Reduced responses to selection after species range expansion

Species range expansion reduces genetic variation at the margins of a species range and should thus compromise the adaptive potential of its marginal populations. Remarkably, this prediction has not previously been tested. Here, we show that populations of the plant Mercurialis annua, which expanded its range into Spain and Portugal from North Africa after the Pleistocene glaciation, respond to selection on a key life-history trait less well than populations from the species' historical refugium. Our results provide direct evidence of a decline in adaptive potential across the geographic range of a species after a shift in its distribution. Predicting evolutionary responses to environmental change will thus need to account for the genetic heterogeneity of species and the spatial dynamics of their geographic distributions.     

Fluvial perturbance in the Western Amazon basin: regulation by long-term sub-andean tectonics

Haffer's refuge theory proposes that during the arid climatic phases of the late Pleistocene, tropical lowland forests of Amazonia were reduced to isolated patches contributing to the high species richness of the present-day forest. The theory was developed because no obvious historic or modern geomorphic isolation barriers were recorded in Amazonia. Analyses of radar images combined with stratigraphical data show that in the basinal forelands of the tectonically active Andes the geological setting causes long-term fluvial perturbance. This leads to a temporally structured highly complex mosaic of fossil and present floodplains. These dynamics have been present with varying activity and geographic range during the Tertiary and Quaternary, providing site-turnover that has not been recognized by the biogeographic tradition of the Amazon basin.     

Reconstructing past ocean pH-depth profiles

Measurement of boron isotope compositions in species of planktonic foraminifera that calcified their tests at different depths in the water column are used to reconstruct the pH profile of the upper water column of the tropical ocean. Results for five time windows from the middle Miocene to the late Pleistocene indicate pH-depth profiles similar to that of the modern ocean in this area, which suggests that this method may greatly aid in our understanding of the global carbon cycle.     

Ancient DNA evidence for Old World origin of New World dogs

Mitochondrial DNA sequences isolated from ancient dog remains from Latin America and Alaska showed that native American dogs originated from multiple Old World lineages of dogs that accompanied late Pleistocene humans across the Bering Strait. One clade of dog sequences was unique to the New World, which is consistent with a period of geographic isolation. This unique clade was absent from a large sample of modern dogs, which implies that European colonists systematically discouraged the breeding of native American dogs.     

Umbrella Pine, Sciadopitys verticillata: Past and Present Distribution in Japan

The umbrella pine, Sciadopitys verticillata S. and Z., a native Japanese conifer species and the only present member of the genus Sciadopitys, has become rapidly restricted in its geographic distribution since the beginning of intensified human activities. In Japan the genus was more widely distributed throughout the Pliocene and in the postglacial hypsithermal and slightly later times (R IIIa). In other parts of the world the genus has not appeared in the fossil record since the early Pleistocene. Conservation of this species is needed.     

Rise and fall of the Beringian steppe bison

The widespread extinctions of large mammals at the end of the Pleistocene epoch have often been attributed to the depredations of humans; here we present genetic evidence that questions this assumption. We used ancient DNA and Bayesian techniques to reconstruct a detailed genetic history of bison throughout the late Pleistocene and Holocene epochs. Our analyses depict a large diverse population living throughout Beringia until around 37,000 years before the present, when the population's genetic diversity began to decline dramatically. The timing of this decline correlates with environmental changes associated with the onset of the last glacial cycle, whereas archaeological evidence does not support the presence of large populations of humans in Eastern Beringia until more than 15,000 years later.     

中国近海真鲷遗传变异的线粒体控制区序列分析

测定了辽宁东港、广东大亚湾和广西东兴3个海域各15尾真鲷的线粒体控制区5′端660bp的核苷酸序列,发现91个可变位点,64个简约信息位点。在45尾样品中共检测到43个单倍型,3个群体的平均单倍型多样性和核苷酸多样性分别为(0.99～1)和(0.02522～0.02579),表现出较高的单倍型多样性和核苷酸多样性。在真鲷个体NJ树上出现3个谱系,各谱系中不同地理来源的个体比例相当,不呈现明显的地理聚群,推测各谱系大约形成于晚更新世的末期。Tajima’sD呈负值但不显著(P0.08),表明真鲷历史上没有发生快速扩张,种群大小稳定。群体间遗传分化指数Fst都为负值(-0.0001～-0.0188)但不显著(P0.1);AMOVA分析显示遗传变异主要集中在群体内的个体间(100.49%),而群体间的遗传变异很小(-0.49%);表明我国近海真鲷群体有可能是同一种群。     

A cheetah-like cat in the north american pleistocene

The discovery of abundant skeletal remains of Felis trumani from a late Pleistocene deposit in Wyoming shows that it was as highly modified for cursorial locomotion as the cheetah (Acinonyx). Several other Pleistocene felids that have been regarded as pumas seem to be related forms. The late Pleistocene fauna of the Big Horn Basin in Wyoming is dominated by cursorial taxa.     

Molecular analysis of plant migration and refugia in the Arctic

The arctic flora is thought to have originated during the late Tertiary, approximately 3 million years ago. Plant migration routes during colonization of the Arctic are currently unknown, and uncertainty remains over where arctic plants survived Pleistocene glaciations. A phylogenetic analysis of chloroplast DNA variation in the purple saxifrage (Saxifraga oppositifolia) indicates that this plant first occurred in the Arctic in western Beringia before it migrated east and west to achieve a circumpolar distribution. The geographical distribution of chloroplast DNA variation in the species supports the hypothesis that, during Pleistocene glaciations, some plant refugia were located in the Arctic as well as at more southern latitudes.     

Late pleistocene faunal extinctions in southern patagonia

Major environmental changes recorded in pollen records from various sites in southern Patagonia and Tierra del Fuego are also reflected in pollen and cuticle data from dung of the late Pleistocene groundsloth. The most prominent change was the large-scale reduction of steppe environment about 10,000 years ago, which coincides with the latest dates for extinctions of many large grazers such as the giant groundsloth. Stress on food resources for all the large grazers may well have hastened their extinction. Hunting pressure by paleoindians may have been the final blow.     

环境和扩散对草地群落构建的影响

植物群落构建机制是生态学研究的热点之一。长久以来这个难题并没有得到很好的解释,且争议较多。生态位理论或中性理论,或是二者的共同作用,这样的结论在不同的研究中都有印证。以黄土高原子午岭地区的草地群落为例,对3种不同的草地群落(5a的弃耕地、阴坡和阳坡的草地)进行了野外群落学调查,采用Mantel test和主轴邻距法(PCNM)分析方法,研究了空间地理距离和环境资源差异对于草本植物群落分布的影响,结果表明:地理距离和环境差异共同解释了群落组成相似性的79.3%,剔除环境因子的影响,地理距离解释了群落组成相似性的33.8%;而剔除地理距离的影响,环境因子解释了群落组成相似性的14.2%。无论是生态位理论还是中性理论,其在黄土高原草本群落构建过程中都有作用,但中性理论扮演了更为重要的角色。     

珠江水系特有卷口鱼遗传变异的线粒体Cytb基因序列分析

测定了广西合山、柳州、桂平和广东郁南等4个地理群体43尾卷口鱼线粒体Cytb基因1041bp,结果检测到8个单倍型,7个多态位点。4个地理群体的单倍型多样性为0.248～0.700,核苷酸多样性为0.00022～0.00070,表明所分析的卷口鱼群体单倍型多样性和核苷酸多样性低。在分子系统树上,不同地理来源的卷口鱼混杂分布在一起,没有形成明显的谱系结构和地理聚群;4个群体两两间的Fst值为-0.028～0.116,但均不显著(P0.08);AMOVA分析表明1.70%(P=0.21)的分子差异来自群体间,而98.3%的分子差异位于群体内部;表明4个地理群体间没有显著遗传分化。单倍型网络图呈星状结构,中性检测Tajima’sD和Fu’sFS均为显著负值,核苷酸不对称分布分析呈单峰模式,表明珠江卷口鱼可能曾经历过种群的快速扩张,推测在晚更新世(1.5～3.9万年前)出现种群扩张。     

Geographical trends in numbers of species

Geographic variation in the number of coexisting plant and animal species (species density) often follows repeated patterns; best known is the general increase in species richness from temperate to tropical latitudes. Here we undertake a quantitative analysis of geographic trends in species density for the terrestrial vertebrate faunas of the United States and Australia. Trends in numbers of species of amphibians, reptiles, birds, and mammals are described and are correlated with geographic variation in abiotic environmental measures. Intercontinental comparisons reveal general patterns as well as intriguing and profound differences in vertebrate distributions.     

大同盆地晚更新世以来气候变化

为了更好的了解大同盆地过去气候的变化过程,找出其气候变化规律,预测未来气候变化趋势,更好地指导农业生产。研究通过对沉积剖面地层的观察与样品的测年,运用磁化率和粒度指标,恢复了大同盆地晚更新世以来的气候变化：整体呈现出暖湿—冷干—暖干的气候旋回特征,分为上更新世许家窑组暖湿期、马兰组干冷期及全新世暖干期,并且气候有逐渐干旱化趋势。部分学者对而近些年降水与气温变化的研究以及未来气候趋势的预测,更证实了这一结论的合理性。总之,大同盆地晚更新世以来气候总体呈干旱化趋势,这一结论将为本区干旱化农业发展政策的制定提供可靠的科学依据。     

Widespread origins of domestic horse lineages

Domestication entails control of wild species and is generally regarded as a complex process confined to a restricted area and culture. Previous DNA sequence analyses of several domestic species have suggested only a limited number of origination events. We analyzed mitochondrial DNA (mtDNA) control region sequences of 191 domestic horses and found a high diversity of matrilines. Sequence analysis of equids from archaeological sites and late Pleistocene deposits showed that this diversity was not due to an accelerated mutation rate or an ancient domestication event. Consequently, high mtDNA sequence diversity of horses implies an unprecedented and widespread integration of matrilines and an extensive utilization and taming of wild horses. However, genetic variation at nuclear markers is partitioned among horse breeds and may reflect sex-biased dispersal and breeding.     

安徽沿江圩丘农区水稻田杂草区系及草害的研究

本文报道了自１９８５年至１９９０年间，对安徽沿江圩丘农区的６０．４公顷水稻田杂草种群数量调查和大面积的普查结果。共采集标本１０００余份。发现并记载水稻田杂草２８科、４５属Ｊ７４种，田边及回埂杂草２９科、７５属、１４２种，以及２种安徽省植物地理分布新记录种。恶性和区域性恶性稻田杂草有种草、节节菜、鸭舌草、牛毛毡、矮慈菇以及水莎草、眼子菜和猪毛草。早、中稻田的主要杂草群落是稗草十鸭舌草十节节菜十小茨藻，草害较严重；晚稻田则是以节节菜十牛毛毡十鸭舌草十矮慈菇为主，草害较轻。造成早、晚稻田杂草发生差异的主要因素是，栽培措施和生长季节引起的生态因子的不同。因此，该区稻田除草策略是，早稻田除稗、晚稻田除早便发。     

Albumin and Australian frogs: molecular data a challenge to speciation model

Vertebrate speciation in the southwest of Australia has long been viewed as resulting from multiple invasions of eastern source stocks during the Pleistocene. Microcomplement fixation studies of serum albumin evolution in frogs of the genus Heleioporus provide the first hard data on age and phylogenetic relationships among species in this genus and lead to rejection of the multiple invasion model in favor of speciation occurring in Western Australia. The albumin molecular clock was used to estimate that the species divergences in this genus occurred between 4 million to 12 million years ago in the late Tertiary (Pliocene-Miocene), rather than in the Quaternary (the last 2 million years).     

Rapid diversification of a species-rich genus of neotropical rain forest trees

Species richness in the tropics has been attributed to the gradual accumulation of species over a long geological period in stable equatorial climates or, conversely, to speciation in response to late Tertiary geological events and unstable Pleistocene climates. DNA sequence data are consistent with recent diversification in Inga, a species-rich neotropical tree genus. We estimate that speciation was concentrated in the past 10 million years, with many species arising as recently as 2 million years ago. This coincides with the more recent major uplifts of the Andes, the bridging of the Isthmus of Panama, and Quaternary glacial cycles. Inga may be representative of other species-rich neotropical genera with rapid growth and reproduction, which contribute substantially to species numbers in the world's most diverse flora.     

A high-resolution paleoclimate record spanning the past 25,000 years in southern East Africa

High-resolution profiles of the mass accumulation rate of biogenic silica and other geochemical proxies in two piston cores from northern Lake Malawi provide a climate signal for this part of tropical Africa spanning the past 25,000 years. The biogenic silica mass accumulation rate was low during the relatively dry late Pleistocene, when the river flux of silica to the lake was suppressed. Millennial-scale fluctuations, due to upwelling intensity, in the late Pleistocene climate of the Lake Malawi basin appear to have been closely linked to the Northern Hemisphere climate until 11 thousand years ago. Relatively cold conditions in the Northern Hemisphere coincided with more frequent north winds over the Malawi basin, perhaps resulting from a more southward migration of the Intertropical Convergence Zone.     

El Nino-like climate teleconnections in new england during the late pleistocene

A glacial varve chronology from New England spanning the 4000-year period from 17,500 to 13,500 calendar years before the present was analyzed for evidence of climate variability during the late Pleistocene. The chronology shows a distinct interannual (3 to 5 years) band of enhanced variability suggestive of El Nino-Southern Oscillation (ENSO) teleconnections into North America during the late Pleistocene, when the Laurentide ice sheet was near its maximum extent and climatic boundary conditions were different than those of today. This interannual variability largely disappears by the young end of the 4000-year chronology, with only the highest frequency components (roughly 3-year period) persisting. This record provides evidence of ENSO-like climate variability during near-peak glacial conditions.