Martin Rene P, Dias Abigail S, Summers Adam P, Gerringer Mackenzie E
Department of Ecology and Evolutionary Biology and Biodiversity Institute, 1345 Jayhawk Boulevard, University of Kansas, Lawrence, KS 66045, USA.
Department of Biology, Sonoma State University, 1801 E. Cotati Ave., Rohnert Park, CA 94928, USA.
Integr Org Biol. 2022 Oct 16;4(1):obac044. doi: 10.1093/iob/obac044. eCollection 2022.
Extreme abiotic factors in deep-sea environments, such as near-freezing temperatures, low light, and high hydrostatic pressure, drive the evolution of adaptations that allow organisms to survive under these conditions. Pelagic and benthopelagic fishes that have invaded the deep sea face physiological challenges from increased compression of gasses at depth, which limits the use of gas cavities as a buoyancy aid. One adaptation observed in deep-sea fishes to increase buoyancy is a decrease of high-density tissues. In this study, we analyze mineralization of high-density skeletal tissue in rattails (family Macrouridae), a group of widespread benthopelagic fishes that occur from surface waters to greater than 7000 m depth. We test the hypothesis that rattail species decrease bone density with increasing habitat depth as an adaptation to maintaining buoyancy while living under high hydrostatic pressures. We performed micro-computed tomography (micro-CT) scans on 15 species and 20 specimens of rattails and included two standards of known hydroxyapatite concentration (phantoms) to approximate voxel brightness to bone density. Bone density was compared across four bones (eleventh vertebra, lower jaw, pelvic girdle, and first dorsal-fin pterygiophore). On average, the lower jaw was significantly denser than the other bones. We found no correlation between bone density and depth or between bone density and phylogenetic relationships. Instead, we observed that bone density increases with increasing specimen length within and between species. This study adds to the growing body of work that suggests bone density can increase with growth in fishes, and that bone density does not vary in a straightforward way with depth.
深海环境中的极端非生物因素，如接近冰点的温度、低光照和高静水压力，推动了生物适应性的进化，使生物体能够在这些条件下生存。侵入深海的远洋和底栖远洋鱼类面临着因深度增加导致气体压缩而带来的生理挑战，这限制了气腔作为浮力辅助工具的使用。在深海鱼类中观察到的一种增加浮力的适应性变化是高密度组织的减少。在本研究中，我们分析了鼠尾鱼（鼠尾鱼科）高密度骨骼组织的矿化情况，鼠尾鱼是一类广泛分布的底栖远洋鱼类，从表层水域到深度超过7000米的区域均有出现。我们检验了这样一个假设：随着栖息地深度的增加，鼠尾鱼物种会降低骨密度，以适应在高静水压力下生存时维持浮力的需要。我们对15个物种的20个鼠尾鱼标本进行了显微计算机断层扫描（micro-CT），并纳入了两种已知羟基磷灰石浓度的标准物（模型），以将体素亮度近似为骨密度。对四块骨骼（第十一椎骨、下颌、骨盆带和第一背鳍鳍担骨）的骨密度进行了比较。平均而言，下颌骨的密度明显高于其他骨骼。我们发现骨密度与深度之间或骨密度与系统发育关系之间均无相关性。相反，我们观察到，在物种内部和物种之间，骨密度随着标本长度的增加而增加。这项研究为越来越多的研究工作增添了内容，这些研究表明鱼类的骨密度会随着生长而增加，并且骨密度不会随深度以直接的方式变化。
