1

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

2

Environment determines biasMaternal condition – sons gain more in RS

when times are good

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

3

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

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

4

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

5

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

6

Are humans ever truly altruistic?

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

7

Cooperative acts are directed toward kin.

Proportion of your genes in future generations can be increased indirectly by helping relatives

Kin selection

Hamilton’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)

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

8

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.

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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

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:

11

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

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

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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 use

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Belding’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

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