Table 2

Key features of the three L. saxatilis morph pairs.

locationmorphssizeshell formhabitatadaptationassortative matingaembryo sizeincompatibility in intermediate morph
UKHsmallthin, wide aperturehigh shoreresistant to wave actionyes, I=0.9–1largestrong, elevated rate of embryo abortion
Mlargethick, narrow aperturemid shoreresistant to crab predationsmall
SpainRBlargethick, ridged, narrow aperturehigh shore (barnacles)resistant to crab predationyes, I=0.5–0.9smallweak, depression in embryo size and number
SUsmallthin, wide aperturelower shore (mussels)resistant to wave actionlarge
SwedenEsmallthin, wide apertureexposedresistant to wave actionyes, I=0.6unknownunknown
Slargethick, narrow apertureshelteredresistant to crab predationunknownunknown
  • a I is an index of assortative mating: I=0, random mating; I=1, complete assortment.