Table 1.

Summary of data gathered from ecotype pairs of Littorina saxatilis in Spain, the UK and Sweden.

	Spain		UK		Sweden		references
ecotype	RB	SU	M	H	S	E
metapopulation structure	coastal and large islands		coastal		small islands
age of establishment	<40 000 yr BP		<10 000 yr BP		<10 000 yr BP		Quesada et al. (2007)
morphological phenotype	large, thick-shelled, narrow aperture, ridged	small, thin-shelled, large aperture, smooth	large, thick-shelled, narrow aperture, smooth	small, thin-shelled, large aperture, smooth	large, thick-shelled, narrow aperture, smooth	small, thin-shelled, large aperture, smooth	Johannesson & Johannesson (1996); Hollander et al. (2006); Conde-Padin et al. (2009)
behavioural phenotype	warya	bolda			wary	bold	Johannesson & Johannesson (1996)
habitat	upper intertidal	lower intertidal	mean intertidal boulders	upper intertidal vertical cliffs	intertidal cliffs	intertidal boulders	Janson (1982); Johannesson et al. (1983); Grahame et al. (2006)
inferred main selection	crabs	waves	crabs	waves	crabs	waves	Johannesson (1986)
hybrid zone extension	sympatricb		sympatricb (low density)		parapatric
hybrid fitness	hybrids as fit as parental forms in hybrid zone		inconclusive, possibly postzygotic barrier		bounded hybrid superiority		Janson (1983); Hull et al. (1996); Rolán-Alvarez et al. (1997); Johannesson et al. (2000); Cruz & Garcia (2001)
evidence of reproductive barrier	assortative mating in microsympatric sites in the field		assortative mating in laboratory experiments		assortative mating in laboratory experiments		Johannesson et al. (1995); Pickles & Grahame (1999); Hollander et al. (2005); Johannesson et al. (2008)
neutral gene flow over hybrid zone compared with within-ecotypec	8.8% (allozymes)		29.2% (AFLP)		12.7% (microsatellites)		Rolán-Alvarez et al. (1996); Panova et al. (2006); Grahame et al. (2006); Galindo et al. (2009)
	19.4% (AFLP)
	7.5% (microsatellites)

^aPersonal observation.

^bFollowing the definition of Futuyama & Mayer (1980). All individuals are capable of crossing the hybrid zone.

^cNm over hybrid zone compared with Nm over same distance within populations of pure ecotype.