Ankhelyi Madeleine V, Wainwright Dylan K, Lauder George V
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138.
J Morphol. 2018 Aug;279(8):1132-1154. doi: 10.1002/jmor.20836. Epub 2018 May 29.
Shark skin is covered with numerous placoid scales or dermal denticles. While previous research has used scanning electron microscopy and histology to demonstrate that denticles vary both around the body of a shark and among species, no previous study has quantified three-dimensional (3D) denticle structure and surface roughness to provide a quantitative analysis of skin surface texture. We quantified differences in denticle shape and size on the skin of three individual smooth dogfish sharks (Mustelus canis) using micro-CT scanning, gel-based surface profilometry, and histology. On each smooth dogfish, we imaged between 8 and 20 distinct areas on the body and fins, and obtained further comparative skin surface data from leopard, Atlantic sharpnose, shortfin mako, spiny dogfish, gulper, angel, and white sharks. We generated 3D images of individual denticles and measured denticle volume, surface area, and crown angle from the micro-CT scans. Surface profilometry was used to quantify metrology variables such as roughness, skew, kurtosis, and the height and spacing of surface features. These measurements confirmed that denticles on different body areas of smooth dogfish varied widely in size, shape, and spacing. Denticles near the snout are smooth, paver-like, and large relative to denticles on the body. Body denticles on smooth dogfish generally have between one and three distinct ridges, a diamond-like surface shape, and a dorsoventral gradient in spacing and roughness. Ridges were spaced on average 56 µm apart, and had a mean height of 6.5 µm, comparable to denticles from shortfin mako sharks, and with narrower spacing and lower heights than other species measured. We observed considerable variation in denticle structure among regions on the pectoral, dorsal, and caudal fins, including a leading-to-trailing edge gradient in roughness for each region. Surface roughness in smooth dogfish varied around the body from 3 to 42 microns.
鲨鱼皮覆盖着无数的盾鳞或皮齿。虽然先前的研究已利用扫描电子显微镜和组织学来证明皮齿在鲨鱼身体周围以及不同物种之间存在差异，但之前尚无研究对三维（3D）皮齿结构和表面粗糙度进行量化，以提供对皮肤表面纹理的定量分析。我们使用微型计算机断层扫描（micro-CT）、基于凝胶的表面轮廓测定法和组织学，对三条平滑狗鲨（皱唇鲨）个体的皮肤上皮齿的形状和大小差异进行了量化。在每条平滑狗鲨身上，我们对身体和鳍上8至20个不同区域进行了成像，并从豹纹鲨、大西洋尖鼻鲨、灰鲭鲨、白斑角鲨、宽咽鱼、天使鲨和大白鲨获取了更多比较性皮肤表面数据。我们生成了单个皮齿的3D图像，并通过微型计算机断层扫描测量了皮齿体积、表面积和冠角。表面轮廓测定法用于量化诸如粗糙度、偏度、峰度以及表面特征的高度和间距等计量变量。这些测量结果证实，平滑狗鲨不同身体部位的皮齿在大小、形状和间距上差异很大。吻部附近的皮齿平滑，类似铺路石，且相对于身体上的皮齿较大。平滑狗鲨身体上的皮齿通常有一到三条明显的脊，表面形状类似菱形，在间距和粗糙度上有背腹梯度。脊平均间距为56微米，平均高度为6.5微米，与灰鲭鲨的皮齿相当，且比其他测量物种的间距更窄、高度更低。我们观察到胸鳍、背鳍和尾鳍各区域之间皮齿结构存在显著差异，包括每个区域从前缘到后缘的粗糙度梯度。平滑狗鲨身体周围的表面粗糙度在3至42微米之间变化。
