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Introduction to Parasite Ecology 1. General Misconceptions Parasites are simple and degenerative - morphological/physi

Introduction to Parasite Ecology 1. General Misconceptions Parasites are simple and degenerative - morphological/physiological comparisons - modern approaches (Brooks and McLennan) - compare ps with closest free-living relatives (2000 characters) - 11% were secondary losses

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Introduction to Parasite Ecology 1. General Misconceptions Parasites are simple and degenerative - morphological/physi

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  1. Introduction to Parasite Ecology 1. General Misconceptions • Parasites are simple and degenerative - morphological/physiological comparisons - modern approaches (Brooks and McLennan) - compare ps with closest free-living relatives (2000 characters) - 11% were secondary losses - 89% were character innovations • Parasites evolve towards small sizes - modern approaches - nematode ps of verts much larger than freeliving types - copepod ps much larger than freeliving • Parasites evolve towards higher fecundities - ???

  2. 2. General Questions • any question in ecology can be applied to ps/hs interactions (e.g. ?) • always more complex because ‘habitat’ can respond 3. History of Parasite Ecology • Life cycle studies - 1845-1880’s (Fasciola, Taenia, Wucheria, Ross’s Nobel Prize) • V. Dogiel (1960’s) - descriptive (kill and count) • Holmes (1960’s) - quantitative • Crofton (1972) - mathematical modeling • Anderson and May (1980’s) • Hamilton (parasites and host sex, parasites and sexual selection) • Now….

  3. Parasite transmission and reproduction • Parasites, and their life-cycles, in context • Natural selection, dispersal, life-cycle adaptations • The ‘life-dinner’ principle Reproduction and Fecundity • Asexual reproduction (no gametes) - advantages? • Generally, protists, intramolluscan stages of trems, and some cestodes • Binary fission (longitudinal (tryps) vs transverse (Ameba) division) • Multiple fission (merogony and sporogony of apicomplexans) • Polyembryony - amplification fo winning genome - Digenean tremotodes (Yikes!) • Miracidia - sporocyst - daughter sporocyst (++) - rediae - daughter redia - cercariae • Cyclophylidean Cestodes - external or internal ‘budding’ (or both)

  4. Sexual reproduction • Dioecy - Parasitic arthropods, nematodes, acanths, apicomplexans • Hermaphroditism - trematodes, cestodes • Natural selection for hermaphroditism? a. Fecundity

  5. Estimates of parasite fecundity

  6. b. Factors affecting fecundity • Parasite-related factors • Size, age, genetics • Idea of ‘reproductive inequalities’ • Host-related factors • Host species, for generalists (e.g. Dicrocoelium in cattle, elk, deer, rabbits) • Host size, e.g. snails and swimmers itch • Host immunity, especially for helminths • experiments with immuno-suppressed hosts • Host diet (carbohydrate) - strong affects on growth rate, gametogenesis, asexual reproduction • Intraspecific interactions (crowding effect)

  7. Worm numbers vs. percapita fecundity Necator Ascaris Schistosoma Trichuris

  8. Interspecific interactions • But…. c. Parasite life-histories • Recall general problem that life-history theory attempts to explain • Fecundity vs body size • Egg number vs egg size • Do parasites, usually with complex life cycles, fit into general life-history theory? • e.g. nematodes of mammals • Trichinella: 2 mm; L1’s after 2 days (pre-patency period); lives several weeks; 35 larvae/day • Ascaris: 30 cm; Pre-patency = 60 days; Patency = 75 weeks; 200,000 eggs/day

  9. Female body volume small low growth few eggs short life large fast growth many eggs long life Life-history variation in 66 intestinal nematodes; Skorping et al., 1991

  10. Life history covariation among various traits of schistosomes of mammals. Each pt is a different species. * Large eggs = few eggs = large mira = many mira *

  11. Why are parasite life-history trade-offs different? • energy availability • costs and avoidance of host immunity • transmission windows • we don’t understand complex life-cycles D. Transmission and dispersal • Passive transmission • e.g. eggs, protist cysts, cystacanths • Transmission of crypto cysts via run-off • Cestodes of birds, filamentous eggs of acanths • ‘egg mimics’ • Reward systems

  12. Active transmission • Miricidia hatching cues, behaviour • Cercariae morphology and behaviour

  13. Sp. 1 (India) Sp. 2 • Daily shedding patterns of schistosome cercariae • patterns • mechanisms S. bovis S. mansoni S. haematobium Sp. 3 S. mansoni (rats) Sp. 1 (Africa) Sp. 4

  14. Miracidia vs cercariae behaviours • Free-living stages of nematodes • Free-living stages of arthropods • Active transmission via vectors • e.g. behaviours of Plasmodium-infectedAnopholes • Circadian rhythms of filarids (Wucheria and canine heartworm) • Mechanisms?

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