Altitudinal variation in the late quaternary vegetational history of Northwest Greece

The palaeoecological sites of Gramousti lake and Rezina marsh, northwest Greece, although only 20 kin apart are at contrasting altitudes of 285 m a.s.1. and 1800 m a.s.1. Altitudinal difference between the two sites is shown to have a significant effect upon the postglacial vegetational history of the region. Rezina marsh is the highest and smallest site to be studied thus far in Greece and provides some of the first evidence for the location of cold‐stage temperate tree refugia. Migration of tree populations is shown to play an insignificant part in the vegetational development of the mountain region, demonstrating the importance of other factors (internal and external) in the diversity of the postglacial woodland.     

Late Quaternary vegetation and climatic history of eastern Nepal

The late Quaternary vegetation and climatic history at high altitude in eastern Nepal was studied through stratigraphy, radiocarbon dating and pollen analysis. The Thulo Pokhari lake (27°41′ N, 87°43′ E, ca. 3980 m a.s.l.) is just above the subalpine Abies spectabilis–Betula utilis forest zone and surrounded by Rhododendron scrub. The climate in the studied area is very humid under the influence of the monsoon. Silty sediments suggesting lake conditions prevailed at the lower part of the sediment samples, whereas the upper part consisted mainly of herbaceous peat indicating a mire condition. The pollen record extends back to ca. 11000 yr bp . Although the absence of major changes between the pollen assemblages of the Pleistocene and those in the Holocene was attributed to the situation of the sampling plot above the forest limit, the results suggest the following history. (1) The abundance of Pinus pollen around 11000 yr bp represents expansion of the area unoccupied by late successional trees and/or a drier condition. Significant occurrence of Picea pollen is noteworthy, since this genus is absent in eastern Nepal at present in spite of its wide distribution throughout the neighbouring areas of the Himalayas. (2) The increase in abundance of Quercus pollen and the decline in Pinus pollen in the latest Pleistocene represent climatic amelioration favourable to late successional mesophytes. (3) The climate was most moist and mild in the SP-III, although the absolute age of the pollen zone is not distinct. The percentages of broadleaved trees such as Alnus, Betula, Carpinus and Corylus were increased at the expense of Quercus and coniferous pollen types. Sedimentation was interrupted by lake level decline and/or glacial advance during the period from ca. 11000–1600 yr bp . (4) The increase in abundance of coniferous pollen types such as Pinus, Abies and Tsuga indicates that the climate became drier and cooler, and the present subalpine forest zone composed of A. spectabilis, T. dumosa and Betula utilis was established around 1600 yr bp . The formation of bog or alpine meadow vegetation during the period was shown by the ¹⁴C dates of the peat and the increase in Rosaceae and herbaceous pollen. (5) The increase in abundance of Ericaceae and Alnus pollen in the SP-V indicates that the present alpine Rhododendron scrub zone has been established since ca. 940 yr bp as a result of human influence on the original vegetation. This interpretation is supported by the decline in the proportion of arboreal pollen. Since the age of the initiation of human influence varies with the altitude and region, further study will be necessary to determine the accurate age.     

干旱区终闾湖泊孢粉记录的环境重建模式——以甘肃石羊河流域终闾湖泊为例

西北干旱区河西走廊东段,石羊河终闾湖泊边缘的三角城剖面全新世早期至末次冰消期292－600cm处155个样孢粉组合,显示云极,圆柏属含亘极高,两者之和达40％－60％,且百分比互为消长,云杉百分比与孢粉浓度,植被分异度成正比,通过对云杉,圆柏属生态习性,传播性能,与其它组分关系,当地特殊的自然地理条件的综合分析,笔者认为剖面中高含量的云杉,圆柏属来自流域上游祁连山,是石羊河搬运的结果,孢粉组合中其它成分有当地的,也有来自山上的,剖面附近表土花粉分析支持这种观点,云杉,圆柏属是判断流环境变化的主要因子,孢粉组合中其它成分可辅助判断环境变化的细节,流域环境重建模式和具体的变化过程中：孢粉组合中的主要成分指示流域山上的植被状况;云杉花粉含量高时,流域有效湿度大,山上云杉林范围扩大,终闾区湖泊发育,整个流域生物分异度,密度,孢粉浓度都大;圆柏属花粉含量高,流域干旱,山上云格林范围急剧减少,整个流域生物分异度,密度减少,孢粉浓度降低,圆柏属受干旱影响较小,数量有所减少,但因补偿递减率的作用,百分比增加,这可为重建我国西部干旱区湖泊孢粉记录的古环境作参考。     

PERCHED AT THE MITO‐NUCLEAR CROSSROADS: DIVERGENT MITOCHONDRIAL LINEAGES CORRELATE WITH ENVIRONMENT IN THE FACE OF ONGOING NUCLEAR GENE FLOW IN AN AUSTRALIAN BIRD

Relationships among multilocus genetic variation, geography, and environment can reveal how evolutionary processes affect genomes. We examined the evolution of an Australian bird, the eastern yellow robin Eopsaltria australis, using mitochondrial (mtDNA) and nuclear (nDNA) genetic markers, and bioclimatic variables. In southeastern Australia, two divergent mtDNA lineages occur east and west of the Great Dividing Range, perpendicular to latitudinal nDNA structure. We evaluated alternative scenarios to explain this striking discordance in landscape genetic patterning. Stochastic mtDNA lineage sorting can be rejected because the mtDNA lineages are essentially distinct geographically for > 1500 km. Vicariance is unlikely: the Great Dividing Range is neither a current barrier nor was it at the Last Glacial Maximum according to species distribution modeling; nuclear gene flow inferred from coalescent analysis affirms this. Female philopatry contradicts known female‐biased dispersal. Contrasting mtDNA and nDNA demographies indicate their evolutionary histories are decoupled. Distance‐based redundancy analysis, in which environmental temperatures explain mtDNA variance above that explained by geographic position and isolation‐by‐distance, favors a nonneutral explanation for mitochondrial phylogeographic patterning. Thus, observed mito‐nuclear discordance accords with environmental selection on a female‐linked trait, such as mtDNA, mtDNA–nDNA interactions or genes on W‐chromosome, driving mitochondrial divergence in the presence of nuclear gene flow.     

PLASTID DNA RESTRICTION ANALYSIS LINKS THE HETEROMORPHIC PHASES OF AN APOMICTIC RED ALGAL LIFE HISTORY1

Gymnogongrus sp. (Phyllophoraceae) from Nova Scotia, Canada, identified tentatively as G. devoniensis (Greville) Schotter, grows in association with an Erythrodermis-like that forms chains of tetrasporangia or bisporangia. The crust resembles tetrasporophytic phases of other Gymnogongrus species, but in culture both it and the G. devoniensis gametophytes cycle independently by apomictic reproduction. A method was developed for extracting organelle DNA from this carrageenophyte genus involving purification of nucleic acids by binding to hydroxylapatite. Plastid DNA from G. devoniensis and bisporangial Erythrodermis-like crusts was compared with that of G. devoniensis and G. crenulatus (Turner) J. Agardh from France and of G. furcellatus (C. Agardh) J. Agardh from Chile. Plastid genomes of all Gymnogongrus species and the Erythrodermis-like crust were approximately 175 kb long. A single 3.5-kb plasmid DNA species was found in G. devoniensis and the Erythrodermis-like bisporophyte but not in other samples. Digestion of plasted DNA with several restriction endonucleases produced identical patterns in G. devoniensis and the Erythrodermis-like bisporophyte from the same location, indicating clearly that these entities represent two phases of an uncoupled life history. These results were confirmed with heteologous probes. A restriction fragment length polymorphism was identified between two Nova Scotian G. devoniensis populations. There was no similarity in restriction patterns between G. devoniensis from Nova Scotia, G. devoniensis from France. G. crenulatus or G. furcellatus, suggesting that molecular taxonomic methods could be important in delineating members of this morphologically variable genus. Further study is necessary to determine whether either Nova Scotian G. devoniensis or French G. devoniensis corresponds to type populations of G. devoniensis from Devon, England.     

A NEW LOOK AT AN ANCIENT ORDER: GENERIC REVISION OF THE BANGIALES (RHODOPHYTA)1

The red algal order Bangiales has been revised as a result of detailed regional studies and the development of expert local knowledge of Bangiales floras, followed by collaborative global analyses based on wide taxon sampling and molecular analyses. Combined analyses of the nuclear SSU rRNA gene and the plastid RUBISCO LSU (rbcL) gene for 157 Bangiales taxa have been conducted. Fifteen genera of Bangiales, seven filamentous and eight foliose, are recognized. This classification includes five newly described and two resurrected genera. This revision constitutes a major change in understanding relationships and evolution in this order. The genus Porphyra is now restricted to five described species and a number of undescribed species. Other foliose taxa previously placed in Porphyra are now recognized to belong to the genera Boreophyllum gen. nov., Clymene gen. nov., Fuscifolium gen. nov., Lysithea gen. nov., Miuraea gen. nov., Pyropia, and Wildemania. Four of the seven filamentous genera recognized in our analyses already have generic names (Bangia, Dione, Minerva, and Pseudobangia), and are all currently monotypic. The unnamed filamentous genera are clearly composed of multiple species, and few of these species have names. Further research is required: the genus to which the marine taxon Bangia fuscopurpurea belongs is not known, and there are also a large number of species previously described as Porphyra for which nuclear SSU ribosomal RNA (nrSSU) or rbcL sequence data should be obtained so that they can be assigned to the appropriate genus.     

THE SYMMETRY OF CORRELATED SELECTION RESPONSES IN ADAPTIVE EVOLUTION: AN EXPERIMENTAL STUDY USING DROSOPHILA

The relationship between the processes of density-dependent and age-specific selection has been investigated by examining a common phenotype, urea resistance, which has apparently evolved in response to each of these selection mechanisms. Twenty populations that have experienced differing levels of age-specific selection show differences in egg-to-adult viability in environments with high levels of urea. Among this group of populations, it appears that resistance to urea is correlated with longevity, but not development time. Ten populations kept at extreme larval densities for many generations also show responses to urea: those kept at high larval densities appear to be most resistant to urea. However, these populations show no differences in adult longevity. An additional five populations were selected directly for urea resistance by adding this compound to the larval food environment. Again, there was a strong response to this artificial selection, with urea resistance increasing dramatically, but these populations showed no response in adult longevity or resistance to crowding when compared to five control populations. There is clearly no simple relationship between longevity and larval urea resistance. It may be that age-specific and density-dependent selection induce similar changes in this phenotype, but do so through different genetic and physiological pathways. We suggest that these data are not consistent with the view of constant and symmetric genetic variance-covariance matrices. These data support a more prominent role for observations of evolutionary trajectories rather than static measurements of genetic components of variance.