Species Interactions - Science in the...

Species Interactions: more than the sum of their parts

Species interactions: more than

the sum of their parts

How species interactions created the world

- Jon

Most organisms cannot live on their own

- Shelbi

Power struggles and partnerships

- Leonora

How species interactions

created the world

Jon Sanders

5

Species interactions have large

effects!

1. What’s in a species interaction?

2. How species interactions created the

world

3. How they can (and have!) destroyed it

6

1. What’s in a species

interaction?

9

Common interactions

• Predation

• Herbivory (plant predation!)

• Parasitism

• Competition

• ...what about positive interactions?

9

10

10

12

Symbiosis

• Commonly: ‘positive’ interactions

• Originally: close interactions

syn = “together;” bios = “life”

• We’re going to use second meaning:

could be positive, negative, or neutral!

12

13

13

+/+

CC BY-NC-ND 2.0 Flickr user scott.tanis http://www.flickr.com/photos/scott-tanis/2674374058/

-/0

http://www.flickr.com/photos/scott-tanis/2674374058/



17

Types of Symbioses

+ -

+ Mutualism Parasitism

0 Commensalis

m Amensalism

These interactions are on a continuum!

Questions?

19

2. How species interactions

created the world

Photo: NASA

22

How did Earth become

complex?

24

How did Earth become

complex?

1) Energy input (life) maintains order

2) Species interactions increase complexity

25

Life = energy

• Energy can come from many sources

• This diversity underlies many species

interactions

25

tie in

26

WORK WORK

Redox = moving electrons

+

– ]

Electron donor

(fuel)

Electron acceptor

(oxidant)

] ]

(REDuction/OXidation)

27

sugar → CO2 CO2 → sugar

O2 → H2O H2O → O2

+

–

]

]

Oxidation Reduction

28


iron → rust rust → iron

O2 → H2O H2O → O2

Hydrogen Sulfide → S S → Hydrogen Sulfide

Oxidation Reduction

H2 → H+ H+ → H2

Nitrogen Gas → Nitrate Nitrate → Nitrogen Gas

29

sugar → CO2

O2 → H2O

Oxidation Reduction

CO2 → sugar


H2O → O2

Hydrogen Sulfide → S S → Hydrogen Sulfide

H2 → H+ H+ → H2

Nitrogen Gas → Nitrate Nitrate → Nitrogen Gas

Methane → CO2 CO2 → Methane

Sulfide → Sulfate Sulfate → Sulfide

Ammonia → Nitrate Nitrate → Ammonia

Nitrite → Nitrate Nitrate → Nitrite

Mn2+ → MnO2 MnO2 → Mn2+

Questions?

Timeline of life on Earth

Prokaryotes

32

Early Earth

was reduced

• No oxygen

• Lots of CO2,

organic

molecules,

hydrogen

32



O2 → H2O H2O → O2

ammonia → N2 N2 → ammonia

33

Early life was structurally

boring

early life complex early life

34

Until

photosynthesi

s! • Uses light to split

water

• SO MUCH

POWER!

• Store that energy

in CO2 --> sugar

• ...produces

oxygen

34

]


O2 → H2O H2O → O2 ]

`

Prokaryotes

Eukaryotes

Animals


36

Endosymbiosis

Non oxygen-utilizing bacterium

Oxygen-utilizing Bacterium

First eukaryote!

37

New species interactions!

Predation

`

Prokaryotes

Eukaryotes

Animals


39

Want to photosynthesize?

• You can’t. But bacteria can!

39

`

Prokaryotes Eukaryotes

Animals

Birth

Loss

Gene Families

Duplication Transfer

David and Alm, Nature 2011

41

3. How species interactions can

destroy worlds

42

The oxygen catastrophe

• Early life was obligately anaerobic --

oxygen was incredibly toxic.

• Oxygenation of atmosphere must have

been devastating!

42

Amensalism:

0/- CC BY-NC-ND 2.0 Flickr user scott.tanis http://www.flickr.com/photos/scott-tanis/2674374058/




Recap

• Species interactions enable new kinds of life

• These interactions have profoundly affected our world




- Jon


- Shelbi


- Leonora

Most organisms cannot

live on their own

Shelbi Russell

Division of Labor

Creative Commons: Donovan Govan; Thomas Thwaites @ www.thetoasterproject.org

• How difficult would it be to

build a toaster from scratch? 404 parts

36 different materials

•Thomas Thwaites Toaster Project: - Mine and smelt

copper, iron, and nickel ore

- Shape metals into pins, heating element,

wires, etc.

- Mica for heating element

- Synthesize plastics

Function for mutualisms:

Overview • Division of tasks depends on:

–Organisms in mutualism

–Environment

• Most common purposes of mutualism:

–Protection

• Ants that protect acacia trees

• Light-producing bacteria that camouflage squid

–Nutrition

• Root fungi that provide nutrition for plants

• Bacteria that harvest energy from reduced chemicals to

feed clams

• Bacterial community that helps humans digest food

Protective mutualisms

• Its a dangerous

world...

–Herbivores

–Predators

–Parasites

–Pathogens

• Certain mutualisms

exist to evade and

confront these

dangers

Clockwise from top: Creative commons: masaki ikeda, Boing-boing; Shelbi Russell

Dan L. Perlman @ ecolibrary.org

Hollow thorns house ants

Trees feed ants

Carbohydrate-rich

nectar

Lipid and protein-rich food

Ants and Acacia trees

Dan L. Perlman @ ecolibrary.org

Ants protect trees

from

• Herbivores

• Other plants

Ants and Acacia trees

Camouflage in the ocean

• Open ocean

presents a

challenge for prey

• Many animals have

adopted white bellies to

avoid detection

Top to bottom: Creative Commons: Fbattail; Wolfgang_Striewski

Questions?

Function for mutualisms:

Overview • Division of tasks depends on:

–Organisms in mutualism

–Environment

• Most common purposes of mutualism:

–Protection

• Ants that protect acacia trees

• Light-producing bacteria that camouflage squid

–Nutrition

• Root fungi that provide nutrition for plants

• Bacteria that harvest energy from reduced chemicals to

feed clams

• Bacterial community that helps humans digest food

Nutritional mutualisms

• Nutrient poor diet

• Difficult to access nutrients

• Environments with unconventional energy

sources

Mycorrhizal fungi and Plants

Top to bottom, left to right: Creative commons: Adrian.benko; BetacommandBot; Malene; Thergothon; Tocekas.

• Help plants

acquire nutrients

• >80% of plant

species

• 400 million

years old

• Important for

soil colonization

The human ecosystem

• 90% of cells in the human body are bacterial

–99% of genes belong to them

• Hundreds of bacterial species in the gut alone

• Excrete our body weight in bacteria each year

• Without gut symbionts, we would need to

consume 30% more calories

Questions?

Mutualisms are a source of

evolutionary novelty

• A different way to adapt to a new

environment or way of life.

• The skill does not need to be evolved, just

the association.

Benefits must outweigh the

costs • Host and symbionts are in vulnerable

positions.

No cheaters

• However, the relationship is not always

balanced...




- Jon


- Shelbi


- Leonora

Power struggles and

partnerships

Leonora Bittleston

Outline

• Costs and benefits in species

interactions

• Cheating and how to counteract it

– Mutualisms that become parasitic and vice

versa

• Influence of humans and climate change

on species interactions

Types of Symbioses

+ -

+ Mutualism Parasitism

0 Commensalism Amensalism

Note: these interactions are on a continuum!

Mutualism: depends on costs

and benefits

Overall positive outcome if the cost of what you

give is less than the benefit you receive.

Partner A Partner B

You can think of a mutualism as a

romantic relationship…

Microsoft Office Clip Art Gallery

…Or an

economic

partnership

• Exchange of goods

• Agreement

between partners


Outline


interactions



versa



Cheating

• One partner receives benefit but gives little or

nothing in return

• Advantageous to evolve cheating

Maria Sarah

Cheating:

bacteria and plants

• Bacteria called

Rhizobia provide

nutrients to plants in

exchange for sugar

• Cheating bacteria

don’t produce

nutrients, but still get

the sugars

Microsoft Office Clip Art Gallery, Wikimedia Commons: Ninjatacoshel

How does a mutually beneficial

interaction persist?

1.Partner feedback

2.Partner choice

3.Time scales

4.Sanctions

1. Partner feedback

Maria Sarah

Partner Feedback: plants and fungi


2. Partner choice

Maria Sarah

Bill

Questions?

3. Time scales

Maria Sarah

Time scales: ants and acacias

Species 1:

good

defender but

high resource

use

Species 2:

good

defender but

sterilizes

plant

•Plants house and feed ants

•Ants protect plants from

herbivores

Jon Sanders

Time scales

Each ant colony lives only

about 10 years, while the

trees live 150 to 200 years

Species 3 Species 1 Species 4

10 years

150 years

10 years

Jon Sanders, Microsoft Office Clip Art Gallery

Species 2

• Expensive insurance against infrequent

but severe threat

• ELEPHANTS!


4. Sanctions

Maria Sarah

Fig tree wasps

• Trees need specialized wasps as pollinators

•Wasps need to develop inside figs

Wikimedia commons: Prashanthns, Leonora Bittleston

Tiny

wasp

Sanctions

• Some wasps lay eggs in figs without performing time-consuming pollination

• Trees abort figs that have wasp eggs but have not been pollinated, killing both fig and developing wasps

• Happens more in fig species where the wasp partners commonly cheat

Wikimedia commons: Prashanthns

Mutualisms can become

parasitic, but can it go the other

way?

Yes!

Wolbachia

• Bacterial parasites that infect about 60% of insect species

• Generally have a negative impact on reproduction and fitness

• Often passed through females, and exhibit ‘son-killing’


Parasite to mutualist

Bacteria provide

essential B vitamins

for bedbugs

Flikr: Gilles San Martin

Outline


interactions



versa



Human influence on a mutualism

• Heavy fertilization

of fields changes

fungal community

• Fewer mutualists

Fertilizer

Creative commons: Adrian.benko

Climate change and timing shifts

• Out of 1598 different species, 41% were

impacted by a global average warming of 0.6°C

(1.1°F)


Interaction mismatches

• For example: plants flower at

different times from when

insects emerge

• Even small changes can

disrupt interactions


91

Closing thoughts

• Species interactions have large impacts on humans

and the world around us

• Most organisms need other organisms to survive

• Relationships between species are complex and can

change with their environment

Jon Sanders

Thank you! SITN would like to acknowledge the following

organizations for their generous support.

Harvard Medical School Office of Communications and External Relations

Division of Medical Sciences

The Harvard Graduate School of Arts and Sciences (GSAS)

The Harvard Biomedical Graduate Students Organization (BGSO)

The Harvard/MIT COOP

Restaurant Associates

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