Reproduction: the Origins of Sex

Biology Reproduction: The origins of sex

Organisms reproduce in all sorts of weird and wonderful ways and scientists have just discovered that a type of fish that existed over 360 million years ago was the first to to have sexual intercourse, like many animals, including humans, still do. In this lesson you will investigate the following: • What is reproduction? • What are the different types of reproduction? • What are some of the advantages and disadvantages of these types of reproduction? So, let’s produce some answers!

This is a print version of an interactive online lesson. To sign up for the real thing or for curriculum details about the lesson go to www.cosmosforschools.com Introduction: Reproduction (P1)

Scientists have discovered the origins of sexual intercourse through studying fossils of armour-plated fish called antiarch placoderms that became extinct some 360 million years ago.

The fish, which gave rise to all current vertebrates with jaws, including humans, were the first animals to develop specific male and female genitalia.

Before the placoderms all reproduction was through external fertilisation, in which sperm and eggs are expelled into the water to unite – the way many modern fish do. But the scientists found evidence the placoderms changed all this. They discovered structures in the fossils that they interpret as bony "claspers" — male organs that penetrate the female and deliver sperm. They say the placoderms would have had sex side by side.

But the discovery that the animals had penetrative sex is perhaps less surprising than the fact that the bony fishes that follow placoderms in the evolutionary tree show no evidence for internal fertilisation. That means that some of the placoderms' descendants had to "re-invent" sex organs such as claspers in sharks and rays and penises in mammals and birds.

Read the original Cosmos blog post here.

Loading... Poll 1

Hypothesise: While the antiarch placoderms are the first known organisms to have had sexual intercourse, organisms have been reproducing sexually for approximately 2 billion years. Other organisms reproduce asexually – that is, without a partner.

Without doing any research, suggest which of the following organisms you think reproduce sexually.

Note: Some organisms can reproduce both sexually and asexually!

Koalas

Bacteria

Yeast

Sea anemone

Cacti Gather: Reproduction (P1)

Sexual reproduction

Sexual reproduction requires two parent cells. These cells are known as gametes and each holds half of the genetic information of their parent. Male gametes are known as sperm and female gametes are known as eggs (or ova). When the two gametes fuse a zygote is formed – a process known as fertilisation. The offspring hold a full complement of genetic information, half from the male and half from the female.

Question 1

Define: In your own words, define the term sexual reproduction. Question 2 Question 3

Remember: The male gametes are known as eggs. Recall: Female gametes contain 50% of the female's genes.

True True

False False

Question 4

List: In the table below, describe internal and external fertilisation and provide an example of a species that uses this type of fertilisation.

Type of fertilisation Brief description Example Internal fertilisation External fertilisation

Asexual reproduction

Question 5

Define: In your own words, define the term asexual reproduction. Question 6

Identify: The video clip describes three types of asexual reproduction: cell division, budding and splitting. Use the line drawing tool to link the species in the sketchpad below with their method of asexual reproduction. Process: Reproduction (P1)

Whether sexually or asexually, organisms reproduce in all sorts of weird and wonderful ways. In the case of the redback and dark fishing spiders the males are eaten alive by the female during sex!

The following fun facts about the dark fishing spider will help you answer questions 1–4 below:

During mating season the males outnumber the females 3:1. The weight of the female spider is 14 times that of the male. Each female can produce 1000 spiderlings, which she carries around and guards in a webbed nest.

Question 1 Question 2

Calculate: A population of dark fishing spiders has 20 Calculate: At the beginning of mating season a population of females. How many males spiders would you expect there to be dark fishing spiders has 30 males. How many female spiders at the beginning of mating season? would you expect there to be?

Question 3 Question 4

Calculate: A female dark fishing spider was found to weigh 7 Calculate: There are 15 male dark fishing spiders in a grams. What would you expect a male to weigh? population. How many offspring could be produced? Question 5

Investigate: Complete the table below. For the "Parental care rating" use the following system:

"0" – parents take no care of offspring.

"1" – parents care for seeds or fertilised eggs.

"2" – parents care for offspring after they are born or hatched.

For the other columns use the answers below:

Zygotes develop into seeds in fruit before dispersal by being eaten | Offspring spends 1 month developing in uterus then 7 months in pouch living on mother's milk and pap. Then stays another 5 months carried on mother's back | Parents not present at fertilisation – no care of offspring. Split individuals are fully developed, just need to grow new arms.

Organism Image Method of Offspring Number Number of offspring: Parent Parental care: reproductio genetical of Notes al care Notes n ly offsprin rating identical g per to year parents? Escherichia coli Can’t identify parents – A common gut Yes 1 individual becomes 2 bacteria "daughter" individuals, fully developed.

Phascolarctos cinereus Sexual 1 Koala (internal)

Ophiactis Thousands of eggs and savignyi sperm released into the 0 Brittle star ocean seasonally where they are fertilised. Many offspring eaten. Often individuals split to produce two new individuals. Carnegiea Only starts flowering at 30 gigantea years old. 2,000 seeds per Saguaro fruit, 20–100 fruit per cactus plant. Very few seeds grow to maturity.

Latrodectus Female keeps egg sac in hasselti 1,000 to her web for 3–6 weeks Redback 2,500 until young emerge. spider They stay on the web a few days, sometimes eating siblings, before leaving. Question 6

Think: What are some of the advantages and disadvantages of sexual and asexual reproduction? Propose why each may have led to evolutionary success.

Hint: You may share ideas about this task in the discussion board at the bottom of this page. If it is closed ask your teacher to open it. Apply: Reproduction (P2)

Essay: Sexual vs asexual reproduction

Question 1

Write a 200-250-word essay in response to the following question:

"If there were only asexual reproduction, how would this affect the world as we know it?"

Use the project space below to construct your essay. You may wish to use a mind map to brainstorm your ideas and the text widget to write your essay. Career: Reproduction (P2)

As a child from a small village in Slovenia, Simona Kralj-Fišer didn't know she wanted to be a scientist. She didn't even know that such a profession existed. Simona thought that the only way to have a career in science was to be an astronaut, with the next best option to be a medical doctor. And so she dreamed of becoming a doctor.

When Simona had to choose the subjects she wanted to study in school she was torn between her interests in biology, psychology, geography, and literature. Finally, she settled on biology – and soon realised there was more to science than just medicine and space travel.

Now, she is a researcher and lecturer of behavioural genetics at the Slovenian Academy of Sciences and Arts, where she's a specialist in the curious mating behaviours of nephilid spiders. There's no shortage of interesting and exciting things when it comes to the spiders, like how female spiders are physically incapable of mating more than twice in their lives. But what fascinates Simona the most about the spiders is possibly the most bizarre aspect of their behaviour – female spiders eat their mates after mating. It's a thrilling thing to watch, although Simona admits she always hopes the poor male spider will survive its romantic encounter!

Like many other scientists, every day at work is different for Simona. She does everything from the most technical work that involves rearing her spiders and doing lab maintenance, to carrying out experiments, analysing data, writing papers, and teaching her students. But her favourite thing to do is watch her spiders at work.

When she isn’t attending to her arachnids, Simona makes time for her hobbies, which include reading, hiking, collecting mushrooms and fruit from the forest, and spending time with her family.

Question 1

Imagine: When she took biology at school Simona discovered that there was more to science than being a doctor or astronaut. In fact, there is a science angle to many of the activities we undertake or interests that we have in our everyday lives.

Write down two or three things that you enjoy doing, and some of the different ways that science is involved in these. Cosmos Live Learning team

Lesson authors: Deborah Taylor and Samantha Webber Editors: Bill Condie, Jim Rountree and James Whitmore Artists: Robyn Adderly and Anton Banulski Education director: Daniel Pikler Image credits: Getty images, Shutterstock and iStock. Video credits: Flinders University, Mark Drollinger and YouTube.