キリンの長い首の進化の原動力はセックスではなく食べ物だったことが新たな研究で判明(Food, not sex, drove the evolution of giraffes’ long neck, new study finds)

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2024-06-03 ペンシルベニア州立大学(PennState)

ペンシルベニア州立大学の生物学者たちは、キリンの長い首の進化について新しい洞察を提供する研究を行いました。従来の「ネック・フォー・セックス」仮説は、オス同士の競争が首の長さを決定したと主張しますが、研究チームはメスのキリンの方が相対的に長い首を持つことを発見しました。これは、メスの高い栄養要求が首の長さの進化を促進した可能性を示唆しています。研究は野生と飼育下のマサイキリンの体の比率を調査し、メスが樹木の深い部分の葉を取るために首を伸ばしていることが確認されました。この発見は、キリンの生態と遺伝学を理解し、保護対策を立てる上で重要です。

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マサイキリンのプロポーションにおける性的二型とキリンの首の進化 Sexual dimorphisms in body proportions of Masai giraffes and the evolution of the giraffe’s neck

Douglas R. Cavener,Monica L. Bond,Lan Wu-Cavener,George G. Lohay,Mia W. Cavener,Xiaoyi Hou,David L. Pearce & Derek E. Lee
Mammalian Biology  Published:03 June 2024
DOI:https://doi.org/10.1007/s42991-024-00424-4

キリンの長い首の進化の原動力はセックスではなく食べ物だったことが新たな研究で判明(Food, not sex, drove the evolution of giraffes’ long neck, new study finds)

Abstract

Giraffes exhibit a large sexual dimorphism in body size. Whether sexual dimorphisms also exist in body proportions of the axial and appendicular skeleton has been debated, particularly regarding the giraffe’s iconic long neck. We examined the anatomical proportions of the neck, forelegs, hindlegs, and body trunk of the Masai giraffe (G. tippelskirchi) in captive and wild populations. We found that female Masai giraffes have proportionally longer necks relative to their forelegs than males in contradiction to the original necks-for-sex hypothesis that proposed that the evolution of the giraffe’s long neck was driven by male-male competition. However, male neck width and apparent mass are proportionally larger than females’, supporting a modification of the necks-for-sex hypothesis. Moreover, male foreleg length is proportionally longer whereas female trunk length is proportionally longer. These sexual dimorphisms were found in both captive and wild Masai giraffes. We speculate that the initial evolution of the giraffe’s long neck and legs was driven by interspecific competition and the maternal nutritional demands of gestation and lactation through natural selection to gain a competitive advantage in browsing, and then later the neck mass was further increased as a consequence of male-male competition and sexual selection. Differences in the proportions of major body components define sex phenotypes, but several giraffes display opposite-sex phenotypes with a significantly higher level of discordancy seen in captive males. We speculate that body proportion sexual dimorphisms are maintained in the wild by natural and/or sexual selection, but in captivity selection is relaxed resulting in a higher occurrence of discordances in sexual phenotypes.

生物環境工学
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