The eating habits of antelopes and their relatives are responsible, at least in part, for the creation of the savanna, according to a new study.
The finding provides an answer to one of the big questions in the Earth’s ecological history. Scientists made the discovery in an unusual way—by starting with what they observe today and then working backwards.
You may have seen pictures or films of gazelles delicately picking leaves off branches full of wicked-looking spikes that are several centimeters long. Scientists uncovered what happened in the past by mapping the distribution and evolution of the spiny plants on which gazelles and their relatives like to feed today.
“It’s been difficult to get a picture of how savanna ecosystems evolved because the conditions needed to preserve animal and plant fossils are very different from one another,” says Jonathan Davies, a member of the research team and an expert in phylogenetic analysis who teaches biology at McGill University.
“But…we were able to sequence and compare DNA from nearly 2,000 trees, and show that African plants only developed spines about 15 million years ago. That was about the same time that a new type of mammal—antelope and their relatives—spread across the continent following the collision between the continental plates of Africa and Eurasia.”
Prior to this collision, the large, now extinct, ancestors of browsing elephants and hyrax had dominated the African continent. “Elephants were so massive that they simply tromped over the trees so spines provided little defense against them,” says Tristan Charles-Dominique of the University of Cape Town, the lead author of the study.
“But the antelopes who came after them were highly efficient browsers, often using their lips to take delicate bites from the leaves of these plants. So it is likely that plants developed spines to defend themselves against these new plant ‘predators.’”
What emerges from the research is a picture of a remarkable “arms race” of evolution between plants and plant-eaters. The arrival of a new and efficient group of herbivores on the African continent that feasted upon young forest trees opened up the ancient forests to the spread of grass. Spiny plants evolved and developed longer and longer spines in response, in an attempt to protect themselves from these browsers.
One of the implications of the study, according to William Bond, who is also based at the University of Cape Town, is that the loss of large mammals like antelope as a result of human activity may have profound impacts on the African landscape, with today’s savannas reverting to thicket or forest.
The findings appear in the Proceedings of the National Academy of Sciences. Funding came from the Mellon Foundation, the Claude Leon Foundation, the South African National Research Foundation, Genome Canada, the Ontario Genomics Institute, the International Development Research Centre, the University of Johannesburg Analytical Facility, and the Royal Society.
Source: McGill University