Phylogenomics reveals the history of host use in mosquitoes

Blood-feeding patterns of mosquitoes (Diptera: Culicidae) collected in an area of high arbovirus transmission in West-Central Brazil

Mosquitoes target a wide range of vertebrate species for blood meal and study of these vector-host interactions enhances our knowledge of how vector-borne viruses are transmitted. In the last decades, West-Central Brazil has faced the emergence and reemergence of several arboviruses, with a great public health impact. In addition to the well-known Aedes-borne viruses, such as dengue, Zika, and chikungunya, other arboviruses have spread throughout the country and constitute a continuous public health concern. We report results of blood meal analysis of mosquitoes (Diptera: Culicidae) collected in urbanized areas of West-Central Brazil during a Zika virus surveillance between 2017 and 2018. Amplification and sequencing of mitochondrial DNA were used to determine vertebrate origin. A total of 284 blood-engorged mosquitoes belong to 6 genera and 12 species were collected. Of these, we successfully identified blood meal in 146 (51.4%). Collections of blood-fed individuals were dominated by species of Culex (65.8%) and Aedes (25.4%). Overall, blood meal profiles demonstrated that humans were the main source (56.8%). Despite anthropophilic preferences, Aedes aegypti also fed on domestic (12.5%) and wild mammals (8.3%). Culex spp. showed an ornithophilic pattern. Humans made up 80% (n = 20) of blood meals from Aedes albopictus while 20% (n = 5) were from horses. Our results expand the knowledge regarding the vertebrate species used as hosts by mosquitoes in urbanized areas of Brazil. The variety of vertebrate species, including rodents, bats, and humans used by the local mosquitoes, highlights the continuous risk for spillover events.

Sequencing and description of mitochondrial genome of Coquillettidia venezuelensis, Trichoprosopon digitatum and Uranotaenia calosomata (Diptera: Culicidae)

Mosquitoes constitute a monophyletic taxon with approximately 3,700 species, widely distributed across continents and recognized as primary vectors of various infectious agents. Despite their medical importance, limited information is available on the evolutionary biology and molecular taxonomy of many mosquito species. In this study, we report the complete mitochondrial genome sequences of Coquillettidia venezuelensis Theobald, 1912, Trichoprosopon digitatum Rondani, 1848, and Uranotaenia calosomata Dyar & Knab, 1907, collected from the Brazilian Amazon. Sequencing was performed using the NextSeq 500 platform, resulting in genomes averaging 15,329 bp in length, comprising 37 functional subunits (13 PCGs, 22 tRNA, and 2 rRNA) and an A+T-rich control region. Comparative analyses revealed conserved genome organization, codon usage bias favoring AT-rich codons, and evidence of purifying selection acting on PCGs. Notably, a unique tRNA gene rearrangement was identified in Tr. digitatum, supporting its association with the Sabethini tribe. Phylogenetic reconstruction using concatenated PCGs confirmed the monophyly of major mosquito lineages, corroborating current taxonomic classifications and previous molecular and morphological studies. Our findings enrich the genetic resources available for Culicidae, contributing to improved molecular taxonomy and evolutionary understanding of these taxa. Additionally, this study highlights the potential of using transcriptomic data to recover mitochondrial genomes, offering a valuable tool for future systematic and eco-epidemiological research. Integration of mitochondrial data with nuclear markers and expanded taxonomic sampling is recommended to enhance resolution of deeper phylogenetic relationships within Culicidae.

Phylogenetic taxonomy of the Zambian Anopheles coustani group using a mitogenomics approach

Background

Mosquito species belonging to the Anopheles coustani group have been implicated in driving residual malaria transmission in sub-Saharan Africa and are regarded as an established primary vector in Madagascar. The morphological identification of mosquitoes in this group is challenging due to cryptic features and their molecular confirmation is difficult due to a paucity of reference sequence data representing all members of the group. Conventional molecular barcoding with the cytochrome oxidase I (COI) gene and the internal transcribed spacer 2 (ITS2) region targets is limited in their discrimination and conclusive identification of members of species complexes. In contrast, complete mitochondrial genomes (mitogenomes) have demonstrated much improved power over barcodes to be useful in rectifying taxonomic discrepancies in Culicidae.

Methods

We utilized a genome skimming approach via shallow shotgun sequencing on individual mosquito specimens to generate sequence reads for mitogenome assembly. Bayesian inferred phylogenies and molecular dating estimations were perfomed on the concatenated protein coding genes using the Bayesian Evolutionary Analysis by Sampling Trees 2 (BEAST 2) platform. Divergence estimates were calibrated on published calucations for Anopheles-Aedes.

Results

This study generated 17 new complete mitogenomes which were comprable to reference An. coustani mitogenomes in the GenBank repository by having 13 protein coding, 22 transfer RNA and 2 ribosomal RNA genes, with an average length of 15,400 bp and AT content of 78.3%. Bayesian inference using the concatenated protein coding genes from the generated and publicly available mitogenomes yielded six clades: one for each of the four taxa targeted in this study, the GenBank references, and a currently unknown species. Divergence times estimated that the An. coustani group separated from the An. gambiae complex approximately 110 million years ago (MYA), and members within the complex diverged at times points ranging from~34 MYA to as recent as ~7 MYA.

Conclusions

These findings demonstrate the value of mitochondrial genomes in differentiating cryptic taxa and help to confirm morphological identities of An. coustani s.s., An. paludis, An. zeimanni and An. tenebrosus. Divergence estimates with the An. coustani group are similar to those for well-studied anopheline vector groups. These analyses also highlight the likely prescence of other cryptic An. coustani group members circulating in Zambia.

Blow fly larvae socially integrate termite nests through morphological and chemical mimicry

Nests of ecosystem-dominant eusocial insects like ants and termites offer stable, nutrient-rich, and protected habitats that may be exploited by other organisms. Several arthropod lineages managed to breach nest defenses and become inquilines, mutualists, predators, parasitoids, or social parasites.1,2,3,4 However, achieving social integration requires extreme morphological, behavioral, and physiological adaptations.5 Among flies, only scuttle flies (Phoridae) are well-known social parasites,2 although interactions with termites (predation, scavenging, and putative parasitism) have also been mentioned in anecdotal reports for blow flies (Rhiniinae6,7,8,9,10 and Bengaliinae11,12,13) and flesh flies (Miltogramminae14,15,16). Here, we report a fly larva found to be socially integrated within nests of the termite Anacanthotermes ochraceus (Burmeister) in Morocco. Behavioral, chemical, and morphological analyses show that colony integration, including communication and grooming, is achieved through unique adaptations. The chemical profiles of the fly larvae perfectly match those of the termites at the colony level. Notably, the posterior part of the larvae mimics a termite's head, and the long papillae that imitate the termites' antennae surround the entire body. Based on phylogenomics, we show that the larvae belong to the blow fly genus Rhyncomya (Calliphoridae: Rhiniinae). Our results support the hypothesis that the enigmatic blow fly subfamily Prosthetosomatinae (only known from larvae observed in termite nests17,18,19,20) is Rhiniinae. Thus, we demonstrate that the diverse schizophoran flies evolved social integration independently from the 150-million-year-diverged Phoridae radiation. This discovery sheds light on the repeated evolution of termitophily within the order Diptera. VIDEO ABSTRACT.

From macro to micro: De novo genomes of Aedes mosquitoes enable comparative genomics among close and distant relatives

The yellow fever mosquito (Aedes aegypti) is an organism of high medical importance because it is the primary vector for diseases such as yellow fever, Zika, dengue, and chikungunya. Its medical importance has made it a subject of numerous efforts to understand their biology. One such effort, was the development of a high-quality reference genome (AaegL5). However, this reference genome was sourced from a highly inbred laboratory strain with unknown geographic origin. Thus, the reference is not representative of a wild mosquito, let alone one from its native range in sub-Saharan Africa. To better understand the genetic architecture of Ae. aegypti and their sister species, we developed two de novo chromosome-scale genomes with sequences sourced from single individuals: one of Ae. aegypti formosus (Aaf) from Burkina Faso and one of Ae. mascarensis (Am) from Mauritius. Both genomes exhibit high contiguity and gene completeness, comparable to AaegL5. While Aaf exhibits high degree of synteny to AaegL5, it also exhibits several large inversions. We further conducted comparative genomic analyses using our genomes and other publicly available culicid reference genomes to find extensive chromosomal rearrangements between major lineages. Overrepresentation analysis of expanded genes in Aaf, AaegL5, and Am revealed that while the overarching category of genes that have expanded are similar, the specific genes that have expanded differ. Our findings elucidate novel insights into chromosome evolution at both microevolutionary and macroevolutionary scales. The genomic resources we present are additions to the arsenal of biologists in understanding mosquito biology and genome evolution.

Meta-analyses of Culex blood-meals indicates strong regional effect on feeding patterns

Understanding host utilization by mosquito vectors is essential to assess the risk of vector-borne diseases. Many studies have investigated the feeding patterns of Culex mosquitoes by molecular analysis of blood-meals from field collected mosquitoes. However, these individual small-scale studies only provide a limited understanding of the complex host-vector interactions when considered in isolation. Here, we analyze the Culex blood-feeding data from 109 publications over the last 15 years to provide a global insight into the feeding patterns of Culex mosquitoes, with particular reference to vectors of currently emerging Culex-borne viruses such as West Nile and Usutu. Data on 29990 blood-meals from 70 different Culex species were extracted from published literature. The percentage of blood-meals on amphibian, avian, human, non-human mammalian, and reptilian hosts was determined for each Culex species. Our analysis showed that feeding patterns were not significantly explained by mosquito species-level phylogeny, indicating that external factors play an important role in determining mosquito feeding patterns. For Cx. quinquefasciatus, 'Cx. pipiens pooled', and Cx. tritaeniorhynchus, feeding patterns were compared across the world's seven biogeographical realms. Culex tritaeniorhynchus, 'Cx. pipiens pooled' and Cx. quinquefasciatus all had significantly varied feeding patterns between realms. These results demonstrate that feeding patterns of Culex mosquitoes vary between species but can also vary between geographically distinct populations of the same species, indicating that regional or population-level adaptations are major drivers of host utilization. Ultimately, these findings support the surveillance of vector-borne diseases by specifying which host groups are most likely to be at risk.

Pathogens spread by high-altitude windborne mosquitoes

Recent studies have revealed that many mosquito species regularly engage in high-altitude windborne migration, but its epidemiological significance was debated. The hypothesis that high-altitude mosquitoes spread pathogens over large distances has not been directly tested. Here, we report for the first time that high-altitude windborne mosquitoes are commonly infected with arboviruses, protozoans, and helminths affecting vertebrates and humans, and provide the first description of this pathogen-vector aerial network. A total of 1,017 female mosquitoes (81.4%, N=1,249) intercepted on nets suspended from helium balloons at altitudes of 120-290 m above ground over Mali and Ghana were screened for infection with arboviruses, plasmodia, and filariae, using pan-genus qPCR analyses followed by sequencing of positive samples. The mosquito fauna collected at altitude comprised 61 species, across 9 genera, dominated by Culex, Aedes, and Anopheles. Infection and infectiousness rates of high-altitude migrant mosquitoes were 7.2% and 4.4% with plasmodia, 1.6% and 0.6% with filariae, 3.5% and 1.1% with flaviviruses, respectively. Nineteen mosquito-borne pathogens were identified, including three arboviruses: dengue, West Nile and M'Poko viruses, 13 putative plasmodia species including Plasmodium matutinum and P. relictum, three filariids, including Pelecitus spp., 27 insect-specific viruses and 5 non-mosquito-borne pathogens (e.g., Trypanosoma theileri). Confirmed head-thorax (disseminated) infections of multiple pathogens in multiple mosquito species, eg., Culex perexiguus, Coquilletidia metallica, Mansonia uniformis, and Anopheles squamosus provides evidence that pathogens carried by high-altitude windborne mosquitoes are infectious and likely capable of infecting naïve hosts far from their starting location. This traffic of sylvatic pathogens may be key to their maintenance among foci as well as initiating outbreaks away from them.

Mosquitoes feeding on ectothermic hosts: from host seeking to pathogen transmission

While much research has centered on mosquitoes transmitting pathogens to mammals and birds, several species feed on cold-blooded hosts, including amphibians, reptiles, fish, and various invertebrates. Despite limited knowledge about these alternative feeding habits, delving into their biology offers valuable insights into the evolutionary origins of blood feeding and aids in developing comprehensive epidemiological models for vector-borne diseases. This review sheds light on these 'alternative' hosts, highlighting recent discoveries in this field and probing into the evolutionary theories surrounding blood feeding in mosquitoes. Additionally, we delve into the host-seeking cues used by ectotherm-feeding mosquitoes and the physiological and mechanical challenges inherent in feeding on cold-blooded animals, contrasting them with endotherm-feeding mosquitoes. Finally, we examine the pathogens these mosquitoes can transmit. While our understanding of mosquitoes with alternative hosts remains incomplete, this review synthesizes existing knowledge, offering insights into the biology and ecology of mosquito species that target cold-blooded hosts.

Host location by arthropod vectors: are microorganisms in control?

Vector-borne microorganisms are dependent on their arthropod vector for their transmission to and from vertebrates. The 'parasite manipulation hypothesis' states that microorganisms are likely to evolve manipulations of such interactions for their own selective benefit. Recent breakthroughs uncovered novel ecological interactions initiated by vector-borne microorganisms, which are linked to different stages of the host location by their arthropod vectors. Therefore, we give an actualised overview of the various means through which vector-borne microorganisms impact their vertebrate and arthropod hosts to ultimately benefit their own transmission. Harnessing the directionality and underlying mechanisms of these interactions driven by vector-borne microorganisms may provide tools to reduce the spread of pathogenic vector-borne microorganisms.

Insights from multigene analysis: first report of a Southeast Asian Mosquito, Aedes (Mucidus) laniger (Diptera: Culicidae) on Jeju Island from Korea

BACKGROUND

Certain mosquitoes are known as dominant vectors worldwide, and transmit infectious diseases. The expansion of mosquito habitats due to climate change and increased human activities poses a significant health threat by facilitating the spread of various non-native infectious diseases. This study focused on the detection of the Southeast Asian mosquito species, Aedes (Mucidus) laniger (Wiedemann, 1820) on Jeju Island, the southernmost region of the Republic of Korea (ROK), highlighting the potential risks associated with the spread of vector-borne diseases, particularly emphasizing the elevated likelihood of invasion by Southeast Asian mosquitoes.

METHODS

Field surveys were conducted in August 2023 on Jeju Island. Adult mosquitoes were collected using BG-sentinel traps and identified to the species level using taxonomic keys. Morphological and molecular analyses were employed to confirm species designations. Molecular data, including mitochondrial and nuclear genes, were used for phylogenetic analysis, which was performed to compare and identify among recorded subgenera in ROK. Species distribution modeling for Ae. laniger was performed to predict potential habitats using R package 'BIOMOD2'.

RESULTS

The two specimens of Ae. laniger were collected for the first time on Jeju Island. Morphological and molecular analyses confirmed the identity of this species within the subgenus Mucidus and validated the first record of this species in the ROK. We employed a simple multigene phylogenetic analysis to confirm a new mosquito record at the genus and subgenus levels, finally validating the consistency between morphological identification and molecular phylogenetic outcomes. Furthermore, we have updated the taxonomic keys for the genus Aedes in the ROK, and revised mosquito lists for Jeju Island, incorporating the inclusion of Ae. laniger. On the basis of species distribution modeling, the area of suitable habitat for Ae. laniger is expected to expand due to climate change, but this change did not appear to be meaningful in East Asia.

CONCLUSIONS

This case offers the first report of the Southeast Asian mosquito, Ae. laniger, in the ROK. The detection of this species on Jeju Island suggests the potential establishment of a breeding population their habitat and raises concerns about further expansion into the Korean Peninsula. Considering the annual occurrence of mosquito-borne disease cases in the Southeast Asia, it is essential to conduct monitoring not only in Jeju Island, where Ae. laniger has been identified, but also across the entire Korean Peninsula.

JW, Vieira DBR, Brandão RCF, Medeiros DBDA, Nunes Neto JP. Sequencing and Description of the Mitochondrial Genome of Orthopodomyia fascipes (Diptera: Culicidae)

The genus Orthopodomyia Theobald, 1904 (Diptera: Culicidae) comprises 36 wild mosquito species, with distribution largely restricted to tropical and temperate areas, most of which are not recognized as vectors of epidemiological importance due to the lack of information related to their bionomy and involvement in the cycle transmission of infectious agents. Furthermore, their evolutionary relationships are not completely understood, reflecting the scarcity of genetic information about the genus. Therefore, in this study, we report the first complete description of the mitochondrial genome of a Neotropical species representing the genus, Orthopodomyia fascipes Coquillet, 1906, collected in the Brazilian Amazon region. Using High Throughput Sequencing, we obtained a mitochondrial sequence of 15,598 bp, with an average coverage of 418.5×, comprising 37 functional subunits and a final portion rich in A + T, corresponding to the control region. The phylogenetic analysis, using Maximum Likelihood and Bayesian Inference based on the 13 protein-coding genes, corroborated the monophyly of Culicidae and its two subfamilies, supporting the proximity between the tribes Orthopodomyiini and Mansoniini, partially disagreeing with previous studies based on the use of molecular and morphological markers. The information generated in this study contributes to a better understanding of the taxonomy and evolutionary history of the genus and other groups of Culicidae.

Rearing and Shipping of Uranotaenia lowii, a Frog-Biting Mosquito

Many studies on mosquito biology rely on laboratory-reared colonies, emphasizing the need for standardized protocols to investigate critical aspects such as disease biology, mosquito behavior, and vector control methods. While much knowledge is derived from anthropophilic species from genera like Anopheles, Aedes, and Culex, there is a growing interest in studying mosquitoes that feed on non-human hosts. This interest stems from the desire to gain a deeper understanding of the evolution of diverse host range use and host specificity. However, there is currently a limited number of comprehensive protocols for studying such species. Considering this gap, we present a protocol for rearing Uranotaenia lowii, a mosquito species specialized in feeding on anuran amphibians by eavesdropping on host-emitted sound cues. Additionally, we provide instructions for successfully shipping live specimens to promote research on this species and similar ones. This protocol helps fill the current gap in comprehensive guidelines for rearing and maintaining colonies of anuran host-biting mosquitoes. It serves as a valuable resource for researchers seeking to establish colonies of mosquito species from the Uranotaeniini tribe. Ultimately, this protocol may facilitate research on the evolutionary ecology of Culicidae, as this family has recently been proposed to have originated from a frog-feeding ancestor. Key features • Rearing and maintenance of colonies of non-human host-biting mosquitoes that feed on frogs using host-emitted acoustic cues. • Provides shipping guidelines aimed to enhance the establishment of colonies by new research groups and specimen exchanges between labs.

Trends of Mansonia (Diptera, Culicidae, Mansoniini) in Porto Velho: Seasonal patterns and meteorological influences

Entomological research is vital for shaping strategies to control mosquito vectors. Its significance also reaches into environmental management, aiming to prevent inconveniences caused by non-vector mosquitoes like the Mansonia Blanchard, 1901 mosquito. In this study, we carried out a five-year (2019-2023) monitoring of these mosquitoes at ten sites in Porto Velho, Rondônia, using SkeeterVac SV3100 automatic traps positioned between the two hydroelectric complexes on the Madeira River. Throughout this period, we sampled 153,125 mosquitoes, of which the Mansonia genus accounted for 54% of the total, indicating its prevalence in the region. ARIMA analysis revealed seasonal patterns of Mansonia spp., highlighting periods of peak density. Notably, a significant decreasing trend in local abundance was observed from July 2021 (25th epidemiological week) until the end of the study. Wind speed was observed to be the most relevant meteorological factor influencing the abundance of Mansonia spp. especially in the Joana D'Arc settlement, although additional investigation is needed to comprehensively analyze other local events and gain a deeper understanding of the ecological patterns of this genus in the Amazon region.

Finding divergent sequences of homomorphic sex chromosomes via diploidized nanopore-based assembly from a single male

Although homomorphic sex chromosomes can have non-recombining regions with elevated sequence divergence between its complements, such divergence signals can be difficult to detect bioinformatically. If found in genomes of e.g. insect pests, these sequences could be targeted by the engineered genetic sexing and control systems. Here, we report an approach that can leverage long-read nanopore sequencing of a single XY male to identify divergent regions of homomorphic sex chromosomes. Long-read data are used for de novo genome assembly that is diploidized in a way that maximizes sex-specific differences between its haploid complements. We show that the correct assembly phasing is supported by the mapping of nanopore reads from the male's haploid Y-bearing sperm cells. The approach revealed a highly divergent region (HDR) near the centromere of the homomorphic sex chromosome of Aedes aegypti, the most important arboviral vector, for which there is a great interest in creating new genetic control tools. HDR is located ~5Mb downstream of the known male-determining locus on chromosome 1 and is significantly enriched for ovary-biased genes. While recombination in HDR ceased relatively recently (~1.4 MYA), HDR gametologs have divergent exons and introns of protein coding genes, and most lncRNA genes became X-specific. Megabases of previously invisible sex-linked sequences provide new putative targets for engineering the genetic systems to control this deadly mosquito. Broadly, our approach expands the toolbox for studying cryptic structure of sex chromosomes.

Blood-feeding patterns of Culex pipiens biotype pipiens and pipiens/molestus hybrids in relation to avian community composition in urban habitats

BACKGROUND

Culex pipiens sensu stricto (s.s.) is considered the primary vector of Usutu virus and West Nile virus, and consists of two morphologically identical but behaviourally distinct biotypes (Cx. pipiens biotype pipiens and Cx. pipiens biotype molestus) and their hybrids. Both biotypes are expected to differ in their feeding behaviour, and pipiens/molestus hybrids are presumed to display intermediate feeding behaviour. However, the evidence for distinct feeding patterns is scarce, and to date no studies have related differences in feeding patterns to differences in host abundance.

METHODS

Mosquitoes were collected using CO2-baited traps. We collected blood-engorged Cx. pipiens/torrentium specimens from 12 contrasting urban sites, namely six city parks and six residential areas. Blood engorged Cx. pipiens/torrentium mosquitoes were identified to the species and biotype/hybrid level via real-time polymerase chain reaction (PCR). We performed blood meal analysis via PCR and Sanger sequencing. Additionally, avian host communities were surveyed via vocal sounds and/or visual observation.

RESULTS

We selected 64 blood-engorged Cx. pipiens/torrentium mosquitoes of which we successfully determined the host origin of 55 specimens. Of these, 38 belonged to biotype pipiens, 14 were pipiens/molestus hybrids and the identity of three specimens could not be determined. No blood-engorged biotype molestus or Cx. torrentium specimens were collected. We observed no differences in feeding patterns between biotype pipiens and pipiens/molestus hybrids across different habitats. Avian community composition differed between city parks and residential areas, whereas overall avian abundance did not differ between the two habitat types.

CONCLUSIONS

Our results show the following: (1) Cx. pipiens s.s. feeding patterns did not differ between city parks and residential areas, regardless of whether individuals were identified as biotype pipiens or pipiens/molestus hybrids. (2) We detected differences in host availability between city parks and residential areas. (3) We show that in both urban habitat types, biotype pipiens and pipiens/molestus hybrids fed on both mammalian and avian hosts. This underscores the potential role in arbovirus transmission of biotype pipiens and pipiens/molestus hybrids.

Integrated phylogenomic approaches in insect systematics

The increased accessibility of genomic and imaging methods, and the improved access to ecological, spatial, and other natural history-related data is allowing for insect systematics to grow and find answers to central evolutionary and taxonomic questions. Today, integrated studies in insect phylogenomics and systematics are combining natural history, behavior, developmental biology, morphology, fossils, geographic range data, and ecological interactions. This integration is contributing to the clarification of evolutionary relationships, and the recognition of the role played by these factors on the evolution of insects. Future work should continue to build on these advances, seeking to further increase open-access databasing and support for natural history research, as well as expand its analytical palettes.

Neofunctionalization driven by positive selection led to the retention of the loqs2 gene encoding an Aedes specific dsRNA binding protein

BACKGROUND

Mosquito borne viruses, such as dengue, Zika, yellow fever and Chikungunya, cause millions of infections every year. These viruses are mostly transmitted by two urban-adapted mosquito species, Aedes aegypti and Aedes albopictus. Although mechanistic understanding remains largely unknown, Aedes mosquitoes may have unique adaptations that lower the impact of viral infection. Recently, we reported the identification of an Aedes specific double-stranded RNA binding protein (dsRBP), named Loqs2, that is involved in the control of infection by dengue and Zika viruses in mosquitoes. Preliminary analyses suggested that the loqs2 gene is a paralog of loquacious (loqs) and r2d2, two co-factors of the RNA interference (RNAi) pathway, a major antiviral mechanism in insects.

RESULTS

Here we analyzed the origin and evolution of loqs2. Our data suggest that loqs2 originated from two independent duplications of the first double-stranded RNA binding domain of loqs that occurred before the origin of the Aedes Stegomyia subgenus, around 31 million years ago. We show that the loqs2 gene is evolving under relaxed purifying selection at a faster pace than loqs, with evidence of neofunctionalization driven by positive selection. Accordingly, we observed that Loqs2 is localized mainly in the nucleus, different from R2D2 and both isoforms of Loqs that are cytoplasmic. In contrast to r2d2 and loqs, loqs2 expression is stage- and tissue-specific, restricted mostly to reproductive tissues in adult Ae. aegypti and Ae. albopictus. Transgenic mosquitoes engineered to express loqs2 ubiquitously undergo developmental arrest at larval stages that correlates with massive dysregulation of gene expression without major effects on microRNAs or other endogenous small RNAs, classically associated with RNA interference.

CONCLUSIONS

Our results uncover the peculiar origin and neofunctionalization of loqs2 driven by positive selection. This study shows an example of unique adaptations in Aedes mosquitoes that could ultimately help explain their effectiveness as virus vectors.

The chromosome-scale genome assembly for the West Nile vector Culex quinquefasciatus uncovers patterns of genome evolution in mosquitoes

BACKGROUND

Understanding genome organization and evolution is important for species involved in transmission of human diseases, such as mosquitoes. Anophelinae and Culicinae subfamilies of mosquitoes show striking differences in genome sizes, sex chromosome arrangements, behavior, and ability to transmit pathogens. However, the genomic basis of these differences is not fully understood.

METHODS

In this study, we used a combination of advanced genome technologies such as Oxford Nanopore Technology sequencing, Hi-C scaffolding, Bionano, and cytogenetic mapping to develop an improved chromosome-scale genome assembly for the West Nile vector Culex quinquefasciatus.

RESULTS

We then used this assembly to annotate odorant receptors, odorant binding proteins, and transposable elements. A genomic region containing male-specific sequences on chromosome 1 and a polymorphic inversion on chromosome 3 were identified in the Cx. quinquefasciatus genome. In addition, the genome of Cx. quinquefasciatus was compared with the genomes of other mosquitoes such as malaria vectors An. coluzzi and An. albimanus, and the vector of arboviruses Ae. aegypti. Our work confirms significant expansion of the two chemosensory gene families in Cx. quinquefasciatus, as well as a significant increase and relocation of the transposable elements in both Cx. quinquefasciatus and Ae. aegypti relative to the Anophelines. Phylogenetic analysis clarifies the divergence time between the mosquito species. Our study provides new insights into chromosomal evolution in mosquitoes and finds that the X chromosome of Anophelinae and the sex-determining chromosome 1 of Culicinae have a significantly higher rate of evolution than autosomes.

CONCLUSION

The improved Cx. quinquefasciatus genome assembly uncovered new details of mosquito genome evolution and has the potential to speed up the development of novel vector control strategies.

Mechanisms of Yellow Fever Transmission: Gleaning the Overlooked Records of Importance and Identifying Problems, Puzzles, Serious Issues, Surprises and Research Questions

In viral disease research, few diseases can compete with yellow fever for the volume of literature, historical significance, richness of the topics and the amount of strong interest among both scientists and laypersons. While the major foci of viral disease research shifted to other more pressing new diseases in recent decades, many critically important basic tasks still remain unfinished for yellow fever. Some of the examples include the mechanisms of transmission, the process leading to outbreak occurrence, environmental factors, dispersal, and viral persistence in nature. In this review, these subjects are analyzed in depth, based on information not only in old but in modern literatures, to fill in blanks and to update the current understanding on these topics. As a result, many valuable facts, ideas, and other types of information that complement the present knowledge were discovered. Very serious questions about the validity of the arbovirus concept and some research practices were also identified. The characteristics of YFV and its pattern of transmission that make this virus unique among viruses transmitted by Ae. aegypti were also explored. Another emphasis was identification of research questions. The discovery of a few historical surprises was an unexpected benefit.