Arthropods are among the most successful animals on the planet. They populate the sea (horseshoe crabs), the sky (fruit flies) and the earth (scorpions) in large numbers and are defined by their exoskeletal outsides and segmented legs and bodies.
These adaptable, modular pieces can explain why these animals are so well suited for life in every corner of the planet. Their joined legs and split bodies also help to give hints as to how they have developed.
A new study published March 26, 2018 in the Proceedings of the National Academy of Sciences University of Wisconsin-Madison researchers Emily Setton and Prashant Sharma show that the common house spider and its Arachnidae renounce a gene that participates in segmented minds instead recycle legends to accomplish this task.
"We study spiders, scorpions, and others a broader evolutionary history and a glimpse of the complex world of arthropods," says Setton, a major in anthropology and biology, when she graduated as one of only two study authors. "The world is a great place full of amazing variety, we want to know how it happens, how to build an animal?"
Sharma, a professor of integrative biology, came to the UW-Madison Museum of Natural History in 2015 from the American and researched some of the scariest, most crab-like species on the planet, such as poisonous Arizona scorpions, Colorado tarantulas and huge ones , Blind Sea Spiders from the Antarctic
"We work with really difficult animals for learning," he says. "A big question for the lab is, how is genetic diversity genetically, evolutionarily built, how are old lineages related, and what are the genetic mechanisms that underlie the differences between them?"
For example, how can the same appendages – and the same sequences of the genetic code – make the lobster claws also the mouthparts of a moth, the raptoric front legs of a praying mantis and the eye of a flatworm?
In the study, Setton and Sharma show that a pair of genes known as Sp6-9 and Dll, which are normally used to tell a developing insect or arachnid embryo where legs grow, are from a group Arachnids was also used to tell the embryo where to build its head. These spiders lack another gene called Sp5, which normally leads to correct head segmentation in other arthropods, such as fruit flies.
"This is the plot that tells the story," says Sharma, because it allows scientists like him to follow the evolutionary and genetic history of this group of animals, united by the loss of a particular gene.
"It's a very arachnid-specific loss," adds Setton, who plans to attend a doctoral program this fall. 19659005] It was ingenuity, hard work and a stroke of luck that led her and Sharma to the story in the first place.
Sharma is interested in the development of spider organs for spiders called spiders. He and Setton searched for the genes that determine their formation and explored whether they, like other recycled parts, were modified legs. This led Setton to consider a variety of genes involved in the development of spider-leg development. Unexpectedly, she also found in the elimination of leg development genes in arachnid embryos that their head segments disappeared.
There is a saying in biology that nature is thrifty, or, as Setton explains, "evolution does not want to reinvent the wheel"
It is relatively common for a given gene to have a variety of functions Species are dictated to species, such as the gene that encodes the jawbone of reptiles, and ear bones in humans.
Spiders, scorpions and two other animals testing Setton and Sharma seem to have done this with Sp6-9 and Dll.
Setton also identified a gene called arrow, which, when disrupted, causes a cascade of cellular signaling events for the first time, important relationships between genes of segmentation and leg development in insects and arachnids.
Her work has proven to be challenging and personally fulfilling.
"I love that I can come and be curious every day," says Setton, who graduated in December
It does not hurt that she is not afraid of spiders. In fact, one of the highlights of working with Sharma on the field is to gain a degree. A postdoctoral fellow in his laboratory plans to collect blind cave arthropods in Israel this summer, and a graduate student went to Australia with him last August
"You go where the animals are," he says.
For the Spiders In the study that helps biologists track the evolutionary history of one of the planet's most prolific animal groups, this means your kitchen window.
Knee depth in the evolution of the spider legs
Emily V.W. Setton et al., "Cooption of an appendage pattern gene cassette in the head segmentation of arachnids" PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1720193115