Project description:Originating from Northeast Asia, the Pacific oyster Crassostrea gigas has been introduced into a large number of countries for aquaculture purpose. Following introduction, the Pacific oyster has turned into an invasive species in an increasing number of coastal areas, notably in Northern Europe. To explore adaptation on reproductive traits of population considered as invasive, we set up a common garden experiment based on the comparison of progenies from two populations of Pacific oyster sampled in France and Denmark. A female-biased sex-ratio and a higher condition index were observed in the Danish progeny, possibly reflecting an evolutionary reproductive strategy to increase the potential success of natural recruitment in recently settled population. Using multifarious statistical approaches and accounting for sex differences we identified several genes differentially expressed between the Danish and French progenies, and with an intermediate expression level in hybrids (additive behavior). Candidate transcripts included mRNA coding for sperm quality and insulin metabolism known to be implicated in coordinated control of reproduction. Our results suggest adaptation of invasive populations during expansion acting on reproductive traits, and in particular on a female-biased sex-ratio, fertility and gamete quality. A common garden experiment was performed in order to compare progenies from two populations of Pacific oyster sampled in France and Denmark and their hybrids. Progenies were reared under standard hatchery and nursery conditions until gonadal maturation. The employed arrays were Agilent 60-mer 4x44K custom microarrays, containing 31,918 C. gigas ESTs, designed by Dheilly et al. (2011).