M. Lazaridou-Dimitriadou

Geographical variation in shell morphology and isoenzymes of Helix aspersa Müller, 1774 (Gastropoda, Pulmonata), the edible land snail, from Greece and Cyprus

Geographic variation of shell morphology and isoenzymes of the edible snail Helix aspersa Müller was studied in 24 different regions of Greece and Cyprus. Principal components analysis and cluster analysis showed a geographical trend in seven variable characters examined jointly. Morphological variation between populations was of a sufficient magnitude to create discriminant functions that were able to classify 100 per cent of the cases correctly in only three populations whereas the classifications of the rest varied from 20 per cent to 60 per cent.For the assessment of the genetic polymorphism 13 enzymic systems with 15 loci and 47 alleles were investigated. Three were monomorphic in all populations. The percentage of polymorphic loci (P) ranged from 33.3 per cent to 66.7 per cent and the mean expected heterozygosity from 0.152 to 0.254. Significant deviations from Hardy-Weinberg equilibrium were found in most loci in most populations. Polymorphism varied greatly from one population to another, but there was not correlation between morphological and genetic variation.Spatial autocorrelation in continental populations tended to decrease significantly with increasing distance for several loci. The results found by correspondence analysis and the dendrogram produced by the UPGMA algorithm using Neis identity (I) showed that the degree of genetic identity was high among the populations studied, apart from the group of N. W. Greek populations. The pattern of genetic diversity seem to be influenced by different forces in continental and island populations.

Integrative Evaluation of the Ecological Quality of Metalliferous Streams (Chalkidiki, Macedonia, Hellas)

The present study reports on a year-long (November 1997–November 1998) study of water quality in streams of the Olympias and Skouries areas of Chalkidiki (Hellas), subject to past and present mining activities. Benthic macroinvertebrates were collected from 18 sampling sites at five sampling intervals, while several physicochemical parameters of the water (D.O., pH, temperature, nutrients etc.) were also measured. Five European biotic indices and scores and two multivariate statistical methods (CANOCO, FUZZY) were applied to the macroinvertebrate data. The concentration of various trace metals in the water, sediment, fish and crustaceans were also measured. Most sampling stations exhibited a highly diverse macroinvertebrate fauna during the whole year. However, a slight amelioration of water quality was observed during the high-flow period (winter and early spring), regarding diversity of several invertebrate groups, especially pollution-sensitive families, which decreased. The European biotic indices and scores proved to be relatively ineffective in describing water quality and it is suggested that an Hellenic biotic indice or score should be created. The bioaccumulation studies indicated variable effects of trace metals and organic load on macroinvertebrates according to the degree of load.

Contribution to the ecological quality of Aliakmon river (Macedonia, Greece): a multivariate approach

In the present study, an attempt was made to estimate the water quality of Aliakmon river using five biotic scores (based on benthic macroinvertebrates), physicochemical variables and multivariate data analyzes. Benthic and chemical samples were obtained from 20 sites, during the low flow season (September, 1995). Benthic macroinvertebrates were collected with the three minute kick-sweep method and several physicochemical parameters (D.O., pH, temperature, nutrients etc.) were measured. The multivariate techniques FUZZY and CANOCO were applied to the data. Aliakmon river appeared to have poorer water quality during the low flow season than during the high flow season as determined by comparison with a previous survey undertaken in April 1995. The upstream sites had better water quality than the downstream sites. The performance of the biotic scores was generally satisfactory, but in some cases they were deficient in distinguishing between running waters of good and excellent water quality. On the contrary, the multifactorial analyzes, which consider the abundance of the taxonomic groups, appeared to be more appropriate for the classification of the sites based on the structure of their biocommunities.

Inverse temperature acclimation of heart rate in hibernating land snails.

SummaryThe heart rates of quiescent land snailsHelix lucorum andH. aspersa were recorded by impedance pneumography over several days. When snails acclimated to warm, humid, long days were transferred in late autumn to cool, dry, short days, in order to permit hibernation inverse rotational acclimation occurred, so that heart rates at low temperatures were lowered. However, temperature dependence increased so that heart rates at higher temperatures showed less difference. When hibernatingH. lucorum were brought into warm conditions and allowed to emerge from hibernation, their heart rates at low temperatures were raised. WarmacclimatedH. lucorum showed lower rates and higher temperature dependence before hibernation than after emergence: this may assist their entry into hibernation.H. lucorum showed a higher temperature dependence thanH. aspersa whether warm- or cold-acclimated: this may reflect the lower summer temperatures experienced by this population ofH. lucorum and the obligate nature of their winter dormancy.

EFFECT OF CROWDING ON GROWTH AND MORTALITY IN THE EDIBLE SNAIL HELIX LUCORUM (GASTROPODA: PULMONATA) IN GREECE

ABSTRACT The effect of crowding on growth and mortality in Helix lucorum L. hatched in the laboratory was tested experimentally. The higher the number of grouped individuals, the smaller was the growth and the higher the mortality. The optimum density for this snail under the conditions studied seemed to be 50 individuals/m2 floor area. Densities observed in nature ranged 3–80 individuals/m2.

Evolution of digestion of carbohydrates in the separate parts of the digestive tract of the edible snail Helix lucorum (Gastropoda: Pulmonata: Stylommatophora) during a complete 24-hour cycle and the first days of starvation

In the present study we examined carbohydrase activities during a complete 24-h cycle and during the first days of starvation in both adult and juvenile snails. The results indicated the predominant role of the digestive gland in the secretions of the enzymes responsible for degradation of most of the carbohydrates tested. Salivary glands secreted some digestive enzymes but in amounts lower than secreted by the digestive gland. Enzymatic activities fluctuated during the first hours of digestion and also after the digestive tract was empty. The relatively high enzymatic activities recorded 24 h after the intake of food and during starvation could be due to the circadian rhythm of this species and/or to the participation of an existing microflora in the digestive tract of Helix lucorum. The double origin (exogenous and endogenous) of some digestive enzymes such as cellulases is discussed.