Wednesday, March 16, 2016

How Fast Is Fast

The cheetah is one quick cat, but it often confused
with the leopard. Here is a guide. The cheetah has
single black spots, while the leopard has rosettes -
dark spots or circles with light fur in the middle. The 
cheetah is taller and skinnier, with a barrel chest.
Finally, the cheetah has “tear stains” dark lines that
run from its eyes to its mouth.

Take a look at these short videos and then we will ask today’s question. Those little guys are awfully fast, especially the Chromatium. Some seem to dart all the way through the field while others move around in circles or stay mostly still. Bacteria must be the fastest things around.

The question of the day:
Just how fast are microscopic organisms? And for that matter, what is the best way to measure speed in organisms of vastly different sizes?

The fastest terrestrial animal is the cheetah; it is scary fast, to the tune of 70 mph over short distances, like in this video. From a dead stop, the cheetah can hit 60 miles per hour in just three seconds. Cheetah races are popular attractions in many zoos right now. You run and the zoo keepers time you. Then they have the cheetah run and you get to compare times – you won’t win. Biologically, they're built for this speed.

We talked a couple weeks ago about how the hyoid is the only bone in humans that is not attached to any other bone, but in cheetahs, the clavicle bones of their shoulders are built this way. They attach only to muscle, so that it offers the cat extra length in its stretch as is reaches forward for its next step.

The cheetah uses it tail as a rudder and counterbalance as it 
runs. In these pictures, you can see that its tail flattens out to 
act as a sail. It can catch wind or cut through the wind to help 
in turns and balance. This is the only cat that can flatten its 
tail without the aid of a slamming door or a rocking chair.

Any prey animal worth his or her salt will try to turn and have the cheetah run past them, but this cat can go from a top speed to near zero in a mere second. It has claws on the backs its front paws so it can slam its front legs into the ground and have them catch like extra brakes.

Turning is also engineered into this fast cat. Its tail, unlike other cats, is flat, so it can use it as a rudder in turns. Also unique to cats, cheetah claws do not retract. They are always sticking out, so that they can grip the ground and push off for more speed and control in the turns. (click here for the newest mechanism identified in cheetah speed)

If we look up in the sky, there are some pretty fast animals there too. The peregrine falcon is considered to be the fastest bird, hitting over 220 mph when in its hunting dive. The falcon uses this speed to catch other birds right out of the air, as they almost always take their prey on the wing.

The difference is that this speed is achieved with the aid of gravity, it is only in diving that they can go this fast. In horizontal flight, the peregrine can manage only a measly 55-60 mph, not quite as good as the cheetah. If you tossed a cheetah out of a plane, it could achieve a terminal velocity of 200 mph, nearly the same as the falcon, the difference being that a cheetah is not accustomed to assuming an aerodynamic position going straight down. It would probably look rather scared and flail a lot – I don’t recommend trying this.
The white-throated needletail is a sleekly designed
bird, with swept back wings and a large chest. The
chest is large to accommodate huge breast muscles
and a larger than normal heart a lungs. Its tail can be
splayed out for turns, or turned into a needle shape
to reduce drag.

If you want top speed in flapping flight from a bird, bet on the white-throated needletail. It used to be considered a member of the swift family (appropriately named), but is now in its own genus. With a tail wind and the proper motivation, these small birds can reach speeds of 100 mph. Living on the northern coasts of Australia, it is bigger than you might expect for a fast bird, especially one that used to be considered a swift. It has long, swept back wings that help it pick up speed and still be able to maneuver.

Most airplanes have this swept wing design to improve flight characteristics; and as with many of humans so called ideas, we stole it from nature. However, we are getting better at stealing. New aircraft wing designs are based on the swifts’ ability to wing morph, changing the shape of its wings to take better advantage of the flying conditions at the time.

If we drop down into the seas, we can look at speed in the fishes. The sailfish is considered to be fastest. It is of course built in a streamlined fashion, meant to build the speed needed to catch the fish and octopuses it eats. It has been clocked at 68 mph, which in my book makes it faster than the cheetah, since it is moving through water, a much more dense medium as compared to air.

The long upper jaw of the sailfish isn’t just for cutting
through the water. It can skewer large fish with it while
hunting, although this isn’t its normal hunting behavior.  
Sailfish have been seen to cut mackerel in half with a
flick of the bill. Its cousin the marlin has a bill that can
cut through the hull of small boats.

So how do bacteria stack up against these speeds? Not too well, despite what we saw in the first video. The fastest bacteria, members of the Vibrio family, move about 200 µm/sec – this is about 0.00045 mph (0.00072 kph). Even my teenage son on his way to clean his room moves faster than that! However, when you sneeze, you send bacteria (and mucus) out of your nose and mouth at over 100 mph – you can almost hear the little bugs screaming.

Because we are looking at a very small area under the microscope, it appears that the bacteria are covering a good distance. But at 1000x magnification, the least magnification you would need to observe bacteria, the field is usually just 500-800 µm across (0.02-0.03 inches). This makes the bacteria appear to be moving quickly.

Vibro cholerae is a gram negative bacteria with a single
polar (meaning at one end) flagellum. This long
appendage rotates and provides the locomotive force for
this fastest species of bacteria. The flagellar motor can
spin in either direction and is driven by a sodium ion
gradient. Too much salt and it slows down; not enough
salt, it slows down. It’s like a microbial Goldilocks.

Like the fish, bacteria are moving through an aqueous (water) medium, so the density is much greater. But it is even worse for them because of their small size. The effects of density are much larger on small organisms, sort of like us trying to walk through a pool filled with caramel (not a bad idea).

But what if we measured speed in a different manner, say….. bodies lengths per second. Vibrio are approximately 2 µm (0.00008 inches) in length and they move about 200 µm/sec. This is about 100 body lengths per second. Now that seems pretty fast, especially for swimming through something thick. 

How does that compare to our other candidates:

                                                Avg. Length            Top speed (kph)               Body lengths/sec
Cheetah                                     125 cm                         112.7                                     25.0
White throated needle tail           25 cm                         160.9                                    178.7
Sailfish                                      340 cm                         109.4                                      8.9
Vibro cholerae bacteria            0.0002 cm                   0.00072                                   100
S. Giant Darner dragonfly          12.7 cm                       57.9                                       126
Australian tiger beetle                0.10 cm                        9.01                                    2502.8

So the bacteria are pretty fast, it just depends on how you measure it. But the needle tail still holds its own, even though it is only traveling through air. Comparatively, Usain Bolt moves at a top speed of about 6.2 body lengths/sec. Since humans walk upright, we could measure him at body depths/sec, which makes him sound faster, about 30 body depths/sec (assume 15 inch body depth). But we don’t all run like Usain Bolt.

Black horseflies can measure up to 1 inch in length. They
pester people and domestic animals, but worse, can carry
mosquitoes, only the females feed on blood, the gentler
males prefer nectar and help pollinate many flower species.
I could make an analogy between horseflies and humans,
but I won’
In the table above I gave you a couple more examples so that we can find an overall winner.  As always, nothing seems to top the insect world, the Australian tiger beetle can move at over 2500 body lengths/sec, while the darner dragonfly shown above is merely the scientifically confirmed fastest flying insect. However, if you want to go with the most recent estimate for the male horsefly (Hybomitra hinei wrighti), we are talking about speeds of 145 kph when he's in pursuit of a female- typical male behavior. That works out to roughly 4000 body lengths/second!

Next week we can look at plants lifting weights; they have to be in shape in order to photosynthesize!

Penny E. Hudson, Sandra A. Corr and Alan M. Wilson (2012). High speed galloping in the cheetah (Acinonyx jubatus) and the racing greyhound (Canis familiaris): spatio-temporal and kinetic characteristics J Exp Biol DOI: 10.1242/​jeb.066720

Wilson RP, Griffiths IW, Mills MG, Carbone C, Wilson JW, & Scantlebury DM (2015). Mass enhances speed but diminishes turn capacity in terrestrial pursuit predators. eLife, 4 PMID: 26252515

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