In the 1980s, there were only a dozen or more pink pigeons in the wild. Known to scholars as Neswenas Mairy, this species is only found in Mauritius, the Indian Ocean island that was once home to the dodo. Like the dodo, the pink pigeon has made an easy target for cats, rats, and other predators introduced by humans, who have also chipped away nearly all of their native forests. Unlike the dodo, the pink pigeon has made a remarkable revival since then.
Fortunately, the Mauritius Wildlife Foundation had already taken 12 birds from the wild in the 1970s and 1980s to form a captive group. The offspring of these birds were then released during the 1990s and early 2000s, and there are now at least 400 birds living in the wild. This species has even been officially listed twice, from “endangered” to “vulnerable.”
However, such severe population bottleneck can lead to significant ‘genetic erosion’, in which species become less genetically healthy as many animals are closely related. To examine the exact effect, we worked with a team of scientists to sequence the DNA of 175 birds sampled between 1993 and 2010 during a population recovery period. Our results are now published in the journal biology protection. Disappointingly, we found that species continued to lose genetic diversity even as overall numbers increased during a successful conservation rescue program. We speculated that the bottleneck must have altered something in the pink pigeon’s DNA.
To understand the reason for this ongoing genetic erosion, we looked at data of 1,112 pink pigeons in European and American zoos. These data were collected over four decades, and included each bird’s level of reproductive success and longevity along with levels of inbreeding calculated using pedigrees. Based on the relationship between these factors, we found that the species carried an alarmingly high ‘genetic burden’.
Genetic load mainly consists of several harmful recessive mutations that have the potential to reduce an animal’s ability to reproduce. This can be seen, for example, in the fewer eggs that hatch, or in the number of young who successfully raise the nest. Before the bottleneck of pink pigeons, the effects of these mutations were hidden because there were plenty of healthy genetic variants around to offset the harmful factors. However, small populations are more susceptible to random fluctuations in genetic makeup, which makes it possible for harmful mutations to have an effect.
Inbreeding can also cause these mutations to become more harmful, if the offspring of two related individuals inherit the same harmful mutation. When this occurs, the healthy genetic variant will no longer mask the detrimental effect of the mutation and the individual may fail to hatch or hatch the nest. We believe this caused the continuing genetic erosion of pink pigeons in the wild.
Ultimately, all 480 or so free-living birds are related to some degree to the ten that managed to survive in the wild in the 1980s, and the 12 that were used to make up the captive-born population. This resulted in slow and long-term inbreeding. In turn, this meant that pigeons were less successful at hatching eggs and eggs, and did not live long.
Since only the fittest pigeons were likely to hatch, grow and reproduce, there were fewer birds actively contributing to the next generation (and losing genetic diversity), even as their overall numbers increased. Thus, the population continued to lose genetic variance despite the growth in size.
What we learned from this study is that in order for pink pigeons to avoid extinction, we will need to reproduce offspring of birds bred at the Jersey Zoo and other zoos in the European Union. This flower pigeon harbors genetic diversity that has since been lost from Mauritius, and reintroducing it would lower the level of relatedness on the island.
Our study also shows that conservation cannot simply stop after a population appears to have recovered in numbers. We believe genomic analyzes are essential to truly assess the conservation needs of a species and its recovery potential. This cannot be done only by analyzing population numbers. The data generated by the Earth Biogenome project will be useful in identifying species most at risk of extinction. The project aims to sequence two million or so species in the next 10 years. Not only will this data aid our assessment of biodiversity, but it should also be used to guide future conservation actions.
The study found that not everything is rosy for the pink bath
Introduction of the conversation
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