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Recent genetic connectivity found among chimpanzee subspecies

Even though chimpanzees are typically divided into four geographical subspecies, some studies have found evidence of genetic connectivity among all populations. 

In a new study from the Max Planck Institute for Evolutionary Anthropology, experts have discovered recent genetic connectivity between chimpanzee subspecies, despite periods of isolation.

“Given the high degree of behavioral variability and flexibility across chimpanzee populations, characterizing range-wide patterns of genetic diversity in chimpanzees is important for understanding how they adapt to changing environmental conditions,” explained the researchers.

In collaboration with the Pan African Programme: The Cultured Chimpanzee (PanAf), an international team of experts collected over 5,000 fecal samples from 55 sites across the chimpanzee range in 18 countries. This is by far the most complete sampling of chimpanzees to date.

“Collecting these samples was often a daunting task for our amazing field teams. The chimpanzees were almost all unhabituated to human presence, so it took a lot of patience, skill and luck to find chimpanzee dung at each of the sites,” said study senior author Mimi Arandjelovic.

“We used rapidly-evolving genetic markers that reflect the recent population history of species and, in combination with the dense sampling from across their range, we show that chimpanzee subspecies have been connected, or, more likely, reconnected, for extended periods during the most recent maximal expansion of African forests,” said study first author Jack Lester.

This means that although chimpanzees were separated into different subspecies in their distant past – prior to human disturbances – the geographic barriers were permeable to chimpanzee dispersal. 

“It is widely thought that chimpanzees persisted in forest refugia during glacial periods, which has likely been responsible for isolating groups of populations which we now recognize as subspecies,” explained study co-author Paolo Gratton. 

“Our results from fast-evolving microsatellite DNA markers however indicate that genetic connectivity in the most recent millennia mainly mirrors geographic distance and local factors, masking the older subspecies subdivisions.”

According to PanAf co-director Hjalmar Kuehl, the results suggest that the great behavioral diversity observed in chimpanzees is not due to local genetic adaptation but to their reliance on behavioral flexibility to respond to changes in their environment.

At sites that were associated with human disturbances and pressures, the researchers noted signals of reductions in diversity. There were even some locations where no chimpanzees were detected, even though they had been present in recent decades. 

“Although not unforeseen, we were disheartened to already find the influence of human impacts at some field sites where genetic diversity was markedly lower than what we expected,” said Lester.

The findings highlight the importance of genetic connectivity for chimpanzees in their recent history. While chimpanzees are adaptable and can survive in human-modified landscapes, they are currently facing multiple threats including habitat loss and diseases. The results of this study indicate that if habitat fragmentation and isolation continue, there will be serious consequences for the genetic health and viability of chimpanzees.

Christophe Boesch, co-director of the PanAf and director of the Wild Chimpanzee Foundation, concluded that every effort should be made to re-establish and maintain dispersal corridors across their range, with perhaps special attention to trans-national protected areas.

The study is published in the journal Communications Biology.

By Chrissy Sexton, Staff Writer

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