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. 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 ’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….

4.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)

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

Estimates of parasite fecundity

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)

Necator Ascaris Schistosoma Trichuris Worm numbers vs. percapita fecundity

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

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

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

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

-Active transmission -Miricidia hatching cues, behaviour -Cercariae morphology and behaviour

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

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