BIOE 109 Summer 2009 Lecture 9- Part II Kin selection.

BIOE 109Summer 2009

Lecture 9- Part IIKin selection

Types of social interactions

“Actor” “Recipient”

outcome of interaction measured in terms of fitness i.e. units of surviving offspring

Actor benefits Actor harmed Recipientbenefits

Recipient harmed



outcome of interaction measured in terms of fitness i.e. units of surviving offspring

Actor benefits Actor harmed Recipient Cooperativebenefits

Recipientharmed



Actor benefits Actor harmed Recipient Cooperative Altruisticbenefits

Recipientharmed




Recipient Selfish harmed




Recipient Selfish Spitefulharmed





Rare -an allele that results in fitness losses for both R&A would be eliminated by Natural selection

Co-operation and altruism

The evolution of altruism

• an altruistic act benefits a recipient at a cost to the actor



• Why does altruism exist in nature? how can altruistic behaviors evolve?

Bill Hamilton (1936 – 2000)

http://www.blackwellpublishing.com/ridley/video_gallery/WH_What_is_the_problem_of.asp



• Why does altruism exist in nature? how can altruistic behaviors evolve?

Br – C > 0



• Why does altruism exist in nature?how can altruistic behaviors evolve? Br – C > 0

let B = benefit to recipient



• Why does altruism exist in nature? how can altruistic behaviors evolve? Br – C > 0


let C = cost to actor (Both B and C are measure in units of surviving offspring)



• Why does altruism exist in nature? Br – C > 0 how can altruistic behaviors evolve?


let C = cost to actor

let r = coefficient of relatedness between actor and recipient



• Why does altruism exist in nature? Br – C > 0 how can altruistic behaviors evolve?




An allele for an altruistic behavior will be favored if:

Br – C > 0



• Why does altruism exist in nature?how can altruistic behaviors evolve? Br – C > 0





Br – C > 0 or Br > C



• Why does altruism exist in nature? how can altruistic behaviors evolve? Br – C > 0





Br – C > 0 or Br > C

• this is called “Hamilton’s rule”

Hamilton’s rule and the concept of inclusive fitness


• “inclusive fitness” is equivalent to an individual’s total fitness



Inclusive fitness



Inclusive fitness

“Direct” component

(i.e., individual’s own reproduction)



Inclusive fitness

“Direct” component “Indirect” component

(i.e., individual’s own (i.e., act of individual that reproduction) increases fitness of its relatives)



Inclusive fitness

“Direct” component “Indirect” component

(i.e., individual’s own (i.e., act of individual that reproduction) increases fitness of its relatives)

kin selection is a form of natural selection favoring the spread of alleles that increases the indirect component of fitness.

A deeper look into Hamilton's rulewhich is ……..

A deeper look into Hamilton's rulewhich is ……..

Br > C

What is the coefficient of relatedness (r)?

What is the coefficient of relatedness?

• r is the probability that homologous alleles present in different individuals are “identical by descent”.



• the inbreeding coefficient, F, is the probability that two homologous alleles present in the same individual are identical by descent.




• r can be estimated from:





1. pedigrees





1. pedigrees 2. genetic estimates of relatedness

Estimating r from pedigrees


(1/2 * 1/2 )= 1/4

Parents contribute ½ of their genes….The prob that genes are IBD in each step= 1/2


(1/2 * 1/2 )+(1/2 * 1/2 )= 1/2


(1/2 * 1/2 * 1/2)= 1/8

Examples of Kin Selection

http://www.youtube.com/watch?v=T3BgJ_BPm-M&feature=related

Selfish or Altruistic?

Alarm calls are given to warn kin

Hoogland 1983

Helping at the nest in bee-eaters

Examples of Kin Selection :

Helping at the nest in bee-eaters

Examples of Kin Selection :

MotherDaughter Daughter/ Helper

Each helper is responsible for an additional 0.47 offspring being raised!

Each parent, unaided, is able to raise 0.51 offspring…………

Helping at the nest in bee-eaters, why?

Mother-Daughter

Actor

Recipient

1/2

r = 1/2Sister Sister

Bee-eaters direct help to close relatives

*relatedness matters!

Emlen et al. 1995


• Hamilton’s rule


• Hamilton’s rule• Breeding Conditions

• nest sites difficult to obtain, create and maintain• finding a mate is difficult• scarcity of food • defense of nests


• Hamilton’s rule (Genetic predisposition)• Breeding Conditions (Ecological Constraint)


• Hamilton’s rule• Breeding Conditions• First time breeders pay a slight cost:


• Hamilton’s rule• Breeding Conditions• First time breeders pay a slight cost

-Each helper is responsible for an additional 0.47 offspring being raised!

-Each parent, unaided, is able to raise 0.51 offspring

The evolution of eusociality


• in eusocial species some individuals forego reproduction to aid in the rearing of others.


• in eusocial species some individuals forego reproduction to aid in the rearing of others. • most common in the Hymenoptera (ants, bees, and wasps)


• in eusocial species some individuals forego reproduction to aid in the rearing of others. • most common in the Hymenoptera (ants, bees, and wasps) Three characteristics of eusociality:


• in eusocial species some individuals forego reproduction to aid in the rearing of others. • most common in the Hymenoptera (ants, bees, and wasps) Three characteristics of eusociality: 1. overlapping generations of parents and their offspring


• in eusocial species some individuals forego reproduction to aid in the rearing of others. • most common in the Hymenoptera (ants, bees, and wasps) Three characteristics of eusociality: 1. overlapping generations of parents and their offspring 2. cooperative brood care


• in eusocial species some individuals forego reproduction to aid in the rearing of others. • most common in the Hymenoptera (ants, bees, and wasps) Three characteristics of eusociality: 1. overlapping generations of parents and their offspring 2. cooperative brood care 3. specialized castes of non-reproductive workers.

Why should eusociality be so common in the Hymenoptera?

Worker Drone Queen

Sterile Reproductive


• Hamilton suggested it is was due to haplodiploidy:


• Hamilton suggested it is was due to haplodiploidy: • females develop from fertilized eggs (diploid)

• males develop from unfertilized eggs (haploid)

Haplodiploidy skews relatedness

Degree of relatedness (r)

Comparison Diploid Haplodiploid


Comparison Diploid Haplodiploid sister – sister ½ ¾

Sister

1

/2

Sister

1

/2

Half of a female’s genes come from the father; the probability that a copy of one of these is shared by with the sister is 1.

r = (1/2*1/2) + (1/2*1) = 3/4


Comparison Diploid Haplodiploid sister – sister ½ ¾ mother – daughter ½ ½

Daughter


Comparison Diploid Haplodiploid sister – sister ½ ¾ mother – daughter ½ ½ sister – brother ½ ¼

r = 1/4


Comparison Diploid Haplodiploid sister – sister ½ ¾ mother – daughter ½ ½ sister – brother ½ ¼ • the inclusive fitness of female workers is highest if they help produce more sisters!

Create= Queen–Worker conflict, who wins?

Does haplodiploidy explain the evolution of eusociality?


NO!


NO!

1. Many colonies in eusocial species are founded by more than one queen.


NO!


• workers in these colonies have r = 0.


NO!


• workers in these colonies can have r = 0.

2. Many eusocial colonies have more than one father.


NO!


• workers in these colonies can have r = 0.

2. Many eusocial colonies have more than one father.

• the average r among workers is far below ¾.


NO!

3. Many eusocial species are not haplodiploid and not all haplodiploids are eusocial.

Examples: termites (diploid) are eusocial


NO!

1. Many eusocial species are not haplodiploid and not all haplodiploids are eusocial.

A phylogeny of the hymenoptera

A phylogeny of the hymenoptera

Eusociality evolved in groups that build complex nests and that care fortheir young ones for extended periods.

A eusocial mammal – the naked mole-rat

Naked mole-rat queens maintain control by bullying

Sherman 1991

Factors contributing to evolution of eusociality

• Nesting behaviors: complex nests with prolonged care for young ones

• Inbreeding: leads to very high relatedness coefficient (r)• Group defense against predation• Severely constrained breeding opportunities

NOT haplodiploidy!

The evolution of reciprocal altruism

Bob Trivers 1943 -


• this form of altruism may occur among unrelated individuals.


• this form of altruism may occur among unrelated individuals. Trivers suggested that two conditions must be met:


• this form of altruism may occur among unrelated individuals. Trivers suggested that two conditions must be met: 1. Cost must be ≤ to the benefit received.

• Cost low, benefit high


• this form of altruism may occur among unrelated individuals. Trivers suggested that two conditions must be met: 1. Cost must be ≤ to the benefit received. • otherwise they will not be favored by selection


• this form of altruism may occur among unrelated individuals. Trivers suggested that two conditions must be met: 1. Cost must be ≤ to the benefit received. • otherwise they will not be favored by selection 2. Individuals that fail to reciprocate must be punished.


• this form of altruism may occur among unrelated individuals. Trivers suggested that two conditions must be met: 1. Cost must be ≤ to the benefit received. • otherwise they will not be favored by selection 2. Individuals that fail to reciprocate must be punished. • otherwise cheaters can invade the population.

Trivers proposed that three factors might facilitate reciprocal alturism:


1. Groups are stable


1. Groups are stable 2. Opportunities for altruism are numerous


1. Groups are stable 2. Opportunities for altruism are numerous 3. Altruists interact in symmetrical situations

Blood-sharing in vampire bats


http://www.youtube.com/watch?v=9Va9ull44yw


Wilkinson 1984

Displaying both reciprocal altruism and kin selection

BIOE 109 Summer 2009 Lecture 9- Part II Kin selection.

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Transcript of BIOE 109 Summer 2009 Lecture 9- Part II Kin selection.