Multiple Miocene Melastomataceae dispersal between Madagascar, Africa and India

Melastomataceae sensu stricto (excluding Memecylaceae) comprise some 3000 species in the neotropics, 1000 in Asia, 240 in Africa, and 230 in Madagascar. Previous family-wide morphological and DNA analyses have shown that the Madagascan species belong to at least three unrelated lineages, which were hypothesized to have arrived by trans-oceanic dispersal. An alternative hypothesis posits that the ancestors of Madagascan, as well as Indian, Melastomataceae arrived from Africa in the Late Cretaceous. This study tests these hypotheses in a Bayesian framework, using three combined sequence datasets analysed under a relaxed clock and simultaneously calibrated with fossils, some not previously used. The new fossil calibration comes from a re-dated possibly Middle or Upper Eocene Brazilian fossil of Melastomeae. Tectonic events were also tentatively used as constraints because of concerns that some of the family's fossils are difficult to assign to nodes in the phylogeny. Regardless of how the data were calibrated, the estimated divergence times of Madagascan and Indian lineages were too young for Cretaceous explanations to hold. This was true even of the oldest ages within the 95% credibility interval around each estimate. Madagascar's Melastomeae appear to have arrived from Africa during the Miocene. Medinilla, with some 70 species in Madagascar and two in Africa, too, arrived during the Miocene, but from Asia. Gravesia, with 100 species in Madagascar and four in east and west Africa, also appears to date to the Miocene, but its monophyly has not been tested. The study afforded an opportunity to compare divergence time estimates obtained earlier with strict clocks and single calibrations, with estimates based on relaxed clocks and different multiple calibrations and taxon sampling.     

First afrosoricid out of Africa: an example of Pliocene ‘tourism’ in Europe

The afrosoricids are an endemic order exclusively from Africa with a very scarce fossil record. In this work, we present the first record outside this continent. The “otter shrew” Europotamogale melkarti n. gen. n. sp. was found in the Moreda 3 karstic fill site in Granada (Spain), of MN15 age (mid-Pliocene). This new taxon confirms the semiaquatic faunal interchange between Europe and Africa. We hypothesize that this tenrecid, representative of a family frequently present in the Central African faunas, migrated to the north of the continent via the Sahabi river system that connected North and Central Africa. Europotamogale n. gen. is the first known afrosoricid that migrated between the two continents. It was present in Europe for a very short time (as a ‘tourist genus’). To date, this phenomenon has only been described in genera of European origin, such as the pika Prolagus or the mouse Apodemus.     

Historical biogeography of Androcymbium Willd. (Colchicaceae) in Africa: evidence from cpDNA RFLPs

The cpDNA restriction variation in 39 populations representing a geographical sampling of 18 species of Androcymbium in southwestern and northern Africa was examined to assess the historical biogeography of the genus. The cpDNA phylogeny indicates that the disjunction between South and North Africa is best explained by the dispersal of southern African ancestors into North Africa. Divergence time estimates suggest that the geographic range of the genus may have extended considerably north (perhaps to Tanzania and Kenya) prior to the global desiccation of Africa in the Miocene. Further expansion of the genus northward was probably stalled until climatic changes in the late Miocene brought about the gradual replacement of a subtropical woodland savanna with the arid landscape that gave rise to the Sahara. Aridification of the northern quarter of the continent provided the ecological conditions for fostering the expansion of Androcymbium along the Mediterranean fringe (probably east to west) and its introduction into the Canary Islands. Unlike their South African congeners, the northern species have experienced expansions, fragmentations, and local extinctions in response to the severe climatic shifts in this area during the Pliocene-Pleistocene. According to our divergence time estimates, the arid track may have already existed as a continuous area connecting southern and northern Africa in the late Miocene.     

Studies of fossil hyaenids: the genera Hyaenictis Gaudry and Chasmaporthetes Hay, with a reconsideration of the Hyaenidae of Langebaanweg, South Africa

The fossil hyaenids from Langebaanweg in South Africa are revised taxonomically using both morphological comparisons and measurement data. Ictilherium preforfex is found to be a synonym of Ikelohyaena abronia . Other hyaenid taxa in this fauna are Hyaenictitherium namaquensis, Chasmaporthetes australis and a new taxon similar to Chasmaporthetes australis in the size and shape of the M₁, trigonid and other characters, but differing from this taxon in having short P₃ relative to P₂, a smaller anterior accessory cusp on P₄ and M₂, present. This taxon has previously been referred to Euryboas sp***, but comparison with Eurasian hyaenids indicates that it shares diagnostic characters with Hyaenictis graeca , type species of the genus Hyaenictis . This genus is poorly known and its content is reviewed. We find that only the new species from Langebaanweg, formally described as Hyaenictis hendeyi sp. nov. , and the Spanish Hyaenictis almerai probably belong in this genus, while other taxa intermittently referred to Hyaenictis belong to other genera. Thus, neither Leecyaena bosei nor Chasmaporthetes silberbergi belong in Hyaenictis .     

Systematic placement of an enigmatic Southeast Asian taxon Eupetes macrocerus and implications for the biogeography of a main songbird radiation, the Passerida

Biogeographic connections between Australia and other continents are still poorly understood although the plate tectonics of the Indo-Pacific region is now well described. Eupetes macrocerus is an enigmatic taxon distributed in a small area on the Malay Peninsula and on Sumatra and Borneo. It has generally been associated with Ptilorrhoa in New Guinea on the other side of Wallace's Line, but a relationship with the West African Picathartes has also been suggested. Using three nuclear markers, we demonstrate that Eupetes is the sister taxon of the South African genus Chaetops, and their sister taxon in turn being Picathartes, with a divergence in the Eocene. Thus, this clade is distributed in remote corners of Africa and Asia, which makes the biogeographic history of these birds very intriguing. The most parsimonious explanation would be that they represent a relictual basal group in the Passerida clade established after a long-distance dispersal from the Australo-Papuan region to Africa. Many earlier taxonomic arrangements may have been based on assumptions about relationships with similar-looking forms in the same, or adjacent, biogeographic regions, and revisions with molecular data may uncover such cases of neglect of ancient relictual patterns reflecting past connections between the continents.     

The Origin,Dispersal and Formation of the Distribution Pattern of Swertia L. (Gentianaceae)

The genus Swertia is one of the large genera in Gentianaceae, including 154 species, 16 series and 11 sections. It is disjunctly distributed in Europe, Asia, Africa and N. America, but entirely absent from Oceania and S. America. According to Takhtajan’s (1978) regionalization of the world flora, Swertia is found in 14 regions. Eastern Asiatic region with 86 species, of which 58 are local endemics, 13 series and 9 sections, ranks the first among all the regions. The highest concentration of the taxa and endemics in Eastern Asiatic region occurs in SW China-Himalayan area (Sikang-Yunnan P. , W. Sichuan, W. Yunnan-Guichou Plateau of China and NE. Burma, N. Burmense P. , E. Himalayan P. and Khasi-Manipur P. ). In this area there are 74 species (48 endemics), 12 series, and 9 sections; thus about half species of the world total, three quarters of series and 82% of sections occur in this small area. Besides, the taxa at different evolutionary stages in Swertia also survive here. It is an indication that SW. China-Himalayan area is a major distribution centre of the genus Swertia. In addition, Sudan-Zambezian Region in Africa, with 22 species, 4 series and 2 sections, is a second distribution centre. The primitive type of the genus Swertia is Sect. Rugosa which consists of 2 series and 23 species. It is highly centred in the mountains of SW. China (Yunnan, Sichuan, Guizhou and SE. Xizang) where 2 series and 16 species occur. Among them 15 species of Ser. Rugosae were considered as the most primitive groups in this genus. From our study, the outgroup of Swertia is the genus Latouchea Frahch. , which is distributed in Yunnan, Sichuan, Guizhou, Hunan, Guangdong, Guangxi and Fujian. The two groups overlap in distribution in SW. China. According to the principle of common origin, the ancestor of two genera ap peared most probably in this overlapping area. It was inferred that SW. China Was the birth-place of the genus Swertia. Four sections of Swertia have different disjunct distribution patterns: Sect. Ophelia is of Tropic Asia, Africa and Madagascar disjunct distribution; sect. Swertia is of north temperate distribution; sect. Spinosisemina is in Tropical Asia (Trop. India to S. China and Philipines); sect. Platynema also is in Tropical Asia (Java, Sumatra, Himalayas to SW. China). These disjunct patterns indicate that the Swertia floras between the continents or between continent and islands have a connection with each other. From paleogeographical analysis, Swertia plants dispersed to Madagascar before the Late Cretaceous, to SE. Asian Islands in the Pleistocene, to North America in the Miocene. The distribution of Swertia in Madagascar might be later than that in Asia. Therefore the origin time of the genus Swertia was at least not later than the Late Cretaceous, and might be back to the Mid-Cretaceous. The genus Swertia first fully developed and differentiated, forming some taxa at different evolutionary stages (Rugosa, Swertia, Poephila, Ophelia and Platynema etc. ) in the original area, and these taxa quickly dispersed in certain directions during the Late Cretaceous-Middle Tertiary when the global climate was warm and no much change. There seem to be three main dispersal routes from the origin area to different continents; (1) The westward route i. e. from SW. China, along the Himalayas area to Kashmir, Pakistan, Afghanistan and Iran, and then southwestwards into Africa throuth Arabia. Four sections (Poephila, Macranthos, Kingdon-Wardia and Ophelia) took this dispersal route. Most species of sect. Ophelia dispersed along this route, but a few along southern route and north ern route. Sect. Ophelia greatly differentiated in Africa and the African endemic sectionSect. Montana was derived from it. The two sections form there a second distribution center of Swertia. (2) The southward route, i. e. towards S. India through the Himalayas, and towards SE. Asian islands through C. and S. China, Indo-China. Along this dispersal route sect. Platynema, Sect. Spinosisemina and a few species of Sect. Ophelia dispersed; (3) The northward rout, i. e. northwards across N. China, C. Asia to a high latitude of Euasia, and also through E. Asia into N. America. The following groups took this route: sect. Rugosa, sect. Swertia, sect. Frasera, sect. Heteranthos and sect. Ophelia ser. Dichotomae. Therefore, it seems that the genus Swertia originated in SW. China and then dispersed from there to N. and S. Asia, Africa, Europe and North America and formed the moderndistribution pattern of this genus.     

Molecular phylogeny of Phalaenopsis Blume (Orchidaceae) on the basis of plastid and nuclear DNA

Representatives of the genus Ancistrocladus, woody lianas of tropical Africa and Asia, contain pharmaceutically interesting alkaloids and have been the subjects of intensive phytochemical investigations. In Southeast Asia, Ancistrocladus tectorius, previously regarded as the only species of the genus from this region, is extremely polymorphic with respect to naphthylisoquinoline alkaloids, indicating that this taxon might be comprised of several morphologically similar species. We performed a comparative study of the ITS region of nuclear rDNA and of the trnK intron of cpDNA as well as an ISSR fingerprint analysis. Using 75 samples of A. tectorius from 21 locations in comparison to samples of other Ancistrocladus species from Asia and from West and Central Africa, we investigated patterns of species differentiation within this taxon. We found the high variability of chemical compounds described for A. tectorius to be paralleled by a high genetic variability of the units that have been assigned to this taxon. Samples assigned to A. tectorius were paraphyletic with respect to species from the Indian subcontinent, and intraspecific variability was comparable to interspecific variability among the African taxa. In addition, groups of individuals occurring in sympatry were found to be more similar to those from other locations, suggesting low levels of gene flow between those sympatric groups. This indicates either a considerable number of hybridization events during the evolution of A. tectorius or the existence of several distinguishable species not yet recognized. Our results are a first step in the development of species or population-specific markers for the prediction of the alkaloid spectrum of samples. This will help to improve the reproducibility of phytochemical research on Ancistrocladus.     

The making of the African mtDNA landscape

Africa presents the most complex genetic picture of any continent, with a time depth for mitochondrial DNA (mtDNA) lineages >100,000 years. The most recent widespread demographic shift within the continent was most probably the Bantu dispersals, which archaeological and linguistic evidence suggest originated in West Africa 3,000-4,000 years ago, spreading both east and south. Here, we have carried out a thorough phylogeographic analysis of mtDNA variation in a total of 2,847 samples from throughout the continent, including 307 new sequences from southeast African Bantu speakers. The results suggest that the southeast Bantu speakers have a composite origin on the maternal line of descent, with approximately 44% of lineages deriving from West Africa, approximately 21% from either West or Central Africa, approximately 30% from East Africa, and approximately 5% from southern African Khoisan-speaking groups. The ages of the major founder types of both West and East African origin are consistent with the likely timing of Bantu dispersals, with those from the west somewhat predating those from the east. Despite this composite picture, the southeastern African Bantu groups are indistinguishable from each other with respect to their mtDNA, suggesting that they either had a common origin at the point of entry into southeastern Africa or have undergone very extensive gene flow since.     

Phylogenetic relationships of the enigmatic land snail genus Prestonella: the missing African element in the Gondwanan superfamily Orthalicoidea (Mollusca: Stylommatophora)

The land snail superfamily Orthalicoidea, although generally assumed to be of Gondwanan origin, is considered by the majority of recent authors to be absent from the African continent. However, two poorly-known African genera, Aillya and Prestonella , have historically been referred to the orthalicoid family Bulimulidae s.l. Anatomical study of Aillya has subsequently shown it to be morphologically distinct from the Bulimulidae and referable to a family of its own, outside the Orthalicoidea, but Prestonella has remained an enigmatic taxon of unknown affinity. Using molecular and morphological evidence, we demonstrate conclusively that Prestonella is indeed a member of the Bulimulidae s.l. We thus confirm that this family is represented in Africa, and that it has a classical disjunct, tri-continental southern distribution. Thus, either the origin of the family must at the least predate the separation of Africa and South America in the Mid Cretaceous (under a vicariance scenario) or there must have been subsequent dispersal between the isolated Gondwanan fragments. In view of the limited dispersal ability of terrestrial snails, we consider the former more likely. Anatomically, Prestonella exhibits many character states thought to be plesiomorphic, suggesting a relationship with the subfamily Bulimulinae. Bayesian analysis of nuclear DNA sequence data places it as sister group (posterior probability = 1.0) to an Australasian clade comprising Bothriembryon and Placostylus . However, taxon sampling within the Orthalicoidea is currently inadequate to permit meaningful resolution of subfamilial affinity using molecular data. Similarly, although those orthalicoid taxa for which molecular data are available comprise a well-supported clade, the relationships of this clade to other stylommatophoran clades remain unresolved.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 203–221.     

Origin and evolution of African Polystoma (Monogenea: Polystomatidae) assessed by molecular methods

Among Polystomatidae (Monogenea), the genus Polystoma, which mainly infests neobatrachian hosts, is the most diverse and occurs principally in Africa, from where half the species have been reported. Previous molecular phylogenetic studies have shown that this genus originated in South America, and later colonised Eurasia and Africa. No mention was made on dispersal corridors between Europe and Africa or of the origin of the African Polystoma radiation. Therefore, a molecular phylogeny was inferred from ITS1 sequences of 21 taxa comprising two species from America, seven representatives from Europe and 12 from Africa. The topology of the phylogenetic tree reveals that a single event of colonisation took place from Europe to Africa and that the putative host carrying along the ancestral polystome is to be found among ancestral pelobatids. Percentage divergences estimates suggest that some presumably distinct vesicular species in unrelated South African anurans and some neotenic forms found in several distinct hosts in Ivory Coast, could, in fact, belong to two single polystome species parasitising divergent hosts. Two main factors are identified that may explain the diversity of African polystomes: (i), we propose that following some degree of generalism, at least during the juvenile stages of both hosts and parasites, distinctive larval behaviour of polystomes engenders isolation between parasite populations that precludes sympatric speciations; (ii), cospeciation events between Ptychadena hosts and their parasites are another factor of diversification of Polystoma on the African continent. Finally, we discuss the systematic status of the Madagascan parasite Metapolystoma, as well as the colonisation of Madagascar by the host Ptychadena mascareniensis.     

世界蓑藓属植物分布式样及其系统演化和生物地理学意义

蓑藓属（Macromitrium）是苔藓植物分类、生态学研究及生物多样性保护的重要类群。以“Index Muscorum”中的14个藓类植物地理分布单位为分析区域,基于标本信息和相关文献,在分类修订的基础上,统计了世界蓑藓属274种植物在14个地理单位的分布数据,基于这些数据,应用聚类分析和除趋势对应分析法,分别得到了14个地理单位的聚类图和三维空间图,直观展示了世界蓑藓属植物的地理分布格局。发现蓑藓属植物区系在东亚（As2）、大洋洲（Oc）、南亚和东南亚（As3,As4）、非洲（Afr2,Afr3,Afr4）、中美洲-南美洲（Am2,Am3,Am4,Am5）、澳洲（Austr1,Austr2）存在区域分化。热带亚洲和热带美洲是世界蓑藓属植物的多样化中心。除长柄蓑藓（M.microstomum（Hook.&Grev.）Schwägr.）在14个地理单位均有分布外,大部分种类分布限于少数或仅一个地理单位。蓑藓属植物在东亚、热带亚洲、热带美洲和澳洲不仅种类存在明显分化,而且形态性状也有区域特点。根据蓑藓属植物的现代分布式样,探讨了其系统演化和生物地理学意义。     

Fossil legumes from the Middle Eocene (46.0 Ma) Mahenge Flora of Singida, Tanzania

Middle Eocene age caesalpinioid and mimosoid legume leaves are reported from the Mahenge site in north-central Tanzania. The Mahenge flora complements a sparse Paleogene tropical African fossil plant record, which until now consisted of a single macrobotanical assemblage, limited palynological studies in West Africa and Egypt, and fossil wood studies primarily from poorly dated deposits. Mahenge leaf macrofossils have the potential to add significantly to what is known of the evolutionary history of extant African plant groups and to expand our currently limited knowledge of African Paleogene environments. The site is associated with a kimberlite eruption and demonstrates the potential value of kimberlite-associated lake deposits as much-needed resources for African Paleogene floras. In this report we document a relatively diverse component of the flora consisting of the leaves of at least five species of Leguminosae. A new species of the extant genus Acacia (Mimosoideae), described herein, is represented by a bipinnate leaf. Another taxon is described as a new species of the extant genus Aphanocalyx (Caesalpinioideae), and a third leaf type may be related to the extant genus Cynometra (Caesalpinioideae). Two additional leaf types are less well understood: one appears to be referable to the Caesalpinioideae and subfamily affinities of the other taxon are unknown.     

Paraphyletic taxa and taxonomic chaining: evaluating the classification of braconine wasps (Hymenoptera: Braconidae) using 28S D2-3 rDNA sequences and morphological characters

The parasitoid wasp subfamily Braconinae is dominated by the type genus Bracon , a genus which probably now contains more than 1000 described species and no reliable subgeneric groupings. By analysing 28S D2-3 rDNA sequences in representative braconines we show that the genus is paraphyletic. It is unlikely that sufficient molecular data will be amassed, or new morphological characters discovered, in the foreseeable future to divide this huge amorphous genus into reciprocally monophyletic clades. As we believe that it is unsatisfactory to leave this situation as it stands we propose that Bracon should be treated formally as a likely paraphyletic taxon, and we argue that the ICZN should consider creating such a category. On the basis of our estimated phylogeny we also propose a revised classification for this subfamily that avoids paraphyletic tribes and subtribes, replacing several of these with informal genus groups.     

The phylogenetic structure of primate communities: variation within and across continents

Aim Our goals are: (1) to examine the relative degree of phylogenetic overdispersion or clustering of species in communities relative to the entire species pool, (2) to test for across‐continent differences in community phylogenetic structure, and (3) to examine the relationship between species richness and community phylogenetic structure. Location Africa, Madagascar, Asia, and the Neotropics. Methods We collected species composition and phylogenetic data for over 100 primate communities. For each community, we calculated two measures of phylogenetic structure: (1) the net relatedness index (NRI), which provides a measure of the mean pairwise phylogenetic distance among all species in the community; and (2) the nearest taxon index (NTI), which measures the relative phylogenetic distance among the closest related species in a community. Both measures are relative to the phylogeny of the species in the entire species pool. The phylocom package uses a randomization procedure to test whether the NRI and NTI values are higher or lower than expected by chance alone. In addition, we used a Kruskal–Wallis test to examine differences in NRI and NTI across continents, and linear regressions to examine the relationship between species richness and NRI/NTI. Results We found that the majority of individual primate communities in Africa, Asia and the Neotropics consist of member species that are neither more nor less closely related than expected by chance alone. Yet 37% of Malagasy communities contain species that are more distantly related to each other compared with random species assemblages. Also, we found that the average degree of relatedness among species in communities differed significantly across continents, with African and Malagasy communities consisting of more distantly related taxa compared with communities in Asia and the Neotropics. Finally, we found a significant negative relationship between species richness and phylogenetic distance among species in African, Asian and Malagasy communities. The average relatedness among species in communities decreased as community size increased. Main conclusions The majority of individual primate communities exhibit a phylogenetic structure no different from random. Yet there are across‐continent differences in the phylogenetic structure of primate communities that probably result from the unique ecological and evolutionary characteristics exhibited by the endemic species found on each continent. In particular, the recent extinctions of numerous primates on Madagascar are likely responsible for the low levels of evolutionary relatedness among species in Malagasy communities.     

A small stem-galliform bird (Aves: Paraortygidae) from the Eocene of Uzbekistan

Landfowl (order Galliformes) are among the most characteristic birds of the modern avian faunas, but their early evolutionary history is insufficiently known. The diversity of previously described Eocene galliforms implies a great role of Eocene diversification in the early evolution of this group. However, almost nothing is known about the Eocene diversity of galliforms in Asia, even though this large continent with a variety of habitats might have played a significant role in their early evolution. Here we describe a partial coracoid from the Lutetian–Bartonian of Uzbekistan, which is the oldest diagnosable galliform bird in Asia, and is further the first landbird known from this geographical area. The specimen displays a unique morphology with few autapomorphies and an unexpected combination of similarities with the African genus Scopelortyx and Eurasian Paraortyx, and hence is described as a new taxon, Xorazmortyx turkestanensis gen. et sp. nov., within the extinct family Paraortygidae, being the first Asian representative of this clade. Similarities with the African genus Scopelortyx indicate a connection of land bird faunas between northern Africa/Arabia and Asia in the middle Eocene. Better dispersal abilities of the early galliforms Paraortygidae are inferred from the osteology of their pectoral girdle and the humerus, which do not show adaptations to the powerful burst take off (escape flight), characteristic of most modern Phasianidae.     

Ancient SINEs from African endemic mammals

Afrotheria is a newly recognized taxon comprising elephants, hyraxes, sea cows, aardvarks, golden moles, tenrecs, and elephant shrews, each of which originated in Africa. Although some members of this taxon were once classified into distantly related groups, recent molecular studies have demonstrated their close relationships. It was suggested that this group emerged as a result of physical isolation of the African continent during the successive breakup events of Gondowanaland. In this study, a novel family of SINEs, designated AfroSINEs, was isolated and characterized from the genomes of afrotherians. This SINE family is distributed exclusively among the afrotherian species, confirming their monophyletic relationships. Furthermore, a distinct subfamily, which shares a deletion in the middle region of the SINE, was identified. The distribution of this subfamily is apparently restricted to the genomes of hyraxes, elephants, and sea cows, suggesting monophyly of these three groups, which was previously proposed as Paenungulata. We characterized the structures of the AfroSINEs from all afrotherian representatives by PCR, and we discuss how they were generated as well as the phylogenetic relationships of their host species.     

Evolution of Hawaiian Drosophilidae. II. Patterns and Rates of Chromosome Evolution in an Antopocerus Phylogeny

The phylogenetic relationships of seven species of the genus Antopocerus (Family Drosophilidae) have been determined by means of a study of the metaphase configurations and polytene chromosomes. Based on biogeographical, behavioral and cytogenetic information, A. longiseta from Molokai is tentatively identified as the primitive species of the genus. The metaphase karyotypes of all Antopocerus species are either five pairs of rod chromosomes and a pair of dots (5R1D), or six rods (6R). Heterochromatin additions converted the dots to rods. Chromosome breakpoints for inversions also are clustered at heterochromatic loci. The chromosome segments between heterochromatic loci may represent sets of functionally related loci, evolving as a unit. The rate of chromosomal inversion substitution is estimated in the origin of the taxon (probably a subgenus of Drosophila rather than a separate genus). It averages no greater than one substitution per 1,000 years, or one per 5,000 generations. The average genetic death rate per generation of one individual per hundred is required to achieve this substitution rate. The rate of inversion substitution during radiation of this taxon may be only 4.4 x 10^-3 times as fast as that present in forming the taxon. Alternatively, radiation may have required only 250,000 years if rates of substitution are the same as in the origination of the taxon. Average rates of substitution reflect genetic accidents, selection pressures and rates of adaptation to new niches, as well as the rate of encountering new niches. Rate of adaptation probably is much greater in this instance than rate of encountering new niches. Therefore, the average rate of evolution reflects more nearly biogeographic and ecological factors than genetic factors.     

Molecular phylogenetic analysis of Commiphora (Burseraceae) yields insight on the evolution and historical biogeography of an "impossible" genus

Expansion of the arid zone of sub-Saharan tropical Africa during the Miocene is posited as a significant contributing factor in the evolution of contemporary African flora. Nevertheless, few molecular phylogenetic studies have tested this hypothesis using reconstructed historical biogeographies of plants within this zone. Here, we present a molecular phylogeny of Commiphora, a predominantly tropical African, arid-adapted tree genus, in order to test the monophyly of its taxonomic sections and identify clades that will help direct future study of this species-rich and geographically widespread taxon. We then use multiple fossil calibrations of Commiphora phylogeny to determine the timing of well-supported diversification events within the genus and interpret these age estimates to determine the relative contribution of vicariance and dispersal in the expansion of Commiphora's geographic range. We find that Commiphora is sister to Vietnamese Bursera tonkinensis and that its crown group radiation corresponds with the onset of the Miocene.     

楝科（Meliaceae）的地理分布

楝科为泛热带分布科,全世界有５１属,约５５０—６００种,分布于旧世界热带地区有４６属,热带美洲有８属．热带亚洲和热带非洲为楝科两大现代分布中心．中国楝科共１５属,６１种,占世界属总数的２９％,种总数的１０％。中国楝科的分布是在全球楝科分布区的边缘,主要分布于中国西南部及南部诸省,种类由西南向东南递减。中国楝科属的分布区类型可归为５类：１．热带亚洲、非洲和中南美洲间断分布（１属）;２．旧世界热带分布（３属）;３,热带亚洲至热带大洋洲分布（２属）;４．热带亚洲至热带非洲分布（１属）;５．热带亚洲分布（８属）。中国楝科种的分布区类型仅有２类：１．热带亚洲分布（３１种）;２．中国特有分布（３０种）。楝科植物的起源推断在早白垩纪。中国楝科植物由印度—马来西亚成分及特有成分组成。热带亚洲的楝科植物主要是通过中南半岛和中国云南。广西和海南等地发生联系,而菲律宾和台湾之间可有直接的联系。