Phylogeography of the Coastal Mosquito Aedes togoi across Climatic Zones: Testing an Anthropogenic Dispersal Hypothesis

Abstract

The coastal mosquito Aedes togoi occurs more or less continuously from subarctic to subtropic zones along the coasts of the Japanese islands and the East Asian mainland. It occurs also in tropical Southeast Asia and the North American Pacific coast, and the populations there are thought to have been introduced from Japan by ship. To test this hypothesis, the genetic divergence among geographic populations of A. togoi was studied using one mitochondrial and three nuclear gene sequences. We detected 71 mitochondrial haplotypes forming four lineages, with high nucleotide diversity around temperate Japan and declining towards peripheral ranges. The major lineage (L1) comprised 57 haplotypes from temperate and subarctic zones in Japan and Southeast Asia including southern China and Taiwan. Two other lineages were found from subtropical islands (L3) and a subarctic area (L4) of Japan. The Canadian population showed one unique haplotype (L2) diverged from the other lineages. In the combined nuclear gene tree, individuals with mitochondrial L4 haplotypes diverged from those with the other mitochondrial haplotypes L1—L3; although individuals with L1—L3 haplotypes showed shallow divergences in the nuclear gene sequences, individuals from Southeast Asia and Canada each formed a monophyletic group. Overall, the genetic composition of the Southeast Asian populations was closely related to that of temperate Japanese populations, suggesting recent gene flow between these regions. The Canadian population might have originated from anthropogenic introduction from somewhere in Asia, but the possibility that it could have spread across the Beringian land bridge cannot be ruled out.

Modeled distributions ofAedes japonicus japonicusandAedes togoi(Diptera: Culicidae) in the United States, Canada, and northern Latin America

“…Fortyfour North American Ae. togoi records ( Figure 2) were taken from a combination of literature sources (Belton and Belton 1989, Stephen et al 2006, Sota et al 2015, Petersen et al 2017, from personal collection records in Port Renfrew, BC, and Victoria, BC (D. Peach, pers. obs.…”

Modelling the Putative Ancient Distribution of the Coastal Rock Pool MosquitoAedes togoi

“…Ae. togoi is found in coastal areas of east Asia, from subtropical to subarctic environments (Petrishcheva 1948, Tanaka et al 1979, Sota et al 2015, while a peripheral population of Ae. togoi also exists in the Pacific Northwest of North America along the coast of southern British Columbia, Canada (BC) and northern Washington, USA (Belton 1983, Darsie and Ward 2005, Peach 2018, Peach et al 2019.…”

“…togoi also exists in the Pacific Northwest of North America along the coast of southern British Columbia, Canada (BC) and northern Washington, USA (Belton 1983, Darsie and Ward 2005, Peach 2018, Peach et al 2019. The provenance of this population is unknown (Sota et al 2015, Peach 2018, and two alternative hypotheses have been proposed to explain the presence of Ae. togoi in North America: invasion via anthropogenic dispersal and arrival via natural Beringian dispersal.…”

“…Conversely, there is some evidence for anthropogenic dispersal of Ae. togoi in parts of Asia (Sota et al 2015) where it has been found on ships travelling between islands (Bohart 1956) and breeding in artifical containers (Tanaka et al 1979) and the bilges of ships (Hsiao and Bohart 1946). One report suggests that certain populations of Ae.…”

“…Taiwan, and other parts of Southeast Asia, a lineage from the subtropical islands of Japan, a lineage from subarctic Japan, and a lineage from Canada (Sota et al 2015). If the Ae.…”