Experimental Evidence of Differences in Life History Characteristics and Interactions Between Cryptic Species of Diplostomum (Digenea)

Recent DNA studies have uncovered diversity in sympatric species of Diplostomum (Digenea), a cosmopolitan parasite with a three host life-cycle infecting a piscivorous bird, snail and fish at different stages during its life cycle. The goal of this dissertation was to elucidate the basic life history characteristics and interactions of molecularly delineated sympatric cryptic species within fish and bird hosts. Using nomenclature from previous molecular studies, the species were designated as Diplostomum sp. 1, Diplostomum sp. 4 and Diplostomum baeri. The species of Diplostomum studied in each chapter depended on the experimental maintenance of the life cycle in the laboratory over consecutive years. Chapter 1 tested fish host specificity and both Diplostomum sp. 1 and Diplostomum sp. 4 successfully established in phylogenetically diverse fishes classifying them as generalists. Chapter 2 tested temporal heterogeneity on establishment success in rainbow trout (Oncorhynchus mykiss). The data revealed no effect for Diplostomum sp. 4, but a decline in establishment success for Diplostomum sp. 1 in challenge infections. This is indicative of the importance of priority establishment for this species. Chapter 3 examined intestinal spatial distribution and range and fecundity in the bird (Larus delawarensis) host in single and mixed infections. There was a statistically significant shift in intestinal distribution in mixed-species infections for only for D. baeri when Diplostomum sp. 1 was also present. Further, Diplostomum sp. 4 experienced a decline in fecundity in mixed infections with in the presence of Diplostomum sp. 1 whereas fecundity of Diplostomum sp. 1 increased in mixed infections with D. baeri, indicative of interspecific interaction. Chapter 4 then examined life history characteristics and found interspecific differences in egg size and number, where Diplostomum sp. 4 had larger and more numerous eggs than Diplostomum sp. 1. However, there was no intraspecific relationship between egg size and number, nor egg and adult fluke size. Lastly, Chapter 5 revealed faster egg development and greater hatching success for Diplostomum sp. 4 compared to Diplostomum sp. 1. Overall, this dissertation provides novel experimental evidence of host specifity, interactions in both the fish and bird hosts and life-history differences, helpful in species identification, between cryptic species