Choanoflagellates, choanocytes, and animal multicellularity

Abstract. It is widely accepted that multicellular animals (metazoans) constitute a monophyletic unit, deriving from ancestral choanoflagellate‐like protists that gave rise to simple choanocyte‐bearing metazoans. However, a re‐assessment of molecular and histological evidence on choanoflagellates, sponge choanocytes, and other metazoan cells reveals that the status of choanocytes as a fundamental cell type in metazoan evolution is unrealistic. Rather, choanocytes are specialized cells that develop from non‐collared ciliated cells during sponge embryogenesis. Although choanocytes of adult sponges have no obvious homologue among metazoans, larval cells transdifferentiating into choanocytes at metamorphosis do have such homologues. The evidence reviewed here also indicates that sponge larvae are architecturally closer than adult sponges to the remaining metazoans. This may mean that the basic multicellular organismal architecture from which diploblasts evolved, that is, the putative planktonic archimetazoan, was more similar to a modern poriferan larva lacking choanocytes than to an adult sponge. Alternatively, it may mean that other metazoans evolved from a neotenous larva of ancient sponges. Indeed, the Porifera possess some features of intriguing evolutionary significance: (1) widespread occurrence of internal fertilization and a notable diversity of gastrulation modes, (2) dispersal through architecturally complex lecithotrophic larvae, in which an ephemeral archenteron (in dispherula larvae) and multiciliated and syncytial cells (in trichimella larvae) occur, (3) acquisition of direct development by some groups, and (4) replacement of choanocyte‐based filter‐feeding by carnivory in some sponges. Together, these features strongly suggest that the Porifera may have a longer and more complicated evolutionary history than traditionally assumed, and also that the simple anatomy of modern adult sponges may have resulted from a secondary simplification. This makes the idea of a neotenous evolution less likely than that of a larva‐like choanocyte‐lacking archimetazoan. From this perspective, the view that choanoflagellates may be simplified sponge‐derived metazoans, rather than protists, emerges as a viable alternative hypothesis. This idea neither conflicts with the available evidence nor can be disproved by it, and must be specifically re‐examined by further approaches combining morphological and molecular information. Interestingly, several microbial lin°Cages lacking choanocyte‐like morphology, such as Corallochytrea, Cristidiscoidea, Ministeriida, and Mesomycetozoea, have recently been placed at the boundary between fungi and animals, becoming a promising source of information in addition to the choanoflagellates in the search for the unicellular origin of animal multicellularity.     

文昌鱼的实验室繁育及子二代获得

文昌鱼特殊的进化地位、简单的器官系统和终生透明的躯体等特征,使其很有希望成为一个新型实验室模式动物。要实现文昌鱼的模式动物化,实验室内全人工条件下繁殖是关键的第一步。为此,我们于2003年9月和2004年4月两次采集产于厦门海域的2种文昌鱼,开展实验室内养殖研究。经过3年多的持续实验室养殖,继2005年夏季于实验室内繁殖出子一代文昌鱼后,又在2006年夏季成功获得了这两种文昌鱼的子二代,初步实现文昌鱼在实验室内的全人工养殖。对子代文昌鱼养殖的初步观察发现,不同水温对生长发育速度有一定影响,提示有可能通过水温控制实现文昌鱼一年多次产卵的目的。目前这两种文昌鱼子二代幼体已完成变态,进入亚成体生长发育阶段,其体长分别已达14.6mm(日本文昌鱼Branchiostomajaponicum)和6.5mm(白氏文昌鱼B.belcheri)。     

Juvenile animal studies for the development of paediatric medicines: a description and conclusions from a European medicines agency workshop on juvenile animal testing for nonclinical assessors

A workshop organised by the European Medicines Agency involved assessors and experts present in a Nonclinical Working Group evaluating juvenile animal studies for Paediatric Investigation Plans in collaboration with the Paediatric Committee and the Safety Working Party of the Committee for Human Medicinal Products. The objective of the workshop was to analyse which juvenile animal studies proposals were received and agreed by the Paediatric Committee, to check consistency and how to apply the existing European guideline on juvenile animal studies. A comparison of main organ system development in man vs. animal species was presented to guide the review and to support species selection and protocol design. An analysis of juvenile animal studies included in finalised PIP's was also presented. Out of 109 paediatric investigation plans finalised between November 2008 and March 2009, 43 included one or more juvenile animal studies. In most cases the preferred species was the rat; one species only was requested to be studied (20/22), but in a minority two species were required (2/22). When deciding on the characteristics of the juvenile animal studies, such as age of animals at study start, the age of the children targeted by the medicine was considered. It is expected that the increasing experience gained by Applicants and Regulators will allow further refining the criteria for these juvenile animal studies. Further research on this topic is highly encouraged in the European Regulatory framework. Birth Defects Res (Part B) 89:467–473, 2010. © 2010 Wiley‐Liss, Inc.     

Ant visitation to extrafloral nectaries decreases herbivory and increases fruit set in Chamaecrista debilis (Fabaceae) in a Neotropical savanna

Studies of ant–plant relationships elucidate how top-down effects of the third trophic level can affect the biomass, richness, and/or species composition of plants. Although widespread in the neotropics, few studies have so far examined the direct effects of ants on plant fitness. Here, through experimental manipulation (ant-exclusion) under natural conditions, we examined the effect of ant visitation to extrafloral nectaries on leaf herbivory and fruit set in Chamaecrista debilis in the Brazilian savanna. As opposed to other Chamaecrista species, our results showed that visiting ants (15 species) significantly reduce herbivory and increase fruit set by more than 50% compared to plants from which ants were excluded. This mutualistic system is facultative in nature, and corroborates the potential beneficial role of exudate-feeding ants as anti-herbivore agents of tropical plants.     

海洋动物来源微生物的共培养研究进展

近年来,由于一些新疾病的发生和细菌耐药性的出现,微生物来源次级代谢产物的筛选重复率越来越高,微生物一些代谢基因在现有实验室条件下无法表达,所以需要发现新的微生物资源,同时找到激活微生物代谢产物基因的方法.海洋动物体内蕴含着大量的共附生微生物资源,可以产生很多具有生物活性的化合物,是潜在的药用资源.本文综述了近年来海洋动...     

The influence of fire frequency on the structure and botanical composition of savanna ecosystems

Savannas cover 60% of the land surface in Southern Africa, with fires and herbivory playing a key role in their ecology. The Limpopo National Park (LNP) is a 10,000 km² conservation area in southern Mozambique and key to protecting savannas in the region. Fire is an important factor in LNP's landscapes, but little is known about its role in the park's ecology. In this study, we explored the interaction between fire frequency (FF), landscape type, and vegetation. To assess the FF, we analyzed ten years of the Moderate resolution Imaging Spectroradiometer (MODIS) burned area product (2003–2013). A stratified random sampling approach was used to assess biodiversity across three dominant landscapes (Nwambia Sandveld‐NS, Lebombo North‐LN, and Shrubveld Mopane on Calcrete‐C) and two FF levels (low—twice or less; and high—3 times or more, during 10 years). Six ha were sampled in each stratum, except for the LN versus high FF in which low accessibility allowed only 3 ha sampling. FF was higher in NS and LN landscapes, where 25% and 34% of the area, respectively, burned more than three times in 10 years. The landscape type was the main determinant of grass composition and biomass. However, in the sandy NS biomass was higher under high FF. The three landscapes supported three different tree/shrub communities, but FF resulted in compositional variations in NS and LN. Fire frequency had no marked influence on woody structural parameters (height, density, and phytomass). We concluded that the savannas in LNP are mainly driven by landscape type (geology), but FF may impose specific modifications. We recommend a fire laissez‐faire management system for most of the park and a long‐term monitoring system of vegetation to address vegetation changes related to fire. Fire management should be coordinated with the neighboring Kruger National Park, given its long history of fire management. Synthesis: This study revealed that grass and tree/shrub density, biomass, and composition in LNP are determined by the landscape type, but FF determines some important modifications. We conclude that at the current levels FF is not dramatically affecting the savanna ecosystem in the LNP (Figure 1). However, an increase in FF may drive key ecosystem changes in grass biomass and tree/shrub species composition, height, phytomass, and density.