Counter Intuitive Behaviour Flashcards
Why do humans eat so many sweets and soft drinks? Proximate and ultimate causes.
Sweets and soft drinks contain sugar, which tastes sweet to people.
Sweet taste is remembered as good; the memory of pleasure leads people to eat or drink more of the same.
Sugar, which is present in sweets and soft drinks, is an energy source that helps keep people alive.
Our ancestors depended on sugar-rich fruits; we have inherited the same tastes that they had.
Our genes shape the development of nerve cells that provide perceptions of sweetness and pleasure.
In the past, individuals who liked sugar left more descendants than those who were indifferent to sweet-tasting foods.
The sensory input from taste receptors in the tongue to selected brain cells leads to a positively reinforcing sensation of sweetness.
Group selection & Individual Selection
When dominant male is displaced, his infants are killed. New makes are often the killers. Does infanticide advance a male’s reproductive success?
Favoured by natural selection, at individual level
Infanticide frees females to become pregnant sooner. The male becomes a father sooner, and has more offspring before he is himself overthrown by another male.
The Logic of Group selection
Individual’s behaviours are adaptations that assist survival of the group. e.g. reproducing less to avoid overexploiting resources. Groups with self restraining or altruistic individuals will survive better.
BUT individual selection is typically stronger. Groups with the characteristics necessary for group selection are rare.
When individuals are long lived and intergroup competition is high
there’s an advantage to altruistic group selection
When individuals are short lived and competition within the group is high
there’s an advantage to individual selection
Infanticide in Meerkats
Social groups with dominant female and subordinates. Pregnant female will kill the pups of other females - even that of the dominant female.
Mothers decrease competition and increase quality of their offspring.
Dominants suppress subordinates from reproducing by being aggressive. If other meerkats are pregnant, the chance of a pup surviving decreases dramatically (SLIDES).
Autotomy
When bees cast off their stinger
Bees have a barbed sting
Easy to go in, hard to get out. The sting injects venom into the flesh. It also injects alarm pheromones, highly volatile small molecules which make other bees more likely to sting.
Self-sacrificng bees
Honeybee workers rarely reproduce, instead they rear close relatives (kin selection). They save their reproductive investment by protecting them.
Sex change in Anthias fish
Females change into males when a large dominant male dies and leaves an opening in the population.
Garden spiders
Male waits for female to mature then plucks web. Sometime’s gets eaten.
Some males tie down the female.
Some makes give a nuptial gift to distract the female.
Black widow, Latrodectus mactans. Latro: servant. Dektes: Biter
Females much larger than males (450mg vs. 5mg). Lives longer (2yrs vs. 2-4 months).
Males mature at a younger age. A female mates with several males.
In redback spiders he faces forwards on female’s abdomen then somersaults backwards into her jaws.
Benefit of being 1st Male Cannibalised
Effect of cannibalism on first male’s paternity
If first male is cannibalised
6/9 females reject second male (67%)
If first male is not cannibalised
1/23 females reject second male (4%)
Difference is highly significant (P = 0.001, Fisher Exact Test)
Female is less likely to remate if she cannibalises the first male
Benefit of 2nd male being cannibalised
Longer copulation duration meaning higher paternity
Bean Weevil oedaegus
Covered in hard spines which damage female. But female kicks the male, dislodges him sooner and has less damage than without the kicking behaviour. If a female is damaged, there’s no difference in fecundity after mating but there is a difference in lifespan after 2 damaging matings.
