In the natural world, survival often hinges on an organism’s ability to perceive and respond to its environment. While humans rely heavily on sight and hearing, many creatures possess sensory abilities far beyond our own. Two remarkable examples of this are the greater wax moth, with its astonishing ultrasonic hearing, and the mantis shrimp, known for having the most complex visual system in the animal kingdom. These unique adaptations offer insights into how evolutionary pressures shape sensory organs to optimize survival in different habitats, whether it’s avoiding predation or capturing prey. Through these creatures, we see nature’s incredible diversity in action.
Hearing : The Greater Wax Moth
It goes without saying that us humans have pretty good hearing. Hearing occurs when sound waves stimulate the nerves of the inner ear. The sound then travels through nerve pathways to the brain. The intensity of the sound is measured in decibels (db). To put it into context a whisper is about 20 db, a concert 80-120 db and a jet engine 140-180 db. Humans process sounds between 20-20,000 db. Sounds louder than 85 db is deafening. In terms of sound freguency (Hz) humans can process between 20-20,000Hz. This may seem like a large number but the greater wax moth is capable of hearing frequencies up to 300,000Hz. Human brains cant even process such high frequencies. This sensitivity is mainly an evolutionary adaptation to avoid predation by bats, which use echolocation in the ultrasonic range (typically around 20–120 kHz).
The moth’s ear has evolved to detect these high-frequency bat calls, giving it a chance to escape before it is detected by a hunting bat. The greater wax moth’s hearing is an example of a co-evolutionary arms race between prey and predator. Bats evolved echolocation to hunt at night, while prey like the greater wax moth evolved highly sensitive ultrasonic hearing to detect these echolocation calls and escape.
The greater wax moth’s hearing system is based on two tympanal (eardrum-like) membranes located on the sides of its thorax. These tympanal membranes are connected to a specialized organ known as the acoustic sensilla. Each tympanum is about 50 micrometers thick and vibrates in response to sound waves. Beneath the membrane, sensory cells are embedded within a structure called the Müller’s organ, which is responsible for converting the mechanical vibrations into neural signals.
Key Components of the Hearing System:
1. Tympanal Membrane: A thin, highly sensitive structure that vibrates when exposed to sound waves, particularly in the ultrasonic range.
2. Müller’s Organ: This structure contains the sensory neurons (mechanoreceptors) that detect mechanical vibrations and convert them into electrical signals that can be transmitted to the central nervous system.
3. Auditory Nerves: These nerves relay signals from Müller’s organ to the brain, where they are processed and interpreted as sound.
If you want to learn more about the evolutionary arms race you can watch the video below from Terra Matter. https://youtu.be/YCc2mXHLSQ4
Vision : The Mantis Shrimp
The mantis shrimp is a small marine crustacean known for its lightning fast movement when capturing prey. (There punch has the same acceleration as a 22 caliber bullet). But what sets this animal apart is not its ability to make the surrounding water boil to the temperature of the sun but its excellent vision. They hold the record for the most complex visual system.
Mantis shrimp have compound eyes ( like flies) made up of tens of thousands of ommatidia (elements containing photoreceptors, support cells and pigment cells). They have 12 photoreceptors and can see UV, visible and polarized light. Humans on the other hand have 3 photoreceptors.
Polarized light-----light that vibrates on the same plane
The middle of the eye has six rows of modified ommatidia called the mid band. Each row is specialized to detect a certain wavelength of light or polarized light. The first four rows detect visible light and UV. In fact each row contains a different receptor to detect UV giving the mantis excellent UV vision. The last two rows detect polarized light.
In the ocean light can be polarized when it bounces off molecules in water. Mantis shrimp can see up to six types of polarization. Horizontal, vertical, the two diagonals and two types of circular polarization ( clockwise and anticlockwise).
While polarization can be difficult to intuit, you can imagine light waves as a bunch of different strings that each have one end attached to a wall. If you shake them randomly, they will vibrate in every direction; that is how non-polarized light behaves. If you only the shake the strings up and down, restricting vibrations to one direction, then that is like vertically polarized light. Light can be polarized in different directions. Polarized sunglasses take advantage of this phenomenon: They reduce glare by filtering out horizontally polarized light that bounces off a road or water surface.
Mantis shrimp can as well perceive depth with one eye and move each eye independently. Like most animals they require a form of gaze stabilization
Gaze stabilization: When an organism accounts for visual errors caused by existential factors such as blur in order to have a clear view.
The most prominent forms of gaze stabilization for the mantis shrimp is pitch, yaw and roll (torsional). This allows for rapid colour recognition allowing them to quickly attack prey or make a rapid escape in case a predator is detected.
The extraordinary senses of the greater wax moth and mantis shrimp serve as fascinating examples of how evolution tailors organisms to their environments, leading to remarkable adaptations. The moth’s ultrasonic hearing, an evolutionary response to evade bat predators, showcases the ongoing arms race between predator and prey. Meanwhile, the mantis shrimp’s unparalleled visual system, which includes the ability to detect polarized light and perceive depth with a single eye, highlights the complexities of life beneath the ocean surface. These animals remind us that while human senses are impressive, nature holds many other, sometimes more advanced, sensory systems designed to ensure survival in a wide range of ecosystems. Understanding these adaptations not only broadens our knowledge of biology but also inspires advancements in technology and science.
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