Contrasting demographic history and phylogeographical patterns in two Indo-Pacific gastropods

Marine species with ranges that span the Indo-Australian Archipelago (IAA) exhibit a range of phylogeographical patterns, most of which are interpreted in the context of vicariance between Indian and Pacific Ocean populations during Pliocene and Pleistocene low sea-level stands. However, patterns often vary among ecologically similar taxa, sometimes even within genera. This study compares phylogeographical patterns in two species of highly dispersive neritid gastropod, Nerita albicilla and Nerita plicata, with nearly sympatric ranges that span the Indo-Pacific. Mitochondrial COI sequences from >1000 individuals from 97 sites reveal similar phylogenies in both species (two divergent clades differing by 3.2% and 2.3%, for N. albicilla and N. plicata, respectively). However, despite ecological similarity and congeneric status, the two species exhibit phylogeographical discordance. N. albicilla has maintained reciprocal monophyly of Indian and Pacific Ocean populations, while N. plicata is panmictic between oceans, but displays a genetic cline in the Central Pacific. Although this difference might be explained by qualitatively different demographic histories, parameter estimates from three coalescent models indicate that both species have high levels of gene flow between demes (2Nem>75), and share a common history of population expansion that is likely associated with cyclical flooding of continental shelves and island lagoons following low sea-level stands. Results indicate that ecologically similar, codistributed species may respond very differently to shared environmental processes, suggesting that relatively minor differences in traits such as pelagic larval duration or microhabitat association may profoundly impact phylogeographical structure.     

Life history of a lacustrine ostracod

The ostracod Cypria turneri has one generation per year in Mirror Lake, New Hampshire. Juveniles hatch in January through May and reach maturity by August. The life history of this ostracod suggests that the turnover rate of the population is low.     

沈阳市地面苔藓植物的分布及对环境因子的响应

应用双向指示种分析法(TWINSPAN)和除趋势对应分析法(DCA),对沈阳市57种苔藓植物分布格局进行了分析.结果将20个样点划分为三个组,其中组l样点所含种类不足10种;组2在10~20种之间;而组3多在20种以上.从组1到组3,物种丰富度逐渐增加;分类与排序的结果与样点的实际物种分布特点基本一致.采用典范对应分析(CCA)对其中20个样点的35种主要地面苔藓植物与环境因子间的关系进行了分析.发现土壤含水量、人为干扰度和乔木层郁闭度是影响沈阳市苔藓植物分布的主要因素.同时根据环境凶子的影响,将沈阳市主要地面苔藓植物分为两类,其中第一类多为顶蒴藓类:而第二类则主要为侧蒴藓类.     

钦州湾秋季和春季浮游动物分布特征及影响因素

为了解钦州湾浮游动物群落的时空分布特征及与主要环境因子的关系,于2014年10月和2015年3月进行了秋季和春季两航次的调查。结果表明:该海湾的浮游动物群落有明显的季节变化。秋季共鉴定出12类87种,其中优势种有太平洋纺锤水蚤(Acartia pacifica)、肥胖三角溞(Evadne tergestina)、亨生莹虾(Lucifer hanseni)、百陶箭虫(Sagitta bedoti)和长尾类幼虫(Macrura larvae);春季共鉴定出11类48种,优势种为中华哲水蚤(Calanus sinicus)和太平洋纺锤水蚤;秋季浮游动物的平均丰度、生物量和多样性指数(528.92个/m~3、110.60 mg/m~3和2.22)均高于春季(48.30个/m~3、61.10 mg/m~3和1.70)。空间分布上,钦州湾外湾浮游动物丰度、生物量和多样性指数的平均值皆高于内湾。多维尺度分析表明,秋季内湾群落相似性较高,春季外湾浮游动物群落相似性较高。相关性分析表明盐度与营养盐是影响钦州湾浮游动物分布的主要环境因子。与2011—2012年数据相比,钦州湾浮游动物群落结构已趋于单一化和小型化,以致生物量明显下降。这一现象主要与钦州湾海水富营养化以及大面积高密度牡蛎养殖有密切的关系。     

Impact of environmental factors on couplings between bacterial community composition and ectoenzymatic activities in a lacustrine ecosystem

This study examined the effects of temporal changes in bacterial community composition (BCC) and environmental factors on potential ectoenzymatic activities (α-glucosidase, β-glucosidase, alkaline phosphatase and leucine aminopeptidase) in a lacustrine ecosystem (Sep reservoir, France). BCC was assessed by terminal restriction fragment length polymorphism. Physical parameters, and inorganic and organic nutrient concentrations (dissolved carbohydrates and proteins) were measured in lakes and tributaries. According to the multivariate statistics (redundancy analysis), physical and chemical factors explained the largest part of leucine aminopeptidase activity, whereas the temporal changes of other ectoenzymatic activities were partly dependent on the variations in the BCC. In particular, the occurrence of occasional bacterial populations seemed to explain a lot of the variation in rates and patterns of polymer hydrolysis. The relation observed in this study between the bacterial structure and activity is discussed within the framework of biodiversity–ecosystem functioning.     

Fine-scale patterns of vegetation and environmental factors on an ombrotrophic mire expanse: a numerical approach

The vegetation within an ombrotrophic mire expanse in SE Norway is studied in detail. Percentage cover of 45 species in 436 sample plots (16 ×16 cm), dispersed on 26 transects, are recorded. In addition, species abundance in 6976 subplots (4×4 cm) are recorded. 14 variables are recorded for each of the sample plots, while only distance to the water-table is estimated for the subplots. Spatial co-ordinates are supplied for all sample- and subplots. DCA ordination of a data-set consisting of 412 sample plots reveals two ecologically interpretable vegetational gradients: the hummock-hollow gradient (DCA 1), and a gradient associated with the peat-production of the bottom layer (DCA 2). Passive DCA of subplots is used to get an impression of within sample plot heterogeneity, and shows that the fine-scale compositional turnover may be considerable. Partitioning of the variation in species abundance data is done by use of (partial) CCA. The fraction of unexplained variation is rather large for all the tested data-sets, but within the total variation explained, both distance to the water-table and spatial structure explain large parts.     

Vegetation patterns related to environmental factors in a Negev Desert watershed

Three strip transects, each ca 100 contiguous 0.5×1 m² quadrats, were sampled during the spring bloom of March 1981 across four surface structural units of a Negev Desert research watershed at Sede Boqer, Israel. Presence of all vascular plants was recorded. Data were subjected to detrended correspondence analysis (DCA ordination), and resulting spatial patterns of species distribution and abundance were compared. Large-scale gradients of vegetation were related to differences in soil moisture availability among the four structural units. Where micro-scale vegetation patterns were important, these correlated with rock and crevice microtopography. Species richness was influenced by high numbers of therophytes on the dry upper slope of the watershed and their reduced importance on the lower three units. Relationships between vegetational patterns and known ecosystem properties of the watershed are discussed.     

Range size and environmental calcium requirements of British freshwater gastropods

Calcium is an essential requirement for the successful growth and development of gastropod molluscs. Data for British freshwater gastropods were used to examine the relationship between environmental calcium requirements and British and European range sizes. At both spatial scales calciphile species, which require a high level of environmental calcium, had significantly smaller range sizes than species able to exploit a wide range of environmental calcium levels. However, at least in Britain, range size may also be influenced by the availability of suitable habitat. British and European range sizes were significantly correlated. This study provides evidence for niche‐based explanations of range size variation, and suggests that both niche breadth and niche availability are important in determining range size.     

Community assembly in Nothobranchius annual fishes: Nested patterns,environmental niche and biogeographic history

The assembly of local communities from regional species pools is shaped by historical aspects of distribution, environmental conditions, and biotic interactions. We studied local community assembly patterns in African annual killifishes of the genus Nothobranchius (Cyprinodontiformes), investigating data from 168 communities across the entire range of regionally co‐existing species. Nothobranchius are small fishes associated with annually desiccating pools. We detected a nested pattern of local communities in one region (Southern Mozambique, with Nothobranchius furzeri as the core and dominant species), but no nestedness was found in the second region (Central Mozambique, with Nothobranchius orthonotus being the dominant species). A checkerboard pattern of local Nothobranchius community assembly was demonstrated in both regions. Multivariate environmental niche modeling revealed moderate differences in environmental niche occupancy between three monophyletic clades that largely co‐occurred geographically and greater differences between strictly allopatric species within the clades. Most variation among species was observed along an altitudinal gradient; N. furzeri and Nothobranchius kadleci were absent from coastal plains, Nothobranchius pienaari, Nothobranchius rachovii, and Nothobranchius krysanovi were associated with lower altitude and N. orthonotus was intermediate and geographically most widespread species. We discuss implications for ecological and evolutionary research in this taxon.     

Lifetime growth in wild meerkats: incorporating life history and environmental factors into a standard growth model

Lifetime records of changes in individual size or mass in wild animals are scarce and, as such, few studies have attempted to model variation in these traits across the lifespan or to assess the factors that affect them. However, quantifying lifetime growth is essential for understanding trade-offs between growth and other life history parameters, such as reproductive performance or survival. Here, we used model selection based on information theory to measure changes in body mass over the lifespan of wild meerkats, and compared the relative fits of several standard growth models (monomolecular, von Bertalanffy, Gompertz, logistic and Richards). We found that meerkats exhibit monomolecular growth, with the best model incorporating separate growth rates before and after nutritional independence, as well as effects of season and total rainfall in the previous nine months. Our study demonstrates how simple growth curves may be improved by considering life history and environmental factors, which may be particularly relevant when quantifying growth patterns in wild populations.     

Review article: Toward a history of European racism

George L. Mosse, Toward the Final Solution: A History of European Racism. London, Dent, & New York, Fertig, 1979. Illustrated, xvi + 277 pp.£10.     

Geographic and environmental factors controlling life history and morphology inPrasiola stipitata Suhr

Summary The vertical distribution of meiotic and non-meiotic plants, of the spore-formation types, of the presence of filamentous stage and, in some cases, of thallus sizes was analyzed in 57 populations ofPrasiola stipitata, collected on both sides of the Atlantic.A vertical zonation exists within the limits of thePrasiola stipitata belt. In the higher levels there are less or no meiotic plants, the thallus size is smaller and the filamentous (Rosenvingiella-) stage may be present. In the lower levels, the ratio of meiotic plants as well as the size of the thallus increases and the filamentous stage is absent. The distribution of marginal and variegated sporophytes does not present a clear pattern, though the marginal type often seems to prevail in the higher levels and the variegated type in the lower. Seasonality is apparent in the decrease of both thallus size and of the ratio of meiotic plants towards the end of the growth season.On the eastern shores of the Atlantic growth is perennial and meiotic plants are infrequent or absent from about 55° latitude northwards. South of this line growth is seasonal and meiotic plants are abundant. On the western shores of the Atlantic growth is perennial and gametophytes are absent from 44° latitude northwards.Dedicated to my venerated teacher, Prof. Dr.Lothar Geitler, for his 70th birthday.     

Quantifying effects of environmental and geographical factors on patterns of genetic differentiation

Elucidating the factors influencing genetic differentiation is an important task in biology, and the relative contribution from natural selection and genetic drift has long been debated. In this study, we used a regression-based approach to simultaneously estimate the quantitative contributions of environmental adaptation and isolation by distance on genetic variation in Boechera stricta, a wild relative of Arabidopsis. Patterns of discrete and continuous genetic differentiation coexist within this species. For the discrete differentiation between two major genetic groups, environment has larger contribution than geography, and we also identified a significant environment-by-geography interaction effect. Elsewhere in the species range, we found a latitudinal cline of genetic variation reflecting only isolation by distance. To further confirm the effect of environmental selection on genetic divergence, we identified the specific environmental variables predicting local genotypes in allopatric and sympatric regions. Water availability was identified as the possible cause of differential local adaptation in both geographical regions, confirming the role of environmental adaptation in driving and maintaining genetic differentiation between the two major genetic groups. In addition, the environment-by-geography interaction is further confirmed by the finding that water availability is represented by different environmental factors in the allopatric and sympatric regions. In conclusion, this study shows that geographical and environmental factors together created stronger and more discrete genetic differentiation than isolation by distance alone, which only produced a gradual, clinal pattern of genetic variation. These findings emphasize the importance of environmental selection in shaping patterns of species-wide genetic variation in the natural environment.     

An environmental (pre)history of European fishing: past and future archaeological contributions to sustainable fisheries

This paper explores the past and potential contribution of archaeology to marine historical ecology. The primary focus is European fishing of marine and diadromous taxa, with global comparisons highlighting the wider applicability of archaeological approaches. The review illustrates how study of excavated fish bones, otoliths and shells can inform our understanding of: (a) changes in biogeography, including the previous distribution of lost species; (b) long-term fluctuations in the aquatic environment, including climate change; (c) the intensity of exploitation and other anthropogenic effects; (d) trade, commodification and globalisation. These issues are also relevant to inform fisheries conservation and management targets. Equally important, the long (pre)history of European fishing raises awareness of our ecological heritage debt, owed for centuries of wealth, sustenance and well-being, and for which we share collective responsibility. This debt represents both a loss and a reason for optimism, insofar as it is a reservoir of potential to be filled by careful stewardship of our rivers, lakes, seas and oceans.