selectie sexuala Flashcards
What is natural selection based upon?
Biological variation
Competition over limited resources
Why are there traits that compromise personal survival?
Peacocks have feathers which increases their risk of being caught by tigers.
Peahens show preference for peacocks who have the most eye spots.
What is sexual selection?
Traits that promote mating and reproductive success, sometimes at a cost to personal long-term survival.
What does biological fitness measure?
NOT how long you personally live.
But your reproductive success - how many copies of your genes survive
What is sexual dimorphism?
Darwin thought that sexual selection could explain certain types of sexual dimorphism (when males and females differ in terms of physical or behavioural traits)
What is the basis for sexual dimorphism?
Males are often bigger than females and they possess fighting features. This is due to male to male competition over mates.
Males with better fighting features are more able to win in a competition and they will have more babies and those features will be passed on.
What is the basis of sexual dimorphism in terms of female choice?
Darwin suggested that males possess certain features because females prefer them.
But that was rejected.
We can’t know if peacock have huge feature to attract females or to intimidate other males.
What is male promiscuity?
Due to a greater variance in male versus female potential reproductive success
Males chances of fathering young increasing with every new female they are able to mate with
While most females generally can only become pregnant once
Hence males more than females will benefit from every extra act of mating with a fresh mate
What is one explanation for why females are choosier?
Females are choosier because of greater parental investment (Trivers)
Thus, females have more to lose than males if they mate with a poor quality mate.
But it is difficult to measure parental investment.
What is differential potential reproduction rates?
Instead of looking at parental investment we should look at differential potential reproduction rates.
Differential potential offspring reproduction rates can be worked out mathematically in terms of maximum numbers of matings required for maximum potential offspring.
So whichever sex’s reproductive potential is in relatively short supply becomes a limiting, and thereby valuable resource for the other sex and worth competing for (Vincent)
Sex role reversal
Females are not always the limiting factor and males are the ones who are going to compete.
Male seahorses carry females’ eggs in a brood pouch. The size of the pouch can become a limiting factor coz it can only fit so many eggs.
In monogamous species, where the males will only carry one females clutch of eggs, the males fight each other to gain a mate.
In polygamous species, where males will carry more than one females eggs in its pouch, the females fight each other to gain access to limited space in male’s pouches
What is paternity uncertainty?
Males suffer from this - males who help raise babies do not want to waste their energy raising another male’s young.
Why do females seek adulterous affairs?
If the female becomes pregnant by a more genetically healthy and attractive male than their mate, but their mate helps raise the resultant babies, they gain a reproductive advantage.
Kempenaers found females engage in adulterous affairs with big, attractive, long-lived males.
Evidence to support female choice:
Originally female choice was rejected.
Female choice: African Widowbirds
Condition 1: gave birds tail extension
Condition 2: shortened tails
Condition 3: left tails alone
Condition 4: cut tails and glued them back again to the same length
Birds with artificially lengthened tails acquired more mates
How is female choice characterised?
- Good genes hypothesis
- Good taste or sexy son hypothesis
