Genetic diversity and phylogenetic relationships of tsetse flies of the palpalis group in Congo Brazzaville based on mitochondrial cox1 gene sequences

Genetic diversity, phylogenetic and phylogeographic analysis of Anopheles culicifacies species complex using ITS2 and COI sequences

Anopheles culicifacies is the major vector of malaria in Sri Lanka and the Indian subcontinent which is characterized as a species complex with five sibling species provisionally designated as A, B, C, D and E. The current study was carried out to understand the phylogenetic and phylogeographic relationships between the sibling species of the species complex while observing their genetic diversity and genetic differentiation. Thirty-five ITS2 and seventy-seven COI sequences of An. culicifacies species complex reported from different geographical locations of Asia and China at the NCBI public database were used for the analysis. Bayesian likelihood trees were generated for the phylogenetic analysis. The divergence of the species complex was obtained from the Bayesian phylogeographic model in BEAST. There were two clades of the sibling species of An. culicifacies species complex as A, D and B, C and E in both phylogenetic and phylogeographic analysis using ITS2 sequences. Based on the highly divergent COI sequences and the high mutation rate of the mitochondrial genome, there were four and three clades in both phylogenetic and phylogeographic analysis using COI sequences. The diversification of An. culicifacies species complex was obtained as ranging from 20.25 to 24.12 Mya and 22.37 to 26.22 Mya based on ITS2 and COI phylogeographic analysis respectively. There was a recent diversification of the sibling species A and D than the sibling species B, C and E. Low haplotype diversity was observed in the sequences reported from Sri Lanka in both ITS2 and COI analysis that can be due to bottlenecks resulting from the intense malaria control efforts. A high genetic differentiation was achieved for some populations due to the large geographical distance. The high genetic diversity based on the five sibling species implies the possibility of maintaining a relatively high effective population size despite the vector control efforts.

Molecular characterization and genetic diversity of three Stomoxys flies S. bengalensis, S. calcitrans, and S. sitiens (Diptera: Muscidae) in Central Thailand

Stomoxys flies (Diptera: Muscidae) are hematophagous ectoparasites of medical and veterinary importance. In this study, three Stomoxys species, i.e. S. bengalensis, S. calcitrans, and S. sitiens, were collected from three provinces in Central Thailand with the aim of estimating the genetic divergence between species, for species identification, as well as within species, for a genetic diversity study based on the cytochrome c oxidase subunit I (COI) gene. Our results showed that the average intraspecific genetic divergences of Stomoxys flies ranged from 0.11% in S. sitiens to 0.98% in S. calcitrans, whereas the average interspecific genetic divergences ranged from 5.24% between S. sitiens and S. bengalensis to 6.69% between S. calcitrans and S. bengalensis. In addition, there was no overlap between the intraspecific and interspecific genetic divergences. The COI sequence analysis revealed a high haplotype diversity and low nucleotide diversity, reflecting a rapid population expansion after past bottlenecks. Moreover, there was no significant difference (P > 0.05) in the pairwise population differentiation (Fst) among Stomoxys flies in Central Thailand, because of the lack of natural barriers, thus allowing genetic exchange between them. The monitoring of the haplotype network revealed that two lineages of S. calcitrans in Central Thailand were distributed in all study areas, including the Nakhon Pathom, Pathum Thani, and Saraburi Provinces. These findings may improve our understanding of the genetic patterns of these three Stomoxys flies, as well as the underlying biological mechanisms, which is knowledge that can be used for further effective control of these flies.

Population Structure and Migration Patterns of the Tsetse Fly Glossina fuscipes in Congo-Brazzaville

Tsetse flies of the palpalis group, particularly Glossina fuscipes, are the main vectors of human African trypanosomiasis or sleeping sickness in Congo-Brazzaville. They transmit the deadly human parasite, Trypanosoma brucei gambiense and other trypanosomes that cause animal trypanosomiasis. Knowledge on diversity, population structure, population size, and gene flow is a prerequisite for designing effective tsetse control strategies. There is limited published information on these parameters including migration patterns of G. fuscipes in Congo-Brazzaville. We genotyped 288 samples of G. fuscipes from Bomassa (BMSA), Bouemba (BEMB), and Talangai (TLG) locations at 10 microsatellite loci and determined levels of genetic diversity, differentiation, structuring, and gene flow among populations. We observed high genetic diversity in all three localities. Mean expected heterozygosity was 0.77 ± 0.04, and mean allelic richness was 11.2 ± 1.35. Deficiency of heterozygosity was observed in all populations with positive and significant F IS values (0.077-0.149). Structure analysis revealed three clusters with genetic admixtures, evidence of closely related but potentially different taxa within G. fuscipes. Genetic differentiation indices were low but significant (F ST = 0.049, P < 0.05), indicating ongoing gene flow countered with a stronger force of drift. We recorded significant migration from all the three populations, suggesting exchange of genetic information between and among locations. Ne estimates revealed high and infinite population sizes in BEMB and TLG. These critical factors should be considered when planning area-wide tsetse control interventions in the country to prevent resurgence of tsetse from relict populations and/or reinvasion of cleared habitats.