In the picture of skate evolution that the researchers have reconstructed, at some point after the skate lineage diverged from sharks, they acquired a mutation in an enhancer that made their hoxa<\/i> genes active in both the front and the back of their pectoral fins. And within the new tissues growing along the anterior of the fin, genome rearrangements caused the PCP pathway to be activated by enhancers in a different TAD, which had the further effect of making the fin extend forward and fuse with the animal\u2019s head.<\/p>\n

\u201cBy forming the winglike structure, [the skates] are able now to inhabit a whole different ecological niche, the bottom of the ocean,\u201d Amemiya explained.<\/p>\n

Stingrays, mantas and other rays are closely related to skates (they are all classified as \u201cbatoid\u201d fishes), and their similarly pancaked shape is probably due to the same genome rearrangements. The rays, however, have also modified their winglike fins in ways that basically allow them to fly through the water. \u201cThe skates have these undulations of the fin and stay on the bottom, but manta rays can come to the surface and have a whole different way of locomotion,\u201d Amemiya said.<\/p>\n

Although evolutionary developmental biologists have previously speculated that these changes in the 3D architecture of a genome might be possible, this is probably one of the first papers to clearly link them to fairly big changes in body shape, Marl\u00e9taz said.<\/p>\n

Lupi\u00e1\u00f1ez also believes the findings have significance that reaches far beyond an understanding of skates. \u201cThis is a completely new way to think about evolution,\u201d he said. Structural rearrangements \u201ccan cause a gene to be activated in a place where it should not be.\u201d He added: \u201cThis can be a mechanism of disease, but it can also serve as a driver of evolution.\u201d<\/p>\n<\/div>\n

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