Ring species as bridges between microevolution and speciation

A demonstration of how small changes can lead to species-level differences is provided by ring species, in which two reproductively isolated forms are connected by a chain of intermediate populations. We review proposed cases of ring species and the insights they provide into speciation. Ring species have been viewed both as illustrations of the history of divergence of two species from their common ancestor and as demonstrations that speciation can occur in spite of gene flow between the diverging forms. Theoretical models predict that speciation with gene flow can occur when there is divergent ecological selection, and geographical differentiation increases the likelihood of speciation. Thus ring species are ideal systems for research into the role of both ecological and geographical differentiation in speciation, but few examples have been studied in detail. The Greenish warbler is a ring species in which two northward expansions around the Tibetan plateau have been accompanied by parallel evolution in morphology, ecology, and song length and complexity. However, songs have diverged in structure, resulting in a lack of recognition where the reproductively isolated forms come into contact in Siberia. Our analysis suggests that these differences could have arisen even with gene flow, and that parallel rather than divergent ecological changes have led to divergence in sexually selected traits and subsequent speciation.     

松辽盆地三肇地区泉头组三段上部介形类化石的指相意义

松辽盆地三肇地区白垩系下统泉头组三段上部(杨三组—杨一组)以大套的紫红、红色砂、泥岩沉积为主,在紫红色泥岩中含有较丰富、完整的介形类及其它门类化石。以往认为,这套以红色为基调的地层属河流相沉积。对其中介形类等化石的古生态、埋藏特征及丰度变化的研究表明,该地层的沉积环境应为浅水湖泊环境,而非河流等水上环境。湖相沉积自杨三组就已存在,向上分布范围不断扩大,反映了湖泊水域面积呈现逐渐扩大的趋势。     

外生菌根真菌在大型露天煤矿生态修复中的应用研究

在霍林河露天煤矿脆弱生态地带的生态修复中,应用菌根生物技术,选用露天开采的剥离物绿色泥岩,以施肥和不施肥、泥岩氮化等处理进行了不同条件的盆载模拟试验,结果表明,绿色泥岩接种菌根菌剂,不施肥的感染率和成活率均高出施肥的1.21～2.78倍和1.0～2.7倍,供试的菌根菌剂中,010、A和B菌剂对贫瘠和渗透率低的土壤条件表现出较强的调控能力,泥岩氢化地其理化条件虽能有所改善,但氨和磷聚集使幼苗成活时间甚短。     

Digging deeper: why we need more Proterozoic algal fossils and how to get them

Known Proterozoic algal fossils raise compelling questions about the origin and diversification of cyanobacteria and eukaryotic algae, and their ecological influence in deep time. This Perspectives article describes particular examples of persistent evolutionary and biogeochemical issues whose resolution would be aided by additional algal fossil evidence from Proterozoic deposits, which have been the subjects of recent intensive study. New Proterozoic geosciences literature relevant to the early diversification of algae is surveyed. Previously underappreciated algal traits that might improve taxonomic attributions of fossil remains are highlighted. Processes that phycologists could use to improve detection of algal fossils are recommended. Potential geological sources of new Proterozoic fossils are suggested.     

Upper Carboniferous ostracode assemblages from a mixed carbonate–terrigenous-mud environment

The Upper Carboniferous Beil Limestone Member (Lecompton Formation; Virgilian) from the Midcontinent of North America was deposited in a tropical, shallow-marine environment in which varying amounts of terrigenous mud were mixed with carbonate sediment. Shallowing of the sea occurred during deposition so that the upper part of the Beil was deposited much nearer to shore than the lower part. Mean relative abundances of 24 species of ostracodes in 51 samples differed among three stratigraphical subdivisions of the Beil and allowed recognition of two assemblages. Most species of the Cryptobairdia seminalis–Bairdia pompilioides assemblage, characteristic of the lower part of the Beil, were negatively correlated with percent terrigenous mud. On the other hand, abundant species of the Moorites minutus–Bairdia beedei assemblage, consisting of the C. seminalis and the Cavellina nebrascensis subassemblages, respectively, of the middle and upper parts, were positively correlated with percent terrigenous mud. Ordinations by non-metric multidimensional scaling showed similar groupings of species. Species diversity was negatively correlated with content of terrigenous mud.