贵州寒武系第二统杷榔组有壳变形虫的新发现*

有壳变形虫(testate amoebae)的演化历史最早可追溯至新元古代早期, 以该时期北美、华北、挪威以及澳洲等多个地区浅海相碳酸盐岩、页岩中发现的瓶状微体化石(vase-shaped microfossils)为标志。此前认为, 显生宙的有壳变形虫最早出现在早泥盆世。长期以来, 早古生代的地层中未发现这类原生生物的明确化石证据。本研究通过对岩石样品进行常规孢粉酸泡分析处理和切磨岩石薄片, 获取原位保存的化石标本的技术方法, 从贵州东部剑河县交榜剖面出露的寒武系杷榔组(第2统第4阶)中获得数枚有壳变形虫(testate amoebae)化石标本。基于标本的显微形态特征, 并结合激光拉曼光谱等研究, 对原先记述为疑源类的Plagasphaera balangensis和P. sp. A两形态种进行重新认识和描述。由于它们在结构和形态上与一些现生的鳞壳虫目(Euglyphida)有壳变形虫极为相似, 因此将先前定为疑源类的Plagasphaera balangensis和P. sp. A两形态属、种名, 分别修订为Palaeoassulina balangensis gen. et sp. nov.和?Palaeoassulina sp. A。该发现不仅将显生宙有壳变形虫的原有化石记录从晚古生代泥盆纪向前延伸至寒武纪早期, 还为调查研究有壳变形虫的系统演化提供关键的生物化石证据。     

Description of Phaeobola aeris gen. nov., sp. nov (Rhizaria,Cercozoa, Euglyphida) Sheds Light on Euglyphida’s Dark Matter

The majority of Euglyphida species are characterised by shells with imbricated silica scales. Environmental surveys indicate a large unexplored diversity and recent efforts hinted at a certain diversity of yet undescribed, inconspicuous, scale-lacking Euglyphida. Here we describe Phaeobola aeris gen. nov., sp. nov. that shows a variety of morphological characters typical for the Euglyphida but lacks silica scales-instead, this species bears an agglutinated test. Neither its morphology nor phylogenetic placement allows its assignment to any currently described family. We erected the yet monospecific genus Phaeobola gen. nov., which with yet available data remain Euglyphida incertae sedis.     

中国有壳肉足虫(原生动物)五新纪录描述

描述了采自云南、湖北和广东的5种有壳肉足虫,隶属原生动物亚界,肉鞭门,叶足纲,表壳目,均为国内新纪录种:非游巧装表壳虫Arcella artocrtea aplanata Grospietsch,1954;具角肋表壳虫A.costata angulosa (Perty) Playfair,1918;拟普通盘状表壳虫A.discoides pseudovulgaris Deflandre ,1928;光滑弯凸表壳虫A.gibbosa laevis Deflandre ,1928;球形叉口砂壳虫Difflugia gramen globulosa Stěpánek et Jirí,1958.     

Plant functional group diversity promotes soil protist diversity

We tested whether effects of plant diversity can propagate through food webs, down to heterotrophic protists not linked directly to plants. To this end we synthesised grassland ecosystems with varying numbers of plant functional groups (FGN) and assessed corresponding changes in testate amoebae communities. The number of plant species was kept constant. When FGN was increased from 1 to 3, species number and total community density of live testate amoebae were enhanced according to a linear and a saturating function, respectively. From FGN 1 to 2, the appearance of new testate amoebae species did not affect the presence of the resident species, whereas, from FGN 2 to 3 about one quarter of the resident testate amoebae species was replaced, without altering the total species number. Overall, density by species increased, while evenness of the testate amoebae community was not affected by FGN; although Trinema lineare, one of the most common species, became more abundant. The observed relationship between plant functional group diversity and testate amoebae diversity could shed new light on the biogeographical distribution patterns of protists.     

Effects of short-term nutrient addition on microfauna density in a Mediterranean stream

We performed a stream fertilisation experiment in an oligotrophic, forested, undisturbed stream by increasing nitrogen and phosphorus concentrations. The effect of nutrient loading on microfauna was studied over 6 months. A before after control impact (BACI) design was used to determine the outcome of the addition by comparing three upstream non-enriched reaches with an enriched one downstream. Ciliates such as Hymenostomata (Frontonia, Lembadion, Paramecium, Cyclidium) and Pleurostomatida (Litonotus) showed a positive response to fertilisation. No significant changes were detected for flagellates and testate amoebae. Mean density values observed (0.2–3×10³ ind cm⁻²) were compared with those found in literature.     

A Guide to the Study and Identification of Fossil Testate Amoebae in Quaternary Lake Sediments

Fossil shells of testate amoebae, commonly found in Quaternary sediments, provide another key for the interpretation of the recent history of lakes. Outline drawings and details of shell composition provide the micropalaeontologist with a practical guide to the taxonomy of these organisms.     

SSU rRNA reveals a sequential increase in shell complexity among the euglyphid testate amoebae (Rhizaria: Euglyphida)

The existing data on the molecular phylogeny of filose testate amoebae from order Euglyphida has revealed contradictions between traditional morphological classification and SSU rRNA phylogeny and, moreover, the position of several important genera remained unknown. We therefore carried out a study aiming to fill several important gaps and better understand the relationships among the main euglyphid testate amoebae and the evolutionary steps that led to the present diversity at a higher level. We obtained new SSU rRNA sequences from five genera and seven species. This new phylogeny obtained shows that (1) the clade formed by species of genera Assulina and Placocista branches unambiguously at the base of the subclade of Euglyphida comprising all members of the family Trinematidae and genus Euglypha, (2) family Trinematidae (Trachelocorythion, Trinema, and Corythion) branches as a sister group to genus Euglypha, (3) three newly sequenced Euglypha species (E. cf. ciliata, E. penardi, and E. compressa) form a new clade within the genus. Since our results show that Assulina and Placocista do not belong to the Euglyphidae (unless the Trinematidae are also included in this family), we propose the creation of a new family named Assulinidae. Consequently, we give a family status to the genera Euglypha and (tentatively) Scutiglypha, which become the new family Euglyphidae. The evolutionary pattern suggested by SSU rRNA phylogeny shows a clear tendency towards increasing morphological complexity of the shell characterised by changes in the symmetry (migration of the aperture to a ventral position and/or compression of the shell) and the appearance of specialised scales at the aperture (in families Trinematidae and Euglyphidae).     

The testate lobose amoebae (order Arcellinida Kent, 1880) finally find their home within Amoebozoa

Testate lobose amoebae (order Arcellinida Kent, 1880) are common in all aquatic and terrestrial habitats, yet they are one of the last higher taxa of unicellular eukaryotes that has not found its place in the tree of life. The morphological approach did not allow to ascertain the evolutionary origin of the group or to prove its monophyly. To solve these challenging problems, we analyzed partial small-subunit ribosomal RNA (SSU rRNA) genes of seven testate lobose amoebae from two out of the three suborders and seven out of the 13 families belonging to the Arcellinida. Our data support the monophyly of the order and clearly establish its position among Amoebozoa, as a sister-group to the clade comprising families Amoebidae and Hartmannellidae. Complete SSU rRNA gene sequences from two species and a partial actin sequence from one species confirm this position. Our phylogenetic analyses including representatives of all sequenced lineages of lobose amoebae suggest that a rigid test appeared only once during the evolution of the Amoebozoa, and allow reinterpretation of some morphological characters used in the systematics of Arcellinida.     

Ribosomal RNA genes challenge the monophyly of the Hyalospheniidae (Amoebozoa: Arcellinida)

To date only five partial and two complete SSU rRNA gene sequences are available for the lobose testate amoebae (Arcellinida). Consequently, the phylogenetic relationships among taxa and the definition of species are still largely dependant on morphological characters of uncertain value, which causes confusion in the phylogeny, taxonomy and the debate on cosmopolitanism of free-living protists. Here we present a SSU rRNA-based phylogeny of the Hyalospheniidae including the most common species. Similar to the filose testate amoebae of the order Euglyphida the most basal clades have a terminal aperture; the ventral position of the pseudostome appears to be a derived character. Family Hyalospheniidae appears paraphyletic and is separated into three clades: (1) Heleopera sphagni, (2) Heleopera rosea and Argynnia dentistoma and (3) the rest of the species from genera Apodera, Hyalosphenia, Porosia and Nebela. Our data support the validity of morphological characters used to define species among the Hyalospheniidae and even suggest that taxa described as varieties may deserve the rank of species (e.g. N. penardiana var. minor). Finally our results suggest that the genera Hyalosphenia and Nebela are paraphyletic, and that Porosia bigibbosa branches inside the main Nebela clade.