3. Chemical Communication and Semiochemicals: Olfaction

What are the two major sensory modalities in chemoreception?

Smell (olfaction) and Taste (gustation)

- they work together!

What is olfaction?

Olfactory reception, or the sense of smell.

What is gustation?

Contact reception, or the sense of taste.

What environmental factors affect the transmission of chemical signals?

Fluid dynamics, thermodynamics, and micrometeorology.

Distance issue (from sender to recipient)

Volatile molecules do not move quickly

Types of transmission

Current flow of fluids

Diffusion (on a gradient)

Direct contact

Difference with physical stimuli (visual and auditory)

Directionality, Speed, Temporal pattern, Spectrum

Directionality

Irregular path, from high to low concentration of odorant molecules

What will influence directionality

Currents

Speed

Diffusion is slow... based on movement of individual molecules

Temporal pattern

Almost none, or quickly lost after released. Diffusion and current flow in fact often break temporal patterns

Spectrum

No physical continuous dimensions

Hydro-solubility

Water-solubility, evaporates fast > gets message out faster

Lipo-solubility

Fat-solubility, doesn't evaporate > message lasts longer

What is solubility determined by

The molecule's polarity

What is the significance of molecule polarity in solubility?

Polar molecules dissolve in water, while non-polar molecules dissolve well in oils.

- polar bears like water!

What is the difference in solubility for large versus small molecules?

Large molecules do not dissolve or evaporate well, while small molecules do.

The production of chemical signals is highly determined by

The type of transmission and the medium

What type of odours are typically hydrophobic?

Contact odours, often pheromones, which are usually lipids or large hydrocarbons.

Size-restriction of molecules in waterborne

Do not count, heaviness of the molecules matters less

What is required for waterborne odourants?

They need to be water-soluble and are often large organic compounds.

Airborne odourants 3 factors

Volatile, Stimulus, and Environment

Airborne Volatile

evaporation needed

airborne stimulus

molecular size, weight, and shape are important

airborne environment

Wind and convectional turbulences

Atmospheric conditions

Micro-meteorology

Pedology

What are scent plumes related to

Climatic/environmental factors

What is a scent plume?

A visualization of wind movement, showing how scent molecules disperse. SMOKE BOMB

Smoke bomb

Skin flakes, hair, etc

- dog manhunt on campus

What is the key issue with understanding scent plumes

Stability of atmospheric (macro and micro)

- ground temp and air temp

The greater the difference in air and ground temp means what

the more unstable the air and the greater the turbulance

Trailing

Following scent > highest gradient concentration BEFORE acquiring source

- find the track

Trailing includes what

Air scenting

tracking

on actual tracks, AFTER acquiring source

What is the main interference of scent plumes

1. Wind

then temperature, humidity, and barometric pressure

What is the significance of diffusion in odour transmission?

Diffusion is dominant in the absence of current flow and is influenced by the size and interaction of molecules.

How does barometric pressure affect scent transmission?

Hyperbaric and hypobaric conditions

Hyperbaric conditions (high pressure)

scent dissipates quickly but hugs the ground

- pushes it down

Hypobaric conditions (low pressure)

initial scent travels higher and further

What does hypobaric conditions smell like

rain

- presence of anions/negative ions

- until fog, snow, etc

Interacting actors of temperature

Evaporating point, molecular weight, boiling point

Low evaporation at low temperatures

Slow fading

High evaporation at high temperatures

quick fading

Low evaporation at high molecular weight

oils and other fatty substances

Boiling point

Low boiling point > more likely to smell than high boiling point substances

Thermal convection and turbulence at high temperature

High temperature = thermal convection = high turbulence

High humidity in the air (close to or at saturation)

Decreases the spread of odours

- BAD for TRAILING

High humidity in the ground

will trap odours at ground level

- GOOD for TRACKING