The Invisible Language of Nature

Chemical communication, an invisible yet powerful dialogue within the natural world, plays a crucial role in the interactions between different species. One fascinating aspect of this is the concept of kairomones, chemicals emitted by one species that beneficially affect another, often at the emitter's expense. Unlike pheromones, which influence the same species, kairomones involve cross-species interactions. 

Kairomones are a subtle yet potent force in nature's complex web. For example, human kairomones can significantly influence mosquito behavior. When humans exhale, they release carbon dioxide, L-(+)-lactic acid, and ammonia, unwittingly signaling their presence to mosquitoes. This chemical signal is a dinner bell for these insects, guiding them to their next blood meal. This interaction, while advantageous for the mosquito, is a clear disadvantage for humans, particularly considering the role mosquitoes play in transmitting diseases.

The study of human kairomones opens a window into understanding and potentially controlling mosquito populations. A recent study highlighted the potential of geraniol in reducing mosquito attraction by 69-78% to a mixture of key human kairomones like carbon dioxide, L-(+)-lactic acid, and ammonia.

This chemical dialogue extends beyond animals to the plant kingdom. Plants, though lacking a nervous system or traditional senses, have their own form of communication, often mediated by chemicals. For instance, when a plant is under attack, it can release volatile compounds to attract predators of the herbivores harming it. Interestingly, these chemicals can also alert nearby plants of potential danger.

A case study involving sagebrush and wild tobacco plants provides insight into this phenomenon. When sagebrush is damaged, it releases methyl jasmonate, a volatile compound that nearby tobacco plants detect, triggering an increase in their production of defensive agents. This chemical warning system, however, seems to have a very limited range.

The study of chemical communication in nature, whether between humans and mosquitoes or among plants, is an ongoing journey of discovery. It reveals the intricate and often hidden ways in which life on Earth interacts and adapts. As research continues, we may find more innovative ways to apply this knowledge, from controlling pests to understanding ecosystem dynamics.

Chemical communication remains a fascinating and largely uncharted frontier, offering a glimpse into the sophisticated and silent language of nature.

REFERENCES 

Coutinho-Abreu IV, Jamshidi O, Raban R, Atabakhsh K, Merriman JA, Akbari OS. Identification of human skin microbiome odorants that manipulate mosquito landing behavior. Sci Rep. 2024 Jan 18;14(1):1631. doi: 10.1038/s41598-023-50182-5. PMID: 38238397; PMCID: PMC10796395.

Karban R, Shiojiri K, Huntzinger M, McCall AC. Damage-induced resistance in sagebrush: volatiles are key to intra- and interplant communication. Ecology. 2006 Apr;87(4):922-30. doi: 10.1890/0012-9658(2006)87[922:drisva]2.0.co;2. PMID: 16676536.

Chemical & Engineering News: Critter Chemistry - Plants to Bugs: Buzz Off! (acs.org) by Sophie Wilkinson, Chemical & Engineering News, American Chemical Society

The short film "Descendants" provides a creative exploration of nature's interconnectedness: http://vimeo.com/8642276

https://entomology.ucdavis.edu/people/richard-karban

https://swissplantscienceweb.unibas.ch/en/farmer/

https://www.ice.mpg.de/person/111845

When it Smells Like Team Spirit

Why do we connect and collaborate, deciding to "walk in the light of creative altruism" instead of the "darkness of destructive selfishness"?

Is it because of subtle behavioral clues that make us "click" and consider the other person a part of the group? Or is it because it smells like team spirit?

It very well might be. We (literally) smell love, victory, fear, along with chemicals that motivate us to cooperate. As was recently shown in double-blind placebo-controlled studies that quantitatively measured generosity and cooperation. Androstadienone, a rather unpleasant smelling molecule abundant in male sweat could make us more cooperative and more likely to think of the other person as "one of us". This molecule, created from male sex hormone testosterone possibly with the help of coryneform bacteria living under arms, was previously shown to have an effect on women - depending on social context and the time in their menstrual cycle. Even though androstadienone does not smell particularly plaasant - rather musky, with subtle urine-like and alcohol notes - merely smelling it is sufficient to maintain high levels of energy-boosting hormone cortisol  - possibly by inhibiting an enzyme (the 11β-hydroxysteroid dehydrogenase type 1 aka 11β-HSD1) responsible for its reactivation from cortisone.

Androstadienone

Androstadienone is related to another steroid estratetraenol found in the urine of pregnant women. Both molecules in large concentrations can affect mood -  improving it in females (also increasing their feeling of being focused and sensitivity to pain) while suppressing males. High testosterone males might even get depressed. So it might not be a good idea to sweat too much, but the right amount of sweating is actually helpful. If you are a male. When it comes to men deciding to cooperate with women, chemistry alone is less helpful. As in the old monkey experiment (Michael and Zumpe, 1982) where the best female strategy was to block male's access to other female monkeys. So, don't sweat it ladies. Just be dominant.

REFERENCES

Huoviala P, & Rantala MJ (2013). A Putative Human Pheromone, Androstadienone, Increases Cooperation between Men. PloS one, 8 (5) PMID: 23717389

Lundström JN, Hummel T, & Olsson MJ (2003). Individual differences in sensitivity to the odor of 4,16-androstadien-3-one. Chemical senses, 28 (7), 643-50 PMID: 14578126

 Michael RP, Zumpe D.  (1982) Influence of olfactory signals on the reproductive behaviour of social groups of rhesus monkeys (Macaca mulatta). J Endocrinol. 95(2):189-205. PMID: 7175415