Ch.6 Chemical signals

Propagation

Molecule itself must be detected, and can move by
current, diffusion, or direct contact. This refers to the movement and spread of molecules through a medium

Propagation impacts

Directionality, speed, temporal pattern, and spectrum

Hormones

a regulatory substance produced in an organism and transported in tissue fluids such as blood or sap to stimulate specific cells or tissues into action

Semiochemicals

chemical signals emitted by organisms (plants, animals, insects) that induce behavioral or physiological responses in others, acting as crucial communication tools

Pheromones

chemical signals released by animals and insects to trigger social, reproductive, or behavioral responses in members of the same species. They work as specialized, often wind-borne, chemical messengers that communicate danger, territory, or mating availability, frequently detected via a specialized organ.

Volatility

The ability of pheromone molecules to easily evaporate or sublimate into the air from a liquid or solid source, enabling them to travel through the atmosphere and act at a distance from the producer.

How does oxygen effect volatility

Oxygen acts as a primary degradative agent on airborne pheromones, reducing their volatility and effectiveness by breaking down compounds containing double bonds and aldehyde groups. Oxygen can create dipole interactions (diminish volatility)

Specificity

the ability of chemical signals, transmitted through the air, to elicit precise behavioral or physiological responses exclusively in members of the same species. It ensures that the signal is understood only by the intended recipients, often involving a unique chemical compound or a specific ratio of a mixture (blend) of volatile compounds that only conspecifics can detect and act upon

Too small and _____ is insufficient

specificity

Too big and _____ is insufficient

volatility

_______ is important for airborne odorants.

Volatility

Waterborne pheromones

a chemical substance released by an aquatic organism into the surrounding water that triggers a specific behavioral or physiological response in other members of the same species

______ is not applicable for waterborne chemicals.

Volatility

waterborne chemicals will float if

they are mostly made of carbons and hydrogens

____ pheromones are water soluble

Waterborne

Waterborne chemicals need to be _____ for ____ and _____

water soluble; dispersal and detection

____ pheromones are characterized by their high solubility and polar chemical nature

Waterborne

Solubility is dictated by ____

polarity

Longer carbon chains make molecule less ___, decreasing _____

polar ; solubility

Contact Pheromones

chemical substances secreted by organisms, such as sweat or oil, placed and left in environment, that cause behavioral or physiological responses in others of the same species upon physical contact or close proximity

______ pheromones are typically hydrophobic

Contact

Cuticular Hydrocarbon blends

vital contact pheromones and recognition cues for mate selection, kin recognition, and social regulation in many insects

Cuticular Hydrocarbon blends are

Species specific; Non-volatile, so contact receptors on antenna or feet must be used; Colony insects groom each other, creating a colony specific blend

an exposed gland allowing the pheromone to evaporate is a method of

dissemination by direct release into air/water

the spraying of a pheromone is a method of

dissemination by direct release into air/water

self-generated currents

(fluid movement) in aquatic species, such as crabs, act as convective transport mechanisms, fanning chemical pheromones toward potential mates. These active, voluntary currents help convey sexual signals over distance, often carrying volatile fatty acids or lipids released via urine or skin, which are then detected by the recipient's sensory antennas.

self generated currents are a method of

dissemination by direct release into air/water

Using hair dispersal to increase surface area for vaporization is a method of

dissemination by deposition onto the senders body

Grooming is a method of

dissemination by deposition onto the senders body

Harderian glands

Glands found in many animals that function as pheromones to signal reproductive state, stress, and identity. These secretions are disseminated onto the fur through specialized grooming behavior, acting as a key mechanism for social and sexual communication.

Uropygial gland

Glands found at the base of bird tails used to disseminate lipid-based pheromones and preen oil by rubbing being rubbed against by their beak or head.

Passive dissemination

dissemination of pheromones involves the slow, continuous release of chemical signals into the environment without active propulsion or energy expenditure by the producer. Common in insects and some mammals, this method relies on evaporation from specialized glands, bodily fluids (urine, sweat), or synthetic dispensers, influencing behavior like mating or alarm responses.

Passive dissemination is a method of

dissemination through deposition onto solid substrates

Conjugated steroids

steroid hormones (testosterone, estrogen, corticoids) that have been bound to another molecule by liver for excretion purposes

Diffusion

spreads pheromones over short distances through random movement; Molecules move from areas of high concentration to low concentration. It is inherently slow and generally effective only for short-range communication

Current flow

responsible for long-range transport, often creating turbulent, patchy plumes that allow insects and animals to track signals to their source; Transport is driven by wind, water, or active fanning. This mechanism moves pheromones rapidly and is responsible for creating filamentous, intermittent "patches" of odor, rather than a smooth gradient

What two mechanisms does the dissemination of pheromones rely on

Diffusion and current flow which determine the speed, range, and structure of the signal

Diffusion becomes ____ relevant as current increases

less

Reynolds number (Re)

tells you whether diffusion or current flow will be more relevant

Small Re means ______ is more relevant

diffusion

Large Re means ______ is more relevant

current

Re =

(Flow velocity * dispersal distance)/ fluid viscosity

Diffusion coefficient (D) is affected by

Size of molecule, How molecule interacts with medium, How molecules in medium interact with each other

Active Space

area around source in which a receiver may detect stimulus

Active space depends on

Q - how much pheromone is released(moles)

K - how sensitive receiver is to pheromone (moles/mm³)

Active space increases as long as there is

a gradient of increasing concentration >K

when molecules will disperse faster than they arrive at the active space boundary, active space ____

begins to shrink

equation for Max active space

r_max = (3Q/4πK)^1/3

equation for time to reach max active space

t_max = r²/D

Costs that come with diffusion

Current flow takes over at distance regardless, Body size limits Q(how much pheromone is released), Diffusion can be slow, especially in water

Transmission by current flow is ___ than diffusion

Faster

Transmission by current flow goes farther than diffusion because

molecules are not spreading in all directions... concentrations in plume remains higher

Laminar flow

All parts of medium move in same direction with same velocity

Turbulent flow

Flow hindered in one location relative to another...generating torque on the fluid and generating vortices in very unpredictable and complex patterns

How does air temperature affect Chemical signal propagation

Can affect volatility of compounds, Organisms evolve compounds that work best at temperatures they live in

How does UV radiation affect Chemical signal propagation

Ionizing energy denatures compound

How does moisture and humidity affect Chemical signal propagation

Water molecules compete with pheromones for substrate binding sites, Volatile molecules evaporate more quickly when moisture or humidity are higher

Detecting airborne or waterborne chemical

Likely from distant sources...so sparse density, Need to sample a lot of air or water quickly

n vertebrates, most air goes to lungs/gills...but a portion of air directed to chamber containing _____ _____

olfactory epithelium

Terrestrial vertebrates can increase portion of air
moving over olfactory epithelium by _____ or ______

sniffing harder or scrunching nose

Arthropods have ____ covering antennae for olfactory sensing

sensilla

Contact receptors

important for detecting nonvolatile and insoluble compounds, used to detect cuticular chemicals in insects

Kinesis

“Random” walk in which the speed, or rate of turning changes in response to stimulus...but turns are random with respect to the stimulus source

Taxis

Organism detects orientation of active space relative to itself, and turns appropriately (toward or away the stimulus)

Tropotaxis

Taxis that involves 2 receptors sampling simultaneously usually on different parts of the body

Klinotaxis

Taxis that involves sequential sampling by a single receptor moved through the active space

polarized odor trails

chemical scent paths that convey directional information, allowing insects, animals, or dogs to determine which way to follow the trail

Anemotaxis

coupling orientation of current flow with detection of chemical to discern direction

rheotaxis

coupling orientation of current flow with detection of chemical to discern direction in water

Casting

a technique used by animals to locate a scent source by moving in a crosswind, zigzag pattern when the odor plume is lost