Sea spiders regrow other body parts besides limbs, study shows

After having their lower halves amputated, the majority of the spiders recovered and produced new muscles.
Nergis Firtina
Sea spider.
Sea spider.

David Haintz/iStock 

A new study shows that sea spiders may regenerate body components following amputation in addition to limbs.

As reported by Science News, several species can regenerate lost body parts even though it's not frequent. However, scientists believed that an arthropod's ability to grow new legs was the extent of its abilities, maybe because of their hard exteriors, which prevent them from growing new body parts.

"Nobody had expected this," said senior author of the study Gerhard Scholtz of Humboldt University in Berlin to Phys. "We were the first to show that this is possible."

"Crabs can even automatically get rid of their limbs if they are attacked," Scholtz said. "They replace it by a new limb," he added.

Most of the spiders recovered

Even after having their lower halves amputated, the majority of the 19 young spiders recovered and produced new muscles and other portions of their lower halves; however, the regeneration wasn't always perfect. Some of the young spiders had six or seven legs rather than eight.

Four adults did not regenerate, according to biologist and co-author of the study Georg Brenneis. This may be the case because adults no longer molt as they grow, which suggests that regeneration and molting are somehow related. Two newborn sea spiders likewise showed no signs of regeneration. The spiders managed to survive despite having only four legs and no anus. The two regurgitated waste out of their mouths rather than passing it.

Sea spiders regrow other body parts besides limbs, study shows
Live subadult male (ventral view) directly after a molt, featuring three freshly regenerated, transparent legs (small white arrowheads).

Solving the mechanism could be the next step

The next step might be to look for the regrowth mechanism. "We can try to find out on the cellular level and the molecular level what indicates the regeneration," Scholtz said, as per Phys.

"In the end, maybe the mechanisms we detect in arthropods may help medical treatments of limb loss or finger loss and so on in humans," Scholtz added. "This is always the hope."

The study was published in PNAS on January 23.

Study abstract:

Regenerative abilities and their evolution in the different animal lineages have fascinated generations of biologists. While some taxa are capable of restoring entire individuals from small body fragments, others can regrow only specific structures or lack structural regeneration completely. In contrast to many other protostomes, including the segmented annelids, molting animals (Ecdysozoa) are commonly considered incapable of primary body axis regeneration, which has been hypothesized to be linked to the evolution of their protective cuticular exoskeleton. This holds also for the extraordinarily diverse, segmented arthropods. Contradicting this long-standing paradigm, we here show that immatures of the sea spider Pycnogonum litorale reestablish the posterior body pole after transverse amputation and can regrow almost complete segments and the terminal body region, including the hindgut, anus, and musculature. Depending on the amputation level, normal phenotypes or hypomeric six-legged forms develop. Remarkably, also the hypomeric animals regain reproductive functionality by ectopic formation of gonoducts and gonopores. The discovery of such complex regenerative patterns in an extant arthropod challenges the hitherto widely assumed evolutionary loss of axial regeneration during ecdysozoan evolution. Rather, the branching of sea spiders at the base of Chelicerata and their likely ancestral anamorphic development suggests that the arthropod stem species may have featured similar regenerative capabilities. Accordingly, our results provide an incentive for renewed comparative regeneration studies across ecdysozoans, with the aim to resolve whether this trait was potentially even inherited from the protostome ancestor.

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