EvoLiteracy News 02 04 2016
I am gradually returning to posting on EvoLiteracy after some intense traveling (Hawaii) and finishing manuscripts that could not wait. Not unusual at the end of each year. Plus, I have a book in the making (coauthored with Avelina Espinosa), actually it is in production and shall be out soon.
Speaking of Hawaii. While in Oahu, Nature published a note on the feral chickens of Kauai, one of the smaller islands in the Hawaiian archipelago, located West of Oahu. I have been to Kauai once (2014); it is another amazing island, full of nature and less populated than Oahu (where Honolulu is located), or Maui, or the Big Island, which have substantial human development, large towns and cities.
The note on the feral chickens is short (you can read it here), but I found the beautiful illustration by Emily Willoughby (below) quite informative, a graphic summary of the story. Keep in mind that “feralization” is NOT domestication in reverse. Evolution does not work backwards, or in return to a previous stage; at least not in the way that some people may think. For example, if humans are left in the wild for many generations, say thousands of years, they will not “turn into” Neanderthals or early Cro-Magnons. That will simply not happen… Anyway, that is material for another posting.
As much as domestication, feralization is a complex evolutionary phenomena. Domestication is heavily driven by artificial selection (humans select); feralization is driven by natural selection (nature selects). To this we must add the fact that domestic and feral chickens are freely and constantly hybridizing in Hawaii. Therefore, the reader can imagine a continuum of phenotypes (and genotypes) in Hawaiian Gallus.
The feral chickens of Hawaii (Moa in Hawaiian) are indeed descendants of junglefowl ancestors (Gallus gallus) brought to the islands by Polynesian settlers (at least 1,000 years ago), but because some of the early birds lived in close proximity to humans, they developed domestic features, now hybridized with wild-type-like features “freely ranging” within the birds. For example, the comb size is under heavy sexual-selection pressure among the feral chickens, but it is under more relaxed selection among the domesticated birds. Overall, feral chickens have larger and more intensely colored combs than domestic chickens.
The domesticated birds do not incubate their eggs (a byproduct of humans constantly removing the eggs) as much as the feral chickens, and the feral hens seem to lay eggs less frequently (possibly seasonally) than their domesticated sisters. The feral birds grow faster than the domestic ones, which makes them, as adults, smaller than the domesticated chickens. The feral birds have grey legs, the domestic have yellow legs; however, both yellow- and grey-legs are common among the feral chickens of Kauai (does that tell you something?).
Finally, the plumage color is illustrative of the hybrid ancestry of today’s free-ranging roosters and hens of Kauai (i.e. a mix of junglefowl red-black plumage with the white feathers typical of the domestic chickens).
If interested in scientific info about the mixed ancestry and admixture in Kauai’s feral chickens, take a look at Gering et al. (2015), or the hybrid origin of the domestic chicken by Eriksson et al. (2008), or the genetic basis of traits that differentiate modern domestic species from their wild counterparts by Flink et al. (2013), or comparative analysis of the chicken genome by Hillier et al. (2004). Next time you visit Hawaii remember to honor these elegant birds. They are everywhere. — GPC