Joshi, S. G. | Search bioRxiv

bioRxiv2023

Aeroplane wing, a new recessive autosomal phenotypic marker in malaria vector, Anopheles stephensi Liston

A novel and distinct mutant, with an aeroplane wing (ae) phenotype, is reported for the first time in the urban malaria vector, Anopheles stephensi. The mutant mosquitoes exhibit extended wings that are easily visible to naked eyes in both sexes. This mutant was first observed in a nutritionally stressed experimental isofemale line and characterized for its genetic inheritance and other related parameters. Meticulous and strategic genetic crosses revealed that the ae gene is an autosomal, recessive, non-sex-linked and monogenic trait with full penetrance and uniform expression in the adult stage. Cytogenetic study of the ovarian polytene chromosome revealed an inversion on the 3L chromosome (3Li) in both the ae mutant and its parent line. No significant differences in wing venation and other parameters were observed in ae mutants compared to their normal parental lines. This ae mutant would be an excellent marker that can be used by researchers to study the function of related genes within the genome. Author summaryIn the present study, we have established and describe the inheritance of an unusual novel aeroplane (ae) winged mutant in Anopheles stephensi, an urban malaria vector in India. The ae mutant lines exhibit three open-wing orientations in both the sexes of adults viz. left (LW), right (RW) and double wing (DW) during its resting phase. Through various inbreeding crosses we demonstrated the mode of inheritance of the ae gene to be autosomal, recessive and monogenic in nature. The morphometric studies of eggs and wings revealed that mutant lines are on par with their parental lines. Cytogenetic study of polytene chromosome of ae mutant revealed the presence of heterogenic inversion on the 3L chromosome arm, which might help in adaptation mechanism. We strongly believe that ae phenotypic markers have great applications bridging both basic and applied genetic research such as constructing linkage maps, identifying loci of quantitative and/or qualitative traits and as guides for insect transformation studies.

genetics↗

bioRxiv2022

Enrichment of phenotype among biological forms of Anopheles stephensi Liston through establishment of isofemale lines

The success of vector management programs relies on knowledge of the biology and genetic make-up of mosquitoes so that they can be interlaced with modern tools for developing suitable intervention strategies. There are many reports available for rearing varied species of mosquito vectors. However, there are limited studies addressing the development of isofemale lines among mosquitoes to homogenize the population to obtain both high-quality genome assemblies and enrichment of phenotype. Anopheles stephensi, an urban malaria vector, is one of the major invasive vectors of malaria distributed throughout the Indian subcontinent, Middle East, and has recently been expanding its range in Africa. With the existence of three biological forms, distinctly identifiable based on the number of ridges on eggs with varying vectorial competence, An. stephensi is a perfect species for developing a method for the successful establishment of isofemale lines, which can be tested for retention of the expected vectorial competence for the various forms. We describe the key steps in the establishment and validation of isofemale lines, which include monitoring the transgenerational fitness traits, morphometrics of eggs, and adult wing size during every generation. After the initial inbreeding depression, as proof of the tedious selection process, no significant morphometric differences were observed in the wings and egg size between the parental and their respective isofemale lines. We observed a significant change in the vectorial competence between the respective isofemale and parental lines enriching expected differential susceptibility towards malaria parasites by the type and intermediate forms. Interestingly, IndCh and IndInt strains showed variations in resistance to different insecticides belonging to all the four major classes. These variant lines have been characterized for their levels of homozygosity both at the phenotype and genotype levels and can be used as a standard reference or as a biological resource for other studies related to urban malaria research. Author summaryIsofemale lines can be a valuable resource for characterizing and enhancing several genotypic and phenotypic traits. This is the first detailed report of the establishment of two isofemale lines of type and intermediate biological forms in Anopheles stephensi. The work encompasses the characterization of fitness traits among the two lines through a transgenerational study. Further, isofemale colonies were established and used to characterize insecticide susceptibility and vector competence. The study provides valuable insights into the differential susceptibility status of the parental and isofemale to different insecticides belonging to the same class. Corroborating with the earlier hypothesis we exemplify the high vector competence in type form than the intermediate from using homozygous isofemale lines. Using these isofemale lines it is now possible to study host-parasite interactions and identify factors that might be responsible for altered susceptibility and increased vector competence in An. stephensi biological forms that would also pave way for developing better vector management strategies.

genetics↗