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Phylogenetic relationships between unicellular aquatic organisms

Phylogenetic relationships between unicellular aquatic organisms. purple sulfur bacteria, methanotrophs, chemotrophic or autotrophic can’t tolerate O 2. Prokaryotic inorganic chemotrophs. cyanobacteria (tolerate O 2 , heterocysts). heterotrophic bacteria

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Phylogenetic relationships between unicellular aquatic organisms

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  1. Phylogenetic relationships between unicellular aquatic organisms purple sulfur bacteria, methanotrophs, chemotrophic or autotrophic can’t tolerate O2 Prokaryotic inorganic chemotrophs cyanobacteria (tolerate O2, heterocysts) heterotrophic bacteria eat organic resources, predators or decomposers endosymbiosis Diversification of phytoplankton is largely driven by evolution of new photosynthetic pigments eukaryotes

  2. Cyanobacteria- prokaryotes1350 described “species”

  3. Why are cyanobacteria so famous? • Evolved 2.5 bya, first to use water as a source of electrons in photosynthesis • N-fixers, transformed global N cycle • produced O2, transformed atmosphere into oxidizing environment • ancestors of all eukaryotic life by endosymbiosis with bacteria • gave rise to green algae 250mya • now mostly known as a sign of pollution and for toxic compounds

  4. Chlorophytes- green algae6,000 “species” Scenedesmus Pediastrum Volvox Spirogyra

  5. Why are chlorophytes so famous? • appeared 250mya • have chloroplasts • use chlorophyll-a and b • have had their chloroplasts stolen by euglenids, among others • evolved flagellae

  6. Euglenophytes1000 species

  7. Bacillariophyta- Diatoms200 general, 106 “species”

  8. Why are diatoms so famous? • appeared 185mya • the frustule (silicate petri dish) • the auxospore (sexual stage) • associated with silica availability

  9. Chrysophytes- golden brown500 “species” Dinobryon More species in fresh than salt water

  10. Cryptophytes100 “species” Cryptomonas

  11. Pigments of phytoplankton • All have chlorophyll-a • phycobilin in cyanobacteria • carotenoids in chrysophyta and bacillariophyta • chl-aand chl-bin chlorophytes • xanthophylls, mainly in cyanobacteria • Pigments have different spectral properties, can be used to identify broad groups

  12. Deer Lake 0 0 2 2 4 4 6 6 8 8 Greens 10 10 Bluegreens depth (m) Diatoms Cryptophytes 12 12 Total 14 14 8 10 12 14 16 18 20 10 20 30 40 50 60 70 temperature (deg C) chlorophyll (ug/L) Loon Lake 0 0 2 2 4 4 6 6 8 8 10 10 depth (m) 12 12 14 14 8 10 12 14 16 18 20 2 4 6 8 10 12 temperature (deg C) chlorophyll (ug/L)

  13. P and cyanobacteria (N-fixers)Smith 1983 Science 221:669

  14. Distribution of lake phytoplankton taxa

  15. Sinking phytoplankton • Stokes equation • v = 2gr2(ρ’- ρ)/9η • g=gravitational acceleration • r=radius (assuming sphere) • ρ=fluid density • ρ’=algae density • η=viscosity (stickiness) • Adaptations to sinking • density (gas vacuoles, e.g.) • shape (don’t be a sphere) • size (r)

  16. growth phytoplankton population What happens to phytoplankton? Sinking (15-40% of PP) Grazing by zooplankton (35-75% of PP) affected by: turbulent mixing cell size, density, shape adaptations for: morphology (spines, mucous coats) chemical defenses life history adaptations colonial life history adaptations for: gas vacuoles flagella (pyrophytes, cryptophytes)

  17. Fates of production in different systemsCebrian 1999 American Naturalist 154:449 More production consumed by herbivores in aquatic systems, more detritus accumulation on land

  18. Wind re-suspends sinking phytoplankton

  19. How do sinking losses change with productivity?

  20. What happens to phytoplankton that sink? • Either lost to hypolimnion, aphotic zone • Live as periphyton in littoral zone of lake

  21. How does periphyton production compare to phytoplankton?Vadeboncoeur et al. 2003 Limnology and Oceanography 48:1408 % benthic of whole lake primary production

  22. Why is benthic productivity important?

  23. Benthic vs. fish prey for big fish

  24. Productivity from bottom to topVadeboncoeur et al. 2002 Bioscience 52: 44

  25. Effects of cell size • competition • SA/V • grazing • gape limitation of zooplankton • sinking • Stoke’s equation

  26. Things we’d like to know about phytoplankton • What determines their nutritional quality for herbivores? • What determines their diversity? • What determines their productivity?

  27. What determines nutritional quality of phytoplankton for zooplankton? • Elemental composition • Biochemical composition • Chemical defenses

  28. Effects of cell chemistryDeMott et al. 1998 Limnology and Oceanography 43:1147 Daphnia grows better on phytoplankton with lots of P

  29. BUT lakes with lots of P have different phytoplankton with less essential Fatty AcidsMuller-Navarra et al. 2003 Nature 427: 69

  30. What limits energy transfer from phytoplankton to zooplankton? • Food quantity (more zooplankton in eutrophic lakes) McCauley et al. 1988 Am Nat 132:383 • Food quality • Is it elements or molecules? P or fatty acids?

  31. What determines trophic efficiency?

  32. What determines trophic efficiency?Cebrian, Shurin et al. 2008 PLoS ONE Aquatic ecosystems Terrestrial ecosystems Not productivity (apparently)

  33. Nutrients!

  34. Things we know to affect trophic efficiency: • Total productivity • goes down with productivity • Loss of benthic productivity • Low quality of algae in eutrophic lakes • Algal quality • mineral nutrients, N and P • Essential Fatty Acids

  35. What controls phytoplankton diversity? Paradox of the plankton: How can so many phytoplankton coexist if they all need the same things (light, C, N, P, etc.)? G.E. Hutchinson 1959 American Naturalist 93:145 Based on Gausse’s axiom of competitive exclusion

  36. Solutions to the paradox (and evidence for them)

  37. Solutions to the paradox 1: Multiple Resources Tilman’s resource ratio hypothesis- Tilman 1981 Ecology 62:802 Measured growth of 4 Diatom species on Si and P Predicted the outcome of competition- who wins? Growth rate Silicate Phosphate

  38. The outcome of competition in lab experiments Theory- based on monocultures low Si:P high Si:P intermediate Si:P

  39. Does this work in the real world?Interlandi and Kilham 2001 Ecology 82:1270 Measured phytoplankton diversity and resource availability (N, P, Si, light) over two years in three lakes

  40. Phytoplankton diversity is highest in Yellowstone Lakes when more resources are limitingInterlandi and Kilham 2001 Ecology 82:1270

  41. Where do tradeoffs come from?Lichtman et al. 2007 Ecology Letters mu = maximum growth Q = cell nutrient content m = mortality Vmax = maximum uptake R = nutrient concentration in the environment R’ = nutrient concentration where growth = 0 K = Half saturation content

  42. How do these things affect R*? How are these traits related to each other?

  43. Tradeoffs between saturation, uptake and nutrient demand High minimum nutrient concentration (Qmin) -> fast growth rate Fast growth -> low R* (no tradeoff)

  44. Has a lot to do with cell size Big cells take up nutrients faster, but need more nutrients for growth

  45. Lessons from correlations in functional traits: • Species that can take up nutrients quickly are more sensitive to low nutrients • Big species can take up nutrients faster but don’t do as well at low nutrients

  46. Can phytoplankton partition the light spectrum?Stomp et al. 2004 Nature 432:104 phycocyanin Grew two cyanobacteria in white light (all wave- lengths), or with only red or green wavelengths phycoerythrin

  47. More diverse phytoplankton communities capture more light Streibel et al. 2009 American Naturalist

  48. Lessons from resource competition theories • tradeoffs can allow coexistence -> promote diversity • evidence for tradeoffs in multiple dimensions • different nutrients • different wavelengths of light • growth vs. need for nutrients

  49. Solutions to the paradox 2:Keystone predators Prevent competitive exclusion by eating dominant competitors Paine 1966 American Naturalist 100:65 Originally from intertidal zone- Sea stars eating mussels

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