Thesis

An analysis of Helminth infections in Bufo boreas and Hylas regilla in Southern California

A study was made of the helminth parasites infecting the Pacific treefrog, Hyla regilla, and the California toad, Bufo boreas, at Malibu Creek and Big Tujunga, California. Malibu Creek represented a cool, humid coastal habitat and Big Tujunga represented an arid inland wash habitat. Examinations of the frogs were performed on a regular basis to determine seasonal infection rates. Frogs were collected and necropsied, and helminths were isolated and identified from prepared slides. Statistical tests were used to analyze associations between size of host and sex of host with infection rates. Different infection rates between localities and hosts were analyzed statistically. Nematodes were the most frequent helminths found, and of these, Oswaldocruzia was most abundant. Rhabdias, Cosmocercoides, Distoichometra, and Glypthelmins were also recovered. Oswaldocruzia infections in Hyla regilla and Distoichometra infections in Bufo boreas are recorded here for the first time. Seasonal occurrence of the helminths showed no definite pattern. Regression analyses indicated that helminth intensity varied significantly with host size. Erratic seasonal fluctuations of infection were related to the distribution of host age groups. Significant differences between localities existed regarding the incidence of infection. Factors responsible for these differences included host age, host-parasite density, and environmental conditions affecting infective helminth larvae. Significant differences between host species did not exist regarding incidence and intensity of infection. Both hosts were sympatric, inhabited similar environments, and were subject to similar infections.

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