The Fongoli savanna in southeast Senegal offers a unique ecosystem. Temperatures can rise above 110 degrees Fahrenheit with brush fires sweeping across. The chimpanzees who live on these savannas weren’t well understood. Erin Wessling at the Max Planck Institute for Evolutionary Anthropology studied these chimpanzees. She compared these chimps to forest chimpanzees. The Fongoli savanna chimps offer a unique window to early hominids since millions of years ago Australopithecus and the like moved from the forest the grass lands. By studying the Fongoli chimpanzees we can understand how difficult the transition was, and the ecological influence towards major changes seen in humans, like upright walking, sweat glands and loss of body hair.
The Fongoli chimpanzees offer evidence of how stressful it can be to cope with the intense heat of a savanna, rather than the forest. They don’t roam far from water sources and shift some of their hunts for food to nighttime. Credit Frans Lanting/lanting.com
Wessling published findings in the Journal of Human Evolution last week. Before any sort of studying occurred, getting the apes accustomed to the group took 4 years. Some unique behaviors were noted that contrasted to forest chimps. See, forest chimps get their water content from their diet — i.e. eating fruit. The Fongoli chimps don’t readily have fruit so they need to drink regularly. They rarely ventured away from sources of water. Also the Fongoli chimps rested mostly during the heat of the day. They searched for food at dusk, and sometimes swam in ponds during the wet season. At nights they are more socially active than forest chimps.
Wessling decided to analyze urine for creatine, cortisol and C-peptide. The C-peptide reflects nutrition, while creatine reflects hydration and lastly cortisol, a steroid hormone, reflects stress. You can imagine the challenges on collecting urine from savanna chimps in the arid climate of Fongoli. Somehow, Wessling collected 368 urine samples from 20 chimps. The chimps’ c-peptide levels showed adequate calories food. We already knew Fongoli chimps fish for termites with sticks! The other two lab values painted a different picture. Many of the chimps had produced high levels of cortisol. Life on the savanna is very stressful. And their creatinine levels were also high, evidence that the heat of the savanna caused them to become dehydrated.
Africa’s rainforests and savannas have waxed and waned in size and distribution over time. This is happening in west Africa and millions of years ago this happened in east Africa. Hominids moved into open savanna grasslands, like that seen now in Fongoli. By studying the Fongoli chimps we can see how early hominids may have changed some of their behaviors, they may stayed near water and shifed lot of activity from day to night. But the hard-pressed heat offered a lot of stress which may have selected for higher sweat glands and less body hair.
