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Lecture 12

BIOB50Winter2012 Lecture 12.docx - includes lecture and text notes (with pictures!)

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Department
Biological Sciences
Course
BIOB50H3
Professor
Marc Cadotte
Semester
Winter

Description
BIOB50Winter2012 Lecture 12 Parasitism Chapter 13 Case Study Enslaver Parasites o Some parasites can alter the behaviour of their host in order to complete their life cycles o The hairworm may induce its host the cricket to commit suicide by altering its perception of thirstNT taurine in insects regulates the brains ability to sense a lack of waterwhen this is changed the perception of thirst is altered to the point where the cricket jumps in water because of the sensation of thirst and drowns allowing the hairworm to continue its life cycle o Not all enslaver parasites appear to act by manipulating the hosts chemistry but the mechanisms are still unknown o Many other parasites enslave their hostso Some fungi alter the perching behaviour of their fly hosts so that their spores can be dispersed more easily o Figure 132 Enslaved by a Fungusflies infected by the fungus perch in an atypical HIGH position from which fungal spores can easily spread to healthy flies which typically perch on the upper surfaces of the LOW lying vegetation where they are exposed to fungal sporeso Rats infected with the protozoan parasite Toxoplasma gondii do not avoid cats and in some cases are actually attracted to cats o This increases the chance that the parasite will be transmitted to the next host in its complex life cycle which is the catCase Study Revisited Tropical Parasitoid Wasp Example o The parasitoid wasp Hymenoepimecis argyraphaga manipulates its host the orbweaving spider Plesiometa argyra to spin a special cocoon webo The larval stage of the wasp attaches to the exterior of a spiders abdomen and sucks the spiders body fluids o When fully grown it induces the spider to make a special cocoon web o Once the spider has built the web the larva kills and eats the spider o The larva then spins a cocoon and attaches it to the cocoon web o As the larva completes its development in the cocoon the cocoon web serves as a strong support that protects the larva from being swept away from torrential rains o A parasitized spider builds normal webs right up to the night when the wasp induces it to make a cocoon websuggest was may inject chemical that alters spider behaviouro Eberhard 2001 removed larvae from their hosts several hours before time when a cocoon web would be usually madewasp removal resulted in the construction of a web which was similar to the cocoon web but more often resulted in the construction of a web that differed substantially from both normal and cocoon webs o In the days that followed the removal some spiders partially recovered the ability to make normal webs o Conclusion parasite induces construction of a cocoon web by injecting a fast acting chemical into the spider o The achemical appears to act in dose dependent mannerotherwise all spider would build cocoon webs instead of webs of an intermediate form o The chemical appears to interrupt the spiders usual sequence of web building behavioursIntroduction o Symbionts are organisms that live in or on other organismso More than half of the millions of species that live on Earth are symbionts o Our own bodies can be home to many other species 1
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