Pheromones
Pheromones are chemical communication signals between organisms of the same species. A sender emits minute amounts of pheromone into the environment, and a receiver detects the signal in specialized olfactory receptors. Pheromones deliver information about food, domination, sex, and territory. Their advantage is that they can be transmitted in the dark and around obstacles. In addition, a small amount lasts for hours or even days, and has a good range. A disadvantage of pheromones is that they depend on diffusion or currents for transmission and that can be a slow process.
Many types of seaweed use pheromones for sexual reproduction. When an egg breaks out of the female sex organ, oogonium, at the tip of the plant, it sinks to the ocean floor and secretes pheromones into the water. Drifting parcels of sperm detect the chemical signal, burst open, and release the sperm. The male gametes swim toward the source and swarm around the egg. One billionth of a gram of pheromone from the egg is enough to signal the sperm.
Insects use pheromones in their reproductive and social behaviors. A female silkworm produces a pheromone called bombykol. A male's antenna detects the pheromone from several kilometers or miles away. Bombykol is so potent that the male responds when it stimulates only forty out of his 40,000 receptors. Ants use pheromones for alarm signals, recognition odors, and trail marking. During trailing behavior, scout ants release pheromones that guide other ants to the food. Worker honey bees perform round dances and waggle dances in the hive to communicate the distance and direction of food outside the hive. Scientists believe that pheromones help reveal the food source location as well. The queen bee also produces pheromones that help control the activities of the hive. Farmers use pheromones as a safe way to control the insects that destroy their crops. A pheromone spray distracts the males and keeps them from finding females. This reduces the insect population.
Vertebrates use pheromones for sex attractants, dominance, and marking territory. It is familiar to see dogs use urine to mark their territory. Canadian researchers report a more unusual behavior in snake mating behavior. Every spring, tens of thousands of redsided garter snakes emerge from hibernation looking for mates. When a female awakes, a swarm of males piles around her forming a mating ball of about 100 snakes. The males flick their pink, black tipped tongues, rub their chins up and down the female's body, and undulate until she picks a mate. How the female picks a mate is a mystery, but some researchers believe that it depends on pheromones.
Studies show that pheromones play a role in human behavior. In 1971, biophysicist Martha K. McClintock at the University of Chicago reported that women who live in college dormitories tend to have coinciding menstrual cycles. Scientists theorize that pheromones synchronize the monthly cycles of women living in close quarters. Experiments done by McClintock and her colleague Kathleen Stern support the pheromone theory.
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