NRU :: Browsing by Author "Caccone, Adalgisa"

Browsing by Author "Caccone, Adalgisa"

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Analysis of Multiple Tsetse Fly Populations in Uganda Reveals Limited Diversity and Species-Specific Gut Microbiota
(Applied and Environmental Microbiology, 2014) Aksoy, Emre; Telleria, Erich L.; Echodu, Richard; Wu, Yineng; Okedi, Loyce M.; Weiss, Brian L.; Aksoy, Serap; Caccone, Adalgisa
The invertebrate microbiome contributes to multiple aspects of host physiology, including nutrient supplementation and immune maturation processes. We identified and compared gut microbial abundance and diversity in natural tsetse flies from Uganda using five genetically distinct populations of Glossina fuscipes fuscipes and multiple tsetse species (Glossina morsitans morsitans, G. f. fuscipes, and Glossina pallidipes) that occur in sympatry in one location. We used multiple approaches, including deep sequencing of the V4 hypervariable region of the 16S rRNA gene, 16S rRNA gene clone libraries, and bacterium-specific quantitative PCR (qPCR), to investigate the levels and patterns of gut microbial diversity from a total of 151 individuals. Our results show extremely limited diversity in field flies of different tsetse species. The obligate endosymbiont Wigglesworthia dominated all samples (>99%), but we also observed wide prevalence of low-density Sodalis (tsetse’s commensal endosymbiont) infections (<0.05%). There were also several individuals (22%) with high Sodalis density, which also carried coinfections with Serratia. Albeit in low density, we noted differences in microbiota composition among the genetically distinct G. f. fuscipes flies and between different sympatric species. Interestingly, Wigglesworthia density varied in different species (104 to 106 normalized genomes), with G. f. fuscipes having the highest levels. We describe the factors that may be responsible for the reduced diversity of tsetse’s gut microbiota compared to those of other insects. Additionally, we discuss the implications of Wigglesworthia and Sodalis density variations as they relate to trypanosome transmission dynamics and vector competence variations associated with different tsetse species.
Evidence of temporal stability in allelic and mitochondrial haplotype diversity in populations of Glossina fuscipes fuscipes (Diptera: Glossinidae) in northern Uganda
(Parasites & Vectors, 2016) Opiro, Robert; Saarman, Norah P.; Echodu, Richard; Opiyo, Elizabeth A.; Dion, Kirstin; Halyard, Alexis; Aksoy, Serap; Caccone, Adalgisa
Glossina fuscipes fuscipes is a tsetse species of high economic importance in Uganda where it is responsible for transmitting animal African trypanosomiasis (AAT) and both the chronic and acute forms of human African trypanosomiasis (HAT). We used genotype data from 17 microsatellites and a mitochondrial DNA marker to assess temporal changes in gene frequency for samples collected between the periods ranging from 2008 to 2014 in nine localities spanning regions known to harbor the two forms of HAT in northern Uganda. Results: Our findings suggest that the majority of the studied populations in both HAT foci are genetically stable across the time span sampled. Pairwise estimates of differentiation using standardized FST and Jost’s DEST between time points sampled for each site were generally low and ranged between 0.0019 and 0.1312 for both sets of indices. We observed the highest values of FST and DEST between time points sampled from Kitgum (KT), Karuma (KR), Moyo (MY) and Pader (PD), and the possible reasons for this are discussed. Effective population size (Ne) estimates using Waple’s temporal method ranged from 103 (95 % CI: 73–138) in Kitgum to 962 (95 % CI: 669–1309) in Oculoi (OC). Additionally, evidence of a bottleneck event was detected in only one population at one time point sampled; Aminakwach (AM-27) from December 2014 (P < 0.03889). Conclusion: Findings suggest general temporal stability of tsetse vectors in foci of both forms of HAT in northern Uganda. Genetic stability and the moderate effective population sizes imply that a re-emergence of vectors from local residual populations missed by control efforts is an important risk. This underscores the need for more sensitive sampling and monitoring to detect residual populations following control activities.
Genetic diversity and population structure of the tsetse fly Glossina fuscipes fuscipes (Diptera: Glossinidae) in Northern Uganda: Implications for vector control
(PLOS Neglected Tropical Diseases, 2017) Opiro, Robert; Saarman, Norah P.; Echodu, Richard; Opiyo, Elizabeth A.; Dion, Kirstin; Halyard, Alexis; Dunn, Augustine W.; Aksoy, Serap; Caccone, Adalgisa
Uganda is the only country where the chronic and acute forms of human African Trypanosomiasis (HAT) or sleeping sickness both occur and are separated by < 100 km in areas north of Lake Kyoga. In Uganda, Glossina fuscipes fuscipes is the main vector of the Trypanosoma parasites responsible for these diseases as well for the animal African Trypanosomiasis (AAT), or Nagana. We used highly polymorphic microsatellite loci and a mitochondrial DNA (mtDNA) marker to provide fine scale spatial resolution of genetic structure of G. f. fuscipes from 42 sampling sites from the northern region of Uganda where a merger of the two disease belts is feared. Based on microsatellite analyses, we found that G. f. fuscipes in northern Uganda are structured into three distinct genetic clusters with varying degrees of interconnectivity among them. Based on genetic assignment and spatial location, we grouped the sampling sites into four genetic units corresponding to northwestern Uganda in the Albert Nile drainage, northeastern Uganda in the Lake Kyoga drainage, western Uganda in the Victoria Nile drainage, and a transition zone between the two northern genetic clusters characterized by high level of genetic admixture. An analysis using HYBRIDLAB supported a hybrid swarm model as most consistent with tsetse genotypes in these admixed samples. Results of mtDNA analyses revealed the presence of 30 haplotypes representing three main haplogroups, whose location broadly overlaps with the microsatellite defined clusters. Migration analyses based on microsatellites point to moderate migration among the northern units located in the Albert Nile, Achwa River, Okole River, and Lake Kyoga drainages, but not between the northern units and the Victoria Nile drainage in the west. Effective population size estimates were variable with low to moderate sizes in most populations and with evidence of recent population bottlenecks, especially in the northeast unit of the Lake Kyoga drainage. Our microsatellite and mtDNA based analyses indicate that G. f. fuscipes movement along the Achwa and Okole rivers may facilitate northwest expansion of the Rhodesiense disease belt in Uganda. We identified tsetse migration corridors and recommend a rolling carpet approach from south of Lake Kyoga northward to minimize disease dispersal and prevent vector re-colonization. Additionally, our findings highlight the need for continuing tsetse monitoring efforts during and after control.
Genetic Diversity and Population Structure of Trypanosoma brucei in Uganda: Implications for the Epidemiology of Sleeping Sickness and Nagana
(PLoS neglected tropical diseases, 2015) Echodu, Richard; Sistrom, Mark; Bateta, Rosemary; Murilla, Grace; Okedi, Loyce; Aksoy, Serap; Enyioha, Chineme; Enyaru, John; Opiyo, Elizabeth; Gibson, Wendy; Caccone, Adalgisa
While Human African Trypanosomiasis (HAT) is in decline on the continent of Africa, the disease still remains a major health problem in Uganda. There are recurrent sporadic outbreaks in the traditionally endemic areas in south-east Uganda, and continued spread to new unaffected areas in central Uganda. We evaluated the evolutionary dynamics underpinning the origin of new foci and the impact of host species on parasite genetic diversity in Uganda. We genotyped 269 Trypanosoma brucei isolates collected from different regions in Uganda and southwestern Kenya at 17 microsatellite loci, and checked for the presence of the SRA gene that confers human infectivity to T. b. rhodesiense. Results Both Bayesian clustering methods and Discriminant Analysis of Principal Components partition Trypanosoma brucei isolates obtained from Uganda and southwestern Kenya into three distinct genetic clusters. Clusters 1 and 3 include isolates from central and southern Uganda, while cluster 2 contains mostly isolates from southwestern Kenya. These three clusters are not sorted by subspecies designation (T. b. brucei vs T. b. rhodesiense), host or date of collection. The analyses also show evidence of genetic admixture among the three genetic clusters and long-range dispersal, suggesting recent and possibly on-going gene flow between them. Conclusions Our results show that the expansion of the disease to the new foci in central Uganda occurred from the northward spread of T. b. rhodesiense (Tbr). They also confirm the emergence of the human infective strains (Tbr) from non-infective T. b. brucei (Tbb) strains of different genetic backgrounds, and the importance of cattle as Tbr reservoir, as confounders that shape the epidemiology of sleeping sickness in the region.
Genetically Distinct Glossina fuscipes fuscipes Populations in the Lake Kyoga Region of Uganda and Its Relevance for Human African Trypanosomiasis
(BioMed research international, 2013) Echodu, Richard; Sistrom, Mark; Hyseni, Chaz; Enyaru, John; Okedi, Loyce; Aksoy, Serap; Caccone, Adalgisa
Tsetse flies (Glossina spp.) are the sole vectors of Trypanosoma brucei—the agent of human (HAT) and animal (AAT) trypanosomiasis. Glossina fuscipes fuscipes (Gff ) is the main vector species in Uganda—the only country where the two forms of HAT disease (rhodesiense and gambiense) occur, with gambiense limited to the northwest. Gff populations cluster in three genetically distinct groups in northern, southern, and western Uganda, respectively, with a contact zone present in central Uganda. Understanding the dynamics of this contact zone is epidemiologically important as the merger of the two diseases is amajor health concern.We used mitochondrial and microsatellite DNA data fromGff samples in the contact zone to understand its spatial extent and temporal stability.We show that this zone is relatively narrow, extending through central Uganda alongmajor rivers with south to north introgression but displaying no sex-biased dispersal. Lack of obvious vicariant barriers suggests that either environmental conditions or reciprocal competitive exclusion could explain the patterns of genetic differentiation observed. Lack of admixture between northern and southern populations may prevent the sympatry of the two forms of HAT disease, although continued control efforts are needed to prevent the recolonization of tsetse-free regions by neighboring populations.
Genome-wide association of trypanosome infection status in the tsetse fly Glossina fuscipes, the major vector of African trypanosomiasis in Uganda
(Research Square, 2022) Saarman, Norah; Son, Jae Hak; Zhao, Hongyu; Cosme, Luciano; Kong, Yong; Li, Mo; Wang, Shiyu; Weiss, Brian; Echodu, Richard; Opiro, Robert; Aksoy, Serap; Caccone, Adalgisa
The primary vector of the trypanosome parasite causing human and animal African trypanosomiasis in Uganda is the riverine tsetse fly Glossina fuscipes fuscipes (Gff). We conducted a genome-wide association (GWA) analysis with field-caught Gff. To increase statistical power, we first improved the Gff genome assembly with whole genome 10X Chromium sequencing, used ddRAD-seq to identify autosomal versus sex-chromosomal regions of the genome with data from 96,965 SNPs, and conducted a GWA with a subset of 50,960 autosomal SNPs from 351 flies. Results assigned a full third of the genome to the sex chromosome, suggested possible sex-chromosome aneuploidy in Gff, and identified a single autosomal SNP to be highly associated with trypanosome infection. The top SNP was ~ 1200 bp upstream of the gene lecithin cholesterol acyltransferase (LCAT), an important component of the molecular pathway that initiates trypanosome lysis and protection in mammals. Results indicate that variation upstream of LCAT and/or linked genetic elements are associated with trypanosome infection susceptibility in Gff. This suggests that there may be naturally occurring genetic variation in Gff that can protect against trypanosome infection, thereby paving the way for targeted research into novel vector control strategies that can promote parasite resistance in natural populations.
High Levels of Genetic Differentiation between Ugandan Glossina fuscipes fuscipes Populations Separated by Lake Kyoga
(PLoS Neglected Tropical Diseases, 2008) Abila, Patrick P.; Slotman, Michel A.; Parmakelis, Aristeidis; Dion, Kirstin B.; Robinson, Alan S.; Muwanika, Vincent B.; Enyaru, John C. K.; Lokedi, Loyce M.; Aksoy, Serap; Caccone, Adalgisa
Glossina fuscipes fuscipes is the major vector of human African trypanosomiasis, commonly referred to as sleeping sickness, in Uganda. In western and eastern Africa, the disease has distinct clinical manifestations and is caused by two different parasites: Trypanosoma brucei rhodesiense and T. b. gambiense. Uganda is exceptional in that it harbors both parasites, which are separated by a narrow 160-km belt. This separation is puzzling considering there are no restrictions on the movement of people and animals across this region. Methodology and Results: We investigated whether genetic heterogeneity of G. f. fuscipes vector populations can provide an explanation for this disjunct distribution of the Trypanosoma parasites. Therefore, we examined genetic structuring of G. f. fuscipes populations across Uganda using newly developed microsatellite markers, as well as mtDNA. Our data show that G. f. fuscipes populations are highly structured, with two clearly defined clusters that are separated by Lake Kyoga, located in central Uganda. Interestingly, we did not find a correlation between genetic heterogeneity and the type of Trypanosoma parasite transmitted. Conclusions: The lack of a correlation between genetic structuring of G. f. fuscipes populations and the distribution of T. b. gambiense and T. b. rhodesiense indicates that it is unlikely that genetic heterogeneity of G. f. fuscipes populations explains the disjunct distribution of the parasites. These results have important epidemiological implications, suggesting that a fusion of the two disease distributions is unlikely to be prevented by an incompatibility between vector populations and parasite.
Implications of Microfauna-Host Interactions for Trypanosome Transmission Dynamics in Glossina fuscipes fuscipes in Uganda
(Applied and Environmental Microbiology, 2012) Alam, Uzma; Hyseni, Chaz; Symula, Rebecca E.; Brelsfoard, Corey; Wu, Yineng; Kruglov, Oleg; Wang, Jingwen; Echodu, Richard; Alioni, Victor; Okedi, Loyce M.; Caccone, Adalgisa; Aksoya, Serap
Tsetse flies (Diptera: Glossinidae) are vectors for African trypanosomes (Euglenozoa: kinetoplastida), protozoan parasites that cause African trypanosomiasis in humans (HAT) and nagana in livestock. In addition to trypanosomes, two symbiotic bacteria (Wigglesworthia glossinidia and Sodalis glossinidius) and two parasitic microbes, Wolbachia and a salivary gland hypertrophy virus (SGHV), have been described in tsetse. Here we determined the prevalence of and coinfection dynamics between Wolbachia, trypanosomes, and SGHV in Glossina fuscipes fuscipes in Uganda over a large geographical scale spanning the range of host genetic and spatial diversity. Using a multivariate analysis approach, we uncovered complex coinfection dynamics between the pathogens and statistically significant associations between host genetic groups and pathogen prevalence. It is important to note that these coinfection dynamics and associations with the host were not apparent by univariate analysis. These associations between host genotype and pathogen are particularly evident for Wolbachia and SGHV where host groups are inversely correlated for Wolbachia and SGHV prevalence. On the other hand, trypanosome infection prevalence is more complex and covaries with the presence of the other two pathogens, highlighting the importance of examining multiple pathogens simultaneously before making generalizations about infection and spatial patterns. It is imperative to note that these novel findings would have been missed if we had employed the standard univariate analysis used in previous studies. Our results are discussed in the context of disease epidemiology and vector control.
Patterns of Genome-Wide Variation in Glossina fuscipes fuscipes Tsetse Flies from Uganda
(Genes, Genomes, Genetics, 2016) Gloria-Soria, Andrea; Dunn, W. Augustine; Telleria, Erich L.; Evans, Benjamin R.; Okedi, Loyce; Echodu, Richard; Warren, Wesley C.; Montague, Michael J.; Aksoy, Serap; Caccone, Adalgisa
The tsetse fly Glossina fuscipes fuscipes (Gff) is the insect vector of the two forms of Human African Trypanosomiasis (HAT) that exist in Uganda. Understanding Gff population dynamics, and the underlying genetics of epidemiologically relevant phenotypes is key to reducing disease transmission. Using ddRAD sequence technology, complemented with whole-genome sequencing, we developed a panel of 73,000 single-nucleotide polymorphisms (SNPs) distributed across the Gff genome that can be used for population genomics and to perform genome-wide-association studies. We used these markers to estimate genomic patterns of linkage disequilibrium (LD) in Gff, and used the information, in combination with outlier-locus detection tests, to identify candidate regions of the genome under selection. LD in individual populations decays to half of its maximum value (r2 max/2) between 1359 and 2429 bp. The overall LD estimated for the species reaches r2 max/2 at 708 bp, an order of magnitude slower than in Drosophila. Using 53 infected (Trypanosoma spp.) and uninfected flies from four genetically distinct Ugandan populations adapted to different environmental conditions, we were able to identify SNPs associated with the infection status of the fly and local environmental adaptation. The extent of LD in Gff likely facilitated the detection of loci under selection, despite the small sample size. Furthermore, it is probable that LD in the regions identified is much higher than the average genomic LD due to strong selection. Our results show that even modest sample sizes can reveal significant genetic associations in this species, which has implications for future studies given the difficulties of collecting field specimens with contrasting phenotypes for association analysis.
The population genomics of multiple tsetse fly (Glossina fuscipes fuscipes) admixture zones in Uganda
(Saarman, N. P., Opiro, R., Hyseni, C., Echodu, R., Opiyo, E. A., Dion, K., ... & Caccone, A. (2019). The population genomics of multiple tsetse fly (Glossina fuscipes fuscipes) admixture zones in Uganda. Molecular ecology, 28(1), 66-85., 2019) Saarman, Norah P.; Opiro, Robert; Hyseni, Chaz; Echodu, Richard; Opiyo, Elizabeth A.; Dion, Kirstin; Johnson, Thomas; Aksoy, Serap; Caccone, Adalgisa
Understanding the mechanisms that enforce, maintain or reverse the process of speciation is an important challenge in evolutionary biology. This study investigates the patterns of divergence and discusses the processes that form and maintain divergent lineages of the tsetse fly Glossina fuscipes fuscipes in Uganda. We sampled 251 flies from 18 sites spanning known genetic lineages and the four admixture zones between them. We apply population genomics, hybrid zone and approximate Bayesian computation to the analysis of three types of genetic markers: 55,267 double-digest restriction site-associated DNA (ddRAD) SNPs to assess genome-wide admixture, 16 microsatellites to provide continuity with published data and accurate biogeographic modelling, and a 491-bp fragment of mitochondrial cytochrome oxidase I and II to infer maternal inheritance patterns. Admixture zones correspond with regions impacted by the reorganization of Uganda's river networks that occurred during the formation of the West African Rift system over the last several hundred thousand years. Because tsetse fly population distributions are defined by rivers, admixture zones likely represent both old and new regions of secondary contact. Our results indicate that older hybrid zones contain mostly parental types, while younger zones contain variable hybrid types resulting from multiple generations of interbreeding. These findings suggest that reproductive barriers are nearly complete in the older admixture zones, while nearly absent in the younger admixture zones. Findings are consistent with predictions of hybrid zone theory: Populations in zones of secondary contact transition rapidly from early to late stages of speciation or collapse all together.
A spatial genetics approach to inform vector control of tsetse flies (Glossina fuscipes fuscipes) in Northern Uganda
(Ecology and evolution, 2018) Saarman, Norah; Burak, Mary; Opiro, Robert; Hyseni, Chaz; Echodu, Richard; Dion, Kirstin; Opiyo, Elizabeth A.; Dunn, Augustine W.; Amatulli, Giuseppe; Aksoy, Serap; Caccone, Adalgisa
Tsetse flies (genus Glossina) are the only vector for the parasitic trypanosomes responsible for sleeping sickness and nagana across sub-Saharan Africa. In Uganda, the tsetse fly Glossina fuscipes fuscipes is responsible for transmission of the parasite in 90% of sleeping sickness cases, and co-occurrence of both forms of human-infective trypanosomes makes vector control a priority. We use population genetic data from 38 samples from northern Uganda in a novel methodological pipeline that integrates genetic data, remotely sensed environmental data, and hundreds of field-survey observations. This methodological pipeline identifies isolated habitat by first identifying environmental parameters correlated with genetic differentiation, second, predicting spatial connectivity using field-survey observations and the most predictive environmental parameter(s), and third, overlaying the connectivity surface onto a habitat suitability map. Results from this pipeline indicated that net photosynthesis was the strongest predictor of genetic differentiation in G. f. fuscipes in northern Uganda. The resulting connectivity surface identified a large area of well-connected habitat in northwestern Uganda, and twenty-four isolated patches on the northeastern margin of the G. f. fuscipes distribution. We tested this novel methodological pipeline by completing an ad hoc sample and genetic screen of G. f. fuscipes s amples f rom a m odel-predicted isolated patch, and evaluated whether the ad hoc sample was in fact as genetically isolated as predicted. Results indicated that genetic isolation of the ad hoc sample was as genetically isolated as predicted, with differentiation well above estimates made in samples from within well-connected habitat separated by similar geographic distances. This work has important practical implications for the control of tsetse and other disease vectors, because it provides a way to identify isolated populations where it will be safer and easier to implement vector control and that should be prioritized as study sites during the development and improvement of vector control methods.
Spatio-temporal distribution of Spiroplasma infections in the tsetse fly (Glossina fuscipes fuscipes) in northern Uganda
(PLOS Neglected Tropical Diseases, 2019) Schneider, Daniela I.; Saarman, Norah; Onyango, Maria G.; Hyseni, Chaz; Opiro, Robert; Echodu, Richard; O’Neill, Michelle; Bloch, Danielle; Vigneron, Aure´lien; Johnson, T. J.; Dion, Kirstin; Weiss, Brian L.; Opiyo, Elizabeth; Caccone, Adalgisa; Aksoy, Serap
Tsetse flies (Glossina spp.) are vectors of parasitic trypanosomes, which cause human (HAT) and animal African trypanosomiasis (AAT) in sub-Saharan Africa. In Uganda, Glossina fuscipes fuscipes (Gff) is the main vector of HAT, where it transmits Gambiense disease in the northwest and Rhodesiense disease in central, southeast and western regions. Endosymbionts can influence transmission efficiency of parasites through their insect vectors via conferring a protective effect against the parasite. It is known that the bacterium Spiroplasma is capable of protecting its Drosophila host from infection with a parasitic nematode. This endosymbiont can also impact its host’s population structure via altering host reproductive traits. Here, we used field collections across 26 different Gff sampling sites in northern and western Uganda to investigate the association of Spiroplasma with geographic origin, seasonal conditions, Gff genetic background and sex, and trypanosome infection status. We also investigated the influence of Spiroplasma on Gff vector competence to trypanosome infections under laboratory conditions. Generalized linear models (GLM) showed that Spiroplasma probability was correlated with the geographic origin of Gff host and with the season of collection, with higher prevalence found in flies within the Albert Nile (0.42 vs 0.16) and Achwa River (0.36 vs 0.08) watersheds and with higher prevalence detected in flies collected in the intermediate than wet season. In contrast, there was no significant correlation of Spiroplasma prevalence with Gff host genetic background or sex once geographic origin was accounted for in generalized linear models. Additionally, we found a potential negative correlation of Spiroplasma with trypanosome infection, with only 2% of Spiroplasma infected flies harboring trypanosome co-infections. We also found that in a laboratory line of Gff, parasitic trypanosomes are less likely to colonize the midgut in individuals that harbor Spiroplasma infection. These results indicate that Spiroplasma infections in tsetse may be maintained by not only maternal but also via horizontal transmission routes, and Spiroplasma infections may also have important effects on trypanosome transmission efficiency of the host tsetse. Potential functional effects of Spiroplasma infection in Gff could have impacts on vector control approaches to reduce trypanosome infections.
Taking advantage of genomic data to develop reliable microsatellite loci in Trypanosoma brucei
(Molecular Ecology Resources, 2013) Sistrom, Mark; Echodu, Richard; Hyseni, Chaz; Enyaru, John; Aksoy, Serap; Caccone, Adalgisa
Taking advantage of the annotated genome of Trypanosoma brucei, a unicellular eukaryotic parasite which causes sleeping sickness across sub3Saharan Africa, this study develops 11 variable microsatellite loci, which reliably amplify in poor and unknown quality DNA samples. We provide insights into effective screening methods to develop microsatellite loci from genomic resources and a set of markers to study regional population variation in this important parasite.
Temporal stability of Glossina fuscipes fuscipes populations in Uganda
(Parasites & vectors, 2011) Echodu, Richard; Beadell, Jon S.; Okedi, Loyce M.; Hyseni, Chaz; Aksoy, Serap; Caccone, Adalgisa
Glossina fuscipes, a riverine species of tsetse, is the major vector of human African trypanosomiasis (HAT) in sub-Saharan Africa. Understanding the population dynamics, and specifically the temporal stability, of G. fuscipes will be important for informing vector control activities. We evaluated genetic changes over time in seven populations of the subspecies G. f. fuscipes distributed across southeastern Uganda, including a zone of contact between two historically isolated lineages. A total of 667 tsetse flies were genotyped at 16 microsatellite loci and at one mitochondrial locus. Results: Results of an AMOVA indicated that time of sampling did not explain a significant proportion of the variance in allele frequencies observed across all samples. Estimates of differentiation between samples from a single population ranged from approximately 0 to 0.019, using Jost’s DEST. Effective population size estimates using momentum-based and likelihood methods were generally large. We observed significant change in mitochondrial haplotype frequencies in just one population, located along the zone of contact. The change in haplotypes was not accompanied by changes in microsatellite frequencies, raising the possibility of asymmetric mating compatibility in this zone. Conclusion: Our results suggest that populations of G. f. fuscipes were stable over the 8-12 generations studied. Future studies should aim to reconcile these data with observed seasonal fluctuations in the apparent density of tsetse.
Wolbachia association with the tsetse fly, Glossina fuscipes fuscipes, reveals high levels of genetic diversity and complex evolutionary dynamics
(BMC evolutionary biology, 2013) Symula, Rebecca E.; Alam, Uzma; Brelsfoard, Corey; Wu, Yineng; Echodu, Richard; Okedi, Loyce M.; Aksoy, Serap; Caccone, Adalgisa
Wolbachia pipientis, a diverse group of α-proteobacteria, can alter arthropod host reproduction and confer a reproductive advantage to Wolbachia-infected females (cytoplasmic incompatibility (CI)). This advantage can alter host population genetics because Wolbachia-infected females produce more offspring with their own mitochondrial DNA (mtDNA) haplotypes than uninfected females. Thus, these host haplotypes become common or fixed (selective sweep). Although simulations suggest that for a CI-mediated sweep to occur, there must be a transient phase with repeated initial infections of multiple individual hosts by different Wolbachia strains, this has not been observed empirically. Wolbachia has been found in the tsetse fly, Glossina fuscipes fuscipes, but it is not limited to a single host haplotype, suggesting that CI did not impact its population structure. However, host population genetic differentiation could have been generated if multiple Wolbachia strains interacted in some populations. Here, we investigated Wolbachia genetic variation in G. f. fuscipes populations of known host genetic composition in Uganda. We tested for the presence of multiple Wolbachia strains using Multi-Locus Sequence Typing (MLST) and for an association between geographic region and host mtDNA haplotype using Wolbachia DNA sequence from a variable locus, groEL (heat shock protein 60). Results: MLST demonstrated that some G. f. fuscipes carry Wolbachia strains from two lineages. GroEL revealed high levels of sequence diversity within and between individuals (Haplotype diversity = 0.945). We found Wolbachia associated with 26 host mtDNA haplotypes, an unprecedented result. We observed a geographical association of one Wolbachia lineage with southern host mtDNA haplotypes, but it was non-significant (p = 0.16). Though most Wolbachia-infected host haplotypes were those found in the contact region between host mtDNA groups, this association was non-significant (p = 0.17). Conclusions: High Wolbachia sequence diversity and the association of Wolbachia with multiple host haplotypes suggest that different Wolbachia strains infected G. f. fuscipes multiple times independently. We suggest that these observations reflect a transient phase in Wolbachia evolution that is influenced by the long gestation and low reproductive output of tsetse. Although G. f. fuscipes is superinfected with Wolbachia, our data does not support that bidirectional CI has influenced host genetic diversity in Uganda.

Browsing by Author "Caccone, Adalgisa"

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