In 1898, two male lions terrorized a bridge builders’ camp on the Tsavo River in Kenya. The lions, huge and maneless, crept into the camp at night, raided the tents and dragged away their victims. Tsavo’s infamous “man-eaters” killed at least 28 people before they were shot dead by Lieutenant Colonel John Henry Patterson, the project’s civil engineer. Patterson sold the lions’ remains to the Field Museum of Natural History in Chicago in 1925.
In a new study, Field Museum researchers collaborated with scientists at the University of Illinois Urbana-Champaign on an in-depth analysis of hairs carefully extracted from lions’ broken teeth. The study used microscopy and genomics to identify some of the species that lions consumed. The findings are reported in the journal. Current biology.
The original discovery of the hairs came in the early 1990s, when Thomas Gnoske, director of collections at the Field Museum, found the lions’ skulls in storage and examined them for signs of what they had consumed. He was the first to determine that they were older adult males, despite not having a mane. He was also the first to notice that thousands of broken and compacted hairs had accumulated in the exposed cavities of the lions’ damaged teeth during their lifetime.
In 2001, Gnoske and Julian Kerbis Peterhans, a professor at Roosevelt University and associate curator at the Field Museum, first reported the damaged state of the teeth (which they hypothesized could have contributed to predation on humans by lions) and the presence of hairs embedded in broken and partially healed teeth. A preliminary analysis of some of the hairs suggested they were from eland, impala, oryx, porcupine, wild boar and zebra.
In the new study, Gnoske and Peterhans provided a new examination of some of the hairs. Co-authors Ogeto Mwebi, senior research scientist at the National Museums of Kenya; and Nduhiu Gitahi, a researcher at the University of Nairobi, carried out the microscopic analysis of the hairs. U. of I. postdoctoral researcher Alida de Flamingh led genomic research on hairs with U. of I. anthropology professor Ripan S. Malhi. They focused on a separate sample of four individual hairs and three bundles of hairs taken from the lions’ teeth.
Malhi, de Flamingh and their colleagues are developing new techniques to learn about the past by sequencing and analyzing ancient DNA preserved in biological artifacts. His work in partnership with indigenous communities has yielded numerous insights into human migration and the pre- and post-colonial history of the Americas. They have helped develop tools to determine the species and geographical origins of the current and ancient tusks of African elephants. They have advanced their efforts to isolate and sequence DNA from museum specimens and have traced the migration and genomic history of dogs in the Americas.
In the current work, de Flamingh searched for and first found familiar marks of age-related degradation in what remained of the nuclear DNA in the hairs of lions’ teeth.
“To establish the authenticity of the sample we are analyzing, we look to see if the DNA has these patterns that are normally found in ancient DNA,” he said.
Once the samples were authenticated, de Flamingh focused on the mitochondrial DNA. In humans and other animals, the mitochondrial genome is inherited from the mother and can be used to trace matrilineal lineages through time.
According to the researchers, targeting hair mtDNA has several advantages. Previous studies have found that the hair structure preserves mtDNA and protects it from external contamination. MtDNA is also much more abundant than nuclear DNA in cells.
“And because the mitochondrial genome is much smaller than the nuclear genome, it is easier to reconstruct into potential prey species,” de Flamingh said.
The team created a database of mtDNA profiles of potential prey species. This reference database was compared with mtDNA profiles obtained from hairs. The researchers took into account species suggested in the above analysis and those known to be present in Tsavo at the time the lions were alive.
The researchers also developed methods to extract and analyze mtDNA from hair fragments.
“We were even able to get DNA from fragments that were shorter than a little fingernail,” de Flamingh said.
“Traditionally, when people want to get DNA from hairs, they focus on the follicle, which will have a lot of nuclear DNA,” Malhi said. “But these were fragments of hair shafts that were more than 100 years old.”
The effort produced a treasure trove of information.
“DNA analysis of the hair identified giraffes, humans, oryx, antelope, wildebeest and zebra as prey, and also identified hairs that originated from lions,” the researchers reported.
The lions were found to share the same mitochondrial genome inherited from the mother, supporting early reports theorizing that they were siblings. Their mtDNA was also consistent with an origin in Kenya or Tanzania.
The team discovered that the lions had devoured at least two giraffes, along with a zebra that likely originated in the Tsavo region.
The discovery of wildebeest mtDNA was surprising because the closest wildebeest population in the late 1890s was about 50 miles away, the researchers said. Historical reports, however, note that the lions left the Tsavo region for about six months before resuming their attacks on the bridge builders’ camp.
The absence of buffalo DNA and the presence of a single buffalo hair, identified by microscopy, was surprising, de Flamingh said. “From what the Tsavo lions eat today, we know that buffalo is the preferred prey,” he said.
“Colonel Patterson kept a handwritten field diary during his stay in Tsavo,” said Kerbis Peterhans. “But he never recorded in his diary having seen buffalo or indigenous cattle.”
At the time, cattle and buffalo populations in this part of Africa were devastated by rinderpest, a highly contagious viral disease brought to Africa from India in the early 1880s, Kerbis Peterhans said.
“It virtually wiped out cattle and their wild relatives, including the Cape buffalo,” he said.
The human hair mitogenome has a wide geographic distribution and the scientists declined to describe or analyze it further for the current study.
“There may still be descendants in the region today and, to practice ethical and responsible science, we are using community-based methods to expand the human aspects of the broader project,” they wrote.
The new findings are an important expansion of the types of data that can be extracted from skulls and hairs from the past, the researchers said.
“We now know that we can reconstruct complete mitochondrial genomes from hair fragments from lions that are more than 100 years old,” de Flamingh said.
There were thousands of hairs embedded in the lions’ teeth, compacted over a period of years, the researchers said. Additional analyzes will allow scientists to at least partially reconstruct the lions’ diet over time and perhaps determine when their habit of hunting humans began.
Malhi is also affiliated with the Carl R. Woese Institute for Genomic Biology at the U. of I.
The National Science Foundation and the US Department of Agriculture supported this research.