Genomic shifts, phenotypic clines and fitness costs associated with cold-tolerance in the Asian tiger mosquito. undefined

Climatic variation across geographical gradients is a key driver of genetic differentiation and phenotypic traits evolution, and local adaptation to temperature is expected in widespread species. We investigated the cold tolerance and wing-size changes along the tropical-to-temperate gradient in the native Asian range of the tiger mosquito, Aedes albopictus in relation to adaptive and neutral genetic variation. We refine the phylogeographic structure based on 1,901 SNPs (ddRADseq) from 41 populations and explore the cold response using phenotypic traits (common garden) and ~51,706 SNPs in candidate genes (exon capture) from 9 populations. We confirm the existence of three evolutionary lineages including A) Malaysia, Thailand, Cambodia, and Laos, B) China and Okinawa, C) South Korea and Japan. The average genetic differentiation among candidate genes is 2.5 times higher than among ddRADseq neutral markers suggesting strong selection. We identified signatures of selection in 15 genes in relation to mean temperature including genes involved in lipid metabolism and a circadian clock gene. Allele frequencies at candidate SNPs show two abrupt shifts at ~16°C and 23°C supporting three thermal ecotypes. According to Bergmann’s rule, females are larger at higher latitude, which might provide an evolutionary advantage in colder climate by favoring the storage of energetic reserves. Non-diapausing eggs from temperate populations survive better to cold exposure than those from tropical populations, suggesting they are protected from freezing damages but this cold tolerance has a fitness cost in terms of egg viability. Altogether our results demonstrate the thermal adaptation of A. albopictus across its Asian latitudinal range.