Etikettarkiv: chickens

Different worlds

Publicerat i english, the practice of science av

Some time ago, I gave a seminar about some work involving chicken combs, and I made some offhand remark about how I don’t think that the larger combs of modern layer chickens are the result of direct selection. I think it is more likely to be be a correlated response to selection on reproductive traits. During question time, someone disagreed, proposing that ornamental traits should be very likely to have been under artificial selection.

I choose this example partly because the stakes are so low. I may very well be wrong, but it doesn’t matter for the work at hand. Clearly, I should be more careful to acknowledge all plausible possibilities, and not speculate so much for no reason. But I think this kind of thing is an example of something quite common.

That is: researchers, even those who fit snugly into the same rather narrow sub-field, may make quite different default assumptions about the world. I suspect, for instance, that we were both, in the absence of hard evidence, trying to be conservative in falling back on the most parsimonious explanation. I know that I think of a trait being under direct selection as a strong claim, and ”it may just be hitch-hiking on something else” as a conservative attitude. But on the other hand, one could think of direct artificial selection as a simpler explanation as opposed to a scenario that demands pleiotropy.

I can see a point to both attitudes, and in different contexts, I’d probably think of either direct selection and pleiotropy as the more far-fetched. For example, I am hard pressed to believe that reductions in fearfulness and changes in pigmentation of domestic animals are generally explained by pleiotropic variants.

This is why I think that arguments about Occam’s razor, burdens of proof, and what the appropriate ”null” hypothesis for a certain field is supposed to be, while they may be appealing (especially so when they support your position), are fundamentally unhelpful. And this is why I think incommensurability is not that outlandish a notion. Sometimes, researchers might as well be living in different worlds.

Paper: ”Mixed ancestry and admixture in Kauai’s feral chickens: invasion of domestic genes into ancient Red Junglefowl reservoirs”

Publicerat i english, genetik av

We have a new paper almost out (now in early view) in Molecular Ecology about the chickens on the Pacific island Kauai. These chickens are pretty famous for being everywhere on the island. Where do they come from? If you use your favourite search engine you’ll find an explanation with two possible origins: ancient wild birds brought over by the Polynesians and escaped domestic chickens. This post on Kauaiblog is great:

Hawaii’s official State bird is the Hawaiian Goose, or Nene, but on Kauai, everyone jokes that the “official” birds of the Garden Island are feral chickens, especially the wild roosters.

Wikepedia says the “mua” or red jungle fowl were brought to Kauai by the Polynesians as a source of food, thriving on an island where they have no real predators. /…/
Most locals agree that wild chickens proliferated after Hurricane Iniki ripped across Kauai in 1992, destroying chicken coops and releasing domesticated hens, and well as roosters being bred for cockfighting. Now these brilliantly feathered fowl inhabit every part of this tropical paradise, crowing at all hours of the day and night to the delight or dismay of tourists and locals alike.

In this paper, we look at phenotypes and genetics and find that this dual origin explanation is probably true.

jeff_trimble_kauai_chickens_cc_by_nc_sa

(Chickens on Kauai. This is not from our paper, but by Jeff Trimble (cc:by-sa-nc) published on Flickr. There are so many pretty chicken pictures there!)

Dom, Eben, and Pamela went to Kauai to photograph, record to and collect DNA from the chickens. (I stayed at home and did sequence bioinformatics.) The Kauai chickens look and sound like mixture of wild and domestic chickens. Some of them have the typical Junglefowl plumage, and other have flecks of white. Their crows vary in the length of the characteristic fourth syllable. Also, some of them have yellow legs, a trait that domestic chickens seem to have gotten not from the Red but from the Grey Junglefowl.

We looked at DNA sequences by massively parallel (SOLiD) sequencing of 23 individuals. We find mitochondrial sequences that fall in two haplogroups: E and D. The presence of the D haplogroup, which is the dominating one in ancient DNA sequences from the Pacific, means that there is a Pacific component to their ancestry. The E group, on the other hand, occurs in domestic chickens. It also shows up in some ancient DNA samples from the Pacific, but not from Kauai (and there is a scientific debate about these sequences). The nuclear genome analysis is pretty inconclusive. I think what we would need is some samples of possible domestic source populations (Where did the escapee  chickens came from? Are there other traditional domestic sources?) and a better sampling of Red Junglefowl to make better sense of it.

When we take the plumage, vocalisation and mitochondrial DNA together, it looks like this is a feral admixed population of either Red Junglefowl or traditional Pacific chickens mixed with domestics. A very interesting population indeed.

Kenneth Chang wrote about the paper in New York Times; includes quotes from Eben and Dom.

E Gering, M Johnsson, P Willis, T Getty, D Wright (2015) Mixed ancestry and admixture in Kauai’s feral chickens: invasion of domestic genes into ancient Red Junglefowl reservoirs. Molecular ecology