Chemosignals are chemical substances released by an organism that carry information, influencing the behavior or physiology of others. This form of communication is fundamental across the biological world, used by life from single-celled organisms to complex mammals. The process involves the production and detection of these chemical signals, which can be released from specialized glands. These signals can also be influenced by factors like an organism’s age, health, and emotional state.
The Function of Chemosignals in Animals
In the animal kingdom, chemosignals serve many functions related to survival and reproduction. For social insects like ants, these signals create trails to food sources. An ant discovering food deposits chemical markers on its return to the nest, creating a path for its colony members to follow.
Some species use chemosignals to alert others to danger. When certain fish are injured by a predator, their skin releases an alarm substance into the water. Nearby fish of the same species detect this chemical, prompting them to flee or hide. This rapid, silent alarm system increases the chances of survival for the group.
Mammals use chemosignals to establish and maintain territories. Wolves, for example, deposit urine and other secretions at the boundaries of their domain. These scent marks contain chemicals that communicate the wolf’s identity, social status, and readiness to defend its area, which helps avoid direct confrontations.
Chemosignals are also integral to reproduction. The female silk moth releases a potent airborne chemical called bombykol, which can attract male moths from great distances. The males’ highly sensitive antennae can detect minute quantities of this signal, guiding them to a potential mate. This long-range attraction is a powerful example of how chemical messages facilitate reproductive success.
Pheromones and Other Chemical Messengers
The category of chemosignals is divided into classes based on who sends and receives the message. The most well-known are pheromones, which are chemicals that trigger a response in other members of the same species (intraspecific). The ant’s trail-marking chemical and the fish’s alarm substance are both examples of pheromones.
Chemical signals that travel between different species (interspecific) are known as allelochemicals. Allomones are signals that benefit the sender but not the receiver. The defensive spray of a skunk is a powerful allomone; it repels potential predators, benefiting the skunk while having a negative effect on the recipient.
Conversely, kairomones are interspecific signals that benefit the receiver at the expense of the sender. A predator that hones in on the scent of its prey is responding to a kairomone. For example, a pine beetle can detect the chemicals released by a stressed pine tree, allowing it to find a vulnerable host. In this case, the tree unwillingly signals its weakness to the beetle’s advantage.
Chemosignals in Humans
While human communication is dominated by language and sight, research shows we also produce and respond to chemical signals, often without conscious awareness. Studies have explored emotional contagion through chemicals in sweat. When individuals were exposed to sweat from people experiencing happiness, their facial expressions showed more muscle activity associated with smiling. Conversely, sweat from people feeling fear induced greater activity in facial muscles associated with fearful expressions.
Tears have also been identified as a source of human chemosignals. Research has shown that when men sniffed odorless emotional tears from women, they experienced a reduction in self-reported sexual arousal and a decrease in testosterone levels. Subsequent imaging revealed that sniffing the tears reduced activity in brain areas linked to sexual arousal.
Many animals detect chemosignals using a structure called the vomeronasal organ (VNO), or Jacobson’s organ. This auxiliary olfactory organ is located in the nasal septum of most mammals, reptiles, and amphibians. While humans are born with a VNO-like structure, its functionality is debated. Many researchers believe the human VNO is vestigial, as the genes for its receptors appear non-operational.