If the molecules essential for life had popularity contests, adenosine triphosphate (ATP) would be high society. It is a highly conserved, highly important molecule involved in a wide range of both intracellular and extracellular activities.
It’s unusual, however, to think about any roles ATP might play when its made its way out of an organism and into the environment. For terrestrial life, that kind of “ambient ATP” may not be that consequential but for marine life (particularly carnivorous marine life), environmental ATP can have a profound effect on behavior.
I first learned about the unorthodox role of ATP while taking courses at UCLA in the early 2000’s. My professor, Richard Zimmer (among others), had done research in the 80’s and 90’s on what role ATP might play in mediating feeding activity in marine decapods, specifically California spiny lobsters (Panulirus interruptus).
Another researcher named William E.S. Carr had earlier demonstrated that a relative of P. interruptus known as P. argus possessed chemoreceptors in their olfactory organs that were stimulated by ATP; however, he stopped short of exploring the role those receptors might play in the overall behavior of the lobster.
Prof. Zimmer, expanded on Carr’s work and, after a series of meticulous experiments involving P. interruptus, determined that ATP was a potent chemical mediator of foraging behavior in these crustaceans. Specifically, it elicited locomotive behavior associated with recognizing and finding food.
Essentially, the lobsters interpreted ambient concentrations of ATP as a “molecular dinner bell” and went searching for the source.
So what made ATP such an effective stimulant of feeding behavior? Zimmer proposed that the power behind ATP’s potency lay in its ability to maintain a high “signal to noise” ratio in the environment. In order for a chemical to serve as a good “signal” in a marine environment, it needs to maintain a high concentration relative to the background “noise”. In other words, it has to be able to persist in concentrations greater than those commonly occurring in the surrounding environment.
It is this difference in concentration that helps an organism determine when a signal is a true indicator of a given event and not just “business as usual.” ATP exists in very high concentrations within living or freshly killed organisms and in very low concentrations in the external environment. Thus, if P. interruptus detected any elevated concentrations of ATP in the surrounding seawater, chances were food was nearby.
But why ATP specifically; why not another compound? After all, animals release all sorts of chemicals into the environment. Why not use urea or perhaps ammonium as an indicator of a nearby foodstuff.
Well, consider what detecting ATP specifically in the environment would mean! Since ATP is rapidly converted to adenine monophosphate (AMP) once tissue begins to degrade, it serves as a reliable indicator of injured live or freshly killed prey items. Such live (or very recently deceased) items are, from a carnivore’s standpoint, the most nutritious and generally worth the effort it takes to find and consume them. Compounds like urea and ammonium on the other hand, while also indicators of a potential food source, are produced in large quantities through nitrogen catabolism and the activities of the anaerobic and aerobic bacteria which decompose dead tissue.
From the lobster’s perspective, those kinds of signals would indicate an animal that may have been dead for a while and would thus provide lower-quality nutrition.
Furthermore, from a “chemoreception mechanics” perspective, ammonium and urea are omnipresent in the marine environment and thus would be hard-pressed to maintain the high “signal to noise” ratio that is needed for effective chemoreception.
So there you have it! It turns out that ATP is much more than just the “universal energy currency” you learn about in Biology 101. It’s also a powerful environmental mediator of foraging activity in at least one genus of marine carnivore and I wouldn’t be surprised if you were to find it to have a similar effect in others.
So the next time you happen to be pondering why the Spiny Lobster at your local Aquarium is suddenly scrambling around like crazy, look for the ATP.
References and Further Reading
- Fuzessery, Z. M., Carr, W. E., & Ache, B. W. (1978). Antennular chemosensitivity in the spiny lobster, Panulirus argus: studies of taurine sensitive receptors. The Biological Bulletin, 154(2), 226-240. (PDF)
- Johnson, B. R., & Ache, B. W. (1978). Antennular chemosensitivity in the spiny lobster, Panulirus argus: amino acids as feeding stimuli. Marine & Freshwater Behaviour & Phy, 5(2), 145-157.
- Reeder, P. B., & Ache, B. W. (1980). Chemotaxis in the Florida spiny lobster, Panulirus argus. Animal Behaviour, 28(3), 831-839. (PDF)
- Schmidt, M., & Derby, C. D. (2005). Non-olfactory chemoreceptors in asymmetric setae activate antennular grooming behavior in the Caribbean spiny lobster Panulirus argus. Journal of Experimental Biology, 208(2), 233-248. (PDF)
- Zimmer-Faust, R. K. (1993). ATP: A potential prey attractant evoking carnivory. Limnology and oceanography, 38(6), 1271-1275. (PDF)
- Zimmer-Faust, R. K., Gleeson, R. A., & Carr, W. E. (1988). The behavioral response of spiny lobsters to ATP: evidence for mediation by P2-like chemosensory receptors. The Biological Bulletin, 175(1), 167-174. (PDF)
- Zimmer-Faust, R. K. (1987). Crustacean chemical perception: towards a theory on optimal chemoreception. The Biological Bulletin, 172(1), 10-29. (PDF)
- Zimmer-Faust, R. K., Michel, W. C., Tyre, J. E., & Case, J. F. (1984). Chemical induction of feeding in California spiny lobster, Panulirus interruptus (Randall). Journal of chemical ecology, 10(6), 957-971.
- Zimmer-Faust, R. K., & Case, J. F. (1983). A proposed dual role of odor in foraging by the California spiny lobster, Panulirus interruptus (Randall). The Biological Bulletin, 164(2), 341-353. (PDF)