An international research team led by scientists in Canada has uncovered a likely explanation for one of the more unusual features of snake development: why embryos curl into tight spirals before hatching. This coiling behavior appears to help snakes accommodate the exceptionally long bodies that distinguish them from every other vertebrate. The findings, published in Current Biology, suggest that the spiral forms as the embryo's body rapidly lengthens while its gut acts as a tether.
That physical constraint causes the growing body to buckle and twist into a right-handed coil. "It's like when you adjust the length of a strap and the longer, buckling side of the loop twists," explains senior author and team leader Dr. Tetsuto Miyashita, evolutionary biologist at the Canadian Museum of Nature.
The discovery adds snake embryos to a long list of naturally occurring spiral structures that scientists are still working to understand. "There is a touch of mystery to spirals, and we are only beginning to understand how these shapes are produced in animals, such as our looping intestine, snail shells, and now these beautifully coiled snake embryos," says lead author Alexandra Weber, now a graduate student in zoology at the University of British Columbia. Adds Miyashita: "These puzzles beckon our curiosity.
After all, spiral forms in nature have inspired human creations ranging from rotini pasta, to a barber's pole or even portrayals of the biblical 'Tower of Babel'." The project itself grew out of an unusual circumstance. During the COVID lockdown in 2020, Miyashita was working from home and looking for a research question his students could investigate without access to laboratories or museum collections. "Then the lightbulb turned on.
I had inherited from my PhD advisor this fascination with asymmetries in animal forms. So every time I saw images of snake embryos in papers, I wondered whether they are right- or left-handed in their coiling." That question became the foundation of the study. Miyashita asked Weber, who was then at Carleton University, along with two undergraduate students at the University of Ottawa, to search published research and museum databases for photographs of developing snakes.
"We obtained pictures for more than 900 embryos from 39 snake and other limbless squamate species. That's a statistically robust sample." A clear pattern emerged. During the first several weeks after the eggs were laid, the embryos appeared to coil only dextrally, meaning to the right, as viewed from head to tail.
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