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内容記述 |
With the aim of elucidating the evolutionary origin of junglefowls and their domestication processes, I conducted molecular evolutionary analyses of mitochondrial DNAs for various kinds of birds belonging to the subfamily Phasianinae. I then found that the real matriarchic origin of all the domestic fowls examined in the present study was an Asian continental population of Gallus gallus gallus. The phylogenetic analysis conducted in this study also suggested that the continental population of Gallus gallus gallus is the monophyletic ancestor of all domestic fowls. These findings resolve the long-time controversy concerning monophyletic versus polyphyletic origin theories of domestic fowls. <br /> The present thesis is composed of four chapters. In Chapter 1, as an introduction, I described the evolutionary significance of the domestication processes of junglefowls and the overview of taxonomical problems of birds within the subfamily Phasianinae, particularly junglefowls and domestic fowls. <br /> In Chapter2, attention is focused on the molecular phylogeny of the subfamily Phasianinae. Comparisons of DNA sequences for mitochondrial control regions among 16 avian species belonging to the subfamily Phasianinae, revealed the following: (1) Generalized perdicine birds (quails and partridges) are descended from ancient lineages. Even the closest pair, the common quail of the Japanese subspecies (Coturnix coturnix japonica) and the Chinese bamboo partridge (Bambusicola thoracica), maintained only a 85.7l% identity. (2) The 12 species of phasianine birds previously and presently studied belong to three distinct branches. The first branch is made up exclusively of members of the genus gallus, while the second branch is made up of pheasants of the genera Phasianus, Chrysolophus and Syrmaticus. Gallopheasants of the genus Lophura are distant cousins to these pheasants. The great argus (Argusianus argus) and peafowls of the genus Pavo constitute the third branch. Members of the fourth phasianine branch, such as tragopans and monals, were not included in the present study. (3) The one perdicine species, Bambusicola thoracica, is more closely related to the phasianine genera Gallus and Pavo than to members of other perdicine genera. The above might indicate that Bambusicola belongs to one stem of the perdicine lineage which later split into two sublineages that yielded phasianine birds; one evolving to Gallus, while the other differentiated toward Pavo and related genera. (4) Tandem duplication of the 60-base unit was established as a trait unique to the genus Gallus, which is shared neither by pheasant nor by quail. <br /> In Chapter 3, I discuss evolutionary relationships between red and green junglefowls. The noncoding control region of the mitochondrial DNA of various gallinaceous birds was studied with regard to its RFLP (restriction fragment length polymorphism) and sequences of the first 400 bases. Unlike its close ally green junglefowl, the red junglefowl Gallus gallus is a genetically very diverse species; a 7.0% sequence divergence was seen between those from Thailand (Gallus gallus gallus and Gallus gallus spadiceus) and that of the Indonesian island of Java(Gallus gallus bankiva). Furthermore, the divergence increased to 27.83% when each transversion was regarded as an equivalent of 10 transitions. On the other hand, a mere 0.5-3.0% difference (all transitions) separated various domestic breeds of chicken from two subspecies of Gallus gallus gallus of Thailand, thus indicating a single domestication event in the area inhabited by this subspecies, with the red junglefowl being the origin of all domestic breeds. Only transitions separated six diverse domesticated breeds. Nevertheless, a 2.75% difference was seen between RFLP type I breeds (white leghorn and nagoya) and a RFLP type VIII breed (ayam pelung). The above data suggest that although the mitochondrion of RFLP type V is the main contributor to domestication, hens of other RFLP types also contributed to this event. <br /> Finally, in Chapter 4, the evolutionary origin and dispersal patterns of domestic fowls are discussed from various .aspects of molecular evolution and human history. With the aim of elucidating in more detail, the genealogical origin of the present domestic fowls of the world, I determined mitochondrial DNA (mtDNA) sequences of the D-loop regions for a total of 21 birds which belong to the red junglefowl (Gallus gallus) comprising three subspecies (6 Gallus gallus gallus, 3 Gallus gallus spadiceus and 3 Gallus gallus bankiva) and 9 birds representing diverse domestic breeds (Gallus gallus domesticus) . I also sequenced mtDNAs from 4 green junglefowl (Gallus varius), 2 Cingalese junglefowl (Gallus lafayettei) and 1 grey junglefowl (Gallus sonnerati). I then constructed a phylogenetic tree for these birds using nucleotide sequences, choosing the Japanese quail (Coturnix coturnix japonica) as an outgroup. Moreover, I found that a continental population of Gallus gallus gallus was the real matriarchic origin of all the domestic species examined in the present study. It is also of particular interest to note that there were no discernible differences among Gallus gallus subspecies; Gallus gallus bankiva being a notable exception. This was because Gallus gallus spadiceus and a continental population of Gallus gallus gallus formed a single cluster in the phylogenetic tree. One obvious and distinct feature that customarily separates Gallus gallus gallus from Gallus gallus spadiceus is the color of their ear lobes: white for the former and red for the latter. The fact that domestic breeds of the chicken are of two kinds as to color of ear lobes is a clear reflection of the contribution made by Gallus gallus gallus as well as by Gallus gallus spadiceus to their ancestry. Gallus gallus bankiva, on the other hand, is a distinct entity, thus, deserving its subspecies status. This implies that a continental population of Gallus gallus gallus was the monophyletic ancestor of all domestic breeds. I also discuss the possible significance of the initial dispersal pattern of present domestic fowls, utilizing the phylogenetic tree. |
要旨・審査要旨 / Abstract, Screening Result (341.5 kB)
