Fate of dietary linoleic and linolenic acids in the land snail Cepaea nemoralis (L.)

• 1.1. Linoleic and linolenic acids resorbed from the diet are introduced into the lipid metabolism, but a major part is degradated to carbon dioxide, negating any obvious sparing effect.
• 2.2. Despite the predominance of the linoleic fatty acid series in the snail structural lipids linoleic acid is less effectively incorporated into the phospholipids than is linolenic acid, which may be correlated with the de novo production of linoleic acid in the snail.
• 3.3. Linoleic and linolenic acid chains incorporated into the phospholipids are rapidly elongated and dehydrogenated, while in the triglycerides these precursor acids remain metabolically unaltered.

     

Variation in populations of Cepaea nemoralis (L.) in North Spain

In a survey of 105 populations of Cepaea nemoralis sampled in North Spain, the distribution of morph polymorphism seems to have a climatic component. The area sampled corresponds with the two main climatic regions in the Iberian Peninsula: Green and Brown Iberia, which have an Atlantic and Continental climate, respectively. Paler colour and banding phenotypes are found in the Atlantic zone, while the dark ones are commoner in Brown Iberia. This may arise from climatic selection related to behaviour patterns, which may be particularly important in limiting situations with harsh climates.     

The role of food in the dynamics of populations of the landsnail Cepaea nemoralis

Summary The food of the landsnail Cepaea nemoralis has been studied in natural environments.The diet of Cepaea in nature consists predominantly of senescent or dead plant material. Green material of some species, especially Urtica dioica, is also eaten in large quantities and algae, animal remains, fungi and, possibly, living aphids and thripses are included in the diet.The place where a snail is found during the day usually has a great predictive value for the food it ate during the preceding night. There are, however, exceptions. Species such as Aegopodium podagraria, Calystegia sepium and Phragmites communis are used very often to sit on but are hardly ever eaten. On the other hand species such as Urtica dioica and Ranunculus repens were very much favoured as foodplants but much less favoured as resting places. The distribution of the snails over the various components of the vegetation is not random and neither is the selection of food. The snail distribution does not explain the food selection or vice versa.Quantity of food probably is hardly ever limiting for the distribution and abundance of Cepaea. Some essential components may, however, very well be in short supply and thus be limiting.     

Biosynthesis of saturated and unsaturated fatty acids by a T-strain mycoplasma (Ureaplasma).

A human T mycoplasma (Ureaplasma urealyticum) incorporated radioactivity into its lipids from [1-14C]acetate in the growth medium. Methanolysis of the lipids showed the label to be confined almost entirely to the methyl esters of the fatty acids. About 80% of the label was associated with the methyl esters of the saturated fatty acids, and the rest was found in the unsaturated methyl ester fraction. Gas-liquid chromatography of the saturated methyl esters showed the label to be present in the peaks of palmitate, myristate, and stearate, whereas in the unsaturated methyl ester fraction most of the radioactivity emerged in the peak of palmitoleate. The addition of either oleic or palmitic acid to the growth medium markedly decreased the organisms' incorporation of radioactivity from acetate. It is concluded that the T mycoplasma strain is capable of de novo synthesis of both saturated and unsaturated fatty acids, in this respect differing from all of the Mycoplasma and Acholeplasma strains investigated to date.     

Variation in the distribution and fitness of the brown morph of Cepaea nemoralis (L.)

The distribution of the brown rnorph of the landsnail Cepaea nemoralis in part of the Brendon Hills, Somerset is described. The morph is at a high frequency on north-facing slopes, valley bottoms, and in a broad partly-enclosed basin. It is argued that low temperature is the selective agent. Alternative explanations are considered. In two population cages adult brown-shelled snails survived less well than pink five-banded ones during the summer months, this trend being reversed in the autumn. It is concluded that the experimental results support the 'climatic' interpretation of distributional data.     

Variation in body colour in western Irish populations of Cepaea nemoralis (L.)

Samples of Cepaea nemoralis (L.) taken from sand-dune, lowland and mountain populations show differences in body colour. Overall, sand-dune populations are much paler than those in the other two areas. On sand-dunes, darker and more variable populations are found in densely vegetated habitats; in the lowland, darker forms occur further inland but there is no correlation with vegetation; mountain populations are darker and less variable on north- than south-facing slopes. Overall differences between areas can be ascribed to climatic selection and differences in variation within areas to niche width.     

Gene frequencies, genetic background and environment in Pyrenean populations of Cepaea nemoralis (L.)

Microgeographical genetic differentiation of populations of the polymorphic land snail Cepaea nemoralis (L.) has been the subject of intensive investigation. The importance of environmental selection acting at the loci which control the shell polymorphism in determining the distribution of genes in this species remains a matter of considerable controversy. Some populations of C. nemoralis in the central Pyrenees show striking local associations of morph frequency (and particularly of the frequency of unhanded shells) with topography which have been ascribed to the action of natural selection.
In the Ter valley (eastern Spanish Pyrenees) populations described here, however, the pattern of association of the frequencies of the shell morphs with topography is quite different from that found in the central Pyrenees. In particular, the distribution of unhanded shells is almost the inverse of that found in some previously studied populations. The general picture of variation in relation to topography in Pyrenean C. nemoralis populations is now seen to be one of great local consistency within valley systems, but of considerable differences between valley systems. This variation in population structure may be due either to cryptic and undetected environmental differences between valley systems or to evolutionary divergence between their C. nemoralis populations. The difficulty of deciding between these two conflicting hypotheses emphasizes the limitations of the technique of simply examining the distribution of individual genes in natural populations as a method of analysing their evolutionary history.     

Temporal morph frequency changes in sand‐dune populations of Cepaea nemoralis (L.)

Changes in morph frequency over time in sand‐dune populations of Cepaea nemoralis in the British Isles have been examined using the Evolution Megalab database. Frequencies in colonies on a sand dune at Berrow, Somerset were estimated in 2008–9. This extends a survey started in 1926 by A. E. Boycott and C. Diver and continued in the mid‐20th Century by B. C. Clarke and J. J. Murray. An increase in the frequency of the mid‐banded morph, noted in earlier work, has continued. The apparent decrease in brown was not confirmed but the yellow frequency has increased. At a range of dunes in the British Isles, comparisons between data from the mid‐20th Century and the early 21st Century indicate an increase in yellow and mid‐banded morphs and a decrease in banding and brown morphs. These results differ from the overall trends derived from Europe‐wide comparison of early data with Evolution Megalab data, in which banded and mid‐banded increased in frequency, whereas there was no overall change in yellow. The general pattern of regional variation has been retained, although there is also high heterogeneity between samples, suggesting that a variety of factors are involved in explaining the changes. The mean shifts in frequency are consistent with climatic change over the period. Dunes are probably the most likely habitat in which to detect such a change. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 108 , 315–322.     

The habitats of the land snail Cepaea nemoralis (L.) on downland and their ecogenetie significance

Population densities of adult Cepaea nemoralis (L.) were estimated for nine chalk grassland sites on the South Downs. Estimates of cover, species composition and height of vegetation were also obtained. The density of C. nemoralis was positively associated with Bromus erectus cover, and negatively with Festuca spp. cover. This finding, confirmed by an earlier survey, suggests that the density of C. nemoralis in chalk grassland is directly or indirectly governed by mammalian grazing pressure, and not by the availability of suitable food. Intensely grazed downland is an unsuitable, or at best a marginal habitat for C. nemoralis. This conclusion is discussed with particular reference to 'area effects' in the shell character polymorphism, often found in downland populations of C. nemoralis.