> What is a species? Biologists have been debating the best definition for a very long time.
Indeed, there has been almost a pitched battle, almost back as far as when the word “species” was invented. Some taxonomists are “splitters” and describe every variant as a new species, while others are “lumpers” and believe that there are fewer species with more variability. Darwin referred to the battle in a letter in 1857, see https://en.wikipedia.org/wiki/Lumpers_and_splitters. One of the latest salvos in the battle was from lumpers from Kew Gardens in 2010, when they proposed drastically reducing the registered number of plant species.
> Past studies have shown that mitochondrial genotype tends to be very good at showing species boundaries between birds. This “mitonuclear compatibility species concept” helps explain the fact that the abrupt transitions between mitochondrial genotypes at species boundaries correspond with abrupt transitions
That could be … that could be just lack of data. Mitochondrial sequencing is very much easier and cheaper than nuclear DNA sequencing, so there could be a hundred times more vertebrate species with mitochondrial sequencing than with nuclear DNA sequencing. At the moment we couldn’t sort species by nuclear DNA because not nearly enough nuclear DNA sequences have been completed.
I would dearly like to see a sequencing of Australian corvid species. It’s very difficult to tell some of these apart by appearance, behaviour and call. I strongly suspect successful interbreeding where the species overlap. So in some cases they may be subspecies rather than separate species.
The new proposal won’t help with fossil species.