May.16, 2013

How does a caterpillar turn into a butterfly? Scientists from the University of Manchester have taken 3D images of a caterpillar and watched the whole process using micro-CT scanning technology. And they are amazing.

Left: Chrysalis of a painted lady butterfly, showing breathing tubes (blue) and guts (red), at day 1 (left), day 13 (centre) and day 16 (right). Credit: Lowe et al. 2013. Interface.

Studies of model insects have greatly increased our understanding of animal development. Until now, studying metamorphosing insects has mainly involved dissection. But as you might know, dissection destroys the specimen. So researchers were never able to follow the full development of a creature.

So researchers came up with a new idea - using micro-computed tomography, or micro-CT scanning to get images of the insects. Two teams of scientists, Tristan Rowe and Russell Garwood from the University of Manchester and Thomas Simonsen from London's Natural History Museum use high-resolution X-ray computed tomography (CT) to overcome these issues, and three-dimensionally image numerous lepidopteran pupae throughout their development.

The researchers scanned nine painted lady butterflies in their chrysalis, over a period of 16 days.

Painted lady butterfly chrysalis during metamorphosis. Breathing tubes in blue; guts in red. (Credit: Tristan Lowe, Russell J Garwood, Thomas J Simonsen)

This study has revealed — in three dimensions at various stages in development — a number of the organ systems, principally the tracheae and portions of the gut. The insect's guts change shape within the body, but never disappear entirely. It also demonstrates early and rapid development of the tracheae, which become visible in scans just 12 h after pupation.

"This suggests that there is less remodelling of the tracheal system than previously expected, and is methodologically important because the tracheal system is an often-understudied character system in development." Note the researchers in their paper.

Researchers say that this form of time-lapse CT-scanning they've developed could allow faster and more detailed developmental studies on a wider range of taxa than is presently possible.

However, there are a number of limitations when applying micro-CT to insects. A number of tissues, for example, the muscles and central nervous system — are not resolved in the current scans due to lack of contrast. And ionizing radiation causes tissue damage and thus risks altering the development of the specimen when repeatedly scanned.

This technique doesn't drastically revolutionise what we knew about metamorphosis, but it does provide some small insights and gives scientists new options for their experiments.

To understand more about the process, you can read Ed Yong's story here which explains why it's important to watch the whole process instead of only collecting the data of different caterpillars at different stages in the transformation.

The full research paper, "Metamorphosis revealed: time-lapse three-dimensional imaging inside a living chrysalis", can be read for free here.

 

 

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