斜纹夜蛾幼虫造血器官的形态、组织及超微结构

斜纹夜蛾Spodoptera litura Fabricius幼虫的造血器官位于翅芽部位,由发育层次不同的许多细胞岛和一些单个或成串的梭形细胞组成.各细胞岛或细胞均裹有一层非细胞性膜鞘.环绕同一翅芽的众多细胞岛和细胞相互间由其膜鞘连结成簇.膜鞘紧裹着的单个或成串梭形细胞具未分化细胞特征.发育初期的单个细胞岛体积较小,直径约20—45μm以下,岛内均为排列紧密的分化中未成形原血细胞.较发育的细胞岛体积较大,细胞间排列较松,岛内除原血细胞外,还出现少量浆血细胞、颗粒细胞和小球细胞的分化.此外,还发现一个具颗粒细胞和小球细胞特征的混合细胞类型.发育初期的细胞岛膜鞘表面结构完好.随着岛内细胞的增殖分化,膜鞘出现破裂,且破裂逐渐增大,以致完全破裂而裸露岛内细胞团,以此释放血细胞.大量血细胞释放出现于幼虫预备脱皮至下一龄幼虫初期的造血器官.各龄幼虫的各发育阶段血淋巴血细胞总数(THC)的变动与造血器官释放血细胞密切相关.     

Hydraulic failure and tree dieback are associated with high wood density in a temperate forest under extreme drought

Catastrophic hydraulic failure will likely be an important mechanism contributing to large‐scale tree dieback caused by increased frequency and intensity of droughts under global climate change. To compare the susceptibility of 22 temperate deciduous tree and shrub species to hydraulic failure during a record drought in the southeastern USA, we quantified leaf desiccation, native embolism, wood density, stomatal conductance and predawn and midday leaf water potential at four sites with varying drought intensities. At the two driest sites, there was widespread leaf wilting and desiccation, and most species exhibited predawn leaf water potentials of ≤3 MPa and >60% loss of xylem conductivity in branches. Although species with high wood density were more resistant to cavitation, they had higher levels of native embolism and greater canopy dieback than species with low wood density. This unexpected result can be explained by the failure of species with dense wood to avert a decline in water potential to dangerous levels during the drought. Leaf water potential was negatively correlated with wood density, and the relationship was strongest under conditions of severe water deficit. Species with low wood density avoided catastrophic embolism by relying on an avoidance strategy that involves partial drought deciduousness, higher sensitivity of stomata to leaf water potential and perhaps greater rooting depth. These species therefore maintained water potential at levels that ensured a greater margin of safety against embolism. These differences among species may mediate rapid shifts in species composition of temperate forests if droughts intensify due to climate change.     

Impact of simulated drought on ecosystem biomass production: an experimental test in stream mesocosms

Climate models predict widespread shifts in precipitation patterns and increases in the frequency of extreme events such as droughts, but consequences for key processes in affected ecosystems remains poorly understood. A 2‐year manipulative experiment used a series of stream mesocosms to test the effect of recurrent drought disturbance on the composition and secondary production of macroinvertebrate consumer assemblages and functional groups. On average, secondary production in drought‐disturbed communities (mean 4.5 g m^?2 yr^?1) was less than half of that that in controls (mean 10.4 g m^?2 yr^?1). The effects of the drought differed among functional feeding groups, with substantial declines for detritivore shredders (by 69%) and engulfing predators (by 94%). Contrasting responses were evident among taxa within most functional feeding groups, ranging from extirpation to irruptions in the case of several small midge larvae, but production of most species was suppressed. Taxon‐specific responses were related to body mass and voltinism. The ratio of production to biomass (community P/B) increased under drought, reflecting a shift in production from large long‐lived taxa to smaller taxa with faster life cycles. This research provides some of the first experimental evidence of the profound effects that droughts can have on both the structure and functioning of aquatic ecosystems.     

Population biology of swift (Apus apus) ectoparasites in relation to host reproductive success

Abstract.

• 1 We censused ectoparasite populations of adult and nestling swifts over the course of the host's breeding season. Nearly all of the birds were infested with chewing lice and two-thirds of the nests were infested with louse flies. Feather mites were observed but not quantified.
• 2 Lice and louse flies both showed aggregated distributions among hosts. Louse eggs, hatched lice and adult louse flies had negative binomial distributions, whereas the aggregated distribution of louse fly pupae was not adequately described by negative binomial or Poisson models.
• 3 Transmission of lice from parents to offspring was documented. A comparison of the age structure of lice on parents and offspring indicated that most transmission was by nymphal lice.
• 4 Host reproductive success and survival appeared to be independent of the number of lice or louse flies. Neither parasite correlated with the number, body mass, or date of fledging of young birds, nor with the overwinter survival of adults. We caution, however, that experimental manipulations of parasite load are required for a definitive test of the impact of ectoparasites on evolutionary fitness components.

     

Contrasting levels of genetic diversity between the historically rare orchid Cypripedium japonicum and the historically common orchid Cypripedium macranthos in South Korea

Many terrestrial orchids are historically rare and occur in small, spatially isolated populations. Theory predicts that such species will harbour low levels of genetic variation within populations and will exhibit a high degree of population genetic divergence, primarily as a result of genetic drift. If the origin of the present‐day populations is relatively recent from the same genetically depauperate source population, a complete lack of genetic differentiation between conspecific populations is expected. If a terrestrial orchid was historically common with moderate or high levels of genetic diversity, but has experienced more recent anthropogenic disturbance as a result of over‐collection, it would still exhibit initial levels of genetic variation within populations and a low degree of genetic divergence between populations. To test these predictions, we examined the genetic diversity in six populations (N = 131) of the historically and currently rare Cypripedium japonicum and in four populations (N = 94) of the historically common but now rare C. macranthos from South Korea. Fourteen putative allozyme loci resolved from eight enzyme systems revealed no variation either within or among populations of C. japonicum, which supports the first prediction. In contrast, populations of C. macranthos harboured high levels of genetic variation (mean percentage of polymorphic loci %P = 46.7; mean expected heterozygosity H_e = 0.185) and exhibited a low degree of population genetic divergence (G_ST = 0.059), supporting the second prediction. The lack of genetic variation both within and among conspecific populations of C. japonicum may suggest that populations originated from the same genetically depauperate ancestral population. The high levels of genetic diversity maintained in populations of C. macranthos suggest that the collection‐mediated decrease in the number of individuals is still too recent for long‐term effects on genetic variation. Based on current demographic and genetic data, in situ and ex situ conservation strategies should be provided to preserve genetic variation and to ensure the long‐term survival of the two species in the Korean Peninsula. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 119–129.     

Effects of phenolic substances on metabolism of exogenous indole-3-acetic acid in maize stems

Four-day-old stem segments of Zea mays L. cv. Seneca 60 were treated sequentially with phenolic substances and indole-3-acetic [2-¹⁴C] acid ([2-¹⁴C]IAA). Formation of bound IAA was rapid, but a pretreatment with p-coumaric acid, ferulic acid or 4-methylumbelliferone decreased the level of bound IAA. The decrease is not likely related to the effect of the phenolics on enzymic oxidation of IAA, since the level of free IAA was not limiting and the activity of ferulic acid in enzymic oxidation of IAA is different from that of p-coumaric acid and 4-methylum-belliferone. Apparently these compounds inhibited the formation of bound IAA and consequently caused an accumulation of free IAA. In contrast, caffeic acid, protocatechuic acid and 2,3-dihydro-2, 2-dimethyl-7-benzofuranol had little effect. After the uptake of IAA there was a slow but steady incorporation of the radioactivity into the 80% ethanol-insoluble, 1 M NaOH-soluble fraction. Phenolic substances also affected this process. The compounds which are cofactors of IAA-oxidase increased the incorporation while those which are inhibitors of IAA-oxidase decreased the incorporation. Results suggest that the phenolics also affected the enzymic oxidation of IAA in vivo in the same way as in vitro.     

Low Socioeconomic Status and Female-Biased Parental Investment: The Mukogodo Example

Hierarchies of wealth and ethnic prestige among East African herders present an opportunity to test the Trivers-Willard hypothesis that low socioeconomic status should correlate with female biases in parental investment. The Mukogodo are at the bottom of such a regional hierarchy due to their poverty and low status as former hunters. As a result of these factors, Mukogodo men have lower polygyny rates than their neighbors, and Mukogodo women have higher mean reproductive success than Mukogodo men. The data fulfill the prediction that there should be a bias in parental investment in favor of daughters. The sex ratio of the 0–4 age group and the reported sex ratio at birth are both female-biased. Although there is no evidence of infanticide, sons may be neglected in favor of daughters. Evidence from a dispensary and from a clinic run by a Catholic mission both show that the Mukogodo take daughters for treatment more often than they take sons. Also, daughters may be nursed longer than sons.     

蓖麻蚕变态期神经系统的变化及脑的胆碱酯酶活性研究

蓖麻蚕在变态期间,脑及腹神经索产生了一系列的变化。脑外部形态的显著变化是体积的增大,视叶的出现及脑与食管下神经节的愈合。由幼虫上簇开始至成虫羽化,共约19天。在此期间,脑的宽度由0.93毫米增至2.48毫米。视叶出现于幼虫上簇后第四天,即化蛹前一天;发育至化蛹后第七天,食管下神经节完全与脑愈合成环状。幼虫脑组织比较简单,视叶尚未显明分化,只是在脑的两侧前方有成团的神经细胞聚合而成的“原基”,成虫视叶组织即由这些原基分化而来。蕈体尚不完整,仅蕈体柄显明。化蛹后,视觉中枢的三个纤维区——神经节层,外髓和内髓——都已出现,中心体也清楚可见。化蛹后第九天,视叶的三个纤维区之间的交叉纤维显明地出现,其它各部分如中心体、脑桥体、腹体及嗅觉中枢都完全分化出来。脑构造的复杂化也明显表现在内部组织的分化上。 腹神经索的变化主要是缩短和神经节的合并。最显著的缩短阶段是在预蛹期,整条神经索由原来的43毫来缩短为29毫米。食管下神经节与脑愈合,腹部第一二神经节并入后胸神经节,第六、七、八神经节合并成一大型的复合神经节,这样便由原来的八个腹神经节减少了一半。胸部三个神经节则因菱形区的消失而互相靠拢。 从化蛹后第九天起至成虫羽化,除了脑的体积稍有增大以外,整个中枢神经系统基本上没有多大变化。 在整个变态期间,脑ChE的活性渐进增高,酶的水解率(微克分子Ach毫克脑/30分钟)开始时为0.078微米,最后至第十八天竟增至0.485微米,总共约增长六倍左右。     

Biomass and seed yields of big bluestem, switchgrass, and intermediate wheatgrass in response to manure and harvest timing at two topographic positions

A principle attribute of perennial grasses for biomass energy is the potential for high yields on marginal lands. Objectives of this study were to compare biomass and seed production of intermediate wheatgrass ( Thinopyrum intermedium [Host] Barkworth and D.R. Dewey), big bluestem ( Andropogon gerardii Vitman), and switchgrass ( Panicum virgatum L.) as affected by harvest timing and manure application on two topographic positions (footslope and backslope). Footslope is the hillslope position that forms the inclined surface at the base of a slope and backslope forms the steepest, middle position of the hillslope. Grasses were harvested for biomass at anthesis (summer), after a killing frost (autumn), or the following spring after overwintering in the field. Seed was harvested at maturity during 2003 and 2004. Two rates of beef cattle ( Bos taurus L.) manure (target rates of 0 and 150 kg total-N ha⁻¹) were surface applied annually. Maximum annual biomass yield ranged from 4.4 to 5.2, 2.7 to 4.2, and 3.7 to 5.6 Mg ha⁻¹ for intermediate wheatgrass, big bluestem, and switchgrass, respectively. Biomass yields were not different between fall and spring harvest treatments. Biomass yields of big bluestem and switchgrass at the backslope position were 86% and 96% of biomass yields at the footslope position with normal precipitation, respectively. Manure application increased biomass yield approximately 30% during the second year on both topographic positions. The highest seed yield was obtained from intermediate wheatgrass, followed by switchgrass and big bluestem. Utilizing these management practices in our environment, it appears that switchgrass and big bluestem could be allowed to overwinter in the field without suffering appreciable loss of biomass.