[ad_1]
A new study has revealed that insect wings evolved from a random growth or “lobe” on the legs of one of their crustacean ancestors who moved to the mainland some 300 million years ago.
US researchers say sections of the crustacean’s leg were gradually pushed back into its body to support its weight as it moved from sea to land.
After the leg segments were incorporated into the body, they gradually expanded, likely to allow for controlled sliding and descent from the fall, and later formed mobile insect wings.
Researchers at the Marine Biological Laboratory (MBL) in Massachusetts say the mystery of how insects evolved wings has baffled biologists for more than a century.
They used clues from scientific articles dating back to the 19th century along with CRISPR-Cas9, a powerful genetic modification tool, to work out the differences in the leg segments that led to evolutionary change.
Their work builds on the 2010 discovery that insects and crustaceans classified as arthropods are closely related, as revealed by genetic similarities.
Scroll down for the video
Researchers at the Marine Biological Laboratory used CRISPR-Cas9 to process the differences in the leg segments that led to the evolutionary change. The graph above shows the changes in the leg segments giving way to the wings: when the ancestral crustacean moved to land, the leg section closest to the body was pushed back into the body
“Previously, based on morphology, everyone had classified insects into the myriapod group, along with millipedes and millipedes,” said study author Dr Heather Bruce, MBL research associate.
“And if you search myriapods for the origin of insect wings, you won’t find anything.
So insect wings were thought of as new structures that arose in insects and didn’t have a corresponding structure in the ancestor, because the researchers were looking for the insect’s ancestor in the wrong place.
After the crustacean ancestor moved to the earth’s home some 300 million years ago, the leg segments closest to its body were incorporated into the body wall during embryonic development.
“The leg lobes then moved to the insect’s back and those later formed wings,” said Dr. Bruce.
Bruce was studying the “genetic instructions” for the legs of a crustacean, the tiny beach parhyale.
Details in a creature’s morphology can be discovered from its genetic codes, which can be revealed by genetic modification tools such as CRISPR-Cas9.
“Arthropod legs are made up of segments separated by flexible joints so they can move,” said Dr. Bruce at MailOnline.
“These segments are modeled in the embryo by genes that shape the legs, including the ones I studied in the article.”
Injection of CRISPR solution into embryos of crustaceans (Parhyale hawaiiensis). P. hawaiensis is the most genetically tractable crustacean for biological research
In the parhyale, as in many other crustaceans, each of its legs has seven segments, while in insects each leg has six segments.
For the study, Dr. Bruce and her team looked at parhyale hawaiensis, a species of the genus parhyale.
P. hawaiensis is the most genetically tractable crustacean for biological research and is a good substitute for crustaceans from 300 million years ago.
“Insects evolved from crustaceans millions of years ago, so unfortunately we don’t have access to the last common ancestor of parhyale and insects,” said Dr. Bruce at MailOnline.
“But since the parhyale and insects are cousins and the parhyale is a crustacean and therefore retains many of the characteristics that the ancestor had, we used the parhyale to represent the ancestral characteristics that interested us.”
The researchers compared the segmented legs of parhyale with the segmented legs of two other insects: the common fruit fly Drosophila and the tribolium beetle.
Parhyale, drosophila, and tribolium are all phylum arthropods.
The insects incorporated two ancestral leg segments of the crustaceans (labeled 7 in red and 8 in pink) into the body wall. The lobe on leg segment 8 later formed the wing in insects, while this corresponding structure in crustaceans forms a hardened plate (tergal plate)
Using CRISPR-Cas9, he sequenced the P. hawaiensis genome and systematically disabled five leg modeling genes shared by parhyale, fruit fly and beetle.
“The leg segments of crustaceans and insects are aligned: they correspond to each other in a one-to-one way,” said Dr. Bruce.
‘I used CRISPR-Cas9 to “eliminate” (mutate the gene in the genome so that it no longer works) each of these genes in parhyale, and then compared my results with what has already been published in insects for each of these genes. ‘
This showed that those genes corresponded to the six leg segments furthest from the body wall, at the end of the leg.
But the parhyale has an additional seventh leg segment near its body wall.
Dr. Bruce referred to an 1893 study that insects had incorporated their proximal leg region (the one closest to the body) into the body wall.
A more recent theory from the 1980s suggested that the small lobes on the leg subsequently moved to the back and formed wings.
“I thought, wow, my genomic and embryonic data support these old theories,” he said.
In the photo, a group of parhyale crustaceans eating. Parhyales belong to the classification of arthropods, which also includes insects such as beetles
From this, he concluded that insect wings evolved from existing structures found in the common ancestor of crustaceans and insects.
Although the wings are a consequence of what is now the insect’s body wall, they owe their origin to the leg segment of an ancestral arthropod.
“People are very excited about the idea that something like insect wings may have been a new breakthrough of evolution,” said MBL director Nipam Patel.
“But one of the stories that emerges from genomic comparisons is that nothing is brand new – everything came from somewhere – and you can, in fact, figure out where.”
The study was published in Nature Ecology & Evolution.
WHAT IS CRISPR-CAS9?
Crispr-Cas9 is a tool for making precise changes to DNA, discovered in bacteria.
The acronym stands for “Clustered Regularly Inter-Spaced Palindromic Repeats”.
The technique involves a DNA cutting enzyme and a small label that tells the enzyme where to cut.
The CRISPR / Cas9 technique uses tags that identify the location of the mutation and an enzyme, which acts like tiny scissors, to cut the DNA at a precise point, allowing the removal of small portions of a gene
By modifying this tag, scientists are able to target the enzyme to specific regions of the DNA and make precise cuts wherever they want.
It was used to “silence” genes, effectively shutting them down.
When the cellular machinery repairs the DNA break, it removes a small piece of DNA.
In this way, researchers can precisely deactivate specific genes in the genome.
The approach has previously been used to modify the HBB gene responsible for a condition called β-thalassemia.
.
[ad_2]
Source link
