Human-Mediated Marine Dispersal Influences the Population Structure of Aedes aegypti in the Philippine Archipelago

Abstract

BackgroundDengue virus (DENV) is an extraordinary health burden on global scale, but still lacks effective vaccine. The Philippines is endemic for dengue fever, but massive employment of insecticides favored the development of resistance mutations in its major vector, Aedes aegypti. Alternative vector control strategies consist in releasing artificially modified mosquitos in the wild, but knowledge on their dispersal ability is necessary for a successful implementation. Despite being documented that Ae. aegypti can be passively transported for long distances, no study to date has been aimed at understanding whether human marine transportation can substantially shape the migration patterns of this mosquito. With thousands of islands connected by a dense network of ships, the Philippines is an ideal environment to fill this knowledge gap.Methodology/principal findingsLarvae of Ae. aegypti from 15 seaports in seven major islands of central-western Philippines were collected and genotyped at seven microsatellite loci. Low genetic structure and considerable gene flow was found in the area. Univariate and multivariate regression analyses suggested that anthropic factors (specifically the amount of processed cargo and human population density) can explain the observed population structure, while geographical distance was not correlated. Interestingly, cargo shipments seem to be more efficient than passenger ships in transporting Ae. aegypti. Bayesian clustering confirmed that Ae. aegypti from busy ports are more genetically similar, while populations from idle ports are relatively structured, regardless of the geographical distance that separates them.Conclusions/significanceThe results confirmed the pivotal role of marine human-mediated long-range dispersal in determining the population structure of Ae. aegypti. Hopefully corroborated by further research, the present findings could assist the design of more effective vector control strategies.

Fine-Scale Population Genetic Structure of Dengue Mosquito Vector, Aedes aegypti and its Association to Local Dengue Incidence

“…However, it revealed a considerable number of genetic clusters (K=5). These findings are consistent with previous population genetic studies with micro-geographic scales [11,14,16] and local studies in the Philippines [54,59]. Furthermore, these studies reported low genetic differentiation but with substantial number of inferred genetic clusters (K = 3-9).…”

“…aegypti by human-mediated transportation. It is believed that mosquito vectors occasionally travel in long distances by taking advantage human-aided transportation routes via land, sea or air [52,53,54] as Ae. aegypti eggs, larvae and adults have been found in commercial trucks and ships through tire importation [55,56].…”

“…aegypti eggs, larvae and adults have been found in commercial trucks and ships through tire importation [55,56]. In addition, transportation zones such as airports [57] and docks/ports [54,56] can be littered with larvae and pupae of the mosquito vector, thus acting as the source population. Rapid urbanization (e.g.…”

The hitchhiker's guide to becoming invasive: exotic mosquitoes spread across a US state by human transport not autonomous flight

“…) although fewer have explicitly tested the effects of human transportation on the spread of an invasive species (but see Fonzi et al . regarding boat traffic among islands). Medley et al .…”

“…j. japonicus has been human-mediated. Many studies of mosquito population genetics have invoked human-aided long-distance dispersal (LDD) as an explanation for low genetic differentiation between geographically distant populations (Lehmann et al 1996;Huber et al 2004;Brown et al 2011;Brelsfoard & Dobson 2012;Damal et al 2013) although fewer have explicitly tested the effects of human transportation on the spread of an invasive species (but see Fonzi et al 2015 regarding boat traffic among islands). Medley et al (2014) studied the effects of land cover types on the US expansion of another aggressive invader, Aedes albopictus, using nine microsatellite loci.…”