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Eusociality

Eusociality. Conflicts over reproduction Definition and occurrence Explanations for worker sterility Routes to sociality. Definition. Overlapping generations Reproductive division of labor including nonreproductive (or sterile) workers Caste polymorphism (in some cases)

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Eusociality

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  1. Eusociality • Conflicts over reproduction • Definition and occurrence • Explanations for worker sterility • Routes to sociality

  2. Definition • Overlapping generations • Reproductive division of labor including nonreproductive (or sterile) workers • Caste polymorphism (in some cases) • Parental care in a permanent nest

  3. Hymenoptera:ants, bees and wasps S C E

  4. Ants show caste polymorphism

  5. Isoptera - all termites

  6. Social aphids

  7. Gall-forming thrips

  8. Carribean snapping shrimp

  9. Naked mole rats

  10. Social spiders Communal, but no sterile caste

  11. Why worker sterility? • Kin selection • Parental manipulation

  12. Haplo-diploidy and relatedness

  13. 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.

  14. Worker policing in honeybees “Queenright” “Queenless”

  15. 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).

  16. 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

  17. 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

  18. Routes to sociality Predict r < 0.5 Predict r > 0.5

  19. Paper wasps, often single foundress

  20. Swarm founding wasps

  21. Inbreeding-outbreeding cycles in termites Termites are diploid. Both sexes help. In some species, multiple reproductives occur. If these are produced by inbreeding over multiple generations, then termites within a colony could be very closely related

  22. Inbreeding in mole rats?

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