Fine-scale spatial and temporal population genetics ofAedes japonicus, a new US mosquito, reveal multiple introductions

Abstract

The newly introduced mosquito Aedes japonicus has expanded from its original range in Northeastern Asia to 29 US states (including Hawaii) plus Canada and northern Europe. Our objectives were to test an earlier hypothesis of multiple introductions of this species to the Northeastern US and evaluate putative temporal changes in genetic makeup. Using a panel of seven microsatellite loci, we confirmed the existence of two abundant genetic forms in specimens originally collected in 1999-2000 (F(ST) value based on microsatellite data = 0.26) that matches the disjunctive distribution of mitochondrial haplotypes. To examine the distribution of the two genetic 'types' across Pennsylvania we created a fine-scale genetic map of Ae. japonicus using 439 specimens collected from 54 Pennsylvania counties in 2002-2003. We also made direct comparisons between collections in 1999-2000 and new collections made in 2004-2005 obtained from the same areas in the northeastern US. We observed that the strong association between mtDNA haplotype and microsatellite signature seen in 1999-2000 had weakened significantly by 2002 across Pennsylvania, a trend continued to some extent in 2004-2005 in PA, NJ, and NY, indicating that once easily distinguishable separate introductions are merging. The two expanding genetic forms create a complex correlation between spatial and genetic distances. The existence of multiple introductions would be obscured without sampling early and across time with highly polymorphic molecular markers. Our results provide a high-resolution analysis of the spatial and temporal dynamics of a newly introduced disease vector and argue that successive introductions may be a common pattern for invasive mosquitoes.

A Review of the Invasive Mosquitoes in Europe: Ecology, Public Health Risks, and Control Options

“…The genetic diversity of the invasive species probably also plays an important role in its adaptation and therefore the speed of dispersion. Studies of the genetic structure of A. japonicus in the U.S. (Fonseca et al 2010) and Belgium (Coosemans et al 2009) reveal that in both countries multiple introductions probably have occurred. Genetic groups therefore appear to be recombining, increasing species diversity, and thus enhancing the invasive capacity of the species.…”

Evidence that implicit assumptions of ‘no evolution’ of disease vectors in changing environments can be violated on a rapid timescale

“…Both these types of DNA loci are highly variable and provide useful and somewhat independent information on demographic history [46]. We found evidence of multiple separate introductions to the USA and to Europe that often mixed and expanded [41,42,47 …”

“…j. japonicus from Japan and Korea and exotic populations in the USA and Europe using variation at seven existing microsatellite loci [45] as well as at nad4, a mitochondrial locus ( [40][41][42][43][44]; DM Fonseca 2015, unpublished data). Both these types of DNA loci are highly variable and provide useful and somewhat independent information on demographic history [46].…”

“…B 370: 20140136 with other vector species, Ae. j. japonicus is an outstanding model system because we have detailed data on the genetics of its expansion outside its native range [40][41][42][43][44]. This expansion is very recent but already extensive in continental USA, Europe and Hawaii, and occurred at a time when many mosquito surveillance programmes were already 'on alert' monitoring the expansion of Ae.…”

“…albopictus giving us timely knowledge of its arrival in each subsequent location. Specimens for genetic analysis were often collected shortly after its detection in many of the new locations, in some cases allowing detailed spatial genetic studies that have given us the ability to observe both how invasive populations differ from their source population in native environments [40] and how the invasive populations change over space [41,42] and time [42] as they spread through different climate-related environmental conditions in the new regions invaded [43,44].…”