Minelli Alessandro, Brena Carlo, Deflorian Gianluca, Maruzzo Diego, Fusco Giuseppe
Department of Biology, University of Padova, Via Ugo Bassi 58 B, 35131 Padua, Italy.
Dev Genes Evol. 2006 Jul-Aug;216(7-8):373-83. doi: 10.1007/s00427-006-0075-6. Epub 2006 May 3.
The traditional framework for the description of arthropod development takes the molt-to-molt interval as the fundamental unit of periodization, which is similar to the morphological picture of the main body axis as a series of segments. Developmental time is described as the subdivision into a few major stages of one or more instars each, which is similar to the subdivision of the main body axis into regions of one to many segments each. Parallel to recent criticisms to the segment as the fundamental building block of arthropod anatomy, we argue that, while a firm subdivision of development in stages is useful for describing arthropod ontogeny, this is limiting as a starting point for studying its evolution. Evolutionary change affects the association between different developmental processes, some of which are continuous in time whereas others are linked to the molting cycle. Events occurring but once in life (hatching; first achieving sexual maturity) are traditionally used to establish boundaries between major units of arthropod developmental time, but these boundaries are quite labile. The presence of embryonic molts, the 'gray zone' of development accompanying hatching (with the frequent delivery of an immature whose qualification as 'free-embryo' or ordinary postembryonic stage is arbitrary), and the frequent decoupling of growth and molting suggest a different view. Beyond the simple comparison of developmental schedules in terms of heterochrony, the flexible canvas we suggest for the analysis of arthropod development opens new vistas into its evolution. Examples are provided as to the origin of holometaboly and hypermetaboly within the insects.
描述节肢动物发育的传统框架将两次蜕皮之间的间隔作为分期的基本单位，这类似于将主体轴的形态描绘为一系列体节。发育时间被描述为细分为每个一龄或多龄的几个主要阶段，这类似于将主体轴细分为每个由一到多个体节组成的区域。与近期对体节作为节肢动物解剖学基本构建单元的批评类似，我们认为，虽然将发育明确细分为不同阶段对于描述节肢动物个体发育很有用，但作为研究其进化的起点，这存在局限性。进化变化会影响不同发育过程之间的关联，其中一些发育过程在时间上是连续的，而其他一些则与蜕皮周期相关。传统上，将一生中仅发生一次的事件（孵化；首次达到性成熟）用于确定节肢动物发育时间主要单元之间的界限，但这些界限相当不稳定。胚胎蜕皮的存在、孵化时发育的“灰色地带”（经常产出一个不成熟个体，其被界定为“自由胚胎”或普通胚后阶段具有任意性）以及生长与蜕皮频繁解耦，都表明了一种不同的观点。除了在发育异时性方面对发育时间表进行简单比较之外，我们建议用于分析节肢动物发育的灵活框架为其进化研究开辟了新的视角。文中给出了关于昆虫全变态和过变态起源的例子。
