Morphological and physiological correlates of niche breadth in two species of Espeletia (Compositae) in the Venezuelan Andes

Summary We compared adaptive strategies in two plants of Venezuelan páramos (alpine areas): the widely distributed, caulescent, and pubescent Espeletia schultzii Wedd. with the acaulescent, nearly glabrous E. atropurpurea A.C. Smith which is restricted to mesic sites just above treeline. Both species occur together at 3,450 m, near treeline.Physiologically, E. schultzii was more drought resistant than E. atropurpurea, and was better adapted for carbon dioxide fixation under low temperatures. The densely pubescent leaves of E. schultzii are highly reflective; this increases the intensity of light needed for photosynthetic saturation and influences leaf temperature. Leaf pubescence may reduce the level of insect predation.Measurements of leaf productivity indicate higher values for E. atropurpurea during the rainy season and higher values for E. schultzii during the dry season. However, annual values of leaf productivity are similar for both species.Benefits of specialization in E. atropurpurea include reduced costs for stem and leaf hair production, higher growth rates during the rainy season and the ability to grow beneath canopies of some larger arborescent species. Costs of specialization include lower growth rates during the dry season, great susceptibility to insect predation and restriction to low elevation, mesic sites.     

Interspecific interactions among species of the coral genus Porites from Okinawa, Japan

Analysis of field established xenogeneic interactions among five Porites species from Sesoko Island, Okinawa, revealed a transitive type of hierarchy as: P. rus > P. cylindrica > P. lobata > P. australiensis> P. lutea. Out of the 111 interspecific encounters studied, in only 5.4% reciprocal interactions were recorded, and in a single case, the opposite directionality of hierarchy was documented. Allogeneic encounters were also observed. A single major effector mechanism, an overgrowth (together with secondary outcomes such as the formation of small points of rejection, bleaching and pink color formation along a narrow peripheral belt of contacting tissues), was the only response in all 10 xenogeneic and 5 allogeneic combinations. In some massive colonies, a long contacting line of up to 50 cm was established. No sign for allelopathy, stand-off or rejection from a distance (i.e., by sweeper tentacles, sweeper polyps) was observed. Results are discussed with the accumulated data on Porites species from different reefs, worldwide, confirming that this genus is commonly lower in the hierarchy of xenogeneic interactions.     

甘肃宝积山盆地中侏罗世植物群地质时代及植物区系探讨

本文对甘肃宝积山盆地中侏罗世植物群地质时代及植物区系进行了探讨,共统计植物大化石18属53种,主要包括银杏纲10属24种,真蕨纲5属22种,苏铁纲1属3种,松柏纲1属2种,楔叶纲1属2种。该植物群在组成特征上表现为银杏类、真蕨类植物繁盛,其他植物类群相对贫乏。基于该植物群特征与国内其他植物群的对比,提出其地质时代为中侏罗世Aalenian期–Bajocian期。通过哈曼、欧式距离、罗杰斯–塔尼莫特和索卡尔–施尼斯4种方法对宝积山盆地及中国北方其余11个中侏罗世植物群进行系统聚类分析,在此基础上进一步划分了中国北方植物区系。通过计算属、种相似性系数,探讨宝积山邻近植物区系间的亲缘关系,结果表明宝积山植物区系与同属西北地区的华亭植物区系关系较为亲近。     

Remote sensing of larch phenological cycle and analysis of relationships with climate in the Alpine region

This research aims at developing a remote sensing technique for monitoring the interannual variability of the European larch phenological cycle in the Alpine region of Aosta Valley (Northern Italy) and to evaluate its relationships with climatic factors. Phenological field observations were conducted in eight test sites from 2005 to 2007 to determine the dates of completion of different phenological phases. MODerate Resolution Imaging Spectrometer (MODIS) 250 m 16‐days normalized difference vegetation index (NDVI) time series were fitted with double logistic curves and the dates corresponding to different features of the curves were determined. Comparison with field data showed that the features of the fitted NDVI curve that allowed the best estimate of the start and end of the growing season were the zeroes of its third derivative (MAE of 6 and 4 days, respectively). The start and end of season were also estimated with the spring warming (SW) and growing season index (GSI) phenological models. MODIS start and end of season dates generally agreed with those obtained by the SW and GSI climate‐driven phenological models. However, phenological models provided erroneous results when applied in years with anomalous meteorological conditions. The relationships between interannual variability of the larch phenological cycle and climate were investigated by comparing the mean start and end of season yearly anomalies with air temperature anomalies. A strong linear relationship (R²=0.91) was found between mean spring temperatures and mean start of season dates, with an increase of 1 °C in mean spring temperature leading to a 7‐day anticipation of mean larch bud‐burst date. Leaf coloring dates were found to be best related with mean September temperature (R²=0.77), but with higher spring temperatures appearing to lead to earlier leaf coloring.     

Strontium isotopes in Melanopsis sp. as indicators of variation in hydrology and climate in the Upper Jordan Valley during the Early-Middle Pleistocene, and wider implications

Aquifers dominated by Pleistocene basalts and Jurassic to Cretaceous calcareous rocks feed the Hula basin which is drained by the Jordan River into Lake Kinneret. The sedimentary sequence of Lower-Middle Pleistocene Benot Ya‘akov Formation (BYF) exposed by excavations of the 0.78 Ma lake-side site of Gesher Benot Ya‘aqov (GBY) consists of six cycles representing ca. 100 ka history of the Hula basin. This study characterizes the types of water sources in the catchment, tests the use of the Strontium (Sr) isotopes in the common extant snail Melanopsis sp. as a tracer for water in its habitat, and uses this tracer in the fossil specimens from GBY to investigate the palaeohydrology of the Hula paleolake during the corresponding period.The Sr isotope composition (⁸⁷Sr/⁸⁶Sr) of extant Melanopsis shells in the Hula catchment range widely (0.7046-0.7079). These analyses define distinct groups of water sources and aquifers, while the Jordan River at the GBY site has values around 0.70685. The values for fossil Melanopsis from GBY vary along stratigraphy; they are highest around 0.70710 in Cycles 1 and 2, decrease to around 0.70685 in Cycle 3, and exhibit upward trending fluctuations in the subsequent cycles to 0.70703 in Cycle 6. This trend reveals the dominance of the Hermon Jurassic aquifer during the earlier, colder periods before the Matuyama-Brunhes Boundary (MBB) and enhanced influence of the Golan basaltic aquifers, in subsequent warmer periods, indicating that the MBB coincides with climate warming as supported by other indicators. Hence, this global geochronological indicator of 0.78 Ma is also potentially a global palaeoclimatic marker. The similarity between the Sr isotope composition of the Jordan River waters and Melanopsis and those from Cycle 3 suggests that the current climate corresponds to that of the warmest period within the record of GBY, clarifying the comparative interpretation of this 100 k.yr. climate record.     

Non-local interactions between light induced processes inCalliphora photoreceptors

Summary The prolonged depolarizing afterpotential (PDA) is a phenomenon which is tightly linked to visual pigment conversion. In order to determine whether processes underlying PDA induction and depression can spread in space, the PDA was recorded intracellularly in white-eyedCalliphora R1-6 photoreceptors and used to examine interactions between processes induced by activating statistically different photopigment molecules (Figs. 3–6). It was found that a PDA induced by converting some fraction of rhodopsin (R) molecules forward into the metarhodopsin (M) state can be completely depressed by equal or smaller amounts of pigment conversion, backward from metarhodopsin to rhodopsin even when largely different sets of pigment molecules were shifted in the respective directions, in agreement with previous experiments conducted on the barnacle. The characteristics of the afterpotentials obtained following the cessation of strong blue and green light stimuli which did not cause a net pigment conversion was examined (Figs. 7, 8). It was found that these afterpotentials, obtained when nonet R to M conversion took place, could not be depressed by an opposite net large M to R pigment conversion. Accordingly we propose to restrict the term PDA to an afterpotential which can be depressed by a net M to R pigment conversion. It is concluded: (a) that some processes underlying PDA induction and depression inCalliphora must interact at a distance which extends at least to the nearest neighboring pigment molecule, and (b) that inCalliphora photoreceptors net pigment conversion is required in order to induce and depress a PDA.Abbreviations R rhodopsin - M metarhodopsin - R to M rhodopsin to metarhodopsin pigment conversion - M to R metarhodopsin to rhodopsin pigment conversion - PDA prolonged depolarizing afterpotential - ERG electroretinogram - M potential metarhodopsin potential - ERP early receptor potential