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Social Relations

Chapter 7

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Outline

• Introduction• Mate Choice• Mate Choice and Sexual Selection in Guppies• Mate Choice Among Scorpionflies• Nonrandom Mating Among Wild Radish• Sociality• Cooperative Breeders

Green Woodhoopoes African Lions

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Introduction

• Behavioral Ecology: Study of social relations. Interactions between organisms and the

environment mediated by behavior.• Sociobiology: Branch of biology concerned

with study of social relations.• Fitness: Number of offspring (genes)

contributed by an individual to future generations.

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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. Charnov et.al. identified (3) conditions

favoring hermaphroditic populations: Low mobility limiting male:male

competition. Low overlap in resource demands by

male and female structures. Sharing of costs for male and female

function.

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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 and Sexual Selection in Guppies

• Endler performed natural selection study to test color pattern in guppies. When freed from predation, average

number of spots of male guppies increased.• Kodric-Brown reported reproductive success

was determined by a combination of male attractiveness and dominance status. Observed attractive males tend to be

dominant, court more, and have brighter colors.

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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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Nonrandom Mating Among Wild Radish

• Wild radish flowers have both male (stamens) and female (pistils) parts, but cannot self-pollinate.

• Marshall found non-random mating in wild radish populations. Interference Competition - Aggressive or

inhibitory interaction between individuals.

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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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Sociality

• 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.

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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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Green Woodhoopoes

• Ligons 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

• Packer and Pusey studied cooperation among 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.

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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.

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Review

• Introduction• Mate Choice• Mate Choice and Sexual Selection in

Guppies• Mate Choice Among Scorpionflies• Nonrandom Mating Among Wild Radish• Sociality• Cooperative Breeders

Green Woodhoopoes African Lions

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