here
Symmetry
• Symmetry of body form: similarity of left and
right sides.
• Related to developmental stability
• Which is related to ability to adapt to change.
Summary: good gene hypothesis
• Females should choose males with “good
genes”
• How do they do it?
• Survival tests and health evaluations
• Obviously equating health with genetic well
being.
• Likely not something “conscious” related to
evolutionary selection of those who do select
the “right thing”.
Runaway Sexual selection
• This one is tricky
• Example: two genes exist, one for a trait in
males and another for mating preference in
females.
• Key is that over time these two genes become
associated with each other: if male trait gene
is in male offspring, mating preference will be
in their sisters
And it gets more complicated!
• If a proportion of females have gene for
brightly colored males and rest don’t
• If male coloration is genetic, then females that
prefer bright colors will mate with the bright
ones
• Now have offspring with both traits
• Assume: coloration is switched on in males,
preference in females
Lastly
• So, have females with preference trait also
have latent color trait.
• If, as they prefer, mate with colorful male, will
produce young male who are even more
colorful AND females that prefer color MORE
than their mothers did!
• Etc. etc. in a positive feedback or runaway
selection.
Example
• Book gives one about stalk-eyed flies where
after many generations of females only having
access to short stalk-eyed males
• Given the choice they preferred short stalkeyed males.
• Another example might be height in humans.
• Some females prefer tall men: offspring (male
and female) have tall gene AND preference for
tall males
Examples
• So daughters, who prefer tall men also have
tall genes to pass on and pair up with tall
genes from mate.
• The key to all of this is that preference for a
trait is in itself a genetic trait that can be
passed on!
Sensory exploitation
• Sensory bias; preexisting bias
• Females initially prefer traits that elicit greatest
stimulation of sensory systems
• Example: red berries good and nutritious
• Females equate red with good and nutritious
• IF red color shows up in males, females will show
preference for it.
• Proposes the origin of female preference for a
trait
Example
• Primates with trichromatic vision: can see reds
and oranges
• Initially to help find red-orange fruits
• Females also have preference for red-orange
skin/hair coloration in males
• IF Sensory bias: “preference” for red-orange
developed as a foraging aid had to come first.
What did they find?
• Evidence that trichromatic vision evolved
BEFORE red coloration in males.
• The key here is ability to sense a trait comes
from a sensory capability that developed
BEFORE and for some other reason, than that
trait, which predisposes the female to prefer
that trait.
• Cart and horse thing.
Learning and Mate Choice
• So far talking about female choice as having a
strong genetic base.
• Need to examine role of learning in this
• How much of a role it plays?
• What kind of learning?
Sexual imprinting
• Review: imprinting is learning a behavior after
brief exposure to it during a critical period
• Two lines of research:
• 1) cross-fostering: do young raised with
adaptive parents, show different preferences?
• 2) Novel traits: Introduce a novel trait and see
if young use this in their mate preference
Example
• Novel traits: Mannikin bird – put red feather
on parents’ heads.
• Do young with red feather parents, then
prefer opposite sex with red feathers?
• Answer seems to be YES!
• Various other examples supporting idea that
there is a certain amount of imprinting going
on
Traditional conditioning and mate
choice
• Can individuals be “trained” or conditioned to
modify their mate choice?
• Quail: brown and blond
• Male brown raised brown, imprinted on
brown.
• Given opportunity to mate with blond but
only opportunity to “see” brown female.
• Result: after time, when had choice, preferred
blond female.
What does this mean?
• Mate choice may be imprinted BUT can be
overridden by conditioning.
• IF positive reinforcement for change, will
possibly change
• IF also negative reinforcement against
imprinted, will most likely change.
Cultural Transmission and mate choice
• Mate-choice copying: Female’s mate-choice
preference affected by preferences of other
females in population – mate choice peer
pressure!!
• Defined operationally: If Y - X > 0, then mate
copying!!??
• X - chance of male mating IF he has not recently
• Y – chance of male mating IF he has recently
done so
Mate-choice copying
• So… If a male becomes preferred by other
females because he has mated with previous
ones, that is mate-choice copying.
• Example: female black grouse
• Dominate male can account for 80% of
breeding.
Black grouse
• Is this because of mate-choice copying?
• Observed that older females mated earlier
and younger ones, “followed suite” mating
with the same males.
• Is it because they copied older ones?
Black grouse
• Tested by putting in dummy female birds
randomly in males’ territories.
• Males with more dummy females, regardless
of location on lek, attracted more real
females!
• So evidence for mate-choice copying
Song learning and mate choice
• Many birds use songs
• Males learn songs
• Females who also hear songs develop
preference
• Evidence of learning when switch juveniles to
other subpopulation with DIFFERENT songs
• Males learn new songs AND females seem to
prefer them.
• Might be combination of imprinting/copying
Cultural transmission
• Summary
• Females “learn” mate choice by copying other
females: often older ones.
• Advantage? “trust” older birds’ judgment.
• In birds, males learn song that females
develop preferences for.
Mate choice summary
• Genetic basis: four models; Direct benefits,
good genes, runaway selection, sensory
exploitation.
• Ways to explain how mate-choice can be
maintained or originate
• Learning: Imprinting, cultural transmission
• Ways mating preferences are passed on
beyond genes, though may still have genetic
basis!
Mate-choice summary
• Usually involves female and how she may
develop mating preferences
• Important point: In all of this we tend to talk
like individuals “purposely” do this.
• E.g. survival testing
• Behavior passes selection filter and may not
be purposely done but just what is done by
those that survive. No good, bad, divas,
vamps, charlatans, etc. Terms we use!
here
Lets look at the males!
• Said that we now realize females are doing the
choosing and thus shaping male
anatomy/behavior.
• So now have basis for the male behaviors, still
need to look at what they are.
• Males, like females not “purposely” doing
behaviors, what is shaped by selection, sexual
selection.
So what do males have to do?
• Mainly involves some type of male-male
competition.
• As mentioned, this is the glamorous part of
sexual behavior: males butting heads,
dancing, etc.
• Now know it is often a health test but…
• Need to look at a little closer
Male-male competition before
copulation
• Often the “testing” of males’ genetic quality
done before females choose mate.
• These are the dramatic ones!
• However often very stereotypic in pattern
• What males need to do BUT don’t want to get
killed doing it!
• Goes from initial mutual assessment to final
combat if needed.
Example
• Red deer: Each step is designed to test the
relative strength of the other.
• Less evenly matched, quicker
inferior one leaves
• More evenly
matched, more likely
to end in fight.
Lots of talk, little action!
• The “glamour” of it all is mostly the elaborate
testing that goes on before actual physical
combat.
• Most times, very little combat, just between
closely matched males.
• Designed to maximize access to females while
minimizing injuries from serious fights.
• Elaborate displays often for other males!
When it comes to a fight!
• Often anatomical adaptations
• Thick manes on lions!!
• Spongy bones on bighorn sheep
Male-male competition by
interference
• Interference while attempting to copulate
• Heavier larger males often interrupt
copulation attempts by lighter smaller males
• Sometimes solicited by females: If not the
male she wants, attracts attention of larger
more dominate male (Elephant seals).
Cuckoldry and male-male
competition
•
•
•
•
Males mating with other male’s female/s
Lots of examples in wild
Age old practice
Attempts by “subordinate” males to out
compete dominate males via “trickery”
Cuckoldry
• Book example: Blue gills
• Three different male morphs: parental,
sneaker and satellite.
• Parental male attracts females
• Sneaker males sneak in and release
sperm as male and female are doing the
same
• Satellite: look like females!
Female-female competition
• Commonly accepted that females choose
• Males compete, a test for choice by females
• If we have a system where many females mate
with the “winning” males, no real competition
among females.
• BUT…. In many cases, there will only be one
female mating with the winner/s
• Territorial birds, wolf packs (one alpha male
and female), lots of examples
So how decided which female gets
the winner?
• Very little studied aspect of mate choice.
• In humans, it is the stuff of sitcoms and high
school drama/pop songs!
• In nature???
• When female birds come north, males already
have territories: Assume there is some type of
contest among females as to who goes where.
• Some might be age, older ones
• Some, re-mate with same from previous year
Female-female competition
• In wolves, there is aggression between alpha
female and subordinate ones: interference
competition if male attempts to mate with
other females
• Basically, males initially compete to be chosen
but once you win, you become a limited
resource and should be competed for!
• Need lots of study in this.
Overall summary
• First step in reproduction: mate choice
• Females have most to loose so most times do
the choosing
• Basically various tests designed to determine
genetic status of potential mates.
• LOTS of variation, even within species!
• Designed to get over those awkward initial
steps!
Mating systems (chap 7)
• Ok, you have now decided on with whom your
going to reproduce.
• Saw lots of variation, lets try and make some
sense out of it all.
• Are there basic categories of mating systems?
• Well, yes and no….
• Why do some species use certain systems and
others different ones?
Mating systems
• So will look at two major things:
• 1) Types of mating systems
• 2) Evolution of different systems
Types of mating systems
• Four basic types: figure sums them up
regarding participants, in general!
First Monogamous mating systems
• One male-one female only! True love!
• At least for a mating season
• Sometimes for life but rarely.
• Commonly change partners next season
• Termed: Serial Monogamy
Long term: Fitness consequences?
• For female: If you have a good one, you stay
with him. Sounds like a country-western
song!
• For male? Might lead to more offspring: old
field mice experiment.
Fitness consequences?
• For both, reduces energy and time needed to
find a mate.
• Can reproduce sooner.
• If territorial, experienced pair can gain/hold
on to territory.
• Various reasons why staying together over
time advantageous.
Serial Monogamy?
• What are advantages?
• Short-lived species: serial not by choice, mate
dies
• Monogamous during raising of young is
advantage
• Switching partners, either sex, increases
variability of your offspring.
Just how Monogamous are they??
• Monogamy sounds good but how well is it
practiced?
• Long term monogamy? Old field mice?
• 10% were not genetically related to male
Serial monogamy?
• Even in one season serial monogamy, are they
truly monogamous??
Monogamy
• Of socially monogamous bird species studied,
only 14% found to be genetically
monogamous!
• Extra-pair copulations 11% up to 50% in some
species!
• What is going on!!? Soap operas!!
• Two types of “cheating”!
• Cuckoldry: where other male mates with
“your” partner. E.g. purple martins.
Monogamy??
• Promiscuity: Females side: If she mates with
more than one, promiscuous.
• Two player game!
• Reasons? Male: more genetic offspring,
female: more genetically diverse offspring.
• Example: Female blue tits with “cheat” with
only “quality males” i.e. high ranking males or
males from farther away (the foreign factor!),
leads to outbreeding!
Monogamy summary
• For female, can see more advantages
• For male may lead to higher overall
reproductive output.
• However, may not be as blissful as it seems!
• What one would expect regarding natural
variation in a trait or behavior.
• Depending on selection force will depend on
how Monogamous a species will be.
Polygamous mating systems
• For many species, this selection force leads to
other non-monogamous mating behaviors.
• A common one is Polygamous mating systems
• Defined: either males or females have more
than one mate during a given breeding
season.
Two forms
• Polygyny: male mates with more than one
• Polyandry: female mates with more than one
male
• Can be simultaneous: leks, elk
• Can be sequential: Jacanas
Polygyny
•
•
•
•
•
One male: many females
Passive: Males do not defend females
Leks or arena mating, an example
Saw earlier, males compete for favored locations
Females then come, bypassing “inferior” locations
and mate with male in favored one
• One male can inseminate up to 80-90% of females.
Polygyny
• Active: Male actively defends actively defend
access to females
• Female defense polygyny
• Example: Epsilon wasp where males mature
earlier, locate cells where females will emerge
and defend them.
• When females emerge, they mate with the
territorial male.
In between
• Lots of variation between arena mating and
female defense polygyny.
• Many ungulates such as elk: male defends or
tries to, a harem. Kind of female defense but
more fluid relative to female participation, she
chooses to stay with male.
• Other ungulates: pronghorn, have lek like
behavior but can be more mobile.
here
Advantages?
• Females: do not need to compete for “better
male/s”.
• Assured of access to “best” genes
• Males: Obvious advantage to winner
• Losers? Often related to winner so don’t lose
so much genetically!
Polyandry
• Female with many males:
• Jacanas, tropical shore bird
• Sex reversal: males incubate eggs/defends
young
• Female lays eggs
sequentially in several
male nests
-how do males know eggs
are theirs?? 93% of the time
Polyandry
• Rare in vertebrates but seems very common in
social insects: ants, bees, termites
• One queen mates with many males (some
worker males, some especially raised, lots of
variation)
• Result: colony made up of one female lineage
but many male ones.
Advantages to female?
• Sperm replenishment: New supply, no need to store
sperm
• Material benefits:
- Nutrients: nuptial gifts, chemicals in seminal fluids
female can use, male parental care.
• Genetic benefits: Increases genetic variance of
offspring
• Convenience: avoids costs of avoiding copulation
attempts
Promiscuous mating systems
• So far one male; many females or one female:
many males
• If have both within population, referred to as
Promiscuous mating systems.
• Two types:
• 1)truly promiscuous: many males mating with
many females usually with no pair bonds
forming.
Polygynandry
• Second type of promiscuous system
• Here several males form pair bonds with
several females. Dunnock: small passerine
bird is example.
• # of mates variable
Summary
• Again, quite a range of mating systems have
been discovered.
• Basically all possible combinations and even
some in between.
• But why so many?
• Why such variability?
Why variability?
• Each represents an approach to capturing new
energy for the population AND passing on
genes
• Each system represents a functional way both
of these are achieved, under the
environmental conditions that exist.
• As with selection for body traits, there are
selection pressures that favor one over the
other, including within the same species!
• What can be some of those selection
pressures?
Ecological drivers
• Remember: goals are 1) add young to the
population and 2) “improve” genetic quality of
offspring.
• Both of these can be considered related to
resource levels and distribution.
Resource distribution
• Again, female driven
• No general need to find mates BUT definite
need for resources.
• Based on this proposed that female
distribution/mating patterns tied to resource
distribution.
• Males follow female distribution
Resource distribution
• Dispersed resources: females must cover
larger area and makes it difficult for male to
mate/defend more than one female
• Clumped resources: Many females can use
same resource in small area, defendable by
one male, leads to polygynous systems
• Resources range from disperse to clumped in
a continuum so proposed that at some point
becomes more advantageous for females to
participate in a polygynous system.
• Called the Polygyny threshold model (PTM)
• Basically, when female can be more
productive in a multiple mate system than in a
monogamous one, should see a switch to
Polygyny.
• Still a theory but would explain the range of
mating systems across species.
• May also help understand multiple systems in
single species.
• Difference in resource distribution across a
species range, could then lead to differences
in mating systems.
Last words
• Mating systems important: How individuals
interact for reproduction.
• Can be considered the most important intra
species or social behaviors.
• However, note that type of behavior we see
impacted by environment:
• So even for most “pure” behavior, behavioral
ecology emerges
• But before we move on to behaviors of
individuals with environment, including other
species.
• Cover several other intra-specific or social
behaviors not directly related to reproduction
• Cooperation, play, aggression, etc.
• These none directly sexual social behaviors
can be found in all species, solitary to truly
social.
• Just vary in types and amounts.
• Viewed as behaviors of interactions between
and among individuals.
• Involve communication, learning, innate.
First question
• First questions to ask are how and why such
social behaviors develop?
• For example: warning calls: why put yourself
at risk for the group?
• Perplexed many ethologists for long time.
• Began looking at relatedness of individuals.
• Know parent and offspring related but…
Kinship
• Briefly mentioned examples of related
individuals: leks, bee hives
• Others: wolf packs, lion prides, flocks of geese,
etc.
• One emerging observation is that there are a
lot of groups of animals where members are
related.
• Also that this relatedness affects the degree of
social behaviors we see.
Kinship theory
• Began to look at this relationship and how it
could affect the evolution of social behavior
• Led to new area: Kinship theory
• Basic idea behind kinship theory is:
• Social behaviors of species evolves …where
individual will value its neighbor’s fitness
against its own according to the coefficients of
relationship….
• So your degree of social behavior will depend
on how related the other participants or
recipients are to you.
• Thus the concept of kinship
• Defined: probability that individuals share
genes they have inherited from common
ancestors.
• “identical by decent” : genes from common
ancestors.
• Can calculate relatedness: stuff of genealogy.
• Do you have common genes with the Queen?
Why is this important?
• Can view evolution working on individual: If
you survive, your genes passed on.
• Kinship: your genes not the only copies out
there!
• If you help someone with “your” genes
survive, this behavior would be selected for
• Most likely this would be someone related to
you: kin
• So you can be “more fit” by helping relatives
• Idea of inclusive fitness
• So that is the evolutionary driver behind these
social behaviors.
• What are some of the basic predictions?
Start with the family
•
•
•
•
•
Since members of family closest related….
Emlen in late 90’s proposed 15 predictions!
Pg. 270 of your text.
Some important ones:
1) Family groups will become unstable when
reproductive opportunities arise.
- You will stay with the family until you have a
chance to reproduce
Families
• 2) Family stability will be the greatest in
groups that control high quality resources
• Concept of dynasties: Not just humans!!
- Survival advantage to
pass on inheritance
to offspring
Helping around the house
• 3) Help rearing offspring will be highest
between closest genetic relatives.
• You will take care of your brother and maybe
your cousin but more than that, you will need
to get PAID!!
One more
• 4) Replacement mates will invest less in
existing offspring than in biological parents.
- Cinderella, Snow white, the list goes on!
- Lions, tigers, oh my: infanticide!
Central theme
• Central to all these is that the closer your
related the more cooperative social behaviors
you will have.
• We can use kinship theory to directly explain
behaviors we see.
• Parental care: is obvious, but not universal!
• Will look at this one in more detail
Cooperation behavior
• This covers a lot of behaviors and will cover
separately.
• One interesting one that kinship theory
predicts is when conflicts would arise!
• Example: sibling rivalry
Sibling rivalry
• Basically, when resources plentiful, advantage
to share with your sib.
• When scarce, that advantage is reduced.
• Remember you are your closest relative!!
here
Parental care
• Next logical step: Producing them is the easy
part, raising them is more difficult!
• Just as important as mate choice/mating
systems.
• Does no good to pick a good one if you let
your young die! Or does it??
• What is the best way to be a parent? Is there
a best way???
Parental care
• Wide variety: would seem to contradict
kinship theory:
• Would predict ALWAYS see extended parental
care
• Your offspring best shot at future!
• Need to look at variation and see how we can
reconcile this with kinship theory.
Ranges of parental care
•
•
•
•
•
Four states:
1) no parental care
2) maternal care
3) paternal care
4) biparental care
What are the considerations?
• Why one form in one and different one in
another?
• Benefits: Obviously, this is your link to the
future….
• Costs: But… how much are you willing to pay
for this?
• As cold as it may sound, may just be an
economic cost/benefit analysis!
Benefits?
• Benefits double sided.
• Benefits to your offspring IF you put a lot of
care into them
• Benefits to you IF you put in little AND they
survive! (increased reproductive
opportunities)
• So there are benefits for and against parental
care!
• The underlying benefit is to your fitness
What are the costs?
• Same idea, costs in caring and not!
• Cost in production: how much did you put into
them?
• Cost of not taking care of them: they will die!
• Cost of taking care of them: you die, you lose
other reproductive opportunities,
• Again, cost is to your fitness
Easiest to see
• Animals where both sexes release large
quantities of gametes into the water.
• No cost in production
• Playing the odds, which evidentially works!
• Low cost regarding survival of SOME young
• Benefits to you: successful without cost of
caring for them
• So, no or little parental care!
The rest little more complex
• First case: males vs females
• Why do females usually exhibit more parental
care than males??
• First possibility:
• Female investment: invest much more energy
than males so “have more to lose” if offspring
fail…. Thus provide more care.
• Sounds good!
But…
• In many species, females make large
investments into eggs only to leave them in
total care of males!
• So not automatic, need to assess fitness gains
or loses after young produced.
Another “rule”?
• Lets look at it from the male’s view.
• Cost benefit ratio of male to give care will
normally be higher than that for females.
• Assume: amount of energy invested in care
reduces male and female future reproductive
output equally.
• In this case, cost to male and female would be
equal…. Unless, not all offspring are his!
• Does not “pay” for male to lose future
reproductive opportunities caring for young
not his own.
• Also IF care by one is sufficient, then evolution
pressure (better cost benefit ratio) for male to
NOT care for young and inseminate as many
females as he can (Polygyny)
• So not just that the female has invested so
much but that it is advantageous for the male
NOT to!!
Good fathers!
• But there are instances where males do
provide care!
• Male only: Seems contrary to above.
However common in fish.
• Why? In cases studied, it seems the cost to the
male is less than to the female.
• Example: Stickleback fish – males can guard
up to 10 clutches of eggs/females only
produce 7 without guarding, one if she
guarded.
Result?
• IF female cares for young also loses weight,
which is related to fecundity!
• More advantageous for female NOT to care for
young than it is disadvantageous for males to
care for them!
• Interplay with other anatomical/physiological
traits that co-evolve with reproduction.
Maternal and paternal care
• Many species exhibit care by both parents.
• Monogamous breeders (usually)
• Still, male could do better if he was not
monogamous nor gave care, why should he?
• Development of young: altricial vs precocial
Needs both!
• Again, constraint from other selection factors.
• If young altricial, may need care of both to
survive.
• Strong selection pressure for males who stay!
• Why see these two forms: altricial vs
precocial?
In birds
• Nesting environment:
• More dangerous ground
favors precocial.
• Selection pressure for
successful use of a given
niche dictates parenting
patterns.
Trophic position
• Prey: ungulates precocial: need to be “ground
ready”!
• Also, can develop longer, no need to move real
fast to catch grass!
• Predators: Disadvantage to have young inside
for 9 months! Get them out quick, your
mobile but then have to care for them!
• Again, interplay with environmental factors.
• Basic idea is the relative cost benefit ratio of
parenting for males and females.
• Usually, this ratio is larger (less favorable) for
males, so paternal care is rare.
• Cases where is larger for females and in these
cases roles switch.
• Cases where it is approximately equal, dual
parenting.
Given parental care….
• Ok someone is taking care of the kids!
• What are some of the parental care behaviors
that are important?
• Young identification would be nice!
• If your kids are the only ones around, no
problem!
• Many species breed and raise their young in
groups. Happy Feet! Seals, ocean birds, bison
• “Wonder of nature” mother is able to come
and find her young out of a gang of kids.
• How does she (or he) do it?
• One major one is vocal communication:
voice/song recognition
• Odors also play a role
• Related to whether there is a need for
recognition.
Does it always work?
• Apparently not!
• Major parenting deviation: Brood parasitism!
• Female of another species lays eggs in other
bird’s nest!
• Goes counter to offspring
recognition!
Parasite and host
• Advantage to parasite: get someone else to
successfully raise kids!
• African cuckoos lay up to 25 eggs per season,
one per host nest!
• Need to get around recognition:
• Similar species, similar eggs
• Solitary species with little recognition ability.
• Arms race between parasite and host!
And the young?
• A side point: young parasites adapted to
enhancing survival over host chicks!
Parental favoritism
• Another consideration is behavior of parents
to individual young.
• Saw differences in sibling rivalry but is it all
just the kids?
• Parents actively show bias toward young
• Older/larger ones, not just size or aggression
• Parents seem to be evaluating reproductive
value of offspring
Reproductive value of offspring
• How young beg for food indicator of health,
especially in times of low resources
• How they look! Mouth gap color, brighter –
gets more attention
• Alternate hypothesis: brighter color =
healthier!
• Current active research into if parents can
judge reproductive value and give food to
those with higher value!
here
Parental abandonment
• Will a mother defend its young to the death?
• Commonly held belief/myth.
• What would kinship theory predict?
• You are your closest relative so to put yourself
in danger to save some one only half related
to you….
• Go ahead kill them, I can make more….
Inbreeding behavior
• Can’t leave kinship and parental care without
talking about “inbreeding” or incest: mating
between close relatives, including motherson, father-daughter, brother-sister.
• In one instance we see selective advantages of
helping related individuals
• But genetically, view this type of gene
concentration, Inbreeding, as bad!
Is it done?
• Almost all species practice some level of
inbreeding.
• Male cougars will mate with their daughters
• Humans, even with their ridged taboos against
it, do it. Some cultures more acceptable.
• Royal families!
• Read the histories and a lot of them married
daughters, sisters, even mothers
Why do it?
• Out of necessity: small isolated populations,
no other choice.
• Genetic advantages??
Advantages?
• Kinship theory deals with helping closely
related to enhance passage of your genes.
• Logically would extend to reproducing with
closely related individuals!
• Why take the change with a genetic stranger
when only have 50% chance of passing on
“good” genes and will be heterozygous!!
• If your offspring have your “good” gene, 50%
chance next offspring will be homozygous!
New Genes
• Only way for new genetic material is via
mutation.
• Difficult to imagine how a single mutation, no
matter how good it is, will increase in a
population without inbreeding!
• So good side of inbreeding behavior is that it
can concentrate new genetic material
• Also increase more rapidly “good” existing
genes.
Down side?
• Can also pass and concentrate “bad” genes!
• This is where human taboos have developed
• To try and prevent the concentration of such
genes
• Many of our genetic diseases today are
concentrated in ethnic groups.
• Inbreeding depression: can lead to variety of
fitness reductions: sperm deformities,
reduced reproductive output,
Then why do it?
• Under “natural” natural selection, will be
strong selection pressure on small inbreeding
groups.
• Form of group selection: IF your small group
does have deleterious genes, will not do well
as a group – increased selection against them
• IF your small group does NOT have deleterious
genes but also good genes, GREAT!!
Summary on parental care
• Various factors involved:
• 1) can young live without care?
• 2) If needed, will depend on relative
cost/benefit for males vs females.
• 3) The amount of investment by female not
only determining factor
• 4) How it may affect future reproductive
opportunities.
Summary
• Related again to environment that can
override and dictate if and what form of
parental care is necessary.
• In that framework, relative cost/benefit ratios
play out.
Cooperation (Chap 9)
• Talked about kinship theory and how it could
favor cooperation among related individuals.
• However we also see cooperation occurring
among unrelated or genetically more distant
individuals.
• Can’t evoke kinship selection as reason so how
can we evolutionarily justify this type of
behavior?
Over view
• Actually imbedded in an overall view of
cooperation, which includes kin selection
• In this scheme there
are four pathways
to cooperative
behavior.
Reciprocity
• Why would unrelated individuals help each
other?? What is evolutionary advantage?
• Reciprocal altruism:
• 1) Individual A pays a cost to help B
• 2) Cost “paid up” in future IF B helps A
• Such a system might be favored by natural
selection
How does it work?
•
•
•
•
Depends on chances that you will get a payoff
Reduces it to a probability problem
Can be envisioned in the light of game theory
Most games: whether you win or not depends
on the reciprocal action of the other players
• R. L. Trivers suggested it could be understood
via a math game: Prisoner’s dilemma
Prisoner’s dilemma
• 2 prisoners, both
guilty
• Separate rooms
• Either cooperate
with each other,
don’t “squeal” on
other
• Or squeal.
• Each outcome has
different penalties/
rewards
• R, S, P, T.
• What do you do?
• IF:T > R > P > S
• You have a dilemma!
Prisoner’s dilemma
• Obvious the most
tempting is to tell: T –
home free!
• BUT only if your buddy
chooses not to tell! (R)
• If you both choose to
tell (P), your toast!
• THAT is the dilemma!
What is the right thing to do?
• In a single incidence, it is a dilemma
• But lets extend this a little: you have gone
through the first time.
• Now your faced with it again WITH the same
partner!!
• Now what do you do???
• Depends on what your partner did last time!
The if, then rule
• If your partner cooperated last time, then you
will cooperate this time, you trust him!
• If he squealed on you, then you squeal on him
this time and only get 3 years rather than 5!
• Called Tit for Tat or reciprocity-based response
Characteristics of reciprocity
• Nice: you are never the first to “cheat”
• Retaliatory: IF he cheats on you, next time you
will!
• Forgiving:
Current action
based on last
of other.
What does this have to do with
animals?
• Attempt to explain when no-related
individuals would help (cooperate) each other.
• And when they wouldn’t!
• Example: predator inspection in guppies:
• Usually two guppies advance from group to
inspect danger level from predator
Possibilities
•
•
•
•
•
•
1) go together (cooperation)
2) one goes, other lags (cheats)
3) visa versa
4) both lag back
Classic Prisoner’s dilemma
You gain most IF you lag back: you live AND
you assess danger (If buddy gets eaten, high
danger!!!)
• Both gain, but not as much if both go
(cooperate).
• So, tendency to cheat, tendency to cooperate
• What do you do?
• Depends on what your co-inspector did
before!
• IF he cheated AND you survived, it is best to
cheat on him next time, IF your stuck with him
• IF he cooperated, this is the one you want to
go with in the future, thus cooperation!!
How about non-lethal situations?
• Reciprocity
• Example: vampire bats
• Need to have a blood meal. If they don’t get
one, often will beg from one that has.
• IF it gives it to you, more likely to also give it
to that one if table is turned.
• If you give first, likely will ask same one in
future, should reciprocate!
Summary: Reciprocity
• Game theory can provide insights and testable
predictions regarding non-related
cooperation.
• Basic premise is that your actions based on
past experience with potential cooperator.
• Somewhat selfish, you do it because you know
the other one will “pay you back”!
• But it seems to work…as a model!
Byproduct mutualism
• Second possible way cooperation behavior can
develop
Defined
• Cooperation is a byproduct of the fact that an
individual would incur an immediate HIGH
cost or penalty IF it did not act cooperatively!!
• Talk about incentives!!
• The immediate benefit from cooperating
would outweigh that of cheating.
• Your damned if you don’t but saved if you do!
How does it differ from
reciprocity?
• 1) the cost of cheating is so high, never really
a consideration.
• 2) don’t need to think about past performance
of partner, in this case it will ALWAYS be in
best interest of both!
Example?
• Chirrup calls in sparrows: no or little food,
fewer calls to bring conspecifics
• More food, more
calls!
Explanation
• Explained as byproduct mutualism:
• When there is a lot of food, and the bird
wants to stay long to eat it, best to have
others around for predator detection.
• Price of staying longer by self, greater than
price of sharing food, so cooperate!!
Wolves
• Live in related pack, kinship
• BUT part of it is byproduct mutualism in that
can’t hunt large animals alone!
• Indicates the blurry lines that can exist among
the different causes of cooperation!
Summary
• Cooperation can evolve IF benefits of not
cooperating are extremely low and benefit of
cooperating are high, will be selection for
cooperation even if unrelated.
Group selection
• Controversial concept
• Distinguishes between within and between
group selection
• Argument is that between group selection
favors cooperation because groups that
cooperate survive better than those that
don’t.
• Proposed as possible reason for such things as
alarm calls.
• Not advantageous to individual but is to
group.
• A group that has more “selfless” callers, does
better.
here
• Group selection in itself is controversial and as
a promoter of cooperation behavior, may be
stretching it!
• Does provide different way of looking at this
type of behavior.
Interspecific mutualism
• Last type of cooperation behavior to cover
• We are all familiar with mutualism
• Two species providing service to the other for
benefit of each.
• LOTS of examples
• General idea is BECAUSE they both benefit,
results in the behavior.
Summary of Cooperation
• Four proposed ways it could develop
• 1) If your GENES benefit (Kin selection)
• 2) If YOU benefit: depends on the chances
that the other will
will help in future.
• 3) If you don’t help, your toast!
• 4) If you help and it helps group, selected for
• All have their basis in the selfish gene concept.
Play (Chap 15)
• Now turn our attention to specific behaviors
we see either in the individual or in the group.
• First of these is play
• Want to look at types of play
• And function of play
What is play?
• Can we define it??
• We know it when we see it but difficult to
define!
• Bekoff and Byers (1981): motor activity
performed that appears purposeless, contains
motor patterns from other contexts, usually in
a modified form and altered temporal
sequence.
What is Play?
•
•
•
•
Important points:
1) should not be for a specific reason
2) contains other behaviors
3) Which are modified in some manner.
• Definition centers on form rather than
function.
Sounds good but…
• Is an animal in a cage, pacing back and forth
with seemingly no purpose play?
• How do we know it is purposeless?
• Is it purposeless?
• 1) we may not be able to tell!
• 2) may have purpose or potential benefit later
Others?
•
•
•
•
•
•
•
•
Many have tried.
So why don’t we?
Practice
Future social status
Teaching
Building alliances
Building social bonds
Defining future sexual bonds
• Learning social/survival skills
• Passing the time
• Stress reliever
• Maybe a possible one is: behaviors that don’t
seem to have direct connection to some
immediate end, e.g. eating, building a nest,
etc., the animal appears to “take pleasure in”
doing it, and possibly learns from it.
Where does this leave us?
• Back where we started!
• May not be able to define it exactly but MOST
times when we see it, we know it!
Types of play
• May not be able to define it but we can
categorize it!
• Three different types of play recognized
• 1) Object play
• 2) locomotor play
• 3) social play
Object play
• Centers on use of inanimate objects, sticks,
rocks, feathers, Barbie, GI Joe, etc.
• Found in a wide array of taxa
• Well studied in captive animals
• Wide variation, try to distinguish it from
Object exploration: trying to figure out what
an object is
• Object play: trying to see what they can do
with it.
Object Play
• In some, novelty seems more important than
an object’s characteristics: shininess or
conspicuousness.
• In some, will use over again….toys??
Locomotor play
• As name indicates, involves some type of
movement.
• Most common is leaping
• Can also be running turning, somersaults,
shaking, etc. LOTS of variation
Social play
• Again, as name indicates, playing with
someone else.
• Can consist of what we would classify as play:
stalking, crouching, chasing
• Majority consists of “play fighting” (sexual
play)
Function of play?
• Basic categories, pretty straight forward.
• But… is it “purposeless”?
• Saw in our discussion of defining it, most
believe there is/are reason/s behind play.
• What would be the function or benefits of
play?
Benefits
• Can look at each category to see how each
type may have a “purpose”
• Then we can look at an overall theory on
function.
Functions of object play
• 1) In ravens: enables them to better identify
new food sources.
• 2) Helps in prey recognition: parent brings
dead prey that young play with (playing with
your food is a good thing!)
• 3) can build paw-eye coordination
• 4) extension of #3, practice hunting
techniques IF “object” is live prey.
Locomotor play
• Two major hypotheses:
• 1) Exercise and training of specific motor skills
needed later.
- can see this in both predator and prey where
running, turning, jumping, etc. is important.
Exercise and training
•
•
•
•
•
•
•
List of benefits:
Increased oxygen uptake
Decreased heart rate
Increased total blood volume
Bone development
Modification of muscle fiber
Modification of cerebellar synapse distribution
Exercise and training
• Byers and Walker (1995) listed 19 possible
benefits.
• Only found two that were likely permanent
and advantage to adult
• BUT all the rest likely easier to maintain as an
adult IF you do so as a juvenile.
Locomotor play
• 2) Provides opportunity to learn area
• Way of learning what each area provides and
their juxtaposition.
• Valuable again to both predator and prey
Social play
• Three possible functions proposed
• 1) same sex play may build alliances that
would be useful in later life
- A form of socialization and bonding
Social play
• 2) May improve physical skills for fighting,
hunting, mating.
• - Often seen more in males than in females
• 3) May improve cognitive skills
- Use play to assess their own abilities
- Often young of same age play, equal partner
- Learn how to fight, without harm, practice
One question: how do you know
he is just playing?
• If this is practice for later, real fighting, how do
the participants know this is not the real
thing?
• 1) Order and frequency of play activity not
the same as the real thing: exaggerated and
misplaced
Not the real thing
• 2) Play markers or signals: stereotypic
activities designed to signal intent. Behaviors
of dogs: pawing, bowing, etc.
• 3) Role reversal or self-handicapping
- Here what would normally be a dominate
individual will take a subordinate role, let the
other one “win”.
- Letting your little brother “beat” you or he may
not play with you!
here
General theory
• Some separate/some overlap.
• How about a general theory?
• Main function of all play is to develop physical
and psychological skills to handle unexpected
events were you lose control.
- Increases versatility of movements used to
recover loss of balance
- enhance ability of animals to cope with
unexpected stressful situations
Summary
• Three types of play, based on whether you
play with objects, yourself, or others.
• Each has some unique functions and common
ones
• Overall function is to prepare individual, not
just for adulthood, but for the uncertainties of
adulthood
• Increases your reaction capabilities and coping
skills.
Aggressive behavior (Chap 14)
• Not all fun and games!
• As mentioned, play gets you ready for adult
life, one filled with a lot of aggression