Biology subjects

Segard, A.

Publications and source records attributed to Segard, A..

7 recordsLinked to original sources

bioRxiv2026

Population genetic structure and connectivity of Glossina palpalis gambiensis and G. morsitans submorsitans in Southwestern Senegal

In sub-Saharan Africa, human and animal health is threatened by African trypanosomoses. These diseases are caused by trypanosomes that are transmitted primarily by tsetse flies. Vector control remains one of the most effective strategies for reducing disease transmission, but requires a minimum level of knowledge of the population biology, ecology and dispersal patterns of the targeted vectors. In this respect, population genetic approaches using appropriate polymorphic genetic markers can provide valuable tools to inform and optimize control strategies. Senegal is currently engaged in a national tsetse control programme and has been identified as a study country within a European Union-funded research initiative, COMBAT (controlling and progressively minimizing the burden of animal trypanosomosis). Baseline entomological studies are currently underway in the Sine Saloum (Southern Senegal). This preliminary study aimed to characterize the population genetic structure and connectivity of tsetse fly species present in Southern Senegal, Glossina palpalis gambiensis and G. morsitans submorsitans, in order to assess their population sizes (geographically and demographically), population densities and dispersal capacities. The two species exhibited markedly contrasting population structures. The first, G. p. gambiensis, displayed an isolation by distance with rather dense subpopulations exchanging immigrants at short distances (1.6 km/generation) and continuously from Sine-Saloum to Casamance, in line with the apparent continuity of the mangrove network found along this coast. In contrast, G. m. submorsitans presented a relatively dense population over a 75 km wide area, fragmented into sparsely distributed, very dense and interconnected pockets. These findings indicate that G. p. gambiensis likely constitutes a large metapopulation comprising 3266 effective individuals on average (and up to 7765), whereas G. m. submorsitans appeared as a single and large population, scattered in small pockets that could be readily replenished by immigrants from distant areas in case of control. These results suggest that elimination is not a realistic option for any of these two populations. Alternatively, localized integrated pest management is likely to be the most effective approach for controlling the negative effects of these biting flies on domestic animals, by reducing trypanosome transmission. However, further entomological investigations and the use of more informative genetic markers are needed to obtain a more precise understanding of the epidemiological processes involved.

ecology↗

bioRxiv2025

Unravelling genetic differentiation between Glossina brevipalpis populations from two distant National Parks in Mozambique

African trypanosomosis (AT), caused by protozoan parasites of the genus Trypanosoma, has plagued the African continent for centuries, affecting both humans and animals. Vector control represents an efficient way to reduce the burden of AT. In Mozambique, control campaigns reshaped tsetse fly distribution to what it is today, with Glossina brevipalpis and G. austeni as the dominant species in the South. Additionally, G. brevipalpis can be found in two National parks, Gorongosa National Park in the Centre and Maputo National Park in the South, with an 840 km wide tsetse-free zone between them. In order to improve our knowledge of the genetic diversity and gene flow of these populations and their probable isolation, we undertook a population genetics study with 11 microsatellite loci. We found that these two zones behave as isolated subpopulations, only exchanging a few individuals per year. To explain this finding, we suggest the existence of undocumented pocket populations between the two parks, or, in the absence of these, the accidental translocation of tsetse flies during human-driven animal transportation. We concluded that such undocumented means of dispersal should be explored further in studies investigating Glossina populations, to allow for the design of more efficient control strategies.

evolutionary biology↗

bioRxiv2023

Trypanosoma brucei gambiense group 2 experimental in vivo life cycle: from procyclic to bloodstream form.

Trypanosoma brucei gambiense (Tbg) group 2 is a subgroup of trypanosomes able to infect humans in West and Central Africa. Unlike other agents causing sleeping sickness such as Tbg group 1 and Trypanosoma brucei rhodesiense, Tbg2 lacks the typical molecular markers associated with resistance to human serum. Only thirty-six strains of Tbg2 have been documented, and therefore, very limited research has been conducted despite its zoonotic nature. Some of these strains are only available in their procyclic form which hinders human serum resistance assays and mechanistic studies. Furthermore, the understanding of Tbg2s potential to infect tsetse flies and mammalian hosts is limited. In this study, 165 Glossina palpalis gambiensis flies were experimentally infected with procyclic Tbg2 parasites. 35 days post-infection, 43 flies out of the 80 still alive flies were found Tbg2 PCR-positive in the saliva. These flies were able to infect 3 out of the 4 mice used for blood-feeding. Dissection revealed that only six flies really carried mature infections in their midguts and salivary glands. Importantly, a single fly with a mature infection was sufficient to infect a mammalian host. This Tbg2 transmission success confirms that Tbg2 strains can establish in tsetse flies and infect mammalian hosts. The study describes an effective in vivo protocol for transforming Tbg2 from procyclic to bloodstream form, reproducing the complete Tbg2 cycle from G. p. gambiensis to mice. These findings provide valuable insights into Tbg2s host infectivity, and will facilitate further research on mechanisms of human serum resistance.

microbiology↗

bioRxiv2023

Population genetics of Glossina palpalis gambiensis in the sleeping sickness focus of Boffa (Guinea) before and after eight years of vector control: no effect of control despite a significant decrease of human exposure to the disease

Human African trypanosomosis (HAT), also known as sleeping sickness, is still a major concern in endemic countries. Its cyclical vector are biting insects of the genus Glossina or tsetse flies. In Guinea, the mangrove ecosystem contains the main HAT foci of Western Africa. There, the cyclical vector is Glossina palpalis gambiensis. A still ongoing vector control campaign (VCC) started in 2011 in the focus of Boffa, using tiny targets, with a 79% tsetse density reduction in 2016 and significant impact on the prevalence of the disease (from 0.3% in 2011 to 0.11% in 2013, 0.0352% in 2016 and 0.0097% in 2019). To assess the sustainability of these results, we have studied the impact of this VCC on the population biology of G. p. gambiensis in Boffa. We used the genotyping at 11 microsatellite markers and population genetic tools of tsetse flies from different sites and at different dates before and after the beginning of the VCC. In variance with a significant impact of VCC on the apparent densities of flies captured in the traps deployed, the global population of G. p. gambiensis displayed no variation of the sex-ratio, no genetic signature of control, and behaved as a very large population occupying the entire zone. This implies that targets deployment efficiently protected the human populations locally, but did not impact tsetse flies where targets cannot be deployed and where the main tsetse population exploits available resources. We thus recommend the pursuit of vector control measures with the same strategy, through the joint effect of VCC and medical surveys and treatments, in order to protect human populations from HAT infections until the disease can be considered as entirely eradicated from the focus.

evolutionary biology↗

bioRxiv2018

Sexual selection and inbreeding: two efficient ways to limit the accumulation of deleterious mutations

Theory and empirical data showed that two processes can boost selection against deleterious mutations, thus facilitating the purging of the mutation load: inbreeding, by exposing recessive deleterious alleles to selection in homozygous form, and sexual selection, by enhancing the relative reproductive success of males with small mutation loads. These processes tend to be mutually exclusive because sexual selection is reduced under mating systems that promote inbreeding, such as self-fertilization in hermaphrodites. We estimated the relative efficiency of inbreeding and sexual selection at purging the genetic load, using 50 generations of experimental evolution, in a hermaphroditic snail (Physa acuta). To this end, we generated lines that were exposed to various intensities of inbreeding, sexual selection (on the male function) and nonsexual selection (on the female function). We measured how these regimes affected the mutation load, quantified through the survival of outcrossed and selfed juveniles. We found that juvenile survival strongly decreased in outbred lines with reduced male selection, but not when female selection was relaxed, showing that male-specific sexual selection does purge deleterious mutations. However, in lines exposed to inbreeding, where sexual selection was also relaxed, survival did not decrease, and even increased for self-fertilized juveniles, showing that purging through inbreeding can compensate for the absence of sexual selection. Our results point to the further question of whether a mixed strategy combining the advantages of both mechanisms of genetic purging could be evolutionary stable.

evolutionary biology↗

bioRxiv2018

Identification of general patterns of sex-biased expression in Daphnia, a genus with environmental sex determination

Daphnia reproduce by cyclic-parthenogenesis, where phases of asexual reproduction are intermitted by sexual production of diapause stages. This life cycle, together with environmental sex determination, allow the comparison of gene expression between genetically identical males and females. We investigated gene expression differences between males and females in four genotypes of Daphnia magna and compared the results with published data on sex-biased gene expression in two other Daphnia species, each representing one of the major phylogenetic clades within the genus. We found that 42% of all annotated genes showed sex-biased expression in D. magna. This proportion is similar both to estimates from other Daphnia species as well as from species with genetic sex determination, suggesting that sex-biased expression is not reduced under environmental sex determination. Among 7453 single copy, one-to-one orthologs in the three Daphnia species, 707 consistently showed sex-biased expression and 675 were biased in the same direction in all three species. Hence these genes represent a core-set of genes with consistent sex-differential expression in the genus. A functional analysis identified that several of them are involved in known sex determination pathways. Moreover, 75% were overexpressed in females rather than males, a pattern that appears to be a general feature of sex-biased gene expression in Daphnia.\n\nShort summaryIn some species with environmental sex determination, gene expression can be compared between genetically identical males and females. Here, we investigated sex-biased expression in one such species, D. magna, and compared it with data from two congeners. We found that all three species have a common set of 675 genes with consistent differential expression and with a strong bias towards overexpression in females rather than males. Moreover, the proportion of sex-biased genes in each of the three Daphnia species was similar to Drosophila species with genetic sex determination, suggesting that sex-biased expression is not necessarily reduced under environmental sex determination.

genomics↗

bioRxiv2018

Long-term prevalence data reveals spillover dynamics in a multi-host (Artemia), multi-parasite (Microsporidia) community

In the study of multi-host parasites, it is often found that host species contribute asymmetrically to parasite transmission, with cascading effects on parasite dynamics and overall community structure. Yet, identifying which of the host species contribute to parasite transmission and maintenance is a recurring challenge. Here, we approach this issue by taking advantage of natural variation in the community composition of host species. We studied the horizontally transmitted microsporidians Anostracospora rigaudi and Enterocytospora artemiae in a Southern French metacommunity of their brine shrimp hosts, Artemia franciscana and Artemia parthenogenetica. Within the metacommunity, patches can contain either or both of the Artemia host species, so that long-term prevalence data can provide a direct link between the presence of the two host species and the persistence of the two parasites. First, we show that the microsporidian A. rigaudi is a spillover parasite: it was unable to persist in the absence of its maintenance host A. parthenogenetica. This result was particularly striking in light of A. rigaudis high prevalence (in the field) and high infectivity (when tested in the lab) in both hosts. Moreover, A. parthenogeneticas seasonal presence imposed seasonality on the rate of spillover, causing cyclical pseudo-endemics in the spillover host A. franciscana. Second, while our prevalence data was sufficient to identify E. artemiae as either a spillover or a facultative multi-host parasite, we could not distinguish between the two possibilities. This study supports the importance of studying the community context of multi-host parasites, and demonstrates that in appropriate multi-host systems, sampling across a range of conditions and host communities can lead to clear conclusions about the drivers of parasite persistence.

ecology↗