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Lemurs are among the best-known representatives of Madagascar's animal kingdom. They make up more than 15% of all primate species living today—even though the island covers less than 1% of Earth's land surface.

An international research team involving the German Primate Center—Leibniz Institute for Primate Research (DPZ) has now shown: The species diversity of lemurs is not the result of a single large radiation, as is often assumed for animals on islands. Instead, the species evolved in multiple successive radiations—up to the middle and later Pleistocene (around 500,000 years ago). It is also remarkable that interbreeding between different lemur species—hybridizations—do not represent evolutionary deadends, but have even contributed to the emergence of new species.

The work is in the journal Nature Communications.

Lemurs belong to the strepsirrhines—an early lineage in primate evolution that split off from monkeys, apes and humans (haplorrhines) more than 70 million years ago. Their ancestors arrived in Madagascar around 53 million years ago, where they adapted to different habitats: from rainforests to dry and thorny forests and to mountain and coastal forests. Today, more than 100 lemur species are known. At least 16 more have become extinct in the last 2,000 years since humans colonized the island.

How new species evolved

The scientists analyzed genetic material of 79 lemur species and found that around five to six million years ago, there was a particularly strong increase of new species, especially in three genera: the mouse lemurs (Microcebus), the true lemurs (Eulemur) and the sportive lemurs (Lepilemur).

This surprised the researchers, as speciation normally slows down after an initial, rapid phase, which began in lemurs around 53 million years ago. However, these three genera not only showed a high rate of new species long after the first radiations, but also intensively exchanged genetic material between species of the same genus.

"Our analyses show that lemurs split into new species much more frequently than their closest relatives, the lorises in Africa and Asia. We were also able to show that genetic exchange, i.e. hybridization between species, was an important driver of this diversity," explains Dietmar Zinner, primate researcher in the Cognitive Ethology Laboratory at the DPZ. He worked on the study together with his colleagues Peter Kappeler, Behavioral Ecology and Sociobiology Unit, and Christian Roos, Primate Genetics Laboratory.

While lemurs produced on average 0.44 new species per million years, lorises had a speciation rate of only 0.15 new species per million years. In some groups, hybrid species were even four times more common in lemurs than species that evolved by the divergence of lineages.

The new findings help us to better understand their evolutionary history and thus to plan future conservation measures in a more targeted manner. On the one hand, hybridization can create diversity, but on the other hand it can also lead to the loss of rare species.

"In the future, conservation concepts must also take genetic diversity and the role of hybridization into account," emphasizes Zinner.

How knowledge about genes can contribute to conservation

Today, around 95% of all lemur species are considered endangered: their habitats are being destroyed and climate change is threatening them. The fact that lemurs have great potential for speciation is good news from the researchers' point of view.

"Nevertheless, this is not a license to neglect species conservation," says Roos. "Without protective measures, many of the lemur species will go extinct before they can make use of this potential."

For researchers, this means that further genomic analyses are urgently needed in order to understand the role of hybridization and environmental factors in the formation of species even more precisely. For Roos, one thing is clear when it comes to protecting lemurs: "The more we know about their evolutionary history and genetic diversity, the better we can secure their future."