If you think the dating world is tough for a human, consider for a moment the Nopoli rock-climbing goby of Hawaii, which scales waterfalls up to 100 feet high in order to breed. To put this feat in perspective, it’s the equivalent of a man of average height scaling the 29,029 feet of Mount Everest!
The process leading to this incredible feat is, quite literally, jaw-dropping: the tiny one-inch goby propels itself up the waterfall rocks with two suckers – one, common to all gobies, on the belly, and a second, particular to one goby genus, that develops when the mouth migrates from the tip of its head to its chin over the course of 36 to 48 hours, before it embarks on its journey. The fish uses these dual suckers alternately to inch up the rocky substrate of waterfalls to the waters above where the goby mates and deposits eggs in streams. Upon hatching, these juvenile gobies are swept into the ocean where they develop for several months before they return to freshwater streams and pools upstream where they may live for several years. To mate, the gobies of this new generation must repeat the waterfall-climbing process themselves.
The metamorphosis of the goby’s mouth shifting to serve as a sucker under the chin is also significant because with this change, the usually omnivorous Nopoli goby feeds almost exclusively on algae scraped from the rocks it climbs to scale the waterfalls. Scientists studying the gobies in a field laboratory in Hawaii examined the fish’s movement while feeding on algae-covered glass and climbing stimulated by falling water, and concluded that the fish uses nearly identical movements and motions in both tasks. This similarity leads scientists to believe that the Nopoli goby repurposed one of the behaviors for the other, an evolutionary phenomenon known as exaptation, where, as the scientists explain in their paper, “one specific function appears to have been coopted for another function.” The scientists give as the classic example of exaptation birds’ feathers, which may originally have served as insulation, and only after changes in morphology, been coopted to serve a role in flight.
In the rock-climbing gobies, scientists do not yet know which function begat the other, but one thing is certain – these evolutionary adaptations have created one incredible little fish!