Biology

Symbiosis

Cuckoos lay their eggs in the nests of other bird species and so avoid the hard work involved in raising chicks. This is just one of the diverse ways that different species live together.

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Introduction: Symbiosis

Cuckoos are unusual among birds for not building their own nests. Instead, a female cuckoo swoops down on anotherbird's nest, knocks out one of the eggs and lays one of her own to replace it. The host returns to ᎅ�nd the same number ofeggs and often fails to notice the swap.

Scientists have just discovered how cuckoos have been getting away with this for so long. It seems the crafty birds doprovide something useful in return for the free childcare.

While studying crows’ breeding habits in Spain, scientists observed lots of cuckoos laying eggs in the nests of crows andmagpies. If the magpies noticed the deception, they fought back and threw out the cuckoo eggs. But the crows allowed theeggs to stay, let them hatch and then fed the cuckoo chicks as they grew.

Curious, the scientists investigated, taking note of how well the crows with cuckoos did compared to those without. Theydiscovered that when they handled the cuckoo chicks, the little birds released a foul-smelling substance that predatorswouldn’t eat. So by having the baby cuckoos in their nests the crow parents could leave their own chicks while they went o䂟�in search of food, knowing that the cuckoos would protect them.

It’s a great example of two species helping each other out.

Read the full Cosmos Magazine article here.

Left: Cuckoo chicks release a foul-smelling slime that seems to drive some predators away. Right: Sea anemones sometimes hitchhike on the back of hermit crabs.

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Question 1

Identify: Describe at least ᎅ�ve interactions with other organisms that you frequently have in your life. These do notnecessarily have to be interactions with other humans and they do not have to all be positive interactions. Place apositive [+] sign next to the individuals that are beneᎅ�ting from the relationship, a negative [–] sign next to theindividuals that are being harmed by the relationship, and a neutral [0] sign next to the individuals that are una䂟�ected bythe relationship.

For example: I [+] like to interact with my dog [+]. He helps me to feel happy and I teach him new things.

Hint: To share your answer with your class, ask your teacher to open the discussion board at the bottom of this page andwrite your answer there as well.

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Gather: Symbiosis

Di�erent types of symbiosisAll organisms are dependent on other organisms in some way. For example, during its lifetime, an animal such as akangaroo is likely to interact with millions of other organisms including microbes, parasites, mates, predators and food.

In contrast with predator–prey relationships, where the predator attacks the prey with the intention of killing and eating it,symbiotic relationships occur where diϹerent species interact and live side by side with each other.

Symbiosis refers to a long-term ecological interaction between diϹerent species that live close together, where one ormore of the species bene�ts. Think back to the answers you gave to the question in the Introduction section. You may nowrecognize that each of the interactions you described can be classi�ed as symbiotic.

There are, in fact, three diϹerent categories of symbiotic relationships:

1. Parasitism

2. Commensalism

3. Mutualism

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Credit: Symbiosis: Mutualism, Commensalism, and Parasitism by Untamed Science (YouTube).

0:00 / 5:16

Question 1

Notes: Use this space to take notes for the video.

Note: This is not a question and is optional, but we recommend taking notes – they will help you remember the main points of thevideo and also help if you need to come back to answer a question or review the lesson.

Question 2

Recall: A commensalistic relationship is when one speciesbene�ts and the other species is harmed.

True

False

I'm not sure

Question 3

Recall: Clown�sh are protected from predators by livingamong anemones. They also chase away animals thatmight harm the anemones. What sort of symbioticrelationship is this?

Parasitism

Commensalism

Mutualism

I'm not sure

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Question 4

Select: When you eat yoghurt, you ingest bacteria thattake up residence in your gut. Who bene�ts from thisrelationship?

You, because the bacteria help you digest food

The bacteria, because your body providesthem with a place to live

Neither you nor the bacteria

I'm not sure

Question 5

Explain: Lions hunt gazelles for food. Why is this not anexample of a symbiotic relationship?

In a symbiotic relationship both species mustbene�t

Symbiotic relationships are always betweenmembers of the same species

Symbiosis only applies to certain species, suchas �sh and bacteria

Symbiotic relationships require species livingtogether – this is a predator–prey relationship

I'm not sure

Question 6

Classify: Oryxes, shown on the right, eat grass andproduce lots of dung. Dung beetles eat the dung and thefemales lay their eggs in it.

What type of relationship is this?

Parasitism

Commensalism

Mutualism

Not symbiotic

I'm not sure

Question 7

Identify: Which of the following are examples of symbiotic relationships that might be found in a typical home?

Fleas living on a dog

Pet gold�sh in a �shbowl that the owner enjoys watching

Fungus living on the skin of gold�sh, damaging their health

Human parents caring for their children

Fungus living on the skin of humans but not causing any harm

I'm not sure

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Question 8

Match: With the help of the information in the media clip above, drag and drop the labels and descriptions to identify thetype of symbiotic relationship shown in each picture.

Question 9

Complete: Select one of the examples in the question above and assign a number to each species to complete thefollowing table.

Example selected

Species 1

Species 2

Describe what you think wouldhappen to the population ofspecies 1 if species 2 was nolonger present

Describe what you thinkwould happen to the populationof species 2 if species 1 was nolonger present

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Question 10

Describe: Each set of graphs represents one of the three types of symbiosis. Analyze the graphs to identify the type ofsymbiotic relationship represented by each set and brie�y explain your choices.

Set Type of symbiotic relationship Explanation

A

B

C

Below are three sets of graphs showing the populations of two species over time, living separately and together. Withineach set, let's call the species represented by the red line species 1 and the species represented by the blue line species 2.

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Process: Symbiosis

A closer look at parasitismIf your pet has ever had Ȫeas then you've already witnessed parasitism in action. Parasites can bene떠t from therelationship with their hosts in a number of ways:

by obtaining nutrients from them,

by gaining protection from predators, and

by being given free transport.

Parasites are adapted to living either inside their hosts or on their outer surfaces. They can only survive by reproducingoȪspring that are capable of 떠nding new hosts.

Question 1

Recall: The only way that parasites bene떠t from theirhosts is by obtaining nutrients.

True

False

I'm not sure

Question 2

Apply: Mistletoe is a plant that grows up around atree and derives water and nutrients from it.

Which two features make this a case of parasitism?

The mistletoe bene떠ts by obtaining nutrientsfrom its host

The mistletoe is harmed by having its sunlightblocked by the host tree

The host tree is neither bene떠ted nor harmed

The host tree is harmed by losing nutrients tothe mistletoe

I'm not sure

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Left: Fleas live symbiotically with cats. What kind of symbiotic relationship is it? Right: Scanning electron micrograph of a cat Ȫea (Ctenocephalides felis).

Although a parasite harms its host, by de떠nition, the relationship ideally doesn't lead to the host's death. If thathappened, the parasite would have to 떠nd another home.

However, some parasites are more destructive than others and can have unusual eȪects on the behaviour of their hosts...

Credit: Zombie Animals that Exist in Nature | Zombie Attack by Howcast (YouTube).

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Question 3

Notes: Use this space to take notes for the video.

Note: This is not a question and is optional.

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Question 4

Explain: The parasites responsible for creating "zombie animals" manipulate their hosts' behaviour so that they can spreadto new hosts.

Use the information provided in the video to summarize the eȪects on the hosts' behaviour and propose explanations forhow this helps the parasites spread.

Hostorganism

ImageDescription of how the parasite

changes the behaviour of its hostProposed explanation of how this

helps the parasite spread

Snail

Ant

Cricket

Many parasites have complex "life histories" with multiple stages involving more than one host species. The following videoshows the life cycle of the dog and cat tapeworm which provides an example of how this works.

Credit: Dipylidium Caninum – The Life Cycle of the Dog & Cat Tapeworm by Michael Sims/Sally Cantle (YouTube).

0:00 / 4:44

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Question 5

Notes: Use this space to take notes for the video.

Note: This is not a question and is optional.

Question 6

Complete: Drag the terms into their correct locations on the following life cycle diagram of the dog and cat tapeworm.

Question 7

Suggest: Dog and cat tapeworms are much smaller, and develop much faster, than their hosts. This is also true of thecuckoo chicks described in the Cosmos Magazine article, which are smaller and develop much faster than the crow chicksthey share a nest with.

Suggest some advantages that small size and quick development might give a parasite.

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Project: Symbiosis

Design your own parasite

These nasty little parasites, shown in yellow, cause a disease in humans called "sleeping sickness". They enter the bloodstream through the bite of a tsetse 㗎�y, causing the host fevers, headaches and sleeping di��culties, among other symptoms. This coloured scanning electron microscope

image shows them amongst red blood cells. Credit: Eye of Science / SPL Creative / Getty Images.

Imagine that you're a scientist at the World Health Organization (WHO). Your main role is to research parasitic diseases andunusual parasite-host interactions.

Sometimes you ꛈ�nd yourself thinking about what life might be like as a parasite....

Credit: Thinking like a parasite | The Biology Journey by The Fuse School (YouTube).

0:00 / 2:23

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Question 1

Notes: Use this space to take notes for the video.

Note: This is not a question and is optional.

Parasites have adapted to survive best in their host's speciꛈ�c environment.

These adaptations might be:

structural – e.g. a mouth with hooks to attach to a host's intestines,

physiological – e.g. the ability to digest blood to obtain energy, or

behavioural – e.g. making a cricket jump into water.

Question 2

Create: Your challenge in this activity is to design an original, never before discovered, parasite that has adapted to survivein a speciꛈ�c host.

The following questions will help guide you through the design process of your parasite and its host. Type your answers tothe questions in the project space below.

1. What type of organism will your parasite's host be?

2. What environment will the host live in?

3. What will the body size and shape of your parasite be?

4. What methods of travel will your parasite use to reach the host?

5. What part of the host's body – either on the inside or the outside – will your parasite infect?

6. What strategies will your parasite use to obtain its food?

7. What damage will your parasite do to the host?

8. What evasive or defensive strategies will your parasite use to avoid being killed by the host?

Give scientiꛈ�c names to your parasite and its host.

Now create a visual representation of your parasite and its host, with labels that describe how each of its features helpit survive. Identify these adaptations as structural, physiological or behavioural. You may wish to design your parasite andhost on poster paper, photograph it and upload the image below.

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Career: Symbiosis

Sly tricksters, singing divas, and musical drummers are just a few of the many interesting characters NaomiLangmore meets through her job. But she doesn't work in Hollywood – Naomi is a zoologist from the Australian NationalUniversity who studies the complex and often amusing world of birds.

Naomi spent the �rst eight years of her life in Papua NewGuinea. Although she left the lush rainforests behind,Naomi’s love for animals followed her all the way back toCanberra, Australia, where she moved to attend school.Growing up with lots of di�erent pets, Naomi learnt shecould make a career out of doing what she loved most –studying animal behaviour as a behavioural ecologist.

She pursued her dream by studying biology andpsychology in high school. But Naomi credits her Englishclasses with polishing her writing ability, a skill crucial for asuccessful career in science.

Throughout her career, Naomi has looked at many curiousaspects of bird behaviour. She has studied how cuckoostrick other birds into raising their babies, why female birdssing, and even how cockatoos drum out a beat using treebranches. Being able to answer these fascinatingquestions in biology is incredibly exciting, she says. ForNaomi, it’s the best job in the world.

Much like the birds she studies, Naomi’s lifestyle changesdrastically with the seasons. In the spring and summer,she gets to watch her birds out in the �eld. The life of abird is a busy one, and Naomi usually has her hands fullkeeping up to date with the many social dramas in a �ock.When autumn and winter roll around, Naomi returns touniversity to spend the cold months indoors, teaching andwriting.

Even when she isn’t working, Naomi enjoys the wilderness.She loves going camping, bird-watching and bush-walkingwith her family and her dog, Panda.

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Question 1

Research: Naomi's career as a behavioural ecologist developed out of a love for animals, which she has had sincechildhood. Think back to when you were a child...which animals did you love? Were you fascinated by worms, beetles orlizards – or perhaps even daddy-long-legs spiders? 

Using the internet, research a parasite-host relationship that your favourite childhood animal is involved in. Identifywhether it is playing the role of parasite or host and describe how it bene�ts or is harmed by the relationship. As part ofyour research, locate a country and institution (e.g university) where research about this parasite-host relationship is takingplace. 

Image Credits

Introduction: Daniela Canestrari and National Geographic;Gather: ViviSuArt and Biophoto Associates; Getty Images,Adobe Stock

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Test: Symbiosis

Note: There may be more than one correct answer to the multiple-choice questions below.

Question 1 (1 mark)

In a symbiotic relationship at least one organism alwaysbene២�ts.

True

False

I'm not sure

Question 2 (1 mark)

Symbiosis always takes place between members of thesame species.

True

False

I'm not sure

Question 3 (1 mark)

Commensalism is when one species bene២�ts from therelationship and the other species:

also bene២�ts

is harmed

neither bene២�ts nor su៌�ers harm

I'm not sure

Question 4 (1 mark)

Which of the following are symbiotic relationships?

Parasite and host

Predator and prey

Parent and o៌�spring

Cleaner ២�sh and shark

I'm not sure

Oxpeckers are birds that live on large animals in Sub-Saharan Africa, such as the bu៌�alo shown on the left.

The oxpecker feeds on ticks which in turn feed on thebu៌�alo's blood. The oxpecker bene២�ts by gaining ameal and the bu៌�alo bene២�ts by having the harmful ticksremoved.

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Question 5 (1 mark)

What type of relationship do the oxpecker and bu៌�alohave?

Parasitism

Commensalism

Mutualism

Not symbiotic

I'm not sure

Question 6 (1 mark)

What type of relationship do the tick and bu៌�alo have?

Parasitism

Commensalism

Mutualism

Not symbiotic

I'm not sure

Question 7 (1 mark)

The oxpecker eats the ticks. Is this a symbiotic relationship?

Yes, because one organism bene២�ts from the other

Yes, because any interaction between organisms of di៌�erent species is symbiotic

No, because one organism dies straight away so it is a predator–prey relationship

No, because neither species bene២�ts

I'm not sure

Question 8 (1 mark)

Oxpeckers bene២�t zebras too. As well as feeding on ticks,they often squawk and ២�y o៌� when predators approach,warning the zebras of danger. Sometimes, however, therelationship changes. If a zebra is injured, oxpeckers mightdrink blood from the wound. This prevents it from healingand leaves it open to infection.

How would you classify this new relationship between thezebra and oxpecker?

Parasitism

Commensalism

Mutualism

Not symbiotic

I'm not sure

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Question 9 (1 mark)

Lions kill and eat animals such as zebra and wildebeestand then jackals scavenge on the leftover remains. Thejackals bene២�t from the lions without harming orbene២�ting them in return.

What type of relationship is this?

Parasitism

Commensalism

Mutualism

Not symbiotic

I'm not sure

Question 10 (1 mark)

Clown២�sh make their homes among the stinging tentaclesof sea anemones. The clown២�sh gain protectionfrom predators while attracting prey for the anemones toeat.

Why is this an example of mutualism?

The clown២�sh bene២�t but the anemones areneither bene២�ted nor harmed

The anemones bene២�t but the clown២�sh areneither bene២�ted nor harmed

The clown២�sh and anemones both bene២�t

The anemones are harmed by the clown២�sh

The clown២�sh are harmed by the anemones'stinging tentacles

I'm not sure

Question 11 (1 mark)

A commensalistic relationship exists between cattle andcertain birds called egrets. When cattle graze, their hoovesstir up insects which the egrets then eat.

Why is this an example of commensalism?

The egrets bene២�t but the cattle are neitherbene២�ted nor harmed

The cattle bene២�t but the egrets are neitherbene២�ted nor harmed

The egrets and cattle both bene២�t

The cattle are harmed by the egrets

The egrets are harmed by the cattle

I'm not sure

Question 12 (1 mark)

Tapeworms obtain all the nutrients they need from the gutof the animal in which they live. Some tapeworms that livein humans can grow to over 10 meters long!

What type of animal is a tapeworm?

Predator

Prey

Parasite

Scavenger

I'm not sure

Question 13 (1 mark)

What is the term given to the animal in which thetapeworm lives?

Human

Host

Predator

Prey

I'm not sure

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Total available marks: 18

Question 14 (1 mark)

In which of the following ways can parasites bene២�t fromtheir hosts?

Nutrients

Protection

Transport

I'm not sure

Question 15 (1 mark)

Which of the following are examples of parasiticrelationships that might be found in a typical home?

Fleas living on a cat

Pet gold២�sh living in a ២�shbowl

Fungus living on the skin of gold២�sh, damagingtheir health

Fungus living on the skin of humans but notcausing them any harm

I'm not sure

Question 16 (1 mark)

Learning goal 1: Describe what symbiosis is. Are predator-prey relationships symbiotic?

Question 17 (1 mark)

Learning goal 2: In all symbiotic relationships, one species bene២�ts. Distinguish between the three types of symbiosis bydescribing whether the other species bene២�ts or is harmed.

Question 18 (1 mark)

Learning goal 3: Mistletoe is a parasitic plant that grows up around trees of other species. Tapeworms are parasites thatlive in the guts of animals such as cats, dogs and humans.

Both of these parasites derive nutrients from their hosts. What additional bene២�t(s) do tapeworms obtain compared tomistletoe?

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