Week 4, part 2- Adaptations to sperm competition. Flashcards
What has evolved?
How many adaptations are there?
Adaptations have evolved as a result of the selection pressures associated with sperm competition.
6.
Adaptation 1- Prolonged copulation/mate guarding:
What happens in various species in relation to this?
Give an example of an insect which does this. Explain.
Males latch onto females and guard them to prevent other males gaining access to them.
Tiger beetle- Males use large mandibles to grab the females thorax. The male then rides on top of the female for a prolonged period of time after mating to discourage other suitors.
Continuation from adaptation 1- Prolonged copulation/mate guarding:
What can what the tiger beetles are doing be thought of as? Why?
What is the reason they do this?
This can be thought of as an adaptation in response to sperm competition because guarding prevents other males from delivering sperm to that female (after one male has delivered sperm). The new males sperm will be in her to compete with his.
Last male precedence.
Continuation from adaptation 1- Prolonged copulation/mate guarding- last male precedence:
Who is last male precedence seen in?
What does last male precedence mean?
Why does he have an advantage? Explain with an example.
It is seen in insects where females store the sperm and then use it to fertilise their eggs when they lay it.
It means that the last male that mates with a female has an advantage not the first male.
Females have a sperm storage organ (a pipe or tube with a dead end). Whatever you put into that storage organ first is going to be stuck at the back and is going to come out last. If a male mates with a female his sperm will go in, when another does his sperm will go in also but we will be at the front. The second male will have an advantage because his sperm will be at the front of the queue.
Continuation from adaptation 1- Prolonged copulation/mate guarding- last male precedence:
What pays off?
What do other species exhibit?
Last male precedence pays off for a male to prevent other males mating with her after he has mated with her.
Other species exhibit first male precedence (more like a race).
Continuation from adaptation 1- Prolonged copulation/mate guarding- last male precedence:
What is there a trade-off between?
What does data from a study on milkweed beetles show?
There is a trade-off. The male could leave and look for other females for additional copulations and benefit from that or he could stay and guard.
It shows that guarding compared not guarding increased the percentage of offspring they get to father by being the last male. It improves their reproductive success overall.
2- Copulatory plugs:
What is an animal which has copulatory plugs and what is that?
Do we know if this is effective and if it used for the reason we think it is?
Rats- after mating with a female, the male leaves a hard sticky plug in her which blocks her reproductive tract.
No.
Continuation from 2- Copulatory plugs:
What do insects engage in?
Can damsel fly species mate with one or multiple females?
How do damsel fly species who mate with multiple females penis look?
LOOK AT PICTURES ON SLIDE 8.
Sperm displacement behaviour.
Yes.
The damsel fly species who mates with multiple females have little spikes on their penises. These spikes help pull out sperm from rival males and empty the females reproductive tract so they can put their sperm in. The species where they only mate with one female like a thin long line.
Continuation from 2- Copulatory plugs- sperm:
What is a sperm cell designed to do?
What is the first part of the sperm?
What is the second part of the sperm?
Does sperm vary in a lot of species?
What is rat (rodent) sperm like?
It is designed to get genetic material into the egg.
The first part is the genetic material.
The middle part has energy for the tail to thrash around and propel the sperm forward.
Yes.
It is longer than humans and the sperm has hooked heads.
What has nothing to do with each other?
Give an example.
Why might this be the case?
What is the most important thing for a male in a sperm competition?
The size of sperm has nothing to do with body size like rats are small and have big sperm.
It maybe the case that in species with lots of sperm competition, their sperm needs to be bigger and swim faster.
The number of sperm a male enters into the competition.
Sperm competition theory:
What applies?
Explain it.
What is the previous similar to?
Who is most likely to be successful?
Raffle or lottery principles applies.
For example, lets say you are entering a raffle competition in your school, you will buy tickets. The more tickets you buy, the greater your chances of winning.
Sperm competition.
The male who delivers the most sperm.
Continuation from sperm competition theory:
Since delivering the most sperm is helpful, why cant males just make more and deliver it?
Do trade offs happen over evolutionary time when the species gets designed by sexual selection and in the lifespan of individual males?
What is there a trade off between?
There is a trade off. Male cannot produce an infinite number of sperm because there is a cost to making it. Energy is needed to make them and as there is millions this is not trivial.
Yes.
There is a trade off between the cost of sperm production against risk of sperm competition (the
benefits of being able to produce a lot of sperm to deal with sperm competition).
Continuation from sperm competition theory:
Who made the sperm competition theory and when?
What did he create?
Geoff Parker in the 1970s.
He created mathematical models to predict what males should do in different contexts.
Continuation from sperm competition theory- Between species differences:
What is this going to be about?
What should you expect to see in species where there is a lot of sperm competition?
Essentially, what?
The first prediction of the sperm competition theory.
In species where there is a lot of sperm competition, you should expect to see males investing more in sperm production (more sperm, more success).
Investment in sperm production is greater in species that experience high levels of sperm competition.
Continuation from sperm competition theory- Between species differences:
What is one way to measure how males are investing in sperm production?
What do species with multi-male mating systems have over those with monogamous or single-male systems?
One way to measure how much males are investing in sperm production is to look at the testes.
Larger testes.
