Ecological results. A) Gaping behaviour of the eastern and western lineages, each trial is plotted separately, B) Strength of attachment (blocks pooled), each trial plotted separately, C) High and low intertidal limits of P. perna western and eastern lineages. Dots depict mild outliers (i.e. outliers outside the inner fences) and stars are extreme outliers (i.e. outliers outside the outer fences).