| Summary: | The freshwater pearl mussel, Margaritifera margaritifera, is an endangered bivalve which has suffered a serious decline across its Holarctic distribution. It has a complex life cycle which involves an obligate parasitic stage on a suitable host. M. margaritifera populations are very host specific, and they are able to metamorphose only on the gills of Atlantic salmon (Salmo salar), sea trout (Salmo trutta f. trutta) or brown trout (S. trutta f. fario). Currently, the main concern is the lack of juvenile recruitment and survival in organically enriched river sediments. Consequently, several conservation programmes are rearing mussels in hatcheries, for eventual release back into their natural habitat when they are older and better able to survive. Although M. margaritifera do not reproduce on their hosts, their survival is highly dependent on the presence of suitable hosts. The main purpose of this study was to improve our understanding of the host-parasite interactions and their influence on glochidial or juvenile mussel fitness, with the aim of providing information that could be used to refine future conservation strategies. In the first experiment, the duration of the parasitic phase had a significant positive influence on post parasitic fitness of juvenile mussels in eight populations in Norway. Fitness was measured as size at excystment, post parasitic growth and survival. The strong positive relationship observed between the test variables clearly indicated that glochidial growth and development were dependent on individual host-parasite compatibility. In the same experiment, temperature was also observed to be an important factor governing excystment of juvenile mussels, with higher temperatures decreasing the duration of the parasitic phase. The variation in host suitability has been linked to environmental conditions, host age and/or size, genetic composition of the host and parasite, or a combination of these factors. Therefore, in the second experiment, the effect of host age on glochidial infestation ...
|
|---|