CSHL scientists are part of consortium that sequences platypus genome

CSHL team separately reports findings about mammalian evolution gleaned from comparative study of small-RNA function in platypus

By any account, the platypus is an odd creature. It’s got a broad, rubbery bill that brings to mind a duck….but it swims more like a beaver….yet it lays eggs and can inject poisonous venom, like a reptile. No wonder it was considered an elaborate hoax by scientists who examined the first specimen pelt shipped to England from the colony of New South Wales in 1799.

In the May 9 issue of Nature, a consortium of scientists including Cold Spring Harbor Laboratory’s (CSHL) Gregory J. Hannon, Ph.D., published results of an international effort to sequence the platypus genome. It reveals evolutionary secrets that go far beyond the obvious fact that the creature, found exclusively in eastern and southern Australia, including the island-state of Tasmania, is neither a typical mammal nor typical reptile.

In fact, the platypus is a member of a mammalian species called the monotremes, which includes only four other subspecies (the other four being echidnas, varieties of spiny anteaters). The monotremes diverged from other primitive mammals about 166 million years ago, in the late Jurassic period -- a fact corroborated indirectly in the newly sequenced genome.

Finding Evolutionary Clues in Genome Sequence

“The broad purpose of our consortium was to understand features unique to the platypus and other monotremes, by identifying in its genome various innovations performed by evolution over eons of time,” said Dr. Hannon, a CSHL professor. “The evidence of how these innovations occurred, quite literally, is written in the sequence of the nucleotides in the platypus genome.”

Take the platypus’s distinct mode of rearing its offspring. All of the mammals, in addition to being warm-blooded, can be grouped according to their modes of gestation. Marsupials like the kangaroo rear profoundly immature young in external pouches for extended periods of time. Eutherian mammals like mice and humans protect their progeny for lengthy periods in an inner womb prior to giving birth. The platypus and other monotremes, in sharp contrast, retain the reptilian mode of gestation, being egg-layers; yet like other mammals the female platypus feeds her newborn with milk, albeit milk that’s secreted through broad patches of skin rather than teats.