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Social Relations

Chapter 7

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Introduction

• Behavioral Ecology: Interactions between organisms and the environment mediated by behavior.

• Sociobiology: Branch of biology concerned with study of social relations; intraspecific behavioral interactions.

• Fitness: Number of offspring (genes) contributed by an individual to future generations. Sexual reproduction. Survival of young.

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Introduction

• Fundamental Question: What is male and female ?

Females produce fewer, larger, more energetically costly gametes.

Males produce more, smaller, less energetically costly gametes.

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Gamete Dimorphism is Huge

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Introduction

• Female reproduction success is thought to be limited by resource access.

• Male reproduction success is limited by mate access.

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Number of matesM

ean

# o

ffsp

rin

g p

rod

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MalesFemales

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Introduction

• Hermaphrodites Exhibit both male and female function.

Simultaneous Sequential

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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Simultaneous

Hermaphroditic Reef Fish

Protandry = ♂→♀Protogyny =♀→♂Protogyny =♀→♂

Protogyny =♀→♂

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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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Intrasexual selection

Intersexual selection

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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 as nuptial offering to female.

Larger males are more successful. Small males offer spit.

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Nonrandom Mating Among Wild Radish

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

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

inhibitory interaction between individuals. Some characteristic of the pollen from

certain individuals increases pollination success seed plants.

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Sociality

• Evolution of sociality is generally accompanied by: Cooperative feeding (or other assistance) Defense of the social group. Restricted reproductive opportunities.

• Cooperation generally involves exchanges of resources or other forms of assistance.

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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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Packer and Pusey studied cooperation among African lions in the Serengeti.

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Acorn Woodpeckers (Melanerpes formicivorus)

•Live in groups of up to 16 individuals.

•Cooperative defense of acorn stores and raising of young.

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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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