Chemical Signals
• Types
• Production
• Transmission
• Reception
Olfactory signal features
• Directionality– Generally propagate away, but rarely linear
• Transmission speed– Depends on diffusion rates, wind speeds
• Temporal pattern– Difficult to turn on and off
• Spectrum– Multi-dimensional
Chemical signals
• Hormone– Chemical signals used within individuals– Produced by endocrine glands
• Pheromone– Chemical signals used between conspecifics– Produced by exocrine glands
• Allomone– Chemical signals used between species
Pheromone examples
Diffusion rate is inverselyrelated to molecule size.Small compounds are volatile.Large compounds canpersist
Odor glands in mammal skin
Vertebrate glands
Scent dissemination strategies
Female marking by greater spear-nosed bats
Multi-modal signalling in sac-winged bats
Scent glands in ants
Diffusion of a scent puff
K = threshold of detection, rA = active space, t = time
Active space is dynamic
There is a maximum size ofactive space which is set bythe detection threshold andamount of odorant released
Media affects transmission
Q = number of molecules releasedK = detection thresholdD = diffusion rate
Diffusion from a trail
Treat as if there are a series of single emissions from a moving source
Diffusion in laminar flow
Diffusion in turbulent flow
Moth active space in wind
Insect odor receptor organs
Insect olfactory sensilla
Vertebrate odor receptor organs
Vomeronasal organ detects steroid hormones in urine
Olfactory receptor cell
Olfactory receptor proteinshave 7 trans-membranedomains, but belong to a gene family with over1000 loci. Receptor cellsAre short-lived (< 60 d),and express a single protein.creates odor-topic map inolfactory bulb
Gradient detection and orientation
• Simultaneous sampling– Requires paired olfactory receptors at sides of
body.– Need wide head or nose on appendage
(antenna)
• Sequential sampling– Animals follow concentration gradient, requires
tracking back and forth across trail.
Moth scent tracking
Animals follow concentrationgradient, requires trackingback and forth across trail.Some have paired olfactoryreceptors at sides of body.