Brachiopod shell thickness links environment and evolution

While it is well established that the shapes and sizes of shells are strongly phylogenetically controlled, little is known about the phylogenetic constraints on shell thickness. Yet, shell thickness is likely to be sensitive to environmental fluctuations and has the potential to illuminate environmental perturbations through deep time. Here we systematically quantify the thickness of the anterior brachiopod shell which protects the filtration chamber and is thus considered functionally homologous across higher taxa of brachiopods. Our data come from 66 genera and 10 different orders and shows well-defined upper and lower boundaries of anterior shell thickness. For Ordovician and Silurian brachiopods we find significant order-level differences and a trend of increasing shell thickness with water depth. Modern (Cenozoic) brachiopods, by comparison, fall into the lower half of observed shell thicknesses. Among Ordovician–Silurian brachiopods, older stocks commonly have thicker shells, and thick-shelled taxa contributed more prominently to the Great Ordovician Biodiversification but suffered more severely during the Late Ordovician Mass Extinction. Our data highlight a significant reduction in maximum and minimum shell thickness following the Late Ordovician mass extinction. This points towards stronger selection pressure for energy-efficient shell secretion during times of crisis.     

Stratigraphic and dynamic effects of sediment reworking by Great Lakes zoobenthos

Recent sediments of the North American Great Lakes are inhabited by numerous species of macrobenthos which alter the physical and chemical properties of sediments and modify interface transport characteristics. Distributions of such radionuclides as cesium-137, lead-210, and isotopes of plutonium exhibit a zone of constant activity extending down from the sediment-water interface from 1 to 15 cm. Recent studies have confirmed that radiometrically determined mixed depths are consistent with the vertical distribution of oligochaete worms and the amphipod,Pontoporeia hoyi. Generally, 90% of the benthos are contained within the radiometrically defined mixed zone. Where comparisons are possible, rates of sediment reworking by ‘conveyor belt’ species are comparable to or exceed sedimentation rates. Systematic variations in the mixed depth occur within depositional basins with greatest depths tending to be associated with least consolidated, organically rich materials. A quantitative steady-state mixing model accounts satisfactorily for observed radioactivity and heavy metal profiles. Bioturbation appears to be an important process, limiting the resolution with which historical records of particle-associated contaminants may be reconstructed from sediment cores. As bioturbation serves to maintain contact of contaminated sediments with overlying water, this time may also characterize the long-term lake recovery for contaminants removed by burial. As the time varies with location, a mean for an entire lake is not well known, but is on the order of 20 years for Lake Huron. Contribution No. 300 of the Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan.     

Invasion genetics from eDNA and thousands of larvae: A targeted metabarcoding assay that distinguishes species and population variation of zebra and quagga mussels

Identifying species and population genetic compositions of biological invasions at early life stages and/or from environmental (e)DNA using targeted high‐throughput sequencing (HTS) metabarcode assays offers powerful and cost‐effective means for early detection, analysis of spread patterns, and evaluating population changes. The present study develops, tests, and applies this method with a targeted sequence assay designed to simultaneously identify and distinguish between the closely related invasive Eurasian zebra and quagga mussels (Dreissena polymorpha and D. rostriformis) and their relatives and discern their respective population genetic patterns. Invasions of these dreissenid mussel species have markedly changed freshwater ecosystems throughout North America and Europe, exerting severe ecological and economic damage. Their planktonic early life stages (eggs and larvae) are morphologically indistinguishable, yet each species exerts differential ecological effects, with the quagga often outcompeting the zebra mussel as adults. Our targeted assay analyzes genetic variation from a diagnostic sequence region of the mitochondrial (mt)DNA cytochrome oxidase I (COI) gene, to assess temporal and spatial inter‐ and intra‐specific genetic variability. The assay facilitates analysis of environmental (e)DNA from water, early life stages from thousands of individuals, and simultaneous analysis of 50–100 tagged field‐collected samples. Experiments evaluated its accuracy and performance using: (a) mock laboratory communities containing known DNA quantities per taxon, (b) aquaria with mixed‐species/haplotype compositions of adults, and (c) field‐collected water and plankton versus traditional sampling of adult communities. Results delineated species compositions, relative abundances, and population‐level diversity differences among ecosystems, habitats, time series, and life stages from two allopatric concurrent invasions in the Great Lakes (Lake Erie) and the Hudson River, which had separate founding histories. Findings demonstrate application of this targeted assay and our approach to accurately and simultaneously discern species‐ and population‐level differences across spatial and temporal scales, facilitating early detection and ecological understanding of biological invasions.     

Determining the growing season of land vegetation on the basis of plant phenology and satellite data in Northern China

The objectives of this study are to explore the relationships between plant phenology and satellite-sensor-derived measures of greenness, and to advance a new procedure for determining the growing season of land vegetation at the regional scale. Three phenological stations were selected as sample sites to represent different climatic zones and vegetation types in northern China. The mixed data set consists of occurrence dates of all observed phenophases for 50–70 kinds of trees and shrubs from 1983 to 1988. Using these data, we calculated the cumulative frequency of phenophases in every 5-day period (pentad) throughout each year, and also drew the cumulative frequency distribution curve for all station-years, in order to reveal the typical seasonal characteristics of these plant communities. The growing season was set as the time interval between 5% and 95% of the phenological cumulative frequency. Average lengths of the growing season varied between 188 days in the northern, to 259 days in the southern part of the research region. The beginning and end dates of the surface growing season were then applied each year as time thresholds, to determine the corresponding 10-day peak greenness values from normalized difference vegetation index curves for 8-km² pixels overlying the phenological stations. Our results show that, at the beginning of the growing season, the largest average greenness value occurs in the southern part, then in the northern, and finally the middle part of the research region. In contrast, at the end of the growing season, the largest average greenness value is measured in the northern part, next in the middle and lastly the southern part of the research region. In future studies, these derived NDVI thresholds can be applied to determine the growing season of similar plant communities at other sites, which lack surface phenological data. Received: 29 November 1999 / Revised: 14 March 2000 / Accepted: 15 March 2000     

全球陆地保护地与城市距离变化分析

在城市用地和保护地都快速扩张的背景下, 保护地与城市之间的距离在急剧缩小, 然而这并未引起人们的足够关注。城市对保护地的负面影响具有尺度效应, 且随着距离的接近, 负面影响也将加剧, 因此保护地与城市距离的远近可成为衡量负面影响大小的重要依据。本文基于全球保护地和大城市及城市用地分布数据, 对全球、洲际、地区和国家尺度1950-2010年城市与保护地距离的变化进行分析。结果表明: (1)在4个尺度上, 保护地与城市的距离都在不断缩小。欧洲和西欧是保护地与城市距离最近的洲和地区, 而大洋洲和澳大利亚及新西兰则是距离最远的洲和地区。在面积排名前20的保护地大国中, 中国是保护地与城市平均最近距离最小的国家, 其与50万以上人口城市的平均最近距离在2010年仅为143.5 km。(2)根据城市与保护地距离的现状及其变化, 可将保护地排名前60的国家分成5类: (a)距离很近, 靠近速度慢, 如西欧国家; (b)距离近, 靠近速度适中, 如中国、美国; (c)距离较近, 靠近速度快, 如沙特阿拉伯、厄瓜多尔; (d)距离较远, 靠近速度较慢, 如巴西、加拿大、俄罗斯联邦; (e)距离远, 靠近速度较快, 如澳大利亚、非洲大多数国家。(3)全球范围内, 越来越多生物多样性较高的保护地将面临被城市影响的境地。该结果以期引起大家对全球保护地与城市距离急剧缩短现象的关注和警惕。     

Phylogeny of the Procyonidae (Mammalia: Carnivora): molecules, morphology and the Great American Interchange

The Procyonidae (Mammalia: Carnivora) have played a central role in resolving the controversial systematics of the giant and red pandas, but phylogenetic relationships of species within the family itself have received much less attention. Cladistic analyses of morphological characters conducted during the last two decades have resulted in topologies that group ecologically and morphologically similar taxa together. Specifically, the highly arboreal and frugivorous kinkajou (Potos flavus) and olingos (Bassaricyon) define one clade, whereas the more terrestrial and omnivorous coatis (Nasua), raccoons (Procyon), and ringtails (Bassariscus) define another clade, with the similar-sized Nasua and Procyon joined as sister taxa in this latter group. These relationships, however, have not been tested with molecular sequence data. We examined procyonid phylogenetics based on combined data from nine nuclear and two mitochondrial gene segments totaling 6534bp. We were able to fully resolve relationships within the family with strongly supported and congruent results from maximum parsimony, maximum likelihood, minimum evolution, and Bayesian analyses. We identified three distinct lineages within the family: a (Nasua, Bassaricyon) clade, a (Bassariscus, Procyon) clade, and a Potos lineage, the last of which is sister to the other two clades. These findings, which are in strong disagreement with prior fossil and morphology-based assessments of procyonid relationships, reemphasize the morphological and ecological flexibility of these taxa. In particular, morphological similarities between unrelated genera possibly reflect convergence associated with similar lifestyles and diets rather than ancestry. Furthermore, incongruence between the molecular supermatrix and a morphological character matrix comprised mostly of dental characters [Baskin, J.A., 2004. Bassariscus and Probassariscus (Mammalia, Carnivora, Procyonidae) from the early Barstovian (Middle Miocene). J. Vert. Paleo. 24, 709-720] may be due to non-independence among atomized dental characters that does not take into account the high developmental genetic correlation of these characters. Finally, molecular divergence dating analyses using a relaxed molecular clock approach suggest that intergeneric and intrageneric splits in the Procyonidae mostly occurred in the Miocene. The inferred divergence times for intrageneric splits for several genera whose ranges are bisected by the Panamanian Isthmus is significant because they suggest diversification well precedes the Great American Interchange, which has long been considered a primary underlying mechanism for procyonid evolution.     

Seasonal Abundance and Species Richness of Birds in Common Reed Habitats in Lake Erie

Abstract: Common reed (Phragmites australis) forms dense stands with deep layers of residual organic matter that negatively affects plant diversity and possibly habitat use by wetland birds. We sought to determine whether seasonal relative abundance and species richness of birds varied among 3 habitat types in Great Lakes coastal wetland complexes recently invaded by common reed. We used fixed-distance point counts to determine species relative abundances and species richness in edge and interior locales within common reed, cattail (Typha spp.), and meadow marsh habitats of various sizes during 2 summers (2001 and 2002) and 1 autumn (2001) at Long Point, Lake Erie, Ontario, Canada. We found that total relative abundance and species richness of birds were greater in common reed habitat compared to cattail or meadow marsh habitats. However, we also found that relative abundance of marsh-nesting birds was greater in meadow marsh habitat than in cattail and common reed during summer. Lastly, we found that, irrespective of habitat type, habitat edges had higher total relative abundance and species richness of birds than did habitat interiors. Our results show that common reed provides suitable habitat for a diversity of landbirds during summer and autumn but only limited habitat for many marsh-nesting birds during summer. Based on these results, we recommend restoration of meadow marsh habitat through reduction of common reed in Great Lakes wetlands where providing habitat for breeding marsh-nesting birds is an objective. Managers also might consider reducing the size of nonnative common reed stands to increase edge effect and use by birds, possibly including wetland birds.     

A new relictual buthid scorpion from the region of the Great Rift Valley in Kenya (Scorpiones,Buthidae)

A new genus and species of peri-Saharian buthid scorpion is described on the basis of single specimen collected in the Great Rift Valley, North of Kenya. This new scorpion taxon represents yet another endemic relict element for the faunas of the peri-Saharian regions. Comments are also included on the evolution of the Sahara and peri-Saharian regions and its possible consequences on the distribution of the extant scorpion fauna.     

On the relationship between water table depth and water vapor and carbon dioxide fluxes in a minerotrophic fen

The focus of this study is the relationship between water table depth (WTD) and water vapor [evapotranspiration (ET)] and carbon dioxide [CO₂; net ecosystem exchange (NEE)] fluxes in a fen in western Canada. We analyzed hydrological and eddy covariance measurements from four snow‐free periods (2003–2006) with contrasting meteorological conditions to establish the link between daily WTD and ET and gross ecosystem CO₂ exchange (GEE) and ecosystem respiration (R_eco; NEE=R_eco?GEE), respectively: 2003 was warm and dry, 2004 was cool and wet, and 2005 and 2006 were both wet. In 2003, the water table (WT) was below the ground surface. In 2004, the WT rose above the ground surface, and in 2005 and 2006, the WT stayed well above the ground surface. There were no significant differences in total ET (～316 mm period^?1), but total NEE was significantly different (2003: 8 g C m^?2 period^?1; 2004: ?139 g C m^?2 period^?1; 2005: ?163 g C m^?2 period^?1; 2006: ?195 g C m^?2 period^?1), mostly due to differences in total GEE (2003: 327 g C m^?2 period^?1; 2004: 513 g C m^?2 period^?1; 2005: 411 g C m^?2 period^?1; 2006: 556 g C m^?2 period^?1). Variation in ET is mostly explained by radiation (67%), and the contribution of WTD is only minor (33%). WTD controls the compensating contributions of different land surface components, resulting in similar total ET regardless of the hydrological conditions. WTD and temperature each contribute about half to the explained variation in GEE up to a threshold ponding depth, below which temperature alone is the key explanatory variable. WTD is only of minor importance for the variation in R_eco, which is mainly controlled by temperature. Our study implies that future peatland modeling efforts explicitly consider topographic and hydrogeological influences on WTD.