对蜜蜂性别决定和蜂王级型确立理论的新诠释

从全新视角概貌性解读蜜蜂Apis诸多生殖机制,依据的就是蜂王或产卵工蜂的卵子发生、性别决定假说、性位点研究以及蜂王级型确立机制。这种不同于单倍-二倍性性别决定机制的新诠释,适用于明确性别决定机制、简化定向育种方法、减少比较性实验的难度和时间、实施亲子鉴定和抽象并量化种群的概念。     

Asexual queen succession in the subterranean termite Reticulitermes virginicus

Termite colonies are founded by a pair of primary reproductives. In many species, including subterranean termites (family Rhinotermitidae), the primary king and queen can be succeeded by neotenic reproductives that are produced from workers or nymphs within the colony. It is generally believed that these neotenics inbreed within the colony, sometimes for many generations. Here, we show that primary queens of the North American subterranean termite, Reticulitermes virginicus, are replaced by numerous parthenogenetically produced female neotenics. We collected functional female neotenics from five colonies of R. virginicus in North Carolina and Texas, USA. Genetic analysis at eight microsatellite loci showed that 91-100% of the neotenics present within a colony were homozygous at all loci, indicating that they were produced through automictic parthenogenesis with terminal fusion. In contrast, workers, soldiers and alates were almost exclusively sexually produced by mating between the female neotenics and a single king. This is the second termite species shown to undergo asexual queen succession, a system first described in the Japanese species, Reticulitermes speratus. Thus, the conditional use of sexual and asexual reproduction to produce members of different castes may be widespread within Reticulitermes and possibly other subterranean termites.     

Genetic caste determination in Pogonomyrmex harvester ants imposes costs during colony founding

Some populations of Pogonomyrmex harvester ants comprise genetically differentiated pairs of interbreeding lineages. Queens mate with males of their own and of the alternate lineage and produce pure-lineage offspring which develop into queens and inter-lineage offspring which develop into workers. Here we tested whether such genetic caste determination is associated with costs in terms of the ability to optimally allocate resources to the production of queens and workers. During the stage of colony founding, when only workers are produced, queens laid a high proportion of pure-lineage eggs but the large majority of these eggs failed to develop. As a consequence, the number of offspring produced by incipient colonies decreased linearly with the proportion of pure-lineage eggs laid by queens. Moreover, queens of the lineage most commonly represented in a given mating flight produced more pure-lineage eggs, in line with the view that they mate randomly with the two types of males and indiscriminately use their sperm. Altogether these results predict frequency-dependent selection on pairs of lineages because queens of the more common lineage will produce more pure-lineage eggs and their colonies be less successful during the stage of colony founding, which may be an important force maintaining the coexistence of pairs of lineages within populations.     

Characterization and distribution of Pogonomyrmex harvester ant lineages with genetic caste determination

Genetic caste determination has been described in two populations of Pogonomyrmex harvester ants, each comprising a pair of interbreeding lineages. Queens mate with males of their own and of the alternate lineage and produce two types of diploid offspring, those fertilized by males of the queens' lineage which develop into queens and those fertilized by males of the other lineage which develop into workers. Each of the lineages has been shown to be itself of hybrid origin between the species Pogonomyrmex barbatus and Pogonomyrmex rugosus, which both have typical, environmentally determined caste differentiation. In a large scale genetic survey across 35 sites in Arizona, New Mexico and Texas, we found that genetic caste determination associated with pairs of interbreeding lineages occurred frequently (in 26 out of the 35 sites). Overall, we identified eight lineages with genetic caste determination that always co-occurred in the same complementary lineage pairs. Three of the four lineage pairs appear to have a common origin while their relationship with the fourth remains unclear. The level of genetic differentiation among these eight lineages was significantly higher than the differentiation between P. rugosus and P. barbatus, which questions the appropriate taxonomic status of these genetic lineages. In addition to being genetically isolated from one another, all lineages with genetic caste determination were genetically distinct from P. rugosus and P. barbatus, even when colonies of interbreeding lineages co-occurred with colonies of either putative parent at the same site. Such nearly complete reproductive isolation between the lineages and the species with environmental caste determination might prevent the genetic caste determination system to be swept away by gene flow.     

On the origin of termite workers: weighing up the phylogenetic evidence

Resolving the phylogenetic history of a 'true' worker caste in termites is essential to our understanding of termite eusocial evolution. Whether this caste is ancient and monophyletic or derived and polyphyletic will have a tremendous impact on our interpretation of termite eusocial history and remains an outstanding question in termite biology. Recent work has begun to re-examine this question in light of new phylogenetic information, but new questions have now arisen about how best to model character state changes in termite caste systems. In the present paper, we compare the models of Grandcolas and D'Haese [J. Evol. Biol. 15 (2002) 885] and Thompson et al. [J. Evol Biol. 13 (2000) 8691 and attempt to make explicit how these proposals differ with respect to the number of, and homology between, character states. We highlight the support each model has for the two principal, but competing, evolutionary hypotheses outlined above.     

尖唇散白蚁的孤雌生殖行为及初建群体研究

为了证明尖唇散白蚁Reticulitermes aculabialis Tsai et Hwang是否存在孤雌生殖行为和探讨其初建群体的发育特征,本文对尖唇散白蚁分飞成虫进行雌雌配对（FF）和雌雄配对（FM）人工饲养对比研究。结果显示：FM和FF组的筑巢时间和筑巢活动相似;在建巢初期（配对第5天）FF配对组和FM配对组死亡率分别为11．33％和2．67％,FF配对组死亡率显著高于FM组;产卵前FM组的2只雌性个体和FF组的雌性个体卵巢发育程度一致,都有已经完成卵黄积累的成熟卵母细胞。6个月后,FF配对组有7组产生后代,FM配对组有17组产生后代;FF组子代数目显著低于FM组,分别平均为（7．00±1．58）个和（10．33±1．21）个;FF子代全为2～3龄工蚁,而FM组有由3-4龄工蚁分化的低龄兵蚁。最后,我们对新建群体分化出的第一只兵蚁与成熟巢群中的兵蚁进行了形态学比较。我们的结果表明,尖唇散白蚁具有孤雌生殖行为,并且分飞成虫通过雌雌配对和雌雄配对初建群体在发育模式上有显著差异,雌雌成虫配对采用孤雌生殖方式繁殖有可能是野外尖唇散白蚁建群的另一种方式。     

Adaptation of a radiochemical assay for juvenile hormone biosynthesis to study caste differentiation in a primitive termite

A radiochemical assay measuring juvenile hormone synthesis by corpora allata incubated in vitro was adapted for use with the termite Zootermopsis angusticollis. Corpora allata from 3–4-day old virgin female neotenic reproductives were used in these studies because this caste showed the highest rates of juvenile hormone synthesis (0.6 pmol h^?1 per pair corpora allata). Juvenile hormone-III synthesis was linear for up to 6 h over the range of concentrations of labelled l-methionine from 27–280 μM. Rates of juvenile hormone synthesis were stimulated up to 10-fold in a dose-dependent manner by the addition of farnesoic acid to the incubation medium. However, the relatively high concentration of 120 μM farnesoic acid reduced the rates of juvenile hormone synthesis. The radiochemical assay was used to determine rates of juvenile hormone synthesis in vitro by corpora allata from larvae with a queen and king vs orphaned larvae. The presence of reproductives resulted in a suppression of larval corpus allatum activity relative to orphaned controls.     

Soldier caste influences on candidate primer pheromone levels and juvenile hormone-dependent caste differentiation in workers of the termite Reticulitermes flavipes

Caste systems and the division of labor they make possible are common underlying features of all social insects. Multiple extrinsic factors have been shown to impact caste composition in social insect colonies. Primer pheromones are one type of extrinsic caste-regulatory factor; they are chemical signaling molecules produced by certain colony members to impact developmental physiology of recipient nestmates. However, only limited evidence exists regarding primer pheromones and their actions in eusocial termites. In previous research we identified two soldier-produced terpenes, γ-cadinene (CAD) and γ-cadinenal (ALD), as candidate primer pheromones of the lower termite Reticulitermes flavipes. In the present study we tested hypotheses related to CAD and ALD action in recipient individuals. We examined the influences of terminally developed soldier termites on (1) CAD and ALD levels and (2) caste differentiation in developmentally totipotent workers. Our findings show CAD and ALD (respectively) are caste stimulatory and inhibitory components of chemical blends present in soldier heads, ALD levels increase significantly (10.9×) in workers only in the presence of soldiers, and soldiers can reduce developmental-hormone response thresholds of workers, presumably via ALD action. These findings provide novel evidence supporting that CAD and ALD are authentic caste-regulatory primer pheromones in Reticulitermes.     

The origin of a 'true' worker caste in termites: mapping the real world on the phylogenetic tree

The evolution of the 'true' worker caste in termites is not decisively inferred by coding and mapping both this character and the foraging behaviour on a phylogenetic tree. Answering to Thompson et al. (2000, 2003), and with reference to Grandcolas and D'Haese (2002), we show that this indecisive inference depends on the correct consideration paid to the outgroups. These last ones could be non subsocial cockroaches, or some wood-eating subsocial cockroaches often considered misleadingly as living ancestors, or even any hemimetabolous insects, all of them would be unambiguously lacking 'true' worker caste and pseudergate caste and not showing the 'one-piece' life type foraging behaviour. These statements derive from observing, coding and mapping the real world on the tree without making ad hoc assumptions. In that respect, because termites do not exist in isolation, apart from the tree of life, mapping the character of interest on the tree must be applied to the outgroups as well.     

Patterns of neotenic differentiation in a subterranean termite, Reticulitermes speratus (Isoptera: Rhinotermitidae)

Plasticity in the caste developmental pathway is a remarkable characteristic of termite societies. In Reticulitermes, two types of neotenic reproductive, nymphoids and ergatoids, may differentiate from nymphs and workers and take over reproduction in the colony after the death of the original primary reproductive pair. We examined the dynamics of newly differentiated nymphoids and ergatoids in experimentally orphaned laboratory colonies of R. speratus with different caste compositions. The period required for differentiation of nymphoids was shorter than that for differentiation of ergatoids. The sex ratio of neotenics was strongly female‐biased, particularly in ergatoids. The results suggested that the number of differentiated ergatoids was restricted by the existence of nymphs or nymphoids in a colony. Workers were assumed to kill most newly differentiated neotenics. Attack reflecting conflict between colony members is probably an important mechanism to control neotenic emergence.     

非编码RNA调控真社会性昆虫品级分化和个体分工的研究进展

真社会性昆虫是最具代表性的表型可塑性的研究对象之一,其个体之间分工协作的社会性生活方式增强了整个群体的环境适应性和繁殖力。真社会性昆虫虽然具有相同的遗传背景,个体之间却表现出明显的品级分化和个体分工,这是由环境和遗传共同影响的。表观遗传被认为是应对环境条件下重塑基因表达的主要机制,非编码RNA作为一类广泛参与机体生命活动的不编码蛋白的功能性RNA,在真社会性昆虫的品级分化、个体分工等方面起着重要的调控作用。本文从微小RNA、长链非编码RNA、环状RNA、与PIWI蛋白相作用的RNA等非编码RNA,对蜜蜂、蚂蚁及白蚁等真社会性昆虫的非编码RNA调控机制研究进展进行了综述,以加深对真社会性昆虫内在遗传分子基础的理解和认识,也为害虫防治领域提供新的研发视角。     

Effect of juvenile hormone on caste determination and colony processes in the bumblebee Bombus terrestris

To investigate the role of juvenile hormone (JH) in caste determination, first and second instar larvae of Bombus terrestris were topically treated with one of three doses (2, 10, or 20 g/larva) of JH dissolved in acetone. Treated larvae belonged to very young colonies that had just been started by their queen. Therefore, all larvae were supposedly destined to develop into workers. Our study demonstrates that a single application of JH in the first or second instar can lead to the development of queens and that this effect is dose- and instar-dependent. The brood (second, or third brood of the colony) to which the larvae belonged also had an effect. A clear size dimorphism of the female castes exists in B. terrestris. In this study, however, intermediates also developed from treated larvae. In fact, even untreated larvae in a treated colony developed into queens and intermediates, depending on the total dose of JH applied to the colony. There are no indications that a larva, once determined to become a queen, can be forced to become a worker by means of malnutrition. Treatment with JH also had an influence on colony processes. For instance, the appearance of queen larvae resulted in the advanced start of reproduction by workers and egg robbery, the so called competition point. This indicates again the close relationship between queen rearing and the queen-worker conflict. However, the ultimate function of this casual connection is still unclear. Further, the queen reacted to the treatment by switching to the laying of haploid eggs at an earlier date in the colony development compared to untreated colonies.     

Morphology and gonad development of normal soldiers and reproductive soldiers of the termite Zootermopsis nevadensis nevadensis (Isoptera, Archotermopsidae)

Reproductive or neotenic soldiers of the Archotermopsid Zootermopsis nevadensisnevadensis (Hagen) are compared to sterile soldiers and primary male reproductives. Several head capsule morphometrics correlate significantly with gonad size across all forms and both sexes of soldiers. The easily observed field character of ratio of mandible length to labrum length is a consistent and reliable feature of head capsule external morphology for predicting gonad development and reproductive potential of soldier forms regardless of age, sex, or live weight.     

Worker caste determination in the army ant Eciton burchellii

Elaborate division of labour has contributed significantly to the ecological success of social insects. Division of labour is achieved either by behavioural task specialization or by morphological specialization of colony members. In physical caste systems, the diet and rearing environment of developing larvae is known to determine the phenotype of adult individuals, but recent studies have shown that genetic components also contribute to the determination of worker caste. One of the most extreme cases of worker caste differentiation occurs in the army ant genus Eciton, where queens mate with many males and colonies are therefore composed of numerous full-sister subfamilies. This high intracolonial genetic diversity, in combination with the extreme caste polymorphism, provides an excellent test system for studying the extent to which caste determination is genetically controlled. Here we show that genetic effects contribute significantly to worker caste fate in Eciton burchellii. We conclude that the combination of polyandry and genetic variation for caste determination may have facilitated the evolution of worker caste diversity in some lineages of social insects.     

Testing the importance of the distribution of worker sizes to colony performance in the ant species <Emphasis Type="Italic">Formica obscuripes</Emphasis> Forel

We examined the relationship between colony performance and the distribution of worker sizes within colonies in the ant species, Formica obscuripes. We manipulated the distribution of worker sizes within colonies and found that experimental colonies whose distributions mimicked the natural distributions retained a larger percentage of colony biomass over three weeks when fed on honeydew, relative to colonies composed of only large or only small workers. In natural colonies most of the variation in worker sizes was found within, as opposed, to between colonies, suggesting that homeostatic mechanisms within colonies regulated the distribution of worker sizes. While there were no disjunctions in the distribution of worker sizes within colonies, the distribution tended to be bimodal. This study demonstrates that the distribution of worker sizes within colonies is important even for ant species that lack discrete worker castes. Received 31 October 2006; revised 26 December 2006; accepted 4 January 2007.     

Morphological discordance of the new trypanosomatid species phylogenetically associated with the genus crithidia

Three new species of monoxenous parasites from the Neotropical Heteroptera are described on the basis of the ultrastructure of cells in culture, as well as gene sequences of Spliced Leader (SL) RNA, glyceraldehyde phosphate dehydrogenase (GAPDH) and small subunit (SSU) rRNA. The results have highlighted a striking discrepancy between the morphological (dis)similarities and the phylogenetic affinities among the insect trypanosomatids. Although each of the new species is characterized by a distinct set of morphological characters, based on the predominant promastigotes observed in culture, each of them has been provisionally assigned to the genus Leptomonas pending the future revision of this genus. Yet, instead of the phylogenetic affinity with the other members of this polyphyletic genus, the new species are most closely related to Crithidia species. Thus, the extremely long promastigotes of Leptomonas acus sp. n. and the unique morphological features found in Leptomonas bifurcata sp. n. sharply contrast with their respective relatives C. fasciculata and C. deanei both of which are typical choanomastigotes. The results clearly show that the current classification at the genus level is misleading and needs to be revised. The phylogenetic clades potentially representing the candidate new genera of monoxenous trypanosomatids have started to emerge from the presented analyses.