11-20 lecture notes

7/30/2019 11-20 Lecture Notes

1/12

u ua smsas

ynam c

n erac ons

o ay sques ons:

I. Tree oppersan ants

II. Mycorrhizal andendophytic fungi

III. Nitrogenfixingbacteria

IV. Antsthatfarmfungi

V. Pollination


2/12

I. Treeho er and ant interaction in text

A.Whyisthisinteractioncontingent?

B.What

would

ha en

over

time

if

s ider

densit

were

loweveryyearandhoneydewproductionexpensive?

Because treehopper benefits from the interaction only if there is

predation from spiders. Otherwise they are producing honeydew even though

they would gain no benefit from doing such an action. There is no longer

any mutualism.

They would produce less and less honeydew because it cost resources and

they gain no fitness benefit from producing it.

They could also try to push the ants out, an "antagonistic interaction".


3/12

II.Plantsandfungi

A.Mycorrhizal fungi

Fungigrowing

on

roots

photograph?- Lot more fungi present than plant root.- Extending access to water and

nutrients.

- Fungi are connected (physical

contacts). They are connecting different

plant individuals.


4/12

II.Plantsandfungi,continued

Mushroomformingfungiaretheonlyorganisms

(besidesafewbacterialspecies)thatcandigestthe

gn n oun nwoo . n ngenera , ung are

extremelyefficient

at

digesting

large,

complex

organic

Thebody

of

afungus

has

an

extremely

high

surface

.

areaforabsorbingnutrients.More surface area means higher rate of absorption.


5/12


6/12

Experiment:

Growplantseedlingsonculturedishes

inthelab,withfungi.

TOP:addlabeledsucrosetotheplant,

.

BOTTOM:add

labeled

P

to

the

fungus;

lots of 0 su ar to the lant.

3 4

In the top, it goes from root to 2 because they could

exchange for it.

On the bottom, it would go from fungi to 4 because they

could exchange for it.


7/12


u

x

supporteachother(independentandcorroborating),or

Birch-fir: parasitic.

Lab experiment: mutualistic.

They aren't corroborating.

They are conflicting.

Why does the parasitic thing happen?

- Maybe fungi wants to keep other tree going as an investment for

potentially more resource in the future.


8/12

B. Endo h tic fun i


Fungifoundgrowingonleaves,stems

es gnanexper men o es e ypo es s a a ea

endophytic fungusspecies

is

mutualistic with

strangler

fig

.

Treatmentgroups:

Controlledconditions:

Test:

Outcomevariable:

3 groups, one fungi, one seedling and

one with both.

Just randomize to account for

differences. Have large sample size.

See a priori thing.

Fitness.

When you are just starting out, it might

be better not to have a priori hypothesis

just so you can observe more.

Randomize to control for water,

shade, pH, salinity, etc.


9/12

.

SpeciesofRhizobium andFrankia colonizerootcellsin

legume

family

plants

and

alder

2

aminogroups(NH2)thatcanbeusedtobuildproteins,

nucleicacids

and

other

ke

molecules.

Nitrogenfixationisextremelyenergyintensive(energyin

u

u

y

.There is a complex signaling system between the two groups for this to

happen, the question is why do they do this from the perspective of the

plant?

They would do it to prevent parasitic species imitating the fungi and

steal energy from the plant.


10/12

IV.Antsandfungi

fungiinundergroundcoloniesandeat

them.

Afungus

called

Escovopsis feeds

on

Leucoagaricus.

Theantscarrybacteriafromthegenus

Stre tom ces ontheir

bodies.

The

bacteria

producecompoundsthataretoxicto

Escovopsis.

Leafcutterantcoloniesalsocontainbacteriafrom

thegenusKlebsiella.Thesebacterialiveinthe

fungalgardensandfixatmosphericN2 intoforms

thatare

used

by

the

Leucoagaricus and

the

ants.


11/12

IV.Antsandfungi,continued

(farmedfungi),Escovopis (pathogenicfungus),Klebsiella

Nfixin bacterium ,Stre tom ces antifun ala ent

bacterium),and

the

ants.


12/12

V.Pollination

Whatisthebasisofthismutualism?

Cheatinginyuccamoths

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