PHENOTYPIC VARIATION ALONG A CLINE IN ALLOZYME AND KARYOTYPE FREQUENCIES, AND ITS RELATIONSHIP WITH HABITAT, IN THE DOG-WHELK NUCELLA-LAPILLUS, L

The dog-whelk Nucella lapillus exhibits a number of phenotypic variati ons and genetic polymorphisms which correlate with habitat-specific en vironmental pressures, especially those associated with wave action an d temperature. This study investigates the relationship between geneti c composition (karyotypic and electophoretic variation) and phenotypic differentiation in N. lapillus sampled at 15 points along an 8 km str etch of coastline. Coincident clinal variation in gene frequencies and shell shape is described; they covary with differences in karyotype a nd also with growth. Laboratory-reared young show that differences in phenotype (shell shape and growth) are inherited. Experimental evidenc e is presented that specific shell shapes are adaptive under condition s of thermal stress. Together with the well-established correlations b etween shell shape and shore exposure, this association provides an ar gument for a relationship between genetic composition, phenotype and h abitat in this species.