We tested the hypothesis that deep-sea fishes have poorly mineralized bone relative to shallower-dwelling species using data from a single family that spans a large depth range. The family Liparidae (snailfishes, Cottiformes) has representatives across the entire habitable depth range for bony fishes (0 m–> 8000 m), making them an ideal model for studying depth-related trends in a confined phylogeny. We used micro-computed tomography (micro-CT) scanning to test three aspects of skeletal reduction in snailfishes (50 species) across a full range of habitat depths: 1) reduction of structural dimensions, 2) loss of skeletal elements, and 3) reduction in bone density. Using depth data from the literature, we found that with increasing depth, the length of the dentary, neurocranium, and suborbital bones decreases. The ventral suction disk decreases width with increasing maximum habitat depth and is lost entirely in some deeper-living taxa, though not all. Although visual declines in bone density in deeper-living taxa were evident across full skeletons, individual densities of the lower jaw, vertebra, suction disk, hypural plate, and otoliths did not significantly decline with any depth metric. However, pelagic and polar taxa tended to show lower density bones compared to other species in the family. We propose that skeletal reductions allow snailfishes to maintain neutral buoyancy at great depths in the water column, while supporting efficient feeding and locomotion strategies. These findings suggest that changes in skeletal structure are non-linear and are driven not only by hydrostatic pressure, but by other environmental factors and by evolutionary ancestry, calling the existing paradigm into question.

中文翻译：

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栖息地影响蜗牛鱼（Liparidae 科）的骨骼形态和密度

我们使用跨越大深度范围的单个科的数据检验了这样的假设，即深海鱼类相对于浅栖物种而言骨骼矿化程度较差。Liparidae科（蜗牛鱼，Cottiformes）在硬骨鱼的整个适居深度范围（0米–> 8000米）中具有代表，使它们成为研究有限系统发育中与深度相关的趋势的理想模型。我们使用微型计算机断层扫描 (micro-CT) 扫描来测试各种栖息地深度的蜗牛鱼（50 种）骨骼减少的三个方面：1) 结构尺寸的减少，2) 骨骼元素的损失，以及 3)骨密度降低。利用文献中的深度数据，我们发现随着深度的增加，齿骨、神经颅骨和眶下骨的长度减小。腹侧吸盘的宽度随着最大栖息地深度的增加而减小，并且在一些更深的生活类群中完全消失，尽管不是全部。尽管在整个骨骼中，更深层次生物类群的骨密度明显下降，但下颌、椎骨、吸盘、上膜板和耳石的个体密度并没有随着任何深度指标而显着下降。然而，与科中的其他物种相比，远洋和极地类群的骨骼密度往往较低。我们认为，骨骼的减少使蜗牛鱼能够在水体深处保持中性浮力，同时支持有效的进食和运动策略。这些发现表明，骨骼结构的变化是非线性的，不仅受到静水压力的驱动，而且还受到其他环境因素和进化祖先的驱动，这对现有的范式提出了质疑。