Type of Stimulus Carried by Pheromones

Pheromones are:

Correct Answer: Olfactory stimulus

Pheromones are chemical messengers that carry information between individuals of the same species and act as an olfactory (smell-based) stimulus.

Key Facts About Pheromones

• Pheromones are chemical signals detected by the Vomeronasal organ (VNO), also known as the organ of Jacobson
• Located in the roof of the mouth or nasal cavity in most vertebrates
• They act within the same species (intraspecific communication) — not between different species

Important Pheromones in Animals

• Bitch (female dog) estrus: Vaginal secretion contains methyl-p-hydroxy benzoate
• Boar (male pig) saliva: Contains 5α-androstenone — triggers the standing reflex (lordosis) in sows

Classical Pheromone Phenomena in Mice

• Whitten effect: Introduction of a male mouse into a group of female mice → release of GnRH → synchronization of estrus in females
• Bruce effect: Introduction of a strange male mouse into recently bred females → blockage of prolactin release → termination of pregnancy
• Ram effect: Similar to Whitten effect but in ewes (female sheep) — introduction of a ram synchronizes estrus