Environmental Cues,Endocrine Factors,and Reproductive Diapause in Male Insects

Environmental cues, mostly photoperiod and temperature, mediated by effects on the neuroendocrine system, control reproductive diapause in female insects. Arrest of oocyte development characterizes female reproductive diapause, which has two major adaptive functions: It improves chances of survival during unfavorable season(s), and/or it confines oviposition to that period of the year that is optimal for survival of the eggs and progeny. Although reproductive diapause is less well studied in male insects, there may be no sex-dependent differences in regard to the first of these functions. The second one, however, is not valid for the male; instead, selection pressure directs the male's reproductive strategy toward maximum chances of fertilization of the female's eggs with minimum waste of energy. Therefore, in species with female reproductive diapause, the males may or may not exhibit diapause, but if they do, their diapause must be adapted to that existing in conspecific females. Male reproductive diapause is defined as a reversible state of inability of the male to inseminate receptive females. In relation to reproductive diapause, there are several patterns of coadaptations between male reproductive strategy and timing of female receptivity, (a) In some insects, the females are receptive in the early part of their diapause; mating occurs during this period and there is no diapause in the male. The male dies shortly after copulation and the female stores the sperms to fertilize the eggs that develop after termination of the female's diapause, (b) In some species, as in the grasshopper Anacridium aegyptium, females are receptive during diapause; though oocyte development is arrested, copulation occurs and the stored sperms fertilize the eggs when the female's diapause ends. Males were claimed to have no diapause, but recent studies have revealed the presence of a reproductive diapause in a proportion of the males. This and other cases show that female receptivity during reproductive diapause may or may not be accompanied by male reproductive diapause. If there is a reproductive diapause in the male, it is controlled by the same endocrine mechanism, the corpora allata (CA), as in the females, (c) In many species females are refractory during their diapause. In these cases, males exhibit reproductive diapause, which may be light, as in the beetle Oulema melanopus, or well established, as in certain grasshoppers, butterflies, and beetles. In the latter cases, male diapause is controlled by similar environmental cues (photoperiod, temperature) and by the same intrinsic mechanism (neuroendocrine system, especially CA) as female diapause. Nevertheless, male diapause is less intense; the environmental cues leading to its termination are less complex and/or less extreme, so male diapause terminates before that of the females. Presumably, male diapause is under two antagonistic selection pressures: A male should not waste energy by courting dia-pausing refractory females, but he should be ready to copulate as soon as the females become receptive, otherwise he may lose in the competition between males for females. Some further strategies, which do not seem to fit the above patterns, are also outlined.     

Influence of MDR1 C1236T polymorphism on lopinavir plasma concentration and virological response in HIV-1-infected children

Background

Variability in MDR1 and PXR has been associated with differences in drug plasma levels and response to antiretroviral therapy. We investigated whether polymorphisms in MDR1 (T-129C, C1236T and C3435T) and PXR (C63396T) affect lopinavir plasma concentration and the virological or immunological response to HAART in HIV-1-infected children.

Methods

Genotypes were identified in 100 blood donors and 38 HIV-1-infected children. All children received HAART with lopinavir boosted with ritonavir (LPV/r) at the time of LPV plasma level quantification, before (C_trough) and between 1 and 2 h after (C_post-dose) the administration of the next dose of drug. CD4⁺ T-cell counts and plasma viral load were analyzed before and after the initiation of LPV/r.

Results

MDR1 1236T, MDR1 3435T and PXR 63396T alleles showed a frequency of ~ 50% while the MDR1 -129C allele only reached 5%. Children heterozygotes 1236CT showed a significantly lower LPV C_post-dose than homozygotes 1236TT (median C_post-dose = 3.04 μg/ml and 6.50 μg/ml, respectively; p = 0.016). Children heterozygotes 1236CT also had a lower decrease of viral load after 36 weeks of LPV/r exposure compared with homozygotes 1236CC (median viral load changes = − 0.50 log₁₀ copies/ml and − 2.08 log₁₀ copies/ml, respectively; p = 0.047). No effect on the immunological response was observed for polymorphisms of MDR1 or PXR.

Conclusions

Our results suggest that the MDR1 C1236T SNP significantly reduces LPV plasma concentration affecting the virological response to HAART. Heterozygotes 1236CT might have an altered level of P-gp expression/activity in enterocytes and CD4⁺ T lymphocytes that limits the absorption of LPV leading to an impaired virological suppression.     

The ‘New Wave’ in plant demographic inference: more loci and more individuals

Plant population genetic surveys are starting to take full advantage of technological advances in genotyping methods and of methodological advances in demographic inference. In this issue of Molecular Ecology, Keller et al. (2010) illustrate this trend with a particularly convincing study of rangewide genetic variation in a North American poplar, using both SNP and sequence data. They first investigate population genetic structure by estimating the most likely number of genetic clusters using a more formal approach than most other studies to date. They proceed by estimating gene flow among the inferred populations and by testing predictions on the distribution of low frequency alleles derived from recent work on range expansions.     

Alternative parasite development in transmission strategies: how time flies!

Among parasitic platyhelminths with complex life cycles, it has been well documented that transmission opportunities are the main forces shaping the diversity of life‐history traits and parasite developmental strategies. While deviations in the development pathway usually involve shortening of life cycles, their extension may also occur following perception of remaining time by parasites. Polystoma gallieni, the monogenean parasite of Hyla meridionalis, is able to trigger two alternative developmental strategies depending on the physiological stage of the tadpoles upon which larvae attach. The distribution and reproductive outputs of both resulting phenotypes were surveyed to address questions about the dynamics of transmission in natural environments. Because modifications in the completion of life cycles can have drawbacks which may perturb the dynamic equilibrium of the resulting host–parasite systems, experimental infestations were also performed to assess parasite–parasite interactions. Our results suggest that the bladder adult phenotype, which involves transmission between frogs and tadpoles, is supplied secondarily by the branchial phenotype which involves transmission between tadpoles and metamorphs. They also support the occurrence of finely tuned trade‐offs between hosts and parasites and highlight positive trends behind the extension of direct life cycles, in which host‐derived signals account for the remaining time to achieve parasitic transmission.     

应用高剂量/庇护所策略管理Bt作物抗性的三个基本假设：综述与展望

目前, 抗虫转基因作物的抗性管理方法主要是高剂量/庇护所策略。该策略的有效性取决于3个基本的假设条件：（1）抗虫转基因作物（Bt作物）表达出高剂量的杀虫蛋白, 该剂量使得靶标害虫对Bt杀虫蛋白的抗性表现型为功能性完全隐性或近于完全隐性, 进而使得Bt作物可以杀死几乎所有的抗性杂合个体和所有的敏感性个体;（2）靶标害虫种群的Bt抗性基因起始频率处于很低的水平;（3）源自转基因作物田和非转基因作物田(庇护所)的成虫在田间随机混合并交配。这3个假设必须同时满足, 缺一不可。本文就这3个假设的理论基础和经验研究的进展进行了综合论述, 并着重讨论了随机交配假设的最新研究进展以及今后的研究方向和方法。     

Elementary mode analysis: a useful metabolic pathway analysis tool for characterizing cellular metabolism

Elementary mode analysis is a useful metabolic pathway analysis tool to identify the structure of a metabolic network that links the cellular phenotype to the corresponding genotype. The analysis can decompose the intricate metabolic network comprised of highly interconnected reactions into uniquely organized pathways. These pathways consisting of a minimal set of enzymes that can support steady state operation of cellular metabolism represent independent cellular physiological states. Such pathway definition provides a rigorous basis to systematically characterize cellular phenotypes, metabolic network regulation, robustness, and fragility that facilitate understanding of cell physiology and implementation of metabolic engineering strategies. This mini-review aims to overview the development and application of elementary mode analysis as a metabolic pathway analysis tool in studying cell physiology and as a basis of metabolic engineering.     

Landscape dynamics and evolution of colonizer syndromes: interactions between reproductive effortand dispersal in a metapopulation

The evolutionary consequences of changes in landscape dynamics for the evolution of life history syndromes are studied using a metapopulation model. We consider in turn the long-term effects of a change in the local disturbance rate, in the maximal local population persistence, in habitat productivity, and in habitat fragmentation. We examine the consequences of selective interactions between dispersal and reproductive effort by comparing the outcome of joint evolution to a situation where the species has lost the potential to evolve either its reproductive effort or its dispersal rate. We relax the classical assumption that any occupied site in the metapopulation reaches its carrying capacity immediately after recolonization. Our main conclusions are the following: (1) genetic diversity modifies the range of landscape parameters for which the metapopulation is viable, but it alters very little the qualitative evolutionary trends observed for each trait within this range. Although they are both part of a competition/colonization axis, reproductive effort and dispersal are not substitutable traits: their evolution reflects more directly the change in the landscape dynamics, than a selective interaction among them. (2) no general syndrome of covariation between reproductive effort and dispersal can be predicted: the pattern of association between the two traits depends on the type of change in landscape dynamics and on the saturation level. We review empirical evidence on colonizer syndromes and suggest lines for further empirical work. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigations of �� Initiator Protein-mediated Interaction between Replication Origins �� and �� of the Plasmid R6K

A typical plasmid replicon of Escherichia coli, such as ori γ of R6K, contains tandem iterons (iterated initiator protein binding sites), an AT-rich region that melts upon initiator-iteron interaction, two binding sites for the bacterial initiator protein DnaA, and a binding site for the DNA-bending protein IHF. R6K also contains two structurally atypical origins called α and β that are located on either side of γ and contain a single and a half-iteron, respectively. Individually, these sites do not bind to initiator protein π but access it by DNA looping-mediated interaction with the seven π-bound γ iterons. The π protein exists in 2 interconvertible forms: inert dimers and active monomers. Initiator dimers generally function as negative regulators of replication by promoting iteron pairing (“handcuffing”) between pairs of replicons that turn off both origins. Contrary to this existing paradigm, here we show that both the dimeric and the monomeric π are necessary for ori α-driven plasmid maintenance. Furthermore, efficient looping interaction between α and γ or between 2 γ iterons in vitro also required both forms of π. Why does α-γ iteron pairing promote α activation rather than repression? We show that a weak, transitory α-γ interaction at the iteron pairs was essential for α-driven plasmid maintenance. Swapping the α iteron with one of γ without changing the original sequence context that caused enhanced looping in vitro caused a significant inhibition of α-mediated plasmid maintenance. Therefore, the affinity of α iteron for π-bound γ and not the sequence context determined whether the origin was activated or repressed.     

黄山松土壤可溶性有机质对氮添加的响应及其与细菌群落的关联

为探究黄山松土壤可溶性有机质(DOM)数量和质量对短期氮(N)添加的响应及其与细菌群落的关联,在福建戴云山自然保护区设置不同N添加水平(0、40和80 kg N·hm^-2·a^-1)试验,采用三维荧光与平行因子联用法,并结合高通量测序手段分别对土壤DOM和细菌群落进行分析。结果表明: 与对照相比,N添加整体降低了0～10和10～20 cm土层可溶性有机碳(DOC)含量和DOM腐殖化指数(HIX),其中,高氮(80 kg N·hm^-2·a^-1)添加下均显著降低。平行因子分析法进一步表明N添加下DOM中类腐殖质组分(C1、C2)的相对含量降低。此外,N添加减少了富营养细菌(变形菌门、酸微菌纲)的相对丰度,而增加了贫营养细菌(斯巴达杆菌纲)的相对丰度。富营养细菌的相对丰度与HIX、C1、C2呈显著正相关,与相对易分解的类富里酸组分(C3)呈显著负相关;而贫营养细菌的情况则相反。说明N添加下不同生活策略的细菌类群对DOM中难分解和易分解组分存在明显的偏好性。我们推测N沉降加剧背景下土壤微生物生活策略的转变可能有助于DOM组分的塑造。