BackgroundOriginally native to East Asia, Aedes japonicus japonicus, a potential vector of several arboviruses, has become one of the most invasive mosquito species in the world. After having established in the USA, it is now spreading in Europe, with new populations emerging. In contrast to the USA, the introduction pathways and modes of dispersal in Europe are largely obscure.MethodsTo find out if two recently detected populations of Ae. j. japonicus in The Netherlands and northern Germany go back to new importations or to movements within Europe, the genetic makeup of mosquito specimens from all known European populations was compared. For this purpose, seven microsatellite loci from a representative number of mosquito specimens were genotyped and part of their mitochondrial nad4 gene sequenced.ResultsA novel nad4 haplotype found in the newly discovered Dutch population of Ae. j. japonicus suggests that this population is not closely related to the other European populations but has emanated from a further introduction event. With five nad4 haplotypes, the Dutch population also shows a very high genetic diversity indicating that either the founder population was very large or multiple introductions took place. By contrast, the recently detected North German population could be clearly assigned to one of the two previously determined European Ae. j. japonicus microsatellite genotypes and shows nad4 haplotypes that are known from West Germany.ConclusionAs the European populations of Ae. j. japonicus are geographically separated but genetically mixed, their establishment must be attributed to passive transportation. In addition to intercontinental shipment, it can be assumed that human activities are also responsible for medium- and short-distance overland spread. A better understanding of the processes underlying the introduction and spread of this invasive species will help to increase public awareness of the human-mediated displacement of mosquitoes and to find strategies to avoid it.
The first record of Aedes koreicus was made in the village of Lovrenc na Dravskem Polju, north-eastern part of the country. The discovery of Ae. koreicus in various continental European countries motivated us to revise samples of the collected Aedes japonicus japonicus. We found Ae. koreicus in samples from 2013, where the larvae were misidentified as Ae. j. japonicus. The species was identified morphologically and molecularly. The first discovery of Ae. koreicus advocates an urgent need for a nationwide mosquito surveillance programme.
In Slovenia, two invasive mosquito species are present, Aedes albopictus (Skuse, 1895) (Diptera: Culicidae) and Aedes japonicus (Theobald, 1901) (Diptera: Culicidae). In this study, we examined their actual distribution and suitable habitats for new colonizations. Data from survey of species presence in 2013 and 2015, bioclimatic variables and altitude were used for the construction of predictive maps. We produced various models in Maxent software and tested two bioclimatic variable sets, WorldClim and CHELSA. For the variable selection of A. albopictus modeling we used statistical and expert knowledge-based approach, whereas for A. j. japonicus we used only a statistically based approach. The best performing models for both species were chosen according to AIC score-based evaluation. In 2 yr of sampling, A. albopictus was largely confined to the western half of Slovenia, whereas A. j. japonicus spread significantly and can be considered as an established species in a large part of the country. Comparison of models with WorldClim and CHELSA variables for both species showed models with CHELSA variables as a better tool for prediction. Finally, we validated the models performance in predicting distribution of species according to collected field data. Our study confirms that both species are co-occurring and are sympatric in a large part of the country area. The tested models could be used for future prevention of invasive mosquitoes spreading in other countries with similar bioclimatic conditions.
Invasive species can encounter environments different from their source populations, which may trigger rapid adaptive changes after introduction (niche shift hypothesis). To test this hypothesis, we investigated whether postintroduction evolution is correlated with contrasting environmental conditions between the European invasive and source ranges in the Asian tiger mosquito Aedes albopictus. The comparison of environmental niches occupied in European and source population ranges revealed more than 96% overlap between invasive and source niches, supporting niche conservatism. However, we found evidence for postintroduction genetic evolution by reanalyzing a published ddRADseq genomic dataset from 90 European invasive populations using genotype–environment association (GEA) methods and generalized dissimilarity modeling (GDM). Three loci, among which a putative heat‐shock protein, exhibited significant allelic turnover along the gradient of winter precipitation that could be associated with ongoing range expansion. Wing morphometric traits weakly correlated with environmental gradients within Europe, but wing size differed between invasive and source populations located in different climatic areas. Niche similarities between source and invasive ranges might have facilitated the establishment of populations. Nonetheless, we found evidence for environmental‐induced adaptive changes after introduction. The ability to rapidly evolve observed in invasive populations (genetic shift) together with a large proportion of unfilled potential suitable areas (80%) pave the way to further spread of Ae. albopictus in Europe.
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