September 1, 2019

SHOULDN'T FRET TOO MUCH...:

Darwin's finches continue to inform and confuse: Extinct populations had higher genetic diversity than many survivors. (Stephen Fleischfresser, 9/01/19, Cosmos)

Heather Farrington, Lucinda Lawson and Kenneth Petren of the Department of Biological Sciences at the University of Cincinnati in the US have used the finches to test the robustness of predictive extinction models and the assumptions that underpin them.

One of the common ways to test whether a population or species is likely to go extinct is to measure its genetic diversity: such testing is quick, easy and cheap. Each gene comes in a number of different forms, called alleles.

Genetic diversity refers to the number of different alleles in a population or species; greater diversity is thought to mean that the population or species will have the capacity to adapt should environmental conditions change.

With more diversity comes a higher likelihood that alleles exist in the population that will provide certain individuals with an advantage in changed conditions. These individuals will then outbreed the rest of the population and over time these alleles will become typical of the population or species. This is basically how evolution works.

"Typically, we would expect populations with high genetic diversity to have a greater potential for long-term survival," says Lawson. "Meanwhile, the low-diversity populations would be more likely to go extinct because that's a common pattern as populations decline to few individuals."

She and her colleagues set out to explore this indicator using Darwin's finches, which provide a rare opportunity to test whether genetic diversity really is a predictor of extinction.

By looking at the genetic diversity of 212 tissue samples taken from both museum specimens and living birds, they could compare these to the reality that has played out in the islands' finches, where "many populations went extinct, but far more persisted" over the last 100 years or so. The trio's hypothesis was "that genetic variation was lower in populations that ultimately went extinct, relative to those that are still extant".

What they found was the opposite.

Only one of the extinct finch populations, a species called the vegetarian finch, had lower genetic diversity compared to modern survivors. To make matters more confusing, most of the now extinct populations had indications of higher genetic diversity compared to surviving populations that migrated to other islands.


...no one still thinks they're species.

Posted by at September 1, 2019 10:38 AM

  

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