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Summary good gene hypothesis


									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
• How do they do it?
• Survival tests and health evaluations
• Obviously equating health with genetic well
• 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
• 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
• Now have offspring with both traits
• Assume: coloration is switched on in males,
  preference in females
• 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
• 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 stalk-
  eyed 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
• 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
• 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
• 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
   Traditional conditioning and mate
• Can individuals be “trained” or conditioned to
  modify their mate choice?
• Quail: brown and blond
• Male brown raised brown, imprinted on
• 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
• Defined operationally: If Y - X > 0, then mate
• 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
               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
• So evidence for mate-choice copying
   Song learning and mate choice
• Many birds use songs
• Males learn songs
• Females who also hear songs develop
• 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
• 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
        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
• 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
   So what do males have to do?
• Mainly involves some type of male-male
• 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
• 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.
• 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
• 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 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
•   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”
• 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
• 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
       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
• 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
• Monogamous during raising of young is
• Switching partners, either sex, increases
  variability of your offspring.
Just how Monogamous are they??
• Monogamy sounds good but how well is it
• 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??
• Of socially monogamous bird species studied,
  only 14% found to be genetically
• Extra-pair copulations 11% up to 50% in some
• What is going on!!? Soap operas!!
• Two types of “cheating”!
• Cuckoldry: where other male mates with
  “your” partner. E.g. purple martins.
• 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
                 Two forms
• Polygyny: male mates with more than one
• Polyandry: female mates with more than one

• Can be simultaneous: leks, elk
• Can be sequential: Jacanas
• 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.
• 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
• Assured of access to “best” genes

• Males: Obvious advantage to winner
• Losers? Often related to winner so don’t lose
  so much genetically!
• Female with many males:
• Jacanas, tropical shore bird
• Sex reversal: males incubate eggs/defends
• Female lays eggs
  sequentially in several
  male nests
-how do males know eggs
 are theirs?? 93% of the time
• 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
• Result: colony made up of one female lineage
  but many male ones.
          Advantages to female?
• Sperm replenishment: New supply, no need to store
• Material benefits:
 - Nutrients: nuptial gifts, chemicals in seminal fluids
   female can use, male parental care.
• Genetic benefits: Increases genetic variance of
• Convenience: avoids costs of avoiding copulation
    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
• Second type of promiscuous system
• Here several males form pair bonds with
  several females. Dunnock: small passerine
  bird is example.
• # of mates variable
• 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

• 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
            Ecological drivers
• Remember: goals are 1) add young to the
  population and 2) “improve” genetic quality of
• 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
• 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
• 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
• 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
• 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…
• Briefly mentioned examples of related
  individuals: leks, bee hives
• Others: wolf packs, lion prides, flocks of geese,
• One emerging observation is that there are a
  lot of groups of animals where members are
• 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
• 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
• “identical by decent” : genes from common
• 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
• 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
• 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

• 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!!
               Parental care
• Next logical step: Producing them is the easy
  part, raising them is more difficult!
• Just as important as mate choice/mating
• 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
• 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
• Benefits: Obviously, this is your link to the
• 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 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
• So there are benefits for and against parental
• 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
• 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!
• 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
• 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
• Strong selection pressure for males who stay!
• Why see these two forms: altricial vs
                   In birds
• Nesting environment:
• More dangerous ground
  favors precocial.
• Selection pressure for
  successful use of a given
  niche dictates parenting
             Trophic position
• Prey: ungulates precocial: need to be “ground
• 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
         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
• 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
         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
             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 =
• Current active research into if parents can
  judge reproductive value and give food to
  those with higher value!
        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 mother-
  son, 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
• 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??
• 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
• 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
                Down side?
• Can also pass and concentrate “bad” genes!
• This is where human taboos have developed
• To try and prevent the concentration of such
• 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
• 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
• 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
• Can’t evoke kinship selection as reason so how
  can we evolutionarily justify this type of
                 Over view
• Actually imbedded in an overall view of
  cooperation, which includes kin selection
• In this scheme there
  are four pathways
  to cooperative
• 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
           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
• Separate rooms
• Either cooperate
  with each other,
  don’t “squeal” on
• Or squeal.
• Each outcome has
  different penalties/
• 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
• 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
• Forgiving:
  Current action
   based on last
   of other.
  What does this have to do with
• 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
•   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
• Both gain, but not as much if both go
• So, tendency to cheat, tendency to cooperate
• What do you do?
• Depends on what your co-inspector did
• 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
• 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
• 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
• 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!
• Chirrup calls in sparrows: no or little food,
  fewer calls to bring conspecifics
• More food, more
• 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!!
• 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!
• 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
• Proposed as possible reason for such things as
  alarm calls.
• Not advantageous to individual but is to
• A group that has more “selfless” callers, does

• 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
• Bekoff and Byers (1981): motor activity
  performed that appears purposeless, contains
  motor patterns from other contexts, usually in
  a modified form and altered temporal
                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
           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
•   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

• In some, will use over again….toys??
             Locomotor play
• As name indicates, involves some type of
• 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
            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
• Can look at each category to see how each
  type may have a “purpose”

• Then we can look at an overall theory on
        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
• 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
• 1) Order and frequency of play activity not
  the same as the real thing: exaggerated and
            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!
              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
• Three types of play, based on whether you
  play with objects, yourself, or others.
• Each has some unique functions and common
• Overall function is to prepare individual, not
  just for adulthood, but for the uncertainties of
• Increases your reaction capabilities and coping
   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

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