[Trematode distribution in Littorina saxatilis populations can support the reproductive potential of the host: "toilers" and "idlers" among female periwinkles].

Co-evolution between parasites and their hosts can involve adaptations on the individual and population levels likely to be especially prominent in the systems where parasites have a direct strong impact on the hosts fitness, as is the case with castrating trematodes and their gastropod hosts. We studied populations of the rough periwinkles Littorina saxatilis in the White Sea infested by castrating trematodes to determine whether spatial and temporal variations in the trematode prevalence affect the demographic structure of the host population. Sex, age, reproductive status and infestation of L. saxatilis from 19 populations with different trematode burdens (from < 1 % to 30-50%); in two of these 19 populations (RI and KLN) a long-term monitoring over the period of 15-20 years was also performed. These analyses showed that (1) the average age of gravid females did not correlate with the trematode prevalence of the population, (2) the ratio was skewed towards females, (3) the trematode prevalence in females tended to be higher than in males, (4) the proportion of the non-infested gravid females of the younger ages classes (2-4 years) did not correlate with trematode prevalence of the population. The proportion of young non-infested females that were not reproducing ("idlers") decreased significantly with increasing infestation prevalence when compared among different populations of L. saxatilis, but remained relatively stable within two heavily infested populations RI and KLN despite the year-to-year fluctuations of the infestation prevalence. Thus, a demographic mechanism to compensate for the parasite pressure in L. saxatilis populations may involve the maintenance of a relatively constant proportion of uninfected gravid female ("toilers") at the expense of uninfected, but not reproducing females of fertile age ("idlers"); the latter can be viewed a reproductive reserve of the population tapped into under the conditions of high infestation prevalence. This mechanism, in combination with the previously described elevated individual fecundity of females in heavily infested populations, may compensate for the parasite-induced decrease in the reproductive potential of the host population and ensure the stability of the host-parasite system.

[Morphoprocess and life cycles of organisms].

In developing the ideas of V.N. Beklemishev about an organism as a form, existing in a process of determined transformation and matter/energy exchange, we consider different aspects of the term "morphoprocess" and introduce corresponding additional terms. Momentary morphoprocess characterizes an organism in the given moment of time. This term reflects a constancy of the form ("momentary form"), where the existence of an organism can be imagined as a sequence of "momentary forms". "First derivative" of this momentary characteristic is particular morphoprocess--an organism from its origin to fission/division or death. Compound particular morphoprocess is a determined and reiterating sequence of different particular morphoprocesses. And, at last, general morphoprocess--a "second derivative" of momentary morphoprocess--is rhythmical reiteration of a particular morphoprocess on the long-term scale, an ancestors/descendants lineage. To describe consecutive changes in this material system, the terms ontogenesis and life cycle are used. Ontogenesis characterizes a sequence of the morpho-functional changes of an individual organism during its life, whereas life cycle reflects a sequence of changes during one complete segment of the general morphoprocess represented by a single or several particular morphoprocesses. We also discuss morphoprocess uniformity along with the phase nature of morphoprocesses, both particular and compound particular ones.

[Modification of the structure of penial glands in males of the intertidal molluscs Littorina saxatilis and L. obtusata under the influence of the infestation by trematode parthenites].

Sporocycts of the "pygmaeus" microphallides (Microphallus piriformes) are localized in hepatopancreas and gonads of Littorina molluscs causing total parasitic castration. A histological study of penial glands in Littorina saxatilis and L. obtusata males infested with trematodes M. piriformes has been made. Copulatory organs of noninfested molluscs, molluscs after recent contamination (with not completely formed daughter sporocysts), and molluscs containing mature metacercariae inside daughter sporocysts were examined. Based on the data obtained, probable dynamics of the histological structure of infested glandular apparatus was established. It was shown, that the trematode infestation have an influence on the muscular and secretory parts of penial glands. The wall of the penial gland muscular capsule becomes more fine in infested L. saxatilis. On the contrary, this wall is vastly thicker in infested L. obtusata, as compared with noninfested individuals. Glandular cells of the molluscs' penial glands decreases the amount of granular secret in both species. In L. obtusata the number of secretory cells is shown to be reduced up to their total disappearance. The above pathological changes probably prevent normal function of penial glands.

[Infection of the mollusc Littorina saxatilis with parthenites of trematodes and their impact on a shell form: analysis of populations inhabiting the littoral coast of the White Sea]. / Zarazhennost' partenitami trematod i vozdeistvie parazitov na formu rakoviny briukhonogikh molliuskov Littorna saxatilis: analiz populiatsii, obitaiushchikh na skalistoi litorali Belogo Moria.

12 rocky shore populations of Littorina saxatilis from three islands of Chupa Inlet (Kandalaksha Bay, White Sea) were examined for infection with trematodes. Morphometric characters (6 indexes of the shell and aperture shape) of molluscs were investigated for all these populations. Exposed and sheltered sites were considered at every island and high and low littoral samples were fulfilled at every site. Seven species of trematodes, Podocotyle atomon, Cryptocotyle lingua, Renicola sp., Himasthla sp., Microphallus piriformes, M. pygmaeus, M. pseudopygmaeus, were found. Uneven distribution of trematodes was confirmed by log-linear analysis. Sheltered populations of L. saxatilis have the greater infection prevalence than exposed ones. This is due to the heavy infection with M. piriformes and M. pygmaeus. The prevalences by these trematodes are up to 52.97% and 27.16% respectively in sheltered populations of the host. The prevalence of M. piriformes tend to be higher at the upper shore level of sheltered sites. In a contrast, the prevalence of M. pygmaeus is significantly higher at the low part of such sites. Factor analysis shows a significant association of the indices of L. saxatilis shell shape with three factors. The first one is associated with the "elongation" of a shell and reveals L. saxatilis from the exposed rocky shore to be more elongated than the molluscs from sheltered sites. The second one is connected with the "aperture shape" index. There is an association of this factor with the shore level position of samples. The third factor reflects the affect of trematodes on the shell shape. The molluscs infected with M. piriformes show "elongated" shell shape and relatively smaller aperture. Shall peculiarities of the hosts infected with M. piriformes and M. pygmaeus are somewhat different. The results of the factor analysis is justified by the series of analysis of variances on the values of shell indices (MANOVA) according to the factors "exposure", "shore level" and "infection".

[Genetic heterogeneity in natural populations of Microphallus piriformes and M. pygmaeus parthenites (Trematoda: Microphallidae)]. / Geneticheskaia neodnorodnost' prirodnykh populiatsii partenit Microphallus piriformes i M. pygmaeus (Trematoda: Microphallidae).

The random amplified polymorphic DNA (RAPD) technique was applied for the studies of genetic heterogeny between several natural populations of trematodes belonging to the Microphallida family. Initially, the metacercariae from the daughter sporocysts infestating Littorina saxatilis and Littorina littorea periwinkles were used. Comparison of the banding patterns obtained for the different metacercariae within one sporocyst gave an unpredicted results. For two of three studied species (M. pygmaeus and M. pseudopygmaeus), the considerable differences in RAPD patterning was detected. According to the classical point of view, the process of cercariae (metacercariae in case of the "pygmaeus" group of microphallides) formation does not include DNA recombination. Because of that, all metacercariae within one single sporocyst should be genetically identical. However, data obtained clearly shows that at least in some cases it is not so. We can hardly believe that such result could be a methodological artifact, for not single difference in a RAPD patterns was recorded between the metacercariae within sporocysts of M. piriformes. Moreover, even the 100 fold dilution of the total DNA used for PCR amplification does not change the banding patterns. Hence, our results can not be explained by slight fluctuations in the DNA concentrations between the samples. The most evident conclusion is that we came across yet strange, but real phenomenon--some degree of genetic difference within the progeny of each of the sporocysts--metacercariae. However, the detailed study is needed to understand and interpret these observations correctly. Amplification of the total DNA extracted from the whole sporocysts (containing metacercariae) never showed any differences in RAPD patterns between the parasites been derived from one infestated snail (local parasite hemipopulation). That allowed us to compare different parasite populations referring the RAPD pattern of one sporocyst from a snail to as a representative of one local hemipopulation. Analysis of the RAPD-loci frequencies showed a considerable genetic differences between the subpopulations of M. piriformes, infestating different paraxenic intermediate hosts--L. saxatilis and L. obtusata. This phenomenon was statistically significant for 2 localities of 3 studied. No heterogeny within populations was recorded for M. pygmaeus. Both M. piriformes and M. pygmaeus are characterized by the genetic differentiation in the microgeographic scale (within the Chupa bay of the White sea, the longest distance between the analyzed localities is 20 km). According to the frequencies of the RAPD-loci, parasites from the sheltered locality differ significantly from the parasites of other two localities exposed to the open sea. For both species the degree of genetic similarity between the populations correlates positively with the distance between the localities. We can suppose that the population structure of microphallids depended mainly upon the population structures of their intermediate hosts, definitive hosts and geographical structure of the areal. However, taking into consideration the low motility of snails, we believe that the distribution, migration and species composition of the definitive hosts play the key role in the genetic structuring of M. pygmaeus and M. piriformes hemipopulations. As an addition, the RAPD analysis of the parasite populations from the Barents Sea (East cost of Murman peninsula) and North Sea (Western cost of Sweden) revealed no significant genetic differences between the worms from those places and from the White Sea. However in case of this macrogeographic comparison, insufficient number of samples does not allow us to draw any final conclusions.

[Parasitic systems and the population structure of parasitic organisms]. / Parazitarnye sistemy i struktura populiatsii paraziticheskikh organizmov.

The analysis of population systems is carried out on the basis of the classification of spatial and functional structure of populations developed by V. N. Beklemishev. Two aspects of the structure of population systems are established. Firstly, population systems are composed of the smaller groups characterised by different self-maintenance ability. Secondly, different functional parts are included into these systems in accordance with different stages (phases) of a life cycle. Peculiarities of the population systems are discussed from these points of view. The population system is a functional part of a particular community. Steady interrelationships between population systems in the community ("community links") are the basis on which the complexes of population systems in different species are formed. A prominent example of this is the parasitic systems, that is the population system of a parasite and all connected populations of its hosts. The structure of a parasitic system is examined. In general, it is characterised by a) peculiarities of the life cycle of the parasite, since its population systems are the organising component of the parasitic system; b) subdivision of the environment for parasites. The first trait is discussed from the standpoint of phase structure of populations which is could be clearly seen in parasites, and the second one-from the viewpoint of the availability of distinct microbiotopes connected with different parts of the population system of parasites. It is the subdivision of the parasites' environment and its organisation according to the scale (interspecies, interpopulation or intrapopulation) variability of the hosts, that make it possible to recognise spatial and functional parts in the framework of the parasitic system. The critical review of the terminology used in the population parasitology is presented.

[Age-related characteristics of the infestation of populations of the littoral periwinkles Littorina obtusata and L. saxatilis by trematode parthenitae]. / Vozrastnye osobennosti zarazhennosti populiatsii litoral'nykh molliuskov Littorina obtusata i L. saxatilis partenitami trematod.

Analysis of the age structure of parthenitae of trematodes of sympatric populations of L. obtusata and L. saxatilis was conducted in 1983 for 6 localities in Kandalaksha Bay of the White Sea. 10 species of trematodes were found. The main populational differences in the level of infection are caused by Microphallus piriformes. Species with secondary dispersion in the life cycle are characterized by the increase in the extent of infection in populations with age. In Microphallidae species of "pygmaeus" group the age structure of infection depends on the overage infection of populations: the increase in the parasitic press leads to the maximum turning towards the young part of the snail's population. The establishment of the age structure of infection is considered to be one of the regulation mechanisms in parasite--host relations on the populational level.