MATERIALS AND METHODS
Samples of Chthamalus were collected in the intertidal rocks by us or were donated by colleagues; the barnacles were fixed and stored in 96% ethanol. The samples used for this study are stored at the Israeli National Natural History Collections at the Hebrew University of Jerusalem (for details see Supplementary Material 1).
We examined Chthamalus stellatus populations from 14 different locations (Figure 1): Five locations are on the Eastern Mediterranean basin – Bodrum (Aegean Sea, Turkey), Dubrovnik (middle Adriatic Sea, Croatia), Fažana (north Adriatic Sea, Croatia), Larnaca (Cyprus) and Rethymno (Crete). Three locations are on the Western Mediterranean basin – Bastia (Corsica), Málaga (north Alboran Sea, Spain) and Melilla (south Alboran Sea, Spain). Three locations are in-between the Eastern and the Western basins, in the Mid-Mediterranean zone – Birżebbuġa (Malta), Bizerte (Tunisia) and Pantelleria (Strait of Sicily, Italy). The three remaining locations are in the Northeastern Atlantic Ocean – Biarritz (Bay of Biscay, France), Canary Islands (Macaronesia) and Madeira (Macaronesia).
Individuals from these 14 populations were characterized by two nuclear genetic markers – EF1 and NaKA. Each population included at least 15 individuals for each marker (See Table 1). GenBank accession numbers used in our study are MT296012-247 and MT633576-654 for EF1, MT296286-518 and MT633655-737 for NaKA.