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Palaeobiology: how extreme environments drive evolutionary change in large organisms

Palaeobiology: how extreme environments drive evolutionary change in large organisms. Robin Allaby r.g.allaby@warwick.ac.uk. Lecture content. DEEP TIME the palaeontological record mass extinctions speciation explosions possible mechanims for speciations SHALLOW TIME

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Palaeobiology: how extreme environments drive evolutionary change in large organisms

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  1. Palaeobiology: how extreme environments drive evolutionary change in large organisms Robin Allaby r.g.allaby@warwick.ac.uk

  2. Lecture content • DEEP TIME • the palaeontological record • mass extinctions • speciation explosions • possible mechanims for speciations • SHALLOW TIME • Life coming out of the ice: the last ice age • palaeogenetics • archaeogenetics

  3. What is an extreme environment? • temperature (either hot or cold) • chemistry (unfavourable conditions: CO2, H20, 02 etc.) • violent

  4. The palaeontological record

  5. The palaeontological record carbon dioxide levels over time oxygen levels over time

  6. The 5 mass extinctions mass extinctions occur at period boundaries

  7. Mass radiations followed extinctions.

  8. Extinction 1. Ordovician

  9. Extinction2. Devonian

  10. Extinction 3. Permian - the big one

  11. Extinction 4. Triassic

  12. Extinction 5. Cretaceous

  13. Impact of a 6 mile diameter asteroid The Chicxulub crater is pretty big!

  14. Mass extinction causes 1. Ordovician Ice age (unknown) 2. Devonian Ice age (biotic probably) 3. Permian Global warming (unknown cause) 4. Triassic Global warming (volcanic activity possibly) 5. Cretaceous Asteroid impact

  15. What did mass extinctions kill? • Large organisms (e.g. dinosaurs) • Specialized organisms (e.g. climax community of Carboniferous forests, such as lycopod trees Lepidodendron; e.g. no entirely carnivorous or herbivorous fauna after the Cretaceous event)

  16. Species turnover and extreme environments: the tale of therapsids vs dinosaurs Dimetrodon Pristeroognathus

  17. Replacement rather than competition? extreme environment Does Darwinian evolution happen at all ?

  18. How do mass extinctions increase evolutionary divergence? • Decrease predation pressure, allowing novelties to become established • Decrease competition, allowing previously non-competitive species to rise (more ecological space) • Extreme environmental (stressful) conditions can be associated with increased genetic variability • Change in the ‘fitness landscape’ caused by extreme environment

  19. TE expansions linked to punctuated equilibrium and ‘evolvability’ high TE content, low diversity = evolvable Myotis high TE content, high diversity = stasis Branchiostomus low TE content = stasis Coelocanthus

  20. Does environmental extremity determine the mode of evolution? Phyletic gradualism (as Darwin expected) Punctuated equilibrium (caused by extreme environments?)

  21. Phyletic gradualism in the palaeontological record Sheldon 1987 Nature 330:561-563

  22. Punctuated equilibrium in the palaeontological record Williamson 1981 Nature 293:437-43 BUT see Van Bocxlaer et al 2008.

  23. Different environments have different evolutionary rates See Mestre et al 2009 for deep sea colonization Near shore: horseshoe crabs (300 Mya) Highly specialized, lots of gradual co-evolution e.g. predator prey, pollinating systems (Parsons 1994) Onshore: rich in fossil species (see Hoffmann and Parsons 1997 p.187) Dry habitats: origin of angiosperms (Coiffard et al 2007.)

  24. How does environment drive evolution? • evolutionary patterns determined by intensity of biotic interactions which differ in different environments • fluctuating environments can clear ecological space • continuous fluctuating conditions can prevent adaptation • intermittant stresses can increase genetic variability normally unexpressed

  25. Extreme environments in recent history: evidence from Palaeogenetics and archaeogenetics • directly examine evolutionary change • are morphological changes associated with speciation? • is there more going on that we cannot see due to morphological stasis?

  26. Pleistocene-Holocene

  27. Megafaunal extinctions Hofreiter and Stewart 2009 Current Biology 19:R584-94

  28. Recolonization from refugia Hewitt 2000 Nature 405:907-913

  29. Brown bear recolonization Barnes et al 2002 Science 295:2267-70

  30. Arctic foxes did not contract with glaciers Dalén et al 2007 Proc. Natl. Acad. Sci USA 104:6726-9

  31. Cave bears - multiple species? • look like different species from DNA • we see replacement of one group by the other - not competition. Hofreiter et al 2004 Curr. Biol. 14:40-3 Hofreiter et al 2007 Curr. Biol. 17:R122-123

  32. Competition in mammoths? Gilbert et al 2008 Proc. Natl. Acad. Sci USA 105:8327-32

  33. Mammoth haemoglobin is cold adapted Campbell et al 2010 Nature Genetics 42:536-540

  34. Extreme environments in the Holocene: drought tolerance This barley has the transcription factor for 6-row, but has evolved back into 2 row by another means to cope with drought stress. Palmer et al 2009 PLoS One 4:e6301

  35. Punctuated evolution in cotton during the Holocene

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