Pink pigeons need a "genetic rescue" to survive extinction

In a new study, experts report that a boost in the number of pink pigeons in recent decades will not be enough to save the species from a high risk of extinction. 

An international team of researchers led by the University of East Anglia worked with organizations in Mauritius to investigate the impacts of what ultimately became a genetic “bottleneck” across the island nation’s endemic population of pink pigeons. Across Mauritius, there was a rapid collapse in the number of pink pigeons in the late 1980s. This decline worsened until there were only 12 birds surviving in the wild.

Since then, conservation efforts by the Mauritian Wildlife Foundation, the Durrell Wildlife Conservation Trust, and the Government of Mauritius’ National Parks and Conservation Service paid off. The number of wild pink pigeons reached around 500 birds.

The experts analyzed genetic samples that were collected from 175 pink pigeons over nearly two decades, as conservation efforts took place. Based on the analysis of the DNA, the experts found some disappointing news. 

The researchers discovered that, despite an increase in population, the pink pigeon now has a high genetic load of bad mutations. They explained that these mutations put the birds at considerable risk of extinction in the wild within 100 years without continued conservation actions.

“By studying the genome of a recovered species that was once critically endangered, we can learn how to help other species to bounce back from a population collapse,” said study co-lead author Professor Cock van Oosterhout.

“During the pigeon’s population bottleneck, the gene pool lost a lot of variation, and many bad mutations increased in frequency. This genetic load still poses a severe threat, even though the population has recovered in numbers.”

“The problem is that all individuals are somehow related to each other. They are the descendants of the few ancestors that managed to survive the bottleneck. Hence, it becomes virtually impossible to stop inbreeding, and this exposes these bad mutations. In turn, this can increase the mortality rate, and it could cause the population to collapse again.”

The researchers warn that “genetic rescue” is needed to recover lost genetic variation caused by inbreeding and to reduce the effects of the harmful mutations. This could be achieved by releasing captive-bred birds from UK and EU zoos, they said.

“A captive population of pink pigeons in the Gerald Durrell Endemic Wildlife Sanctuary in Mauritius, jointly managed by the Mauritian Wildlife Foundation and the National Parks and Conservation Service, was established in the 1970s,” said Professor Jim Groombridge from the University of Kent.

“This was used to breed birds for release into the wild, which boosted population numbers. The team also restored habitat by controlling introduced species and provided supplementary food as part of a field programme of intensive conservation management, which further increased the free-living population.”

“We didn’t know how many bad mutations the population carried initially, before the bottleneck,” said co-author Dr. Hernan Morales from University of Copenhagen. “We first had to simulate the ancestral population to find out how many bad mutations could have evolved. We then checked this data with data on inbreeding depression data from zoo populations of the pink pigeon.”

The researchers compared pedigree and fitness data to that of more than 1,000 birds at the Jersey Zoo. The analysis showed that the pink pigeon carried a high genetic load of 15 lethal equivalents. 

“The computer simulations clearly show that just boosting numbers isn’t enough,” said Dr. Morales. “The population also needs ‘genetic rescue’ from more genetically diverse birds bred in European zoos. These birds are not as closely related, and they can help to reduce the level of inbreeding. However, there is a risk that we could introduce other bad mutations from the zoo population into the wild.”

According to study co-author Sam Speak, the team is now analyzing the genome of the pink pigeon from zoo populations in the UK, trying to locate these bad mutations. “We can do this now using bioinformatics tools developed for studying human genetics and the genomes of other model bird species such as the chicken.”

“By using conservation genomics, future reintroduction programmes can avoid releasing individuals with high genetic load,” said Speak. “This would help reduce inbreeding and improve the long-term recovery of threatened species such as the pink pigeon.”

The study is published in the journal Conservation Biology. 

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By Chrissy Sexton, Earth.com Staff Writer