lect 20 - symbiosis

Question 1

symbiosis

Answer 1

intimate association between different species — often beneficial or mutualistic — can lean to parasitism

major source of biological innovation

Question 2

endosymbiosis

Answer 2

endosymbionts usually microbial

one organism (typically microbial) living inside another larger organism

interactions between partners can lie along a continuum from parasitism to mutualism — sometimes hv mito that cause sterility

microbial symbioses are diverse and important (paradigm shift from thinking they were all bad)

Question 3

How infectious organisms are transmitted to new hosts is the most important factor shaping the ecology and evolution of the interaction. what are the 2 types ?

Answer 3

vertical or horizontal transmission

vertical = passed thru mother to offspring (inherited)

horizontal = host gets symbiont from environment

Question 4

vertical transmission

Answer 4

infectious organism passed on from mother to offspring (inherited)

evolutionary interests are strongly aligned — fitness of symbiont depends on fitness of host and vice versa

ex// obligate inherited symbionts
— host needs these symbionts to survive (provide) essential nutrients (example aphids)

ex// facultative inherited symbionts — host can survive without them, symbionts cant live without host

Question 5

horizontal transmission

Answer 5

host acquires symbiont from environment

more opportunity for mismatch and conflict

replication rate may be harming

every generation must acquire their own symbiont from the environment — doesnt come from parents (lateral)

easier to come in contact w symbionts in marine environment vs terrestrial

Question 6

obligate inherited symbionts

Answer 6

vertically transmitted

required by the host — symbiont provides essential nutrients to host that host doesnt get from diet — like things that feed on only animal blood or phloem

hosts cannot survive or reproduce without symbiont and symbiont cant live independently

ex// Buchnera aphidicola (obligate symbiont in aphids) — provide aphids with essential amino acids

Question 7

obligate symbiont example and explanation - explain study

Answer 7

obligate symbiont of aphids — Buchnera aphidicola

Buchnera provides aphids w essential amino acids such as tryptophan

housed in specialized cells called bacteriocytes inside specialized tissues/cells called bacteriomes

Buchnera are intracellular

Buchnera inherited and passed on for abt 200 million years faithfully and exclusively to aphids

STUDY: aphids treated w antibiotics cant reproduce unless they were raised with an artificial diet supplemented w tryptophan
PROVED: bacteria were producing tryptophan

Question 8

obligate symbiont genomes

Answer 8

smallest genomes of all

very little non-coding DNA

the smallest symbiont of all is Nasuia — although Buchnera is very close to the smallest

Question 9

facultative inherited symbionts

Answer 9

inherited from parents

hosts can survive and reproduce without these symbionts — symbionts cant live without hosts

symbionts can only infect new hosts thru maternal inheritance

many facultative inherited symbionts are conditional mutualists — they increase host fitness but only under certain conditions

symbiont fitness is immediately tied to host fitness (bc only passed thru mother)

STUDY: Drosophila flies, parasites, and symbionts
— commonly infected w worm parasite
— flies will pass worms along to each mushroom as they go about their life
— flies sterilized by worms — worms grow inside fly instead of eggs
— inherited bacterial symbiont Spiroplasma poulsonii stops flies from being sterile
— this symbiont is in blood of flies and makes worms small and sick
— strong selection for these kinds of strategies

Question 10

Drosophila fly, worms, and symbionts

Answer 10

example of facultative inherited symbionts

STUDY: Drosophila flies, parasites, and symbionts
— commonly infected w worm parasite
— flies will pass worms along to each mushroom as they go about their life
— flies sterilized by worms — worms grow inside fly instead of eggs
— inherited bacterial symbiont

FOLLOWUP:
— flies on east coast have symbiont but not on west
— only 9 years go by and western flies now have eastern ancestry — numbers of flies having symbionts stayed the same in the east but increased in the west
— RAPID spreading of flies with symbiont - replacing flies without them

ANOTHER STUDY:
— Spiroplasma (symbionts) are costly to keep around when worms not present — would see loss of this symbiont if the benefit of having them isnt as high
— when the worms are present, benefit is high, so will see more of them