Littorina saxatilis Comparative Genomics Hybridization (CGH) study with NimbleGen 090824_L_saxatilis_expr_HX12

Natural selection often produces parallel phenotypic changes in response to a similar adaptive challenge. However, the extent to which parallel gene expression differences and genomic divergence underlie parallel phenotypic traits and whether they are decoupled or not remains largely unexplored. We performed a population genomic study of parallel local adaptation among replicate ecotype pairs of the rough periwinkle (Littorina saxatilis) at a regional geographical scale (NW Spain). We show that phenotypic divergence followed complex evolutionary paths, affecting multiple loci, and including the parallel recruitment of the same genes as well as completely different genes in distinct ecotype pairs. The majority of divergent genes were divergent either for gene expression or coding sequence, but not for both simultaneously, providing evidence for a decoupled evolution among regulatory and coding regions. Overall, our findings suggest that gene expression and coding sequences may evolve independently as a result of being distinctly targeted by evolutionary constraints, and that divergent selection significantly contributed to the process of molecular differentiation among ecotype pairs. Expression array for 25,205 (from which 17,431 satsified the quality criteria) transcripts from Littorina saxatilis with five 60 nt probes per transcript. A full description of the microarray features can be found in Panova et al. (2006). Mol Ecol. 15: 4021-4031. Data correspond to crab (ridged-banded, RB) and wave (sheltered-unbanded, SU) ecotype pooled samples from three Spanish localities. The whole experiment included samples of 72 Galician snails (12 samples per ecotype and locality, 69 samples satisfied quality criteria) for which genomic DNA extracts were individually hybridized to the array.