Fossil Study Sheds Light on Mesozoic Butterfly and Moth Wing Colors

Saturday, April 14, 2018

Ecological restoration of moths in the Cretaceous Burmese amber forest. Image credit: Dinghua Yang.

New research by a team of scientists from the University of Exeter and elsewhere offers an illuminating insight into iridescent colors found on the earliest known lepidopterans, which lived on our planet 200 million years ago (Mesozoic era).

Remarkable scales of lepidopterans (moths and butterflies) exhibit complex structures, many of which produce structural colors that are the basis for diverse communication strategies.

Little is known, however, about the early evolution of lepidopteran scales and their photonic structures.

Dr. Tim Starkey, a researcher in the Department of Physics and Astronomy at the University of Exeter, and colleagues examined fossilized remains of lepidopterans from the United Kingdom, Germany, Kazakhstan, and China, and tarachopterans (a stem group of Amphiesmenoptera) from mid-Cretaceous Burmese amber.

Using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) and using optical models, they found microscopic ridges and grooves in the insect’s wing scales, similar to those seen in today’s moths.

The models revealed these tiny features are photonic structures that would have produced metallic bronze to golden color appearances in the insect wings.

The structural colors of the fossils studied by the team resulted from light scattering by intricate microstructures, extending the evidence for these light-scattering structures in the insect fossil record by more than 130 million years.

Tarachoptera from mid-Cretaceous Burmese amber: (A-D) K. brevicostata, female; (B and C) forewing scales; note the tubercles and setae on wing membrane; (D) scale reconstruction; (E-H) K. brevicostata, male; (E) images of forewing scales detached from the forewing; (F) interpretative sketch of cross section of scale; (G) an image of cross section of forewing scales; (H) an image of cross section of a forewing scale. Scale bars – 0.5 mm (A), 0.1 mm (B), 50 μm (C), 40 μm (E), 20 μm (G), and 2 μm (H). Image credit: B.W., Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences.

“The structural colors exhibited by butterflies and moths have been a longstanding research interest in Exeter, and have helped us develop biologically-inspired optical technologies for the present day,” Dr. Starkey said.

“However, in this study we’ve looked millions of years back in time to early origins of such colors in nature, to understand how and when the evolution of colors in these insects took place.”

“Remarkably, these fossils are among the oldest known representatives of butterflies and moths,” said co-author Dr. Maria McNamara, from the University College Cork, Ireland.

“We didn’t expect to find wing scales preserved, let alone microscopic structures that produce color. This tells us that color was an important driving force in shaping the evolution of wings even in the earliest ancestors of butterflies and moths.”

“Uniquely in this study, we show that impression fossils, i.e. wing prints, are equally as capable as compression fossils at preserving the structure of scales in sufficient detail to elucidate the moths’ 180 million year old colors,” said co-author Dr. Luke McDonald, also from the University College Cork.

The findings appear in the journal Science Advances.

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Qingqing Zhang et al. 2018. Fossil scales illuminate the early evolution of lepidopterans and structural colors. Science Advances 4 (4): e1700988; doi: 10.1126/sciadv.1700988

Source: www.sci-news.com

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