Does operational sex ratio influence relative strength of purging selection in males versus females?

According to theory, sexual selection in males may efficiently purge mutation load of sexual populations, reducing or fully compensating ‘the cost of males’. For this to occur, mutations not only need to be deleterious to both sexes, they also must affect males more than females. A frequently overlooked problem is that relative strength of selection on males versus females may vary between environments, with social conditions being particularly likely to affect selection in males and females differently. Here, we induced mutations in red flour beetles (Tribolium castaneum) and tested their effect in both sexes under three different operational sex ratios (1:2, 1:1 and 2:1). Induced mutations decreased fitness of both males and females, but their effect was not stronger in males. Surprisingly, operational sex ratio did not affect selection against deleterious mutations nor its relative strength in the sexes. Thus, our results show no support for the role of sexual selection in the evolutionary maintenance of sex.     

Grazing simplifies soil micro‐food webs and decouples their relationships with ecosystem functions in grasslands

Livestock grazing often alters aboveground and belowground communities of grasslands and their mediated carbon (C) and nitrogen (N) cycling processes at the local scale. Yet, few have examined whether grazing‐induced changes in soil food webs and their ecosystem functions can be extrapolated to a regional scale. We investigated how large herbivore grazing affects soil micro‐food webs (microbes and nematodes) and ecosystem functions (soil C and N mineralization), using paired grazed and ungrazed plots at 10 locations across the Mongolian Plateau. Our results showed that grazing not only affected plant variables (e.g., biomass and C and N concentrations), but also altered soil substrates (e.g., C and N contents) and soil environment (e.g., soil pH and bulk density). Grazing had strong bottom‐up effects on soil micro‐food webs, leading to more pronounced decreases at higher trophic levels (nematodes) than at lower trophic levels (microbes). Structural equation modeling showed that changes in plant biomass and soil environment dominated grazing effects on microbes, while nematodes were mainly influenced by changes in plant biomass and soil C and N contents; the grazing effects, however, differed greatly among functional groups in the soil micro‐food webs. Grazing reduced soil C and N mineralization rates via changes in plant biomass, soil C and N contents, and soil environment across grasslands on the Mongolian Plateau. Spearman's rank correlation analysis also showed that grazing reduced the correlations between functional groups in soil micro‐food webs and then weakened the correlation between soil micro‐food webs and soil C and N mineralization. These results suggest that changes in soil micro‐food webs resulting from livestock grazing are poor predictors of soil C and N processes at regional scale, and that the relationships between soil food webs and ecosystem functions depend on spatial scales and land‐use changes.     

Bacterial isolates harboring antibiotics and heavy-metal resistance genes co-existing with mobile genetic elements in natural aquatic water bodies

The rise in antibiotic-resistant bacteria and contamination of water bodies is a serious issue that demands immense attention of scientific acumen. Here, we examined the pervasiveness of ESBL producing bacteria in Dal Lake and Wular Lake of Kashmir valley, India. Isolates were screened for antibiotic, heavy metal resistant elements, and their coexistence with mobile genetic elements. Out of two hundred one isolates screened, thirty-eight were found positive for ESBL production. Antibiotic profiling of ESBL positive isolates with 16 different drugs representing β-lactam or -non-β-lactam, exhibited multidrug resistance phenotype among 55% isolates. Molecular characterization revealed the occurrence of drug resistance determinants blaTEM, AmpC, qnrS, and heavy metal resistance genes (MRGs) merB, merP, merT, silE, silP, silS, and arsC. Furthermore, mobile genetic elements IntI, SulI, ISecp1, TN3, TN21 were also detected. Conjugation assay confirmed the transfer of different ARGs, HMRGs, and mobile elements in recipient Escherichia coli J53 AZ^R strain. Plasmid incompatibility studies showed blaTEM to be associated with Inc groups B/O, HI1, HI2, I1, N, FIA, and FIB. Co-occurrence of blaTEM, HMRGs, and mobile elements from the aquatic milieu of Kashmir, India has not been reported so far. From this study, the detection of the blaTEM gene in the bacteria Bacillus simplex and Brevibacterium frigoritolerans are found for the first time. Considering all the facts it becomes crucial to conduct studies in natural aquatic environments that could help depict the epidemiological situations in which the resistance mechanism might have clinical relevance.     

The pulse of the tree is under genetic control: eucalyptus as a case study

The pulse of the tree (diurnal cycle of stem radius fluctuations) has been widely studied as a way of analyzing tree responses to the environment, including the phenotypic plasticity of tree–water relationships in particular. However, the genetic basis of this daily phenotype and its interplay with the environment remain largely unexplored. We characterized the genetic and environmental determinants of this response, by monitoring daily stem radius fluctuation (dSRF) on 210 trees from a Eucalyptus urophylla × E. grandis full‐sib family over 2 years. The dSRF signal was broken down into hydraulic capacitance, assessed as the daily amplitude of shrinkage (DA), and net growth, estimated as the change in maximum radius between two consecutive days (ΔR). The environmental determinants of these two traits were clearly different: DA was positively correlated with atmospheric variables relating to water demand, while ΔR was associated with soil water content. The heritability for these two traits ranged from low to moderate over time, revealing a time‐dependent or environment‐dependent complex genetic determinism. We identified 686 and 384 daily quantitative trait loci (QTL) representing 32 and 31 QTL regions for DA and ΔR, respectively. The identification of gene networks underlying the 27 major genomics regions for both traits generated additional hypotheses concerning the biological mechanisms involved in response to water demand and supply. This study highlights that environmentally induced changes in daily stem radius fluctuation are genetically controlled in trees and suggests that these daily responses integrated over time shape the genetic architecture of mature traits.     

基于灰色三角白化权集对分析模型的喀斯特山区农业生态环境脆弱性评价

生态脆弱性一直是全球变化与可持续发展研究的热点问题,研究农业生态环境脆弱性问题有利于合理利用区域农业资源,提出有效的农业生态环境保护措施。针对农业生态环境脆弱性评价未考虑不同评价级别内各指标之间同、异、反关系,本研究基于灰色三角白化权集对分析(SPA)模型,从生态环境外在脆弱性方面选择人口密度、人均耕地面积、人均造林面积等11个评价指标,对喀斯特山区农业生态环境脆弱性进行评价。结果表明: 研究区农业生态环境比较脆弱,以极度、高度和中度脆弱度为主;极度、高度、中度、轻度和微度农业生态环境脆弱区比例分别为32.4%、14.1%、17.7%、23.6%和12.2%;评价结果与研究区域农业生态环境脆弱性实际状况相符。说明以灰色三角白化权SPA模型评价农业生态环境脆弱性具有可行性,可为农业生态环境脆弱性评价提供一种新的方法和思路。     

青藏高原高寒草甸土壤环境对线虫功能多样性的影响

土壤线虫是地下食物网的重要组成部分, 在生态系统能量流动和物质循环中起着至关重要的作用。大量研究报道了肥力等土壤环境对土壤线虫物种多样性及各功能群多度的影响, 而我们对土壤线虫功能多样性如何响应土壤环境变化依然知之甚少。本研究以群落水平个体大小和个体大小多样性表征土壤线虫功能多样性。在青藏高原高寒草甸选择3个研究点, 调查和分析了不同生境(沟底平地、阴坡、阳坡和山顶)土壤线虫物种多样性、各功能群多度和功能多样性及其与土壤理化因子和植物多样性的关系。结果表明: (1)土壤线虫个体多度和物种多样性在阳坡最高, 随土壤pH值和土壤总磷增加而升高; 而基于个体大小的土壤线虫功能多样性主要受土壤养分影响, 随土壤总氮和有机质增加而增加, 随土壤总磷含量增加而减少; (2)食细菌和食真菌线虫多度在沟底最高, 植食与捕食杂食线虫多度在山顶最低; 除捕食杂食线虫外, 各功能群多度也主要随土壤磷增加而升高; 除食真菌线虫外, 各功能群多度随植物物种丰富度的增加而减少。本研究强调了土壤线虫物种和功能多样性受不同土壤环境因子的影响, 丰富了土壤线虫多样性研究的内容, 为理解高寒草甸土壤动物多样性形成、维持和变化提供了更广阔的 视角。     

Multiple chromosomal inversions contribute to adaptive divergence of a dune sunflower ecotype

Both models and case studies suggest that chromosomal inversions can facilitate adaptation and speciation in the presence of gene flow by suppressing recombination between locally adapted alleles. Until recently, however, it has been laborious and time‐consuming to identify and genotype inversions in natural populations. Here we apply RAD sequencing data and newly developed population genomic approaches to identify putative inversions that differentiate a sand dune ecotype of the prairie sunflower (Helianthus petiolaris) from populations found on the adjacent sand sheet. We detected seven large genomic regions that exhibit a different population structure than the rest of the genome and that vary in frequency between dune and nondune populations. These regions also show high linkage disequilibrium and high heterozygosity between, but not within, arrangements, consistent with the behaviour of large inversions, an inference subsequently validated in part by comparative genetic mapping. Genome–environment association analyses show that key environmental variables, including vegetation cover and soil nitrogen, are significantly associated with inversions. The inversions colocate with previously described “islands of differentiation,” and appear to play an important role in adaptive divergence and incipient speciation within H. petiolaris.     

市县级限制开发区环境功能区划研究——以河北省张家口市为例

限制开发地区是我国主体功能区划中划定的提供重要生态功能和农产品的地区,对其进行环境功能区划对于推动环境功能区划制度落地与实施,以及限制开发区的保护与发展有着重要意义。当前国家及省级的环境功能区划研究已经相对成熟,而市县尺度的限制开发地区环境功能区划相关研究较少。在总结现有环境功能区划研究方法的基础上,以河北省张家口市为例,探讨了市县级限制开发地区环境功能区划体系设计和技术方法,提出了以公里格网作为分析单元,结合县域行政边界,基于环境功能综合评价的结果,从自然生态安全、维护人群健康和区域环境支撑能力等3个方面,开展环境功能区划。基于该方法,将张家口市分为自然生态保留区、生态功能保持区、生态功能恢复区、农产品安全保障区、环境开发准入区、聚居发展维护区6类环境功能区,并根据各环境功能区的主要功能及生态环境特点提出相应的发展建议,以期为该区域管理提供可行的操作手段。本文提出的方法也可为其他限制开发地区的环境功能区划提供参考。