The Sharp-Shooting Skills of Archerfish Were Driven by Competition

By shooting water up at spiders and even small lizards, archerfish are able to knock them into the water before gulping them up. Last year, we discovered that they’re far more skillful target shooters than we thought: Archerfish can adjust the hydrodynamic properties of a jet of water based on the distance of their prey. Now, researchers show that archerfish likely evolved their outstanding set of hunting skills in order to compete with other similarly sized, surface-feeding fish. The halfbeak, Zenarchopterus buffonis, can quickly sense prey – even in the dark. Without sophisticated additions to their hunting technique, archerfish would have lost most of their downed prey to halfbeaks, according to new work published in Current Biology this week. 

In addition to being remarkable marksmen, archerfish have evolved highly efficient visual skills: In the daytime, they can anticipate where their downed prey will fall. A trio led by Stefan Schuster from the University of Bayreuth have been working in the mangrove habitats of Thailand over the past few years, looking for ecological factors that might explain the archerfish’s talents. The team kept noticing the presence of these rival halfbeaks wherever they spotted groups of archerfish. 

On average, it takes archerfish just 90 milliseconds to get their prey item, New Scientist reports, compared with the 253 milliseconds of halfbeaks. But, not only are halfbeaks more numerous than archerfish, they’re also active at all times. In the lab, archerfish were able to hunt at night if there were no halfbeaks around, but it took them much longer to find their quarry after knocking them into the water. 

The halfbeaks, the researchers found, are equipped with water-wave detectors that allow them to quickly sense the impact of prey landing on the water surface above them in the dark. These sensory cells, called neuromasts, are in the skin on their backs, and halfbeaks have about five times more than archerfish. 

“Archerfish were extremely efficient at making the catch in almost all cases by quickly noticing the initial speed and direction of the falling prey and heading right to the point where it would drop,” Schuster tells New Scientist. “Archerfish win when they can use vision, but halfbeaks win in the dark.” 

Competition both among themselves and with other species can drive animals into new niches only available through cognitive investments, Schuster adds.

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24 July 2015 | 6:58 pm – Source: iflscience.com

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