Age of infective larvae affects life-history of subsequent stages of the intestinal nematode Heligmosomoides bakeri

Title from first page of PDF file (viewed Dec. 19, 2011)Committee members: Deborah Kristan (chair), William Kristan, Thomas SpadyKeywords: Heligmosomoides bakeri, host susceptibility, intestinal parasite, life-history, Mus musculus, parasite aging, parasite-host interaction, primary infection, sex-specific survivalThesis (M.S.)--California State University San Marcos, 2011Includes bibliographical references (p. 43-45)For many species, males and females have different rates of survival. This holds true for adult females of the nematode Heligmosomoides bakeri that live longer than adult males in their mouse host, possibly due to a greater protection against host assault. However, it is unknown if male and female nematode parasites have differential survival at the free-living infective larval stage (L3). Therefore, it is hard to know the sex ratio of the initial inoculation of parasites that infect mice. I used Heligmosomoides bakeri, a round worm parasite of wild house mice (Mus musculus), to examine if the sex ratio of infective larva changed with larval age and if larval age affected life-history of subsequent life cycle stages of the parasite. In my experiment, mice were infected with different ages of H. bakeri L3 and I determined sex ratios of worms 3 days (L3), 6 days (fourth stage larvae, L4) and 24 days (adult worms) post-infection. I also measured length of L3, L4, and adult worms and adult female worm reproduction. My results showed that percent survival of alive versus dead L3 decreased as the chronological age of L3 increased. Sex ratio of male and female worms was male-biased for L3 infective larvae but was female-biased for L4 and adult worms. The length of the genital primordium (GP) showed differed for female worms at an L3 age of 6 months and the GP was further from the tail tip in male L3 compared to female L3. The difference in total worm length between male and female worms varied with parasite stage. Lastly, in vitro egg production, percent of females with zero egg production, and egg production by female length showed no differences based on L3 age. Overall, these findings help us to understand the effects of L3 age on life history traits of H. bakeri at all life cycle stages after examining their differential surviva