BIEB 166 Lecture 16 (WI13)

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University of California - San Diego
Biol/Ecology, Behavior, & Evol
BIEB 166
James Nieh

Lecture 16 Introduction - To make a sound, an animal must produce a vibration, modify it to make it biologically useful, and then successfully couple it to the medium ○ Solve the impedance problem - This is difficult enough to do that only arthropods and vertebrates use sounds for communication. Production of sound vibrations Monopoles - A sac (balloon-like) that inflates and contracts - Each sacs acts as a monopole - Sound is radiating outwards from the center North American Sage Grouse Frog - Sac expanding and contracting to project sound Fish Swim bladder 1. Regulates the buoyancy of the fish ○ Adjusting the density of the body ○ More dense: sink to the bottom ○ Less dense: rise to a higher level ○ Sac usually filled with gas (nitrogen), and muscles around the sac contracts/relax to adjust the density inside the sac (contracts, higher pressure, higher density, sinks) 2. Rapidly contact and expand the muscles around the swim bladder to produce sound - The fish is in neutral density of the environment around it Dipoles - Something moves back and forth along an axis - Moving between two different poles Water Strider - Moving front legs between two poles back and forth - If the male is larger in size, it would create ripples of larger size ○ Lower frequency in vibrations, longer wavelengths Tetrapoles - Higher order movements Acoustic short-circuiting - Most animals use dipoles - If the vibrator is small relative to the wavelengths begin produced, then the sound produced is easily short-circuited ○ The waves will propagate from one side of the moving surface to the opposite side and thus not radiate any sound outwards - It is difficult for small animals using dipoles to make sounds with wavelengths their size or larger. It is thus better for them to make sounds with smaller wavelengths (e.g. higher frequencies) ○ The waves tend to bend around the animal if the wavelength is larger than their size, then sound cannot be propagated (short-circuited) Cricket 1. If the wavelength is larger than or equal to the cricket length - the sound waves would tend to move back to its body - Each time the wing move, it generates a slight decrease in pressure around the wings ○ In front of the wings: high pressure ○ Behind the wings: low pressure - The easiest thing is for the molecules to move back into the low pressure zone - Decrease the amplitude of the sound transmitted 2. Wavelength smaller than the cricket length - They would tend to be blocked by the animal's body - They would tend to be blocked by the animal's body - Propagate outward to the environment Speaker box - Bass speakers can generate low frequencies (long wavelengths) - The wavelengths are larger than the size of the speaker - If the speakers are not placed in a speaker box, the molecules would tend to move back to the lower pressure zones (back of the speakers) ○ Creating closed short-circuiting - Function of the enclosure of the speakers is to prevent short-circuiting - The body itself is blocking the short-circuiting Short-circuiting Solutions 1. Creating its own "speaker box" Tree crickets - Building itself a speaker box in order to avoid short-circuiting - Unlike many other animals, the tree crickets can communicate with lower frequencies - The males cut a hole into a leaf (shape of their wings), and then they sit in the hole holding their wings at the surface and vibrating them in order to create the sound ○ Sound is creating by the wing and is blocked by the leaf ○ Propagate out into the environment 2. Limit sounds to high frequencies - Higher frequencies -> short wavelength -> no short-circuiting - Frequency multiplier ○ Allow the animals to make higher frequency sounds and thus avoid short-circuiting ○ A single muscular motion (like a single stroke of the leg) would excite a structure to produce multiple vibrations ○ Multiplies the muscles to a structure so that it can produce more shakes Grasshopper stridulation - Ridges along the legs - A single movement of the leg would cause the ridges to produce higher frequencies (multiple vibrations) - Ridges can be found in a multiple different spots on the anim
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