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Evidence of a reproductive barrier between two forms of the marine periwinkle Littorina fabalis (Gastropoda)

Artikel i vetenskaplig tidskrift
Författare Andrey Tatarenkov
Kerstin Johannesson
Publicerad i Biological Journal of the Linnean Society
Volym 63
Nummer/häfte 3
Sidor 349-365
ISSN 0024-4066
Publiceringsår 1998
Publicerad vid Institutionen för marin ekologi, Tjärnö marinbiologiska laboratorium
Institutionen för marin ekologi
Sidor 349-365
Språk en
Länkar <Go to ISI>://000073798500003
Ämnesord allozymes, arginine kinase, colour variation, cryptic species, growth rate, reproductive isolation, wave exposure, dogwhelk nucella-lapillus, 2 sympatric morphs, saxatilis olivi, allozyme variation, microgeographic variation, genetic-variation, snail, differentiation, prosobranchia, populations
Ämneskategorier Molekylärbiologi, Genetik, Etologi och beteendeekologi, Utvecklingsbiologi

Sammanfattning

Studies of allozyme variation may reveal unexpected patterns of genetic variation which challenge earlier conclusions of species delimitations based on morphological data. However, allozyme variation alone may not be sufficient to resolve this kind of problem. For example, populations of the marine intertidal snail Littorina fabalis (= Littorina mariae) from wave exposed parts and from protected parts of the same shores are distinguished by different alleles of arginine kinase (Ark) while indifferent, or very nearly so, in another 29 loci. Intermediate populations have large deficiencies of exposed/sheltered heterozygote classes of Ark and we have earlier suggested habitat-related selection in this locus as the explanation. In this study we estimated growth rate of individual snails of different Ark-genotypes in three different habitats (exposed, sheltered and intermediate). In all habitats the snails homozygous for alleles of 'exposed' type grew faster and matured at a larger size than did snails homozygous for alleles of 'sheltered' types. This relationship was indirectly confirmed in three additional sites of intermediate exposure where exposed Ark-genotypes dominated among large (>8 mm) snails while the sheltered genotypes dominated among small (<5 mm) snails of truly sympatric samples. We furthermore found small differences in allele frequencies of two other loci (Pgi and Pgm-2) and in shell colour frequencies, comparing sympatric snails of exposed and sheltered Ark-homozygotes. Although we found no signs of habitat-related selection among snails of different Ark-genotype, or selection against heterozygotes, we cannot reject selection in Ark, as our experiments only covered one island, one season and grown-up snails. The coupling between allozyme and phenotypic characters in strictly sympatric samples of snails suggests the presence of two gene pools. Perhaps the large and small forms of L. fabalis represent very closely related cryptic taxa. However, introgression between them seems a possible explanation for the striking similarities in the vast majority of morphological and allozyme characters. (C) 1998 The Linnean Society of London.

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