A startled pronghorn warns its herd with a smell like buttered popcorn
When a pronghorn antelope senses danger, it flares the white hair on its rump and exposes two glands that release a scent people have likened to buttered popcorn. Humans can smell it 20 to 30 metres downwind. It is one of the few alarm pheromones documented in a mammal, a chemical shout aimed at others of its kind.
A pheromone is a chemical released by one organism that changes the behaviour or body of another of the same species. The word was coined in 1959 by Peter Karlson and Martin Lüscher from Greek roots meaning to carry and to stimulate, shortly after Adolf Butenandt pinned down the first one: bombykol, which female silkworm moths release to draw in mates. Earlier naturalists, including Jean-Henri Fabre and Karl von Frisch, had noticed the effects and given them names such as alarm substances.
Ants are masters of the art. Foragers returning with food lay a scent trail of volatile hydrocarbons that others follow and refresh; because it evaporates fast, the trail fades once the food runs out. Pharaoh ants go further, marking dead-end routes with a repellent signal. Some wasps use scent to guide the whole colony to a new nest, and tent caterpillars move in groups by following pheromone paths. Alarm chemicals make aphids scatter but stir bees, ants and wasps to attack.
Sex pheromones can work over astonishing distances; some moths and butterflies detect a potential mate up to 10 kilometres away. Farmers exploit this with baited traps to monitor orchard pests, and aggregation pheromones help control weevils without toxins, working at tiny concentrations. Sea urchins release chemicals that make neighbours spawn in unison. Even bacteria signal: species such as Bacillus subtilis release substances that prime nearby cells to absorb foreign DNA.
Plants join in too. Some, when grazed, emit signals that prompt neighbouring plants to produce bitter tannins. Whether humans use pheromones remains unsettled, but our noses carry receptors called TAARs that detect volatile amines, and one, hTAAR5, responds to trimethylamine, the compound behind a rotten-fish smell. Intriguingly, the equivalent receptor attracts mice to that chemical but repels rats.
Source: Pheromone
