Symbiosis are the intimate relationships that exist between species.

1. Symbiotic Relationships Symbiosis are the intimate relationships that exist between species. Symbiotic relationships give at least one of the participants a nutritional or survival advantage. Parasitism Commensalism Mutualism

2. Parasitism An interaction between two organisms where one species benefits (parasite) and the other species (host) is ‘harmed’ in some way.

3. Parasites Obligate Parasites dependant on the host for survival (viruses) Facultative Parasites that do not need a host to survive. They can live with or without them.

4. Outside or Inside ? Ectoparasites Live on surface of the host Ticks Fleas leeches Endoparasites Live within their host Tapeworm Malaria (plasmodium) Sleeping sickness (trypanosome)

5. Parasite and Host relationship • Balance between receiving nutrients and damage done. • Most parasites do not kill their host. • Host could have some means of defence. • Death of the host means loss for parasite. • Relationship usually stable between them.

6. Transmission of parasite to new host Resistant stages Offspring released by parasite are in dormant or resistant form. When consumed by a host they become active e.g. liver fluke (snail and sheep) Direct Contact Parasite moves between hosts e.g rhinovirus, influenza, head lice. Secondary host species or vectors Organisms that transmit parasites e.g. fleas and ticks. The infectious stage develops inside them and is passed on e.g. toxoplasmosis, malaria

10. Host – parasite specificity • Parasites have often developed with host • Parasites have often shared an evolutionary path. • As hosts defence system affects parasites the most well adapted survive.

11. Defence against parasites Animals Lymphocytes – antibodies Macrophages Preening/grooming Migration Plants Chemicals Localised death of cells to isolate Galls

12. Plant parasites • Viruses tobacco mosaic virus potato leaf roll virus • Bacteria fireblight in apples and pears • Fungi wheat rust grey mould

13. Koch’s postulate for diseases • Pathogen should be present in all diseased organisms but not healthy ones • Pathogen should be able to be isolated and grown in pure culture • A healthy animal inoculated with the pure culture should get the same disease as original animals • The pathogen should be able to be isolated from the newly diseased organisms

14. Commensalism An interaction between two organisms where one species (commensal) benefits and the other species (host) is unaffected.

15. Commensalism • Are there really any pure commensal relationships?

16. Mutualism An interaction between two organisms where both species benefit from the relationship.

17. Mutualism • Organisms involved in mutualistic relationships often benefit from increased levels of metabolites, protection, removal of parasitic organisms. • Organisms also show complementary structures or behaviours.

18. Mutualism • Lichens - fungi and algae • Sea anemone and hermit crab

19. Mutualism Plants often have symbiosis with fungi especially in root systems. Ectomycorrhizae – fungus on outside of cells forming covering sheath of mycelium. Endomycorrhizae – fungus found inside cortex cells.