Proteomic analysis of F1 hybrids and intermediate variants in a Littorina saxatilis hybrid zone

Proteomic analysis was carried out on the Crab (upper-shore) and Wave (lower-shore) ecotypes of Littorina saxatilis from a hybrid zone at Silleiro Cape, Spain. Proteome profiles of individual snails were obtained. Protein expression in F1 hybrid snails bred in the laboratory and snails with intermediate shell phenotypes collected from the mid-shore were compared with Crab and Wave ecotypes using analytical approaches used to study dominance. Multivariate analysis over many protein spots showed that the F1 snails are distinct from both ecotypes but closer to the Wave ecotype. The intermediate snails are highly variable, some closer to the Crab and others to the Wave ecotype. Considered on a protein by protein basis, some proteins are significantly closer in expression to the Crab and others to the Wave ecotype for both F1 and intermediate snails. Furthermore, a significant majority of proteins were closer in expression to the Wave ecotype for the F1, consistent with the multivariate analysis. No such significant majority toward either the Crab or Wave ecotype was observed for the intermediate snails. The closer similarity of F1 and Wave ecotype expression patterns could be the result of similar selective pressures in the similar mid-shore and low-shore environments. For a significantly larger number of proteins, intermediate snails were closer in expression to the ecotype having the lower expression, for both Crab and Wave ecotypes. This is somewhat unexpected as lower expression might be expected to be an indication of impairment of function and lower fitness. Proteomic analysis could be important for the identification of candidate proteins useful for gaining improved understanding of adaptation and barriers to gene flow in hybrid zones.