14 Dec 2010, Global BC: Canadian researchers suggest sponge theory may not hold water

Canadian researchers suggest sponge theory may not hold water
Canadian researchers who probed the traits of a freshwater sponge from Vancouver Island say their findings about the species' "skin" could rewrite the history of animal life and illuminate a primordial family connection between humans and the porous organisms best known for mopping up kitchen spills.

A study by three University of Alberta biologists, which appears in a journal published by the U.S.-based Public Library of Science, shows how the outer tissue of the B.C. specimen acts much like the protective layer of skin that distinguishes almost all other animals, including humans, from the seemingly flow-through sponges.

The discovery, the research team concludes, could eventually force scientists to reclassify sponges closer to our own "eumetazoan" clade of animals, and to rethink humanity's evolutionary roots among these absorbent creatures of the deep.

"It doesn't quite make them into Sponge Bob," study co-author Sally Leys told Postmedia News on Monday. "But it very much does put sponges into the fold with the rest of us."

The U of A team, including Emily Adams and Greg Goss, gathered samples of the common species Spongilla lacustris from Sarita and Rosseau lakes near Bamfield, B.C., about 120 km northwest of Victoria.

Leys said the chief advantage of collecting sponges from Vancouver Island is that their habitats typically don't ice over in winter — allowing access year-round — and that colder weather triggers a degree of shrinkage and dormancy that makes the specimens easier to handle in experiments.

The researchers tested the sponge's "epithelial" membrane to determine whether it can effectively block certain molecules from penetrating the organism's interior — the way a mammal's skin or an insect's outer layer does.

They found that the sponge's membrane provided a "good, tight seal" akin to how a chimpanzee's skin protects against unwanted microbes and chemical invaders.

"It shows that sponges share a physiology with other animals and are not just some odd offshoot," said Leys.

Sponges, fossils of which have been found from about 550 million years ago, are known to be among the earliest complex creatures to appear following the evolution of life from unicellular to multi-celled organisms.

Leys said different camps of scientists have "very polarized perspectives" on whether sponges should remain grouped in a separate branch of animal life from other ancient, blob-like creatures that gave rise — hundreds of millions of years later — to the mammalian class of species that encompasses humans.

The Canadian finding "has relevance to our understanding of the eumetazoa" clade of animals, the study states, because "if sponges have functional epithelia, and epithelia are usually considered to be tissues, then the presence of tissues can no longer be used as (an exclusively) eumetazoan character."

They argue that the specialization of cells resulting in skin "was therefore one of the first defining features of multicellular animals," including the ancestors of modern sponges and humans alike.