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What’s the worlds smallest known living organism?

Mycoplasma weighs < 0.1 pg 10 -13 g. What’s the worlds smallest known living organism?. Largest?. Blue whale = 100 tons 10 8 g. Historically: Largest Mammal: Baluchitherium , a relative of the modern rhinoceros, ~30 tons. Currently : the elephant, at about 5 tons. 10 6 g. 10 7 g.

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What’s the worlds smallest known living organism?

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  1. Mycoplasma weighs < 0.1 pg 10 -13 g What’s the worlds smallest knownliving organism? Largest? Blue whale = 100 tons 108 g

  2. Historically:Largest Mammal: Baluchitherium, a relative of the modern rhinoceros, ~30 tons Currently: the elephant, at about 5 tons. 106 g 107 g Historically: Largest dinosaur: Brachiosaurus, topping out at about 80 tons. 107 g What about the largest terrestrial animals? 1010 g Largest Organism: sequoia at 4,000 tons

  3. The full size range Mycoplasma < 0.1 pg < 10 -13 g Average bacterium 0.1 ng 10 -10 g Large amoeba 0.1 mg 10 -4 g Bee 100 mg 10 -1 g Hamster 100 g 10 2 g Human 100 kg 10 5 g Elephant 5,000 kg (5 tons) 5 x 10 6 g Blue Whale 100 tons 10 8 g Sequoia 5000 tons 10 10 g

  4. Scaling: structural and functional consequences of change in size among otherwise similar organisms. Three basic ways that organisms can change with size: 1. Dimensions 2. Materials used 3. Design

  5. Must be WIDER as well NO 1. Dimensions Can you just make the wall taller? Side view ofbrick wall Does this happen in animals?

  6. elephant 1. Dimensions % of body mass that is skeleton 3.8% Sorex(shrew) 8.8% Human 27%

  7. steel hydrostatic support/exoskeleton bone support 2. Materials used brick

  8. Unicellular organism 0.1 mm = 5 sec 1 mm = Diffusion 10 cm = 3. Design Long bridge Short bridge Tensile support, steel Compressive support, stone Oxygen Delivery—design changes with size Diffusion Problem!: Time to diffuse is proportional to the square of the distance 500 sec ~ 55 days

  9. Unicellular organism Vertebrate Insect • bulk flow delivery • hemoglobin increases oxygen in blood Diffusion through air via tracheal system Diffusion Long bridge Short bridge 3. Design Tensile support, steel Compressive support, stone Oxygen Delivery—design changes with size

  10. Scaling: structural and functional consequences of change in size among otherwise similar organisms. Three basic ways that organisms can change with size: 1. Dimensions 2. Materials used 3. Design Let’s look at this graphically…

  11. A “power” function Physiological parameter of interest Body Mass (M) Scaling Relationships Y = a Xb

  12. A “power” function Physiological parameter of interest Body Mass (M) Scaling Relationships Y = aMb a = proportionality constant b = scaling exponent (describes strength and direction of the effect of mass on Y)

  13. Physiological parameter of interest Body Mass (M) Scaling Relationships Y = a Mb If it scaled in constant proportion… …then b would = 1 This would be an ‘isometric’ relationship But, this is not usually the case …for example:

  14. 8. BODY SIZE affects MR • “Whole animal” O2 consumption • “Mass-specific” O2 consumption

  15. How does whole animal O2 consumption scale with body size? Whole animal O2 consumption (mlO2/hr) Body Mass (M) Y = a Mb • O2 consumption increases with body mass in a regular way • but not in constant proportion b = 0.75

  16. b = 0.75 slope = 0.75 E = a Mb Body mass Log E Y-intercept slope log Body mass log E = log a + b log M Physiologists often use log-log plots • allow for huge range of body sizes • generate a straight line • slope of line = b O2 consumption (E)

  17. How does mass-specific O2 consumption scale with body size? Mass-specific MR (02 consumption per gram of tissue) Log O2/g*hr log Body mass Y = a Mb So b = -0.25 Take log: Slope = -0.25

  18. b: describes relationship of X to Y as Y gets bigger If b = 0 If 0 < b < 1 If b = 1 b = 0.75 No relationship e.g. [hemoglobin] e.g. whole animal metabolic rate Isometric relationship e.g., blood volume in mammals -constant fraction of body mass If b < 0 If b > 1 b = -0.25 e.g., mass specific metabolic rate e.g., bone thickness

  19. Scaling Summary • organisms cover 21 orders of magnitude in size • Processes can scale by changing: • Dimension • Materials • design • Scaling relationships tend to fit a power function • Y = aXb • a = proportionality constant • B = scaling exponent (!!!Very informative!!!) • Two examples: • Whole animal metabolic rate • Mass-specific metabolic rate • How does changing b describe X:Y relationship?

  20. Take the log of both sides Log(SA) = Log(6 V2/3) = Log(6) + 2/3 * Log(V) The actual equation for surface area as a function of volume is SA = 6 V2/3

  21. Take log of both sides to get: Log(y) = Log(a) • b Log(x) The key coefficient—the scaling exponent Real organisms usually are not isometric. Rather, certain proportionschange in a regular fashion. Such non-isometric scaling is calledallometric scaling. An amazing number of biological variables can be described bythe allometric equation: y = a • xb

  22. Slope = 1.08 Ex. Skeleton mass of mammals rises faster thanbody mass. Large mammalshave disproportionately largeskeletons. Log y Log x What the scaling exponent, b, means. Slope = 1 Ex. The cost of applesrises ‘isometrically’ with the mass bought. Log y Log x

  23. Slope = 0.75 Ex. Metabolic raterises with body mass, butless than proportionately. Log y Log x Slope = 0 Ex. Hematocrit inmammals is independentof body mass. Log y Log x Slope = -0.25 Ex. Heart rate in mammalsdecreases with body mass. Log y Log x

  24. b = 1 b = 0.75 b = 0.6 b = 1 b = 0.75 b = 0.6

  25. Example 1: A pressing question: were dinosaurs stupid? Mammals diversifiedin the Cretaceous,between 144 and 65 mya = 65 mya Dinosaurs disappear here(except for lineage leadingto birds). Using allometry.

  26. From Jerison 1969

  27. Brain cast offossil dinosaur From Jerison 1969

  28. Example 2: Big antlers on Irish Elk—10 – 12 feet across! This species went extinct in Ireland about 10,000 years ago. Two outstandingquestions: Why the enormous antlers? And why did they go extinct?

  29. Most of dots represent extant species of deer Irish elk Two species of moose Maximum length of antler Antler length = 0.064 * Shoulder height1.68 Height of shoulder From Gould 1974

  30. Two classes of explanations 1. The allometric relationship itself ‘explains’ the large antlers of of Irish elk. Can only be true if strong physiological constraint. 2. Increasingly strong selection for large antlers in larger species. Rutting moose

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