Lemurs keep evolving new species, even after 50 million years

Lemurs first arrived on the island of Madagascar 53.2 million years ago, probably hitching a ride on a vegetation raft from mainland Africa. The island was predator free, and the lemurs evolved into an abundance of species to thrive in its various habitats—an expansion that hasn’t stopped since. 

Scientists typically expect such rapid species growth to eventually slow down. However, in a study recently published in the journal Nature Communications, a team of researchers presents evidence that lemurs defy this evolutionary principle. 

“Lemurs are often cited as an example of adaptive radiation, as more than 100 extant species have evolved and filled ecological niches on Madagascar,” the researchers wrote in the paper. Adaptive radiation is the rapid increase in the number of species of a certain lineage. “However, recent work suggests that lemurs lack a hallmark of other adaptive radiations: explosive speciation rates that decline over time.”

While you’re probably imagining the iconic black-and-white primate from the PBS Kids show Zoboomafoo, lead author and Oregon State University biologist Katie Everson explained in a statement that lemurs come in numerous different forms—from Earth’s smallest primate (Madame Berthe’s mouse lemur) to a now-extinct lemur species that was as large as a gorilla. Because they are all native to Madagascar, the island hosts a whopping 15 percent of all primate species. 

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In the study, Everson and her colleagues conducted a phylogenomic analysis (the study of evolution through genomes) to investigate lemur evolution, including the timeline of their arrival on Madagascar. “Our analyses reveal multiple bursts of diversification (without subsequent declines) that explain much of today’s lemur diversity,” the researchers explained in the paper, whose work also. Today, three specific groups of lemurs—mouse lemurs, sportive lemurs, and brown lemurs—have very high rates of speciation, or how fast new species form.

Speciation rates provide insight into how quickly biodiversity is created, and can reveal evolutionary patterns, and can serve to compare different animal groups. For instance, the team found that diversification among lorises, bushbabies, and galagos (lemur primate relatives) on continental Africa and Asia is much slower. This indicates that “something special is happening on Madagascar,” Everson admitted in the statement. 

“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,” she added. “That suggests that hybridization in these primates is not an evolutionary dead end, as it often can be, but potential fuel for diversification.”

The iconic animals, however, are at risk of extinction, with 95 percent of lemur species considered threatened. According to the team, the data presented in their study will influence future conservation actions.