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Why different morphs of Littorina fabalis prefer different microhabitats

Nes, S. van (1998) Why different morphs of Littorina fabalis prefer different microhabitats. Master's Thesis / Essay, Biology.

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Abstract

Tatarenkov and Johannesson ('94) have recently found out that the flat periwinlde Littorina fabalis has two different morphs at the West coast of Sweden. They are very similar, but differ in size and in genotype of one (out of 30) allozyme loci, namely arginine kinase (Ark). There is also one distributional difference, and that is that the large morph is the most common in exposed habitats and the small morph is the most common in sheltered habitats. In intermediately exposed areas the two morphs overlap, but there is always a lack of exposed/sheltered heterozygote classes of Ark. This systematic pattern of allozyme variation implies that this or a linked polymorphism is not selectively neutral and habitat- elated selection is suggested. Further research (Tatarenkov and Johannesson '98) has revealed that in all habitats, the snails homozygous for alleles of "exposed" type grow faster and mature at a larger size than do snails homozygous for alleles of "sheltered" types. Therefore Tatarenkov and Johannesson ('98) suggest an alternative explanation to the observed deficiency of Ark-heterozygotes; the presence of two, although possibly communicating, gene pools. There is no character diagnostic between the two morphs, therefore it is still a question whether these are different species (which hybridize) or the same polymorphic species (with two reproductive subunits). In this study, possible factors or interactions of factors which can be important for the habitat-related distribution of the two morphs of Littorina fabalis were examined. I used a transplant experiment to test possible interactions between morph, size and habitat and effects of the individual factors on survival and growth of L. fabalis. To test possible microhabitat "preference", I studied the distribution of the snails on fucoids from exposed versus fucoids from sheltered habitats. This test was done in laboratory. In addition to these experiments I measured pH and oxygen concentration of the sea water at each of the sites used in the transplant experiment, and recorded which fucoid algae were present. I found a possible additional explanation for the habitat-related distribution: The two genotypes could have different morphological and physiological differences partly due to their difference on the Ark locus. The variable pH, favouring different Ark allozymes could therefore be partly responsible for the microhabitat- elated distribution of Littorinafabalis.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:44
Last Modified: 15 Feb 2018 07:44
URI: http://fse.studenttheses.ub.rug.nl/id/eprint/9400

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