Eusociality Conflicts over reproduction Definition and occurrence Explanations for worker sterility...
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Transcript of Eusociality Conflicts over reproduction Definition and occurrence Explanations for worker sterility...
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Eusociality
• Conflicts over reproduction
• Definition and occurrence
• Explanations for worker sterility
• Routes to sociality
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Definition
• Overlapping generations
• Reproductive division of labor including nonreproductive (or sterile) workers– Caste polymorphism (in some cases)
• Parental care in a permanent nest
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Hymenoptera:ants, bees and wasps
S
C E
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Ants show caste polymorphism
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Isoptera - all termites
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Social aphids
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Gall-forming thrips
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Carribean snapping shrimp
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Naked mole rats
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Social spiders
Communal, but no sterile caste
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Why worker sterility?
• Kin selection
• Parental manipulation
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Haplo-diploidy and relatedness
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Why worker sterility? Kin selection
• Because of haplodiploidy, workers are more closely related to sisters (r = 3/4) than to offspring (r = 1/2), assuming females mate once
• But, they are more closely related to male offspring (r = 1/2) and nephews (r = 3/8) than to brothers (r = 1/4). Therefore, workers should lay unfertilized eggs if mothers mate singly (bumblebees, stingless bees)
• If mothers are polyandrous, then female workers may be more closely related to brothers than half-nephews (r = 1/8). Expect workers to kill unfertilized eggs laid by other workers in polyandrous species, e.g. honeybees.
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Worker policing in honeybees
“Queenright”
“Queenless”
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Why worker sterility? Parental manipulation
• If parents can prevent their young from reproducing, then it may be better to help
• A mother that traded eggs with her daughters would trade grandkids (r = 1/4) for offspring (r = 1/2) and gain a 2-fold advantage. Daughter trades offspring for siblings and loses nothing (r =1/2 for both).
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Sex ratio investment• Offspring control: expect 3:1
investment sex ratios because females are related to sisters by 3/4 and to brothers by 1/4
• Parental control: expect 1:1 sex ratios
• Data fit 3:1, rejects parental manipulation
• Only slave-makers are 1:1
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Factors promoting eusociality
• Genetics– High relatedness of workers to reproductives
• Ecology– High cost of dispersal– Need for assistance in nest construction– Reproductive success is proportionately higher
for family than individual– Need to defend a multi-generation nest
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Routes to sociality
Predict r < 0.5 Predict r > 0.5
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Paper wasps, often single foundress
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Swarm founding wasps
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Inbreeding-outbreeding cycles in termites
Termites are diploid.Both sexes help.In some species, multiplereproductives occur.If these are produced byinbreeding over multiplegenerations, then termiteswithin a colony couldbe very closely related
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Inbreeding in mole rats?