Wallabies found to have poor colour vision

Wallabies found to have poor colour vision


 

Contrary to the recently established theory that marsupials have excellent colour vision, research has shown that the wallaby is a rare exception.

The research team, led by Dr Jan Hemmi from the ARC Centre of Excellence in Vision Science and The Australian National University, has shown that Tammar wallabies are much weaker in discriminating different colours because they are missing one type of visual pigment cell.

"Dr Ebeling has demonstrated that wallabies do not have the complete set of three visual pigments in their cones - the vision cells that provide us with colour vision," says Dr Hemmi. "Wallabies are dichromats - they have only two visual pigments out of the three - this means that they get less colour input to their brain and see things similar to other mammals, or a colour-blind human."

"Given that most marsupials are trichromats - having three visual pigments, this poses the million dollar question: why do wallabies differ in colour vision when they come from the same family, as the quokka for instance?"

Dr Hemmi explains that it has long been thought that all mammals have dichromatic vision and that only the primate eye later evolved to have a finer sense of colour discrimination. However, upon the discovery that marsupials may be able to discern colours just as well as humans, it was suggested that the ancestors of the pouched-mammals were always trichromatic whereas placental mammals were dichromatic.

"It is speculated that mammals lost all but two of their ancestors' cone pigments during evolution," he says. "Mammals were proposed to be nocturnal animals early in their evolutionary history, which means they mainly used their rods - vision in low light - to see, instead of their cones - colour vision in bright lights. This could have contributed to the loss of diversity in their vision cells."

"Up to now we still do not have a clear idea of why marsupials are exceptional in their colour vision compared to other mammals. An example of this is the trichromatic dunnart which has a third cone that has not yet been identified."

"Knowing that not all marsupials are trichromats allows us to make comparisons and leads us one step closer to locating the X factor that drives the evolution of good colour vision."

The research team is currently investigating the vision of the brushtail possum, which is a nocturnal marsupial. Their current finding, 'Diversity of color vision: not all Australian marsupials are trichromatic' has been published in the journal PLoS ONE. It can be accessed at http://www.plosone.org/article/info.1371.pone.0014231.

The Vision Centre is funded by the Australian Research Council as the ARC Centre of Excellence in Vision Science.

 

More information:

Dr Wiebke Ebeling (in Hobart), Centre for Marine Science at the University of Tasmania, ph (03) 6226 2904 or 0413 871 108
Dr Jan Hemmi, The Vision Centre and The Australian National University, ph (02) 6125 8561 or 0403 660 221
Professor Trevor Lamb, The Vision Centre, ph +61 (0)2 61258929 or 0434022375
Mandy Thoo, The Vision Centre media contact, 0402 544 391 

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