With more than 165,000 described species, butterflies make up one of the most famous groups of insects in the world. Although the origin of these winged insects dates back to well before the disappearance of the dinosaurs, their genome has remained largely unchanged, despite the enormous diversity of species.
This is an amazing discovery made by a team of British scientists who, by tracing the genetic code of the very first butterflies, identified 32 ancestral chromosomes as the basic elements of almost all Lepidoptera. Their research, published in the journal Ecology and evolution of nature February 21, 2024 offers a new insight into the evolutionary history of butterflies.
32 chromosomes that have remained intact for 250 million years
To achieve these results, Wellcome Sanger Institute PhD student Charlotte Wright and her team collected and studied data on 210 species of butterflies and moths from around the world. Among them the pearly blue Argus (Lysandra Corridon), Hawthorn Pieris (Aporia crataegi) or Mist Moth (Operophtera brumata).
Through a combination of sequencing and assembly, the researchers identified 32 ancestral chromosomes, which they named “Merian elements,” in reference to Maria Sibylla Merian, a pioneering 17th-century German entomologist. These chromosomes are not only common to all selected butterflies and moths, but in most of them they have also remained intact since their last common ancestor, more than 250 million years old.
“We were amazed to see how stable the genome structure of butterflies and moths has remained for so long“, he enthuses Science and the future Charlotte Wright, PhD student and lead author of the study.
Hawthorn moth (Aporia crataegi) photographed in the Ardèche. Credit: Stephane Vitzthum / Biosphoto / Biosphoto via AFP 2/28/24 2:37 PM
Fusion and fission in butterflies
By reconstructing the Lepidoptera phylogenetic tree, the researchers also found that certain groups of species defied these constraints on genome structure and evolved radically different chromosomal rearrangements through fission and fusion.
This is especially true for butterflies belonging to this genus Pierislike Cabbage Pierit (Pieris brassicae) or Piéride de la Rave (Pieris rapae), whose genomes were fragmented and then reorganized about 35 million years ago. Genomes of butterflies belonging to the genus Lysandralike sky azure blue (Lysandra Bellargus), were reorganized recently, about 5 million years ago.
“With such a large amount of data sequenced and assembled on a large scale, this study provides a better understanding of the evolutionary process of butterflies and opens the way for further research.”explains Violaine Llaurens, director of research at CNRS and evolutionary biologist at CIRB, who was not involved in this work.
Thymelicus sylvestris, or Houque’s skipper, is a butterfly found almost everywhere in France. Credits: Sam Ebdon / Wellcome Sanger Institute
British scientists hope to find more clues in the future in rare groups that have escaped the rules of genome structure. “These results are just the beginning of discovering how genetic diversity in Lepidoptera and the factors underlying it could help species conservation.”concludes Charlotte Wright.