Population tree and contained gene tree in selected island and mainland populations of B. attenuatus. Population tree (blue) depicting relationships between populations in the Southern_N clade (right) and their corresponding locations (left). The underlying gene tree is represented in pink. The yellow arrow indicates the location of Raccoon Strait, separating Angel Island from the mainland. Note that "Belvedere" here includes (from north to south) the localities Bluff Point, Tiburon and Belvedere of Table 1, whereas "Sausalito" includes (from north to south) the populations Strawberry Point, Marin City and Sausalito (grouped on the basis of their proximity for population tree analyses, see text for details).