关键词： 系统发育树   熵   基于序列互信息的距离   线粒体完全基因组   比对   距离矩阵   邻位相连方法  

摘要： 本文系统地提出了一种用于完全基因组上基于序列互信息的距离在构建脊椎动物进化史中的应用。传统的序列距离要求进行序列比对，而在整个基因进化史中，诸如重排列的事件破坏了全长比对。并且，目前还没有用于完全基因组进化研究的统计模型。因此，现有的工具和方法诸如多重序列比对和各种序列进化模式不能直接应用于完全基因组上。当前，一些用于完全基因组的不需序列比对的距离已被发展起来，并用于物种进化的分析。在本文中，我们提出了一种新的基于序列互信息的距离。该距离不需要序列比对，并且是基于完全基因组上DNA序列或蛋白质序列的组分向量的。本论文中，我们首先利用互信息定义了一距离，并从数学上给出了严格证明。接着，通过使用完全线粒体基因组，我们将该距离应用于分析64种脊椎动物在进化上的关系，得到了这些物种的系统发育树。该树显示这些线粒体基因组被区分成三个主要的群组。其中，一个群组对应于哺乳类，一个群组对应于鱼类，另外一个群组对应于古生物类(包括鸟类和爬行类)。基于我们新的距离建立的树的拓扑结构与当前广泛认同的脊椎动物的系统发育树是吻合的。

关键词： canopy   fibre content   grass structure   grazing   nitrogen   phosphorus  

摘要： The tree-grass interactions of African savannas are mainly determined by varying rainfall patterns and soil fertility. Large savanna trees are known to modify soil nutrient conditions, but whether this has an impact on the quality of herbaceous vegetation is unclear. However, if this were the case, then the removal of trees might also affect the structure and quality of the grass layer. We studied the impact of large nitrogen- and non-nitrogen fixing trees on the sub-canopy (SC)rass layer in low- and high-rainfall areas of differing soil fertility in eastern and southern Africa. We compared the structure and nutrient levels of SC grasses with those outside the canopy. Grass leaf nitrogen and phosphorus contents beneath tree canopies were elevated at all study sites and were up to 25% higher than those outside the canopy in the site of lowest rainfall and soil fertility. Grass leaf fibre and organic matter (ONI) contents were slightly enhanced beneath tree canopies. At the site of highest rainfall and soil fertility, grasses beneath the canopy had significantly lower ratios of stem:leaf biomass and dead:living leaf material. Grass species composition differed significantly, with the highly nutritious Panicum spp. being most abundant underneath tree crowns. In the two drier study sites, soil nitrogen and OM contents were enhanced by 30% beneath trees. N-fixation capacity of trees did not contribute to the improved quality of grass under the canopy. We conclude that trees improve grass quality, especially in dry savannas. In otherwise nutrient-poor savanna grasslands, the greater abundance of high-quality grass species with higher contents of N and P and favourable grass structure beneath trees could attract grazing ungulates. As these benefits may be lost with tree clearance, trees should be protected in low fertility savannas and their benefits for grazing wildlife recognised in conservation strategies. (c) 2007 Rubel Foundation, ETH Zurich. Published by Elsevier Gmb

关键词： defensive traits   herbivory   leafminers   trichomes  

摘要： Variations in defensive and some other leaf traits were studied in a population of an oak species, Quercus dentata Thunberg, in northern Japan, with reference to attacks by ectophagous herbivores and leafminers. The oak population showed substantial individual variations in concentrations of total phenolics and condensed tannins, nitrogen content, trichome density, leaf area and budburst timing. With the exception of leaf mass per area, which showed a positive relation with leaf toughness and a negative relation with water content, no significant relation was observed between the plant traits studied, suggesting an absence of trade-off or linkage between them. The oaks also showed substantial individual variations in leaf area loss by ectophagous herbivores, densities of major leafminers (Phyllonorycter and Stigmella species) and survival of Phyllonorycter sap-feeding larvae. The density of trichomes showed a significant, negative relation with leaf area loss by ectophagous herbivores, but significant, positive relations with densities of some leafminers. The other leaf traits seldom showed significant relations with herbivore densities or survival. In this oak population, these traits may not have enough variations to be reflected in the abundance and performance of herbivores.

关键词： diversity skewness   tree balance   community structure   primates   phylogeny  

摘要： Life on Earth is characterized by strong diversity skewness: related lineages typically show pronounced variation in diversification success, and clades contain hyperdiverse and depauperate subclades. Previous studies have documented diversity skewness only for entire ( global) clades. We demonstrate methods for measurement and significance testing of diversity skewness of local assemblages and regional biotas;we illustrate this with an analysis of geographic structure in diversity skewness of primate assemblages. For primates, continental faunas differ in diversity skewness from expectations based on the global phylogeny: South American faunas have significantly low skewness and African faunas have significantly high skewness. However, no local assemblage has diversity skewness different from that expected based on sampling the continental fauna. We also document a latitudinal gradient in diversity skewness for the African assemblages and test for ( but do not find) associations of skewness with longitude, local species richness, and net primary productivity. Our data suggest that continental-scale biogeographic events rather than local-scale processes have shaped diversity skewness in modern primate faunas.

关键词： cattle   grazing ecosystems   grassland   impala   inorganic nitrogen   nutrient cycling   non-equilibrium rangelands   phosphorous   wildlife management  

摘要： Large herbivores can both positively and negatively affect primary productivity and rates of nutrient cycling in different ecosystems. Positive effects of grazers in grasslands have been attributed to migratory behavior of the dominant ungulate species and soil fertility. We studied the effects of grazers on aboveground net primary productivity (ANPP) and N cycling on central Kenyan rangeland characterized by intense, chronic grazing by a mixed community of cattle and resident native ungulates. Exclosure studies conducted at high and low levels of soil fertility showed that both soil fertility and annual rainfall patterns mediate the effects of grazers on ANPP and N cycling. In a low-rainfall year with short (1 month) growing seasons, grazers reduced aboveground productivity regardless of soil nutrient availability. However, in a high-rainfall year with a 5-month growing season, grazers increased ANPP on nutrient-rich glades and suppressed ANPP on nutrient-poor bushland sites. Concomitant studies of grazer effects on N cycling revealed complex interactions with the seasonal pattern of N-mineralization and inorganic N availability. Grazers increased the size of the inorganic N pool available to plants at the onset of the growing season, particularly in nutrient-rich glades. However, grazers also decreased N mineralization rates at all sites early in the growing season. Measures of N availability via ion-exchange resin bags suggested that the combined effects of grazers on inorganic N pool fluctuations and N-mineralization rates resulted in a net increase in N availability at glade sites and a net decrease in N availability at bushland sites. The net effect of grazers on soil N availability mirrored grazer effects on ANPP in the high-rainfall year. Overall, our results suggest that grazer effects on N dynamics are closely linked to effects on productivity and resilience to drought. Furthermore, even under optimal conditions of high soil fertility and above-average rai

关键词： Acacia   Balanites   eland   giraffe   spines   thorns   wildlife ranching  

摘要： Some plants respond to browsing with compensatory regrowth of plant tissues and with increased thorn growth. Associations between browsers and their preferred forage were examined through wandering quarter vegetation sampling and observational studies in an effort to understand how some plants respond to browsing by large African herbivores. Acacia seyal (n = 2680) A. drepanolobium (n = 1850), and Balanites glabra (n = 960) were three species of frequently browsed indigenous plants examined on Game Ranching Ltd. in Kenya. There were several statistically significant associations revealed. Individual A. seyal exposed to intensive browser utilization were observed to lose shoot tips, produce long thorns, and have relatively few flowers and fruits. Browser utilization was associated with increased lateral branching in A. drepanolobium and with an increased occurrence of short, thickened spines in B. glabra. Thorns, spines and flowers were measurable indicators of relative browser utilization, and may be useful features to monitor in the management of large African mammals and their prickly forage.

关键词： BOOKS   REVIEWS  

摘要： Reviews the book “Savanna Animals: Fun Facts and Stuff to Do,” by .

关键词： 呼吸道合胞病毒   树鼩   动物模型  

摘要： 探讨用灵长类动物树鼩建立呼吸道合胞病毒（RSV）感染动物模型的可行性。28只树鼩随机分为7组，每组4只，鼻内滴入10^6PFU RSV，感染后每24h检测1组：另取7只树购鼻内滴入100μl Hep-2细胞培养液，滴鼻后每24h检测1只作对照：无菌取树鼩肺组织进行病毒分离、空斑形成实验检测病毒滴度、病理检查和RT-PCR检测肺组织内RSV mRNA表达：结果显示：树鼩感染RSV后，无明显呼吸道感染症状；树鼩肺组织匀浆接种于Hep-2细胞上，第3、4、5实验组出现细胞病变效应（CPE）；树鼩感染RSV后肺部病理改变在3～7d较为明显，主要为间质改变；在10^6 PFU感染浓度下树鼩肺组织内RSV处于低水平复制，复制的高峰期在3～5d，峰值在第4d。提示：树鼩可以用来建立RSV感染的动物模型。

关键词： Anura   Environment   Trematode Infections  

摘要： The emergence or increased prevalence of various parasites may be linked to alterations in host-parasite interactions caused by environmental changes. We investigated prevalence of trematode infections in grey tree frog (Hyla versicolor) tadpoles from ponds in nonagricultural settings versus ponds adjacent to cornfields in southern Ontario. We found that agricultural activity was a significant factor in determining the percentage of tadpoles infected by 1 or more trematodes from 1 or more species (combined trematode infection). However, we found no associations between combined trematode infection and forest cover;pond size;road density;and measures of water quality, such as nitrate level and the presence of the herbicide atrazine. Although combined trematode prevalence was associated only with agricultural activity, prevalence of Alaria species showed a positive association with forest cover. This latter result probably reflects the importance of habitat suitability for the canid definitive hosts of this trematode species.

关键词： Africa   indirect effects   large herbivore   Saccostomus mearnsi   small mammal   snake   Psammophis mossambicus  

摘要： Many large mammal species are declining in African savannas, yet we understand relatively little about how these declines influence other species. Previous studies have shown that the removal of large herbivorous mammals from large-scale, replicated experimental plots results in a dramatic increase in the density of small mammals, an increase that has been attributed to the relaxation of competition between rodents and large herbivores for food resources. To assess whether the removal of large herbivores also influenced a predator of small mammals, we measured the abundance of the locally common olive hissing snake, Psamniophis mossainbicus, over a 19-mo period in plots with and without large herbivores. Psammophis mossambicus was significantly more abundant in plots where large herbivores were removed and rodent numbers were high. Based on results from raptor surveys and measurements of vegetative cover, differences in snake density do not appear to be driven by differences in rates of predation on snakes. Instead, snakes appear to be responding numerically to greater abundances of small-mammal prey in areas from which large herbivores have been excluded. This is the first empirical demonstration of the indirect effects of large herbivores on snake abundance and presents an interesting example of how the influence of dominant and keystone species can move through a food web.