Symbiosis Symbiosis Symbioses species living in close association
Symbiosis
Symbiosis • Symbioses - species living in close association • Parasitism +, - parasite benefits, host harmed • Commensalism +, 0 or 0, 0 can have positive effect for one species or for neither • Mutualism +, + both species benefit
Parasitism and Disease Lyme Disease Cycle in the UK
Parasitism • Parasitism - intimate association between two species in which the parasite obtains its nutrients from a host - parasite usually causes some degree of harm to its host - either reduced growth or reproduction • Pathogen – disease causing agent • Disease – abnormal condition of host due to infection by a pathogen that impairs physiological functioning
Parasites on Plants
Arthropods are green, Fungi are brown, Worms are blue, Protozoa are yellow
Parasitism occurs on a continuum from: • ectoparasites - live outside hosts body and experience same conditions as host - ticks, mites, fleas, aphids • endoparasites - live inside host's body cavity buffered from outside conditions - tapeworms, flukes • intracellular parasites - live inside individual cells of the host - viruses, bacteria, protozoa often called microparasites
Or another way to divide parasites: • microparasites - viruses, bacteria, protozoa - small, often live intracellularly, main point is that they reproduce in host and will have very large numbers in host • macroparasites - tiny to very large - nematodes, tapeworms, flukes - larger individuals that grow in host but multiply by producing infective stages that are shed by host to environment where they infect new hosts
Parasite Transmission • Direct transmission – from one host to another of the same species via air, water, coughing, blood, feces, etc. • Indirect transmission – from one host to another of the same species via another species called a vector • Vector – species which transmits parasite or pathogen from one host to another
Microparasites Macroparasites Direct transmission HIV virus, Amoebic dysentery, Mildews on plants Indirect transmission Plasmodium (mosquito), Plant viruses (aphids), Trypanosoma (tsetse fly) Lice, fleas, ticks, aphids, hookworm, pinworm, mistletoe Tapeworms (various), Schistosomes (snails), Rust fungi
Powdery Mildew on Grape Leaf
Powdery Mildew Life Cycle
Head Lice and Life Cycle
Mistletoe
Mistletoe Life Cycle
Malaria disease cycle
Past and Current Malaria Areas
Potential spread of malaria by 2050
Anopheles minimus
Schistosomiasis - Life cycle of the schistosome worm
Male Schistosome worm
Worldwide incidence of schistosomiasis
Worldwide incidence of schistosomiasis
Rust Fungus Canker
Rust Fungus Life Cycle
Two ways to study parasite numbers • Prevalence – percent of host population that is infected – best for microparasites • Intensity – number of parasite individuals per host – usually best for macroparasites
Parasite burden (intensity of infection) Model data
Parasite burden in bluegills
Bluegill trematode parasites
Frequency of infection Parasites usually occur in aggregated distributions – due to 4 possible factors: 1) random colonization events followed by asexual reproduction in hosts that do get parasitized 2) environmental "hot spots" where parasite eggs and infective stages survive well 3) dispersal constraints - geographic or behavioral barriers limit dispersal of parasites to just a few hosts 4) variation in susceptibility of individual hosts - due to nutrition, genetics
Transmission and survival of parasites • Maximum transmission of parasites occurs at intermediate levels of virulence • Parasites tend to evolve to exist at intermediate levels of virulence
European rabbits as pests in Australia - 1938
Introduced pests in Australia – red fox, rabbit, cat, pig, & goat
Parasite effect on host population Parasite can cause direct mortality but then can only persist in a large host population Usually parasite lowers host reproduction, growth or survival often this effect is indirect by way of 1) lowers host stamina - more subject to predation, competition 2) increases conspicuousness - predation risk increases 3) disorient host via neurological damage 4) alters host response to environmental stimuli
Fungal parasites alter insect behavior Giant w/o and with fungus
Moose and White-tailed Deer
Deer – Moose brain worm interaction
Avian malaria occurs in areas below white line on Island of Hawaii – highest incidence between yellow and white lines
Hawaiian Crow – Extinct in Wild
I’iwi Honeycreeper – highly susceptible to avian malaria
Akiapolaau Honeycreeper – restricted to high elevation today
Amakihi Honeycreeper – shows evidence of evolving resistance
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