Comparative morphology of cephalic exocrine glands among castes of the black ant Lasius niger

The glandular system is crucially involved in main aspects of ant social life. The function of glands has been primarily studied in the workers (the non-reproductive individuals in a colony). In contrast, little information is available on queens (the reproductive females in a colony) or males in spite of the obvious functional differences between these castes. Here we report a comparison of the general morphology of the mandibular, propharyngeal and postpharyngeal glands between the three castes of the black ant Lasius niger. The analysis clearly shows that all these cephalic glands differ in relative size between castes and suggests a link between gland structure and its behavioral role in queens, workers and males. In particular, males present a hypertrophied mandibular gland. This is consistent with the fact that these glands might be the source of the sex pheromone in this caste. By contrast, queens exhibited the most developed postpharyngeal glands. This is consistent with the production of particular cues by queens for workers to help them to distinguish between reproductive and non-reproductive females. Finally, the propharyngeal glands were most developed in the worker caste and of similar relative size in males and queens. Their function is still enigmatic.     

Mitosis and cell death in the optic lobes of workers,queens and drones of the honey bee (<Emphasis Type="Italic">Apis mellifera</Emphasis>) during metamorphosis

Colonies of the honey bee, Apis mellifera, consist of males and two female castes: workers and queens. The castes and males from A. mellifera have a distinct morphology, physiology and behaviour that correlate with their roles in the society and are characterized by some brain polymorphisms. Compound eyes are one of the characteristics that differ among the castes and sexes. A. mellifera is a holometabolous insect; therefore, the development of adult organs during metamorphosis, which will produce these differences, requires the precise coordination of three main programmed cellular processes: proliferation, differentiation and death. These processes take place simultaneously during pupation. Our purpose was to investigate cell division and death in the optic lobes (OL) of workers, queens and males during pupation to identify how the differences in the compound eyes in adults of these classes are achieved. The results showed that OL differentiation follows a similar pattern in the three classes of individuals studied, without structural differences in their development. The main non-structural differences involve cell division, mortality rates and timing. The results suggest a modelling of the brain during differentiation, which contributes to the specific functions of each individual class.     

Caste- and sex-specific adaptations within the olfactory pathway in the brain of the ant Camponotus floridanus

Olfaction plays a key role in mediating ant behavior, and ant societies are characterized by caste- and sex-specific division of labor. We propose that caste- and sex-specific adaptations in the olfactory pathway promote differences in olfactory behavior. This study compares olfactory centers in the brain of large (major) workers, small (minor) workers, virgin queens, and males of the carpenter ant Camponotus floridanus. The number of glomeruli in the antennal lobe was similar in the female castes, although the glomerular volumes differed. Males had approximately 45% fewer glomeruli compared to females (approximately 258 and approximately 434) and one antennal sensory tract was absent. A dual output pathway to the mushroom bodies was present in males. In contrast to females, however, the number of glomeruli connected to the medial antennocerebral tract was substantially smaller than those associated with the lateral tract. All glomeruli in the male antennal lobe contained serotonergic processes, whereas in the female castes glomeruli in the large tract six cluster lacked serotonergic innervations. We conclude that differences in general glomerular organization are subtle among the female castes, but sex-specific differences in the number, connectivity and neuromodulatory innervation of glomeruli are substantial and likely to underlie differences in olfactory processing and learning.     

Queen,worker, and male yellowjacket wasps receive different nutrition during development

Nutritional variation among developing larvae is a long-standing hypothesis for how a sterile caste could evolve, with larvae deprived of nutrition becoming sterile or not leaving the nest. In this study, we test whether the three castes of the eusocial yellowjacket wasp (Vespula maculifrons) differ in the trophic source of their larval diet, their overall carbon (C) and nitrogen (N) content, as well as the distribution of C and N across body parts. Virgin queens (gynes) assimilated food from a higher relative trophic level compared to males, and workers were the lowest. Gynes, due to their much greater mass compared to the other castes are much more costly in terms of N, but males have the lowest C:N ratio. The variation in C:N is likely due to differences in life history between males and females (gynes and workers), where females invest more in energy storage (e.g., lipids) compared to males which have very short life spans; the major difference is in the abdomen, where fat is stored. The results of this study complement similar results in ants, which evolved a reproductive division of labor independently, and which diverged from vespid wasps near 150 million years ago. Similarities between how wasp and ant caste determination occurs suggest either a conserved mechanism that predates the evolution of eusociality or convergence on the same mechanism for generating alternative phenotypes. Provisioning N-expensive castes with food from a higher trophic level likely increases efficiency of N delivery because of N-enrichment with increasing trophic level.     

Comparative study of the cuticular hydrocarbon composition of Melipona bicolor Lepeletier, 1836 (Hymenoptera, Meliponini) workers and queens

In social insects, cuticular hydrocarbons are involved in species, kin, caste and nestmate recognition. Gas chromatography and mass spectrometry were used to compare the cuticular hydrocarbon composition of workers, males and queens of Melipona bicolor. The cuticular hydrocarbon composition of this species was found to consist mainly of C23, C25:1, C25, C27:1, C27, C29:1 and C29, which are already present in imagoes that have not yet abandoned the brood cell. This composition varied quantitatively and qualitatively between and within the castes and sexes. The newly emerged workers and young queens (virgins) had similar cuticular hydrocarbon profiles, which were different from those of the males. When the females start executing their tasks in the colony, the cuticular hydrocarbon profile differences appear. The workers have less variety, while the queens conserve or increase the number of cuticular hydrocarbon compounds. The queens have more abdominal tegumentary glands than the workers, which apparently are the source of the new cuticular compounds.     

Caste and colony variations in the chemical composition of the cephalic secretions of the African weaver ant, Oecophylla longinoda

ABSTRACT. Considerable differences were found in the composition of the volatile cephalic chemical of the castes of Oecophylla longinoda. The mandibular glands of minor workers contain a series of primary alcohols, predominantly 1-hexanol, 1-octanol and 1-nonanol, together with nerol and geraniol. Hexanal, 2-butyl-2-octenal and 3-undecanone (components of the mandibular gland secretion of major workers, and which are important stimuli in alarm communication) are absent. Major workers are attracted and arrested by high concentrations of nerol, which is part of a possible mechanism for communication within the nest. The heads of males contain a pungent secretion, which may be used in defence; the major constituents are five aliphatic acids. The quantities of both main and trace constituents of the mandibular gland secretion of major workers were found to vary between colonies collected in different areas of West Africa.     

Quantitative comparison of caste differences in honeybee hemolymph

The honeybee, Apis mellifera, is an invaluable partner in agriculture around the world both for its production of honey and, more importantly, for its role in pollination. Honeybees are largely unexplored at the molecular level despite a long and distinguished career as a model organism for understanding social behavior. Like other eusocial insects, honeybees can be divided into several castes: the queen (fertile female), workers (sterile females), and drones (males). Each caste has different energetic and metabolic requirements, and each differs in its susceptibility to pathogens, many of which have evolved to take advantage of the close social network inside a colony. Hemolymph, arthropods' equivalent to blood, distributes nutrients throughout the bee, and the immune components contained within it form one of the primary lines of defense against invading microorganisms. In this study we have applied qualitative and quantitative proteomics to gain a better understanding of honeybee hemolymph and how it varies among the castes and during development. We found large differences in hemolymph protein composition, especially between larval and adult stage bees and between male and female castes but even between adult workers and queens. We also provide experimental evidence for the expression of several unannotated honeybee genes and for the detection of biomarkers of a viral infection. Our data provide an initial molecular picture of honeybee hemolymph, to a greater depth than previous studies in other insects, and will pave the way for future biochemical studies of innate immunity in this animal.     

Discontinuous gas exchange in the fire ant,Solenopsos invicta Buren: Caste differences and temperature effects

The discontinuous gas exchange cycle (DGC), the cyclic release of CO(2) and uptake of O(2), were investigated in workers and female and male alates of the red imported fire ant, Solenopsis invicta Buren, using real-time CO(2) emission measurement by flow-through respirometry. All S. invicta castes displayed discontinuous emission of CO(2) in the temperature range of 15-25 degrees C, but only male alates and workers exhibited a DGC at 30 degrees C. The closed (C) and flutter (F) periods of the DGC were distinguishable in alates of both sexes at the lowest temperature, but not clearly differentiated in females at temperatures above 15 degrees C, in males above 20 degrees C, or workers at any temperature. DGC frequency increased for all castes as temperature increased, ranging from a low of 0.9+/-0.05 mHz (male alates at 15 degrees C) to 18+/-0.79 mHz (workers at 30 degrees C). O period (or burst) volumes of all castes decreased as temperature increased, and increased with body mass - this mass effect was most pronounced at lower temperatures. Q(10) values for DGC frequency (4.27, 5.81, and 5.62 for workers, female and male alates, respectively) were high compared with Q(10)'s for standard Vdot;(CO(2)). Differences in the salient characteristics of the DGC between castes are presented and discussed, and S. invicta DGC patterns are compared to known values for some other ant species.     

中华红林蚁形态描述、行为观察及社群结构

调查显示,北京百花山上"蚂蚁山"的蚂蚁为我国林区特有的种类——中华红林蚁Formica sinensis。该蚂蚁分布海拔相对较高,通常在针叶林或针阔叶混交林中筑巢,进行社会性生活。成虫有4个品级:大型工蚁、小型工蚁、蚁后和雄蚁。每个成熟蚁巢中有2～4个蚁后,为多蚁后社群结构。夏季蚁巢中同时存在着卵、幼虫、蛹和成虫。目前还只发现工蚁和蚁后休眠越冬。对中华红林蚁的各个虫态和品级进行形态描述和测定,并记述工蚁的觅食、建巢及清巢、防御与进攻等行为习性。首次发现雄蚁具有明显的护巢行为。同时,还发现在工蚁的外出活动中,标记信息素的作用不是很明显。     

Water loss in desert ants: caste variation and the effect of cuticle abrasion

Water loss rates (WLRs) varied across castes (workers > alate males > alate females) for desert ants in the genera Aphaenogaster, Messor and Pogonomyrmex. Exposure to soil caused increased WLRs in workers and foundresses (mated, dealate females), apparently because of cuticular abrasion caused by nest excavation. Moreover, field‐collected workers and foundresses from incipient nests (those exposed to soil) had similar WLRs, as did unabraded workers and alate females (those unexposed to soil). These data call into question previous adaptive scenarios for differences in WLRs across ant species and castes. For live alate females, WLRs increased over two stages. The first increase occurred immediately after mating, and the second occurred for foundresses collected 2 days later from incipient nests. By contrast, WLRs of HCN‐killed females were unaffected by mating, but increased significantly for foundresses collected from 2‐day‐old nests.     

Resource utilization by bumblebee queens, workers and males in a subarctic area

We studied the seasonal dynamics of food niche width and annual niche relations of queens, workers and males of six abundant bumblebee species living on a slope of a subarctic hill in North Sweden. The basic data consist of analyses of pollen contents in nectar loads of individual foragers. At any given time of the season individual foragers utilized frequently more than one flower species during each trip, concentrating, however, most of their efforts on one species only. These "major" species varied between individuals thus widening the foraging niche of the species. No obvious differences were observed in niche widths of the sexes and castes of the species (neither day-to-day nor annual observations). Queens had highest niche overlaps and males the lowest ones. Sexes and castes were separated into groups by their foraging patterns. Differences in proboscis lengths are not obvious niche separating factors at the study area. The environmental uncertainty (in time and space) may occasionally lead to excess of resources, which, in turn, may open possibilities of wide utilization of available flower species, thus rendering close fit between proboscis length and corolla tube depths of the foraged flowers unnecessary.     

Modifications in the oviducts of workers and queens of <Emphasis Type="Italic">Melipona quadrifasciata anthidioides</Emphasis> (Hymenoptera: Apidae) with different ages

The study of morphological features of highly eusocial bees has helped to answer a series of questions concerning their biology. The labor division places the females into two castes, queen with reproductive function and worker with a wide variety of tasks. However, in different species and under different conditions, workers can develop ovaries and lay trophic eggs that are eaten by the queen or used to originate males. In this work, the development of the oviducts was monitored in workers and virgin queens of Melipona quadrifasciata anthidioides specimens of different ages to verify whether there is permanent sterility of these queens and workers due to aging. Lateral and common oviducts of virgin queens aged <7, 10, 15, 20, and 25 days old, physogastric queens, nurse, and forager workers were analyzed for histology and ultrastructure. Although the structural organization of the lateral and common oviducts were very similar, differences in width of the cuticle and the degree of chromatin condensation were observed, indicating differences in the development of this organ of the reproductive system between the castes. It was also demonstrated that electron-lucent vesicles appear to be related to the formation of the cuticle that lines the oviducts. Because no cellular death characteristics were found, it can be inferred that the absence of mating of the queens as old as of 25 days of age does not cause permanent sterility.     

Reproductive and worker castes in the primitively eusocial wasp Belonogaster petiolata (DeGeer) (Hymenoptera: Vespidae): evidence for pre-imaginal differentiation

Until recently, morphological differences between castes in independent-founding polistine wasps were considered absent. This paper investigates the extent of morphological and physiological differences between reproductive (foundress and gyne) and worker castes of Belonogaster petiolata, and tests the hypothesis that caste differentiation in this species occurs pre-imaginally.Foundresses were significantly larger than workers, to the extent that foundress/worker ratios were comparable with those between queens and workers in some swarm-founding Polistinae. Early emerging workers were small, but body size increased over the colony cycle such that late-season workers were similar in size to gynes. In proportion to body size, workers possessed broader heads while foundresses and gynes had broader thoraces and gasters. All queens, 98% of subordinate foundresses, and 95% of over-wintering gynes were inseminated. Workers were never inseminated and lacked mature ovaries in colonies with active queens. However, in the absence of the queen (and other foundresses), 11% of workers developed mature ovaries. Ovarian size and fat content of foundresses and gynes was significantly greater than that of workers. The differences in external morphology and reproductive physiology between castes support the hypothesis that differentiation occurs pre-imaginally. However, imaginal factors, in particular social dominance of the queen, maintain the reproductive subordinance of workers.     

Morphology and number of Ommatidia in the compound eyes of Solenopsis invicta, Solenopsis richteri, and their hybrid (Hymenoptera: Formicidae)

The morphology and number of ommatidia of the compound eyes of Solenopsis invicta, Solenopsis richteri and their hybrid are investigated. Comparisons are made of the morphology and number of ommatidia in S. invicta, S. richteri and their hybrid. Major workers have significantly more facets than minor workers, male reproductive more than female reproductive, and the reproductives more than workers. Workers and reproductives have significantly more ommatidia in S. invicta than in S. richteri and significantly fewer in the hybrid than in either species. The major workers of each species have significantly wider facets than the minor workers, and workers have significantly wider facets than reproductives, which showed no difference in their facet diameter. There are no significant differences when the facet diameter is compared between the members of the castes of different species. These morphological and numerical dissimilarities are discussed in connection with known behavioral differences in the castes.     

Caste and sex specific olfactory glomerular organization and brain architecture in two sympatric ant species Camponotus sericeus and Camponotus compressus (Fabricius, 1798)

We use monoclonal antibodies against synaptic proteins and anterograde tracing with neurobiotin to describe the architecture of the antennal lobes in different castes of two ant species – Camponotus sericeus and Camponotus compressus. The reproductives and worker classes are readily categorized based on size and external morphology. The overall organization of brain neuropile is comparable between castes with differences only in the visual ganglia. Males have a larger fraction of neuropile occupied by the medulla and lobula than females. In the diurnal species, C. sericeus these regions are more highly represented, than in the nocturnal species C. compressus. The most striking differences are in the antennal lobe where males possess a macroglomerulus, which is about ten times larger in volume than the other glomeruli; such a specialization is absent in females. Minor workers possess a significantly larger number of glomeruli than the majors despite the smaller overall volume of the lobe. These caste-specific differences occur mainly within glomerular clusters that receive input from sensory neurons that project in tracts – T4 and T5 – within the antennal nerve. The comparative anatomy of different castes of ants provides an entry point into a future systematic analysis of how divergent brain architectures can arise within a single species.     

Host choice in the phoretic mite Parasitellus fucorum (Mesostigmata: Parasitidae): which bumblebee caste is the best?

Host caste recognition may be important for the dispersal of phoretic mites associated with social insects. All developmental stages of the mite Parasitellus fucorum (Acari: Mesostigmata: Parasitidae) live in the nests of bumblebees (Hymenoptera: Apidae: Bombus). Dispersal occurs by specialised phoretic instars, deutonymphs, which attach to adult bumblebees. Since bumblebee colonies are annual and only young queens overwinter, deutonymphs that are able to discriminate between bumblebee castes and preferentially attach to queens should be favoured by selection. In the field, deutonymphs of P. fucorum were found to be phoretic on bumblebee workers and queens, and in behavioural experiments all castes proved to be attractive as carriers for the mites. However, they preferred queens that had hibernated as carriers when they could choose between workers and queens. In a further experiment, when given a choice, deutonymphs switched from males to young queens but never transferred from a queen to a male. These results suggest that deutonymphs preferentially attach to queens but may also use other castes for transport. Those dispersing on workers and males may try to switch to queens later. Host-switching is possible during copulation and on flowers, where bees of all castes forage. Received: 14 November 1997 / Accepted: 16 February 1998     

Gene expression patterns associated with caste and reproductive status in ants: worker‐specific genes are more derived than queen‐specific ones

Variation in gene expression leads to phenotypic diversity and plays a central role in caste differentiation of eusocial insect species. In social Hymenoptera, females with the same genetic background can develop into queens or workers, which are characterized by divergent morphologies, behaviours and lifespan. Moreover, many social insects exhibit behaviourally distinct worker castes, such as brood‐tenders and foragers. Researchers have just started to explore which genes are differentially expressed to achieve this remarkable phenotypic plasticity. Although the queen is normally the only reproductive individual in the nest, following her removal, young brood‐tending workers often develop ovaries and start to reproduce. Here, we make use of this ability in the ant Temnothorax longispinosus and compare gene expression patterns in the queens and three worker castes along a reproductive gradient. We found the largest expression differences between the queen and the worker castes (~2500 genes) and the smallest differences between infertile brood‐tenders and foragers (~300 genes). The expression profile of fertile workers is more worker‐like, but to a certain extent intermediate between the queen and the infertile worker castes. In contrast to the queen, a high number of differentially expressed genes in the worker castes are of unknown function, pointing to the derived status of hymenopteran workers within insects.