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.