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Platypus sheds light on evolutionary theory

October 20th, 2011
platypus

Missing link between birds and mammals: the platypus of eastern Australia

Arguably Australia’s weirdest animal, the platypus, is at the centre of a new theory about mammalian evolution.

The platypus is a strange, halfway house species, caught in time between the egg layers and the placental mammals. Bridging the gaps between bird, reptile and mammal it is warm-blooded and furry, but lays eggs rather than giving birth to live young. The echidna, also found in Australia, is the only other example.

This is a process that all mammals must have been through at some point in our evolutionary past, as life on Earth, for reasons best known to itself, moved from everyone laying eggs, towards certain species giving birth instead. Monotremes – mammals who still lay eggs – have therefore been very useful in understanding the origin of our sex chromosomes.

Professor Grutzner at the University of Adelaide says that the platypus gives key insight into how the mammalian genome has evolved over the past 200 million years. He has been working on an international project, led by the University of Lausanne in Switzerland, that uses new technology to highlight the active genes within different tissues and organs of different species, from mice to hens to humans.

The study has revealed that certain tissues, like the sexual organs, have evolved faster between different species than brain tissue has. In other words, the brains of different species are not as different as our other parts are.

The platypus was included in the study because of its ‘missing link’ status – representing our distant mammalian relative.

“We already know that our sex chromosomes emerged after the separation of monotremes from other mammals,” Professor Grutzner reports. “This allowed us to examine in this study how the activity of genes changes once they found themselves on a sex chromosome.”

The platypus brain was also found to be particularly active in explorative and navigational activity, something it has in common with fellow forager the mouse, but is less active in some other more domesticated beings.

The research will enable connections to be made between the physiology, anatomy, behaviour and underlying genes of different species, which can eventually help to map evolutionary history with animal characteristics and behaviour.

“It’s a very important starting point for further study,” Professor Grutzner said.

• More information: http://www.adelaide.edu.au/news

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