Riedel Jendrian, Böhme Wolfgang, Bleckmann Horst, Spinner Marlene
University of Bonn, Institute of Zoology, Bonn, Germany.
J Morphol. 2015 Feb;276(2):167-84. doi: 10.1002/jmor.20330. Epub 2014 Oct 18.
Chameleons (Chamaeleonidae) feature many adaptations to their arboreal lifestyle, including zygodactylous feet, a prehensile tail, and epidermal microstructures. In arboreal tree chameleons, the substrate-contacting site of the feet and tail is covered by microscopic hair-like structures (setae) of 6-20 µm length. Their friction enhancing function has been shown in recent studies. Leaf chameleons and one representative of the tree chameleons (Chamaeleo namaquensis) secondarily have become ground-dwelling. Because leaf chameleons are paraphyletic, one could expect that in the three leaf chameleon genera Brookesia, Rhampholeon, and Rieppeleon and the tree chameleon Ch. namaquensis, epidermis has adapted independently to terrestrial locomotion. Using scanning electron microscopy, we investigated the substrate-contacting surfaces of the feet (subdigital) of 17 leaf chameleon species and five tree chameleon species that have not yet been examined. Additionally, surfaces not involved in locomotion, the flanks (dorsolateral), and scale interstices, were examined. Although the subdigital microstructures in leaf chameleons are more diverse than in tree chameleons, we found some features across the genera. The subdigital microornamentation of Rhampholeon spinosus consists of long thin setae and spines, comparable to those of tree chameleons. All other Rhampholeon species have spines or short but broad setae. Rh. spectrum had tooth-like structures instead of setae. Subdigital scales of Brookesia have either thorns or conical scale-tops in the center and feature honeycomb microstructures. In Rieppeleon, subdigital scales have a thorn. Scale surfaces are covered by honeycombs and short hair-like structures (spines). As subdigital scales with a thorn in the center and honeycomb microstructures were also found in the terrestrial tree chameleon Ch. namaquensis, one can assume that this geometry is a convergent adaptation to terrestrial locomotion. Despite the great number of genus-specific traits, the convergent evolution of honey-comb structures in Brookesia, Rieppeleon, and Ch. namaquensis and the high variability of spines and setae in Rhampholeon suggests a rapid adaptation of subdigital microornamentation in Chamaeleonidae.
变色龙（避役科）具有许多适应树栖生活方式的特征，包括对趾型足部、可抓握的尾巴以及表皮微观结构。在树栖的变色龙中，足部和尾巴与底物接触的部位覆盖着长度为6 - 20微米的微小毛发状结构（刚毛）。近期研究已证实了它们增强摩擦力的功能。叶变色龙以及一种树栖变色龙（纳马夸变色龙）后来转变为地栖生活。由于叶变色龙是并系群，因此可以预期，在三个叶变色龙属（侏儒枯叶变色龙属、侏儒变色龙属和丽纹变色龙属）以及树栖变色龙纳马夸变色龙中，表皮已独立适应陆地运动。我们使用扫描电子显微镜，研究了17种叶变色龙和5种尚未研究过的树栖变色龙足部（趾下）与底物接触的表面。此外，还检查了不参与运动的表面，即体侧（背外侧）和鳞片间隙。尽管叶变色龙的趾下微观结构比树栖变色龙的更多样化，但我们在这些属中发现了一些共同特征。多刺侏儒变色龙的趾下微饰由长而细的刚毛和刺组成，与树栖变色龙的类似。所有其他侏儒变色龙属物种都有刺或短而宽的刚毛。光谱侏儒变色龙有齿状结构而非刚毛。枯叶变色龙属的趾下鳞片中央要么有刺，要么有圆锥形的鳞片顶部，并具有蜂窝状微观结构。在丽纹变色龙属中，趾下鳞片有一根刺。鳞片表面覆盖着蜂窝和短毛发状结构（刺）。由于在陆栖树栖变色龙纳马夸变色龙中也发现了中央有刺且具有蜂窝状微观结构的趾下鳞片，因此可以推测这种结构是对陆地运动的趋同适应。尽管有大量属特异性特征，但枯叶变色龙属、丽纹变色龙属和纳马夸变色龙中蜂窝状结构的趋同进化以及侏儒变色龙属中刺和刚毛的高度变异性表明避役科的趾下微饰有快速适应的现象。
