Domestication has witnessed humans achieving incredible things, from agriculture and aquaculture to transforming the wolf into a dog. Such domestication has been observed among non-human invertebrates such as ants who farm aphids and spiders that have pet frogs for driving parasites away. New research published in the journal Nature Communications has detailed an example of domestication in a non-human vertebrate, categorically the longfin damselfish (Stegastes diencaeus). These fish hire planktonic mysid shrimps (Mysidium integrum) to assist them to fertilize algae farms on which they feed.
Throughout their lives, longfin damselfish will spend defending a patch of algae from other sea creatures who may attempt eating it. They run patrols and if there’s no free real estate on which they can farm, they will suck on polyps in the coral until they die and the algae take its place. They are a menace for dying reefs for this reason, and the better they are at farming the larger their garden will grow, eliminating more of the coral in the process. Parrotfish are another species that feed on the algae and will target longfin farms, but despite the difference in size between the two, the longfin is too aggressive to scare parrotfish away.
The fresh analysis establishes why longfins, who normally shield their algae ferociously from every living thing, tolerate swarms of mysid shrimp floating over their yards. It was first required to demonstrate if this behaviour was widespread and so swum a series of 30-meter (98-foot) laps of a reef in Belize, making notes of when they spotted mysid shrimps and which species they were close to. The results proved that mysids were found in close proximity to fish farmers such as the longfins much more than any other species.
To figure out if this association was incidental or a choice made by the shrimps, they gathered some mysids and exposed them to water contaminated by various smells. The mysids proved that they are attracted to the smell of farming damselfish but are indifferent to non-farming fish.
To conclude why mysids would seek out damselfish, they placed some of the shrimps in small, clear plastic bags and put them inside and outside of longfin farms to observe how they reacted. They discovered that the mysids inside the farms benefitted from the longfins as they would protect the shrimp from other fish who wanted to consume the mysids. Those shrimps outside of the farms were not secured and were on the receiving end of multiple predation attempts by other fish.
The final piece of the puzzle was to conclude if the longfins were benefiting from keeping these swarms of mysids above their farms. They suspected that since the shrimps were above the algae, their waste may become fertilizer, meaning the longfins would relish an excellent crop. A survey on longfin farms with and without revealed that farms with mysids were more bountiful than those without.
These various analyses imply longfin damselfish have domesticated mysid shrimps. They offer a safe refuge, and in return, the mysid shrimps deliver the damselfish with fertilizer for its farm.
This association is significant as research has provided insight into the history of domestication among our ancestors. These things occurred long back. In the longfin damselfish, we can observe the initial stages of domestication taking place. This is amazing as it’s almost identical to the proposed series of events that led to our domestication of species such as chickens, cats, dogs and pigs.