Week 4, part 4- Sperm characteristics. Flashcards
What is variable across species?
What does this variability have nothing to do with?
Sperm size.
The size of the animal.
How long is rat sperm?
Can species have a sperm which is very very long?
200 micro metres long.
Yes.
Fruit fly- Drosophilia bifurca.
What is this fruit fly called?
How long is a single sperm cell?
How much do they produce? And what about it?
Is the sperm cell very big that it can block up the females reproductive tract?
Drosophilia.
A single sperm cell can be nearly 6cm long- this is 20x longer than the fly itself.
They do not produce many of them and they are normally bundled up.
Yes.
If males have a fixed amount of energy to make a lot of sperm, what kinds of sperm can they produce?
In terms of the raffle principle, what would be the best thing to do?
They can make lots and lots of tiny ones or make a smaller number of big ones that can swim faster.
For the raffle principle, the success of the sperm competition depends on the number of sperm so it will be better to produce as many sperm as possible.
Sperm design:
Because of the raffle principle, what should sperm competition lead to?
The raffle principle sperm competition should lead to a trade of trade-off between the number of sperm being produced and the size it is possible to make them that is if males have got a fixed amount of energy they can spend on making sperm.
Continuation from sperm design:
Over evolutionary time, how did it come to be very long or very short? Give one idea.
What happens if sperm competition increases?
Because of the raffle competition (lots of sperm competition), males should evolve to produce lots and lots of sperm and have them small because this is what you need to do if you are going to make a lot of them.
There will be many small sperm.
Continuation from sperm design:
What happens if this is right?
When does this all happen?
If this is right, you should expect to see a negative association between sperm size and number across species- In species that produce a lot of sperm, you should expect them to be tiny and in species that do not produce many you should expect them to be large.
Over evolutionary time!, not within the life span- Individual males cannot adjust their own sperm size. Each species has a design like a rat sperm is a specific size.
Alternative possibility- Salmon:
What happens in salmon?
Where is all of this happening? Explain.
In this context, is being able to swim effectively important for success in sperm competition?
In salmon, the males swim up the river, go to a breeding ground where the females lay eggs and when they lay their eggs, lots of males come and try to deliver their sperm.
In fast moving water. The sperm needs to move very hard and quick just to stay near the eggs (they die quick).
Yes.
Sperm design- alternative model:
If size helps a sperm swim effectively (competitive advantage), what might you see?
What should not be observed?
What happens if both size and number are increased?
You might expect to see larger and more sperm in species where there is a lot of sperm competition.
A trade-off.
But if size and number are both increased then the total ejaculate expenditure must increase (the energy they are spending on it).
How can you measure sperm size?
Who has bigger sperm?
Look at slide 9 for a positive association.
Does sperm competition select for bigger sperm?
By looking at things like total length, how big is the head, tail, mid piece etc.
The species with more sperm competition have bigger sperm.
Yes.
What kind of sperm is faster?
Who produces faster sperm?
What does sperm competition select for?
Is it all about tail length?
Longer sperm- they make better progress.
Species with large testes, a sign of a lot of sperm competition, produce faster sperm.
Sperm competition selects for sperm being longer and faster.
Yes.
General findings:
What is the first general finding?
Is it due to an increase in size of all sperm components (like the head and mid piece for example)?
Sperm competition is associated with an increase in total sperm length. This is over evolutionary time!!!, individual males cannot increase the sizes of their sperm.
Yes.
Continuation from general findings:
Can hooked heads get tangled up and form sperm plugs?
What can happen in some rodent species?
As a train, what can happen?
Yes.
In some rodent species (forrest mouse), they can hook together and swim as a team. They are called sperm trains.
As a train they can travel faster than an individual sperm cell can do.
What can be adaptations to sperm competition?
Sperm characteristics like length and swimming speed can be adaptations to sperm competition.
