A small group of fishes — possibly the world’s cleverest carnivorous grazers — feeds on the scales of other fish in the tropics. The different species’ approach differs: some ram their blunt noses into the sides of other fish to prey upon sloughed-off scales, while others open their jaws to gargantuan widths to pry scales off with their teeth.
A team led by biologists at the University of Washington’s Friday Harbor Laboratories is trying to understand these scale-feeding fish and how this odd diet influences their body evolution and behavior. The researchers published their results Jan. 17 in the journal Royal Society Open Science.
“We were expecting that with this specialized scale-eating niche, you would get specialized morphology. Instead, what you get is a mosaic of strategies for the end goal of scale feeding,” said lead author Matthew Kolmann, a postdoctoral researcher at Friday Harbor Laboratories.
“This niche has a hidden complexity to it, and it is yet another story about the incredible diversity of life on Earth.”
The stark differences in jaw and head shape, combined with how each prefers to hunt, shows a great diversity among the small number of species that have evolved to eat scales, the researchers found. Paper. (public access) – Matthew A. Kolmann, Jonathan M. Huie, Kory Evans, Adam P. Summers. Specialized specialists and the narrow niche fallacy: a tale of scale-feeding fishes. Royal Society Open Science, 2018; 5 (1): 171581 DOI: 10.1098/rsos.171581 More.
This seems to be a form of convergence on a goal, a neglected concept in evolution. What unites these species is not minor divergences from common ancestry so much as a convergent goal (to feed on scales), using whatever morphology exists. They seem not so much driven from behind as pulled from ahead.
See also: Convergent evolution: Researcher “amazed” by similarities between long-extinct marine reptiles and modern life forms that are NOT their descendants
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Evolution appears to converge on goals—but in Darwinian terms, is that possible?