Biological Sciences, Louisiana State University, Baton Rouge, LA, USA.
Department of Biology, West Virginia University, 3139 Life Sciences Building, Morgantown, WV 26506, USA.
Arthropod Struct Dev. 2013 Nov;42(6):443-454. doi: 10.1016/j.asd.2013.07.003. Epub 2013 Jul 31.
The forwards-walking portly crab, Libinia emarginata is an ancient brachyuran. Its phylogenetic position and behavioral repertoire make it an excellent candidate to reveal the adaptations, which were required for brachyuran crabs to complete their transition to sideways-walking from their forwards-walking ancestors. Previously we showed that in common with other forwards-walking (but distantly related) crustaceans, L. emarginata relies more heavily on its more numerous proximal musculature to propel itself forward than its sideways-walking closer relatives. We investigated if the proximal musculature of L. emarginata is innervated by a greater number of motor neurons than that of sideways-walking brachyurans. We found the distal musculature of spider crabs is innervated by a highly conserved number of motor neurons. However, innervation of its proximal musculature is more numerous than in closely-related (sideways-walking) species, resembling in number and morphology those described for forwards-walking crustaceans. We propose that transition from forward- to sideways-walking in crustaceans involved a decreased role for the proximal leg in favor of the more distal merus-carpus joint.
向前行进的肥胖蟹，Libinia emarginata 是一种古老的短尾类动物。它的系统发育位置和行为模式使其成为揭示适应特征的绝佳候选者，这些适应特征是短尾类螃蟹从向前行进的祖先过渡到侧向行进所必需的。之前我们已经表明，与其他向前行进的（但亲缘关系较远的）甲壳类动物一样，L. emarginata 更依赖于其更多的近端肌肉来推动自己向前，而不是它的侧向行进的近亲。我们研究了 L. emarginata 的近端肌肉是否由比侧向行进的短尾类动物更多的运动神经元支配。我们发现，蜘蛛蟹的远端肌肉由高度保守数量的运动神经元支配。然而，其近端肌肉的支配数量比近亲（侧向行进）物种更多，类似于向前行进的甲壳类动物所描述的那些。我们提出，甲壳类动物从向前行进到侧向行进的转变涉及近端腿的作用降低，而更靠近远端的腕节-掌节关节的作用增加。
