Stick Insects' Camouflage Secrets: Chromosomal Shifts Drive Adaptation

Understanding how organisms adapt to their environment is a key question in biology. Researchers have discovered that chromosomal rearrangements, where large DNA segments are flipped or moved, play a significant role in this process. These "macromutations" can cause major changes in traits. Stick insects, like humans, have two sets of chromosomes. This study used advanced techniques to analyze each chromosome copy separately. This revealed how complex chromosomal rearrangements enable stick insects to camouflage themselves on different plants to avoid predators. Published in *Science*, the research highlights two distinct chromosomal rearrangements in stick insects. Millions of DNA bases were flipped and moved, independently in different populations. This explains the adaptive divergence in their cryptic color patterns. The team studied *Timema cristinae* insects from California, adapted to either California lilac (green insects) or chamise shrub (striped insects). The presence or absence of these chromosomal rearrangements almost entirely explains the color pattern differences. "The new phased genomic assembly technology used in this study was a critical piece in helping us examine how color patterns evolved in these insects," said Zachariah Gompert from Utah State University. He added that these mutations are easy to miss using traditional DNA sequencing approaches, and that "structural variation, rather than being rare, may be regularly available to prompt evolution."