Evolution of the turtle bauplan: the topological relationship of the scapula relative to the ribcage

The turtle shell and the relationship of the shoulder girdle inside or ‘deep’ to the ribcage have puzzled neontologists and developmental biologists for more than a century. Recent developmental and fossil data indicate that the shoulder girdle indeed lies inside the shell, but anterior to the ribcage. Developmental biologists compare this orientation to that found in the model organisms mice and chickens, whose scapula lies laterally on top of the ribcage. We analyse the topological relationship of the shoulder girdle relative to the ribcage within a broader phylogenetic context and determine that the condition found in turtles is also found in amphibians, monotreme mammals and lepidosaurs. A vertical scapula anterior to the thoracic ribcage is therefore inferred to be the basal amniote condition and indicates that the condition found in therian mammals and archosaurs (which includes both developmental model organisms: chickens and mice) is derived and not appropriate for studying the developmental origin of the turtle shell. Instead, among amniotes, either monotreme mammals or lepidosaurs should be used.     

稚鳖蛋氨酸的营养需要量

将 90只中华稚鳖随机平均分为六组 ,分别饲喂含蛋氨酸 0 .82 %、1.12 %、1.32 %、1.5 2 %、1.72 %、2 .0 2 %的等能等氮半合成饵料 (胱氨酸为 0 .5 6 % )。结果表明 :蛋氨酸水平对特殊体重生长率 (SGR)、摄饵量 (FI)、饵料系数(FCR)、肝重 (LW)、肝重 /体重 (LW/BW)、体脂肪含量 (BFC)、体蛋氨酸含量 (BMC)、体蛋白沉积率 (PRR)、蛋氨酸沉积率 (MRR)有极显著或显著影响 (P <0 .0 1或P <0 .0 5 ) ,但是对体蛋白含量 (BPC)没有显著影响 (P >0 .0 5 )。在饵料胱氨酸为 0 .5 6 %时 ,稚鳖蛋氨酸需要量为 1.2 8% (风干日粮基础 )或 3.0 7% (蛋白基础 )。     

<Emphasis Type="Italic">Msx</Emphasis> genes are expressed in the carapacial ridge of turtle shell: a study of the European pond turtle,<Emphasis Type="Italic"> Emys orbicularis</Emphasis>

The turtle shell forms by extensive ossification of dermis ventrally and dorsally. The carapacial ridge (CR) controls early dorsal shell formation and is thought to play a similar role in shell growth as the apical ectodermal ridge during limb development. However, the molecular mechanisms underlying carapace development are still unknown. Msx genes are involved in the development of limb mesenchyme and of various skeletal structures. In particular, precocious Msx expression is recorded in skeletal precursors that develop close to the ectoderm, such as vertebral spinous processes or skull. Here, we have studied the embryonic expression of Msx genes in the European pond turtle, Emys orbicularis. The overall Msx expression in head, limb, and trunk is similar to what is observed in other vertebrates. We have focused on the CR area and pre-skeletal shell condensations. The CR expresses Msx genes transiently, in a pattern similar to that of fgf10. In the future carapace domain, the dermis located dorsal to the spinal cord expresses Msx genes, as in other vertebrates, but we did not see expansion of this expression in the dermis located more laterally, on top of the dermomyotomes. In the ventral plastron, although the dermal osseous condensations form in the embryonic Msx-positive somatopleura, we did not observe enhanced Msx expression around these elements. These observations may indicate that common mechanisms participate in limb bud and CR early development, but that pre-differentiation steps differ between shell and other skeletal structures and involve other gene activities than that of Msx genes.Edited by D.A. Weisblat     

为什么应该弃用“进化”而使用“演化”

Although Darwinian evolutionary theory has been widely spread in China, several misconceptions about evolution have been persistent among the general public and even the researchers. Some are simple misunderstandings, including evolution results in progress with organisms are always replaced by better forms through evolution, and humans or primates represent the most advanced organisms. Some are misconceptions about natural selection and imply organisms evolved based on what they need or all the current morphologies or biological phenotypes are the results of adaptation. The spread of these misconceptions in China stem partially from the historical misleading translation of “evolution” to “进化” in Chinese, which includes the meaning of progress with direction into more advance form. Here, we summarize major progresses of the evolutionary theory after the Modern Synthesis and discuss how this misleading translation introduces a barrier in understanding of these new theoretical developments, such as neutral or near-neutral theory, genetic drift hypothesis, trade-off theory, and many new concepts in evo-devo field. Looking back at the development of evolutionary theory over the past few hundred years, we emphasize that a series of revolutionary achievements in the last 30 years have brought about fundamental changes in our basic understanding of the evolution of life. Therefore, we strongly advocate a formal re-introducing of “演化”, a more correct translation of evolution, in textbook and in daily communication among Chinese biological researchers. We anticipate that this change will help to correct some of these deep-rooted misconceptions among general public and will ultimately stimulate the interest of younger generation in conceptually thinking of evolutionary theory.     

Morphological evolution: Estimation principles, patterns, and mechanisms

Directions, modes, specializations, and coordination systems of morphofunctional changes are discussed based on modern data. Phylogenetic heterochronies (pedomorphoses and outstripping), which provide the basis for parallel, mosaic, and saltation development and different rates of morphological evolution, are regarded as important events of morphological diversification. The analysis of specificity and relationships of structural levels of organization (including genetic and epigenetic) and the elaboration of evolutionary principles of their dynamic stability are thought to be the most promising fields of modern research.     

The emotion system promotes diversity and evolvability

Studies on the relationship between the optimal phenotype and its environment have had limited focus on genotype-to-phenotype pathways and their evolutionary consequences. Here, we study how multi-layered trait architecture and its associated constraints prescribe diversity. Using an idealized model of the emotion system in fish, we find that trait architecture yields genetic and phenotypic diversity even in absence of frequency-dependent selection or environmental variation. That is, for a given environment, phenotype frequency distributions are predictable while gene pools are not. The conservation of phenotypic traits among these genetically different populations is due to the multi-layered trait architecture, in which one adaptation at a higher architectural level can be achieved by several different adaptations at a lower level. Our results emphasize the role of convergent evolution and the organismal level of selection. While trait architecture makes individuals more constrained than what has been assumed in optimization theory, the resulting populations are genetically more diverse and adaptable. The emotion system in animals may thus have evolved by natural selection because it simultaneously enhances three important functions, the behavioural robustness of individuals, the evolvability of gene pools and the rate of evolutionary innovation at several architectural levels.     

The adaptive legacy of human evolution: A search for the environment of evolutionary adaptedness

The growth of evolutionary psychology has led to renewed interest in what might be the significant evolutionary heritage of people living today, and in the extent to which humans are suited to a particular adaptive environment—the EEA. The EEA, though, is a new tool in the battery of evolutionary concepts, and it is important both that it is scrutinized for its utility, and that the actual reconstructions of the environments in which humans and hominids evolved are based on sound palaeobiological inference and an appropriate use of the phylogenetic context of primate evolution.