Genetic differentiation in the molluscan species Littorina rudis and Littorina arcana (Prosobranchia: Littorinidae)

Abstract

Six populiiiioii> 01' Li/forinn r u d \ and three or I.. arrnna were screened for rlectl-ophol-ctically tlcrcc riil~lc vat-iiition at 2 1 enzyinr loci. These species repl-odure by ovoviviparity a n d oviparicy respectively, and both are members of the L. saxatilis species complex. The mean coefficient of genetic identity (7) between the two species was high (0.957) and no diagnostic loci were observed. t\llcdc, I k q t i c t i ( y clilli~t-cncrs arc inaintained i n syinpatl-ic population5 or lhr two Fpecics. Intrasprcilic w l c i (~~ 01. / t.;iiigctl ii.otn 0.944 to 0.995 and both sprcirs showrd markrcl intrt--p(~piila'ion geneticIic~rc~wgciiciry, ii li~.itut.c~ consistent with their liinited powers or dispersal. Hetrrozygosity is high i n all populations of both species. Populations of L. rudij have higher mean heterozygosities (I? = 0.153)

Genetic drift in small and recently founded populations of the marine snail Littorina Saxatilis

“…Populations of L. saxatilis differ genetically in allele frequencies on a large geographic scale, as well as over microgeographic distances (<10 m) (Ward and Warwick, 1980;Janson and Ward, 1984). In accordance with this, a gene diversity analysis (Nei, 1973) of the 18 populations from the Koster archipelago reveals differentiation of all five polymorphic loci over this area (8 km2), between 4 and 21 per cent being the fraction of between-population variation (table 2).…”

“…The level of genetic variation were estimated by means of starch gel electrophoresis of 13 allozyme loci. (Methods and allele designations as in Warwick, 1980, andJanson andWard, 1984. ) Five of the loci (Aat-l, Pgm-1, Pgm-2, Mpi, and Pgi) were polymorphic when applying the 0.95 criterion of polymorphism, while the remaining eight (Mdh-1, Idh-l, Odh, Xdh, Sod, Est-1, Lap-i, and Ap-2) were monomorphic.…”

Genetic analysis of ten polymorphic enzyme loci in Littorina saxatilis (Prosobranchia: Mollusca)

“…A full description of the breeding technique is given by Warwick (1983). When sufficient live young were seen, often after repeated matings, the parents were sacrificed and screened for electrophoretically detectable enzyme variation using the methods of Ward and Warwick (1980). If the presumed parental genotypes were such that screening of the offspring would provide useful information, individuals of the Fl generation were reared to a size of 25-40 mm and then electrophoresed.…”

“…Each animal was homogenised in 25 l of 02 M Tris-HC1, pH 80, providing sufficient extract for at least nine enzymes to be screened if desired. Locus and allele designations follow Ward and Warwick (1980) and Janson and Ward (1984).…”

“…In recent years, several papers have been published concerning the extent of genetic differentiation within and between populations of several species of the genus Littorina (e.g., Snyder and Gooch, 1973;Berger, 1977;Ward and Warwick, 1980;Wilkins and O'Regan, 1980;Mastro et a!., 1982;Moyse et al, 1982;Janson and Ward, 1984;Ward and Janson, 1985), a genus which comprises an important group of marine intertidal molluscs. In these studies, the genetic nature of the observed enzyme variation has been inferred, explicitly or implicitly, either by comparison with zymogram patterns of other animal species where formal breeding studies have been carried out or by comparison of phenotype distributions with the genotype distributions expected for genes in Hardy-Weinberg equilibria.…”