Chapter 13 – Ecology
Case study: Hapless cricket: walks to the edge of a body of water, jumps in and drowns,
after drowning a hairworm parasite begins to emerge from the body of the cricket. The
larva enters the cricket’s body and feeds on its tissues, growing from microscopic size into
an adult that fills all of the crickets’ body cavity except its head and legs. When the larvae
are fully grown, they must return to water, where adult males and females cluster in tight
masses to mate. After mating, the next generation of larvae are released to the water where
they will die unless they’re ingested by a terrestrial arthropod host. Enslaver parasites:
fungal species that alter the perching behaviour of their fly hosts such in a way that their
spores can be dispersed more easily. Rats typically engage in predator avoidance behaviours
in areas that show signs of cats, but infected rats with the protozoan parasite: toxoplasma
gondii behave abnormally towards cats (they do not avoid cats, and in some cases they are
attracted to cats). This is a fatal attraction for the rat, but it benefits the parasite because it
increases the chance that the parasite will be transmitted to the next host in its complex life
cycle (the cat). Wasp (hymenoepicmecis argyraphaga manipulates its host, the orb-weaving
spider (Plesiometa argyra) so precisely that shortly before killing the spider, the wasp larva
induces the spider to make a special “cocoon web” This cocoon web looks dramatically
different from the spider’s web, and the larva kills the spider and eats it. The larva then
spins a cocoon in which it’ll complete its development and hangs the cocoon from the web it
induced the spider to make. The cocoon web serves as a strong support that protects the
larva from being swept away by torrential rains.
(Definitions of symbionts, parasite, host, and pathogens are in lecture slides).
Parasites which constitute roughly of 50% of the species on Earth, typically feed on only one
or a few host species.
Pathogens are parasites. Parasites have negative effects: they harm but do not immediately
kill their host (unlike predators).
Our faces: home to mites that feed on exudates from the pores of our skin and secretions at
the base of our eyelashes.
Athlete’s foot: fungus.
Leishmania trpoica can cause disfigurement.
Yersinia pestis: plague.
(Macroparasites andmicroparasites are in lecture)