Download CH13: PREDATION AND HERBIVORY

NOTES
CH13: PREDATION AND HERBIVORY
NOTES
CH14: PARASITISM
Parasitism is a symbiotic relationship between two
organisms, the parasite and the host.
symbionts: species that live in or on other organisms.
• human face is home to mites that feed on fluid emission from
the pores of our skin and secretions at the base of our
eyelashes.
• bacteria and fungi that grow on our skin and under toenail.
• arthropods like lice can live on heads and pubic regions
• bacteria, worms and fungi can live in tissues, organs and body
cavities.
I.
parasites: symbionts that derives nutrients from its host through
consumption of tissue or body fluids; parasitoid: parasitic
insects whose larvae feeds on a single host and always almost
killing it.
• feed only on one or or a few host individuals.
• usually have higher reproductive rate than host.
• can harm but do not immediately kill host.
• most species are attacked by more than one parasite
• even parasites have parasites
• many parasites are closely adapted to particular host species
and specialization explain why there are so many species of
parasites
A. pathogen: parasites that causes disease in the host.
1. visceral: pathogenic infection that induces vomiting,
diarrhea, and intestinal symptoms.
2. infection of blood and tissue
B. ectoparasite: lives in outer body surface of its host.
• ease of dispersal and safe from host’s immune system
• vulnerability to natural enemies
• exposure to natural environment
• feeding is difficult
1. parasitic plants dodder (non-photosynthetic) and
hemiparastic (photosynthetic) mistletoes that obtain
water and food from other plants by growing on them.
2. animal ectoparasites are called herbivores since they
eat plant tissues.
3. fungal ectoparasite Trichophyton rubrum causes athlete's foot.
C. endoparasite: parasites that live inside their host by living in the alimentary canal and live within cells or tissues.
• ease of feeding
• protected from external environment
• safer from natural enemies
• vulnerability to host’s immune system
• dispersal is difficult
1. parasites that live within the alimentary canal rob the host’s
nutrients and do not eat tissues at all. tapeworm Taenia
taeniaeformis uses scolex the suckers and hooks to attach to
intestinal wall of its mammalian host - rodent, rabbits or cats.
2. Yersinia, bacterium that causes the plague and mycobacterium
NOTES
tuberculosis the bacterium that causes TB.
• ectoparasitism and endoparasitism
have advantages and disadvantages
• it is more difficult for endoparasites to
disperse, but they solve this problem by
altering the physiology or behavior of
host in ways that is conducive to their
dispersal; bacterium Vibrio cholerae
that causes cholera and Entamoeba
histolytica causes amoebic dysentery
induces diarrhea, which increases the
chance of dispersal.
• ectoparasites are more exposed to
predators, parasitoids and other
parasites; aphids are attacked by lady
bugs, birds and lethal parasitoids.
• hosts have adaptations for defending
themselves against parasites and
parasites have adaptations for
overcoming host defenses.
• immune systems, biochemical
defenses and symbionts can protect
against parasites.
• protective outer covering like skin
for mammals or exoskeleton for insects that makes it harder for parasites to pierce through or enter.
• encapsulation process kill or render microparasites harmless by covering them with engulfing them into capsules or use
blood cells lamellocytes to form multi-cellular sheaths around large objects.
• immune system kills endoparasites that manage to enter a potential host not protected by protective barrier.
• specialized cells such as B and T cells create memory cells to recognize previously encountered microparasites.
• engulfs and marks with chemical target for later destruction.
• resistant genes (R-genes) are an allele for plants that provides protection against parasites with particular gennotypes.
• non-specific immune system anti-microbial compounds that attack parasites’ cell walls and toxic anti-fungal compounds.
• chemical signals that “warn” cells of imminent danger and stimulate lignin deposits that acts as a barrier for parasites to
spread into other cells.
• regulation of biochemical defenses like transferrin that removes iron from blood serum from specific sites - where
parasites could use for its growth - and stores it in intracellular compartments where parasites cannot access.
• some parasites solved this problem by stealing iron from transferrin directly.
• behavioral change such as change in diet that increases host’s survival; wooly bear caterpillar switch from lupine to
poisonous hemlock; chimpanzees eat bitter plants that kill or paralyzes nematodes.
• some organisms provide defensive symbionts (mutualistic symbiosis) that protects host from pathogens.
• many defensive-symbionts are heritable from host to it offspring.
• parasites have adaptations that circumvent host defenses similar to herbivores and predators.
• toxicity tolerance; strong selection pressure develop counter-defenses
• parasitoid wasps attack fruit-fly by injecting virus-like particles that infect lamellocyte causing it to self-destruct.
• laying eggs with filaments that become embedded into host’s cells making it undetectable to lamellocyte.
• complex-life cycle and development of hundred of genes making it difficult for detection and increase survival.
• parasite-host coevolution arises from selection pressure imposed by the other.
• population of two interacting species evolve together, each in response to selection imposed by the other.
• selection can favor a diversity of host and parasite genotypes: gene-for-gene interaction
•
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MUTUALISM AND COMMENSALISM
I.
Positive interaction: neither species is harmed; both species benefit; benefits outweighs the cost for at least one species
A. two fundamental types of of positive interaction are mutualism and commensalism, which ecologists refer to collectively as
facilitation.
1. mutualism: (+/+ relationship) mutually beneficial interaction between individuals of two species.
2. commensalism: (+/0 relationship) interaction between individuals of two species where one benefit and the other
does not and are not harmed.
a) millions of species form +/0 relationship with organisms that provide habitat in which they live.
b) the species that depends on the habitat provided by another species often has little to no effect on the species
that provide the habitat
•
symbiosis a relationship in which individuals of two species live close physiological contact with each other can
range from parasitism (+/-), commensalism (+/0) and mutualism (+/+)
B. mutualism and commensalism are ubiquitous, can evolve in many ways and have influenced key events in the history of life
as well as growth and survival of organisms of the present day, can be obligate or coevolved or facultative and loosely
structured, can cease to be beneficial under certain circumstances and are common in stressful environment
1. Ubiquitous mutualistic examples
a) vascular plants forming beneficial associations with fungi increasing both species’ growth and survival
(1) mycorrhizae: two types are ectomycorrhizae and arbuscular mycorrhizae that are usually a mutualistic
symbiosis between plant roots and various types of fungi
(a) ectomycorrhizae: fungal partner grows in between root cells and forms mantle or sheath called
hyphae around the exterior of root
(b) arbuscular: fungal partner penetrates the cell wall (but not the cell membrane) and forms and
arbuscule, a branched network
i)
fungi increase the surface area for plant to take up water and soil nutrients
ii) fungi may protect plants from pathogens
iii) fungi improve plant’s growth and survival
iv) plant supply fungi with carbohydrates
b) Atta and Acromyrmex (Attines) known as fungus-growing-plants cultivate fungus and feed on gongylidia that
fungi produce. Ants scrape wax materials from plants that allow fungi to invade and the fungi digest protective
chemicals that plants produce to kill or deter insect herbivory.
c) In oceans, corals and algae form mutualism by corals by providing homes and nutrients (N and P) and light
source to algae while algae provide corals with carbohydrates produced form photosynthesis.
d) mammalian herbivores like cattle and sheep depend on bacteria and protist that live in their guts, which helps
them digest and metabolize cellulose.
e) wood-eating insects have protist that can digest cellulose.
f)
relationship between plants and pollinators - plants benefit from the spread of pollen between flowers and the
pollinator such as bees benefit nourishment from nectar or the pollen itself.
2. Ubiquitous commensalism examples
a) small species that live on large species like lichens found on a bark of a tree
b) harmless bacteria that lives on the human skin
c) many algae, invertebrates and fish in kelp forest depend on the kelp for habitat
(1) they locally go extinct if the kelp are removed
d) million insect species and thousand understory plants live in tropical rainforest and nowhere else depend on the
forest for habitat yet have little to no effect on the trees.
3. mutualism and commensalism can evolve in many different ways
a) different types of ecological interaction can evolve into commensalism or mutualism
(1) mutualism can arise from a host-parasite interaction
(a) in 1996 Kwang Jeon observed that the rod-shaped bacterium often infected and killed Amoeba proteus
and caused it to grow slower and starved faster than uninfected ones. 5-years later, it became one of
the many examples that parasites and hosts can coevolve as the bacterium became harmless to
amoeba and the amoeba had evolved such that it became nucleus dependent on the bacterium for its
normal metabolic functions. Experiments show that neither species could survive without the other.
NOTES
4. Positive interactions can be obligate and coevolved or facultative and loosely structured
a) species-specific and obligate: each partner can only survive and reproduce successfully in the presence of the
other.
(1) cospeciation: a result in which the speciation of one species lead to the speciation of the other, because
the benefits of mutualism to both species are high and mutualistic relationship has been in place for over a
long periods of evolutionary time.
b)