Bird Nathan C, Webb Jacqueline F
Current address: Department of Biological Sciences, University of Rhode Island, 120 Flagg Road, Kingston RI 02881, USA.
Evodevo. 2014 Jun 5;5:21. doi: 10.1186/2041-9139-5-21. eCollection 2014.
The canals of the mechanosensory lateral line system are components of the dermatocranium, and demonstrate phenotypic variation in bony fishes. Widened lateral line canals evolved convergently in a limited number of families of teleost fishes and it had been hypothesized that they evolved from narrow canals via heterochrony and explore modularity in the lateral line system. Two species of cichlids with different canal phenotypes were used to test a hypothesis of heterochrony. Histological material prepared from ontogenetic series of Aulonocara stuartgranti (widened canals) and Tramitichromis sp. (narrow canals) was analyzed using ANCOVA to determine rates of increase in canal diameter and neuromast size (length, width) and to compare the timing of onset of critical stages in canal morphogenesis (enclosure, ossification).
A faster rate of increase in canal diameter and neuromast width (but not length), and a delay in onset of canal morphogenesis were found in Aulonocara relative to Tramitichromis. However, rates of increase in canal diameter and neuromast size among canals, among canal portions and among canals segments reveal similar trends within both species.
The evolution of widened lateral line canals is the result of dissociated heterochrony - acceleration in the rate of increase of both canal diameter and neuromast size, and delay in the onset of canal morphogenesis, in Aulonocara (widened canals) relative to Tramitichromis (narrow canals). Common rates of increase in canal diameter and neuromast size among canal portions in different dermatocranial bones and among canal segments reflect the absence of local heterochronies, and suggest modular integration among canals in each species. Thus, canal and neuromast morphology are more strongly influenced by their identities as features of the lateral line system than by the attributes of the dermatocranial bones in which the canals are found. Rate heterochrony manifested during the larval stage ensures that the widened canal phenotype, known to be associated with benthic prey detection in adult Aulonocara, is already present before feeding commences. Heterochrony can likely explain the convergent evolution of widened lateral line canals among diverse taxa. The lateral line system provides a valuable context for novel analyses of the relationship between developmental processes and the evolution of behaviorally and ecologically relevant phenotypes in fishes.
机械感觉侧线系统的管道是皮颅的组成部分，在硬骨鱼类中表现出表型变异。加宽的侧线管道在有限数量的硬骨鱼科中趋同进化，并且有人推测它们是通过异时性从狭窄管道进化而来，并探讨侧线系统中的模块性。使用两种具有不同管道表型的丽鱼科鱼类来检验异时性假说。对从斯氏孔雀鲷（加宽管道）和特氏丽鲷（狭窄管道）个体发育系列制备的组织学材料进行协方差分析，以确定管道直径和神经丘大小（长度、宽度）的增加速率，并比较管道形态发生关键阶段（封闭、骨化）开始的时间。
相对于特氏丽鲷，在斯氏孔雀鲷中发现管道直径和神经丘宽度（而非长度）的增加速率更快，且管道形态发生开始延迟。然而, 两种鱼类的管道之间、管道部分之间以及管道段之间的管道直径和神经丘大小的增加速率显示出相似的趋势。
加宽侧线管道的进化是解离异时性的结果——相对于特氏丽鲷（狭窄管道），斯氏孔雀鲷（加宽管道）的管道直径和神经丘大小的增加速率加快，且管道形态发生开始延迟。不同皮颅骨骼中的管道部分之间以及管道段之间管道直径和神经丘大小的共同增加速率反映了局部异时性的缺失，并表明每个物种的管道之间存在模块整合。因此，管道和神经丘形态受其作为侧线系统特征的身份影响比受发现管道的皮颅骨骼属性影响更大。幼体阶段表现出的速率异时性确保了已知与成年斯氏孔雀鲷底栖猎物检测相关的加宽管道表型在摄食开始前就已存在。异时性可能解释了不同分类群中加宽侧线管道的趋同进化。侧线系统为鱼类发育过程与行为和生态相关表型进化之间关系的新分析提供了有价值的背景。
