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Genetics give clues to species’ extinction

ROM2013 13563_1A STUDY INTO the DNA of the passenger pigeon (Ectopistes migratorius) has revealed that the species’ once large population could be part of the reason it is now extinct.

Historically an abundant species in North America, with numbers estimated at between three and five billion birds, the passenger pigeon became extinct in the early 1900s due to habitat loss from deforestation and mass culling by humans.

A team of scientists in the USA wanted to find out why the species wasn’t able to survive in at least a few small, isolated populations. Corresponding author of the study Beth Shapiro, professor of ecology and evolutionary biology at UC Santa Cruz, explained: “Passenger pigeons did really well for tens of thousands of years and then suddenly they went extinct. Paradoxically, their enormous population size may have been a factor in their extinction.”

Using DNA recovered from museum specimens from collections at the Royal Ontario Museum and the Denver Museum of Nature & Science, the research team sequenced and assembled mitochondrial and nuclear genomes of passenger pigeons.

Their results confirmed earlier observations of low genetic diversity in the passenger pigeon population, but came to different conclusions from previous researchers. They suggest that this species was well adapted to living in huge flocks, but poorly adapted to living in smaller groups, and the change in population size happened so fast that the birds were unable to adapt.

First author Gemma Murray, a postdoctoral researcher at UC Santa Cruz, said: “We looked at variation in diversity across the genome and found that it wasn’t just lower than expected overall, it was also more variable.”

The analysis revealed patterns in the passenger pigeon genome indicating that the species’ low genetic diversity was the result of natural selection. In comparison, they did not find the same patterns of genetic diversity across the genome in the closely related band-tailed pigeon (Patagioenas fasciata), which has a population of about two million birds native to western North America.

The study was published last month in the journal Science.

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