Herrel Anthony, Deban Stephen M, Schaerlaeken Vicky, Timmermans Jean-Pierre, Adriaens D
Department of Biology, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium.
Physiol Biochem Zool. 2009 Jan-Feb;82(1):29-39. doi: 10.1086/589950.
Extremely specialized and long tongues used for prey capture have evolved independently in plethodontid salamanders and chameleons. In both systems, the demands on tongue projection are probably similar: to maximize projection velocity and distance. Consequently, many of the design features of the projection system in these two groups have converged to an astonishing degree. Both involve the use of power amplification systems based on helically wound muscle fibers that load internal connective tissue sheets as illustrated in previous studies. Demands imposed on tongue retraction, however, are different to some degree. Although in both groups there is a clear demand for retraction capacity (given the long projection distances), in chameleons there is an added demand for force because they eat large and heavy prey. As indicated by our data, plethodontid salamanders have extremely long tongue retractors with normal striated muscle. Chameleons, on the other hand, evolved long retractors of the supercontracting type. Interestingly, our data show that at least in chameleons, the extreme design of the tongue in function of prey capture appears to have consequences on prey transport, resulting in an increased dependence on the hyoid. In turn, this has lead to an increase in transport-cycle duration and an increase in the number of cycles needed to transport prey in comparison with closely related agamid lizards. Clearly, extreme morphological specializations are tuned to functional and ecological demands and may induce a reduced performance in other functions performed by the same set of integrated structures.
在无肺螈科蝾螈和变色龙中，用于捕食的极其特化且长的舌头是独立进化而来的。在这两个系统中，对舌头伸出的要求可能相似：即最大化伸出速度和距离。因此，这两组动物中伸出系统的许多设计特征已经惊人地趋同。两者都涉及使用基于螺旋状缠绕肌肉纤维的功率放大系统，这些肌肉纤维加载内部结缔组织片层，如先前研究所展示的那样。然而，对舌头回缩的要求在一定程度上有所不同。尽管在这两组动物中都对回缩能力有明确要求（考虑到伸出距离很长），但在变色龙中，由于它们捕食的猎物又大又重，所以对力量还有额外要求。正如我们的数据所示，无肺螈科蝾螈具有极长的、由正常横纹肌构成的舌头回缩肌。另一方面，变色龙进化出了超收缩类型的长回缩肌。有趣的是，我们的数据表明，至少在变色龙中，用于捕食功能的舌头的极端设计似乎对猎物运输产生了影响，导致对舌骨的依赖性增加。相应地，这使得运输周期持续时间增加，并且与亲缘关系相近的鬣蜥相比，运输猎物所需的周期数也增加了。显然，极端的形态特化是根据功能和生态需求进行调整的，并且可能会导致由同一组整合结构执行的其他功能的性能下降。
