Lecture 11 Social Relations or Is Sex OverRated

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Lecture 11 Social Relations or - Is Sex
Over-Rated?
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• Outline
• Reproductive strategies
• Fitness, sexual and asexual reproduction
• Sexual selection an aspect of natural selection
• Social structure
• Sociality cooperative behavior patterns
• Eusociality highly structured social
  organizations
• Kin selection altruistic behavior

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• Fitness and Reproduction
• Fitness ability of an organism to transmit
  genetic information from one generation to the
  next
• An organism with good ecological fitness is able
  to reproduce in a particular environment
• Offspring must reproduce
• Involves fecundity, physiological adaptations,
  means of reproduction, time to maturity other
  factors

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• Sexual vs. asexual reproduction
• Asexual
• genetically identical to one parent clonal
• Mitotic cell division processes involved
• Genetic information preserved
• Examples
• Binary fission bacteria, yeasts, protista
• Budding hydra, cniderians
• Plant spread via stolons, bulbs
• Parthenocarpic development

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• What is male and female ?
• Females produce larger, more energetically costly
  gametes.
• Males produce smaller, less energetically costly
  gametes.
• Female reproduction thought to be limited by
  resource access.
• Male reproduction limited by mate access.

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• Sexual Reproduction
• Meiotic cell division involved
• New genetic combinations result
• Haploid gametes ( cells containing one copy only
  of each chromosome) unite
• A zygote is formed
• Develops by mitosis into a multicellular organism
• Many opportunities for new genetic types each
  individual unique

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• Asexual vs. Sexual Reproduction
• Asexual
• rapid increase in clonal population
• rapid
• No variation leaves no opportunity for population
  to adapt to environmental changes
• Sexual
• Various physiological expenses and physical risks
• Reproduction slower
• No guarantee that offspring will be fit for
  environment
• Provides opportunity for new genetic phenotypes
  possibly better fit to environment

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• Sexual Reproduction Forms
• Dioecious plants separate sexes
• two houses male and female plants
• Hermaphroditic both sexes one organism/flower
• Sequential forms one sex at one time, another
  at another
• Monoecious one plant, separate flowers
• One house plant has flowers of two different
  sexes

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• What do we mean by sexual selection?
• How is it a part of natural selection?
• How does it contribute to genetic fitness
• For females?
• For males?
• How is it important in terms of shaping and
  survival of the species?

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• Who to mate with?
• Each parent seeks genetic immortality
• Seek a partner with good fitness potential
• Produces/sires offspring with good reproductive
  potential
• Sexual Selection
• Favors reproduction/mate selection

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• The sexual struggle is of two kinds in the one
  it is between the individuals of the same sex,
  generally the males, in order to drive away or
  kill their rivals, the females remaining passive
  while in the other, the struggle is likewise
  between the individuals of the same sex, in order
  to excite or charm those of the opposite sex,
  generally the females, which no longer remain
  passive, but select the more agreeable partners.
  Charles Darwin, 1871

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• Mate Selection and Sexual Selection
• Competition amongst members of same sex of
  species for mates
• Generally female selects mate- Why?
• Male to achieve reproductive fitness should
  mate with many females But?
• Handicap hypothesis burden of bright plumage or
  other characteristics to attract mate counter to
  survival those surviving such a handicap are
  genetically superior

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• Female peahens prefer to mate with males with
  greater number of eyespots in their tail feathers

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• Intrasexual males compete - selection leads to
  evolution of structures used in combat with other
  males
• Deers antlers or rams horns, bright colors,
  etc.
• selective pressure is for ability to compete
  successfully with members of same sex
• Intersexual selection- Females select amongst
  winners
• agents of selection
• Selection based on various cues appearance and
  behavior
• goal (evolutionary sense) select mate with best
  fitness

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• Mating system The typical number of mates an
  animal has during its breeding season.
• Monogamy One male and one female
• Polygyny One male and many females
• Lek display ground, female selects mate, raises
  young on own
• Polyandry One female and many males
• Polygyny is more common than polyandry
• Promiscuity mating w/o formation of pair bond

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• The benefits of mate choice for the female
• 1. The male that provides the best offspring care
• 2. The male that provides the best territory
• Superior nesting cover
• Abundance of food
• 3. The male that provides the best genes
• 4. Evidence of reproductive success (Fantail
  darter)

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• Intrasexual males compete - selection leads to
  evolution of structures used in combat with other
  males
• Deers antlers or rams horns, bright colors,
  etc.
• selective pressure is for ability to compete
  successfully with members of same sex
• Intersexual selection- Females select amongst
  winners
• agents of selection
• Selection based on various cues appearance and
  behavior
• goal (evolutionary sense) select mate with best
  fitness

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• Reproductive Energy/Effort and Number of
  Offspring
• Limited access to energy/resources results in
  trade-off between number and size of offspring
• ie.- species producing a larger if offspring
  means offspring are smaller, and vice-versa
• Parent provides extended care for young ? fewer
  young produced but greater survival rate

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• Rookery
• Lek
• Communal courtship ground arena
• Males defend small (worthless) territory
• Dominance hierarchy established
• Females select male/mate/move on
• Widespread amongst animals
• Animals prone to predation

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• Kin Selection
• Why do some animals risk their lives to warn
  others?
• Warning trait should be eliminated
• Genetically related trait preserved in close
  relatives
• Some gender bias may be more strongly expressed
  in females

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• Altruism
• Behavior which benefits recipient at cost to
  donor
• Kinship Basis of altruism
• Kin selection
• Fitness gained by preserving genes of close
  relatives
• How related to self (coefficient or relationship)
  is?
• Father/mother
• Full sibling
• Grandparent
• Child
• Neice/nephew

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• Sociality
• Evolution of sociality is generally accompanied
  by
• Cooperative feeding
• Defense of the social group.
• Restricted reproductive opportunities.
• Cooperation generally involves exchanges of
  resources or other forms of assistance.

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• Examples of social behavior
• Birds
• Green woodhoopoes
• Acorn wood peckers
• Mammals
• Lions
• Orcas, other cetacean species

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Cooperative Breeders

• Species living in groups often cooperate in
  rearing offspring.
• What benefit do helpers gain ?
• Inclusive fitness Improve survival and
  reproductive rates of family members.
• Inherited territory May increase helpers
  probability of future reproduction and recruiting
  helpers.
• Kin Selection