馬、ロバ、シマウマの起源は同じと考えられている
じゃあ、進化のどの過程で分岐していったのか？
それは疑問の残るところと思う
最近の研究の主流は、ゲノムです
ゲノム配列を調べて、違うと頃を見つけて、違いがどの時代に発生したのかを計算で求める
ゲノム配列が変化する時間は、だいたい決まっているので、変化した量でだいたいの年代が分かるということ
研究成果がNatureに発表された
これで種の分岐点に新しい知見が得られたということだ
The rich fossil record of equids has made them a model for evolutionary processes. Here we present a 1.12-times coverage draft genome from a horse bone recovered from permafrost dated to approximately 560–780 thousand years before present (kyr bp).
'Recalibrating Equus evolution using the genome sequence of an early Middle Pleistocene horse'
Our data represent the oldest full genome sequence determined so far by almost an order of magnitude. For comparison, we sequenced the genome of a Late Pleistocene horse (43 kyr bp), and modern genomes of five domestic horse breeds (Equus ferus caballus), a Przewalski’s horse (E. f. przewalskii) and a donkey (E. asinus).
Our analyses suggest that the Equus lineage giving rise to all contemporary horses, zebras and donkeys originated 4.0–4.5 million years before present (Myr bp), twice the conventionally accepted time to the most recent common ancestor of the genus Equus. We also find that horse population size fluctuated multiple times over the past 2 Myr, particularly during periods of severe climatic changes. We estimate that the Przewalski’s and domestic horse populations diverged 38–72 kyr bp, and find no evidence of recent admixture between the domestic horse breeds and the Przewalski’s horse investigated. This supports the contention that Przewalski’s horses represent the last surviving wild horse population. We find similar levels of genetic variation among Przewalski’s and domestic populations, indicating that the former are genetically viable and worthy of conservation efforts.
We also find evidence for continuous selection on the immune system and olfaction throughout horse evolution. Finally, we identify 29 genomic regions among horse breeds that deviate from neutrality and show low levels of genetic variation compared to the Przewalski’s horse. Such regions could correspond to loci selected early during domestication.
(Natureの図)
とはいえ、骨からゲノムを抽出して研究するなんて、映画の世界の話だと思ってました
(どちらもBBCから)
で、時を同じくして、GenomeWebとBBCにこの研究成果が紹介されていた
GenomeWeb
こちらは科学寄りのニュースサイトなので、研究者に光を当てた書き方な気がします
Horses, donkeys, and zebras may have split from a shared common ancestor much earlier than once suspected, a new genome sequencing study suggests.
As they reported online today in Nature, investigators at the University of Copenhagen, BGI-Shenzhen, and elsewhere sequenced genomic DNA from the fossilized remains of a horse believed to have lived in what's now the Yukon Territory of Canada as far back as 700,000 years ago or more.
Together with new genome sequences for a 43,000-year-old Pleistocene horse, a present-day Przewalski's horse, five modern-day domestic horses, and a donkey, the ancient genome prompted researchers to propose divergence within the equid lineage going back four million years or more ― about double the time estimated previously.
'Ancient Genome Prompts Rethink of Timing of Evolutionary Events in Horse Lineage'
BBC
BBCは国営放送なので、研究の意義に光を当てた書き方、そして、研究の記事が目につきやすいように、苦労話なども盛り込んで、ドラマ仕立てな気がします
A fragment of a fossilised bone thought to be more than 700,000 years old has yielded the genome of an ancient relative of modern-day horses.
The first approach they tried resulted in relatively poor yields of horse-derived sequences, so they turned to a technology that could directly analyse single molecules of DNA.This proved far more successful - but they still had an abundance of data to plough through.
Using high-powered computers and an existing horse genome sequence as a reference, the scientists sifted through the 12 billion sequencing reads to distinguish between DNA motifs belonging to the ancient horse and those from contaminating organisms, such as bacteria accumulated from the environment.
(中略)
To do this, the scientists also determined the DNA sequence of a donkey, an ancient pre-domestication horse dating back around 43,000 years, five modern horses and a Przewalski's horse, which possibly represents the last surviving truly wild horse population.Family trees, based on similarity of the DNA sequences, revealed the relationships between these equine stable-mates and their longer evolutionary history.
'Ancient horse bone yields oldest DNA sequence'
BBCのScience&Environmentのセクションとはいっても、GenomeWebと同じタイミングで報道されるのは面白い
科学が一般人の興味を惹いているということなんですよね
