The Lothagam North Pillar Site was a communal cemetery constructed and used over a period of several centuries, between about 5,000 and 4,300 years ago. Early herders built a platform approximately 30 meters in diameter and excavated a large cavity in the center to bury their dead. After the cavity was filled and capped with stones, the builders placed large, megalith pillars, some sourced from as much as a kilometer away, on top. Stone circles and cairns were added nearby. An estimated minimum of 580 individuals were densely buried within the central platform cavity of the site. Men, women, and children of different ages, from infants to the elderly, were all buried in the same area, without any particular burials being singled out with special treatment. Additionally, essentially all individuals were buried with personal ornaments and the distribution of ornaments was approximately equal throughout the cemetery. These factors indicate a relatively egalitarian society without strong social stratification.

Historically, archeologists have theorized that people built permanent monuments as reminders of shared history, ideals and culture, when they had established a settled, socially stratified agriculture society with abundant resources and strong leadership. It was believed that a political structure and the resources for specialization were prerequisites to engaging in monument building. Ancient monuments have thus previously been regarded as reliable indicators of complex societies with differentiated social classes. However, the Lothagam North cemetery was constructed by mobile pastoralists who show no evidence of a rigid social hierarchy. “This discovery challenges earlier ideas about monumentality,” explains Elizabeth Sawchuk of Stony Brook University and the Max Planck Institute for the Science of Human History. “Absent other evidence, Lothagam North provides an example of monumentality that is not demonstrably linked to the emergence of hierarchy, forcing us to consider other narratives of social change.”

The discovery is consistent with similar examples elsewhere in Africa and on other continents in which large, monumental structures have been built by groups thought to be egalitarian in their social organization. This research has the potential to reshape global perspectives on how — and why — large groups of people come together to form complex societies. In this case, it appears that Lothagam North was built during a period of profound change. Pastoralism had just been introduced to the Turkana Basin and newcomers arriving with sheep, goats, and cattle would have encountered diverse groups of fisher-hunter-gatherers already living around the lake. Additionally, newcomers and locals faced a difficult environmental situation, as annual rainfall decreased during this period and Lake Turkana shrunk by as much as fifty percent. Early herders may have constructed the cemetery as a place for people to come together to form and maintain social networks to cope with major economic and environmental change.

“The monuments may have served as a place for people to congregate, renew social ties, and reinforce community identity,” states Anneke Janzen also of the Max Planck Institute for the Science of Human History. “Information exchange and interaction through shared ritual may have helped mobile herders navigate a rapidly changing physical landscape.” After several centuries, pastoralism became entrenched and lake levels stabilized. It was around this time that the cemetery ceased to be used.

“The Lothagam North Pillar Site is the earliest known monumental site in eastern Africa, built by the region’s first herders,” states Hildebrand. “This finding makes us reconsider how we define social complexity, and the kinds of motives that lead groups of people to create public architecture.”

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Materials provided by Max Planck Institute for the Science of Human History. Note: Content may be edited for style and length.

Early this spring, Rice University evolutionary biologist Scott Egan stood in a patch of live oak scrub habitat in South Florida and scanned the trees for something he’d never seen outside his lab — a wispy, orange vine twining itself around swollen stems or pea-sized growths on the underside of oak leaves.

Egan needed visual confirmation of something he and his students noticed in the lab a few months earlier: love vine, a parasitic plant, latching onto and feeding off of not the tree itself, but the tumor-like growths made by his favorite insects, gall wasps.

“I went to spots where I knew that my gall-formers and the vines were, and I just blurred my eyes across the tops of the trees,” Egan said, re-enacting the moment he scanned the forest. “And, once you have seen it, you can’t not see it. I’m like, ‘Oh. It’s everywhere. I can’t not find it, on this branch, or on this one or this one.”

For Egan, who has spent 17 years studying gall-forming insects and logged thousands of miles collecting samples from oak forests across a dozen U.S. states, it was a revelation.

“I had never seen this,” Egan said. “But the fact that no one, as far as we know, had ever documented this was incredible because biologists have studied each of these — the vines and the insects — for more than a century.”

In ecological parlance, the find was a new trophic interaction between two species, meaning that one was feeding off the other. “Basically, you have a parasitic plant attacking a parasitic insect inside of another host, a host they share,” he said.

The new discovery is the subject of a paper this week in Current Biology. Egan, an assistant professor of biosciences at Rice, said the find is exciting because it shows a new aspect of nature that hadn’t previously been noticed and because it could offer clues about ways to control agricultural pests and perhaps even fight cancer.

“Galls are like tumors in many ways,” Egan said. “The wasps induce them to grow at the site where they lay their eggs, but the galls are part of the tree. The cells there have the same DNA as any other cell in the tree. They’ve just been reprogrammed to grow and behave in a way that is ultimately harmful to the tree.

“If we can find out how the vines identify the galls, how they zero in on them, it could potentially provide new clues for targeting and fighting cancer,” he said.

Gall-forming wasps are among 13,000 insect species worldwide that use biochemistry to trick trees and other plants into growing their nurseries for them. One species that’s native to Texas and Florida is Belonocnema treatae, — also called B. treatae — which lays its eggs only on the underside of newly growing oak leaves. A mix of venom and proteins laid down with the egg coax the tree into growing a smooth sphere of hard brown material around the egg. Encased inside this crypt, the larval wasp feeds on a steady flow of nutrients drawn directly from the tree’s vascular network, and emerges when it is mature.

In the fall of 2017, study co-author Glen Hood, a Rice Academy Postdoctoral Fellow working in Egan’s lab, had spent three long days gathering samples over a 1,000-mile route that wound through Florida.

“At each site, he finds our gall-formers, collects foliage with our gall wasps on them and seals them in large, 1-gallon plastic bags,” Egan said. “There are up to five bags for each site. So he comes back with a bunch of bags, and we get everyone in the lab together to sit around tables and go through each bag by hand, dividing out the galls from the leaves, stems and other material. It takes all day.”

Graduate student Linyi Zhang and a group of undergraduates were the first to notice the strange S-shaped twist of love vines, or Cassytha filiformis, growing around and between B. treatae galls on the underside of a leaf. Zhang brought the sample to Egan, but he was unconvinced.

“She said, ‘Hey, I think the vine’s attached to the gall,'” Egan recalled. “I looked at it and said, ‘No. They don’t interact. That’s just a fruit or seed from the parasitic plant,’ but she didn’t give up, so we took a closer look under the microscope, and I said, ‘No?! This cannot be.’

“I cut it in half, and right in the center was a fully mature but mummified adult wasp,” Egan said.

The group gathered all the material it had just sorted and went through all of it again. The biologists found several more samples, and in the months since, Egan, Hood, Zhang and co-author Mattheau Comerford, another Ph.D. student, have found dozens more, including examples of the vines attacking other species of gall-forming wasps. Out of 51 dissected samples of B. treatae galls attacked by love vines, 23 contained a desiccated, mummified adult. In contrast, only two of the 101 galls not attacked by vines contained dead wasps.

“The attacks are also associated with different gall sizes,” Egan said. “We found the vines attached to galls that were slightly larger than average. That means the vine is either only attacking larger galls, or the vine is inducing the galls that it attacks to grow bigger, perhaps to draw more energy from them.”

Egan said the discovery of the new trophic interaction is exciting because it shows an aspect of nature that hadn’t previously been noticed and because it’s possible that similar interactions happen between many other species.

“This is the first time anyone has ever discovered a parasitic plant and parasitic gall wasp interacting on a shared host plant,” Egan said. “This could be unique, but biologists have catalogued more than 1,300 species of gall-forming wasps and more than 4,000 species of parasitic plants, so this could just be the tip of the iceberg.”

The organ-on-a-chip concept has garnered significant attention from researchers for about a decade. The idea is to create small-scale, biological structures that mimic a specific organ function, such as transferring oxygen from the air into the bloodstream in the same way that a lung does. The goal is to use these organs-on-a-chip — also called microphysiological models — to expedite high-throughput testing to assess toxicity or to evaluate the effectiveness of new drugs.

But while organ-on-a-chip research has made significant advances in recent years, one obstacle to the use of these structures is the lack of tools designed to actually retrieve data from the system.

“For the most part, the only existing ways of collecting data on what’s happening in an organ-on-a-chip are to conduct a bioassay, histology, or use some other technique that involves destroying the tissue,” says Michael Daniele, corresponding author of a paper on the new biosensor. Daniele is an assistant professor of electrical engineering at North Carolina State University and in the Joint Department of Biomedical Engineering at NC State and the University of North Carolina, Chapel Hill.

“What we really need are tools that provide a means to collect data in real time without affecting the system’s operation,” Daniele says. “That would enable us to collect and analyze data continuously, and offer richer insights into what’s going on. Our new biosensor does exactly that, at least for oxygen levels.”

Oxygen levels vary widely across the body. For example, in a healthy adult, lung tissue has an oxygen concentration of about 15 percent, while the inner lining of the intestine is around 0 percent. This matters because oxygen directly affects tissue function. If you want to know how an organ is going to behave normally, you need to maintain “normal” oxygen levels in your organ-on-a-chip when conducting experiments.

“What this means in practical terms is that we need a way to monitor oxygen levels not only in the organ-on-a-chip’s immediate environment, but in the organ-on-a-chip’s tissue itself,” Daniele says. “And we need to be able to do it in real time. Now we have a way to do that.”

The key to the biosensor is a phosphorescent gel that emits infrared light after being exposed to infrared light. Think of it as an echoing flash. But the lag time between when the gel is exposed to light and when it emits the echoing flash varies, depending on the amount of oxygen in its environment. The more oxygen there is, the shorter the lag time. These lag times last for mere microseconds, but by monitoring those times, researchers can measure the oxygen concentration down to tenths of a percent.

In order for the biosensor to work, researchers must incorporate a thin layer of the gel into an organ-on-a-chip during its fabrication. Because infrared light can pass through tissue, researchers can use a “reader” — which emits infrared light and measures the echoing flash from the phosphorescent gel — to monitor oxygen levels in the tissue repeatedly, with lag times measured in the microseconds.

The research team that developed the biosensor has tested it successfully in three-dimensional scaffolds using human breast epithelial cells to model both healthy and cancerous tissue.

“One of our next steps is to incorporate the biosensor into a system that automatically makes adjustments to maintain the desired oxygen concentration in the organ-on-a-chip,” Daniele says. “We’re also hoping to work with other tissue engineering researchers and industry. We think our biosensor could be a valuable instrument for helping to advance the development of organs-on-a-chip as viable research tools.”

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Materials provided by North Carolina State University. Note: Content may be edited for style and length.