Single origin of a pan-Pacific bird group and upstream colonization of Australasia

Oceanic islands have long served as natural laboratories for understanding the diversification of life. In particular, the many thousands of islands spanning the tropical Pacific support an unparalleled array of terrestrial communities whose patterns of diversity contributed fundamental insights to the development of classical speciation and biogeographic theory. Much of this work is founded on an assumption derived from traditional taxonomic approaches, namely that faunas on these widely separated archipelagos stem from a simple one-way, downstream flow of colonists from continents to islands. Here we show, with the use of molecular phylogenetic data from one of the original bird families used to justify this assumption, that a diverse array of endemic island genera and species are the product of a single radiation that diversified across all major Pacific archipelagos in a non-stepping-stone fashion, and recently recolonized continental areas. The geographic scope and lineage-specific approach of this study reveal evolutionary patterns long obscured by traditional taxonomic surveys and indicate that widely dispersed archipelagos can be sources of biological diversity.     

Unmatched tempo of evolution in Southern African semi-desert ice plants

The Succulent Karoo is an arid region, situated along the west coast of southern Africa. Floristically this region is part of the Greater Cape Flora and is considered one of the Earth's 25 biodiversity hotspots. Of about 5,000 species occurring in this region, more than 40% are endemic. Aizoaceae (ice plants) dominate the Succulent Karoo both in terms of species numbers (1,750 species in 127 genera) and density of coverage. Here we show that a well-supported clade within the Aizoaceae, representing 1,563 species almost exclusively endemic to southern Africa, has diversified very recently and very rapidly. The estimated age for this radiation lies between 3.8 and 8.7 million years (Myr) ago, yielding a per-lineage diversification rate of 0.77-1.75 per million years. Both the number of species involved and the tempo of evolution far surpass those of any previously postulated continental or island plant radiation. Diversification of the group is closely associated with the origin of several morphological features and one anatomical feature. Because species-poor clades lacking these features occur over a very similar distribution area, we propose that these characteristics are key innovations that facilitated this radiation.     

Species diversity can drive speciation

A fundamental question in evolutionary ecology and conservation biology is: why do some areas contain greater species diversity than others? Island biogeographic theory has identified the roles of immigration and extinction in relation to area size and proximity to source areas, and the role of speciation is also recognized as an important factor. However, one as yet unexplored possibility is that species diversity itself might help to promote speciation, and indeed the central tenets of island biogeographic theory support such a prediction. Here we use data for plants and arthropods of the volcanic archipelagos of the Canary and Hawaiian Islands to address whether there is a positive relationship between species diversity and rate of diversification. Our index of diversification for each island is the proportion of species that are endemic, and we test our prediction that this increases with increasing species number. We show that even after controlling for several important physical features of islands, diversification is strongly related to species number.     

Ecology: is speciation driven by species diversity?

Emerson and Kolm show that the proportion of species endemic to an island is positively related to its species richness and, assuming that endemism indexes speciation rate, they infer that greater species diversity accelerates diversification. Here we demonstrate that the same correlation between species richness and percentage endemism can arise even if within-island speciation is negligible, particularly when both endemism and species richness depend on attributes of islands (such as area) that influence the average age of resident populations. Island biogeography theory indicates that, where the average time to extinction is relatively long, diversity increases through colonization, irrespective of whether new species are formed; at the same time, islands on which populations persist for longer accumulate more endemic species as local populations differentiate and populations on neighbouring islands become extinct. We therefore suggest that species richness and endemism are correlated fortuitously owing to their mutual dependence on the life spans of populations on islands, which is unrelated to speciation itself.     

Sympatric speciation in palms on an oceanic island

The origin of species diversity has challenged biologists for over two centuries. Allopatric speciation, the divergence of species resulting from geographical isolation, is well documented. However, sympatric speciation, divergence without geographical isolation, is highly controversial. Claims of sympatric speciation must demonstrate species sympatry, sister relationships, reproductive isolation, and that an earlier allopatric phase is highly unlikely. Here we provide clear support for sympatric speciation in a case study of two species of palm (Arecaceae) on an oceanic island. A large dated phylogenetic tree shows that the two species of Howea, endemic to the remote Lord Howe Island, are sister taxa and diverged from each other well after the island was formed 6.9 million years ago. During fieldwork, we found a substantial disjunction in flowering time that is correlated with soil preference. In addition, a genome scan indicates that few genetic loci are more divergent between the two species than expected under neutrality, a finding consistent with models of sympatric speciation involving disruptive/divergent selection. This case study of sympatric speciation in plants provides an opportunity for refining theoretical models on the origin of species, and new impetus for exploring putative plant and animal examples on oceanic islands.     

Sky islands of southwest China. I: an overview of phylogeographic patterns

Sky islands are high-elevation areas in continental mountain ranges,which are geographically isolated.We adopted this concept for the mountains in southwest China,which are among the most important biodiversity hot spots on earth.We reviewed the phylogeographic studies of this area and highlighted the sky-island features.We concluded that the genetic structures of species in these islands were shaped by complex topography,climate and habitats.The global climate change,such as Pleistocene climate fluctuations and periodic uplift of the Qinghai–Tibetan Plateau,also have important effects on biodiversity and geographic patterns,when species have responded idiosyncratically by changing their distributions or through adaptation.Future research needs in sky islands include multilocus data and comparative phylogeographic studies,integrating with the methodological advances in the other fields.Using these approaches,we can examine to what degree the geographic,climate and/or biological factors,shape strong geographic patterns,promote diversification/speciation and preserve species/genetic diversity.We hope this paper will inspire future work to uncover the mechanism that has generated the endemic biodiversity and to further resolve the most essential problem:How to protect the biodiversity with limited funding during the coming drastic global climate change.     

Speciation along environmental gradients

Traditional discussions of speciation are based on geographical patterns of species ranges. In allopatric speciation, long-term geographical isolation generates reproductively isolated and spatially segregated descendant species. In the absence of geographical barriers, diversification is hindered by gene flow. Yet a growing body of phylogenetic and experimental data suggests that closely related species often occur in sympatry or have adjacent ranges in regions over which environmental changes are gradual and do not prevent gene flow. Theory has identified a variety of evolutionary processes that can result in speciation under sympatric conditions, with some recent advances concentrating on the phenomenon of evolutionary branching. Here we establish a link between geographical patterns and ecological processes of speciation by studying evolutionary branching in spatially structured populations. We show that along an environmental gradient, evolutionary branching can occur much more easily than in non-spatial models. This facilitation is most pronounced for gradients of intermediate slope. Moreover, spatial evolutionary branching readily generates patterns of spatial segregation and abutment between the emerging species. Our results highlight the importance of local processes of adaptive divergence for geographical patterns of speciation, and caution against pitfalls of inferring past speciation processes from present biogeographical patterns.     

Evolutionary biology: Sympatric plant speciation in islands?

Comparative studies of populations, particularly with the help of molecular markers, are necessary to understand the mechanisms of speciation in isolated oceanic archipelagos. Savolainen et al. present comparative data on two endemic species of the palm genus Howea in Lord Howe Island, from which they infer that speciation was sympatric--that is, divergence had occurred in the absence of geographic isolation. However, the landscape of oceanic islands changes dramatically over time, with many disappearing under the sea after 6 million years or more, and Lord Howe Island is in a very late stage of its ontogeny. An alternative explanation, therefore, is that these two species did not evolve in situ but instead that they arose allopatrically after becoming geographically isolated at a time when the island was much larger and more diverse ecologically.     

星斗山自然保护区木本植物区系研究

<正>湖北省星斗山属中亚热带常绿阔叶林地带。有木本植物99科,247属,595种;区系的地区理成份以东亚成份占首位,占总属数(不包括世界分布属)的21％;北温带成份占18％;中国特有成份占5.1％;6个热带性分布成份占42％。与邻近的神农架关系十分密切,尤以中国特有成份更为接近;与华东区系各种地理成份组成比例也很接近,与华南区系关系较为疏远,但本区一些常绿成份具有一定的热带性质。     

Analysis of an evolutionary species-area relationship

Large islands typically have more species than comparable smaller islands. Ecological theories, the most influential being the equilibrium theory of island biogeography, explain the species-area relationship as the outcome of the effect of area on immigration and extinction rates. However, these theories do not apply to taxa on land masses, including continents and large islands, that generate most of their species in situ. In this case, species-area relationships should be driven by higher speciation rates in larger areas, a theory that has never been quantitatively tested. Here we show that Anolis lizards on Caribbean islands meet several expectations of the evolutionary theory. Within-island speciation exceeds immigration as a source of new species on all islands larger than 3,000 km2, whereas speciation is rare on smaller islands. Above this threshold island size, the rate of species proliferation increases with island area, a process that results principally from the positive effects of area on speciation rate. Also as expected, the slope of the species-area relationship jumps sharply above the threshold. Although Anolis lizards have been present on large Caribbean islands for over 30 million years, there are indications that the current number of species still falls below the speciation-extinction equilibrium.     

Accelerated speciation in colour-polymorphic birds

Colour polymorphism exemplifies extreme morphological diversity within populations. It is taxonomically widespread but generally rare. Theory suggests that where colour polymorphism does occur, processes generating and maintaining it can promote speciation but the generality of this claim is unclear. Here we confirm, using species-level molecular phylogenies for five families of non-passerine birds, that colour polymorphism is associated with accelerated speciation rates in the three groups in which polymorphism is most prevalent. In all five groups, colour polymorphism is lost at a significantly greater rate than it is gained. Thus, the general rarity and phylogenetic dispersion of colour polymorphism is accounted for by a combination of higher speciation rate and higher transition rate from polymorphism to monomorphism, consistent with theoretical models where speciation is driven by fixation of one or more morphs. This is corroborated by evidence from a species-level molecular phylogeny of passerines, incorporating 4,128 (66.5%) extant species, that polymorphic species tend to be younger than monomorphic species. Our results provide empirical support for the general proposition, dating from classical evolutionary theory, that colour polymorphism can increase speciation rates.     

宁夏罗山种子植物区系研究

为了研究宁夏罗山国家级自然保护区植物区系科的性质与特点,于2006-2010年对其植物种类进行了野外调查,标本采集,鉴定分类及统计和分析.结果表明,宁夏罗山自然保护区内种子植物有64科、203属、365种,种子植物种类丰富;保护区植物区系年轻,地理成分复杂,具有明显的温带性质;植物区系处于青藏高原植物区系、华北植物区系...     

蒙古高原天门冬属(Asparagus)植物区系生态地理分布研究

蒙古高原天门冬属植物区系的显著特点是 :其东部渗入了东亚中生植物区系成分 (有 5种 ,甚至包括 A.dauricus) ,西部渗入了中亚旱生植物区系成分 ( 3种 ) .由于长期自然选择适应和演化结果 ,蒙古高原本属植物有一个特有种 .此外 ,在贺兰山及祁连山形成了我国青藏高原北部山区的特有种类 ( 1种、1变种 ) .通过 Jascal相似性系数分析 ,蒙古高原天门冬属植物区系与华北、东北、新疆、中西伯利亚的植物区系联系较紧密 .蒙古高原本属植物区系在漫长的演化过程中 ,主要受到热带非洲旱生植物区系和热带亚洲印度—马来西亚中生植物区系的影响 ,分别形成了旱生植物区系成分和中生植物区系成分 ,并且两种植物区系成分在蒙古高原荒漠化草原区形成重叠 ,形成现今蒙古高原天门冬属植物区系格局 .     

河北山地种子植物属的区系地理成分分析

通过详细调查和资料整理,对河北山地种子植物区系649属进行了系统分析,结果显示,河北山地植物区系成分中温带属441属,热带属114属,特有属18属.可以看出温带成分占绝对优势,其中北温带分布属是植物区系的核心,反映出区系典型的温带性质,过渡性突出.同时,分析得出本区系植物种类比较丰富、多样性高、起源古老、特有程度低的特征.     

鄂西木林子自然保护区种子植物区系的初步研究

2.2.1.2 东亚分布属的分析东亚分布是从喜马拉雅一直分布到日本的一些属。东亚分布属(包括变型)在本区系有91属,136种(包括变种),分别占本区系属种数的20.40%和13.01%,隶属于46科。中国东亚分布属共294属,木林子东亚分布属占其31.29%。本区系91属中木本属有48属。木本科18科。在这91属中,仅猕猴挑属(Actinidia)和沿阶草属(Ophiopogon)各有5种,25属2～4种,其他64属仅1种出现于本区系。给人印象深刻的是单种属达13属,占本区系该分布型的14.13%;少种属(2～6种)26属,占该分布型的28.26%;其中古老、孑遗的属种会多,也不乏较为特化的类群,这反映了该分布型植物在亚洲温带区系形成和发展中的关键性作用。     

福建省野生兰科植物区系研究

福建省共有野生兰科植物61属134种(含变种),其中中国特有种27种。种数在5个以上的有石豆兰属、兰属、虾脊兰属、羊耳蒜属、斑叶兰属、玉凤兰属、舌唇兰属和石斛属。福建省野生兰科植物属、种的地理成分可分别划分为15个和14个分布型(变型),其中热带亚洲(印度马来西亚)分布及其变型分别占总属、种数的34.4%和22.4%,热带分布属、种分别有44属、73种,占绝对优势。与邻近地区相比,福建省野生兰科植物与广东共有属、种最多,分别有48属、97种,其次为江西和浙江。福建省野生兰科植物区系具明显的热带性质,地理成分具有明显的从热带向亚热带的过渡性,但组成比较简单,缺少本区特有种,不是近代兰科植物种系的分化中心。     

浅析台湾植物区系

台湾海峡原为大陆的一部分,中新世未,由于断裂而形成海峡,台湾植物区系丰富,与大陆相同的科、属、种类多;共有成分中的古老成分多;台湾与大陆西南地区植物区系关系密切;台湾植物区系中特有种突出,它是大陆岛屿山地植物区系,台湾与菲律宾植物区系关系较少;与日本植物区系有一定联系,而后者属于中国-日本植物区系。     

井冈山蕨类植物区系排序研究

井冈山地处罗霄山脉中段,共有蕨类植物44科,101属,304种(含变种和变型).利用常规方法和区系存在度(VFP)对其科、属进行排序,所得结果相异甚远:常规排序中的大、中型科,在区系存在度排序中并不处开优势地位,在VFP>50%的17个科中,具有10种以上的科仅1科;VFP>30%的14个属中,含有5中以上的属均未进入,在这14个属中,热带性属和温带性属各7个,各占50%,且前者以热带亚洲分布为主,后者以东亚分布及中国特有成分为主.在本区系中,这两者是具标志性特征的重要类群,显然以区系存在度排序所得的结果能更好地反映该区系中科属的相对重要程度.两种排序结果都表明了本区系具有由热带向温带过度且以热带成分为主的性质.     

岷江上游地区种子植物区系初步研究

岷江上游地区位于四川北部,是世界生物多样性保护的热点地区.区系分析结果显示保护区内有种子植物107科,444属,1091种,其中裸子植物6科,11属,42种;被子植物101科,433属,1049种.种子植物科的分布区类型有12个,具有较强的热带性质,泛热带(热带广布Pantropic)型29科,占总科数的40.28%,属的分布区类型有15个,以温带区系成分为主,共225属,占总属数的56.53%,种的分布区类型有15个,其中特有种501个,占总种数的50.81%.该地区区系成分较复杂,特有成分较多,泛热带区系成分具有极其重要的地位.     

广东种子植物区系的特有属研究I．特有现象及特有属的分析

广东省种子植物区系中分布有中国特有属７５属，约含１２８种，隶属于４０科；科属种占中国同类的比例分别为：４５．４％，２３．４％和１７．０％。其中含有丰富的古特有，新特有及地区特有属，它们都是广东亚热带植物区系的特征属；而且在西南一桂东南形成了一个中国特有现象中心。根据这些特有成分的地理分布特点，结合广东及邻近地区古老的区系发展历史来进行分析，广东无疑是中国植物区系或华夏植物区系发生的关键地区之一。