Speciation soon to come.

This week's, or more precisely last week's, evolution story is about the chestnut-bellied monarchs (Monarcha castaneiventris), small insectivorous birds. A paper last year in the August edition of the American Naturalist found that due to a single point mutation an ecological speciation event may have occurred.

In the southeastern Soloman Islands the chestnut-bellied monarch has two distinct subspecies populations. One, M. c. megarhynchus, has a... well chestnut colored belly. The second, M. c. ugiensis has a black colored belly. As it turns out they seem to leave each other alone. The hypothesis of this paper is that this is due to a change in plumage color, and this simple change is what causes the two subspecies to not see each other as sexual partners. Not just that, but they don't even see each other as rivals.

During their experiments, if the findings showed that there was statistically more aggression shown towards those that had the same coloration than those with different coloration, then this would indicate that the two do not see each other as reproductive rivals. If this is true, then it would follow that the two populations do not interbreed with each other. As it so happens, this is what they found.

All of this would show that the hypothesis is correct in that, the main reason for the lack of interbreeding is due to their plumage. Looking into the genetics of this problem they could only find one difference, that one was in the melancortin-1 gene. This gene is responsible for the production of melanin, which gives skin or feathers a darker color.                                    

So in all they found that a split in populations may just be due to a single mutation at the right point in the genome. Yet another example of rapid evolution that can cause expedient speciation. EVOLUTION, IT'S FASCINATING!

Original Paper - Plumage Color Used in Species Recognition
Bridged Description - Catching Speciation in the Act