Experimental elimination of parasites in nature leads to the evolution of increased resistance in hosts

A reduction in the strength of selection is expected to cause the evolution of reduced trait expression. Elimination of a parasite should thus cause the evolution of reduced resistance to that parasite. To test this prediction in nature, we studied the fourth- and eighth-generation descendants of guppies (Poecilia reticulata) introduced into four natural streams following experimental elimination of a common and deleterious parasite (Gyrodactylus spp.). After two generations of laboratory rearing to control for plasticity and maternal effects, we infected individual fish to assess their resistance to the parasite. Contrary to theoretical expectations, the introduced guppy populations had rapidly and repeatably evolved increased resistance to the now-absent parasite. This evolution was not owing to a resistance-tolerance trade-off, nor to differences in productivity among the sites. Instead, a leading candidate hypothesis is that the rapid life-history evolution typical in such introductions pleiotropically increases parasite resistance. Our study adds a new dimension to the growing evidence for contemporary evolution in the wild, and also points to the need for a re-consideration of simple expectations from host–parasite theory. In particular, our results highlight the need for increased consideration of multiple sources of selection and pleiotropy when studying evolution in natural contexts.     

青藏高原高寒草甸植被特征与温度、水分因子关系

以广布于青藏高原的高寒草甸为研究对象,进行模拟增温实验,探讨高寒草甸植被特征与温度、水分因子关系,并试图论证高寒草甸植被是否符合生物多样性代谢理论.结果表明:①高寒草甸植被物种多样性的对数与绝对温度的倒数呈显著线性递减关系,空气-地表-浅层土壤(0-20 cm)温度(R2 ＞0.6,P＜0.01)较深层土壤(40-100 cm)温度(R2＜0.5,P＜0.05)对物种多样性影响大;其植被新陈代谢平均活化能为0.998-1.85 eV,高于生物多样性代谢理论预测值0.6-0.7 eV,这是高寒草甸植被对长期低温环境适应进化的结果.②除趋势对应分析和冗余分析显示,温度对植被地上部分影响较大,而土壤水分对全株影响均较大,适当的增温与降水均可极显著促进高寒草甸植被生长.③逐步回归和通径分析显示,40 cm、60 cm深度土壤水分对植被地上部分产生直接影响,20 cm高度空气相对湿度和40 cm深度土壤温度对其产生间接影响;40 cm深度土壤温度和60 cm深度土壤水分对植被地下部分产生直接影响,红外地表温度对其产生间接影响.深层土壤温度和水分对高寒草甸植被具有影响作用,这可能与增温后冻土的融化有关,但其机理尚待进一步研究.     

The use of statistical tools in field testing of putative effects of genetically modified plants on nontarget organisms

To fulfill existing guidelines, applicants that aim to place their genetically modified (GM) insect‐resistant crop plants on the market are required to provide data from field experiments that address the potential impacts of the GM plants on nontarget organisms (NTO's). Such data may be based on varied experimental designs. The recent EFSA guidance document for environmental risk assessment (2010) does not provide clear and structured suggestions that address the statistics of field trials on effects on NTO's. This review examines existing practices in GM plant field testing such as the way of randomization, replication, and pseudoreplication. Emphasis is placed on the importance of design features used for the field trials in which effects on NTO's are assessed. The importance of statistical power and the positive and negative aspects of various statistical models are discussed. Equivalence and difference testing are compared, and the importance of checking the distribution of experimental data is stressed to decide on the selection of the proper statistical model. While for continuous data (e.g., pH and temperature) classical statistical approaches – for example, analysis of variance (ANOVA) – are appropriate, for discontinuous data (counts) only generalized linear models (GLM) are shown to be efficient. There is no golden rule as to which statistical test is the most appropriate for any experimental situation. In particular, in experiments in which block designs are used and covariates play a role GLMs should be used. Generic advice is offered that will help in both the setting up of field testing and the interpretation and data analysis of the data obtained in this testing. The combination of decision trees and a checklist for field trials, which are provided, will help in the interpretation of the statistical analyses of field trials and to assess whether such analyses were correctly applied.     

Efficacy of a herbal product against Histomonas meleagridis after experimental infection of turkey poults

Abstract

Histomoniasis (infectious enterohepatitis, blackhead) is caused by the protozoan parasite Histomonas meleagridis (H. meleagridis). After the ban of all prophylactic and therapeutic drugs in the European Union, histomoniasis is increasingly responsible for considerable economic problems to the poultry industry. The aim of this study was to investigate the effect of a herbal product with extracts from cinnamon, garlic, lemon, and rosemary on H. meleagridis in turkey poults in vivo. For this purpose, 60 two-week-old poults were divided into three groups. Group 1 received the herbal product in the feed six days before infection and in water three days before infection, then in feed and drinking water until the end of the experiment. Groups 2 and 3 were left untreated. At week 3 of age, Groups 1 and 2 were infected intracloacally with H. meleagridis. Three weeks after infection the surviving birds were euthanized and examined for pathological lesions. Mortality was 20% in Group 1 and 50% in Group 2. There were no deaths in Group 3. DNA of histomonads was detected in all examined caeca and livers of the dead birds, but was not detected in any examined organ of the surviving birds of all groups. There was no noticeable difference in the lesion scores of the dead birds between the groups. The surviving birds of all groups did not show lesions post mortem. Since all effective prophylactic and therapeutic drugs against histomoniasis were banned in the EU, under given conditions the investigated herbal product seems to be an effective alternative for the reduction of mortality in turkeys caused by histomoniasis.     

Yersinia pestis infection and laboratory conditions alter flea-associated bacterial communities

We collected Oropsylla montana from rock squirrels, Spermophilus varigatus, and infected a subset of collected fleas with Yersinia pestis, the etiological agent of plague. We used bar-tagged DNA pyrosequencing to characterize bacterial communities of wild, uninfected controls and infected fleas. Bacterial communities within Y. pestis-infected fleas were substantially more similar to one another than communities within wild or control fleas, suggesting that infection alters the bacterial community in a directed manner such that specific bacterial lineages are severely reduced in abundance or entirely eliminated from the community. Laboratory conditions also significantly altered flea-associated bacterial communities relative to wild communities, but much less so than Y. pestis infection. The abundance of Firmicutes decreased considerably in infected fleas, and Bacteroidetes were almost completely eliminated from both the control and infected fleas. Bartonella and Wolbachia were unaffected or responded positively to Y. pestis infection.     

Determinants of frequency-dependent regulation of Kv1.2-containing potassium channels

Voltage-gated potassium channels are important regulators of electrical excitation in many tissues, with Kv1.2 standing out as an essential contributor in the CNS. Genetic deletion of Kv1.2 invariably leads to early lethality in mice. In humans, mutations affecting Kv1.2 function are linked to epileptic encephalopathy and movement disorders. We have demonstrated that Kv1.2 is subject to a unique regulatory mechanism in which repetitive stimulation leads to dramatic potentiation of current. In this study, we explore the properties and molecular determinants of this use-dependent potentiation/activation. First, we examine how alterations in duty cycle (depolarization and repolarization/recovery times) affect the onset and extent of use-dependent activation. Also, we use trains of repetitive depolarizations to test the effects of a variety of Thr252 (S2-S3 linker) mutations on use-dependent activation. Substitutions of Thr with some sterically similar amino acids (Ser, Val, and Met, but not Cys) retain use-dependent activation, while bulky or charged amino acid substitutions eliminate use-dependence. Introduction of Thr at the equivalent position in other Kv1 channels (1.1, 1.3, 1.4), was not sufficient to transfer the phenotype. We hypothesize that use-dependent activation of Kv1.2 channels is mediated by an extrinsic regulator that binds preferentially to the channel closed state, with Thr252 being necessary but not sufficient for this interaction to alter channel function. These findings extend the conclusions of our recent demonstration of use-dependent activation of Kv1.2-containing channels in hippocampal neurons, by adding new details about the molecular mechanism underlying this effect.     

Determining Immune System Suppression versus CNS Protection for Pharmacological Interventions in Autoimmune Demyelination

A major hallmark of the autoimmune demyelinating disease multiple sclerosis (MS) is immune cell infiltration into the brain and spinal cord resulting in myelin destruction, which not only slows conduction of nerve impulses, but causes axonal injury resulting in motor and cognitive decline. Current treatments for MS focus on attenuating immune cell infiltration into the central nervous system (CNS). These treatments decrease the number of relapses, improving quality of life, but do not completely eliminate relapses so long-term disability is not improved. Therefore, therapeutic agents that protect the CNS are warranted. In both animal models as well as human patients with MS, T cell entry into the CNS is generally considered the initiating inflammatory event. In order to assess if a drug protects the CNS, any potential effects on immune cell infiltration or proliferation in the periphery must be ruled out. This protocol describes how to determine whether CNS protection observed after drug intervention is a consequence of attenuating CNS-infiltrating immune cells or blocking death of CNS cells during inflammatory insults. The ability to examine MS treatments that are protective to the CNS during inflammatory insults is highly critical for the advancement of therapeutic strategies since current treatments reduce, but do not completely eliminate, relapses (i.e., immune cell infiltration), leaving the CNS vulnerable to degeneration.     

Decaying in different clays: implications for soft‐tissue preservation

Lagerstätten, places where soft‐bodied organisms became mineralized, provide a substantial bulk of palaeobiological information, but the detailed mechanisms of how soft‐tissue preservation takes place remain debatable. An experimental taphonomy approach, which allows for direct study of decay and mineralization, offers a means to study the preservational potential of different soft‐bodied organisms under controlled conditions. Here we compare the preservational capacity of two types of clay (kaolinite and montmorillonite) through a long‐term (24 month) experiment involving the burial and decay of small crustaceans. Our experimental design is innovative in that it models catastrophic sedimentation in fine‐grained colloidal suspension, which is believed to form Lagerstätten deposits. We demonstrated better preservation of buried organisms in clays compared to water, and in kaolinite compared to montmorillonite. As aluminium cations were present in high concentrations in kaolinite sediment but not in montmorillonite, the better preservation in kaolinite is attributed to the tanning properties of aluminium, which catalyses cross‐linking in proteins, protecting them from bacterial degradation. Anaerobic environments and acidification also slow down decay, but they are less effective than tanning. Kaolinite and montmorillonite replaced the crustacean integuments differently: in the remains buried in kaolinite, Al and Si were detected in equal proportions, while in those buried in montmorillonite, the Si content appeared to be much higher even in comparison with the initial sample of the clay. These variations probably arose from the different dynamics of acidic hydrolysis in the two clays associated with anaerobic decomposition of organic matter. Our results show that the preservation mechanism includes multi‐component interactions between the solution, mineral, sediment and organic remains; taken separately, any single component explains little. The specific conditions that occur within the colloidal clay sediments can facilitate conservation and start fast mineralization according to chemical properties and elemental content.