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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

– ________ population– _______ reproduction rate – ____ variation – ________opportunity for population to adapt to environmental changes

• Sexual– ________ population– _______ reproduction rate – ____ variation – ________opportunity for population to adapt to environmental changes

– Various physiological expenses and physical risks– No guarantee that offspring will be fit for environment– 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 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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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. 7.26Leaf 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 non-random 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