Pioneer study of population genetics of Rhodnius ecuadoriensis (Hemiptera: Reduviidae) from the central coastand southern Andean regions of Ecuador

Abstract

Effective control of Chagas disease vector populations requires a good understanding of the epidemiological components, including a reliable analysis of the genetic structure of vector populations. Rhodnius ecuadoriensis is the most widespread vector of Chagas disease in Ecuador, occupying domestic, peridomestic and sylvatic habitats. It is widely distributed in the central coast and southern highlands regions of Ecuador, two very different regions in terms of bio-geographical characteristics. To evaluate the genetic relationship among R. ecuadoriensis populations in these two regions, we analyzed genetic variability at two microsatellite loci for 326 specimens (n=122 in Manabí and n=204 in Loja) and the mitochondrial cytochrome b gene (Cyt b) sequences for 174 individuals collected in the two provinces (n=73 and=101 in Manabí and Loja respectively). The individual samples were grouped in populations according to their community of origin. A few populations presented positive F_IS, possible due to Wahlund effect. Significant pairwise differentiation was detected between populations within each province for both genetic markers, and the isolation by distance model was significant for these populations. Microsatellite markers showed significant genetic differentiation between the populations of the two provinces. The partial sequences of the Cyt b gene (578bp) identified a total of 34 haplotypes among 174 specimens sequenced, which translated into high haplotype diversity (Hd=0.929). The haplotype distribution differed among provinces (significant Fisher's exact test). Overall, the genetic differentiation of R. ecuadoriensis between provinces detected in this study is consistent with the biological and phenotypic differences previously observed between Manabí and Loja populations. The current phylogenetic analysis evidenced the monophyly of the populations of R. ecuadoriensis within the R. pallescens species complex; R. pallescens and R. colombiensis were more closely related than they were to R. ecuadoriensis.

Keywords: Chagas disease; Cytochrome b; Ecuador; Microsatellite markers; Panmictic unit; Population genetics; Rhodnius ecuadoriensis; Rhodnius pallescens species complex.

Fig. 1.

Location of samples. Map of Ecuador (in box) and location of the communities where the R. ecuadoriensis were collected in the central coast (Manabí province) and southern Andean (Loja province) regions. The codes in the maps indicate the communities. Manabí province: MBJ, Bejuco; MCA, Cruz Alta; MJM, Jesús María; MMB, Maconta Abajo; MNA, Naranjo Adentro; MZP, Zapallo, MLE, La Encantada. Loja province: LAB, Algarobillo; LAH, Ashimingo; LBR, Bramaderos; LCG, La Ciénega; LEX, La Extensa; LGL, Galápagos; LHY, El Huayco; LND, Naranjo Dulce; LSS, Santa Rosa; LST, Santa Ester; LTR, Tuburo, LLM, El Limón.

Fig. 2.

Result of STRUCTURE analyses. a) Delta K value (Delta K = mean ((|L″(K)|)/SD(L(K))) plotted for K values from 1 to 17 in Structure Harvester software for R. ecuadoriensis. b) Mean of estimated Ln probability of data, plotted for K values from 1 to 17 in Structure Harvester software for R. ecuadoriensis. c) Bar plot estimates of membership coefficients for each R. ecuadoriensis individual, in each of two inferred clusters (k = 2; best fitting with the current set of data). Each individual in the data set is represented by a single vertical line, which is partitioned into different colored segments representing the individual membership estimate in each of the inferred clusters. The current bar plot is one of those obtained with the admixture model and the prior location option, the other options being left as default. Each number in the bar plot correspond to one population: 1, LAB; 2, LAH; 3, LBR; 4, LCG; 5, LEX; 6, LGL; 7, LHY; 8, LND; 9, LSS; 10, LST; 11, LTR; 12 MBJ; 13, MCA; 14, MJM; 15, MMB; 16 MNA; 17, MZP.

Fig. 3.

Cyt b gene median joining network. The network was resolved from 34 haplotypes found in R. ecuadoriensis collected in two provinces (Manabí and Loja) and two haplotypes of R. pallescens used as the outgroup. Black circles are median vectors (mv) that are hypothesized sequences not found in the sample and required to connect the existing haplotypes. The other cycles are nodes corresponding to one haplotype found in the current data set; their size is proportional to the number of haplotypes that form the node. Blue nodes are haplotypes of R. pallescens, green and orange nodes are R. ecuadoriensis haplotypes from Manabí and Loja, respectively. a) General figure of the network; b) enlarged figure that shows only the R. ecuadoriensis haplotypes.

Fig. 4.

Cytochrome b gene phylogenetic analysis using maximum likelihood method. The analysis includes the current R. ecuadoriensis haplotypes (from Loja and Manabí provinces) and GenBank sequences of Rhodnius genus with their accession number. The alignment was 578 bp long and the analysis included 62 nucleotide sequences. The best model of evolution for this data set of sequences was Hasegawa-kishino-Yano with a discrete gamma distribution and the I option (HKI + G + I). The values next to the branches represent the percentage of trees in which the associated sequences clustered together (only values N 75% are shown).