Accumulation of plerocercoids of Triaenophorus crassus in the second intermediate host Coregonus lavaretus and their effect on growth of the host

Patterns of accumulation of Triaenophorus crassus in its second intermediate host whitefish Coregonus lavaretus s.l. were studied between 1991 and 1996 from two host populations in two separate areas of Lake Saimaa, Finland. Whitefish were infected commonly with several T. crassus plerocercoids and the parasites were aggregated into the oldest hosts. In one host population the annual parasite accumulation was 0·9 parasites in all host age groups between 3 and 8 years. In the other host population the annual accumulation was 1·6 parasites in 3–5-year-old fish, but increased up to 3 to 4 parasites per year in fish over 5 years old. The increase did not coincide with the period of maturation or any increase in whitefish growth, both of which could alter the food intake of the fish. The sharp increase in the annual accumulation suggests a threshold intensity above which the probability of acquiring further parasites increases. In spite of a heavy aggregation of parasites there was no evidence of parasite-induced host mortality. The annual increase in mean abundance was not correlated with the mean annual weight increase in 2–4-year-old fish within cohorts. However, evidence of a negative effect of parasites on whitefish growth was revealed by back-calculation of lengths of uninfected and infected whitefish and correlations between length or weight of fish and intensity of infection with fish age. Both analyses suggested that larger young fish harboured more parasites than the smaller ones while in older fish the reverse was true, a pattern that has not been shown earlier for parasitized fish.     

The karyotypes of Triaenophorus nodulosus and T. crassus (Cestoda: Pseudophyllidea)

Two species of the genus Triaenophorus were found to have widely different chromosome sets. The karyotype of T. nodulosus consists of 26 biarmed chromosomes ranging from 1.45 to 6.75 microns long. The diploid set of T. crassus contains 18 chromosomes with a well-distinguished first pair of large metacentric homologues. All the chromosomes with the exception of the last pair of acrocentric elements are biarmed. Their absolute length ranges from 1.50 to 8.50 microns. The possible pathways of karyotype differentiation and the evolution of these species are discussed.     

Effect of Triaenophorus crassus (Cestoda) infection on behavior and susceptibility to predation of the first intermediate host Cyclops strenuus (Copepoda)

Some parasites have been shown to manipulate host behavior so that parasite transmission to the next host is enhanced. Infection with Triaenophorus crassus Forel (Cestoda) caused alterations in the activity and microhabitat selection of the first intermediate host Cyclops strenuus Fischer (Copepoda) in the laboratory. Infected copepods made more starts to swim but spent less time swimming than uninfected copepods. These changes were independent of the intensity of infection. In a water column illuminated from above, infected copepods approached the surface, whereas uninfected ones remained close to the bottom. In the dark both infected and uninfected copepods stayed near the bottom. Finally, infection with T. crassus increased the probability of C. strenuus being eaten by the second intermediate host, whitefish (Coregonus lavaretus L. s.l.), in the laboratory. In experimental infections, 10-day-old procercoids had significantly lower infectivity for whitefish than older (12-, 14-, and 21-day-old) procercoids. Behavioral changes were detected in infected copepods containing procercoids 12 days old or older but not in experiments with 10-day-old procercoids. These results may indicate that T. crassus changes the behavior of the copepod host only after it has become infective to the next host, which is consistent with the active manipulation hypothesis.     

Populational variability of Proteocephalus longicollis (Cestoda: Proteocephalidae) in the vendace Coregonus albula from lakes of Karelia

Populational variability of Proteocephalus longicollis from the vendace inhabiting various types of Karelian water bodies was studied. High phenotypic diversity of the helminth and polymorphism in the cestode's major functional complexes - attachment, trophic and reproduction - are established. High degree of phenotype pool realization was determined for various P. longicollis populations. Traits belonging to different functional complexes were shown to have different variability patterns. The highest stability was shown for the attachment organs of P. longicollis, which had similar values of qualitative indices and nature of variation. The traits of the trophic and reproduction complexes are more variable. The conclusion was made that the high intrapopulation diversity of P. longicollis is a response to high ecological variability of the vendace, and the distinctions in the phenotype variability of the helminth reflect the differences between population development patterns of the parasite (cestode P. longicollis) and its host (vendace Coregonus albula) in lakes of Karelia.     

The importance of host ecology in thelastomatoid (Nematoda: Oxyurida) host specificity

An experimental investigation of host specificity within the Thelastomatoidea is presented by means of a comparison of the thelastomatoids of two panesthiine cockroaches, Panesthia cribrata and P. tryoni tryoni, with those of other log-dwelling arthropods and those of leaf litter dwelling arthropods found near by. 145 log-dwelling and leaf-litter dwelling arthropods, representing adjacent ecological niches, were collected from Lamington National Park, Queensland, Australia. A high degree of thelastomatoid species sharing (19 incidences from 26 specimens) occurs between log-dwelling arthropods and the two cockroach species. No overlap in thelastomatoid fauna was observed between the log dwelling and leaf-litter dwelling groups. Our results suggest that host specificity of thelastomatoids is largely dictated by host ecology.     

Polymorphism and structure of the population of Proteocephalus longicollis Zeder, 1800 (Cestoda: Proteocephalidae) in the vendace Coregonus albula L

Polymorphism and phenotypic diversity of a hostal ecoform of Proteocephalus longicollis from its typical host, the vendace, Coregonus albula L., were studied. A complex phenotypic structure of the parasite population and presence of morphologically different groupings were revealed. We distinguished four groupings based on the external characters and three groupings based on the feed and reproduction features; among latter groupings one has very specific variations of features. We conclude that P. longicollis has high intraspecific and intrapopulation heterogeneity, and the host plays a stabilising role in the parasite species formation.     

Year-class fluctuations in vendace,Coregonus albula (Linnaeus): Who's got the upper hand in intraspecific competition?

The vendace Coregonus albula (L.) populations in the lakes Mjøsa and Osensjøen exhibited fluctuating year-class strength. In Mjøsa, a strong year-class emerged every third year, except for the four year period between the strong year-classes 1969 and 1973. The difference between the strong and weak year-classes decreased from the 1960s, through the 1970s to the 1980s. The Mjøsa vendace matured sexually at age 2 +, and more than ten sexually mature age-groups were present in the population. Growth ceased at maturation, and asymptotic length was 23.6 cm. In Osensjøen, one strong year-class (1969) dominated the population during the period 1976–1987. The Osensjøen vendace matured sexually at age 3, and more than 15 sexually mature age-groups were present in the population. Growth ceased at maturation, and asymptotic length was 28.4 cm. In both lakes, vendace fed on crustacean zooplankton in the epilimnion throughout summer and autumn. Our data indicate that regular year-class oscillations occur as a result of the juvenile survival being negatively correlated to the number of adults.     

Indigenous microflora associated with the tegument of Triaenophorus nodulosus (Cestoda) and the intestine of its pike host

Investigations of the indigenous microflora associated with the mucous intestines of fish and its cestode parasites have been for the first time carried out using the methods of transmission and scanning electron microscopy. New data on the bacterial biodiversity in the cestode and its fish host are obtained. Nanobacteria and spirochaetes are for the first time revealed in a fish host together with the previously known bacteria forming the intestinal microflora of fish. Spirochaetes were shown to be associated with the intestines of a pike host only, while nanobacteria cover abundantly the surface of the apical parts of the intestinal microvilli and the apical parts of the microtriches in the cestode tegument. The similarity of the bacterial floras associated with the apical surface of the parasite tegument and the intestine of the host should be noted. At the same time, deeper bacterial communities represented by obligate symbionts are specific. Thus, there is a normal indigenous microflora in cestodes, associated with the tegumental surface. This symbiotic microflora has specific morphological features and provides the balance of relations in the parasite-host system.     

Fine structure and development of Triaenophorus nodulosus (Cestoda) during metamorphosis: a review

The results of long‐term investigations of tissue differentiation during metamorphosis in the pseudophyllidean cestode Triaenophorus nodulosus are discussed. The process of tissue reorganization during transformation of the free‐swimming coracidium of T. nodulosus to a parasitic procercoid are studied and the development of all specialized systems (tegumental, muscular, excretory, nervous and glandular) are described and compared. As a consequence, the general cytological mechanism of differentiation has been identified in T. nodulosus. The cytodifferentiation processes are characterized by autophagy of the initial specialized cell population and its replacement by a second population with other morphological and functional potentials. The change in specialized cell populations during morphogenesis is caused by a change in the functional requirements of organs. The primitive nature of the differentiation processes in T. nodulosus at the initial stages of tissue formation is confirmed. It is supposed that destruction of the primary cell populations is the result of apoptosis or genetically programmed suicide.     

The food preference of vendace (Coregonus albula) in South Swedish forest lakes including the predation effect on zooplankton populations

Vendace (Coregonus albula, L.) is in the southern part of its distribution area during the summer period restricted to hypolimnion. Food is dominated by Bosmina coregoni and Daphnia sp. The selectivity index is highest for large cladocerans and large copepods.The pelagic crustacean fauna in vendace lakes is dominated by small species like Bosmina coregoni, Daphnia cristata, Thermocyclops and Mesocyclops sp. and Eudiaptomus sp. During periods of maximum vendace abundance only Bosmina coregoni is left of the cladocerans, while the abundance of cyclopoid copepods increases.     

Structure of scolex hooks and genosystematics of Triaenophorus nodulosus (Cestoda: pseudophyllidea) from the Baikal lake

Data on a hook morphology (in plerocercoid and mature helminths) and gene systematics of Triaenophorus nodulosus from the Baikal Lake are presented for the first time. Sequence analysis of rDNA fragments (5'-end portion of 18S rDNA) yelded 562 nucleotid positions.     

Structure of the pharynx in the adult nematode Anguillicoloides crassus (Nematoda: Rhabditida)

The structure of the pharynx of the adult female nematode Anguillicoloides crassus (Spirurina) has been studied for the first time using light and transmission electron microscopy. The cylindrical pharynx consists of a short anterior muscular corpus and an enlarged posterior glandular and muscular postcorpus. The main cellular components of the pharynx of A. crassus include the muscle cells, the marginal cells, the nerve cells, and 1 dorsal and 2 subventral glands. New observations for nematodes include: (1) the non-contractile regions of pharyngeal musculature in the corpus have specific appearance; (2) the ventrosublateral longitudinal nerve in the pharynx has an enlarged, enucleated anterior part, with a pronounced palmate projections; and (3) abundant lysosomelike membranous bodies consisting of myelinlike figures of varied size present in marginal cells and pharyngointestinal valve. The 2 subventral glands and, apparently, the single dorsal gland, have their openings at the same level, i.e., at the border between the corpus and postcorpus. The pharyngeal-intestinal valve joins the pharynx to the intestine. Knowledge of the ultrastructure of these complex characters may be useful in understanding of functional features, and for comparative morphology as well as evolutionary considerations within the Chromadorea.     

Ultrathin structure of the main lateral nerve cords and accompanying elements of Triaenophorus nodulosus (Cestoda: Pseudophyllidea)

The ultrastructure of lateral nerve cords (LNC) of Triaenophorus nodulosus has been studied. 4 of the 6 types of neurones earlier reported for cerebral ganglia are present in LNC: multipolars, bipolars, unipolars and "light"; neurosecretory cells of the 7th type lie in transverse commissures. The growth and formation of LNC occur at the expense of undifferentiated cells found on the cord periphery among mature neurones. LNC are surrounded with specialized envelopes made of cell processes of excretory vessels and a fibrillar matrix formed at early stages of cestode development. In large axons, cisternae of the cross reticulum are detected, which can serve as ultrastructural marker of the synapse. Two types of muscle innervation are determined. The direct innervation of muscular fibres is realized by peripheral neurosecretory neurones, which form contacts of the paracrine type. The central or sarco-neural innervation of muscular fibers occurs in LNC via the entering muscular processes.     

Cytogenetic analysis of three Italian populations of Coregonus lavaretus (Pisces, Salmoniformes) with chromosomal localization of major and minor ribosomal genes, and telomeric repeats

The European whitefish, Coregonus lavaretus, widely distributed in freshwater of northern Europe and introduced into the major lakes of northern Italy, has been restocked in central Italian lakes. In accordance with current managing practices, a reduced number of spawners contribute to reproduction within each lake and a certain degree of isolation is to be expected between populations from different lakes, resulting in the rapid fixing of chromosomal changes. A detailed survey of three populations from different lakes was carried out using classical and molecular cytogenetic techniques, to verify if specific chromosomal markers are present in the distinct populations. The comparative analysis revealed intraspecific variability of NORs and fixed differences in their number in the three populations. A co-localization of major and minor rRNA genes on one chromosome site was also observed. The original data regarding the chromosome mapping of the (TTAGGG)(n) telomeric repeat obtained in this study, demonstrated their exclusively terminal distribution, and a conspicuous inter-chromosomal variation in the number of repeats. The results are compared with data available for populations from native geographic ranges.     

Seasonal movements and habitat use of river whitefish (Coregonus lavaretus) in the Koitajoki River (Finland), as determined by Carlin tagging and acoustic telemetry

In the Koitajoki River, Eastern Finland, there exists a self-sustaining population of river-spawning densely rakered whitefish (Coregonus lavaretus pallasi). The population has been classified as near-threatened due to overexploitation and possible hybridization with the lake-spawning sparsely rakered whitefish form. Thus, knowledge of habitat use, movements, and migrations is important for threat assessment and management decisions. We employed conventional tagging and acoustic telemetry to provide information on movements and home range of the Koitajoki River whitefish. We tagged mature individuals at their spawning areas and followed fish movements by tag recoveries and continuously recording fixed receiving stations. The maximum movement distances were 40–50?km both upstream and downstream from the releasing site. There were indications of a clear seasonal migration pattern and spawning-site fidelity; riverine habitats were mainly occupied for spawning and overwintering, while feeding and growth mainly took place in lacustrine environments within several lakes of the river system. Due to their migratory nature, whitefish is vulnerable to environmental disturbances and overfishing in a large geographic area.     

Distribution and mechanism of the regulation of the pleurocercoid population count of Triaenophorus nodulosus (Cestoda, Triaenophoridae)

The character of the distribution of pleurocercoids of Triaenophorus nodulosus depending on the host age is shown. Their distribution in perch at the age of 0+-4+ is over dispersed in its character and is described by negative binomial. At the age of 5+ to 8+ the distribution of parasites is of regular character that is apparently due to changes in the mechanism of regulation of the parasites number. The regulation mechanism of the number of pleurocercoids of T. nodulosus is discussed.