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PSY 2364Animal Communication

Figure 1

Animal signals Mark E. Laidre, Rufus A. Johnstone Current Biology 2013 23, R829-R833DOI: (10.1016/j.cub.2013.07.070)

Midterm

• Wednesday October 2 – midterm exam

• Midterm exam review sheet is posted on the course web page

http://www.utdallas.edu/~assmann/PSY2364

Sound localization

• Marler (1955) first studied alarm calls in different species of small passerine birds and found important acoustic similarities:

– Single, brief duration “seet” call

– Low amplitude

– High frequency (narrowband)

– Gradual onset

Sound localization• Marler (1955) found that mobbing calls are

repeated, loud calls that attract others. Unlike alarm calls, mobbing calls consist of:

Repeated series of loud “chuck” calls

Wide range of frequencies (broadband)

Sudden sharp onset and offsets

Sound localization

• Marler suggested that alarm signals are shaped by strong selection pressures. Alarm calls reveal a clear trade-off between detectability and localizability.

• Small animals are better at detecting highfrequencies than larger animals (e.g. predators)

• Sounds with a narrow band of frequencies and gradual onsets and offsets are hard to localize.

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Marler’s hypothesis

1. Small animals are better at detecting high frequencies than larger animals (e.g. predators)

2. Sounds with gradual onsets and offsets are hard to localize

3. Narrowband sounds are harder to localize than broadband

4. High frequencies are linked to fear rather than attack

5. Mobbing calls are repeated in a loud voice to attract others

Alarm call detection

1. Amplitude of signal at the source

2. Attenuation characteristics of environment

3. Signal-to-noise ratio at the receiver

4. Sensitivity and discrimination ability of the receiver

Depends on:

Adaptation hypothesis

• Any given sound in the repertoire of a species has been favored by natural selection because its influence on the behavior of other animals is beneficial(i.e., raises the fitness of) the sender and/or his or her close relatives.

Marler’s hypothesis

• Marler (1955) identified some important acoustic differences between alarm calls and mobbing calls in song birds. What were these differences, and how did Marler link these properties to the different functions that these calls serve?

Marler, P. (1955). Characteristics of some animal calls. Nature 176: 6-8

Ecological constraintscommunicating via sound waves

1. energy costs2. overcoming environmental obstacles3. locatability of the source 4. rapid fading5. range of physical complexity

Advantages of sound

1. Sound bends around objects (leaves, tree trunks) that are opaque to visual signals

2. Allows for very rapid changes in pattern

3. Can be more precisely timed than chemical signals

4. Rapid signal decay5. More precisely localizable than

chemical signals

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Advantages of sound

6. Useful for small or cryptically colored species (grasshoppers, crickets, frogs, birds), animals that are nocturnal, or live in dimly lit environments.

7. Large body size allows whales and elephants to produce high intensity, low frequency sounds. Both of these properties increase the range (distance) over which they can communicate with conspecifics.

Design features for long distance communication

• Calling individuals select particular depths and channel sounds so that they are detectable over a range as much as 100 miles.

• High intensity, low frequency sounds, large body size, good signal-to-noise ratio.

Honest Signaling

• Rubenstein & Alcock, ch. 8

• Less contact and fewer aggressive interactions with mating rivals in male European toads when calls were higher in frequency.

• Higher attack rate with small toads (top left) compared to large toads (top right).

Davies and Halliday, 1978

Vocal signals and body sizeOptical Communication

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Optical Communication

• Radiant energy from the visible range of the spectrum of electromagnetic radiation

• Sources of light: the sun, burning objects, lightning, artificial (man-made) lights, bioluminescent plants and animals

• reflected vs. self-generated light

Electromagnetic spectrumDestroys bonds Increases Increases Absorbed

electron energy rotational energy by ions

One nanometer (nm) = 1 x 10-9 meters

,microwave

Color vision and pitch compared

• The human visual system is sensitive to light wavelengths between approximately 380 and 750 nm (or frequencies between 400 and 790 THz), spanning just under 1 octave (a doubling in frequency), which we perceive as the spectrum of colors. In contrast, the human auditory system is sensitive to sound frequencies between 20 Hz and 20,000 Hz, or approximately 10 octaves, which we perceive along the dimension of pitch. (Oxenham, 2019)

Properties of light

• Different frequencies of light are perceived as different colors

• Light varies in intensity

• Light follows the inverse square law

• Wavelength-specific and medium-specific attenuation (selective filtering)

• Light is directional

Properties of light

• Light speed varies depending on the medium, so light shows 3 other properties in common with sound:– reflection

– refraction

– diffraction

Factors affecting opticalsignal transmission

• Absorption- optical energy is lost (absorbed) as it travels through the medium.

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Factors affecting opticalsignal transmission

• Diffraction- light waves bend and spread out as they travel through a narrow aperture.

– Diffraction effects are pronounced when the propagating wavelength is similar in size to the diffracting object

Factors affecting opticalsignal transmission

• Reflection- Optical energy is redirected when it strikes a surface, usually back to its point of origin.

Factors affecting opticalsignal transmission

• Refraction- is the change in direction of a wave due to a change in its speed, most commonly observed when a wave passes from one medium to another.

Optical Communication

• Badges are morphological specializations used as visual signals, such as bright patches of skin, fur, or feathers, horns, casques, or crests.

Example: Use of badges

Anolis carolinensis – Green Anole lizard

Source: http://animaldiversity.unmz.umich.edu/index.html

dewlap

Optical signals for survival

• Camouflage– Color/shape of animal similar to

(usually non-living) background (e.g. snowshoe hare)

• Mimesis– Mimics another plant or animal for

camouflage (e.g. stick insects)

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Sad Underwing Moth

Kingdom: Animalia

Phylum: Arthropoda

Subphylum: Hexapoda

Class: Insecta

Order: Lepidoptera

Family: Erebidae

Genus: Catocala

Species: maestosa

Optical signals for survival

• Aposematic signals: warning signals associated with the unpalatability of a prey animal to potential predators

Optical signals for survival

• Mimicry– An animal species (the mimic) has evolved to

share the visual properties of another animal (the model) through the selective action of a signal receiver (the dupe).

Monarch Viceroy

Optical signals for survival

• Batesian mimicry– one species has evolved to mimic the warning

signals of another species directed at a common predator.

Monarch Viceroy

Optical signals for survival

• Batesian mimicry: one species has evolved to mimic the warning signals of another species directed at a common predator.

• Müllerian mimicry: convergence between two or more species to warn predators of their unpalatability.

Optical signals for survival

Milk Snake(Lampropeltis triangulum)

Coral Snake(Micrurus tener)

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Example: Rapid color changes

Anolis carolinensis – Green Anole lizard

Source: http://animaldiversity.unmz.umich.edu/index.html

Example: Rapid color changes

Sepioloidea lineolata – Australian cuttlefish

Kingdom: AnimaliaPhylum: MolluscaClass: CephalopodaOrder: SepiidaFamily: SepiadariidaeGenus: SepioloideaSpecies: lineolata

Source: http://www.cephbase.dal.ca/index.html

Example: Rapid color changes

Sepia officinalis– male squid display zebra stripes only during aggressive conflicts; normal pattern is mottled or blotchy

Kingdom: AnimaliaPhylum: MolluscaClass: CephalopodaOrder: SepiidaFamily: SepiadariidaeGenus: SepiaSpecies: officinalis

Blue-ringed Octopus(Hapaloclaena lunulata)

1. Warning coloration(blue rings signal danger)

2. Concealing coloration (body colors match coral surroundings)

3. Disruptive coloration(blotches on the skin disguise the outline of the octopus’ body)

Hawaiian sepiolid squid(Euprymna scolopes)

• Camouflage (keeps a "sand coat" on its dorsal surface)

• Counter-shading (a symbiotic bacteria lives in the sepiolid's light organ to produce a weak light under the body of the animal)

Vampire Squid(Vampyroteuthis infernalis)

• Lives in the dark oxygen minimum layer (600-800 m)

• For its size, it has the largest eyes of any animal

• Named for its jet-black skin (but color varies from black to red to purple depending on light conditions)

• Has photophores; lights all over its body; bioluminescent organs at the tips of each arm

Source: http://www.cephbase.dal.ca/index.html

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Bioluminescence

Scyphomedusa, Atolla vanhoeffenihttp://www.lifesci.ucsb.edu/~biolum/organism/photo.html

Bioluminescence

Deep sea squid,Histioteuthis heteropsis

http://www.lifesci.ucsb.edu/~biolum/organism/photo.html

Bioluminescence (lantern fish) Bioluminescence (firefly)

Kingdom: AnimaliaPhylum: ArthropodaClass: InsectaOrder: ColeopteraFamily: LampyridaeGenus: PhotinusSpecies: ??

Deceptive signaling

“Femmes Fatales”

Males are attracted to the species-specific flashing patterns emitted by females.

Predatory fireflies of a different species, Photuris, mimic the species-specific flashing pattern of a Photinus firefly to attract and eat the male.

A female Photuris firefly eats a male Photinus ignitus to obtain defensive compounds called lucibufagins which are distasteful to predators.

Proceedings of the National Academy of Sciences (Sept. 2, 1997, Vol. 94, pp. 9723-9728)

Visual systems

• Vision provides a means of detecting objects in an animal’s surroundings.– Luminance (intensity differences; brightness)

– Reflectance (spectral composition; color)

• Vertebrate visual systems contain two types of receptors:– Rods are more sensitive in low light conditions

– Cones function in daylight and provide the basis for color vision

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Vision

• Visual systems have evolved to detect light.

• This requires trapping the electromagnetic energy and absorbing it by a receptor molecule. This process triggers an electrical response in the receptor neuron.

Properties of color

• Brightness (intensity)

• Hue (dominant wavelength or frequency)

• Chroma (degree of saturation or purity of the dominant frequency)

Rods and conesTrichromatic Color vision

• Human color vision depends on interactions of three types of cone cells in the retina of the eye, each sensitive to a range of wavelengths of light.

Color vision

• Cone cells in the retina contain a pigment derived from a protein (opsin) linked to a small molecule called retinal. The pigment absorbs light energy (photons) which activates retinal neurons, generating action potentials in the optic nerve.

Color vision

• Two different wavelengths of light can produce the same pattern of activation in a cone cell. The outputs of the cone receptors are combined and must be compared at a higher level of the visual nervous system. Color vision result from a decoding of the outputs of the color receptors by the brain.

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Color vision

• Color vision in birds, lizards, turtles and many fish is based on four types of cone cells (tetrachromatic color vision). These animals can distinguish colors in the near ultraviolet range of the spectrum.

• Old World primates and humans have three color receptors; most mammals have only two types (dichromatic color vision).

Goldsmith TH (2006). What birds see. Sci. Am. 69-75

Color vision

• Evidence suggests that the progenitors of mammals lost two of the four types of cone cells during a period in their evolution when they were mainly nocturnal (and color vision was less important for their survival).

Goldsmith TH (2006). What birds see. Sci. Am. 69-75

Color vision

• African monkeys, apes and humans “reclaimed” a third cone through duplication and subsequent mutation of the gene for one of the remaining pigments.

Goldsmith TH (2006). What birds see. Sci. Am. 69-75

Ruby-throated Hummingbird

Further reading

Acoustical communication

• http://sites.sinauer.com/animalcommunication2e/summary02.html

Optical communication

• http://sites.sinauer.com/animalcommunication2e/summary04.html