Investigation of the cytogenetics of marine and terrestrial gastropods

Page, Catherine (1985) Investigation of the cytogenetics of marine and terrestrial gastropods. Doctoral thesis, Polytechnic of North London.


The investigation of the chromosomal variation in populations of the land snail Cepaea nemoralis (L.) marine snail Nucella lapillus (L.) is presented.

The first study (Part 1) concerns the investigation of the karyotype of C. nemoralis in populations from a region of the Berkshire Downs (U.K.)in which there are marked area effects for both the visible and allozymic characters.

The present investigation has shown that there are inter-populational differences in chromosome structure. The differences fall within the range found previously in several widespread populations in the British Isles, Northern Europe and America.

There are no immediately obvious variations in chromosome structure associated with observable environmental variables. There are, however, marked non-random associations of karyomorphs within some of the "area effect populations".

The implications of the distribution of the karyotypic variations between the populations are discussed.

The second study (Part 11) concerns the identification of the chromosome pairs involved in the numerical (Robertsonian) and structural (inversion) polymorphisms of Nucella lapillus and the investigation of the two types of polymorphism in populations of low chromosome number.

A new classification of the karyotype into five main groups A to E has been made. The chromosome pairs thought to contribute to the numerical polymorphism occur in groups A, B and C and the two inversion polymorphisms occur in groups A and C.

The distribution of the two types of chromosomal polymorphism at Rottingdean, Sussex (U.K.) suggest that the inversion polymorphism from group C, and the numerical polymorphism, also from group C, occur independently of each other.

The differences in the distribution of the two polymorphisms in the Rottingdean area and the differences in the distribution of the chromosome pairs involved in the numerical polymorphism in different populations are discussed.

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