DENNIS ODA / DODA@STARBULLETIN.COM Elaine Seaver sits in her office showing the journal Nature, which published the UH study on animal evolution. Behind her are colleagues William Browne, left, Kevin Pang and Mark Martindale.

UH redraws sequence of animals’ evolution

The humble sponge, scientists long believed, was at the base of the animal kingdom's evolutionary tree.

But a landmark study led by a University of Hawaii laboratory shows that a more exotic creature, the comb jellyfish, branched off even earlier from the "tree" that today includes elephants, humans, flatworms and millions of other species, some living between grains of sand.

The four-year study, which used computer programs to analyze volumes of genetic data, reveals surprising ways in which modern animals are related. Centipedes and millipedes, it turns out, are closer kin to spiders than insects.

The approach "shows that the answer to reconstructing the relationship of all living animals is now within reach," says researcher Mark Martindale.

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A four-year study led by the University of Hawaii's Kewalo Marine Laboratory has produced new insights into patterns of animal evolution, says Mark Q. Martindale, director of the lab in the Pacific Bioscience Research Center.

He said some of the more obscure animals need to be studied, "but the approach the Kewalo team has perfected shows that the answer to reconstructing the relationship of all living animals is now within reach."

Understanding the evolutionary relationship of animals "is an important way of understanding the evolution of life on Earth," he said in an interview.

Martindale and Kewalo Lab researchers Andreas Hejnol, David Matus, Kevin Pang, William Browne and Elaine Seaver worked with an international team of experts in molecular and developmental biology, animal systematics, evolutionary biology and computer science.

They knocked down some preconceived ideas about animal relationships and confirmed others, Martindale said.

For instance, he said, mollusks -- such as snails, clams and sea slugs -- have a long history of being put together in one big group, but there is not a single morphological (structural) character that unifies them.

"Molecular biology groups all the animals together," he said, adding, "This sort of approach is validated because it provides an independent rationale for grouping all mollusks together even though nobody could think of one single thing that would unify the whole group."

The researchers analyzed DNA data from animal samples collected from Hawaii's shoreline and waters and from marine labs around the world. Results were reported in the April 10 issue of the journal Nature.

DENNIS ODA / DODA@STARBULLETIN.COM Elaine Seaver, left, associate professor at the Pacific Bioscience Research Center; Mark Martindale, director of the Kewalo Marine Laboratory and a specialist in evolutionary developmental biology; William Browne, PBRC assistant researcher; and graduate student Kevin Pang pose for a picture outside one of their labs outfitted with a collecting tank to house specimens. The Kewalo Marine Laboratory is next to the ocean, so they can pump in fresh sea water.

"They place animals onto this preconceived notion of what the progress of evolution was," he said. "It was the best they could do based on techniques available to them."

Molecular biology has changed that in the past 10 to 15 years, he said, explaining that it can be used "as a new measure of how animals are related one to another."

"The big problem was, there are many different kinds of animals out there in the real world, and people would only look at certain ones," he said. "They didn't look at all the different weird or small animals or those not of economic or disease relevance."

The researchers doubled the number of different animal groups ever sampled to gain a deeper understanding of their relationships. They collected genes from each species and compared them using complex computer programs at the PBRC Bioinformatics Facility and other computer centers.

"These problems are very sophisticated from a computational point of view," Martindale said. "One figure in the paper took four years for the computer to calculate." Banks of dozens of computers were run simultaneously over months to complete a single run, he said.

"The results showed strong support for many well-agreed-upon nodes but also showed many new relationships that had never been proposed."

In an online report, Science Daily said the "big shocker" was that comb jellyfish, with well-developed tissues, appear to have diverged from other animals before the tissueless sponge. "This finding calls into question the very root of the animal tree of life, which traditionally placed sponges at the base," the report said.

Among other surprises, a close relationship was discovered between ribbon worms and two-shelled invertebrates, and conflicting evidence was resolved about close ties of millipedes and centipedes to spiders rather than insects.

"The real next hurdle is to try and generate computational approaches to understanding these complex data sets," Martindale said.

Scientists generally recognize 30 to 35 different major groupings of animals, known as phyla, that are related to one another by common descent, he said.

Arthropoda is a phylum that includes all insects and crustaceans. Vertebrates are a larger animal phylum including fish, amphibians, reptiles, birds and mammals.

Many animals in the remaining phyla "are quite small and live between sand grains," Martindale said. But he said they "likely evolved well before the larger charismatic megafauna, such as whales, sharks, turtles and ahi that we see with our naked eyes on a day-to-day basis."