Resource competition between two fungal parasites in subterranean termites

Subterranean termites live in large groups in underground nests where the pathogenic pressure of the soil environment has led to the evolution of a complex interaction among individual and social immune mechanisms in the colonies. However, groups of termites under stress can show increased susceptibility to opportunistic parasites. In this study, an isolate of Aspergillus nomius Kurtzman, Horn & Hessltine was obtained from a collapsed termite laboratory colony. We determined that it was primarily a saprophyte and, secondarily, a facultative parasite if the termite immunity is undergoing a form of stress. This was determined by stressing individuals of the Formosan subterranean termite Coptotermes formosanus Shiraki via a co-exposure to the virulent fungal parasite Metarhizium anisopliae (Metch.) Sorokin. We also examined the dynamics of a mixed infection of A. nomius and M. anisopliae in a single termite host. The virulent parasite M. anisopliae debilitated the termite immune system, but the facultative, fast growing parasite A. nomius dominated the mixed infection process. The resource utilization strategy of A. nomius during the infection resulted in successful conidia production, while the chance for M. anisopliae to complete its life cycle was reduced. Our results also suggest that the occurrence of opportunistic parasites such as A. nomius in collapsing termite laboratory colonies is the consequence of a previous stress, not the cause of the stress.     

Unique zinc mass in mandibles separates drywood termites from other groups of termites

Previously, the presence of metals in arthropod mandibles has been linked with harder cuticle, and in termites, a 20% increase in hardness has been found for mandibles containing major quantities of zinc. The current study utilises electron microscopy and energy-dispersive X-ray microanalysis to assess incidence and abundance of metals in all extant subfamilies of the Isoptera. The basal clades contain no zinc and little to no manganese in the cutting edge of the mandible cuticle, suggesting that these states are ancestral for termites. However, experimentation with mandibles in vitro indicates the presence of some elements of the cuticular biochemistry necessary to enable uptake of zinc. The Termopsidae, Serritermitidae, Rhinotermitidae and Termitidae all contain minor quantities of manganese, while trace to minor quantities of zinc occur in all except the Serritermitidae. In contrast, all Kalotermitidae or drywood termites contain major levels of zinc in the mandible edge. Diet and life type are explored as links to metal profiles across the termites. The presence of harder mandibles in the drywood termites may be related to lack of access to free water with which to moisten wood. Scratch tests were applied to a set of mandibles. The coefficient of friction for Cryptotermes primus (Kalotermitidae) mandibles, when compared with species from other subfamilies, indicates that zinc-containing mandibles are likely to be more scratch resistant.     

The frontal gland in workers of Neotropical soldierless termites

The presence of the frontal gland is well established in termite soldiers of Rhinotermitidae, Serritermitidae, and Termitidae. It is one of their main defensive adaptations or even an exclusive weapon. The gland was also occasionally reported in alate imagoes, but never in the worker caste. Here, we report the first observation of a frontal gland in workers of several Neotropical and one African species of Apicotermitinae. The ultrastructure of Aparatermes cingulatus and Anoplotermes nr. subterraneus is described in detail. In these two species, the gland is well-developed, functional and consists of class 1 secretory cells. The presence of envelope cells, wrapping the gland, is an unusual feature, as well as the presence of several zonulae adherens, connecting neighbouring glandular cells. The frontal gland of workers is homologous to this organ in soldiers and imagoes, as evidenced by the same position in the head and its connection to the same muscle. However, the defensive role of the frontal gland in workers remains to be confirmed.     

岩溶地下河反硝化作用的有限性——一个碳酸盐岩管道的实验研究

反硝化作用是公认的去除水体中硝酸盐的路径,但相比于多孔介质,岩溶地下河中反硝化效果具有不确定性.为更好地认识岩溶地下河中反硝化效果,本研究利用天然碳酸盐岩管道几何模型,以乙醇为可利用电子供体(碳源),示踪了控制流速条件下管道流中反硝化作用,并辅以多孔介质流实验进行对比.反应示踪、地球化学印迹和微生物检测结果表明:当碳源缺乏时,反硝化作用没有明显启动的迹象;一旦补充了碳源,溶解氧、硝酸盐浓度和质量都出现了明显衰减,并且有中间产物亚硝酸盐产生,水体碱度增加.然而,即使在碳源充足情况下,管道流中反硝化强度却明显比多孔介质流中强度低,两者硝酸盐生物去除率分别为39.4%和大于99%,生物降解速率分别为0.113和10.8 mg·L~(-1)·h~(-1).推测其原因,一是碳酸盐岩管道内固体表面积与水体积比值低,固体吸着条件不利于微生物生长与发育,降低了硝酸盐去除率;二是管道富含的溶解氧可能延迟了反硝化作用启动,溶解氧降至3.0 mg·L~(-1)左右时硝酸盐浓度才有明显衰减.相比之下,其它环境因素如p H值和温度没有出现明显变化.该研究意义在于:岩溶管道流反硝化去除硝酸盐的潜能是存在的,但即使可利用碳源充足仍具有明显的局限性,这可能意味着岩溶地下河一旦遭受硝酸盐污染,其作为饮用水源的安全风险更大.     

Biodiversity below ground: probing the subterranean ant fauna of Amazonia

Ants are abundant, diverse, and ecologically dominant in tropical forests. Subterranean ants in particular are thought to have a significant environmental impact, although difficulties associated with collecting ants underground and examining their ecology and behavior have limited research. In this paper, we present the results of a study of subterranean ant diversity in Amazonian Ecuador that employs a novel probe to facilitate the discovery of species inhabiting the soil horizon. Forty-seven species of ants in 19 genera, including new and apparently rare species, were collected in probes. Approximately 19% of the species collected at different depths in the soil were unique to probe samples. Analysis of similarity (ANOSIM) results showed that the species composition of ants collected with the probe was significantly different from samples collected using other techniques. Additionally, ANOSIM computations indicated the species assemblage of ants collected 12.5 cm below the surface was significantly different from those found at 25, 37.5, and 50 cm. Ant diversity and species accumulation rates decreased with increasing depth. There were no species unique to the lowest depths, suggesting that subterranean ants may not be distributed deep in the soil in Amazonia due to the high water table. The technique we describe could be used to gain new insights into the distribution and biology of subterranean ant species and other members of the species-rich soil invertebrate macrofauna.     

Spiral geometry in the garden spider's orb web

The Science of Nature -     

Extended mutualism between termites and gut microbes: nutritional symbionts contribute to nest hygiene

All higher eukaryotes have established symbiotic relationships with diverse microorganisms. One of the most well-characterized symbiotic systems is that of termites and their intestinal microorganisms, which digest cellulose. Recently, diverse types of symbioses between gut microbes and host organisms including humans have received growing attention for various features of their complex interactions beyond nutrition. In termites, researchers are beginning to explore such function of gut symbionts, but only the contribution to internal immunity against entomopathogen is known in a few species. Here, we report that gut symbionts of the dampwood termite Zootermopsis nevadensis protect nests from the spread of the commensal bacterium Serratia marcescens, which has pathogenic potential. Defaunated termites dispersed S. marcescens in the surrounding environment by feeding on the bacteria, which then survived passage through their alimentary tracts, while non-defaunated termites did not. Loss of gut symbionts caused a significant reduction in intestinal acetate, which is an important carbon source for termites. Culture experiments showed that acetate had significant inhibitory effects on S. marcescens at a concentration as low as 12 mM, which indicated that the intestinal acetate of non-defaunated termites (40–130 mM) was capable of suppressing this bacterium. These results suggest that digestive derivatives produced by intestinal symbionts play an essential role in nest hygiene in addition to their nutritional function for termites. Our study provides a better understanding of the multifunctionality of symbiotic relationships in diverse organisms beyond nutrition.     

岩溶地下河流域水循环方式的降水效应

岩溶水中锶元素来源于碳酸盐岩地层的溶解,其浓度受地层岩性及地下水径流条件的控制.通过对贵州荔波板寨地下河流域微量元素锶的水文地球化学特征分析,发现在纯碳酸盐岩流域范围内,岩溶水中锶浓度只受控于地下水径流条件,因而Ca/Sr值能良好的示踪岩溶区地下水循环.在本文中,以Ca/Sr值为判别依据,将板寨地下河流域7个水样点划分...     

遥感技术在红树林生态监测与研究中的应用进展

遥感技术是红树林生态监测中的关键技术。本文详细介绍了航空图像、陆地卫星、SPOT卫星和几种雷达卫星数据在红树林生态监测中的应用,叙述了经验分类法、波段组合法、植被指数法和基于数理统计理论的各种地学分析法在探测红树林的生态学指标包括面积、分布范围、类内区分和类外区分以及动态变化等的应用和精度对比情况．另外,阐述了全球定位系统、地理信息系统和遥感技术在红树林生态监测中的综合应用的优势以及红树林遥感技术的发展前景。     

In search of the sky compass in the insect brain

Like many vertebrate species, insects rely on a sun compass for spatial orientation and long- range navigation. In addition to the sun, however, insects can also use the polarization pattern of the sky as a reference for estimating navigational directions. Recent analysis of polarization vision pathways in the brain of orthopteroid insects sheds some light onto brain areas that might act as internal navigation centers. Here I review the significance, peripheral mechanisms, and central processing stages for polarization vision in insects with special reference to the locust Schistocerca gregaria. As in other insect species, polarization vision in locusts relies on specialized photoreceptor cells in a small dorsal rim area of the compound eye. Stages in the brain involved in polarized light signaling include specific areas in the lamina, medulla and lobula of the optic lobe and, in the midbrain, the anterior optic tubercle, the lateral accessory lobe, and the central complex. Integration of polarized-light signals with information on solar position appears to start in the optic lobe. In the central complex, polarization-opponent interneurons form a network of interconnected neurons. The organization of the central complex, its connections to thoracic motor centers, and its involvement in the spatial control of locomotion strongly suggest that it serves as a spatial organizer within the insect brain, including the functions of compass orientation and path integration. Time compensation in compass orientation is possibly achieved through a neural pathway from the internal circadian clock in the accessory medulla to the protocerebral bridge of the central complex.     

Numerical analysis of keyhole geometry and temperature profiles in plasma arc welding

In keyhole plasma arc welding (PAW), the formation of the keyhole involves complicated thermo-physical mechanism. The shape and dimensions of the keyhole directly determine the heat deposition along the thickness direction of the test plates, the penetration depth and the weld bead quality. Based on analysis of the forces acting on the weld pool, a keyhole model is established according to the force-balance condition on the keyhole wall. The shape and dimensions of quasi-steady state keyhole are numerically predicted. The keyhole shape and size are used to calibrate some distribution parameters of the combined volumetric heat source which takes into consideration the geometrical feature of welds with larger ratio of penetration depth to width and volumetric distribution characteristic of the plasma heat intensity along the plate thickness direction. The temperature fields on stainless steel plates are numerically simulated. The calculated fusion line at the transverse cross-section of PAW welds are compared with the experimental measurements. It is found that the predicted results are in agreement with the experimental data.     

气候和人类活动对典型岩溶地下河系统径流年际变化的影响

为揭示气候变化与人类活动对岩溶地下河系统年径流量的影响,以南洞地下河为研究对象,利用其1972-2014年的径流量、降水量和蒸散量数据,分析其年际变化特征。研究结果表明：研究期内径流、降水和蒸散均呈现波动减少的趋势。其中流域内径流整体以0.014亿m³/a的速度减少,降水整体以3.14 mm/a的速度减少,蒸散整体以7.94 mm/a的速度减少。通过有序聚类法和Mann-Kendall法综合确定出径流、降水的突变年份为2002年、2008年。通过累积量斜率变化率比较法,定量分解了不同时期气候与人类活动对径流变化影响的贡献率：综合考虑降水和蒸散因素,以人类活动轻微的T₁（1972-2002年）阶段为基准期,气候变化对径流减少的贡献率在T₂（2003-2008年）、T₃（2009-2014年）时期分别为-86.68%、35.92%,人类活动对径流减少的贡献率在T₂、T₃阶段分别为186.68%、64.08%。可见,人类活动是南洞地下河流域径流量年际变化的主导因素,其中生活、生产的直接耗水和土地利用/土地覆被变化影响下径流过程的变化,共同影响着径流年际变化。