Nesho Chipev

Experimental data on the life-cycle of Petasiger grandivesicularis Ishii, 1935 (Trematoda : Echinostomatidae)

Larval stages of an echinostome were found in Planorbis planorbis in a brackish water lake on the Black Sea coast of Bulgaria. The cercaria is a large-tailed form with 19 collar spines. The life-cycle was completed in the laboratory using aquarium-reared fishes (Lebistes reticulatus, Puntius tetrazona tetrazona, P. pentazona pentazona, P. nigrofasciatus, Carassius auratus auratus and Xiphophorus helleri) as second intermediate hosts and canaries as definitive hosts. The redia, cercaria, metacercaria and experimentally reared adults are described. The species is determined as Petasiger grandivesicularis Ishii, 1935, and its cercaria is compared in detail with those of related forms. A key to the known large-tailed echinostome cercariae from the Palaearctic Region is presented.

A model of the dynamics of intramolluscan trematode populations: some problems concerning oscillatory behavior

Abstract A model of the development of a helminth population in a snail host is considered. The model simulates the conditions of a real biological experiment. It is based on the equations of nonlinear age-dependent population dynamics and is investigated numerically using a difference scheme method. An interesting oscillatory behavior dependence on certain parameters is established if the nonlinearity incorporates the population number of a given age group.

Sanionins: Anti‐Inflammatory and Antibacterial Agents with Weak Cytotoxicity from the Antarctic Moss Sanionia georgico‐uncinata

Abstract Sanionins A (1) and B (2) were isolated from the moss Sanionia georgico‐uncinata, collected on the Antarctic Livingston Island. The compounds 1 and 2 were purified by solvent extraction, silica gel column chromatography, and preparative HPLC, consecutively. The structures of the both compounds were elucidated by 1D and 2D NMR experiments and mass spectrometric investigations. These compounds showed activity against important Gram‐positive pathogens, such as mycobacteria, multiresistant staphylococci, and vancomycin resistant enterococci. This activity is combined with antiinflammatoric activity and low cytotoxicity.

Decoy effect and host infection by miracidia within snail communities

The effect of experimental non-host snail (NHS) communities on the infection of Lymnaea truncatula with Paramphistomum daubneyi and Fasciola hepatica miracidia was studied. The results obtained indicated that NHS had variable effects on basic population parameters of host infection. Specifically, NHS were able to produce aggregation of sporocyst number/snail in the experimental host populations. Proposed hypotheses for decoy effect mechanisms failed to explain completely the experimental results. A new mechanism is suggested, based on a distance response of miracidia to snail chemo-attractants, to explain effects of NHS on miracidial host finding behaviour. It is assumed that miracidia have evolved the ability to discriminate among individual snail chemical attractants in a community already at a distance. This attribute of miracidial behaviour allows NHS to induce variations in the effectiveness of individual host localization by miracidia. The resulting aggregation of successful infections/host is assumed to be the specific component of snail decoy effect at the community level. It was also established that NHS affected trematode reproduction in the host inducing a compensatory increase in the intramolluscan population. Intraspecific competition among developmental stages is suggested to be the mechanism of this compensatory reaction.

Physiological diversity of bacterial communities from different soil locations on Livingston Island, South Shetland archipelago, Antarctica

Terrestrial food webs of Antarctica are simple and dominated by microorganisms. Soil bacteria play an important role in nutrient cycling, yet little is known about their capacity to utilize different carbon sources and to participate in site nutrient turnover. Biolog EcoPlate™ was applied to study the catabolic activity and physiological diversity of bacteria inhabiting the soil of moss, vascular plants, and fell field habitats from Livingston Island, Antarctica. Additionally, the number of oligotrophic and copiotrophic bacteria was counted by the agar plate method. Results indicated a lack of site-specific distribution of bacterial abundance, in contrast to bacterial catabolic activity and community level physiological profiles. Community level physiological profiles revealed a common capacity of soil bacteria to intensively utilize polyols, which are cryoprotectants widely produced by Antarctic organisms, as well as site-specific phenolic compounds (vegetated habitats), amino acids/amines (moss habitats), carbohydrates and carboxylic acids (fell field habitat). It was concluded that the physiology of soil bacteria is habitat specific concerning both the rate of catabolic activity and pattern of carbon source utilization.

Isotopic niches of sympatric Gentoo and Chinstrap Penguins: evidence of competition for Antarctic krill?

As climate change, among other factors, is increasingly affecting Antarctic marine systems, competition for prey may increase between predators, particularly in the Antarctic Peninsula which has warmed more than elsewhere. Under such a context, we tested the feeding and trophic ecology of Gentoo (Pygoscelis papua) and Chinstrap (Pygoscelis antarctica) penguins breeding in sympatry at Livingston Island (Antarctic Peninsula) in a single season. We compared the diets of adults (from faecal samples, and stable isotopes in feathers and blood) and chicks (from stomach contents, and stable isotopes in down feathers, toenails and muscles of chicks that had died of unknown causes). Antarctic krill Euphausia superba dominated the diet of both species, although Gentoo Penguins fed on larger Antarctic krill than did Chinstrap Penguins. Stable isotope analyses of adult tissues revealed that both species fed at different niches in successive years, as depicted by the different levels δ13C in feathers (showing values from the previous breeding season) and whole blood (showing values from the current season). Tissues collected from chicks confirmed their diet over different time scales (i.e. days to weeks): Gentoo Penguins fed at a higher trophic level (possibly due to a more varied diet) and in different habitats than Chinstrap Penguins, providing evidence of isotopic niche separation of penguins. Our results may be relevant to the monitoring programmes of the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) and suggest that adult scats, and stomach contents and tissues of recently died chicks, can be used in such programmes.

Origin, state and perspectives of chestnut cultivation in Bulgaria.

The history of Castanea sativa Mill. (sweet chestnut) cultivation has been described on the basis of the available documentation. We have tried to identify the roles of the Greek and Roman civilizations in the dissemination of chestnut cultivation. This paper gives a short overview on the history and present situation of the chestnut cultivation in Bulgaria: presumed quaternary refugia, origin of the chestnut cultivation, driving factors of its diffusion. An attempt is made to describe the actual state of chestnut stands in the two significant regions in Bulgaria, the causes of the decline and future perspective of the European chestnut culture.