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Announcements Movie tonight, 7pm, 151 Evrt: Social Climbers (Life of Mammals)

Announcements Movie tonight, 7pm, 151 Evrt: Social Climbers (Life of Mammals). Overview. Some of the costs & benefits of cooperation. Altruism & selfishness. Relatedness & kin selection. The Major Transitions. 1. Replicating molecules ---> Molecules in protocells.

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Announcements Movie tonight, 7pm, 151 Evrt: Social Climbers (Life of Mammals)

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  1. Announcements Movie tonight, 7pm, 151 Evrt: Social Climbers (Life of Mammals)

  2. Overview Some of the costs & benefits of cooperation. Altruism & selfishness. Relatedness & kin selection.

  3. The Major Transitions 1. Replicating molecules ---> Molecules in protocells 2. Independent replicators ---> Chromosomes 3. RNA as gene and enzyme ---> DNA genes, protein enzymes 4. Bacteria (prokaryotes) ---> Eukaryotes (organelles) 5. Asexual clones ---> Sexual populations 6. Single-celled organisms ---> Multicellularity 7. Solitary individuals ---> Eusocial colonies 8. Primate societies ---> Human societies (language) Maynard Smith & Szathmáry 1995

  4. Transition 6 Unicellularity --> Multicellularity Occurred independently in plants, animals, and fungi (and others). Many occurred simultaneously, during the early Cambrian (~560-600 mya). Suggests that something happened: developmental constraint solved. environmental conditions changed. Allows division of labor, and specialization on certain tasks (differentiation).

  5. Problems that needed solving Differential gene expression Inheritance of cell identity in differentiated tissues. Pattern formation. relative position of cells vs. chemical gradients Soma vs. germ line Why be sterile?

  6. The social amoeba, Dictyostelium discoideum spores fruiting body free-living amoeba multicellullar slug

  7. The social amoeba, Dictyostelium discoideum spores fruiting body free-living amoeba multicellullar slug

  8. The social amoeba, Dictyostelium discoideum • Cheating can be prevented if: • Non-relatives are recognized and excluded. • or • Even mixing occurs within slugs.

  9. Social cheating in Dictyostelium 1. Do unrelated clones mix together to form slugs? • Mixed two clones together in equal proportions. • Used microsatellite markers to genotype sections of slugs. Strassmann et. al (2000) Nature

  10. Social cheating in Dictyostelium 2. Are clones equally represented in the stalk vs. spore? Strassmann et. al (2000) Nature • Genotyped and compared prestalk • vs. prespore.

  11. Social cheating in Dictyostelium • Cheating is not prevented: • Non-relatives are not excluded. • and • Even mixing does not occur within slugs. Some clones appear to be specialized cheaters, but require wild-type clones for stalk formation.

  12. The basics of cooperation & conflict (among cell lineages) In some systems, cheating can - and does - arise. Cheaters often do not do well alone (become parasitic). Bottlenecks increase genetic similarity, and align interests. Control can be imposed by previous generation (maternal effects).

  13. Cell lineages within multicellular organisms In most organisms, germlines are determined via: Somatic Embryogenesis Why be a leaf if you can be an acorn?

  14. Cell lineages within multicellular organisms In most organisms, germlines are determined via: Somatic Embryogenesis Not everyone can become an acorn - plant would die

  15. In most of the organisms we are familiar with, germlines are preformed or formed early

  16. Other potential benefits: dispersal diapause expose bad alleles Potential costs: ecological vulnerability costs and risks of development The unicellular bottleneck Why break down a costly, multicellular organism each generation? Because all cells are genetically identical, r = 1. This aligns interests. When cheaters go through bottleneck, they are non-viable (all acorns).

  17. Transition 7 Solitary individuals to social groups Dispersal is risky Death Finding resources (food, home) Finding mate When the costs of ecological constraints are high, offspring do better by staying home.

  18. Risks of not dispersing: Competing with relatives Limited resources Inbreeding Conflict over reproduction Family-based social groups So an individual’s decision should be determined by the balance of these costs and benefits.

  19. Potential benefits of sociality Pooled resources/shared defenses. Division of labor. Increase indirect fitness (by helping relatives reproduce) Potential costs of sociality Shared resources Parasitism Cheaters

  20. Shared defenses. dilution effect- prey group together in large numbers to overwhelm the feeding capacity of the predator. selfish herd- prey found on the inside of a clump will tend to survive, those on the outside are eaten. Prey constantly moving towards middle of a group and appear flock or school.

  21. Shared resources Packer Caraco and Wolf

  22. Shared resources Fieldfare The larger the colony, the higher probability that some offspring will die of starvation.

  23. Social spiders (Anelosimus) Female fitness increases with group size intially, but then declines in largest groups.

  24. Some re-occurring themes Relatedness and indirect fitness. Conflict between selection at different levels. Why not cheat? What happens when cheaters succeed? New levels of individuality (cells, organisms, colonies) can arise when selection at lower levels is repressed.

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