Roiz, D. | bioRxiv Science

bioRxiv2022

pWCP is a widely distributed and highly conserved Wolbachia plasmid in Culex mosquitoes worldwide

Mosquitoes represent the most important pathogen vectors and are responsible for the spread of a wide variety of poorly treatable diseases. Wolbachia are obligate intracellular bacteria that are widely distributed among arthropods and collectively represents one of the most promising solutions for vector control. In particular, Wolbachia has been shown to limit the transmission of pathogens, and to dramatically affect the reproductive behavior of their host through its phage WO. While much research has focused on deciphering and exploring the biocontrol applications of these WO-related phenotypes, the extent and potential impact of the Wolbachia mobilome remain poorly appreciated. Notably, several Wolbachia plasmids, carrying WO-like genes and Insertion Sequences (IS), thus possibly interrelated to other genetic units of the endosymbiont, have been recently discovered. Here we investigated the diversity and biogeography of the first described plasmid of Wolbachia in Culex pipiens (pWCP) in several islands and continental countries around the world--including Cambodia, Guadeloupe, Martinique, Thailand, and Mexico--together with mosquito strains from colonies that evolved for 2 to 30 years in the laboratory. Together with earlier observation, our results show that pWCP is omnipresent and strikingly conserved among Wolbachia populations within mosquitoes from distant geographies and environmental conditions. These data suggest a critical role for the plasmid in Wolbachia ecology and evolution, and the potential of a great tool for the further genetic dissection or potential manipulation of the endosymbiont.

microbiology↗

bioRxiv2022

Invasion of forested areas in Gabon (Central Africa) by the Asian tiger mosquito and the potential consequences from the One Health perspective

Since its first record in urban areas of Central-Africa in 2000s, the invasive mosquito, Aedes albopictus, has continued to spread across the region, including in remote rural areas, and promoted outbreaks of Aedes-borne diseases, such as dengue, chikungunya and Zika. From the One-Health perspective, such invasion might enhance Ae. albopictus interactions with wild animals in forest ecosystems and favor the spillover of zoonotic arboviruses to humans. From 2014 to 2018, we monitored the steady spread of this mosquito species in the wildlife reserve of La Lope National Park (Gabon), and evaluated the magnitude of its colonization of the rainforest ecosystem using ovitraps, larval surveys, BG-Sentinel traps, and human landing catches following an anthropization gradient. We detected Ae. albopictus in forest galleries up to 15km away from La Lope village. However, Ae. albopictus was significantly more abundant at anthropogenic sites than in less anthropized areas. The number of eggs laid by Ae. albopictus decreased progressively with the distance from the forest fringe up to 200m inside the forest, showing that its occurrence in forest ecosystems is restricted to anthropized-sylvatic interfaces with dense forest. This suggests that Ae. albopictus may act as bridge vector of zoonotic pathogens between wild and anthropogenic compartments.

ecology↗

bioRxiv2022

Multiple invasions, Wolbachia and human-aided transport drive the genetic variability of Aedes albopictus in the Iberian Peninsula

The Asian tiger mosquito, Aedes albopictus, is a highly invasive species that has been spreading rapidly throughout tropical and temperate regions worldwide since the late 1970s. On the Iberian Peninsula, it was first recorded in 2004 near Barcelona. Since then, the species has spread along the Mediterranean coast and is now colonising the Peninsulas inner territories. As with other species of the genus Aedes, the spread of the tiger mosquito has been linked to global shipping routes and road networks. In particular, the transport of adult mosquitoes by car has been shown to augment its natural spreading capacity by orders of magnitude. Much remains unknown, however, about the impact of human-mediated dispersal on the genetic variability of this species. This study aimed to ascertain the factors that have contributed to the spread and the current genetic variation of Ae. albopictus across the Iberian Peninsula, through complex dispersal mechanisms and endosymbiosis with bacteria like Wolbachia. We do so through population genetic analysis of mitochondrial (COI) and nuclear (ITS2) DNA sequences. Overall, both COI and ITS2 markers showed a lack of genetic structure among sampled regions and the presence of worldwide dominant haplotypes, suggesting a pattern of multiple introductions from abroad. We found extremely low levels of variation in COI compared to ITS2, and this lack of mitochondrial polymorphism is likely explained by high Wolbachia prevalence (79%). Multilevel models revealed that greater mosquito fluxes (estimated from commuting patterns and tiger mosquito population distribution) and spatial proximity between sampling sites were associated with lower ITS2 genetic distance, suggesting that rapid short- and medium-distance dispersal is facilitated by humans through vehicular traffic. This study highlights the significant role of human transportation in shaping the genetic attributes of Ae. albopictus and promoting regional gene flow, and underscores the need for a territorially integrated surveillance across scales of this disease-carrying mosquito. Author SummaryThe tiger mosquito, Aedes albopictus, is one of the most invasive species in the world. Native to the tropical forests of Southeast Asia, over the past 30 years it has rapidly spread throughout tropical and temperate regions of the world. Its dramatic expansion has resulted in public health concerns as a consequence of its vector competence for at least 16 viruses. Previous studies showed that Ae. albopictus spread has been facilitated by human-mediated transportation, but much remains unknown about how this has affected its genetic attributes. Here we examined the factors that contributed to shaping the current genetic constitution of Ae. albopictus in the Iberian Peninsula, where the species was first found in 2004, by combining population genetics and Bayesian modelling. We found that both mitochondrial and nuclear DNA markers showed a lack of genetic structure and the presence of worldwide dominant haplotypes, suggesting regular introductions from abroad. Mitochondrial DNA showed little genetic diversity compared to nuclear DNA, likely explained by infection with maternally transmitted bacteria of the genus Wolbachia. Our models indicated that human transportation plays a role in shaping Ae. albopictus nuclear genetic structure by means of passive dispersal of adult tiger mosquitoes through the road network.

genetics↗