Endangered lemurs: Millions of years of diversity at risk

Lemurs – small, large-eyed primates that dwell in Madagascar’s treetops – are a fascinating puzzle in the story of evolution. When they first arrived on the island millions of years ago, they found an incredibly varied landscape, stretching from humid tropical forests in the east to the dry, desert-like regions in the southwest. 

With few other mammals to compete with, these ancestral lemurs branched out into an astonishing range of shapes and sizes, from tiny mouse lemurs no bigger than a teacup to giant sloth lemurs that once roamed the forests. 

Yet in a perplexing twist, even though many species boast remarkably high genetic diversity, nearly 90% of Madagascar’s more than 100 lemur species are on the brink of extinction.

Human and climate effects on lemur diversity

Seeking answers to this paradox, an international team of anthropologists and biologists from University of Montreal (UdeM) and Pompeu Fabra University (PFU) in Spain pursued a genetic line of investigation. 

By sequencing the genomes of 162 lemurs representing 50 different species – an effort larger than any attempted before – they exposed the remarkable variety locked within lemurs’ DNA. 

The findings, published in the journal Nature Ecology & Evolution, shine a light on how both environmental conditions and human influence have shaped lemur populations over time.

The research was led by Professor Joseph Orkin, principal investigator at the UdeM multiomic primate evolution lab, and Spanish research professor Tomas Marques Bonet, head of PFU’s Institute of Evolutionary Biology, 

The project uncovered how Madagascar’s ecology and climatic changes – alongside human presence – have molded lemur genetic diversity and affected their future survival.

Lemurs have high genomic diversity

According to the study, gene flow between various lemur species has been taking place across hundreds of thousands of years. 

“As climatic shifts periodically connected once-isolated habitats, lemurs from different species and populations would interbreed, sharing genetic material that boosted their overall diversity,” Orkin said.

“On top of that, the most diverse species appear to be the ones with fragmented populations in multiple ecosystems across the island. This pattern of isolation and reconnection seems to be building up and redistributing genetic variation across the island.”

Even though many lemurs are now critically endangered, they still possess extremely high genomic diversity. 

“Many species of lemurs have super-high levels of genomic diversity, which seems counterintuitive when you consider that so many of them are critically endangered. It was really exciting to see how the ecology of Madagascar helped to shape the diversity of lemurs,” Orkin added.

Human arrival and its consequences

Although Madagascar’s natural conditions favored diverse lemur populations for ages, human influence altered this balance. The study points to a striking link between the expansion of human populations, deforestation, shifts in hunting, and the sharp decline in lemur numbers. 

It remains unknown exactly when the first humans set foot on the island, but signs suggest a population surge around 1,000 years ago, followed by dramatic changes in the landscape by the 1700s.

“When we looked at the genetic evidence for population declines, we kept seeing these two consistent inflection points around 1,000 and 300 years ago. It was really striking to see such a clear overlap between the timing of human population expansion and the decline of lemur populations,” Orkin said.

Habitats fragmented by logging and clearing not only reduce lemur populations but also sever the natural routes that once facilitated gene flow. Without those connections, inbreeding becomes more likely, placing lemurs – already under threat – in even greater danger.

Human expansion and biodiversity loss

The story of Madagascar’s lemurs carries powerful messages for worldwide conservation efforts. 

“This story isn’t unique to Madagascar,” Orkin said. “Human population expansion is accelerating the loss of biodiversity everywhere we look.”

“But the moral of the story is that humans are only one part of the natural world. The more we learn about how biodiversity is shaped by natural and human forces, the better chance we have of protecting it.”

By preserving natural habitats and ensuring that populations remain connected, there is hope for protecting the genetic richness that has allowed lemurs to thrive for so many millennia.

If conservation strategies succeed, these remarkable creatures may continue to captivate scientists – and the rest of us – for generations to come.

Image Credit: Bernard Gagnon, CC BY-SA, via Wikimedia Commons

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