Palaeo-Evo-Devo of Malacostraca – quantifying crabs and their relatives

螃蟹和它们的近亲，一起代表了Meiura组，今天存在于各种各样的生态系统中，物种数量众多。除了不同的海洋栖息地，在淡水和陆地栖息地也可以找到Meiura的代表。Meiura群体具有相当大的经济重要性，其代表承担着不同的生态角色。Meiura组生态多样性的很大一部分是由幼虫阶段代表的，幼虫阶段构成了浮游生物的重要组成部分。在化石记录中，也有大量的Meiura代表，最早的记录是在中生代。据推测，这些甲壳类动物在当时的生态系统中已经扮演了重要的角色。特别是在白垩纪，根据大量成年螃蟹和近亲的化石，Meiura组的代表似乎已经明显多样化。不幸的是，人们对包括Meiura化石代表的幼虫在内的未成熟阶段几乎一无所知，尽管这些知识对理解化石生态系统很重要。在这个项目中，计划采用一种新的方法来解决Meiura组化石幼虫缺乏的问题。我们认为，这种缺乏并不一定意味着这些化石不存在，而是它们往往不被认为是不存在的。其原因是，特别是后期的幼虫阶段，即所谓的巨型幼虫，可以根据躯干和附属物的特征来确定。然而，在化石中，通常只发现盾和/或螯。在现存的meurans中，这些结构的个体发生变化是已知的，但这些变化相当微妙，不容易作为定性和离散的特征来检测。因此，我们在这个项目中的方法是收集盾形和螯合体形状的定量数据，并对它们进行比较。由此可以得出以下结论：1)可以区分不同的大鳞鱼幼虫和幼鱼早期阶段。2)可以比较现代和化石代表（古进化-devo）的个体发生模式。3)可以检测到不同阶段的体型变化。为了量化形状，将使用椭圆傅立叶分析来研究轮廓，该分析已经成功地应用于类似的研究。有了这些数据，就可以比较Meiura群体中不同进化谱系的变化。不同谱系同时发生的相似变化意味着对环境的相同变化会产生相同方向的反应。这样，这些数据也有助于对气候变化的总体认识。

Crabs and their closer relatives, together representing the group Meiura, are today present in diverse ecosystems with a large number of species. Besides different marine habitats, representatives of Meiura can also be found in freshwater and terrestrial habitats. The group Meiura is of considerable economic importance, and its representatives fulfil diverse ecological roles. A large part of the ecological diversity of the group Meiura is represented by the larval stages, which comprise a significant part of the plankton. Also in the fossil record, representatives of Meiura are known in large numbers, the earliest record being from the Mesozoic. Presumably, these crustaceans have already played an important role in the ecosystems at that time. Especially in the Cretaceous representatives of the group Meiura appear to have diversified significantly, based on numerous fossils of adult crabs and close relatives. Unfortunately, almost nothing is known about the immature stages including the larvae of the fossil representatives of Meiura, even though this knowledge would be important for the understanding of fossil ecosystems. In this project, it is planned to follow a new approach to tackle the problem of the lack of fossil larvae of the group Meiura. We assume that this lack does not necessarily mean that those fossils do not exist, but instead that they are often not recognised as such. The reason for this is that especially the later larval stages, the so-called megalopa larvae, can be determined as such based on characters of the trunk and the appendages. In fossil meiurans, however, usually only the shield and/or the chelae are found. In extant meiurans, ontogenetic changes of these structures are known, yet these are rather subtle and cannot easily be detected as qualitative and discrete characters. Hence, our approach in this project is to gather quantitative data of the shape of shield and chelae and to compare these. In this way, a number of conclusions can be drawn: 1) Distinct megalopa larvae and early juvenile stages can be identified as such. 2) Ontogenetic patterns can be compared between modern and fossil representatives (palaeo-evo-devo). 3) Changes in body size of distinct stages can be detected. To quantify the shape, the outline will be investigated with Elliptic Fourier Analysis, which has already been successfully applied for similar studies. With these data, changes in different evolutionary lineages within the group Meiura should be compared. Similar changes in different lineages at the same time would imply reactions in the same direction on the same changes of the environment. In this way, such data also contribute to a general understanding of a changing climate.