Week 6: Communication and Signalling

Communication with signals

• Any senses, including vision, hearing, smell, taste, touch, and electric senses

• Usually leads to a change in behaviour of recipient

• Can result in slower hormonal changes

Signal definition

alters the behaviour of other organisms, have evolved [in signaller] because of that effect, and work because the receiver’s response has also evolved

Cue definition

• Cue is unintentional from ‘signaller’

• Responses to cues are only evolved in the receiver

Multimodal signals

the use of signal components from two or more sensory modalities

Examples of multimodal signal

• jumping spider combines semaphore + vibrations→ needs both for successful mating

• waggle dance

Features of waggle dance

Bee indicates the location of a desirable nest site (or flower patch)

• Direction indicated by the angle of the waggle run relative to plane of gravity → straight, upward movement (vertically against gravity) represents flying toward the sun, and a downward movement represents flying away from the sun

• Distance indicated by the duration of the waggle run

• bees use “optic flow” of landscape to measure distance

Adaptive value of the waggle dance

• Allows bees to quickly exploit resources, before their discovery by other colonies → monopoly of food sources

• Especially important in patchy, compex environments

Pheromone definition

a chemical signal transmitted between individuals of the same species

What remains an essential step for identifying a pheromone?

Bioassay

• analytical method used to determine the potency, concentration, or biological activity of a substance (e.g., drug, hormone, chemical) by measuring its effect on living organisms, tissues, or cells

Examples of pheromones in social insects

• Alarm pheromones

• Trail pheromones e.g. ants, termites

• Primer effects e.g. queen pheromones

How did pheromones evolve

• As a direct consequence of the organisation of olfaction + natural and sexual selection

• Starts with chemosensory receptor proteins: hugely varied & co-opted from different families

Two main routes for pheromone evolution:

1. Sender Precursors

2. Receiver Sensory Bias

Sender precursors

• pre-existing, non-communicative actions or traits (cues) that become modified into signals

Example:

• Hormones leaking from mature females → males smell sensitive to cue + get females first

• Males selected for greater smell sensitivity + receptor specificity

• Females selected to release more as a signal (pheromone)

Receiver sensory bias

male sexual signals evolve to exploit pre-existing sensory, cognitive, or perceptual mechanisms in females that originally evolved for non-mating contexts like foraging.

Multicomponent pheromones

• many ways to vary – no. & position of double bonds, E/Z, functional groups, ratios of existing molecules

• composed of multiple distinct compounds

When might pheromones not change with speciation?

• Alarm pheromones, NOT species specific (most use (E)-β-farnesene)

When will pheromones change with speciation?

Sex pheromones, species specific, multicomponent, much variation between species

Two kinds of signal cost

Efficacy cost

• minimum cost needed to ensure signal can be reliably perceived, e.g. a cricket song loud enough for a female to hear it

Strategic cost (= handicap)

• wasteful “added-cost” on top of efficacy cost

Issue with handicap theory?

no way of separating efficacy and strategic costs

If not handicap, what does keep signals honest?

• Indices: unfakeable signals

• Shared interest and relatedness

• Punishment of cheaters (social cost)

• Other costs e.g predators

Why does ocean acidification have a strong effect on communication and signalling?

• pH changes chemosensory receptor site and/or ligand shape, charge density etc: they no longer activate

• pH 7.8 can stop responses: polychaete worm sex pheromone + crabs to pheromones

How can we assess potential for future adaptation?

• measure standing genetic variation in climate-sensitive traits

• measure plasticity

• evolution experiments in real time