Small
Wonders: Design in Tiny Creatures
December
2, 2019, 5:52 AM
[[Yes –
everything is much much more complicated than we thought.]]
Miniature designs often require
more foresight and delicate engineering than large designs. For example, think
of how difficult it would be to design a nano air vehicle (NAV) that could flip
over and land feet up on a glass ceiling. Yet we hardly notice when a fly does
that. Scientists who look more closely at these things often stand in awe of
what animals do. Here are some small wonders that deserve our admiration and
respect.
The Fly
Scientists from the U.S. and
India slowed down and magnified how flies could land on a ceiling. In their
paper “Flies land upside down on a ceiling using rapid visually mediated
rotational maneuvers,” published in the AAAS open-access journal Science Advances, they share what they
learned.
Flies
and other insects routinely land upside down on a
ceiling. These inverted landing maneuvers are among the most remarkable
aerobatic feats, yet the full range of these behaviors and their underlying
sensorimotor processes remain largely unknown. Here, we report that successful
inverted landing in flies involves a serial sequence of
well-coordinated behavioral modules, consisting of an initial upward acceleration followed
by rapid body rotation and leg extension, before
terminating with a leg-assisted body swing pivoted around legs
firmly attached to the ceiling. Statistical analyses suggest that rotational
maneuvers are triggered when flies’ relative retinal expansion velocity reaches
a threshold. Also, flies exhibit highly variable pitch and roll rates,
which are strongly correlated to and likely mediated by multiple
sensory cues. When flying with higher forward or lower upward velocities,
flies decrease the pitch rate but increase the degree of leg-assisted swing,
thereby leveraging the transfer of body linear momentum.
[Emphasis added.]
Penn State researchers, who participated
in the study, call this “arguably the most difficult and least-understood
aerobatic maneuver conducted by flying insects.” Lead author Bo Cheng said,
“Ultimately, we want to replicate that in engineering, but we have to
understand it first.” The team was astonished to see how the fly could achieve
four “perfectly timed maneuvers” to land upside down in the blink of an eye:
acceleration, cartwheel, leg extension, and whole-body swing assisted by the
legs.
The fly’s maneuvers “exhibited
remarkably high angular velocity,” the scientists found, as they watched how
the small insect “cartwheels” around its forelegs. Its body comes well equipped
to handle the strain. “This process relies heavily on the adhesion from cushion-like
pads on their feet (called pulvilli), which ensures a firm
grip, and the viscoelasticity of the compliant leg
joints, which damps out impact upon contact.” The research
team was apparently too fascinated with the aerodynamics to speculate about
evolution.
A fly is also well-equipped for
stable flying. Michael Dickinson has been studying insect flight for years in
his specialized lab at Caltech. His team published another “remarkable” paper
in Current Biology, reporting that “Flies
Regulate Wing Motion via Active Control of a Dual-Function Gyroscope.” Fruit
flies are members of Diptera (two-wing), because their shriveled-up hind wings,
called halteres, have been considered vestigial flight wings. Some have thought
they function as gyroscopes. Dickinson decided to test that idea:
Flies
execute their remarkable aerial maneuvers using a set of wing
steering muscles, which are activated at specific phases of the stroke
cycle. The activation phase of these muscles — which determines their
biomechanical output — arises via feedback from mechanoreceptors at
the base of the wings and structures unique to flies called halteres. Evolved
from the hindwings, the tiny halteres oscillate at the same frequency
as the wings, although they serve no aerodynamic function and are
thought to act as gyroscopes. Like the wings, halteres possess
minute control muscles whose activity is modified by descending visual
input, raising the possibility that flies control wing motion by
adjusting the motor output of their halteres, although this hypothesis
has never been directly tested.
Evolutionists who have treated
halteres as useless vestigial organs are now going to have to explain even more
function than previously thought.
Our
results suggest that rather than acting solely as a gyroscope to
detect body rotation, halteres also function as an adjustable clock to
set the spike timing of wing motor neurons, a specialized capability that evolved from
the generic flight circuitry of their four-winged ancestors.
In addition to demonstrating how the efferent control loop of a sensory
structure regulates wing motion, our results provide insight into the
selective scenario that gave rise to the evolution of halteres.
But if the halteres serve useful
timing and control functions now, who is to say they were not original
equipment? After all, dipterans in general are among the most versatile flyers
in the insect world. If something works, as Paul Nelson has pointed out, it’s
not happening by accident. “Although the haltere is commonly described as a
gyroscope,” Dickinson’s team says, “the structure is better interpreted
as a multifunctional sensory organ.” Compared with other insects with four
wings, flies have this advantage: “the wing mechanoreceptors can never provide
as clean a clock signal as the mechanoreceptors on a haltere.”
At best, the benefit can be seen as subfunctionalization of working hindwings.
That would represent an example of devolution, not evolution of new functional
traits. Like a driver low on gas, he eliminated the trunk to get better gas
mileage.
Rapid Antics
A new land speed record has been
discovered in ants. New Scientist writes, “Desert ant runs
so fast it covers 100 times its body length per second.” Reporter Michael
Marshall doesn’t say if the ant cries “Ouch!” at every footstep on the hot
Sahara sand, but this ant looks like a blur as it runs, imitating the Road
Runner of cartoon fame. The ant’s trick is to synchronize all six legs and take
up to 47 steps per second. Hunting for heat-exhausted insects in the daytime,
the Saharan silver ant has another adaptation: its body is coated with silvery
hairs that beat the heat.
Nature’s coverage includes a video showing
the ant’s running technique slowed down by a factor of 44 — and that is still
almost too quick to concentrate on. Galloping at 85 centimeters per second, the
ant practically flies with all its feet off the ground at some points in its
gait. Touching down with three feet on the ground at a time also gives it
stability, like a tripod, that helps keep the ant from sinking into the sand.
Burrow Masters
NASA’s engineers are trying to
solve a problem with their newest lander on Mars, named Insight. Its “mole,” an
instrument designed to burrow 16 feet into the Martian soil to measure
Marsquakes, is stuck at 14 inches. It was equipped with an inertial hammer for
digging, but the soil is proving harder than expected, JPL says. Perhaps they should have
mimicked earthworms instead. How do soft, squishy animals manage to loosen the
soil so effectively?
Helen Briggs of BBC News reports that “The first
global atlas of earthworms has been compiled, based on surveys at 7,000 sites
in 56 countries.” The atlas of global earthworm diversity, published by the
AAAS in Science, begins by explaining why this is
important. “Earthworms are key components of soil ecological communities, performing
vital functions in decomposition and nutrient cycling through
ecosystems.”
Separately, Liu et al. in Current Biology investigated how
“Earthworms Coordinate Soil Biota to Improve Multiple Ecosystem Functions.”
Their key concept was “multifunctionality” of soils, which refers to
“aggregated measures of the ability of ecosystems to simultaneously provide
multiple ecosystem functions.” Their experiments and observations showed that
worms offer their vital contribution primarily by “shifting the functional
composition toward a soil community favoring the bacterial energy channel and
strengthening the biotic associations of soil microbial and microfaunal
communities.” Less important were their effects on soil structure and pH. In
other words, earthworms cooperate with the soil biota to promote the most
possible ecosystem functions.
One cubic meter of soil can
contain 150 individual earthworms, the BBC says. How do soft, flexible
earthworms squeeze through hard soils, then accomplish so much multifunctional
good with small brains and no eyes? These papers don’t get into that, but
suffice it to say, without them, Earth soil would likely be as inhospitable as
that on Mars.
A Dynamic Planet
At many levels, our privileged
planet was designed with the foresight to promote habitability. Environments on
a dynamic planet are likely to change. When the habitat changes, organisms must
be flexible enough to adapt. Intelligent design theory can support
diversification, the “lawn” of life branching at the tips, instead of Darwin’s
tree with a single root. The silver Sahara ant, for instance, could have
diversified from other ants once the Sahara dried up from its former riparian
habitat (as evidenced by river channels detectable under the sand). It would
only require modifications or exaggerations of existing traits: body hairs,
legs, and behaviors.
There are some 6,000 species of
earthworms, including species just a few centimeters in length to giants as
long as 3 meters; these also could have diversified based on their local
environments. A fly’s hind wings could shrink and degrade if the wings
subfunctionalized, moving from multiple purposes to focus on the most important
for its needs. This is not too different from blind cave fish that, having lost
eyes, compensate with exaggerated senses of touch and smell.
None of these considerations
affect the argument from design. Wings, legs, and the ability to burrow do not
happen by accident. We can marvel at the foresight built into these creatures
that become champions at particular traits in their respective family contests.
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