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Is the differential allocation of investment in sons vs. daughters to increase RS
Fisher: Genetic model predicts 1:1 sex ratio at a population level due to mixed ESS
But, there can be biases when:
Relatives interact
There are variable environments that promote one gender over the other
Sex allocation Local resource competition
Biased against the competing sex
Galago
Local mate competition
As before, bias is against the sex that would compete most for mates
Fig wasps
Environment determines biasMaternal condition – sons gain more in RS
when times are good
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Environment determines biasMaternal condition – sons gain more in RS
when times are good
Environment determines biasMothers should have more sons when
she’s mated with a particularly sexy male
Environmental sex determination by temperature
Environment determines bias
Can a temperature provide
a good ‘male environment’
or ‘female environment’?
Do animals ever change their gender over their lifetime in order to increase their LRS?
Sequential hermaphroditism
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Protandry and Protogyny
Depending on ecology, it can be best to be female at large size or male at large size
Protandry Protogyny
Sex change in individuals
females
males
malesfemales
Protogynous sex change
Common in harem-forming reef fish
Often, change controlled by the local situation: when a male dies, largest local female changes sex
blue-headed wrassecleaner wrasse
Protandrous sex changeEx: Anemone fish (clownfish)
monogamous due to anemone size
male success not size dependent. Again, local situation triggers sex change
Finding Nemo: the shocking truth
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So why don’t animals like elephant seals change sex with age and size?
F
M
Categories of social interaction
Recipient
Actor + -+
_
mutualism,cooperation
selfish,parasitic
altruism spitefulness
Are humans ever truly altruistic?
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Social parasitism – “cooperation” actually induced by the recipient to the donors disadvantage.
brood parasitism (fish, birds, insects)
kleptoparasitism
induced regurgitation in insects
kleptoparasitisism
Altruistic behavior is, for the most part, only seemingly altruistic
induced regurgitation
What else can explain seemingly altruistic acts?
Kin selection (Hamilton, 1964)
Mutualism
Reciprocity (Trivers, 1971)
Food sharingwarning calls cooperative breeding
Cooperative acts are directed toward kin.
Proportion of your genes in future generations can be increased indirectly by helping relatives
Kin selectionHamilton’s Rule:
An altruistic trait is selected for if benefit B is large enough so that:
Br > C Br – C > Oor
W.D. Hamilton
Kin selection
r = coefficient of relatedness
(ranges from 0 to 1)
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Determining r
Parent-offspring
(Box 11.2)
“I would be prepared to lay down my life for the sake of 2 brothers or 8 cousins”
J.B.S. Haldane
Inclusive fitness
Avoid ‘double counting’ when considering kin selection.
I found this on a course website:
“For example, suppose that on average a human has two offspring in its life. But you are given the chance to help your sister with her offspring. She has 9 kids. If your act of altruism towards your sister was controlled by a gene, it would spread through the population because 9/2 > 1/(0.25).”
B/C > 1/r
Joe’s RS Joe’s brother’s RS
O O O O O O O O O O
“Strip away” the effects of helping
O O O O O O O O
Modify according to effects of helping
O O O O O O O O
This avoids double counting young
Joe’s inclusive fitness = 3(0.5) + 3(0.25) = 2.25
Calculating inclusive fitness
Not help 4(0.5) = 2Help 2.25
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Using Hamilton’s ruleA version of H’s rule for when you
are forgoing your own offspring
B r (donor to own offspring) 3 .5
C r (donor to recipient) 1 .25> >
Without With
helpers helpers
Fledglings per pair 1.80 2.38
Helpers at the nest in Florida scrub jays
“Extra” offspring due to helping: 2.38 - 1.8 = 0.58Average # of helpers = 1.180.58/1.18 = .49 extra young per helperInclusive fitness of helpers = .49 (0.43) = 0.21
r
hf
m
Altruistic acts should be given to relatives
Black-tailed prairie dogs
Predictions and tests of kin selection
Probability of calling inpresence of relatives or non-relatives.
Male turkey coalitions Dominant males w/partner have 6.1 more
offspring than solitary malesr = .42Solitary males have 0.9 offspring
(.42 x 6.1) – 0.9 > 0 rB – C > 0
1.7 > 0
Tricky to measure B and C
partner
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Using Hamilton’s ruleA version of H’s rule for when you
are forgoing your own offspring
B r (donor to own offspring) 6.1 .5
C r (donor to recipient) 0.9 0.42(0.5)
6.1(0.42x 0.5) - 0.9 (0.5) > 0
1.7 > 0
> >
Ways to signal relatedness or gene similarity
Relatedness signal can be detected by others
Altruistic acts are directed towards those with closest relatedness signals
For kin selection to work, you need:
This predicts kin recognition
Theoretical ‘Green beard effect’ – Dawkins
An allele codes for all three things
Susceptible to false ‘beards’
Ex: Mexican free-tailed bats – pups are placed in a crowded ‘creche’. Pups are recognized via olfactory and vocal cues.
Kin recognition
400 pups per square foot
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Ideally, you’d want genetic markers to be directly detected and acted upon…
Or at least some way of knowing ‘family’
Individual slime moldswere related by either1 or 0
Aggregations avg r = 0.8
Animals trying to direct help toward kin can face same mistakes as brood parasite hosts
Types of cuesChemical - genetic or environmental?
Visual
Sound
When the environment is very heterogeneous, then environmental cues can work well
‘Treat anyone home as kin’ (or imprint)
Genetic cues work better in homogenousenvironments (ex: within the same beehive, some aquatic habitats)
Chemical cues
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Environmental cue examples:
Most social insects use chemical labels to identify nestmates
Ex: Paper wasp larvae absorb nest odor onto their cuticle during development
Chemical cues: environmental
MHC genes are highly polymorphic and often used as recognition cues
The major histocompatability complex is a set of genes used for the recognition of “self” as a part of the immune system.
Chemical cues: genetic
MHC determineglycoproteins oncell membranes
Honeybees can not only identify nest mates via environmental cues, but can also discriminate half vs. full sisters
Chemical cues in useBelding’s ground squirrels – also use environmental and genetic cues
Aggression b/w variouspairs of ground squirrels Freq. of fight Freq. of help
Fig. 11.5
Chemical cues in use
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Chimpanzees can pair mothers with their sons
Visual cues in use Dolphins, Orcas – each have unique whistles
Colonial seabirds – young are in creche and parents find them by call
Sound cues in use