Lung-worms (Nematoda: Pseudaliidae) of harbour porpoises (Phocoena phocoena) in Norwegian waters: patterns of colonization.

We studied the component community of lung-worms of the harbour porpoise, attempting to establish the relative importance of ecological and evolutionary factors on its development. The lungs of 64 porpoises by-caught in Norwegian waters were examined for helminths. Three pseudaliid species were detected. The porpoises appear to be readily colonized by lung-worms, the structure of the component community of calves being fairly similar to that of the remainder. Prenatal and/or transmammary infections might partly account for these early infections. However, host age was correlated with the number of lung-worm species, suggesting that the lung-worms may have heteroxenous cycles similar to other metastrongyloids. The lung-worm species tended to co-occur more often than expected by chance. This pattern is commonly observed in communities formed by phylogenetic relatives. Mean species richness of lung nematodes differed significantly among mammalian orders. However, species richness of marine species seemed very similar to those of most terrestrial species. This evidence suggests that phylogenetic factors seem more important than ecological ones in determining the number of lung-worm species in mammals.

On the morphology of procercoids of the genus Proteocephalus (Cestoda, Proteocephalidea).

The morphology of larvae of four Proteocephalus species from copepod crustaceans as studied by scanning electron microscopy is described. Differences between species in the shape of the body and scolex as well as in the body size and relative position of suckers were revealed. In some species, a host-dependent variability in dimension indices and microthrix density was observed.

Segregation and co-occurrence of larval cestodes in freshwater fishes in the Bothnian Bay, Finland.

Two autogenic (Triaenophorus crassus and T. nodulosus) and four allogenic (Diphyllobothrium latum, D. dendriticum, D. ditremum and Schistocephalus solidus) larval cestode species were found in 13 out of 31 fish species studied from the Bothnian Bay, NE Baltic. Gasterosteus aculeatus was the most heavily infected fish with 4 larval cestode species; for two of them (D. ditremum and S. solidus) the three-spined stickleback was found to be the required fish intermediate host. Among allogenic cestode species, those restricted to different definitive host species segregated their larval population in relation to the fish host, while, for example, D. ditremum and S. solidus, both maturing in fish-eating birds, had the highest percentage of co-occurrences. D. dendriticum, which had the widest range of definitive hosts, was found in the greatest number (8) of fish species and co-occurred with all other species found except T. crassus. The two autogenic species totally segregated their larval population from each other although they both require pike as definitive host. The ecological and evolutionary relationships behind the patterns found for larval cestodes are discussed.

On the infracommunity structure of adult cestodes in freshwater fishes.

The distribution-co-occurrence and exchange of adult cestode species in two fish communities (the Bothnian Bay and Lake Yli-Kitka both in Finland) was studied. Coexistence of two or more mature cestode species in the same fish host population was zero for all fish species studied (33) except pike in the Bothnian Bay and whitefish in the lake. It was found that 60% of the fish species studied in the Bothnian Bay and 80% of the fish species studied from Lake Yli-Kitka harboured only 1 mature cestode species. Exchange of adult cestode species between the different fish species in these two fish communities was found to be as rare as coexistence. The infra-community structure of adult cestodes in freshwater fish thus turned out to be markedly different from what is known to be the situation in birds. The evolutionary explanation behind the differences is discussed.