表观遗传学与蜜蜂级型分化的研究进展

蜜蜂是一种高度社会化的昆虫,一个完整健康的蜂群通常是由蜂王、工蜂和雄蜂组成。尽管蜂王和工蜂的遗传物质相同,但它们在形态特征、行为职能和寿命方面表现出显著的差异。许多研究结果表明,营养因素是造成蜜蜂级型分化现象的主要原因,它可以影响蜂王幼虫和工蜂幼虫体内大量基因和蛋白的差异表达。随着表观遗传学的发展,人们对基因表达的调控机制有了新的认识,它与DNA甲基化、非编码RNA调控和组蛋白乙酰化等密切相关。这也为蜜蜂级型分化的分子机制提供了新的理论。本文就表观遗传学和蜜蜂级型分化的研究进展做一综述。     

Cloning and expression profiling of the DNA methyltransferase Dnmt3 gene in the Chinese honeybee, Apis cerana cerana (Hymenoptera:Apidae )

为探究中华蜜蜂Apis cerana cerana的DNA甲基化模式,本研究采用RT-PCR技术克隆了中华蜜蜂DNA甲基化转移酶3( Dnmt3)基因(GenBank登录号为JQ740768);采用荧光定量PCR检测不同发育时期工蜂(4日龄蛹,1,7和30日龄成年蜂及产卵工蜂)和蜂王(4日龄蛹,1日龄蜂王和产卵蜂王)头部的Dnmt3基因mRNA的表达量.结果表明:该基因cDNA序列全长2 277 bp,编码758个氨基酸残基,预测的蛋白分子量为88.24 kD,等电点为7.85.将中华蜜蜂与其他物种的Dnmt3基因的结构域进行比对,同时将该基因推导的氨基酸序列与其他物种的Dnmt3氨基酸序列进行同源性比对和系统发育分析,发现与西方蜜蜂的Dnmt3序列一致性高达99％.该基因在工蜂和蜂王不同发育时期均有表达,1日龄工蜂与7日龄工蜂中没有显著差异(P＞0.05),30日龄工蜂中的表达量显著高于前两者(P＜0.05);蜂王蛹中的表达量显著高于工蜂蛹(P＜0.05);1日龄的蜂王中的表达量显著高于1日龄的工蜂(P＜0.05);产卵工蜂与产卵蜂王中的表达量没有差异(P＞0.05).这种表达情况提示其可能与工蜂劳动分工及蜜蜂卵巢发育有关.     

蜜蜂群内生殖分工体系的形成及其维持

本文对蜜蜂群内生殖分工体系的形成及其维持机制进行综述。蜜蜂群体具有完善的劳动分工(包括生殖分工)体系,蜂王垄断生殖权力,而工蜂生殖器官发育不完全,在蜂王信息素和幼虫信息素的作用下产卵受到抑制。蜂王的多雄交配机制降低了群内个体间的亲缘关系,但也促进了工蜂间相互监督机制的形成。工蜂间的相互监督,结合蜂王和幼虫信息素对工蜂卵巢发育的影响,解决了蜂王与工蜂、工蜂与工蜂间的生殖利益冲突,保障了蜂群内的生殖分工体系,提高了群体效率,维护了蜂群的真社会性。     

东西方蜜蜂亲缘行为关系研究取得新进展

东方蜜蜂和西方蜜蜂是2个不同的种,二者的亲缘关系很近,但是二者的蜂王和幼虫均具有不同的遗传物质和气味信息素,蜜蜂的气味信息素对蜜蜂的社会行为和行为方式起到非常重要的作用。建立东方蜜蜂和西方蜜蜂的混合饲养蜂群,为研究东方蜜蜂和西方蜜蜂这2个近缘物种间的相互关系提供了一个很好的模式。近日,中国科学院西双版纳热带植物园协同进化组的高级访问学者谭垦教授等,通过测试和分析东方蜜蜂蜂王和西方蜜蜂蜂王的蜂王信息素主要成分的组成和差异,研究蜂王在混合饲养蜂群内对异种工蜂卵巢发育的抑制作用,并探讨了当混合蜂群失去蜂王后,2种工蜂对异种蜜蜂卵和幼虫气味的识别和反应机制。     

蜂群中不同亚家庭的工蜂寿命分析

在蜂群中,蜂王与多个雄蜂自然交尾,形成不同亚家庭.为了研究不同亚家庭中工蜂寿命是否有差异,我们以西方蜜蜂Apis mellifera L.为实验材料,随机从一群自然群中取270只刚孵化的工蜂,单独饲养于有蜜粉脾小蜂箱内,每天将自然死亡个体取出标记.并利用3对微卫星进行个体基因型分析,通过Matesoft软件划分亚家庭,然后分析了各亚家庭工蜂的自然寿命及生存曲线.结果表明:实验蜂群由12个亚家庭组成,其中2个亚家庭工蜂寿命与其他亚家庭存在显著差异(P＜0.05).     

蜂王幼虫与工蜂幼虫发育期食物消耗量的研究

以意大利蜜蜂Apis mellifera ligustica雌性幼虫为试验材料,用鲜王浆、葡萄糖、果糖和酵母抽提物分别配制不同日龄的蜂王幼虫食物和工蜂幼虫食物,采用室内人工饲养蜜蜂幼虫技术饲养12h以内的蜂王幼虫和工蜂幼虫,直到幼虫出现排便和吐丝行为,记录幼虫生长发育期间消耗的总食物量。结果表明:1只蜂王幼虫在生长发育期平均消耗196.8mg蜂王幼虫食物,而1只工蜂幼虫在生长发育期平均消耗139.4mg工蜂幼虫食物。     

中华蜜蜂DNA甲基化转移酶Dnmt3基因克隆及表达谱分析

为探究中华蜜蜂Apis cerana cerana的DNA甲基化模式, 本研究采用RT PCR技术克隆了中华蜜蜂DNA甲基化转移酶3（Dnmt3）基因(GenBank登录号为JQ740768); 采用荧光定量PCR检测不同发育时期工蜂（4日龄蛹, 1, 7和30日龄成年蜂及产卵工蜂）和蜂王（4日龄蛹, 1日龄蜂王和产卵蜂王）头部的Dnmt3基因mRNA的表达量。结果表明： 该基因cDNA序列全长2 277 bp, 编码758个氨基酸残基, 预测的蛋白分子量为88.24 kD, 等电点为7.85。将中华蜜蜂与其他物种的Dnmt3基因的结构域进行比对, 同时将该基因推导的氨基酸序列与其他物种的Dnmt3氨基酸序列进行同源性比对和系统发育分析, 发现与西方蜜蜂的Dnmt3序列一致性高达99%。该基因在工蜂和蜂王不同发育时期均有表达, 1日龄工蜂与7日龄工蜂中没有显著差异(P>0.05), 30日龄工蜂中的表达量显著高于前两者 (P<0.05); 蜂王蛹中的表达量显著高于工蜂蛹 (P<0.05); 1日龄的蜂王中的表达量显著高于1日龄的工蜂(P<0.05); 产卵工蜂与产卵蜂王中的表达量没有差异（P>0.05）。这种表达情况提示其可能与工蜂劳动分工及蜜蜂卵巢发育有关。     

蜜蜂繁殖冲突与雌性蜜蜂信息素研究进展

在营造社会性生活的蜜蜂群体里,蜂王释放出蜂王信息素来控制工蜂卵巢发育及改造王台特性,并吸引雄蜂为之交配,使蜂群正常繁衍。本文在国内外相关研究的基础上,对蜜蜂各蜂种、亚种以及特殊蜂群无政府主义蜂群、海角蜜蜂等雌性蜜蜂信息素成分以及含量变化进行综合论述,并对蜂王主要信息素对工蜂和雄蜂生理影响以及今后的研究趋势作扼要介绍。     

蜜蜂级型分化机理

蜜蜂是整个大自然生态系统中不可或缺的一部分,能有效地为多种植物和农作物授粉。蜜蜂是典型的真社会性昆虫,其生殖劳动分工现象有重要进化意义。而级型分化是导致劳动分工的一个重要因素,蜜蜂级型分化现象的机理研究已成为目前重要的研究热点之一。本文对近年来蜜蜂级型分化机理方面的研究进展进行了综述。国内外很多学者从营养、激素、基因表达、蛋白质和表观遗传等方面对蜜蜂级型分化机理进行了研究。蜂王浆中富含的57 kDa、蜂王幼虫期充足的食物量以及蜂王幼虫期高滴度的保幼激素(JH)和蜕皮激素(MA)等都可促进蜂王卵巢的发育以及诱导蜂王表型产生;而工蜂浆中富含的双香豆酸可诱使工蜂表型的产生。近年研究表明,表皮生长因子受体(Egfr)、胰岛素受体底物基因(Irs)、雷帕霉素基因(Tor)和甲基转移酶3(Dnmt3)等基因均可影响蜂王和工蜂的分化;蛋白质表达谱分析表明,不同时间点的蜂王幼虫和工蜂幼虫表达的差异蛋白质很多;表观遗传分析表明,DNA甲基化、microRNAs以及组蛋白乙酰化均是导致蜂王和工蜂级型分化的因素。此外,发育空间和蜂王浆均可通过调控基因的DNA甲基化水平影响蜜蜂幼虫的级型分化。     

西方蜜蜂不同级型王浆主蛋白MRJP8基因的表达差异

王浆主蛋白在蜜蜂的级型分化中具有重要的功能。为探究mrjp8在西方蜜蜂Apis mellifera不同级型的表达模式及功能差异。【方法】 利用荧光定量PCR技术对西方蜜蜂工蜂、 雄蜂和蜂王不同发育时期和不同组织的mrjp8表达水平进行检测。【结果】 工蜂体内mrjp8在9日龄前后的毒腺组织内特异性高表达, 为参照基因表达量的上万倍, 在其他发育时期和组织的表达量则明显较低, 其表达具有明显的时空特异性; 在雄蜂体内其表达量与对照相当; 在蜂王体内表达量可达参照的近1 000倍, 没有组织特异性。【结论】 mrjp8的这种表达模式提示其在工蜂防御及维系蜂王长寿命方面有积极作用, 这为进一步研究该基因乃至整个王浆蛋白基因家族的进化和功能分化提供了依据。     

Evolutionary transition from single to multiple mating in fungus-growing ants

Queens of leafcutter ants exhibit the highest known levels of multiple mating (up to 10 mates per queen) among ants. Multiple mating may have been selected to increase genetic diversity among nestmate workers, which is hypothesized to be critical in social systems with large, long-lived colonies under severe pressure of pathogens. Advanced fungus-growing (leafcutter) ants have large numbers (104-106 workers) and long-lived colonies, whereas basal genera in the attine tribe have small (< 200 workers) colonies with probably substantially shorter lifespans. Basal attines are therefore expected to have lower queen mating frequencies, similar to those found in most other ants. We tested this prediction by analysing queen mating frequency and colony kin structure in three basal attine species: Myrmicocrypta ednaella, Apterostigma collare and Cyphomyrmex longiscapus. Microsatellite marker analyses revealed that queens in all three species were single mated, and that worker-to-worker relatedness in these basal attine species is very close to 0.75, the value expected under exclusively single mating. Fungus growing per se has therefore not selected for multiple queen mating. Instead, the advanced and highly productive social structure of the higher attine ants, which is fully dependent on the rearing of an ancient clonal fungus, may have necessitated high genetic diversity among nestmate workers. This is not the case in the lower attines, which rear fungi that were more recently derived from free-living fungal populations.     

Gene flow simulations demonstrate resistance of long-lived species to genetic erosion from habitat fragmentation

Habitat fragmentation restricts the movement of individuals across a landscape. In terrestrial and aquatic systems, barriers to movement can modify population and community dynamics at local or regional scales. This study contrasted life history traits related to lifespan with habitat fragmentation to determine impacts on species population genetic structure in the Neuse River Basin, USA. For this, we simulated gene flow among evenly-spaced populations in a river network and tracked individual and population genetics for 200 years. The modeled scenarios represent a full cross between five life history strategies and four riverscapes representing varying degrees of fragmentation. The five life history strategies include species (based on freshwater mussels) with average lifespans ranging from 10 to 50 years and age at maturity from 2 to 6 years. The movement landscapes included a (1) panmictic, (2) stepping-stone landscape allowing movement to only neighboring populations during each dispersal event, (3) partially-fragmented landscape divided by dams currently in the network, and (4) fully-fragmented landscape. Results suggest species with shorter lifespans have higher population genetic structure in fragmented landscapes than species with longer lifespans. Furthermore, species with shorter lifespans in highly fragmented landscapes may be harboring genetic degradation or decline as allele fixation and loss. Although anthropogenic fragmentation of many river systems is only 100–200 years old, the simulation indicates that species can respond genetically in that period of time. Additionally, the time frame of the simulation suggests that genetic impacts of habitat fragmentation in some species present in the Neuse River Basin may not yet be manifesting and restoration activities could be successful.     

Relationships between fine root dynamics and nitrogen availability in Michigan northern hardwood forests

Minirhizotrons were used to observe fine root (Б mm) production, mortality, and longevity over 2 years in four sugar-maple-dominated northern hardwood forests located along a latitudinal temperature gradient. The sites also differed in N availability, allowing us to assess the relative influences of soil temperature and N availability in controlling fine root lifespans. Root production and mortality occurred throughout the year, with most production occurring in the early portion of the growing season (by mid-July). Mortality was distributed much more evenly throughout the year. For surface fine roots (0-10 cm deep), significant differences in root longevity existed among the sites, with median root lifespans for root cohorts produced in 1994 ranging from 405 to 540 days. Estimates of fine root turnover, based on the average of annual root production and mortality as a proportion of standing crop, ranged from 0.50 to 0.68 year^-1 for roots in the upper 30 cm of soil. The patterns across sites in root longevity and turnover did not follow the north to south temperature gradient, but rather corresponded to site differences in N availability, with longer average root lifespans and lower root turnover occurring where N availability was greater. This suggests the possibility that roots are maintained as long as the benefit (nutrients) they provide outweighs the C cost of keeping them alive. Root N concentrations and respiration rates (at a given temperature) were also higher at sites where N availability was greater. It is proposed that greater metabolic activity for roots in nitrogen-rich zones leads to greater carbohydrate allocation to those roots, and that a reduction in root C sink strength when local nutrients are depleted provides a mechanism through which root lifespan is regulated in these forests.     

Life expectancy and onset of foraging in the honeybee (Apis mellifera)

Predictions that precocious foraging in honeybee workers is a result of shortening of their life expectancy were tested in both laboratory and field experiments. In the laboratory experiment, we assessed the impact of anaesthesia with CO₂ and infection with Nosema apis on the lifespan of workers. In the field experiment, the age at onset of foraging was observed in groups of workers with different expected lifespans. In both the experiments, workers originating from one queen inseminated with the semen of one drone were divided into five groups. The first group was anaesthetized with CO₂ on the first day of life. Workers from the other three groups were individually inoculated with a constant number of N. apis spores on the 1st, 6th and 11th days of life. Workers from the fifth control group were neither treated with CO₂ nor inoculated in any way. Both the laboratory and field experiments revealed that anaesthetized and infected workers had shorter expected lifespans compared to control bees. Amongst infected workers, those inoculated earlier in life survived for a significantly shorter period of time in comparison to those infected later in life. In agreement with the expectation, the field experiment showed that anaesthetized and infected workers with shorter expected lifespan start foraging earlier than control workers. Amongst the infected workers, age at inoculation correlated with age at onset of foraging. This means that short-lived workers complete safe nest tasks and begin riskier foraging earlier in life. Our results provide a strong support for the hypothesis that the division of labour in eusocial insects is a consequence of the different expected worker lifespan and different risk associated with their tasks; however, they do not contradict other existing explanations.     

Genetic coregulation of longevity and antioxienzymes in Neurospora crassa

Further analysis of a model of the biochemical genetics of cellular longevity in Neurospora crassa confirms and amplifies the hypothesis that antioxienzymes and lifespans are genetically co-regulated. The model consists of seven classes of closely related strains with genetically determined median lifespans ranging from 7 to 90 days and differing by about 15-day intervals. The nuclear gene mutations Age- and age+ respectively decrease and increase both lifespans and the constitutive enzyme activities relative to the wild-type parent. Here the number of such enzymes correlated with lifespans is extended from 6 to 12. Four of these enzymes have not been previously noted in Neurospora. Statistical analysis indicates that the genes may coordinate the 12 enzymes' activities with respect to one another to facilitate their "collaborative" function. The genes probably perform a regulatory role in the synthesis of the antioxienzymes. Neurospora may have a global unit of genetic function, an oxy-regulon, analogous to that of enteric bacteria.     

Is height related to longevity?

Over the last 100 years, studies have provided mixed results on the mortality and health of tall and short people. However, during the last 30 years, several researchers have found a negative correlation between greater height and longevity based on relatively homogeneous deceased population samples. Findings based on millions of deaths suggest that shorter, smaller bodies have lower death rates and fewer diet-related chronic diseases, especially past middle age. Shorter people also appear to have longer average lifespans. The authors suggest that the differences in longevity between the sexes is due to their height differences because men average about 8.0% taller than women and have a 7.9% lower life expectancy at birth. Animal experiments also show that smaller animals within the same species generally live longer. The relation between height and health has become more important in recent years because rapid developments in genetic engineering will offer parents the opportunity to increase the heights of their children in the near future. The authors contend that we should not be swept along into a new world of increasingly taller generations without careful consideration of the impact of a worldwide population of taller and heavier people.     

Age structure changes and extraordinary lifespan in wild medfly populations

The main purpose of this study was to test the hypotheses that major changes in age structure occur in wild populations of the Mediterranean fruit fly (medfly) and that a substantial fraction of individuals survive to middle age and beyond (> 3-4 weeks). We thus brought reference life tables and deconvolution models to bear on medfly mortality data gathered from a 3-year study of field-captured individuals that were monitored in the laboratory. The average time-to-death of captured females differed between sampling dates by 23.9, 22.7, and 37.0 days in the 2003, 2004, and 2005 field seasons, respectively. These shifts in average times-to-death provided evidence of changes in population age structure. Estimates indicated that middle-aged medflies (> 30 days) were common in the population. A surprise in the study was the extraordinary longevity observed in field-captured medflies. For example, 19 captured females but no reference females survived in the laboratory for 140 days or more, and 6 captured but no reference males survived in the laboratory for 170 days or more. This paper advances the study of aging in the wild by introducing a new method for estimating age structure in insect populations, demonstrating that major changes in age structure occur in field populations of insects, showing that middle-aged individuals are common in the wild, and revealing the extraordinary lifespans of wild-caught individuals due to their early life experience in the field.     

Kin structure and queen execution in the Argentine ant Linepithema humile

Every spring, workers of the Argentine Ant Linepithema humile kill a large proportion of queens within their nests. Although this behaviour inflicts a high energetic cost on the colonies, its biological significance has remained elusive so far. An earlier study showed that the probability of a queen being executed is not related to her weight, fecundity, or age. Here we test the hypothesis that workers collectively eliminate queens to which they are less related, thereby increasing their inclusive fitness. We found no evidence for this hypothesis. Workers of a nest were on average not significantly less related to executed queens than to surviving ones. Moreover, a population genetic analysis revealed that workers were not genetically differentiated between nests. This means that workers of a given nest are equally related to any queen in the population and that there can be no increase in average worker–queen relatedness by selective elimination of queens. Finally, our genetic analyses also showed that, in contrast to workers, queens were significantly genetically differentiated between nests and that there was significant isolation by distance for queens.     

Senescence in the worker honey bee Apis Mellifera

Honey bees are social insects that exhibit striking caste-specific differences in longevity. Queen honey bees live on average 1-2 years, whereas workers live 2-6 weeks in the summer and about 20 weeks in the winter. It is not clear whether queen-worker differences in longevity are due to intrinsic physiological differences in the rate of senescence, to differential exposure to extrinsic factors such as predation and adverse environmental conditions, or both. To determine if the relatively short lifespan of worker bees involves senescence, we measured age-specific resistance to three different physiological stressors (starvation, thermal, and oxidative stress) while eliminating age-related differences in foraging activity and minimizing age-related differences in energy expenditure. Despite these manipulations, older worker bees were still significantly less resistant to all three stressors than were younger bees. These results indicate that the regulation of worker bee lifespan involves senescence, in addition to extrinsic factors.     

利用氧化剂甲基紫精筛选拟南芥寿限延长突变体

在模式动物中的研究表明,寿限延长与氧化胁迫耐受能力密切有关;在模式植物拟南芥中也发现晚花突变体具有更强的抗氧化胁迫能力,但迄今为止未见有关拟南芥寿限延长突变体的研究报道。本文建立了用氧化剂甲基紫精筛选寿限延长突变体的方法,并对用该方法从经快中子诱变的拟南芥Columbia生态型M2代群体中筛选获得的突变体SFNA-9—4进行分析,发现该突变体的抗氧化胁迫能力和寿限均显著增加。由此说明,用该方法筛选拟南芥寿限延长突变体是可行的。