Madagascar is famous for its lemurs; their ancestors arrived 53 million years ago, and the largely predator-free island has allowed them to flourish and diversify. New research suggests lemur evolution is anything but ordinary; they have not plateaued in the same way as most other island species.
Successive evolutionary bursts
Most island species exhibit a single evolutionary radiation, a period of rapid species expansion. Usually, this happens once. Katie Everson and her team at Oregon State University have unearthed compelling evidence that lemur species have not followed this pattern; instead, they have evolved in multiple successive radiations.
A ring-tailed lemur. Photo: Shutterstock
The ancestors of modern lemurs likely arrived on Madagascar aboard natural rafts that floated over from Africa. As the primates adapted to the various ecosystems, over 100 different species of lemurs evolved, all endemic to the island. Sixteen of these species have gone extinct since humans colonised the island 2,000 years ago.
Three groups show particularly high speciation rates: mouse lemurs (Microcebus), sportive lemurs (Lepilemur), and brown lemurs (Eulemur). Researchers looked at the DNA of 129 individual lemurs from 79 different species. The DNA reveals that these groups not only have exceptionally high speciation rates — far exceeding those of their continental cousins like lorises and bushbabies — but also share significant genetic interchange between species.
“The lemur clades with high diversification rates also have high rates of genetic material from one species becoming part of the gene pool of another, a phenomenon known as genomic introgression,” explained Everson. “That suggests that hybridization in these primates is not an evolutionary dead end, as it often can be, but potential fuel for diversification.”
A gray mouse lemur. Photo: Shutterstock
For context, lorises (their distant relatives of mainland Africa and Asia) show a speciation rate of just 0.15 new species per million years. Lemurs average around 0.44.
Rapid evolution not enough to survive humans
Everson warns that even rapid evolution is not saving lemurs from the threats we pose: “At the same time that more and more lemur species are still evolving, we are also driving them rapidly to extinction.”
A depressing 95% of lemur species are now considered threatened. Conservation efforts must now consider not just the preservation of individual species, but the conservation of this incredible evolutionary process.
