Shape relatedness between geographic populations of Culex tritaeniorhynchus, the primary vector of Japanese encephalitis virus: A landmark study

Infect Genet Evol. 2021 Jun;90:104764. doi: 10.1016/j.meegid.2021.104764. Epub 2021 Feb 11.

Abstract

Background: Japanese encephalitis is a severe disease of acute encephalitis, with children and the elderly primarily affected, and with mortality rates reaching over 25%. The virus is transmitted mainly by species of the Culex (Culex) vishnui subgroup, primarily the widely spread Cx. tritaeniorhynchus Giles. The latter is known as a highly migratory mosquito which moves with airflow over large distances. We explored the geometric variation of the wing venation among distant areas of its geographic distribution. Our working hypothesis was that shape variation across geography could reveal known past and present migratory routes.

Materials methods: We compared the wing venation geometry of 236 female Culex tritaeniorhynchus from different locations in the Madagascan (La Reunion), Oriental (Thailand, Vietnam) and Paleartic (Japan) regions. To ascertain the taxonomic signal of the wing venation we also used two species as relative outgroups, Cx. whitmorei and Cx. brevipalpis.

Results: In spite of an increasing morphometric variation as expected with larger geographic dispersion, our Cx. tritaeniorhynchus samples were clustered as a single species when considered relative to other Culex species. The relationships between geographic sites of Cx. tritaeniorhynchus globally conformed with an isolation by distance model. The shape homogeneity of our Palearctic samples (Japan) contrasted with some heterogeneity observed in the Oriental region (Thailand, Vietnam), and could be related to the different regimes of wind trajectories in these regions.

Conclusion: The average shape variation of Culex tritaeniorhynchus disclosed a separation between Madagascan, Oriental and Palearctic regions in accordance with geography. The wing venation not only could reflect geography, it also contained a clear taxonomic signal separating three Culex species. Within Cx. tritaeniorhynchus, a contrasting pattern of shape variation between the Palearctic and the Oriental regions is tentatively explained by the influence of wind trajectories.

Keywords: Culex tritaeniorhynchus; Geometric morphometrics; Japan; La Reunion; Thailand; Vietnam; Winds.