Biology subjects

Caccone, A.

Publications and source records attributed to Caccone, A..

8 recordsLinked to original sources

bioRxiv2026

Mapping tsetse fly connectivity in Uganda with machine learning landscape genetics

Introduction - Tsetse flies (genus Glossina) are biting insects that transmit human and animal trypanosomiases across sub-Saharan Africa, and sustainable vector control depends on understanding dispersal barriers and reinvasion routes. Despite major progress toward elimination, Uganda remains at risk for both human forms of the disease (Trypanosoma brucei gambiense and T. b. rhodesiense) and planners still lack reliable maps of tsetse movement and reinvasion risk. Methods and Results - We address this gap with machine-learning landscape genetics and species distribution models, integrating estimates of population genetic distance and geospatial environmental data to predict and map Glossina fuscipes fuscipes connectivity across Uganda and western Kenya. Inputs included microsatellite genotypes from 11 loci genotyped in 2,736 flies sampled from 87 localities and remotely sensed environmental predictors summarized along least-cost paths. Random forest models predicted patterns of genetic differentiation better than distance-only models, supporting the use of a machine-learning framework for connectivity inference across complex heterogeneous landscapes, and identified variables related to temperature and water availability as the strongest predictors of genetic connectivity. Conclusions - Combining landscape genetics predictions of connectivity with a species distribution model revealed regions with high habitat suitability but low connectivity that represent priority zones for area-wide integrated pest management strategies, including established riverine control tools such as tiny targets and other targeted interventions aimed at reducing reinvasion risk. These results provide biologically interpretable maps and quantitative uncertainty metrics that can guide targeted tsetse control, while providing a transferable analytical pipeline for modeling and mapping genetic connectivity across other species and landscapes.

evolutionary biology↗

bioRxiv2026

Laboratory adaptation and complete genome assembly of a Beposo, Ghana strain of the human hookworm Necator americanus

Laboratory models are invaluable tools for studying parasite biology and pathogenesis, especially for helminth infections. However, the complex life cycles and frequently narrow host specificity of helminths present challenges to maintaining access to critical parasite material in a laboratory setting. This is especially true of Necator americanus, the most common species of hookworm that infects humans globally. Here we report the successful laboratory adaptation of an African strain of N. americanus, originally isolated from infected individuals in Beposo, Ghana. The Beposo strain has been successfully passaged across 9 generations in Golden Syrian hamsters maintained on oral dexamethasone. Differential susceptibility to mebendazole and albendazole was evaluated using an egg hatch assay, and DNA sequencing of the beta-tubulin isotype 1 gene did not identify known resistance-associated mutations in the endemic strain. Sequencing of the mitochondrial COX1 gene revealed that specimens of N. americanus from Ghana, along with reported sequences from Togo, are distinct from those from South America and Asia. Complementary microsatellite-based population analysis revealed substantial genetic variation in the founding parasite population. To further characterize the novel Beposo strain, a draft hybrid genome assembly was generated from genomic DNA extracted from a single adult male worm via an optimized Oxford Nanopore Technologies MinION library preparation approach tailored to low-input sample types. This high-quality assembly, including a complete mitogenome, is 202.8Mb in 950 contigs with an N50 >449 kb. It contains >95% of conserved nematode orthologs in complete single copy and is estimated by homology-based gene prediction to contain 12,804 genes. This study represents the first comprehensive characterization of a strain of N. americanus originating in Africa that has been successfully adapted to a laboratory animal model.

microbiology↗

bioRxiv2023

Aalbo1200: global genetic differentiation and variability of the mosquito Aedes albopictus

The mosquito Aedes albopictus transmits human viruses including dengue and chikungunya and is an extremely successful invasive species expanding into new regions of the world. New tools are needed to complement existing tools to help monitor and control this species. Genomic resources are improving for this species including genome reference sequences, and whole genome sequencing data will help to catalog genetic diversity in this species and further enable genetic analysis. We collected populations of Ae. albopictus from throughout its distribution and generated whole genome sequencing data from population samples. These data will be used to address a number of basic and applied questions for this species. Here, we show genetic differentiation patterns among the tropical and temperate forms, as well as finer scale genetic clustering at the regional and population scale. These data and results will be a valuable resource for further study and tool development for this species.

evolutionary biology↗

bioRxiv2023

Whole-genome sequencing confirms multiple species of Galapagos giant tortoises

Galapagos giant tortoises are endemic to the Galapagos Archipelago, where they are found in isolated populations. While these populations are widely considered distinguishable in morphology, behavior, and genetics, the recent divergence of these taxa has made their status as species controversial. Here, we apply multispecies coalescent methods for species delimitation to whole genome resequencing data from 38 tortoises across all 13 extant taxa to assess support for delimiting these taxa as species. In contrast to previous studies based solely on divergence time, we find strong evidence to reject the hypothesis that all Galapagos giant tortoises belong to a single species. Instead, a conservative interpretation of model-based and divergence-based results indicates that these taxa form a species complex consisting of a minimum of 9 species, with some analyses supporting as many as 13 species. There is mixed support for the species status of taxa living on the same island, with some methods delimiting them as separate species and others suggesting multiple populations of a single species per island. These results make clear that Galapagos giant tortoise taxa represent different stages in the process of speciation, with some taxa further along in that evolutionary process than others. A better understanding of the more complex parts of that process is urgently needed, given the threatened status of Galapagos giant tortoises. Lay SummarySpecies delimitation is a challenging problem in evolutionary biology, but one that is central to the field. Distinguishing species can affect conservation management practices, from conservation status assessments to strategies for breeding programs. More fundamentally, understanding species boundaries affects our ability to assess biodiversity and to study evolutionary processes. The Galapagos Archipelago presents several radiations of closely related taxa that inspired Charles Darwin to develop his theory of evolution by natural selection and later led to foundational case studies in speciation. The Galapagos giant tortoises were one such inspiration. Nearly two centuries later, there is still an ongoing debate about the taxonomic status of these tortoises, with opinions on their status ranging from barely differentiated populations to separate species. Here, we present the first genomic species delimitation of Galapagos giant tortoises and provide convincing evidence that this group is a complex consisting of between 9 and 13 species. These results provide valuable guidance to conservation stakeholders in the Galapagos, while also adding an important case study to the delimitation of island species.

evolutionary biology↗

bioRxiv2020

Improved reference genome of the arboviral vector Aedes albopictus

The Asian tiger mosquito Aedes albopictus is globally expanding and has become the main vector for human arboviruses in Europe. Here we present AalbF2, a dramatically improved assembly of the Ae. albopictus genome that has revealed widespread viral insertions, novel microRNAs and piRNA clusters, the sex determining locus, new immunity genes, and has enabled genome-wide studies of geographically diverse Ae. albopictus populations and analyses of the developmental and stage-dependent network of expression data. Additionally, we built the first physical map for this species with 75% of the assembled genome anchored to the chromosomes. These up-to-date resources of the genome provide a foundation to improve understanding of the adaptation potential and the epidemiological relevance of this species and foster the development of innovative control measures. One Sentence SummaryLong-read and Hi-C-based de novo assembly of the arboviral vector Aedes albopictus genome fosters deeper understanding of its biological features.

genomics↗

bioRxiv2019

Spatio-temporal distribution of Spiroplasma infections in the tsetse fly (Glossina fuscipes fuscipes) in northern Uganda

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 hosts 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.\n\nGeneralized 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.\n\nAuthor SummaryWe investigated the association of symbiotic Spiroplasma with the tsetse fly host Glossina fuscipes fuscipes (Gff) to assess if Spiroplasma infections are correlated with Gff genetic background, geography, or season and its interaction with trypanosome parasites. We analyzed distribution and prevalence of Spiroplasma infections across different Gff sampling sites in northern and western Uganda, and found that the symbiont is unevenly distributed and infections have not reached fixation within these sampling sites. We tested for associations with geographic origin of the collections, seasonal environmental conditions at the time of collection, Gff host genetic background and sex, plus trypanosome co-infections. Spiroplasma prevalence was strongly correlated with geographic origin and seasonal environmental conditions. Our parasite infection data suggested a negative correlation of Spiroplasma with trypanosome infection, with only 5 out of 243 flies harboring trypanosome co-infections. We further investigated the influence of Spiroplasma on trypanosome parasite infections in the laboratory. We found that trypanosomes were less likely to establish an infection in Gff individuals that carried Spiroplasma infections. Our results provide new information on host-endosymbiont dynamics in an important human disease vector, and provide evidence that Spiroplasma may confer partial resistance to Gff trypanosome infections. These findings provide preliminary evidence that a symbiont-based control method could be successful in combating tsetse trypanosome transmission to humans and livestock in sub-Saharan Africa.

epidemiology↗

bioRxiv2017

Theory, practice, and conservation in the age of genomics: the Galapagos giant tortoise as a case study

High-throughput DNA sequencing allows efficient discovery of thousands of single nucleotide polymorphisms (SNPs) in non-model species. Population genetic theory predicts that this large number of independent markers should provide detailed insights into population structure, even when only a few individuals are sampled. Still, sampling design can have a strong impact on such inferences. Here, we use simulations and empirical SNP data to investigate the impacts of sampling design on estimating genetic differentiation among populations that represent three species of Galapagos giant tortoises (Chelonoidis spp.). Though microsatellite and mitochondrial DNA analyses have supported the distinctiveness of these species, a recent study called into question how well these markers matched with data from genomic SNPs, thereby questioning decades of studies in non-model organisms. Using >20,000 genome-wide SNPs from 30 individuals from three Galapagos giant tortoise species, we find distinct structure that matches the relationships described by the traditional genetic markers. Furthermore, we confirm that accurate estimates of genetic differentiation in highly structured natural populations can be obtained using thousands of SNPs and 2-5 individuals, or hundreds of SNPs and 10 individuals, but only if the units of analysis are delineated in a way that is consistent with evolutionary history. We show that the lack of structure in the recent SNP-based study was likely due to unnatural grouping of individuals and erroneous genotype filtering. Our study demonstrates that genomic data enable patterns of genetic differentiation among populations to be elucidated even with few samples per population, and underscores the importance of sampling design. These results have specific implications for studies of population structure in endangered species and subsequent management decisions.\n\n\"Modern molecular techniques provide unprecedented power to understand genetic variation in natural populations. Nevertheless, application of this information requires sound understanding of population genetics theory.\"\n\n- Fred Allendorf (2017, p. 420)

evolutionary biology↗

bioRxiv2017

Reviving A Lost Species: The Case Of The Floreana Galapagos Giant Tortoise Chelonoidis elephantopus

Species are being lost at an unprecedented rate due to human-driven environmental changes. The cases in which species declared extinct can be revived are rare. However, here we report that a remote volcano in the Galapagos Islands hosts many giant tortoises with high ancestry from a species previously declared as extinct: Chelonoidis elephantopus or the Floreana tortoise. Of 150 individuals with distinctive morphology sampled from the volcano, genetic analyses revealed that 65 had C. elephantopus ancestry and thirty-two were translocated from the volcanos slopes to a captive breeding center. A genetically informed captive breeding program now being initiated will, over the next decades, return C. elephantopus tortoises to Floreana Island to serve as engineers of the islands ecosystems. Ironically, it was the haphazard translocations by mariners killing tortoises for food centuries ago that created the unique opportunity to revive this \"lost\" species today.

evolutionary biology↗