雖然海洋為生物提供了廣闊的空間和豐富的資源，但由於海水高滲透壓的環境，對生物維持生理的恆定造成巨大壓力。以全球10,824種的鳥類為例，只有2.7%的鳥類能夠部分或完全使用高滲透壓的鹹水棲地。為了瞭解鳥類如何適應高鹽度環境的演化過程，我們整合鳥類25個目，總共230個物種的腎臟大小、功能性眼眶上鹽腺 (SSG) 和鹽度棲地使用類型。系統發育分析表明具有SSG、大腎臟和利用高鹽度棲地在鳥類中趨同演化。轉換率分析 (Transition rate analysis)表明，具有 SSG 和大腎臟的物種傾向於從低鹽度向高鹽度移動，而其他物種則向相反方向移動。然而，鹽度棲地使用也推動腎臟的演化。生活在高/低鹽度環境中的物種分別傾向於發育更大/更小的腎臟。我們的研究結果表明，SSG 和大腎臟可能是通過適應高鹽度和其他現有功能的共同選擇而演化的。總體而言，不同類型的棲地和生理機制相互作用，形成了鳥類對鹹水棲地環境的適應，我們的研究結果為鳥類的功能多樣性如何演化提供新的見解。

Only a small number of avian species live in salty habitats. To infer how they evolved to tolerate high salinity, we examined how kidney sizes, supraorbital salt glands (SSGs), and the use of salty environments evolved in 230 species spanning 25 avian orders. Phylogenetic analysis suggests that SSGs, large kidneys, and utilization of salty habitats evolved convergently in birds. Transition rate analysis shows that species with SSGs and large kidneys tended to move from low to high salinity, whereas others moved in the opposite direction. However, habitat salinity also drove evolution of kidneys; lineages living in high/low salinity environments tended to develop larger/smaller kidneys, respectively. Our results suggest that SSGs and large kidneys may have evolved by adaptation to high-salinity and co-option of other existing functions. Overall, habitats and physiology interacted with each other to shape avian adaptation to salty environments. Our findings provide new insights into how birds’ functional diversity evolved.

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