A crucial link in the life cycle of one parasitic plant may be found in a surprising place — the bellies of the descendants of an ancient line of rabbits.

Given their propensity for nibbling on gardens and darting across suburban lawns, it can be easy to forget that rabbits are wild animals. But a living reminder of their wildness can be found on two of Japan’s Ryukyu Islands, if you have the patience to look for it: the endangered Amami rabbit, a “living fossil” that looks strikingly similar to ancient Asian rabbits.
One estimate suggests there are fewer than 5,000 of the animals left in the wild. The lives of Amamis (Pentalagus furnessi) are shrouded in mystery due to their rarity, but they seem to play a surprising ecological role as seed dispersers, researchers report January 23 in Ecology.

Seed dispersal is the main point in a plant’s life cycle when it can move to a new location (SN: 11/14/22). So dispersal is crucially important for understanding how plant populations are maintained and how species will respond to climate change, says Haldre Rogers, a biologist at Virginia Tech in Blacksburg, who was not involved with the study. Despite this, seed dispersal hasn’t received much attention, she says. “We don’t know what disperses the seeds of most plants in the world.”

Locals from the Ryukyu Islands were the first to notice that the “iconic yet endangered” Amami rabbit was nibbling on the fruit of another local species, the plant Balanophora yuwanensis, says Kenji Suetsugu, a biologist at Kobe University in Japan.

Rabbits generally like to eat vegetative tissue from plants, like leaves and stems, and so haven’t been thought to contribute much to spreading seeds, which are often housed in fleshy fruits.

To confirm what the locals reported, Suetsugu and graduate student Hiromu Hashiwaki set up camera traps around the island to catch the rabbits in the act. The researchers were able to record rabbits munching on Balanophora fruits 11 times, but still needed to check whether the seeds survived their trip through the bunny tummies.
So the team headed out to the subtropical islands and scooped up rabbit poop, finding Balanophora seeds inside that could still be grown. By swallowing the seeds and pooping them out elsewhere, the Amami rabbits were clearly acting as seed dispersers.

Balanophora plants are parasitic and don’t have chlorophyll, so they can’t use photosynthesis to make food of their own (SN: 3/2/17). Instead, they suck energy away from a host plant. This means where their seeds end up matters, and the Amami rabbits “may facilitate the placement of seeds near the roots of a compatible host” by pooping in underground burrows, Suetsugu says. “Thus, the rabbits likely provide a crucial link between Balanophora and its hosts” that remains to be further explored, he says.
Understanding the ecology of an endangered species like the Amami rabbit can help with conserving both it and the plants that depend on it.

An animal need not be in obvious peril for a change in its number to affect seed dispersal, with potentially negative consequences for the ecosystem. For example, “we think of robins as super common … but they’ve declined a lot in the last 50 years,” Rogers says. “Half as many robins means half as many seeds are getting moved around, even though no one’s worried about robins as a conservation issue.”

Our planet may have had a recent change of heart.

Earth’s inner core may have temporarily stopped rotating relative to the mantle and surface, researchers report in the January 23 Nature Geoscience. Now, the direction of the inner core’s rotation may be reversing — part of what could be a roughly 70-year-long cycle that may influence the length of Earth’s days and its magnetic field — though some researchers are skeptical.

“We see strong evidence that the inner core has been rotating faster than the surface, [but] by around 2009 it nearly stopped,” says geophysicist Xiaodong Song of Peking University in Beijing. “Now it is gradually mov[ing] in the opposite direction.”
Such a profound turnaround might sound bizarre, but Earth is volatile (SN: 1/13/21). Bore through the ever-shifting crust and you’ll enter the titanic mantle, where behemoth masses of rock flow viscously over spans of millions of years, sometimes upwelling to excoriate the overlying crust (SN: 1/11/17, SN: 3/2/17, SN: 2/4/21). Delve deeper and you’ll reach Earth’s liquid outer core. Here, circulating currents of molten metals conjure our planet’s magnetic field (SN: 9/4/15). And at the heart of that melt, you’ll find a revolving, solid metal ball about 70 percent as wide as the moon.

This is the inner core (SN: 1/28/19). Studies have suggested that this solid heart may rotate within the liquid outer core, compelled by the outer core’s magnetic torque. Researchers have also argued the mantle’s immense gravitational pull may apply an erratic brake on the inner core’s rotation, causing it to oscillate.

Evidence for the inner core’s fluctuating rotation first emerged in 1996. Geophysicist Paul Richards of Columbia University’s Lamont-Doherty Earth Observatory in Palisades, N.Y., and Song, then also at Lamont-Doherty, reported that over a span of three decades, seismic waves from earthquakes took different amounts of time to traverse Earth’s solid heart.

The researchers inferred that the inner core rotates at a different speed than the mantle and crust, causing the time differences. The planet spins roughly 360 degrees in a day. Based on their calculations, the researchers estimated that the inner core, on average, rotates about 1 degree per year faster than the rest of Earth.

But other researchers have questioned that conclusion, some suggesting that the core spins slower than Song and Richards’ estimate or doesn’t spin differently at all.

In the new study, while analyzing global seismic data stretching back to the 1990s, Song and geophysicist Yi Yang — also at Peking University — made a surprising observation.
Before 2009, seismic waves generated by sequences and pairs of repeating earthquakes — known as multiplets and doublets — traveled at different rates through the inner core. This indicated the waves from recurring quakes were crossing different parts of the inner core, and that the inner core was rotating at a different pace than the rest of Earth, aligning with Song’s previous research.

But around 2009, the differences in travel times vanished. That suggested the inner core had ceased rotating with respect to the mantle and crust, Yang says. After 2009, these differences returned, but the researchers inferred that the waves were crossing parts of the inner core that suggested it was now rotating in the opposite direction relative to the rest of Earth.

The researchers then pored over records of Alaskan earthquake doublets dating to 1964. While the inner core appeared to rotate steadily for most of that time, it seems to have made another reversal in rotation in the early 1970s, the researchers say.

Song and Yang infer that the inner core may oscillate with a roughly 70-year periodicity — switching directions every 35 years or so. Because the inner core is gravitationally linked to the mantle and magnetically linked to the outer core, the researchers say these oscillations could explain known 60- to 70-year variations in the length of Earth’s days and the behavior of the planet’s magnetic field. However, more work is needed to pin down what mechanisms might be responsible.

But not all researchers are on board. Yang and Song “identif[y] this recent 10-year period [that] has less activity than before, and I think that’s probably reliable,” says geophysicist John Vidale of the University of Southern California in Los Angeles, who was not involved in the research. But beyond that, Vidale says, things get contentious.

In 2022, he and a colleague reported that seismic waves from nuclear tests show the inner core may reverse its rotation every three years or so. Meanwhile, other researchers have proposed that the inner core isn’t moving at all. Instead, they say, changes to the shape of the inner core’s surface could explain the differences in wave travel times.

Future observations will probably help disentangle the discrepancies between these studies, Vidale says. For now, he’s unruffled by the purported chthonic standstill. “In all likelihood, it’s irrelevant to life on the surface, but we don’t actually know what’s happening,” he says. “It’s incumbent on us to figure it out.”

No backside, no problem for some young sea spiders.

The creatures can regenerate nearly complete parts of their bottom halves — including muscles, reproductive organs and the anus — or make do without them, researchers report January 23 in Proceedings of the National Academy of Sciences.

The ability to regrow body parts isn’t super common, but some species manage to pull it off. Some sea slug heads can craft an entirely new body (SN: 3/8/21). Sea spiders and some other arthropods — a group of invertebrates with an exoskeleton — can regrow parts of their legs. But researchers thought new legs were the extent of any arthropod’s powers, perhaps because tough exteriors somehow stop them from regenerating other body parts.
A mishap first clued evolutionary biologist Georg Brenneis in that sea spiders (Pycnogonum litorale) might be able handle more complex repairs too. He accidentally injured one young specimen that he was working on in the lab with forceps. “It wasn’t dead, it was moving, so I just kept it,” says Brenneis, of the University of Vienna. Several months later, the sea spider had an extra leg instead of a scar, he and evolutionary biologist Gerhard Scholtz of Humbolt University of Berlin reported in 2016 in The Science of Nature.

In the new study, most of the 19 young spiders recovered and regrew missing muscles and other parts of their lower halves after amputation, though the regeneration wasn’t always perfect. Some juveniles sported six or seven legs instead of eight.

None of four adults regenerated. That may be because adults no longer shed their skin as they grow, suggesting that regeneration and molting are somehow linked, Brenneis says. Two young sea spiders also didn’t regenerate at all. The animals survived with only four legs and without an anus. Instead of pooping, the pair regurgitated waste out of their mouths.
Next up is figuring out whether other arthropods also regenerate more than scientists thought, and how sea spiders do it, Brenneis says. “I would like to see how it works.”