TOPICS IN PARASITOLOGY 2008 I. INTRODUCTION A. Organisms are categorized by how they acquire energy 1. Energy from non-living sources a.

Transcription

1 TOPICS IN PARASITOLOGY 2008 I. INTRODUCTION A. Organisms are categorized by how they acquire energy 1. Energy from non-living sources a. Plants - sunlight b. Chemosynthetic bacteria inorganic chemicals (1) Hot springs (2) Hydrothermal vents (3) Cold water seeps in Gulf of Mexico c. Fungi/bacteria decomposers Picture slide #1: Methane Cold Seep Community in the Gulf of Mexico Picture slide #2: Chemosynthesis in the Gulf of Mexico: The Bacteria Ranch 2. Energy from other organisms a. ALL animals b. Two options used to acquire food (1) MURDER (a) Predators (b) Victim (= food source) was alive (2) THEFT (a) Herbivores (b) Parasites B. Most animals are parasites 1. All predators, herbivores & omnivores harbor species-specific parasites 2. More kinds and numbers of parasites than free-living organisms 3. Estimated that 2/3's of all animals are parasites C. Equal rights for parasites 1. Parasites are victims of a bad press. a. Non-biological or Walt Disney classification system (1) Good (a) Characteristics (i) Big eyes (ii) Furry (iii)colorful (b) Bunnies, butterflies, Bambi Picture Slide #3: Biology & Hollywood Good Animals (2) Bad (a) Predators (i) Wolves (ii) Snakes (iii)spiders (b) Herbivores that eat garden plants (i) Rabbits (ii) Caterpillars (iii)deer (c) Germs & disease causing organisms

2 b. Freshman biology or Discovery Channel classification system (1) Predators (except perhaps snakes and spiders) belong in the good category (2) Reasoning: Predators remove sick animals from the habitat; thus, they keep ecosystems healthy. c. Policy Implications: (1) Zoos traditionally delouse & deworm all new arrivals including endangered species (2) Efforts to save one species (= host), may cause extinction of many species (= host-specific parasites) 2. Pro-parasite arguments a. Ecosystems exhibiting high species diversity are considered healthy/robust. (1) Parasites (2/3's of all animals) certainly contribute significantly to species diversity (2) Environmental impact surveys almost never include parasites on their species lists. (3) Parasites as biomonitors: Disappearance of a parasite may reflect local extinction of one of the multiple hosts in a parasite s life-cycle b. Cures for cancer and other diseases (1) People have argued that humans lose cures for cancer and other diseases when species become extinct (2) Inter-specific competition among parasites (a) Parasites compete for space within hosts with other species of parasites (b) Evolutionary theory predicts that parasites will develop mechanisms that counteract competitors c. Responsible for health of ecosystems (1) Parasites may enable some hosts to survive in marginal habitats (2) Some parasites increase the likelihood that one host will be eaten by next host in the life-cycle of the parasite (3) Parasites (= larval tapeworms) may make food available for some hosts (= wolves eating moose in winter) at a marginal cost to host Picture Slide #4: Gray Wolves in Yellowstone D. What is a parasite? 1. Traditional textbook definition a. A parasite-host relationship is one... (1) The first species (= parasite) adversely affects the second species (= host) (2) Yet the first species is dependent upon the second. b. Characteristics of a specialized predator (anteater-ant) fulfill above 2

3 criteria 2. Comparison of parasitism & predation Parasitism Lifelong intimacy Do Not Kill Smaller Many/host Predation Brief (slam blam) Kill Larger 1 predator eats many prey 3. Parasites operate on a higher spiritual and moral plane than do predators Picture Slide #5: Parasitism and Hollywood: Luke Skywalker Picture Slide #6: Parasitism and Hollywood: Death Star and TIE Fighter Picture Slide #7: Mascots of the SEC E. SYMBIOSIS 1. Defined a. Literally "living together" b. This course: "Two species living together with a degree of intimacy." c. No judgement as to who benefits, if either 2. PARASITISM a. Parasitism is a symbiotic relationship b. Guest receives benefits (+) at a cost to the host (-) 3. COMMENSALISM = Two species share a common resource a. Guest has access to resource, i.e. food (+) b. Host not affected (0) c. Example of Urechis The fat innkeeper (1) Worm creates burrows in mudflats (2) Worm pumps water through a net of mucus that traps food particles (3) Other creatures in burrow eat food items not consumed by worm Picture Slide #8: Commensalism: Urechis The Fat Innkeeper d. Special types (1) PHORESY (a) Guest (+) carried at minimal cost by host (0) (b) Example (i) Crabs on jellyfish (ii) Do not eat host (iii)dispersal: Ride & drop off Picture Slide #9: Phoresy: Juvenile crabs hitching inside bell of jellyfish (2) INQUILINISM (a) Guest receives protection by living within body cavity of host 3

4 (b) Guest doesnot feed on host, therefore minimal cost to host (c) Example: Pearl fish live in anal cavities of sea cucumbers Picture Slide #10: Inquilinism: Pearl fish and sea cucumber 4. MUTUALISM a. Reciprocity b. Everyone benefits (+, +) c. Example of Cleaner Shrimp (1) Brightly colored and banded (2) Exposed positions (3) Predatory fish will approach and allow shrimp to enter gills and mouth to eat parasites Picture Slide #11: Mutualism: Cleaner Shrimp: Shrimp cleaning mouth of predaceous cod & Cleaning Station: Brightly colored shrimp on anemone tentacles d. Example of Zooxanthellae (1) Algae (dinoflagellates) inside cells of corals, clams and sea anemones (2) Photosynthesis provides sugars to host (3) Guest algae receive nutrients and protection Picture Slide #12: Photosynthetic pigments of zooxanthellae color cells of tropical clam, Tridacna gigas Picture Slide #13: Mutualistic dinoflagellates from cells of the anemone Anthopleura xanthogrammica F. Special trophic interactions of parasites 1. HYPERPARASITE: Parasite of a parasite 2. PARASITIC CASTRATORS a. Parasites that selectively destroy the reproductive organs of their hosts b. Hosts usually live a normal life except that they don't reproduce c. Examples (1) Larval trematodes in snails (2) Rhizocephalan barnacles on crabs and shrimp Picture Slide #14: Parasitic Castrator: Rhizocephalans on a host crab d. Comparison (1) Intimate relationship (2) Host lives, but it is reproductively dead (3) About 1/4 to 1/5 size of host (4) Usually one castrator per host 3. PARASITOIDS a. Some entomophagous insects (= insects that eat other insects) use this approach (1) Ichneumonid & braconid wasps (2) Tachinid & phorid flies 4

5 b. Adult lays egg(s) on/in the larval stage (grub, caterpillar) of prey c. Parasitoid hatches and consumes prey from the inside while victim is still alive (1) Some wasps also paralyze prey and carry it to a nest (2) In many parasitoid-host associations, the prey continue to feed d. Very effective biological control agents Picture Slide #15: Braconid wasp depositing egg inside aphid Picture Slide #16: Wasp larva inside body cavity of live aphid Picture Slide #17: Adult wasp emerging from aphid host Picture Slide #18: Parasitism and Hollywood: John Hurt plays host Picture Slide #19: Parasitism and Hollywood: The emergence of parasites in movies Picture Slides #20-26: Cheap Thoughts by Jack O Brien e. Comparison (1) Intimate relationship (2) Host killed (3) Slightly smaller than host (4) Usually one parasitoid per host 4. MICROPREDATORS a. Comparison (1) Brief (2) Prey not killed (3) Micropredator smaller than prey (4) Micropredator moves from food source to food source b. Examples (1) Mosquito (2) Tick Picture Slide #27-28: More Cheap Thoughts by Jack O Brien 5