Biologists genetically modify “reapers” to better understand their evolution

Opilions, also called mowers, are very common arachnids, used to waiting patiently for food in the recesses of our ceilings. But they can also prove useful to scientists to better understand the evolution of arachnids. A team of researchers genetically modified specimens of opilions to change the length or type of their legs. In addition to allowing the development of more effective genetic tools, this work also enables biologists to clarify certain gray areas concerning the segmentation or even the evolutionary development of arachnids.

Through a process known as RNA interference (RNAi), scientists were able to alter the genetic makeup of opilions so that its distinctive slender limbs became twice as short. This process – which uses a gene’s own DNA sequence and small pieces of RNA to turn off the gene – has been applied to the species Phalangium opilio, one of the most common species of opilions in the world.

A change in genes linked to limb development

The result is indeed an opilion with short legs rather than long ones. The team behind the work hope that experiences can teach us more about how these elongated limbs evolved in the first place. The study was published in the journal Proceedings of the Royal Society B. The research team hopes the work will facilitate the development of more sophisticated tools for functional genetics.

After sequencing the genome of P. opilio, the researchers identified three genes that serve as a map for various parts of the body. They then discovered that two of these genes were turned on in the legs of arachnid embryos. Turning off genes in other embryos produced different legs: at least two of their legs were shorter than normal and had turned into pedipalps, which are limbs used specifically for handling food.

Results of genetic modifications. Compared to the control group, the other groups saw the length and type of their legs change. © Guilherme Gainett et al. 2021

The team then turned off the third gene thought to be linked to the construction of legs in embryos. The legs did not turn into pedipalps, but they did get shorter and lost their tarsomers, the joints used for grip. Similar experiments were carried out on fruit flies.

Better understand the evolution of arachnids

Technically, the species P. opilio is not a spider, but rather a close relative, which makes these creatures useful in understanding how the multitude of different arachnids on our planet evolved. Not all opilions have legs that can wrap around twigs and other objects like these insects, for example. ” For the future, we are interested in understanding how genes give rise to new characteristics of arachnids, such as spider chelicera and scorpion claws, and in leveraging the genome to develop the first transgenic mowers. », Says Gainett.

The idea is that the spider’s genome duplicated itself in the distant past, giving these creatures a wide choice of genes to use for their own unique evolutionary paths – there could be a link between more complex genomes and greater variation in organism. This latest research should prove useful in future work to trace the development of P. opilio and other arachnids, to establish whether the long, slender legs were indeed something that evolved separately in each group of arthropods.

Sources: Proceedings of the Royal Society B

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