Sexually mature and immature yearling male European ground squirrels: a comparison of behavioral and physiological parameters

Early puberty may increase lifetime reproductive success, but may also entail diverse costs. In male European ground squirrels (Spermophilus citellus), age at sexual maturity varies among individuals. We compared sexually active and inactive yearling males under standardized conditions in outdoor enclosures. Non-reproductive yearling males hibernated significantly longer than mature males and emerged when the mating period had already started. Testosterone concentrations peaked in the precocious males during premating and mating, and were depressed in the non-reproductive individuals throughout the study period. Emergence body mass was similar in both groups, although sexually immature males were significantly heavier at the end of the active season. Additionally, non-reproductive yearlings grew faster than precocious individuals. Male–male aggression peaked during mating and the following 4 weeks. Intense aggressive interactions like chases and fights were mostly initiated by reproductive males and were directed towards mature competitors. Aggressive behavior in immature males was mainly expressed as spatial displacements. Non-agonistic interactions with females were only observed in sexually active males. Concentrations of fecal cortisol metabolites did not differ between the two male groups and were elevated in the second half of the active season. Leucocyte numbers were reduced during mating in mature males, whereas in immature animals, cell numbers did not change significantly. Our results indicate that early puberty in European ground squirrels involves lower growth rates, high intrasexual aggression, lower prehibernatory body mass, and probably worse immunological condition during mating.     

高速公路弃土场堆积边坡的生态防护试验

高速公路弃土场边坡的生态恢复与水土保持是公路建设环境保护的重要内容.在京珠高速公路粤境南段3号弃土场开展试验,探讨弃土场堆积边坡的生态防护技术及其应用效果.结果表明:弃土场采用香根草(Vetiveria zizaniodes)生态护坡技术,香根草在无养护措施的情况下能够快速生长形成密集草带,并具先锋植物的优势,1年后坡面植被覆盖率达100%,乡土植物种类增加到16种以上;而对照坡面植被自然恢复缓慢,仅生长少量本地杂草,植被覆盖率只有15%.香根草护坡效果显著,坡面土壤流失量比对照小区减少95.41%,边坡稳定,在一定程度上可代替浆砌片石骨架植草护坡措施.因此,高速公路弃土场边坡可大力推广应用香根草生态护坡技术.     

兔卵巢组织石蜡切片技术的改良

针对常规石蜡切片方法步骤繁多,耗时长,所用的二甲苯试剂对人体健康有较大毒害性的缺陷,探讨提高制作兔卵巢组织石蜡切片质量的方法。试验从脱水和透明环节进行技术改良,用正丁醇与无水乙醇混合剂取代常规的脱水剂和透明剂。该混合剂具有良好的脱水和透明作用。实验结果表明：通过该技术改良,镜下观察组织结构清晰可辨、颜色鲜艳、对比度好、层次分明,组织切片效果良好。试验改良技术的工艺简单,具有质优、省时、快捷和实用性较好等优点,有推广应用价值。     

Relationship between size hierarchy and density of trees in a tropical dry deciduous forest of western India

Questions: Density dependence is thought to restrict exponential growth as well as give rise to size structure in populations. Size hierarchy in trees from tropical dry deciduous forests is studied to ask (1) whether nature of competition is symmetric or asymmetric and (2) what is the self thinning trajectory under a natural gradient of tree density. Location: Western India. Methods: Density was measured as the number of trees in 10‐m radius circular plots (n= 96) and size was measured at DBH. Size variation was evaluated by the Gini coefficient (n= 1239 trees). Results: Size inequality between neighbours decreased with density but in a non‐linear manner. In the backdrop of existing theory this indirectly suggests that competitive interactions may be symmetric over a ‘depletive’ resource such as below‐ground water (rather than a ‘pre‐emptive’ resource such as light), which is very plausible in a semi‐arid environment. The self thinning coefficient derived from the relationship between stem diameter and density (γ～?1/4), is higher than expected from existing models of allometric plant growth (γ=?1/3) which are based on above‐ground interactions alone. Seen in conjunction, these results suggest that above‐ground structures, such as stem size, do not adequately represent the outcome of competitive interactions when below‐ground resources, such as water, may be more important under semi‐arid conditions. Conclusions: The non‐linear relationship between size inequality and density indicates that there exists a density threshold beyond which investment in above‐ground biomass becomes sluggish in semi‐arid, deciduous forests. Since current allometric models do not incorporate below‐ground biomass for trees, these data suggest that a more comprehensive allometric growth model may have higher predictive power and wider applicability.     

Dealing with uncertain absences in habitat modelling: a case study of a rare ground-dwelling parrot

In the development of a species distribution model based on regression techniques such as generalized linear or additive modelling (GLM/GAM), a basic assumption is that records of species presence and absence are real. However, a common concern in many studies examining species distributions is that absences cannot be inferred with certainty. This is particularly the case where the species is rare, difficult to detect and/or does not occupy all available habitat considered suitable. The western ground parrot ( Pezoporus wallicus flaviventris ) of southern Western Australia, Australia, is a case in point, as not only is it rare and difficult to detect, but it is also unlikely to occupy all available suitable habitat. A recent survey of ground parrots provided the opportunity to develop a predictive distribution model. As the data were susceptible to false absences, these were replaced with randomly selected 'pseudo' absences and modelled using GLM. As a comparison, presence-only information was modelled using a relatively new approach, MAXENT, a machine-learning technique that has been shown to perform comparatively well. The predictive performance of both models, as assessed by the receiver operating characteristic plot (ROC) was high (AUC > 0.8), with MAXENT performing only marginally better than the GLM. These approaches both indicated that the ground parrot prefers areas relatively high in altitude, distant from rivers, gently sloping to level habitat, with an intermediate cover of vegetation and where there is a mosaic of vegetation ages. In this case, the use of presence-only information resulted in the identification of important environmental attributes defining the occurrence of the ground parrot, but additional factors that account for the inability of the bird to occupy all suitable habitat should be a component of model refinement.     

Age-dependent use of local and global landmarks during escape: experiments using Columbian ground squirrels

How animals utilize their space often changes during ontogeny, perhaps resulting from alternative use of orientation mechanisms. This study investigated whether landmark-based navigation mechanisms were age-dependent in Columbian ground squirrels (Spermophilus columbianus). In field tests, young (1-2 years old) and adult (3-6 years old) animals had to find an escape burrow when either local, global, or both types of landmarks were obstructed. The comparison of escape times between age groups revealed that adult squirrels found escape burrow faster than young animals if global landmarks were available. However, if only local landmarks were present, young squirrels outperformed older animals. The comparison of escape time within each age group showed that obstruction of global or local landmarks lengthened escape time of adult squirrels. In contrast, young animals had longer escapes only when local landmarks were obstructed. The results suggested that the use of different types of landmarks was age specific.     

Immunogold labeling of cryosections from high-pressure frozen cells

Immunogold labeling of cryosections according to Tokuyasu (Tokuyasu KT. A technique for ultracyotomy of cell suspensions and tissues. J Cell Biol 1973;57:551–565), is an important and widely used method for immunoelectron microscopy. These sections are cut from material that is chemically fixed at room temperature (room temparature fixation, RTF). Lately in many morphological studies fast freezing followed by cryosubstitution fixation (CSF) is used instead of RTF. We have explored some new methods for applying immunogold labeling on cryosections from high‐pressure frozen cells (HepG2 cells, primary chondrocytes) and tissues (cartilage and exocrine pancreas). As immunolabeling has to be carried out on thawed and stable sections, we explored two ways to achieve this: (1) The section fixation method, as briefly reported before (Liou W et al. Histochem Cell Biol 1996;106:41–58 and Möbius W et al. J Histochem Cytochem 2002;50:43–55.) in which cryosections from freshly frozen cells were stabilized in mixtures of sucrose and methyl cellulose and varying concentrations of glutaraldehyde, formaldehyde and uranyl acetate (UA). Only occasionally does this method reveal section areas with excellent cell preservation and negatively stained membranes like Tokuyasu sections of RTF material. (Liou et al.) (2) The rehydration method, a novel approach, in which CSF with glutaraldehyde and/or osmium tetroxide (OsO₄) was followed by rehydration and cryosectioning as in the Tokuyasu method. Especially, the addition of UA and low concentrations of water to the CSF medium favored superb membrane contrast. Immunogold labeling was as efficient as with the Tokuyasu method.     

Prediction of herbage yield in grassland: How well do Ellenberg N‐values perform?

Question: How useful are Ellenberg N‐values for predicting the herbage yield of Central European grasslands in comparison to approaches based on ordination scores of plant species composition or on soil parameters? Location: Central Germany (11°00′‐11°37’E, 50°21‐50°34’N, 500–840 m a.s.l.). Methods: Based on data from a field survey in 2001, the following models were constructed for predicting herbage yield in montane Central European grasslands: (1) Linear regression of mean Ellenberg N‐, R‐ and F‐values; (2) Linear regression of ordination scores derived from Non‐metric Multidimensional Scaling (NMDS) of vegetation data; and (3) Multiple linear regression (MLR) of soil variables. Models were evaluated by cross‐validation and validation with additional data collected in 2002. Results: Best predictions were obtained with models based on species composition. Ellenberg N‐values and NMDS scores performed equally well and better than models based on Ellenberg R‐ or F‐values. Predictions based on soil variables were least accurate. When tested with data from 2002, models based on Ellenberg N‐values or on NMDS scores accurately predicted productivity rank order of sites, but not the actual herbage yield of particular sites. Conclusions: Mean Ellenberg N‐values, which are easy to calculate, are as accurate as ordination scores in predicting herbage yield from plant species composition. In contrast, models based on soil variables may be useful for generating hypotheses about the factors limiting herbage yield, but not for prediction. We support the view that Ellenberg N‐values should be called productivity values rather than nitrogen values.     

Capillary Effects on Natural Remobilization of Pools of Dense Non-Aqueous Phase Liquid Mixtures in Porous Media

The natural remobilization of an initially static mixed dense non-aqueous phase liquid (DNAPL) pool due to dissolution was demonstrated by (Roy et al. 2002 Roy, J. W., Smith, J. E. and Gillham, R. W. 2002. Natural remobilization of multicomponent DNAPL pools due to dissolution. J. Contam. Hydrol., 59: 163–186. [Crossref], [PubMed], [Web of Science ®] [Google Scholar], 2004 Roy, J. W., Smith, J. E. and Gillham, R. W. 2004. Laboratory evidence of natural remobilization of multicomponent DNAPL pools due to dissolution. J. Contam. Hydrol., 74: 145–161. [Crossref], [PubMed], [Web of Science ®] [Google Scholar]) using a compositional mathematical model and laboratory experiments with open pools over a porous medium. The purposes of this study were to: a) demonstrate natural remobilization for a pool within porous media (as opposed to an open pool); and b) analyze the capillary effects associated with residual formation, a changing saturation profile, hysteresis, and aging, as these processes may reduce the potential for natural remobilization of pools in porous media. DNAPL pools comprised of tetrachloroethene and benzene were created within a zone of larger glass beads overlying smaller glass beads, in a water-saturated 2-D flow cell. In one case, remobilization occurred in the form of a DNAPL finger, after 56 days of flushing. In another case, no remobilization had occurred after 64 days of flushing, though the density increased by 430 kg m ^?3 and remobilization was predicted by the compositional model. Comparison of observations with model predictions suggest that contact angle hysteresis, related to an observed change in wettability, was the most significant contributing factor causing overprediction of the potential for natural remobilization.     

Observation on Flower Bud Differentiation of Crape Myrtle in Red Soil Environment

Flower bud differentiation is a key component of plant blooming biology and understanding how it works is vital for flowering regulation and plant genetic breeding, increasing the number and quality of flowering. Red soil is the most widely covered soil type in the world, and it is also the most suitable soil type for crape myrtle planting. The flower buds of crape myrtle (Lagerstroemia indica) planted in red soil were employed as experimental materials in this study, and the distinct periods of differentiation were identified using stereomicroscopy and paraffin sectioning. We optimized the steps of dehydration, transparency, embedding, sectioning and staining when employing paraffin sections. When seen under a microscope, this optimization can make the cell structure of paraffin sections obvious, the tissue structure complete, and the staining clear and natural. The flower bud differentiation process is divided into 7 periods based on anatomical observations of the external morphology and internal structure during flower bud differentiation: undifferentiated period, start of differentiation period, inflorescence differentiation period, calyx differentiation period, petal differentiation period, stamen differentiation period, and pistil differentiation period. The differentiation time is concentrated from the end of May to mid-June. Crape myrtle flower bud differentiation is a complicated process, and the specific regulatory mechanism and affecting elements need to be investigated further.