Chemical Signaling in Water & Air: Pheromones, Allelochemicals, Hormones & Neurotransmitters

Chemical signals mediate communication within and between organisms across environments.

1. Pheromones (Intraspecific)

Released by one individual → affects behavior/physiology of same species.

• Releaser: Immediate behavior (sex attraction, alarm, trail)
• Primer: Physiological change (puberty acceleration, estrus synchronization, caste determination)
• Examples: Bombykol (silkworm), queen mandibular pheromone (bees), androstenone (pigs), MHC peptides (mice/humans debated)

2. Allelochemicals (Interspecific)

Between different species. Subcategories:

• Allomones: Benefit emitter (plant toxins deter herbivores; predator repellents)
• Kairomones: Benefit receiver (prey detects predator odor; parasite finds host)
• Synomones: Mutual benefit (flower scent → pollinator gets nectar, plant gets pollinated)

3. Hormones (Endocrine)

Internal signaling: gland → bloodstream → distant target cells. Regulate growth, metabolism, reproduction, homeostasis. Peptide, steroid, amine classes.

4. Neurotransmitters (Synaptic)

Neuron → synapse → target (neuron, muscle, gland). Fast, point-to-point. Acetylcholine, dopamine, serotonin, glutamate, GABA.

Environmental Transmission

• Air: Volatile, low MW (pheromones, plant volatiles)
• Water: Hydrophilic, larger (aquatic pheromones, allelochemicals)
• Contact: Cuticular hydrocarbons, trail pheromones

These systems overlap: e.g., a compound can be a pheromone to conspecifics and a kairomone to predators. Chemical ecology deciphers this language.