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University of Kansas scientists discover polyps will let unrelated 'others' fuse to them and share tissue

University of Kansas scientists discovered that polyps have no qualms about treating a nonrelated individual like part of the family.

The polyps are plankton-eating Hydrozoa — relatives to jellyfish and sea anemones — that live in shallow waters, sharing precious space and scarce resources in a spot of the ocean that’s teeming with life, from barnacles and clams to other hydrozoans. Each individual polyp is about a centimeter long and bright pink. A colony fits in two cupped hands.

The findings appear in the journal Evolution Letters and were published by researchers at the University of Kansas: Paulyn Cartwright, professor of ecology & evolutionary biology; Maria Orive, associate professor of ecology & evolutionary biology; and doctoral candidate Sally Chang.

In previous research, Cartwright found that unlike their loner relatives, Ectopleura larynx form colonies of “baby” polyps that fuse to the “mother” and share a gastrovascular cavity — basically, a stomach.

“We just got our minds wrapped around the idea that moms and offspring are fusing and sharing resources and that they’re related, but this was very surprising,” Cartwright said of seeing nonrelated individuals as part of one, big happy family. “And they don’t seem to have a problem with it.”

“I collect them in Maine, and everybody knows what they are when you explain them,” Cartwright said. “They’re colorful, and they grow on docks. They’re very conspicuous.”

These particular polyp colonies are different from others in that they are not simply composed of a mother cloning itself. Rather, they reproduce sexually, and the offspring fuse to the parent.

“For over 100 years, people saw them and thought they were budding, because that’s what hydrozoans do,” Cartwright said. “We brought them in the lab, and I never once observed budding.”

Paulyn Cartwright, University of Kansas
Ectopleura 1

Photo Source: University of Kansas

The KU scientists set out to examine the genetic relationships between the polyps of the colony and expected to find individuals that were genetically identical or at least as similar to one another as siblings or as similar as parents to children.

What the team didn’t expect to find was that in addition to close relatives, there were genetically unrelated polyps that fused onto the colony.

“This is super unusual given that in a colony they end up sharing everything from a continuous outer epithelia to an entire digestive system,” Chang said.

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