AsianScientist (Dec. 20, 2017) – A team of researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) have found that worms have several genetic similarities with the vertebrates, a group of organisms that include fish, birds and mammals.
More than 550 million years ago, a major group of animals called the bilaterians, animals with bilateral symmetry, underwent an evolutionary event in which they diverged into two groups, the protostomes and the deuterostomes. The deuterostomes include the vertebrates, comprising fish, birds, amphibians, reptiles and mammals, including humans. The deuterostomes also include some less familiar animals such as sea urchins and starfish.
On the other hand, the protostomes include several invertebrate groups such as insects, spiders, lobsters and flatworms. The worm species studied here belong to a special group within the protostomes called the lophotrochozoans.
Despite their obscure sounding name, lophotrochozoans represent more than one third of known marine animals. This group includes earthworms, leeches, snails, oysters, octopuses and other invertebrate groups, and they play many important ecological roles.
In this study, a team of researchers at OIST analyzed the genomes of two lophotrochozoan worm species, the nemertean Notospermus geniculatus, a ribbon worm, and the phoronid Phoronis australis, a horseshoe worm. They found that ribbon worms and horseshoe worms are evolutionarily closely related, despite looking very different.
Surprisingly, the researchers found that these worms, which are protostomes, share many gene families and gene arrangements with the deuterostomes, the group that includes the vertebrates. For example, they share genes that are involved in multicellularity and maintenance of the body’s internal environment.
The two worms also share a common system for controlling head development; the same mechanism that controls vertebrate head patterning also controls the development of ribbon worm heads and horseshoe worm feeding tentacles. Other protostome groups, such as insects, have lost some of these genetic features.
Conversely, the researchers also found that many genomic features are only found in specific groups of worms, such as genes relating to toxin production and immunity. This shows the dual nature of animal evolution in which certain genes are conserved over evolutionary time, whilst other genes change.
“We show here that animal genome evolution is a dynamic process,” said Dr. Luo Yi-Jyun of OIST who is the first author of the study. “It is fascinating to think that humans have retained some genetic programs which were encoded in our ancient ancestors hundreds of millions of years ago, maintaining a link between ourselves and our distant relatives.”
The article can be found at: Luo et al. (2017) Nemertean and Phoronid Genomes Reveal Lophotrochozoan Evolution and the Origin of Bilaterian Heads.
Source: Okinawa Institute of Science and Technology Graduate University.
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