Course admin

- defect - squeal or accuse other one of more serious crime

- reward for defecting

- forgiven minor crive

- payoff for each strategy depends on behaviour of opponent

If both cooperate

- both get a reward R

If both defect

- both get punished P

If one cooperates and one defects

- defector - set free

- biggest payoff T (temptation)

- cooperator

sucker S

Values of payoffs don’t matter as long as

T > R > P > S

e.g. maximum sentence - 12 years (10 major, 2 minor)

Years saved by strategy

Player A goes first

Player B

cooperate defect

cooperate R = 10 S = 0

Player A

defect T = 12 P = 2

years saved by doing 1 crime not 2

What should a person do?

- If playing 1 round

Player A should defect

- always saves something

because if B cooperates

T > R

if B defects

P > S

If both defect do worse than if

They both cooperate

R > P

Hence the dilemma

After a number of simulations

- best strategy is tit for tat

- cooperate on first move and then do whatever opponent did on preceding move.

Benefits

(1) initially cooperative

(2) quick to retaliate

(3) quick to forgive

Leave for a while

are there examples where the predictions of these models can be seen - MATE ACQUISITION

(1) VIA KIN SELECTION

- in mate acquisition

e.g. wild turkeys

- male progeny of a single brood

- remain as a unit for life

dominance hierarchy

- only dominant male mates

Therefore each family unit - display group

- competes with other groups for females

- single males - no mating

Therefore non-mating males - r.s. because of brother

- for r.s. non mater = 1

- needs to help brother get 4 females

(2) VIA RECIPROCITY

- long tailed manakin - bird

- display sites - 2 males

- not related

- 1 male gets all copulations

Why second male? - females attract only to 2 male sites

- females preference for certain pairs

- if dominant dies - subordinate takes over

COMMUNICATION

- 1975 - Wilson -Sociobiology

- cited communication as one key attribute of a social group

- social groups - increased information flow

- or increased use of stimuli designed to convey information

Communication

- action on the part of one organism that alters of probability pattern of behaviour of another organism in a way that may or may not be adaptive to both

therefore have signaller receiver

(more about this later)

Measurement of communication

- if have individuals A & B

- perform Acts X1 & X2

communication occurs if

p (X2) after X1 p (X2) without X1

Units of communication - bit - binary digit

- one bit - amount of information required to control without error which of two equally probable responses will be chosen by the receiver

e.g. sample situation

- Territorial bird

- 2 equally likely signals

- raise wings - intruder leaves

- lower wings - intruder advances

Therefore each presentation of signal

- 1 bit of information

(allows choice between 2 equally probable )

- if 4 equally probable messages

@ signal - 2 hits

Therefore if H = no. of hits

N = no. of messages

N = 2H or

H = log2 N

and amount of information in a signal

Shannon - Weaver Index

H(X) =

- where cpi is probability of signal Xi

- takes into account idea that not all signals are equally probable

SIGNALS

KINDS & MODALITIES

(A) Kinds

(1) Graded

- more complex

- signal varies in form and intensity

- allows reflection of signallers motivation

e.g. - facial expressions

- dances of honey bees

- seen after in social interaction

(2) Fixed signals

- signal doesn’t vary in form

- on/off

e.g. - alarm calls

(B) MODALITIES

- what media are used to transmit information

(1) Chemical

- maybe oldest form of communication

- use of pheromones

advantage - carry long distance

- low investment

- estimates for insects - 0.2% of budget

disadvantage. - depends on wind for dissemination - unpredictible.

- difficult to track and locate sender

- slow fade time - no complex signals

There are also counter forces at work

(1) should be volatile

- low MW

But (2) need for species specificity

- higher MW - more variants

therefore tradeoff - continuum

- place on this continuum - depends on use

(A) Territorial marks

- stay long time

- e.g. tiger - fatty base

- identity individual

(B) Sexual attractant

(C) alarm - v. volatile - rapid transmission

(2) Visual

- more common in high

- advantages - fast transmission

- sender easy to locate

- low

- complex rich signals

- disadvantage. - unpredictible. habitat complexity

- easy to interrupt

- sender easy to locate

- high risk of exploitation

(3) Acoustic

adv. - long range

- fast transmission

- not dependent on wind

- use at night

disadvantage. - high cost

e.g. - starved crickets - lose 5%/day to signalling

- easy to locate sender

- confusion - several signallers

- major method of long distance communication

- environment constraints

- signal components chosen carefully

- e.g. acoustic in shallow water

- don’t depend on freq. (pitch)

Similarly - Morton - birds - signal transmission in forests

Tactile

- advantages - very short range

- fast transmission

- low cost

- locatable

- low exploitation

- disadvantage. - need close contact

- limited social use

seen in courtship

e.g. Aiken - water bugs

- social feeding in insects/birds

- instigated by

EVOLUTION OF SIGNALS

- where do they come from?

- was one of the major themes of behaviour

30’s 60’s

- a very descriptive phase of analysis

- to answer this - stock with making evolutionary inference

- behaviour doesn’t fossilize

but there are several categories

- suitable precursors

POSSIBLE SIGNAL PRECURSORS

(A) Incomplete functional movements

- begin and aborted

- “intention movements”

e.g. ring billed gull

- jabbing motion - incomplete attack

- become a threat

- fact that movements are incomplete

- reflects motivational conflict

e.g. if remember conflict at edge of territory

- but at border - bird may make intention movements without carrying out threat

- expression of incomplete aggression

- v. common in courtship - e.g. cricket chirp

(B) Completely formed but redirected acts

- often - aggressive acts are fully realized but directed at inappropriate object

- elk in Jasper (pers. obs.)

(C) Contextually irrelevant displays

- e.g. territorial gulls

- to

- displacement behav.

(D) Complete and contextually correct acts

- ruffling of plumage

conflict muscular tension

beat production

automatic response to cool

decrease insulating

effect of feathers

reflux slecking

- allow heat

to escape decr. thermal

gradient

both

are important in

agonistic displays
but all really have so far is an assumption and a set of observations

How do these come to be signals or displays

SELECTIVE FORCES

(1) Identification & Discrimination

- signal - can identity signaller

as (1) individual

(2) member of larger group (e.g. spp.)

- general trend - signals

diverge or converge

Factors resulting in divergence

(1) evol. of spp. i.d. sexual displays

(2) intrasexual selection

(3) chance

(4) predator confusion

Factors resulting in convergence

(1) similar ecol. pressures

- alarm calls

(2) Mimicry

(3) interspp. territoriality

(2) Social Complexity

- based on notion that there are several types of information in annual signals

- types of information can be arranged in a hierarchial fashion

- idea is that as social group becomes more complex

- incr in level of complexity of information transferred

e.g. in

incr. soc. complexity

# signals

Foxes 10

Coyote 18

Wolf 20

Dog 20

- also - graded signals become more important

- as indic. of degree of motivation

(3) Compromise & Allocation

- signals and structures. for signalling

- compromise between often conflicting selection pressures

e.g. a bright colour may be an effective signalling device but no good for concealment

Allocation

- assumes that there is some upper limit on number of that can be devoted to perception and integration of info.

or

- fixed amount of that can be dev. to signalling & structures.

(4) Environmental Constraints

- e.gs. (1) transmission properties of habitat

- forest vs.

(2) transm. prop. of median

- insect acoustics

(5) Sexual Selection

- intersexual

(6) Predation

- signaller will attract predators at - some level - benefits of signalling cost in attr. predators

- several spp.

- evolved signals that are difficult for pred. to detect

- e.g. bird calls (alarm)

- similar

(7) Intrasexual Competition

- male-male competition

- as males compete in signalling

- get increase in signalling effect either in rate of delivery or int

- both involve increase of

males may be doing 1 of 2 things

(1) cooperating

- attract female from wider area

(2) interfering with others signal

either way there is a compromise and optimum level of signalling det’d by

- signalling effort

- reprod. success

survivorship

(1) survivorship decreases with sign. eff.

- predators

- when look at evolution of comm. syst.

- need to modify - scheme presented at first

Plan for evol. of a signal
e.g. of this

- in a few groups have complete sequence in diff species that indic. a possible

- balloon flies - Empididae

- most derived form of courtship

male presents female with hollow balloon woven of silk

- presenting this balloon - signal indic mate quality

-when look at this over whole group see plausible mechanism

(1) male predatory - doesn’t feed female

male predatory feeds female

male entangles prey with silk threads

- female eats prey

male wraps prey in balloon

- female eats prey

complex balloon - smaller prey

- no female feeding

complex balloon - minute prey

- no feeding

complex balloon, no prey

- those are some factors aff each of signalling systems

- Key pt - signal system - result of several - often opposed sel forces

- dep on life cycle of organism

Mating Behaviour

For a long time study of mating

- very descriptive

from early 1900’s to mid or late 1960’s

- focus of almost all work on mating

- description of mating beh.

- ethograms

on as many species as possible

- considered

- detailed descriptions to show how FAP’s worked

- big debate on how ‘Fixed’ they were

- models of how the behavior patterns evolved

e.g.

- could mating behaviour be used to figure out phylogenies

This is where this all stayed until mid 1960’s

- when revival of some of DArwin’s ideas on how mating evolved.

This was his theory of sexual selection

MATING BEHAVIOUR & SEXUAL SELECTION

Current Theory of mating & how it occurs

Darwin - Theory of Sexual Selection

- Step back to theory of natural selection based on observation and deduction

Obs - no species increases as much as it could (more produced than can survive)

therefore struggle for existence

Obs - variation in all organisms that is passed on

therefore some better equipped than others to survive and will pass on this advantage

therefore survival of - differential survival

This is natural selection

but Darwin had one great stumbling block

- male and female differences in some species

Why and how - since they should be under same pressures

Darwin - Theory of sexual selection

- selection in context of reprod. beh. and male/female differences

as originally framed Darwin’s theory had 2 parts

(1) intrasexual selection

- all those structures & behaviours employed by males to fight other males for possession of females

- claws

- antlers

(2) intersexual selection

- all structures and behaviours used to attract females for mating

- song

- bright plumage

etc

- female choice

reaction to Darwin - centred on female choice

e.g. Wallace

Today we theorize about this a bit differently but the basic ideas are still Darwin’s

i.e. that there are two kinds of sexual selection

- now have theor. reasons for why

start with what makes males and females different

- ideas? - - -

The only consistent difference across all organisms that defines one sex from the other - size of gamete

How does this come about

Parker 1970’s

- lots of them but not enough mass to be on cell behaviour

- fewer but competent

- fewer still but very competent

- no go - won’t divide properly

- will divide but fewer contacts

- very few contacts

- greatest success - best combination of numbers

We now use the idea that differentiates in male/female behaviour - rise from differences in reproductive investment

ask - what does each sex have to bring to a mating to achieve RS
Female Male

- expensive egg sperm

- gestation

- parental care

& loss of mating

opportunity

What this means in more general terms

Difference in reproductive effort

higher investment low investment
low reprod. rate high potential reprod. rate
low levels of high levels of

sexual activity sexual activity

leased operational

sex ratio

Selection among competition for

mates mates

Best mate = need to achieve

best fitness greatest # of

benefit fertilizations
A key point to this is operational sex ratio

ratio of number of males: number of females ready for mating

very male-biased

i.e. most spp. have a surplus of females

e.g. of females in Sackville
5000

assume 1:1 numerical sex ratio

remove

- premenstrual females - prepubescent

- post menopausal females - sterile males

- pregnant females

- sterile females

Therefore this biased OSR

- competition in more abundant sex

- selectivity in less abundant

the foregoing - represents a modern view of the mechanisms of the evol. of sexual differences but Darwin’s original idea still holds so have 2 kinds of s.s.

- intersexual

- female choice

- intrasexual

- male - male compet.

both of these play a role in all mating systems

- now see that female choice is more prevalent

therefore start with it

How do females choose mates?

- this question one of the most active areas of ethological research

First and most prominent models for mate choice

Genetic Models of Mate Choice

- all Darwin’s work and subsequent

- assumed a genetic basis to mate choice

(Darwin had no idea how genetics work but knew something had to be going on)

There are 3 kinds of genetic models

(1) Direct Benefits

(2) Good Genes

(3) Runaway Selection

- in some cases there may be considerable overlap but - I’ll look at clear-cut examples

(1) Direct Benefits

- in this model - females choose males that give them a concrete resource - beyond sperm

- this resource increases ability to raise offspring or to survive or both

therefore female who chooses males who provide resources

- do better than females who don’t

e.,g. (1) Nuptial gifts

scorpion flies - Thornhill

when mating - male presents female with a prey stem -

Getting prey - dangerous for male

- risks being eaten (spiders)

If male has no prey and tries to court

- immediately rejected

- size of prey - corr. with how long a mating takes

- this is critical - matings < 7 mins - no sperm transfer

- females that choose male with large prey

- produce more eggs

- increase survivorship (no hunting)

also - male mimic female

(2) Good Genes Models

- this model has had a lot of theorizing around it but very little empirical work

- model suggest

- females should choose males with “good genes”

- i.e. those traits that allow survival of offspring

- apply in situation where the only benefit to females is genes in male sperm

female can be looking for such things as

- genetic complementarily

- some species not related

- capacity for survival

- capacity to dominate rivals

There are several studies showing that this kind of thing may be happening

e.g. of FLUCTUATING ASYMMETRY

- measures how close the sides of a bilaterally symm. animal match

- FA - measured degree of diff. in one side versus another

- idea is that as asymmetry increases

- animal becomes less attractive

- why? - developmental stability

- argues that genetically more fit individuals cope with changing environments (as they mature) better

Any evidence?

- reindeer - more symm. antlers

- better immune systems

- better at coping with parasites

- barn swallows

- if experimentally manipulate tail length

- females prefer more sperm

(3) Final Model - Runaway Sexual Selection

-most difficult

- this model - assumes 2 genes

(1) for trait X in males (more colourful)

(2) for preference for trait X in females

- point here - (1) & (2) are present in both males and females - get turned on differently

therefore females that prefer males with trait X

therefore as frequency of trait so does frequency for it

e.g. of this - stalk-eyed flies

did a standard descriptive selection experiment but took on longest and shortest stalked males x randomly sel. females

- but key point here is

not in males

- but the change noticed in females

i.e. female offspring of long stalked males

- pref. long stalked mates

But other factors can affect mate choice by females

One examples “Cultural Transmission”

- role of social factors in mating

example here is mate choice copying

- in a nutshell

- male’s chances for mating

- increase with recent mating experience

experiment with guppies

- model spent time near one male

- test female - sp[ent more time near chosen male 17 times out of 20

- weakness?

What at Male - Male Competition

Intrasexual

How do males compete with one another?

- best to examine this in species with weak female choice

Direct Fighting

e.g. Fiddler crab

- males search for burrows with females

- mates with female and then defends burrow from other males

(2) Interference

Aiken - bugs

(3) Cuckolodry

- stealing matings from other males

e.g. Sunfish - 3 kinds of males

(1) Parental - larger, aggressive

- build nests

(2) Sneaker - smaller - hide near nest

- swim in when pair are spawning

- shed sperm

(3) Satellite - look like females

- lower themselves between spawning pair

- release sperm

MATING SYSTEMS

What comes out of all the factors involved in deciding who mates with whom

- MATING SYSTEM of a species

Several kinds of mating systems

(1) Monogamy

1 male - 1 female for a poor breeding season

- most common form - serial monogamy

- seen in territorial birds

- one mate for a season - then switch

- few examples of life time monogamy

(2) Polygamous Mating Systems

- male or female has > 1 mate in mating season

Polygamy (multiple mates)
Polygyny Polyandry

(male mates with

several females) (1 female - several males)

- important to note - variance in RS very high

- for example polygynous - often intense competition

therefore some males - lots of mates

- some v. few or none

Several kinds of polygamous mating systems have been identified

(A) Polygyny

(1) Female Defense Polygyny

- females live in permanent groups

- male defend - harem

(2) Resource Defense

- female spatially concentrated at a resource

- male controls resource

e.g. bull frogs - male control ovip.

(3) Lek Polygyny

- males compete with each other for high rank

- females mate with dominant

(4) Scramble Competition

- females clustered in space after time

- high male density

- males try to mate with max # of females

e.g. wood frogs - 1 time/year - female at temp. pond

(B) Polyandry

- not as common

one e.g. jacu;na - Central American shore birds

- female mates sequentially with males on her territory - lays eggs in males territory - males rear offspring

Kinds of Polyandry

(1) Sperm Replenishment

- females mate multiply to get extra sperm

(2) Prostitution

females mate with >1 to get resource male offer only to makes
(3) Resource Defense Polyandry

- female control access to resources

- male may offer more parental care than female

(4) Lek Polyandry

- female compete for dominance in female hierarchy - males mate with high ranking females

- e.g. some primate troops

Benefits of Polyandry

(1) Sperm replenishment

- add to depleted supply

- avoid cost of storage

(2) Material Benefits

(3) Genetic Benefits

- replace “inferior” sperm

- increase genetic variance in offspring

(4) Convenience

- avoid cost of fending off cop. attempts