西喜马拉雅地区气候变化与果蝇分布界限的移动(英文)

在长时间尺度上研究环境变化条件下的种群动态,有助于确定不同物种如何对新的生物和非生物条件做出反应。采纳类似的采集方法在相同的地点,分别于1961－1962年和2003－2004年在西喜马拉雅地区对果蝇种类进行了两次野外调查,对两次调查获得的种类的相对丰富度和优势度指数进行了比较。最近50年的气象数据显示西喜马拉雅平均气温（Tave）发生了显著变化,对该地区的果蝇种类组成及分布界限产生了影响。本研究发现在低海拔的地带Drosophila nepalensis及其他一些冷适应种类的数量明显下降;而Drosophila ananassae及其他一些暖适应种类则进入了低海拔和中海拔地带。D. nepalensis的丰富度与所调查地点的平均气温负相关(r = -0.93±0.03),而对于D. ananassaez则是相反趋势(r=0.90±0.05)。据此认为长期（42年）的气候变化已对西喜马拉雅地区的果蝇种类的分布格局产生了影响。     

Climate change,boundary increase and elongation of a pre‐existing cline: A case study in Drosophila ananassae

During the past two to three decades, Drosophila ananassae, a warm adapted tropical species, has invaded low to mid altitude localities in the western Himalayas. Due to its cold sensitivity, this species had never been recorded from higher latitudes as well as altitudes in India to the 1960s. A latitudinal cline in this desiccation‐sensitive species corresponds with southern humid tropical localities rather than northern drier subtropical localities. An extension of its cline into lowland to midland montane localities has resulted due to global climatic change as well as local thermal effects through anthropogenic impact. However, D. ananassae populations at species borders are characterized by lower genetic variability for body melanization as well as for desiccation resistance. There is a lack of thermal plastic effects for body melanization, and the observed extended cline might represent evolutionary (genetic) response due to selection pressure imposed by drier habitats. A comparison of fecundity, hatchability and viability at three growth temperatures (17, 20 and 25°C) showed significant reduction in trait values at 17°C in D. ananassae. Thus, its recent range expansion into northern montane localities might involve genetic effects on stress‐related traits and plastic effects on life history traits. We suggest that D. ananassae could serve as an indicator species for analyzing range expansion under changing climatic conditions.     

Body melanization and its adaptive role in thermoregulation and tolerance against desiccating conditions in drosophilids

Melanism seems to have evolved independently through diverse mechanisms in various taxa and different ecological factors could be responsible for selective responses. Increased body melanization at higher altitudes as well as latitudes is generally considered to be adaptive for thermoregulation. Physiological traits such as body melanization and desiccation resistance have been investigated independently in diverse insect taxa at three levels: within populations, between populations and among species. A substantial number of Drosophila studies have reported clinal variations in both these traits along latitude. A possible link between these traits had remained unexplored in wild and laboratory populations of ectothermic insect taxa, including drosophilids, to date. Simultaneous analysis of these traits in assorted darker and lighter phenotypes in each population in the present study showed parallel changes for body melanization and desiccation resistance. The mechanistic basis of evolving desiccation resistance was explained on the basis of differential rates of water loss per hour in darker versus lighter phenotypes in six populations of Drosophila melanogaster from adjacent localities differing substantially in altitude all along the Indian subcontinent. Data on cuticular impermeability suggest a possible role of melanization in desiccation tolerance. However, substantial gaps remain in extending these results to other insect taxa and further exploring the physiological and molecular changes involved in melanization for conferring desiccation resistance.     

The Role of Benzyladenine in the Differentiation of Tracheary Elements in Jerusalem Artichoke Tuber Explants Cultured in vitro

The role of benzyladenine (BA) in the differentiation of trachearyelements in Jerusalem artichoke (Helianthus tuberosus L.) tuberexplants was studied. For maximum differentiation of trachearyelements (25–30% of the cell population), treatment withoptimal concentrations of benzyladenine (5.0 mg dm^–3)in the presence of -naphthaleneacetic acid |NAA| (1.0 mg dm^–3)for the first 6 d was as effective as its continued presenceduring the entire 14 d period of study. A majority of the differentiatedtracheary element appeared between the 10th and 14th days ofculture. It was further observed that concentrations of activecytokinins in the tissue were considerably reduced within 2d after transfer from the BA-containing medium to a BA-freemedium. This was shown in three different ways: (1) monitoringthe amount of ethanol-soluble radioactivity at various timesafter transfer from |14C|-BA containing medium to BA-free medium;(2) bioassay of various cytokinin fractions from tissue extractseparated by thin layer chromatography; (3) indirect assay oftissue cytokinin activity through its interaction with abscisicacid for the promotion of auxin-induced cell division in thistissue. Both gibberellic acid (5.0 mg dm^–3) and abscisic acid(2–0 mg dm^–3) effectively inhibited the differentiationof tracheary elements even if provided after 6 d of pre-incubationin a high tracheid inducing medium. However, the appearanceof differentiated cells for the first 2 d after transfer wasnot significantly affected. A hypothetical scheme for the role of benzyladenine in the differentiationof tracheary elements in this tissue is discussed. It is suggestedthat during one or more critical cell divisions in the presenceof optimal levels of benzyladenine, a proportion of cells areinduced or committed for later differentiation into trachearyelements. The high concentrations of benzyladenine requiredduring induction are not needed during the intervening celldivisions, nor for the actual differentiation of the trachearyelements. Key words: Tracheary element differentiation, Jerusalem artichoke (Heliantlus tuberosus), Benzyladenine, Gibberellic acid, Abscisic acid     

Selection for abdominal tergite pigmentation and correlated responses in the trident: a case study in Drosophila melanogaster

In Drosophila melanogaster, abdominal tergite pigmentation and the appearance of a trident‐shaped thoracic pattern exhibit similar biogeographical variation and sensitivity to temperature. These pigmentation traits may be under common selection pressure in natural populations or may be genetically correlated. To investigate the nature of this interaction, replicated populations of D. melanogaster were selected for increased or decreased melanization of the abdominal tergites for 40 generations. Selection for abdominal tergite pigmentation leads to correlated changes in trident formation. Although selection was performed only on female flies, male pigmentation also responded to selection. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 287–294.     

Structure and Organization of the Vascular System in the Rhizome of Drynarioid Ferns

Form and structure of the vascular cylinder of the rhizome of14 species belonging to six genera of drynarioid ferns are described.The study reveals that drynarioid ferns fall into two categories:the Drynaria group (Drynaria, Photinopteris), which is probablythe more primitive, exhibits the alternate two-ranked leaf arrangementand this could have led through suppression to the one-rankedcondition occurring in the Aglaomorpha group (Aglaomorpha, Drynariopsis,Pseudodrynaria, Merinthosorus, Thayeria). It seems that rhizomemorphology provides characters which help to separate differentspecies into the two distinct groups and indicates some phylogenetictrends. The most characteristic feature of the rhizome of drynarioidfern is seen in Thayeria, where some of the leaves on the dorsalsurface of the rhizome are dormant and some of them developon a prominent short, stout phyllopodium. Pteridophyta, Polypodiaceae, rhizome, vascular system, drynarioid ferns