THE LOWER CAMBRIAN EODISCOID TRILOBITE CALODISCUS LOBATUS FROM SWEDEN: MORPHOLOGY, ONTOGENY AND DISTRIBUTION

Abstract:  Several thousand disarticulated remains together with a few complete enrolled specimens of the lower Cambrian eodiscoid trilobite Calodiscus lobatus ( Hall, 1847 ) have been collected at two outcrop areas in Sweden. The material reveals new details of morphology and morphogenesis during ontogenetic development. Size-frequency analyses show that the material from the Fånån rivulet in Jämtland, central Sweden, represents a natural population dominated by juveniles, whereas the material from Gislövshammar in Scania, southern Sweden, has been sorted during postmortem transport. Three stages of protaspid development can be traced and defined as well as all subsequent ontogenetic stages for the cephalon, hypostome and pygidium. The early meraspid pygidium has a pronounced larval notch, which persists, though becoming progressively less distinct in later meraspides. The number of axial rings in the transitory pygidium increases throughout meraspid development until a third and final thoracic segment is liberated. During ontogeny the articulating half-rings are strongly developed, and both meraspides and holaspides were capable of full sphaeroidal enrollment and outstretched postures. The hypostome undergoes some dramatic modifications; in M0 the anterior margin is axe-shaped, by M1 the area of attachment greatly decreases and the hypostome becomes more elongated and pear-shaped, before attaining its adult form, which has an overall resemblance to that of polymerid trilobites. During ontogeny, the hypostome changes from a conterminant attachment to a natant condition, thereby mirroring hypostomal evolution within trilobites generally. The morphology, ontogeny, enrollment, hypostomal development and the presence of calcified protaspides suggest polymerid rather than agnostoid affinities of the eodiscoids.     

Testing the enemy release hypothesis: a review and meta-analysis

One of the most cited hypotheses explaining the inordinate success of a small proportion of introduced plants that become pests is the ‘natural enemies hypothesis’. This states that invasive introduced plants spread rapidly because they are liberated from their co-evolved natural enemies. This hypothesis had not been properly tested until recently. Previous reviews on this topic have been narrative and vote counting in nature. In this review, we carried out quantitative synthesis and meta-analysis using existing literature on plants and their herbivores to test the different components of the enemy release hypothesis. We found supporting evidence in that (1) insect herbivore fauna richness is significantly greater in the native than introduced ranges, and the reduction is skewed disproportionally towards specialists and insects feeding on reproductive parts; and (2) herbivore damage levels are greater on native plants than on introduced invasive congeners. However, herbivore damage levels are only marginally greater for plants in native than in introduced ranges, probably due to the small numbers of this type of study. Studies quantifying herbivore impacts on plant population dynamics are too scarce to make conclusions for either comparison of plants in native vs introduced ranges or of co-occurring native and introduced congeners. For future research, we advocate that more than two-way comparisons between plants in native and introduced ranges, or native and introduced congeners are needed. In addition, the use of herbivore exclusions to quantify the impacts of herbivory on complete sets of population vital rates of native vs introduced species are highly desirable. Furthermore, three-way comparisons among congeners of native plants, introduced invasive, and introduced non-invasive plants can also shed light on the importance of enemy release. Finally, simultaneously testing the enemy release hypothesis and other competing hypotheses will provide significant insights into the mechanisms governing the undesirable success of invasive species.     

Small-scale biogeographical patterns in some groundwater Crustacea, the syncarid, Parabathynellidae

An analysis was made of the micro-distribution patterns of five phylogenetically closely related species belonging to the genus Iberobathynella, a group of subterranean aquatic crustaceans (Syncarida, Parabathynellidae). The two-step model of colonization and speciation seems to provide a valid explanation for the current distribution of a large number of stygobiontic taxa of marine origin (thalassoid). However, with respect to the Iberobathynella, only the colonization of the subterranean environment at the mesoscale level can be explained. The second phase of the model, marine regression, can only explain the colonization of the region by the ancestor; the subsequent evolution and speciation at a smaller scale remain to be explained. Local geological constraints – Upper Triassic gypsiferous mudstone deposits plus faults and thrusting linked to the Alpine Orogeny – are responsible for the appearance of local palaeogeographic phenomena. These may have been the vicariant processes responsible for the geographical and genetic isolation of the ancestral populations of this group, which eventually led to clade divergence. Together with small-scale passive dispersion (11 dispersal events) and local extinction, these processes could be responsible for the current distribution of the five sister taxa inhabiting the caves of the Sierra de la Collada, Spain. A plausible palaeogeographical scenario is offered to explain their present distribution, that clearly came about through chance events.     

The fauna and associated artefacts from the Lower Pleistocene site of Mansourah (Constantine, Algeria)

The site of Mansourah (Constantine, Algeria) had yielded to the early authors, and more recently to the late G. Laplace, a lithic industry associated with a fauna of large Mammals, which looks contemporaneous with that of Aïn Hanech, although it is well-distinct ecologically, and might even be slightly older. The lithic assemblage is completely devoid of any bifacial artefact or cleaver and can only be referred to the Oldowan. Thus, the Mansourah site documents a very early human occupation of North Africa, and perhaps one of the earliest. To cite this article: Y. Chaid-Saoudi et al., C. R. Palevol 5 (2006).     

Sea and colonial-nesting birds of islands in the southern part of Amurskii Liman

The quantity of the nesting couples of sea birds on the islands of the southern part of Amurskii Liman was determined: common heron Ardea cinerea, slaty-backed gull Larus schistisagus, black-tailed gull L. crassirostris, and sooty guillemot Cepphus carbo.     

Ixodid ticks (Acari: Ixodidae) infesting humans in Tokat Province of Turkey: species diversity and seasonal activity

Ixodid ticks (Acari: Ixodidae) are the major vectors of pathogens threatening animal and human health. Tokat Province, Turkey, is a suitable habitat for extended tick activity with its moderate climate and vegetation. In the present study, we surveyed humans visiting health centers to determine the species diversity, geographical distribution, and seasonal activity of ixodid ticks infesting them. Out of 5,999 adult ticks collected from humans from April to September, 2008, 800 ticks were identified to species, while the remaining were identified to genus according to their distinct morphological characteristics. Hyalomma marginatum, Hyalomma detritum, Rhipicephalus bursa, Rhipicephalus (Boophilus) annulatus, Haemaphysalis punctata, Dermacentor marginatus, and Ixodes laguri were the most prevalent tick species among 24 ixodid tick species infesting humans in the region. One of these tick species, Hyalomma isacii was identified as a new record for the ixodid tick fauna of Turkey. Hyalomma species were the most abundant in summer, while Dermacentor and Ixodes species displayed the lowest frequency. Hyalomma aegyptium infestation was very common on humans in the province. Results indicated that a variety of ixodid tick species infest humans depending on the season in the target area. It is possible that a variety of ixodid tick species may contribute to the spread of tick‐borne diseases such as Crimean‐Congo haemorrhagic fever virus (CCHFV), which is endemic in the region.     

长江口湿地三个演替阶段大型底栖动物群落特征

2001—2005年对长江口新生沙洲九段沙(上沙、中沙、下沙)盐沼演替序列不同阶段[盐渍藻类阶段(SA)、海三棱草(Scirpusmariqueter)—草(Scirpustriqueter)阶段(MT)、芦苇(Phragmitesaus-tralis)—互花米草(Spartinaalterniflora)阶段(AA)]的大型底栖动物群落特征进行了分析研究。大型底栖动物群落的物种数、Shannon-Wiener多样性指数、Pielou均匀度指数、密度及生物量都是MT>AA>SA。SA、AA优势种的生活型分别是底内型、穴居型;MT优势种的生活型是底上附着型和穴居型。不同沙洲相同盐沼演替阶段大型底栖动物群落结构都较为相似,盐渍藻类阶段的相似性最高;不同演替阶段间差别明显,SA和AA间差别最大。不同盐沼演替阶段大型底栖动物群落特征的明显差异,既反映了环境沿盐沼演替序列的梯度变化,也体现了不同盐沼对底栖动物群落作用的差别,同时也显示了大型底栖动物对不同盐沼演替阶段生境的适应。     

泸沽湖鱼类区系现状及人为影响成因的初步探讨

泸沽湖是位于滇西北的一个断陷湖泊,为滇川两省共有。文献记录泸沽湖原始的鱼类区系由4种鱼类组成,隶属于裂腹鱼属和泥鳅属。于2001 ,2002和2004年3次考察泸沽湖,进行标本采集和鱼类区系现状调查。查看了采自泸沽湖的鱼类标本518号,结合历史上的采集记录和大量相关文献,确定泸沽湖记录有鱼类12种,隶属于3目4科10属;过度捕捞和毁林造成的泥石流是泸沽湖鱼类区系变化的主要原因。     

南亚热带退化植被重建中土壤动物群落变化

在广东省中部的鹤山市鹤山丘陵综合试验场,分别在草坡、松林、荷木混交林(荷混林)、马占相思林(马占林)和豆科混交林(豆混林)选取5块样地,分别代表5种处理方式(重建植被类型)。在2003~2004年的4个不同季度内分3层取土样,利用Tullgren干漏斗法采集土壤动物,并分析土壤动物群落个体数量、类群丰度和DG指数的变化。研究结果表明,季节、植被类型和土层深度对土壤动物群落的各项指标都有极显著影响(P<0·01,three-way-ANOVA):土壤动物群落指标,在秋季显著为高(P<0·05,DMRT),而夏季显著为低(P<0·05,DMRT);随土层加深而逐级显著降低;不同植被类型比较,豆混林>马占林>荷混林、松林和草坡。此外,植被类型还与季节和土层间存在显著的交互作用:土壤动物群落各项指标秋季最高,不同植被类型间的差异也最大;而土壤动物群落各项指标较高的植被类型内不同土层间的差异也较大。由此推测,对退化生态系统进行人工改造是有积极意义的,而不同植被类型间土壤动物的差异可能与凋落物的数量与质量密切相关。