The morphology of the threespine stickleback and its relation to predators and parasites, from three lakes in western Norway
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We studied the three-spined stickleback (Gasterosteus aculeatus) in three different lakes, with respect to morphology (Dorsal spine numbers and pelvis), distribution and relationship to the parasites Schistocephalus solidus and Glugea anomala and selective predation by fish predators. From these investigations we concluded the following. 1) We found possible indications that fish predators may have an effect on the population of S. solidus and G. anomala, and the morphological traits of the stickleback. 2) The stickleback's morphology related to parasites in Lake Liavatnet, showed that the pelvis reduced group had the lowest total volume of G. anomala cysts. May be due to fish predation pressure, or possibly because the group are hybrids made from introgression in Lake Liavatnet, which makes them less susceptible to G. anomala than the two other groups. The stickleback population from Lake Nesavatnet, we found a difference in prevalence from G. anomala and dorsal spines, as three spines we more infected than two spines. For S. solidus, we found that number of infections was higher and total volume was larger for two dorsal spines than for three. The result was not significant, but was opposite of the result from G. anomala 3) No relationship was indicated between G. anomala and S. solidus, as neither total volume nor number of infections was impaired by the presence of the other parasite.