Sexual Selection Flashcards
Who was the first to notice that one sex often has extravagant features?
Charles Darwin
What is the fundamental difference between the sexes?
Gamete size
What is isogamy?
Equal sized gametes meaning neither male or female forms- this occurs in many simple unicellular organisms
What is anisogamous?
One of the gametes is large, immobile and food rich
The other gamete is small, immobile and essentially just a delivery mechanism for DNA
Why is parental investment usually greater in females than males?
Males: best increase success by finding and fertilising many different females
Females: best increase reproductive success by increasing the rate of converting resources into egg and offspring
What is intrasexual selection?
Competition between members of the same sex (usually males)
The female doesn’t have a choice
What is intersexual selection?
Still competition between (usually) males but the females choose the winner
Give an example of intrasexual selection
Elephant seals
The males are much larger and compete with each other to get all the matings in a harem
Give an example of intersexual selection
Long tailed widow bird
The female selects the male based on their tail length
Andersson (1982) found the birds with elongated tails had significant increases in mating success
In the bower bird what information is the female getting from the bower
An indicator of social status and sperm quality
What is fisher’s hypothesis? (1930)
Females find certain traits attractive, therefore by mating with these attractive males females will have attractive offspring
Also known as the ‘sexy sons’ hypothesis
What is runaway selection?
Where animals develop more and more extravagant traits
It will stop when it becomes too much of a handicap
What is the handicap hypothesis?
Alternative to fisher’s hypothesis
Extravagant male features actually create a handicap and this handicap is why the females choose them because it is a good indicator of male quality
Must be good at surviving to do so with a handicap
What did Hamilton and Zuk (1982) suggest about parasite resistance?
Sexual displays are good indicators of resistance to disease or parasites
Females will choose the ones resistant to disease/parasites
What study supported Hamilton and Zuks theory?
Study on the three spined stickleback
Females chose the reddest males in white light as this was an indicator of fitness and less parasites
In green light there was no effect on choosiness
How can sexual selection lead to behavioural isolation?
Runaway selection can drive reproductive isolation because females select for exaggerated characteristics, if this selection becomes strong enough it can cause behavioural isolation
This can be through courtship display differences etc.
Give an example of behavioural isolation
Hawaiian drosophila
Two different head sizes (narrow or wide)
Found no difference in female choice over head size but there was a difference in mating displays which prevented mating from occurring
What does the faster male theory suggest?
That male sterility is more common than females when bred with relatives due to spermatogenesis being more sensitive to change
Alternatively could be due to sexual selection/conflict causing increased divergence in male genetics
What is sympatric speciation?
Species that share the same habitat but become reproductively isolated from each other
What is allopatric speciation?
When species within the same population become geographically isolated
