Flatworms help UH Mānoa researchers answer evolutionary questions

University of Hawaiʻi at Mānoa
Posted: Nov 2, 2008

Two University of Hawaiʻi at Mānoa scientists have contributed to research that helps answer an evolutionary question about how early organisms developed a "through-gut," with separate orifices for a mouth and an opposite-end anus.

Mark Q. Martindale and Andreas Hejnol work at the Kewalo Marine Lab in the Pacific Biosciences Research Center. The subjects of their research were acoel flatworms, which are easy to collect and raise at Kewalo, and which have been determined to be an evolutionary stepping stone in the development sequence for bilateral animals — animals with a definite left and right side and a definite top and bottom — such as humans.

"Our goal was to discover how the bilaterally symmetrical animals evolved from a simple circular ancestor that looked similar to jelly fish or corals," Hejnol says.

Early animals had a single opening or mouth through which food entered, and out of which undigested food was excreted. Conventional wisdom in the field — and the accepted premise in every zoology text about evolution — is that at some point in evolutionary history, the mouth opening split into two openings (the separate mouth and anus) and thus, bilateral symmetry could not occur without having two openings to the gut. Hejnol and Martindale were able to determine that the anus developed independently as animal bodies grew in size.

"A long gut makes sorting food and waste through a single opening inefficient," says Hejnol, "so they needed to evolve an anus."

Hejnol adds, "Our ancestor was likely a very small, soft-bodied animal that lived between the sand grains in the ocean, similar to the life-style of most acoel species. We are sure that our ongoing studies of the nervous system of these worms will yield to similar important insights into the evolutionary roots of the human brain and spinal cord."

[Note to editors: The scientific paper describing this research was published in the journal NATURE in October and is available by request. Contact Mark Martindale at mqmartin@hawaii.edu, telephone 539-7330, or Andreas Hejnol at hejnol@hawaii.edu, 539-7326.]