The skeletal structure of a fish's gill arches and paired fins are quite similar – enough so that it was once believed the fins evolved from the arches. Although that theory has since been discounted, a new study suggests it may have been right on the money.
First of all, "paired" simply refers to fins that there are a matching set of, like the pectoral fins located at the front of a fish's body. Gill arches are curved pieces of bone or cartilage, each of which supports one of the actual gills. Back in the late 1800s, German anatomist Karl Gegenbaur postulated that paired fins evolved from the gill arches, since the arches appear earlier than the fins in the fossil record.
In subsequent years, that theory was widely disputed. Scientists pointed out that within the fish embryo, the two body parts develop from two different sets of cells – fins come from mesoderm cells, while gill arches come from neural crest cells.
A new study, however, indicates that Gegenbaur may have been right all along. Leading the research was Dr. Andrew Gillis from the University of Cambridge, and Dr. Victoria Sleight, who is now at the University of Aberdeen.
The scientists started by microinjecting fluorescent dyes into the neural crest and mesoderm cells of skate fish embryos, then following which skeletal areas those cells contributed to over the next several weeks. It was found that the paired fins were formed entirely from mesoderm cells, the cartilaginous jaw and first gill arch were formed entirely from neural crest cells, but the rest of the arches were formed from a mixture of both cell types.
"It has long been thought that similarities between the gill and fin skeletons of fishes are merely coincidental," says Gillis. "Our finding that these structures develop from a common pool of cells suggests otherwise – that gills and fins share a much deeper and more substantial evolutionary relationship that is reflected in their embryonic development."
The research is described in a paper that was recently published in the journal eLife.
Source: University of Aberdeen