サメはいかにして地球温度の急上昇を生き延びたのか?(How sharks survived a major spike in Earth’s temperature)

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2024-06-03 カリフォルニア大学リバーサイド校(UCR)

外洋の頂点捕食者として知られているサメは、数百万年前の劇的な地球温暖化の時期に、ずんぐりとした底生動物から進化しました。約9300万年前、火山の溶岩が大量に噴出したことで二酸化炭素濃度が急上昇し、温室気候が生まれ、海水温は最高温度に達した。カリフォルニア大学リバーサイド校の研究者らは、一部のサメが熱に反応して胸びれを伸ばしていることを発見した。この発見は、本日 Current Biology 誌に掲載された論文で報告されている。この発見は、500 種を超える現生および化石化したサメの体長とひれの計測によって行われた。

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白亜紀における外洋性サメの台頭と胸鰭形態の適応進化 The rise of pelagic sharks and adaptive evolution of pectoral fin morphology during the Cretaceous

Phillip C. Sternes,Lars Schmitz,Timothy E. Higham
Current Biology  Published:June 03, 2024
DOI:https://doi.org/10.1016/j.cub.2024.05.016

サメはいかにして地球温度の急上昇を生き延びたのか?(How sharks survived a major spike in Earth’s temperature)

Highlights

•Modern sharks were likely benthic or benthopelagic in origin

•Sharks have independently expanded to the pelagic zone several times

•Pectoral fin shape shows signatures of adaptive evolution

•Sea surface temperature impacts shark evolution

Summary

The emergence and subsequent evolution of pectoral fins is a key point in vertebrate evolution, as pectoral fins are dominant control surfaces for locomotion in extant fishes.1,2,3However, major gaps remain in our understanding of the diversity and evolution of pectoral fins among cartilaginous fishes (Chondrichthyes), a group with an evolutionary history spanning over 400 million years with current selachians (modern sharks) appearing about 200 million years ago.4,5,6Modern sharks are a charismatic group of vertebrates often thought to be predators roaming the open ocean and coastal areas, but most extant species occupy the seafloor.4Here we use an integrative approach to understand what facilitated the expansion to the pelagic realm and what morphological changes accompanied this shift. On the basis of comparative analyses in the framework of a time-calibrated molecular phylogeny,7we show that modern sharks expanded to the pelagic realm no later than the Early Cretaceous (Barremian). The pattern of pectoral fin aspect ratios across selachians is congruent with adaptive evolution, and we identify an increase of the subclade disparity of aspect ratio at a time when sea surface temperatures were at their highest.8The expansion to open ocean habitats likely involved extended bouts of sustained fast swimming, which led to the selection for efficient movement via higher aspect ratio pectoral fins. Swimming performance was likely enhanced in pelagic sharks during this time due to the elevated temperatures in the sea, highlighting that shark evolution has been greatly impacted by climate change.

生物環境工学
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