Sexual Selection Flashcards
What is behavioural ecology?
Studies behavioural adaptations (an action by an organism)
What is organismal ecology?
Studies morphological (structural changes), physiological (internal changes), behavioural (actions) adaptations in response to selective pressure
Two ways behaviours can be explained :
Proximate and ultimate
What is proximate cause?
How a behaviour happens
Ex: when a mimosa is touched it opens ion channels which releases water to make food leaf in half
What is a ultimate cause?
The reason for the trait to have evolved
Ex: when a mimosa is touched it folds in half to appear smaller looking less appetizing and it increases their biological fitness.
Why do behaviours evolve?
For fitness outcomes, with the help of variable and heritable traits.
Types of behaviours: feeding, territorial and sexual (most important)
What is sexual selection?
A type of natural selection that favours individuals with traits that increase their ability to obtain mates.
MATING IS NOT OFTEN RANDOM
What is Fundamental asymmetry of sex
- The energetic cost is huge when creating a large egg, compared to the sperm which requires less resource. (Females invest more in offspring than males)
- females are only limited by resources to produce offsprings
- males are only limited to access of mates not resources.
Bateman-trivers principle (1) & predictions (3)
- Principle: In most species variability is greater in males than females.
- Predictions:
1) females should be picky & males not
2) males should compete access to mates
3) alleles increasing a male’s access to mates is favoured in a population
What is sexual dimorphism?
When males and females of same species look visibly different.
Ex: lions, moose, wood ducks
What are two forms of competition between males & their description?
- Intersexual selection (female choice): males compete with each other for attention of females. (Females interact with males who they choose).
- Intrasexual selection (male-male competition): males compete with each other for reproduction purposes of females. (Males interact with each other to determine who mates with females)
What does Intrasexual selection favour in animals?
It favours the evolution of male armaments (armour) to aid physical competition between males.
Ex: Elephant seals
- uses large noses to fight for territory containing females.
- larger and powerful noses win more fights and have more offspring.
- therefore sexual selection favours of evolution of seals with larger noses
When does intrasexual selection in plants occur?
It Occurs when pollen grains compete to access ovules.
Process: pollen grains land on pistil ( female part of flower), then a pollen tube grows towards ovule and fertilizes them. Pollen tubes that grow and fertilize faster have a better chance of passing on their alleles (sexual selection favours faster growing pollen grains)
What does intersexual selection favour?
-It favours the evolution of male ornamentations (looks) to signal their quality to females.
Ex: male zebra finches have colourful beaks and cheeks. Females choose more brightly coloured mates, suggesting that they are healthier.
Intersexual selection - Mating displays:
Males develop elaborate mating displays to signal their quality as a mate.
Ex: the male superb bird of paradise has vibrant features and complex dance moves, this attract mates.
Intersexual selection - handicap principle:
This principle suggest that males attract females by developing costly morphological or behavioural handicaps. If a male is successful despite of their handicaps he is a good mate.
Ex: peacocks use a lot of energy to produce colourful tails, this makes the bird visible to predators and delays movement.
Intersexual selection- sexy son hypothesis:
It suggests that a female choosing a physically attractive male will produce attractive sons and therefore she will have more grandchildren.
EXTRA: (IMPORTANT)
- females may not directly benefit from this but her overall fitness might increase if hers sons inherit qualities from her mate.
-females may choose to mate with polygamous mate, even though this does not benefit her, her sons might inherit the trait form the father resulting in even more grandchildren.
Can both intersexual & intrasexual selection drive evolution of mating behaviours?
Yes they can.
Example for intersexual selection:
Male dewlap extension only increases in the presence of females not males.
Example for intrasexual selection: (also intersexual)
Males do more pushups in both mating displays to females and in territorial displays to other males.
Is sexual dimorphism only due to sexual selection?
No sexual dimorphism is due to sexual selection AND natural selection.
Example: (IMPORTANT)
If we take the species of mammals, the large males are due to sexual selection, so they can compete with each other for better access to females. The large females (very rare in mammals) are due to natural selection, so they can gain more resources have a higher fitness.
Are small males sometimes favoured by sexual selection?
Yes they are. In species with large females and small males, the females are mostly stationary and the males are highly motile in search of mate. (In this case female body size is due to natural selection, and male body size is due to sexual selection)
The males need to be small to increase access to mates, and females need to be big to increase biological fitness.
