H. De Wolf

Heavy metal accumulation in the periwinkle Littorina littorea, along a pollution gradient in the Scheldt estuary

Inductively coupled plasma atomic emission spectrophotometry (ICP-AES) was used to determine heavy metal concentrations in the shells and soft tissues of the periwinkle Littorina littorea, collected at seven sites along the Scheldt estuary. Several metals accumulate in the animals soft body parts, and are related to the seawards decreasing pollution gradient. No clear correlation with a previously detected shell size patterning could be established.

Allozyme diversity in slugs of the Carinarion complex (Mollusca, Pulmonata)

Previous allozyme analyses of the hermaphroditic terrestrial slugs Arion fasciatus, A. circumscriptus and A. silvaticus (subgenus Carinarion) have suggested that in North America these species are each single monomorphic strains. However, new data on 18 putative enzyme loci show that in western Europe the three taxa, respectively, consist of at least three, two and 12 homozygous multilocus genotypes (strains), which regularly co-occur. The current opinion that American and European Carinarion populations are similarly structured, and that colonization events did not affect the population genetics of North American Carinarion, should therefore be readdressed. The present data also provide the first indication of heterozygosity and possible outcrossing in Carinarion. Nevertheless, uniparental reproduction is confirmed as the main breeding system in West European Carinarion, although the high incidence of multistrain populations in A. silvaticus and A. fasciatus appears at variance with the current model of population genetic structuring in selfing terrestrial pulmonates. Finally, the systematic status of the three Carinarion spp. is tentatively questioned.

Congruence between allozyme and RAPD data in assessing macrogeographical genetic variation in the periwinkle Littorina striata (Mollusca, Gastropoda)

The population genetic structure of the Macaronesian planktonic-developing periwinkle Littorina striata was analysed, using random amplified polymorphic DNA analysis (RAPD). Two primers, yielding six polymorphic loci, were surveyed to infer the population genetic structure of five geographically separated populations (i.e. 10–2000 km). Biased and unbiased allele frequency and heterozygosity levels were estimated and were found to be highly similar. As in previous allozyme studies, our results suggest that populations of L. striata display (i) only little amounts of genetic heterogeneity and population differentiation, (ii) high levels of gene flow, between geographically separated populations and within a single population, between two distinct shell morphs (i.e. nodulose and smooth shells) and (iii) a tendency for northern populations to be less heterozygous than southern populations. The current results reveal a high congruence between allozyme and RAPD data, suggesting that geographically separated populations and different shell morphs share a common gene pool. Given the fact that our RAPD loci might be considered as neutral markers, we conclude that the previously analysed allozymes were representative for L. striatas entire genome.

Intersex and sterility in the periwinkle Littorina littorea (Mollusca: Gastropoda) along the Western Scheldt estuary, The Netherlands.

In this study we present the results of an intersex survey of Littorina littorea along the heavily polluted Western Scheldt estuary (the Netherlands), and record for the first time the intersex phenomenon in L. littorea from Dutch waters. Intersex differed significantly between localities and was the highest in the vicinity of the harbours of Antwerp and Vlissingen, as reflected by the I

Esterase variation in the periwinkle Littorina littorea, along the western and eastern Scheldt estuarium.

Variation in esterase expression (EST) has been investigated in 360 specimens of the periwinkle Littorina littorea collected at nine sites along the polluted western Scheldt and the relatively clean eastern Scheldt estuary. Mean number of EST bands differed among the sites, while a Dice similarity based multi-dimensional scaling along with a minimum spanning tree procedure, revealed an estuary based structuring, clustering the most polluted and least saline like sites together. The underlying factors and mechanisms (i.e. selection, regulation) which are responsible for this structuring remain to be determined.

Lack of significant esterase and myoglobin differentiation in the periwinkle, Littorina striata (Gastropoda, Prosobranchia)

The relationship between gene flow and the maintenance of geographic or morphology-related variation in the polymorphic Macaronesian periwinkle, Littorina striata, was investigated by means of isoelectric focusing of esterases (EST) and myoglobin (Mb). This revealed that: (1) individual EST variation is very high, (2) there is no EST differentiation between sexes, shell morphotypes or wave-exposure regimes, (3) there is no clear macrogeographic patterning of EST variability, although both Cape Verde Islands have the highest, with exception of Flores, mean number of EST bands, and (4) there is no Mb variation, not even between islands separated by more than 2000 km. These results indicate that L. striata shows a high degree of genetic homogeneity among geographic populations and that the morphological patterning in this species persists in the presence of intense gene flow.