Fluctuating asymmetry in Semibalanus balanoides (Crustacea : Cirripedia) at different heights on the shore

Population level studies of fluctuating asymmetry (FA) need to incorporate clinal variation in FA for proper sampling methodologies to be employed to ensure appropriate comparisons between populations are made. FA of adult ac orn barnacles: Semibalanus balanoides, in the intertidal zone offers an exc ellent model system for looking for such variation. This study looked at th e magnitude of FA of S. balanoides at each of three vertical heights in the barnacle zone, in two sites on the Isle of Mull, Scotland. Unsigned FA of width of sutures between tergal and scutal plates: after correcting for siz e and numbers of others touched, showed significant variation across the up per, mid and lower barnacle zone. Specifically, this was a U-shaped pattern , with individuals in the mid-zone being more symmetrical than those at the two extremes. It is proposed that high levels of FA in the upper zone are due to exposure stresses, while biotic factors such as competition impose d evelopmental stress in the lower zone.