Behavioural polymorphisms Flashcards
Animals in the same situations, don’t all respond the same way - why not?
1) Hormones, parasites, neurophysiology, diurnal cycles all affect behaviour – see specialist lectures.
2) Animals play different strategies.
3) Animals have different personalities.
Can individuals in the same species play different strategies?
Yes and this is explored in the game theory “Hawk - Dove game”
What is the “Hawk-Dove game”?
The “hawk” and “dove” are strategies played by players of the same species, NOT two different species.
What does the Hawk do in the “Hawk-Dove game?” in regards to resources
HAWK: very aggressive, always fights for some resource, taken by the winner.
In the “Hawk-Dove game”, what occurs when hawk vs hawk
Fights are costly. Model assumes all hawks are equally strong, so 50% chance of winning a fight.
What does the Dove do in the “Hawk-Dove game?” in regards to resources
never fights for a resource. Initially displays aggression but if the opponent tries to fight, it withdraws before it gets injured. Cost is waste of time.
What happens when Dove vs Dove in “Hawk-Dove game”
Dove meeting dove wins 50% of contests, but takes time.
What happens when Hawk vs Dove in “Hawk-Dove game”
Dove meeting hawk, recognised as hawk quickly so little time cost, no injury.
How do we know whether a strategy will persist?
By looking at it’s Evolutionary Stable Strategies
it depends on the costs and benefits of each strategy!
What are Evolutionary Stable Strategies?
strategies which cannot be invaded by another strategy.
If we have a pure population of doves, is this an evolutionary stable strategy?
If invaded by a hawk, the hawk wins all encounters, gets all the resources and never has to fight so would outcompete doves. So pure dove not an ESS.
If we have a pure population of hawks, is this an evolutionary stable strategy?
If invaded by a dove – doves don’t pay any injury costs, but never win. So fights with hawks are neutral, and doves can persist in hawk populations as long as the resource isn’t vital. So pure hawk not an ESS either.
Are there any values which give a stable mixed population?
If assume winner pays no cost and loser all the costs
you can plot this value for each frequency of hawks and doves to see if there’s any population mix which would be stable.
Where the lines cross is a stable mixture of hawks and doves.
At the ESS point, what would happen if you added individuals of either strategy
lowers fitness of that strategy More Hawks would have lower fitness than that of dove. More Doves (fewer hawks) would have lower fitness than Hawks. So returns to the ESS frequency.
What is the impact of adding a hawk?
As both lines have negative slopes, the addition of any Hawk lowers everyone’s fitness!
What does the game theory explain?
This game explains why most animal contests involve only ritual fighting behaviours rather than outright battles.
Describe how speckled Wood butterflies play Hawk or Dove
- territory ownership of a patch of light on the forest floor
- Whoever gets there first is the owner. Owners play Hawk and defend the territory
- If another male arrives in an occupied light spot, he plays Dove and retreats immediately.
- If two arrive together, they both think they own it and fight by spiralling round each other until one concedes – i.e. they both play Hawk.
Bourgeois strategy!!
What is the bourgeois strategy?
Playing Hawk when owning a territory, but Dove when invading someone else’s territory
Give an example of animals playing bourgeois strategy?
Speckled Wood Butterflies
Give an example of animals playing “anti-bourgeois” strategy
Mexican spiders
How do Mexican Spiders play “anti-bourgeois strategy”
- territories in gaps between stones in walls and rubble.
- territory holder plays Dove, and runs away if attacked.
- attacker plays Hawk and invariably wins.
- get a domino effect of one spider displacing another all across the wall.
Where do mexican spiders hold territory?
in gaps between stones in walls and rubble.
With Mexican spiders, why does the territory holder give in so easily?
If there are lots of territories, but fighting is expensive, then letting an intruder have the territory and avoiding the fight is probably adaptive.
What is anti-bourgeois strategy?
an individual plays Dove when the individual is an owner of the resource, whereas it plays Hawk when it is not an owner
What is war of attrition?
When 2 animals meet in a contest for a resource, the amount of energy they are willing to invest to win that resource are predetermined.
If instead of two choices (attack or run away) the competition is how long to hold out
Give an example of war of attrition
male dung flies aggregate at dung pats to await females who lay eggs there.
- The longer a male waits, the fewer new females he will encounter and the more fights he will have with other males
- But if he goes away too soon he misses out on new females and pays a cost of flight to the next pat.
- If lots of females at a pat, stay longer.
What occurs the longer a male dung fly waits and the shorter he stays
the fewer new females he will encounter and the more fights he will have with other males
if he goes away too soon he misses out on new females and pays a cost of flight to the next pat.
Real animals play multiple strategies in different circumstances, true or false
True
Why do horned beetles have different mating strategies?
Because there are two forms of male: Horned and Unhorned
What are horned male beetles?
Horned males got good nutrition as grubs, grow large and develop horns.
What are unhorned male beetles?
Unhorned males got poor nutrition as grubs, and didn’t grow big enough to grow horns.
How do horned/unhorned beetles mate differently?
- Horned males stand at the entrance to the burrow and drive off intruders.
- Unhorned males cannot attack them, so build a second tunnel which enters the side of the main tunnel, bypassing the male guarding the entrance. The unhorned male mates with the female behind the horned male’s back.
How do side blotched lizards mate differently?
3 male morphs – orange, yellow and blue, which differ in behaviour as well as throat colour.
Orange males are very aggressive and mate with lots of females by taking over the territories of other males =usurpers.
Yellow males don’t defend territories, but mimic females and sneak matings behind the backs of territorial males = sneakers.
Blue males mate guard females so spot sneakers, but lose fights with usurpers = mate guarders
So, like rock-paper-scissors; orange defeats blue, blue defeats yellow, and yellow defeats orange.
What are the usurpers in side blotched lizards?
Orange males are very aggressive and mate with lots of females by taking over the territories of other males
What are the mate guarders in side blotched lizards?
Blue males mate guard females so spot sneakers, but lose fights with usurpers
What are the sneakers in side blotched lizards?
Yellow males don’t defend territories, but mimic females and sneak matings behind the backs of territorial males
Give an example of an evolutionarily stable situation in which no single colour morph can dominate the population.
All three throat colours and their associated behaviours are being maintained through the social interactions and their rock-paper-scissors polymorphism.
Real animals play multiple strategies in different circumstances - what animals do males do this in again?
horned beetles, side blotched lizards
How do guppy females have different breeding strategies?
Two mate choice strategies, depending on life stage and experience:
If young, copy the mate choice of older females;
If old, stick to your own choice.
Real animals play multiple strategies in different circumstances - what animals do females do this in again?
Female – guppies; damsel flies; cuckoos
White Throated Sparrows exist in two forms, what are they?
Tan and White striped
How do White Throated Sparrows behave quite differently (Tan and White striped)
Tan ones are more monogamous, and care for the young better.
White striped ones sing more and are more aggressive
With white throated sparrows, both forms that exist are quite different. Why doesn’t one strategy win?
Pairs mate by negative assortative mating – i.e. prefer to mate with the opposite form.
Mixed pairs do best: one partner gives good parental care, the other defends the territory well. Maintains both morphs in the population.
Also maintained by heterozygote advantage – the heterozygotes are healthier.
How is feeding behaviour maintained as two strategies
Large Cactus Finch – one of Darwin’s finches on the Galapagos
Territories of A and B males randomly distributed if unmated but alternate if mated.
Living next to someone eating differently is best for your food availability.
Two feeding strategies maintained because more efficient to differ from neighbour.
How do the large cactus finches differ?
Males dimorphic in song type: songs A and B
Males with song A vs Song B (large cactus finches)
All eat prickly pear cactus but use different bits.
Males with song A have shorter bills
A males (shorter beaks) tear apart the cactus base and eat the flesh and insect larvae in it.
than song B males.
B males (long beaks) punch holes in the cactus fruit and eat the fleshy pulp.
