ECOL 182R 1st Edition Lecture 25 Outline of Last Lecture I Island diversity A Island biogeography theory II Community as a unit A Superorganisms B Individualistic III Patterns in time A Succession B Predictability Outline of Current Lecture I Specialization A Co speciation II Transmission A Direct vertical horizontal B Indirect III Maximizing transmission Current Lecture Parasitism the most common lifestyle Estimates suggest that as many as half of all species are parasites SO why are so many parasites 1 Almost all free living species have parasites associated with them 2 Most parasites are specialists they attack few or maybe just one species How do we look for specialization A species of parasite found only on one species of host Evidence of coevolution genetic change in one species in response to change in another Occurs in species that are closely interacting How do we look for coevolution Start by looking for the branching of both parasite and host phylogenies in parallel Called co speciation a kind of coevolution when one species host speciates the other one does as well Primates and nematodes are an example the branching patterns mostly match Why are most parasites specialists Most parasites must 1 Find host in a hostile environment 2 Establish on in host may need to cross skin gut wall 3 Evade the host immune system or if ectoparasite behavioral defense grooming swatting 4 Grow reproduce in host 5 Disperse from and find new host Adaptations for one species of host is unlikely to be effective in making them suitable for another kind of host Kinds of parasites Microparasites single cell or viruses Bacteria protists and single celled fungi Macroparasites multicellular Fungi arthropods and parasitic worms like nematodes and flatworms Size influences the way the host is used Micro infect the cells macro are external or in the gut Parasite transmission Direct or indirect Direct means one individual to another of the same species Vertical from parent to offspring in early development Transgenerational Usually mother because eggs have cytoplasm and that s where the gametes get infected Strictly vertically transmitted parasites are unusual because they re dependent on their host and they rarely make their host sick Some manipulate the reproduction to increase their own transmission If vertically transmitted parasites are found in egg cytoplasm what happens to parasites in males They re not transmitted So if this happens to a parasite they turn sons into daughters Ex Some bacteria in insects do this They have a haplodiploid genetic system females are haploid males are diploid Parthenogenesis production from unfertilized egg Horizontal contact with other infected individuals contaminated products Indirect is transmission via another species Horizontal only obviously The other species may be vectors ectoparasites of the host that serve as hypodermic of pathogen or intermediate hosts houses the parasite for part of its life cycle The definitive host is where the reproduction occurs Intermediate hosts amy live in proximity to definitive hosts or may be prey of the final hosts Humans definitive host snails are the intermediate Schistosoma Causes schistosomiasis Common in tropical places What could help reduce the disease transmission Host behavior modification the parasite increases its transmission by changing the behavior of its host How do parasites maximize their transmission For direct horizontally transmitted parasites exit routes may be feces body fluids lesions Transmission dependent on density of hosts and frequency of encounters between infected uninfected individuals For indirect transmission depends on the interactions of the two hosts and the aspects of the habitat like temperature or moisture Virulence is how sick the host gets Generally virulence is related to the speed at which the host is converted into parasites If more virulent parasites reproduce more why aren t all parasites highly virulent Because their host would die Dead hosts may not transmit the parasite Natural selection on parasite virulence acts to maximize transmission of the parasite Biological control program started myxoma virus from S American released in 1950 Why might high virulence lead to low transmission Mosquitos depend on a flowing bloodstream High virulence would kill rabbits mosquitos don t want dead rabbits HIV has both vertical and horizontal transmission
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