Social Relations
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Introduction
• Behavioral Ecology: Study of social relations.
– Interactions control by behavior
• Sociobiology:
– Study of social relations
• Fitness:
– # of offspring contribute individuals to future
generations
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Asexual vs. Sexual Reproduction (high, low, varies)
• Asexual
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________ population
_______ reproduction rate
____ variation
________opportunity for population to adapt to environmental changes
Sexual
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________ population
_______ reproduction rate
____ variation
________opportunity for population to adapt to environmental changes
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Various physiological expenses and physical risks
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No guarantee that offspring will be fit for environment
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Provides opportunity for new genetic phenotypes – possibly better fit to environment
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Introduction
• Fundamental Question:
– 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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Introduction
• Hermaphrodites
– Exhibit both male and female function.
– Most familiar example is plants.
– Sex change
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Fig. 7.1
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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 (Fruit fly link) 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
Courtship birds of paradise
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• The benefits of mate choice for the female
– 1.
– 2.
– 3.
– 4.
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Reproductive Energy/Effort and
Number of Offspring
• Limited access to
energy/resources results in tradeoff 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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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 helper’s probability
of future reproduction and recruiting helpers.
» Kin Selection
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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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• Eusociality
– More complex level of sociality.
• Three major characteristics:
– Individuals of more than one generation living together.
– Cooperative care of young.
– Division of individuals into non-reproductive and
reproductive castes.
– Examples
• Naked mole rats
• Various insects as ants, wasps, termites
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Fig. 7.26
Leaf cutter ant video
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Mate Choice
• Sexual Selection
– Differences in reproductive rates among
individuals as a result of differences in mating
success.
• Intrasexual Selection: Individuals of one sex
compete among themselves for mates.
• Intersexual Selection: Individuals of one sex
consistently choose mates among members of
opposite sex based on a particular trait.
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Mate Choice and Sexual Selection
in Guppies
• Given a choice, female guppies will mate
with brightly colored males.
– Brightly colored males attract predators.
– Color characteristics that have been shown to
confer mating advantage:
• Brightness
• Number of spots
• Total pigmented area
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Mate Choice Among
Scorpionflies
• Adult scorpionflies (genus Panorpa) feed
on dead arthropods in the forest
understory.
– Dead arthropod supplies are often limited.
• Thornhill found that male Panorpa will take
possession of, and guard, dead arthropods.
– Larger males are more successful.
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Fig. 7.11
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Nonrandom Mating Among Wild
Radish
• Wild radish flowers
have both male
(stamens) and female
(pistils) parts, but
cannot self-pollinate.
• Scientist found nonrandom mating in wild
radish populations.
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Green Woodhoopoes
• Scientist found green woodhoopoes live in
territories defended by flocks of 2-16.
– Only one pair breeds.
• Exhibit strong philopatry.
• Scarcity of roost cavities.
– Bulk of young tend to be helpers ranging from
half to full siblings.
• Full siblings share an average of 50% of genes.
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African Lions
• African lions in the Serengeti.
– Prides of female lions include 3-6 adults, but
may contain as many as 18.
• Many forms of cooperation.
– Kin selection and inclusive fitness.
Lion video
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African Lions
• Males cooperate in territory defense.
– Not always made up of close relatives.
– Single males have no chance of claiming and
defending a pride.
• Must form coalitions with other males.
– Probability of siring young depends on rank within coalition.
– Reproductive success more variable in groups of 3-4 than in
groups of 2.
– Larger coalitions composed of relatives.
• Orca video
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