遺伝子混合のコストとベネフィット、ヒヒは近縁種から遺伝子の3分の1を拝借していた (Costs and benefits of genetic mixing. Baboons borrowed a third of their genes from a closely related species)

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2022-08-04 マックス・プランク研究所

In the region around the Amboseli basin of southern Kenya, where two species of baboons have met and intermixed not just once, but multiple times since the species diverged 1.4 million years ago.
© Arielle Fogel, Duke University

ケニア南部の野生ヒヒの新しい遺伝子解析により、そのほとんどが交雑の痕跡をDNAに残していることが明らかになった。交雑の結果、彼らの遺伝的構成の約3分の1は、近縁の別の種の遺伝子で構成されている。
研究者らは、アンボセリに生息する9世代にわたる約440頭のヒヒのゲノムを解析し、アヌビスから受け継いだと思われるDNAの断片を探した。その結果、現在ケニアのアンボセリ地域に生息するヒヒはすべて混血で、アヌビスのDNAが平均してゲノムの約37パーセントを占めていることが判明した。中には、ごく最近、つまり過去7世代以内に起こった交配により、アヌビスの祖先を持つものもいる。しかし、半数近くはもっと昔、数百から数千世代前に混血が起こったのである。
研究者らは、アンボセリのヒヒが交雑の代償を知る手がかりを与えてくれるとしている。RNAシーケンスを用いてヒヒの血液細胞の遺伝子活性を測定したところ、他の遺伝子をオン・オフさせるスイッチのような働きをする借用DNAは自然淘汰される可能性が高いことが判明したのである。

<関連情報>

霊長類の長期野外調査における混血に対する選択と遺伝子制御の多様性 Selection against admixture and gene regulatory divergence in a long-term primate field study

Tauras P. Vilgalys,Arielle S. Fogel,Jordan A. Anderson,Raphael S. Mututua,J. Kinyua Warutere,I. Long’ida Siodi,Sang Yoon Kim ,Tawni N. Voyles ,Jacqueline A. Robinson ,Jeffrey D. Wall,Elizabeth A. Archie ,Susan C. Alberts ,Jenny Tung
Science  Published:4 Aug 2022
DOI: 10.1126/science.abm4917

Hidden selection against interbreeding

Today, humans are the only extant members of our genus, Homo. This was not the case in the past, as we now know that our ancestors shared the planet with other Homo species. It has been suggested that selection against hybrid individuals would have acted against breeding across these species, but such a hypothesis is difficult to test today. To study this question, Vilgalys et al. took advantage of a decades-long dataset on two species of baboon from the Amboseli basin of Kenya. They found evidence of selection against hybrid, or admixed, ancestry similar to what has been predicted for ancestral hominids. Although evidence for selection against hybrids was clear, they also found that individual hybrids can thrive. —SNV

Abstract

Genetic admixture is central to primate evolution. We combined 50 years of field observations of immigration and group demography with genomic data from ~9 generations of hybrid baboons to investigate the consequences of admixture in the wild. Despite no obvious fitness costs to hybrids, we found signatures of selection against admixture similar to those described for archaic hominins. These patterns were concentrated near genes where ancestry is strongly associated with gene expression. Our analyses also show that introgression is partially predictable across the genome. This study demonstrates the value of integrating genomic and field data for revealing how “genomic signatures of selection” (e.g., reduced introgression in low-recombination regions) manifest in nature; moreover, it underscores the importance of other primates as living models for human evolution.

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