In this case, the formations may serve solely to gather fine sediments, which females could use to choose their mate, Jordan said.īut until this idea is tested, nobody will know. The formations are very similar to so-called "bowers" - display sites built by various animals like bowerbirds in which to strut their stuff before mating. "It's a nice clean study because it provides a definite answer to the question - something that is very rare in biology," Jordan said. Research describing the pufferfish formations was published in July in the journal Scientific Reports. D shows the same circle one week after spawning. "A" represents the early stage, B the middle stage and C the final stage. One of the circular formations in various stages of completion. The fact that such a small animal makes such a large formation is "pretty cool, and suggests some underlying biological reason for the size, like poor visibility at depth, or distance between individuals that means males have to make large nests to be found by females," he told LiveScience. When Jordan first heard about the circles, he guessed a much bigger fish would have made them. Kawase said they likely give up their old formations because the circles exhaust the fine sediment in the area, and thus must be built anew in areas with fresh sediment. The male pufferfish don't maintain these formations, and underwater currents wash them away relatively quickly. It takes about seven to nine days for the pufferfish to construct the circles. The speed of water was slowed by nearly 25 percent in the center, where the eggs are laid, the study noted. Then, the downstream peaks and valleys funnel the water outward. ![]() A fluid dynamics test using a half-size model of one of these circles found that the upstream portion of the circle funnels water and fine sediments toward the center. Strangely enough, the male "gathers" the fine sediments using the circular pattern itself, Kawase said. ![]() ![]() Third, the male gathers fine sediments to give the resulting formation a distinctive look and coloring, Kawase said. Second, the male decorates these ridges with fragments of shells. First, they involve radially aligned ridges and valleys outside the nest site. For example, male featherfin cichlids in Africa's Lake Tanganyika build small bowls out of the sand, and display them to females before mating there, said Alex Jordan, a researcher at the University of Texas at Austin who wasn't involved in this study.īut this new pufferfish's geometric patterns have three features never seen before. Males of some species of cichlids (a type of fish) are known to construct crater-shaped mounds that females visit to have their eggs fertilized, Kawase said. A male pufferfish making a valley in the seafloor with his fins on April 23, 2012.
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