Phylogeny of pholcid spiders (Araneae: Pholcidae): combined analysis using morphology and molecules

The spider family Pholcidae comprises a large number of mainly tropical, web-weaving spiders, and is among the most diverse and dominant spider groups in the world. The phylogeny of this family has so far been investigated exclusively using morphological data. Here, we present the first molecular data for the family analyzed in a phylogenetic context. Four different gene regions (12S rRNA, 16S rRNA, cytochrome c oxidase subunit I, 28S rRNA) and 45 morphological characters were scored for 31 pholcid and three outgroup taxa. The data were analyzed both for individual genes, combined molecular data, and molecular plus morphological data, using parsimony, maximum likelihood, and Bayesian methods. Some of the phylogenetic hypotheses obtained previously using morphology alone were also supported by our results, like the monophyly of pholcines and of the New World clade. On the other hand, some of the previous hypotheses could be discarded with some confidence (monophyly of holocnemines, the position of Priscula), and still others need further investigation (the position of holocnemines, ninetines, and Metagonia). The data obtained provide an excellent basis for future investigations of phylogenetic patterns both within the family and among spider families.     

长白山自然保护区阔叶红松林林隙干扰状况的研究

 本文研究了长白山自然保护区阔叶红松林林隙干扰的基本规律,得到了描述林隙干扰状况的一些重要参数。结果表明扩展林隙在阔叶红松林中所占的面积比例是27.36％,而实际林隙所占的面积比例为13.05％,林隙干扰的频率每年约为0.15％;林隙的分布格局是均匀式的。形成林隙最重要的方式是掘根风倒,其次为干基折断;大多数的林隙都是由1～4株形成木形成的,林隙形成木主要是由红松、水曲柳、蒙古栎和紫椴组成;阔叶红松林的主林层乔木在直径为40～60cm和高度为25～30m时,形成林隙的可能性最大。     

Comparative locomotor ecology of gibbons and macaques: Selection of canopy elements for crossing gaps

To examine functional questions of arboreal locomotor ecology, the selection of canopy elements by Bornean agile gibbons (Hylobates agilis) and long-tailed macaques (Macaca fascicularis) was contrasted, and related to locomotor behaviors. The two species, and in some cases, the macaque sexes, varied in their use of most structural elements. Although both species traveled most frequently in the main canopy layer (macaques: 56%, gibbons: 48%), the gibbons strongly preferred the emergent canopy layer and traveled higher than the macaques (31 vs. 23 m above ground) in larger trees (48 vs. 26 cm dbh). Macaques preferred to cross narrower gaps (50% were in the class 0.1–0.5 m wide) than gibbons (42% were 1.6–3.0 m wide), consistent with the maximum gap width each crossed (3.5 m for macaques, 9 m for gibbons). Macaques could cross only 12% of the gaps encountered in the main canopy, and < 5% of the gaps in each of the other four layers. In contrast, all layers appear relatively continuous for gibbons. Specialized locomotor modes were used disproportionately at the beginning and end of travel segments, further indicating that behavior was organized around gap crossings. A model is defined, the Perceived Continuity Index (PCI), which predicts the relative use of canopy strata for each species, based on the percentage of gaps a species can cross, the frequency of gaps, and median length of continuous canopy structure in each canopy layer. The results support the hypothesis that locomotor behaviors, and strategies of selecting canopy strata for travel, are strongly constrained by wide gaps between trees and are ultimately based on selection for efficient direct line travel between distant points. © 1994 Wiley-Liss, Inc.     

Effects of microsite disturbances and herbivory on seedling performance in the perennial herb <Emphasis Type="Italic">Helleborus foetidus</Emphasis> (Ranunculaceae)

The impact of small scale disturbances on the early seedling performance components of Helleborus foetidus (Ranunculaceae) was studied through a transplant experiment. The aims of this study were: (i) to determine if the herbivory pattern depends on microsite disturbance, by the analysis of two of its components, seedling encounter (the probability of at least one seedling being harmed) and seedling exploitation (the proportion of seedling tissue removed once encountered); (ii) to test if seedlings of H. foetidus in disturbed microsites will survive in a greater proportion than seedlings in undisturbed microsites; (iii) to investigate if seedling survival is correlated with the degree of herbivory. Microsite disturbances had a large effect on the herbivory pattern. Seedlings growing in undisturbed vegetation had a 2-fold higher likelihood of being grazed and suffered 1.38-fold higher damage than those growing in disturbed plots. At the end of this experiment, after fourteen months, only 10.4% of the seedlings transplanted were still alive due to seedling desiccation, but no differences on seedling survival were found between disturbed and undisturbed plots. The effect of herbivory and the interactive effect of herbivory and disturbance on seedling survival only reached statistical significance dependent upon site. We concluded that although small scale disturbances had a large impact on herbivory patterns; they had only a minor role in the early seedling survival of H. foetidus. Only locally, small scale disturbances showed an effect on seedling survival through herbivory. Abiotic factors like summer drought and spatial variations determined the early survival of H. foetidus seedlings to a major extent.     

Tree regeneration responses in a lowland Nothofagus-dominated forest after bamboo dieback in South-Central Chile

The bamboo Chusquea quila (Poaceae:Bambuseae) is the most abundant understory species ofNothofagus-dominated forests at low elevations inthe Chilean Lake District. Species of this genus strongly inhibit theestablishment and growth of tree species, especially those of the genusNothofagus. At intervals of many years, this bambooflowerssynchronously and dies, creating large-scale disturbances. The mainobjective of this study was to determine the influence of bamboo dieback ontreeregeneration, especially of shade-intolerant species. The forest studiedis a remnant stand of old-growth forest dominated by emergent individualsof N. obliqua and Eucryphiacordifoliawhich project about 10 m above a main canopy formed byAextoxicon punctatum, Laureliaphilippiana, and Podocarpus saligna. Treeseedlings that established prior to bamboo dieback were recorded in six gapsdensely covered by bamboo. After the dieback event in the early 1990's,recruitment, height growth and survivorship were monitored in four gaps duringtwo growing seasons. After the synchronous mass flowering and death ofChusqueaquila, both reorganization of advance regeneration and new seedlingrecruitment were observed in gaps. The advance regeneration consisted mainly ofthe shade-tolerant species A. punctatum,L. philippiana, and Amomyrtus luma.These species together with E. cordifolia accounted forover 90% of the total individuals in gaps. During the following twoseasons, c. 40% of the advance regeneration either died or was damaged.Root suckers of E. cordifolia and L.philippiana were taller and grew faster than the seedlings of otherspecies. Nothofagus obliqua was unable to establishadvanceregeneration in gaps formerly dominated by bamboo. New recruitment resulted inthe synchronized establishment of treeseedlings, especially less shade-tolerant species such as N.obliqua, Aristotelia chilensis,Rhaphithamnus spinosus, and E.cordifolia. These species recruited into the gaps almost entirelyduring the first season right after the bamboo dieback. However, by the end ofthe second season, these species had a lower density due to a combination oflower recruitment rate, shortened recruitment period, and greater mortalityratecompared to the shade-tolerant species. New bamboo seedlings grew fasterand were more abundant than tree seedlings, except for root suckers (bothnew establishment and advance regeneration) of E.cordifolia which is more likely to successfully recruit into thecanopy. Seedlings of N. obliqua compete poorly with bambooseedlings; its successful recruitment may require bamboo flowering coincidentwith a mast seed year for the tree species.     

A method for detecting distant evolutionary relationships between protein or nucleic acid sequences in the presence of deletions or insertions

Summary A method for detecting homology between two protein or nucleic acid sequences which require insertions or deletions for optimum alignment has been devised for use with a computer. Sequences are assessed for possible relationship by Monte Carlo methods involving comparisons between the alignment of the real sequences and alignments of randomly scrambled sequences of the Same composition as the real sequences, each alignment having the optimum number of gaps. As each gap is successively introduced into a comparison (real or random) a maximum score is determined from the similarity of the aligned residues. From the distribution of the maximum alignment scores of randomly scrambled sequences having the same number of gaps, the percentage of random comparisons having higher scores is determined, and the smallest of these percentage levels for each pair of sequences (real or random) indicates the optimum alignment. The fraction of the comparisons of random sequences having percentage levels at their optimum alignment below that of the real sequence comparison at its optimum estimates the probability that such an alignment might have arisen by chance. Related sequences are detected since their optimum alignment score, by virtue of a contribution from ancestral homology in addition to optimised random considerations, occupies a more extreme position in the appropriate frequency distribution of scores than do the majority of optimum scores of randomly scrambled sequences in their appropriate distributions.Application of this optimum match method of sequence comparison shows that the sensitivity of the maximum match method of Needleman and Wunsch (1970) decreases quite dramatically with sequence comparisons which require only a few gaps for a reasonable alignment, or when sequences differ greatly in length. The maximum match method as applied by Barker and Dayhoff (1972) has the additional disadvantage that deletions which have occurred in the longer of two homologous protein sequences further decrease the sensitivity of detection of relationship. The constrained match method of Sankoff and Cedergren (1973) is seen to be misleading since large increments in the alignment score from added gaps do not necessarily result in a high total alignment score required to demonstrate sequence homology.     

Effects of flood-influenced factors on seed germination of Ambrosia tenuifolia

Strong fluctuations are exhibited by populations of the perennial herb Ambrosia tenuifolia in the grasslands of the Salado basin (Province of Buenos Aires, Argentina), an area frequently enduring prolonged floods. Flooding causes the death of most dicotyledon plants of the community, A. tenuifolia among them, opening numerous gaps of various sizes. After the recession of the flood the density of A. tenuifolia seedlings was higher in flooded than in non-flooded plots and it was larger in wider gaps. Canopy removal in non-flooded plots increased field seedling emergence of A. tenuifolia up to the levels found in flooded plots. Responses of the seeds in the soil to gap-associated environmental factors such as light quality and temperature regime were studied both in the field and under controlled were studied both in the field and under controlled conditions. Seedling emergence was significantly enhanced when the red:far-red ratio of natural light reaching the soil surface under the canopy of nonflooded plots was increased by means of copper sulfate filters. The influence of light quality and temperature on germination of the soil seed population was also tested using grassland soil monoliths or mesocosms, transported from the field to the laboratory, in which the canopy was clipped and the soil exposed to either red or far-red light and kept at constant or fluctuating temperatures. Significant seedling emergence was observed only when the soil samples were exposed to red light and incubated at alternating temperatures. No emergence was recorded in samples exposed to far-red light or incubated at a constant 25°C. Seeds stored dry in the laboratory were also stimulated to germinate by red light and alternating temperatures but only after dormancy was sufficiently decreased by low temperature stratification or by low temperature under immersion. The results are consistent with the hypothesis that primary dormancy of A. tenuifolia seeds is decreased by low temperatures in winter even if the seeds are submerged as happens when floods occur. The decrease in dormancy makes the seeds prone to be stimulated to germinate by the Pfr form of phytochrome in combination with alternating temperatures. These conditions are likely to be met in the gaps opened by the flood-caused death of dicotyledon plants.