well established in 10 provinces, from Buenos Aires up to the country's northern frontiers. This paper presents estimates of genetic variability in Ae. aegypti populations from central Argentina and determinations of genetic distances among them. We analyzed allozymic frequencies at 11 loci in samples from 3 localities. The proportion of polymorphic loci varied between 27.3 and 63.6. Expected mean heterozygosity ranged from 0.090 to 0.161 and Rogers' similarity among samples ranged between 0.909 and 0.958. The lack of relationship between genetic and geographic distances is in agreement with a recent colonization of the studied area. The mean Wright's coefficient FST value (0.065) indicates low levels of genetic differentiation among populations from different localities. Given the recent reinfestation with this mosquito in Argentina, the high levels of polymorphism found could indicate multiple introductions of representative samples from genetically different subpopulations.

Restricted gene flow in Calomys musculinus (Rodentia, Muridae), the natural reservoir of Junin virus.

Random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) markers were used to evaluate the relative contribution of gene flow as a determinant of the population genetic structure of the wild rodent Calomys musculinus (the reservoir of Argentine hemorrhagic fever [AHF]) in central Argentina. One hundred eighty-seven individuals from 13 populations (9 of them from the endemic zone of AHF and 5 from areas outside it) were analyzed using 78 polymorphic RAPD loci. Genetic variation within each population was high; each individual was characterized by a unique RAPD phenotype. C. musculinus populations showed a moderate to high genetic subdivision and a random pattern of differentiation. Populations separated by the same geographic distance showed very different degrees of genetic divergence. The results indicate that populations of C. musculinus have colonized their present ranges relatively recently and differentiation by genetic drift has proceeded faster than homogenization by gene flow at the macrogeographic scale analyzed (10-700 km).

Patterns of evolution in Graomys griseoflavus (Rodentia, Cricetidae). I. Protein polymorphism in populations with different chromosome numbers.

Protein polymorphism has been studied by means of starch gel electrophoresis of tissue extracts in three population samples of Graomys griseoflavus collected at different sites in central-west Argentina. Individuals from two of the samples had chromosomal number 2n = 42 and those from the other sample, 2n = 38, 37 or 36. A total of 28 loci were analyzed. High levels of variability were observed in three samples (P ranging between 0.46 and 0.66; H (epsilon) from 0.160 to 0.188). Genetic distance values between populations with different chromosome numbers were 0.088 and 0.093. Tests in the laboratory showed the existence of post-zygotic reproductive isolation between animals with 2n = 42 and those with 2n = 38, 37 or 36.

Inheritance of random amplified polymorphic DNA (RAPD-PCR) markers and their use in population genetic studies of Calomys musculinus (Rodentia, Muridae), the reservoir of Argentine hemorrhagic fever.

In order to assess the reliability of RAPD markers in the estimation of the genetic structure of natural populations of the murid rodent Calomys musculinus (reservoir of Junin virus, ethiological agent of Argentine Hemorrhagic Fever), we have analyzed the heritability of RAPD bands in 10 parents and their offspring (33 individuals). Fourteen out of a total of 119 bands obtained were absent in the parental patterns, but consistently amplified in offspring from some families. These bands can be eliminated from analyses. Overall degree of band sharing between individuals, including non-parental bands, correctly grouped members of a family in the same cluster in a UPGMA tree, with a high bootstrap percentage. Results support the usefulness of RAPDs as hereditable markers. One hundred polymorphic RAPD loci were identified in three natural populations of C. musculinus. Mean expected heterozygosity in three natural populations ranged from 0.206 to 0.220. Allele frequency based and phenotype based measures of genetic differentiation among natural populations of C. musculinus gave similar results (Weir and Cockerham's theta = 0.133; Excoffier et al.'s phi = 0.127). These values were considerably higher than those found previously using allozymes as genetic markers, and are compatible with moderate to low levels of gene flow among populations.

Oligoryzomys flavescens (Rodentia, Muridae): gene flow among populations from central-eastern Argentina.

In species acting as hosts of infectious agents, the extent of gene flow between populations is of particular interest because the expansion of different infectious diseases is usually related to the dispersal of the host. We have estimated levels of gene flow among populations of the sigmodontine rodent Oligoryzomys flavescens, in which high titers of antibodies have been detected for a Hantavirus in Argentina that produces a severe pulmonary syndrome. Enzyme polymorphism was studied by means of starch gel electrophoresis in 10 populations from the area where human cases of Hantavirus have occurred. Genetic differentiation between populations was calculated from FST values with the equation Nm = [(1/FST) - 1]/4. To assess the relative importance of current gene flow and historical associations between populations, the relationship of population pairwise log Nm and log geographic distance was examined. Low FST (mean = 0.038) and high Nm (15.27) values suggest high levels of gene flow among populations. The lack of an isolation by distance pattern would indicate that this species has recently colonized the area. The northernmost population, located on the margin of a great river, shows very high levels of gene flow with the downstream populations despite the large geographic distances. Passive transport of animals down the river by floating plants would promote unidirectional gene flow. This fact and the highest mean heterozygosity of that northernmost population suggest it is a center of dispersal within the species' range.

Heterozygosity and gene flow in populations of Calomys laucha (Rodentia, Cricetidae).

Enzyme polymorphism was studied by means of starch gel electrophoresis on five population samples of Calomys laucha collected in different sites and seasons. C. laucha, a cricetid rodent inhabiting preferentially cultivated fields in the central-eastern plains of Argentina, is a reservoir-host of Junin virus, agent of Argentine hemorrhagic fever. Results show high levels of genic variability in all the samples (P from 62.50 to 77.27; H from 0.118 to 0.163) and low genetic distance among populations (D from 0.0024 to 0.0167). Estimations of gene flow (mean Nm = 10.78) indicate a high migration capability of the species and the possibility of further dispersal of Junin virus.

Enzyme polymorphism in a population of Calomys musculinus (Rodentia, Cricetidae).

NAD-linked lactate malate, glycerophosphate, alcohol and nonspecific dehydrogenases, aspartate aminotransferases, and soluble esterases from extracts of tissues of individuals from a wild population of Calomys musculinus (Rodentia, Cricetidae) have been analyzed by means of starch gel electrophoresis and specific staining. Allelic frequencies and heterozygosity have been determined. Mendelian inheritance of some of the variants detected was confirmed by breeding experiments. Ten out of fifteen (66.6%) of the genetic loci investigated presented polymorphism. Mean heterozygosity per locus was very high (H = 0.2014, SE 0.046).