In an interesting new study that set out to shed light on the domestication of the barnyard chicken, researchers have suggested that traits we associate with modern domestic chickens may have appeared much later than originally assumed. The results have been published in the journal Proceedings of the National Academy of Sciences.
Humans have been selecting for particular desirable traits in numerous plant and animal species for thousands of years, and it is becoming increasingly evident that historic populations are often vastly different from modern day counterparts.
The genes responsible for particular traits that are now widespread in domestic breeds, called domestication genes, are assumed to have been selected for very early on in the domestication process. This is in contrast to the genes which are responsible for traits present in only a few closely related modern breeds (improvement genes), for example ridges in Rhodesian ridgebacks and excessive skin in Shar-Peis, which are presumed to have emerged much later in the domestication process. But many studies have relied solely on data from modern populations to make such inferences, leading to an incomplete picture.
In this particular study, researchers wanted to gain an insight into the history of domestic barnyard chickens, which are descended from a wild bird called the Red Junglefowl. To do this they analyzed DNA samples obtained from the remains of 80 European chickens that lived 200-2300 years ago.
Two genes were of particular interest in this study as they are known to differ between modern domestic chickens and their ancient counterparts. These are BCD02 which results in yellow skin color, and TSHR which is involved in thyroid hormone production. Modern domestic chickens have a mutation is TSHR which is thought to be linked to the ability to lay eggs all year round, which is not observed in Red Junglefowl.
The team found that although the gene responsible for yellow skin was present in the ancient chickens, the phenotype was rare; only 1 of the chickens sampled had the yellow skin which is common in domestic chickens today. Less than half of the chickens also had the mutant TSHR which is found in modern domestic chickens, meaning that the mutation which was assumed to be critical during early domestication was actually not subjected to strong selection until much later in time.
Together, these results suggest that just because a trait is now widespread in domestic populations, it does not necessarily mean that it was present early on during selection. They also suggest that these particular traits have only become ubiquitous in the population within the last 500 years, despite the fact that barnyard chickens have been around for thousands of years. “It’s a blink of an eye from an evolutionary perspective,” said co-author of the study Greger Larson in a press-release.
“It demonstrates that the pets and livestock we know today- dogs, chickens, horses, cows- are probably radically different from the ones our great-great-grandparents knew,” he added.