Facultative polygyny in Ectatomma tuberculatum (Formicidae, Ectatomminae)

Summary. Polygyny, the presence of several mated queens within the same colony, is widespread in insect societies. This phenomenon is commonly associated with ecological constraints such as limited nest sites. In habitats where solitary nest foundation is risky, monogynous colonies can reintegrate young daughter queens (secondary polygyny). We studied the reproductive structure (i.e. queen number) of the ectatommine ant Ectatomma tuberculatum from Bahia State, Brazil. This species was found to present facultative polygyny: out of a total of 130 colonies collected, 39.2% were monogynous, while 43.8% were polygynous. Polygynous colonies had significantly more workers than monogynous ones. Queen number in polygynous colonies ranged from 2 to 26, with an average of 4 ± 4 queens per colony. All nestmate queens were egg-layers with no apparent dominance hierarchy or agonistic behavior. Non-nestmate queens were adopted by monogynous colonies suggesting that polygyny is secondary, originating through queen adoption. This species is characterized by an open recognition system, which probably allows a switch from monogynous to polygynous colonies. The behavioral acts of queens showed that resident queens remained frequently immobile on or near the brood, contrarily to alien or adopted queens and gynes. In addition, monogynous queens showed no behavioral or physiological (i.e. by ovarian status) differences in comparison with polygynous ones. Secondary or facultative polygyny, probably associated with queen adoption, may have been favored in particular environmental conditions. Indeed, by increasing colony productivity (i.e. number of workers) and territory size (by budding and polydomy), polygyny could uphold E. tuberculatum as a dominant species in the mosaic of arboreal ants in Neotropical habitats.Received 7 April 2004; revised 11 November 2004; accepted 15 November 2004.     

Rhipicephalus sanguinius: localization of vitellogenin synthesis by immunological methods and electron microscopy

In ovipositing Rhipicephalus sanguinius (Latrelle), complete immunological identity existed between vitellogenin from the midgut, fat body, and hemolymph and vitellin from eggs. This supported the hypothesis that the same vitellogenin was synthesized by both the midgut and fat body, then released into the hemolymph and transported to the ovary. Vitellogenin was taken up unaltered by the oocytes during vitellogenesis to become vitellin. Antivitellogenin did not react with host (dog) hemoglobin. Transmission electron microscopy showed specialized cells with large amounts of rough endoplasmic reticulum, Golgi complexes, and secretory granules in the midgut and fat body of ovipositing females that were absent in the midgut and fat body of fed males. It is suggested that these cells synthesize vitellogenin.     

Temporal polyethism, life expectancy, and entropy of workers of the ant Ectatomma vizottoi Almeida, 1987 (Formicidae: Ectatomminae)

We investigated the changes in the behavioral repertoire over the course of life and determined the life expectancy and entropy of workers of the ant Ectatomma vizottoi. Newly emerged ants were individually marked with model airplane paint for observation of behaviors and determination of the age and life expectancy. Ants were divided into two groups: young and old workers. The 36 behaviors observed were divided into eight categories. Workers exhibit a clear division of tasks throughout their lives, with young workers performing more tasks inside the colony and old workers, outside, unlike species that have small colonies. This species also exhibits an intermediate life expectancy compared to workers of other species that are also intermediary in size. This supports the hypothesis of a relationship between size and maximum life expectancy, but it also suggests that other factors may also be acting in concert. Entropy value shows a high mortality rate during the first life intervals.     

Division of labor inPonera pennsylvannica (Formicidae: Ponerinae)

Summary We examined division of labor and colony demography in the antPonera pennsylvannica. Observation of three colonies with individually marked workers revealed a high degree of interindividual behavioral variation and a rough but consistent division of labor between brood tenders and foragers. This division was present both in colonies consisting entirely of workers produced in the previous summer and in colonies containing freshly eclosed ants. Two colonies showed typical age-based polyethism, with young ants focusing on brood care and overwintered ants on foraging. No such age basis was detected in the third colony. This difference may relate to variability in brood production schedules. Colonies showing temporal polyethism had two peaks of brood production and thus had relatively large brood populations when the first young workers eclosed, while the third colony had only one peak and little brood for the young workers to tend. Even if young ants have a lower threshold for brood care, it may have been concealed in the latter situation. Demographic data indicate that natural colonies produce one brood per year and that workers typically eclose into colonies with relatively low brood care demands. This suggests that overwintered workers do most of a colony's work and that the division of labor among overwintered ants is the more important one under natural conditions. The basis of this division is as yet unknown. These results also suggest that small colony size, univoltine brood schedule and a close association between foraging and brood care do not preclude division of labor among specialized castes, as has been suggested for another ponerine species (Traniello 1978).     

Behavioral Repertoire, Age Polyethism and Adult Transport in Ectatomma opaciventre (Formicidae: Ponerinae)

This study describes the behavioral repertoire of a mature colony of Ectatomma opaciventre Roger. Twenty-eight different behavioral acts were recorded from 4538 individual observations. There was evidence of age polyethism, with young workers performing significantly more brood care and allogrooming than older workers. Experiments were also performed to investigate the behavioral organization of nest relocation in E. opaciventre. This complex social behavior was regulated by a few workers which specialized in transporting nestmates, including other workers, winged gynes, males, and the queen. Winged gynes were also observed performing adult transport. The carrying posture utilized in E. opaciventre is similar to that in other ponerines, although some idiosyncratic features were detected.     

Ultrastructural changes in the fat body of adult female Aedes aegypti in relationship to vitellogenin synthesis

Summary The ultrastructure of the fat body of Aedes aegypti was followed from emergence through a blood meal. Changes in the volume of protein granules and lipid droplets were also examined. The relationship of these events to the known endocrinology of vitellogenin synthesis in mosquitoes is discussed.Massachusetts Experiment Station Paper No. 2130. Supported by the Massachusetts Agricultural Experiment Station, Project n° 356, and by NIH grant n° AI-11909     

In vivo role of 20-hydroxyecdysone in the regulation of the vitellogenin mRNA and egg development in the American dog tick, Dermacentor variabilis (Say)

Injection of the hormone 20-hydroxyecdysone (20-E) into partially fed (virgin) female adults of the American dog tick, Dermacentor variabilis, while they are attached and feeding on the rabbit host, initiated the expression of the vitellogenin (Vg) gene, and Vg protein secretion and uptake by the ovary. The induction of egg production by 20-E in this bioassay was dose dependent in the range of 1-50 times the concentration normally found in a replete, vitellogenic female. Ticks examined 4 d after the 50 x treatment were still attached to the host, had numerous enlarged vitellin-filled (brown) oocytes in their ovaries, but had not engorged to repletion. The ovaries reached weights similar to those found in untreated, replete (mated) females (pre-oviposition) while solvent-injected controls demonstrated no increase in oocyte size or increase in ovary weight. An increase in the levels of a putative Vg protein was observed in hemolymph samples collected 1, 2 and 3d post-20-E injection but was not observed in the corresponding solvent controls as determined by native PAGE. Analysis of the ecdysteroid-induced protein by tryptic digestion-mass fingerprinting and BLASTP found that the putative Vg had the strongest match to GP80 (U49934), the partial sequence for the vitellogenin protein from Boophilus microplus. A partial Vg cDNA was cloned and sequenced from replete females of D. variabilis with a high similarity to GP80. Using this message as a probe, Northern blots conducted with RNA collected from partially fed, virgin females 1, 2 and 3d post-20-E injection showed upregulation of the Vg mRNA on all 3 days. Controls injected with solvent only showed no Vg mRNA. Injections with juvenile hormone III did not stimulate Vg expression, oocyte growth or full engorgement. These studies indicate that ecdysteroids and not JH can initiate expression of the Vg gene, Vg protein synthesis and release into hemolymph, and Vg uptake into developing oocytes under bioassay conditions mimicking normal feeding on the host.     

Glandular Epithelium as a Possible Source of a Fertility Signal in Ectatomma tuberculatum (Hymenoptera: Formicidae) Queens

The wax layer covering the insect''s cuticle plays an important protective role, as for example, uncontrolled water loss. In social insects, wax production is well-known in some bees that use it for nest building. Curiously, mated-fertile queens of the ant Ectatomma tuberculatum produce an uncommon extra-wax coat and, consequently queens (mated-fertile females) are matte due to such extra cuticular hydrocarbon (CHC) coat that covers the cuticle and masks the brightness of the queens'' cuticle while gynes (virgin-infertile queens) are shiny. In this study, histological analysis showed differences in the epidermis between fertile (i.e., queens or gynes with highly ovarian activity) and infertile females (gynes or workers with non developed ovaries). In fertile females the epidermis is a single layer of cubic cells found in all body segments whereas in infertile females it is a thin layer of flattened cells. Ultrastructural features showed active secretory tissue from fertile females similar to the glandular epithelium of wax-producing bees (type I gland). Different hypotheses related to the functions of the glandular epithelium exclusive to the E. tuberculatum fertile queens are discussed.     

Polyethism within hunters of the ponerine ant,Ectatomma ruidum Roger (Formicidae,Ponerinae)

Summary During laboratory experiments, two categories of prey-foraging workers were found inEctatomma ruidum: stingers and transporters. When numerous live drosophila were offered to the ants, one group of hunters specialized in killing the prey and another in transporting simultaneously the dead drosophila to the nest. Sometimes, there was a transfer of prey by a stinger towards a transporter, after an active soliciting of the transporter by antennation or by using the forelegs. We found high positive correlations between the colony size and the number of ants in each subcaste. A negative correlation existed between the colony size and the proportion of hunters. However, the proportion of workers in the two behavioral subcastes of hunters was stable in spite of differences in colony size. The phylogenetic interest of this type of cooperative predation is discussed.     

A ribosome-free extract from cultured cells improves recovery of polysomes from the mosquito fat body: analysis of vitellogenin and ribosomal protein rpL34 gene expression

We have examined the association of ribosomal protein rpL34 mRNA with polysomes in Aedes albopictus C7-10 cells in culture using a simple, two-step sucrose gradient. In growing cells, 40-50% of the ribosomes were engaged on polysomes. This proportion could be increased to 80% when metabolism was stimulated by refeeding the cells with fresh medium. Conversely, ribosomes shifted off polysomes when cells were starved with phosphate-buffered saline or cell lysates were treated with puromycin. When similar approaches were used with fat body from blood-fed female Aedes aegypti mosquitoes, we were unable to obtain the polysome fraction that contained vitellogenin mRNA, which is abundantly translated after a blood meal. Addition of post-mitochondrial supernatant from fat body to polysomes from cultured cells shifted the polysome profile towards smaller polysomes and monosomes, in a dose-dependent fashion. Disruption of fat body tissue in a post-ribosomal supernatant from refed cells improved the recovery of polysomes, demonstrating both the engagement of vitellogenin mRNA on polysomes and the mobilization of rpL34 from messenger-ribonuceloprotein particles onto polysomes in blood-fed mosquitoes. These observations suggested that ribonucleases remain active when polysomes are prepared from mosquito fat body, and that cell culture supernatant contains a ribonuclease inhibitor.     

Molecular characterization and expression pattern of Spodoptera litura (Lepidoptera: Noctuidae) vitellogenin, and its response to lead stress

Vitellogenin (Vg) cDNA from Spodoptera litura Fabricius was cloned and sequenced. The open reading frame (ORF) of Vg cDNA was 5247 nucleotides in length (GenBank Accession no. EU095334), which encoded for a protein of 1748 amino acids. S. litura Vg comprised three conserved regions (Vitellogenin-N domain, DUF1943 and von Willebrand factor type D domain (VWD)), a 17 amino-acid signal peptide and a RXXR cleavage signal (RTIR). The highly conserved GL/ICG motif, the DGXR motif and cysteine residues were found in the C-terminus of the Vg. Vg mRNA was found specifically in the female fat body. Vg expression was first transcribed in 6th day female pupae and levels increased with insect development. The maximum level of Vg mRNA appeared in 24-h-old adults. When S. litura larvae were exposed to lead (Pb) (25-200 mg Pb/kg), there was a significant inhibition in Vg of female adults. The start of Vg expression was advanced ahead by Pb, from 6th day pupae to 3rd day or 4th day pupae. Low levels of Vg in male adults were also induced by low concentrations of Pb (12.5 and 25 mg Pb/kg). These data show that Pb stress elicits an important Vg response in S. litura.     

Vitellogenesis in both sexes of gonochoristic mud shrimp, Upogebia major (Crustacea): analyses of vitellogenin gene expression and vitellogenin processing

The mud shrimp, Upogebia major is a gonochoristic species with distinct sexual dimorphism; however, the male has the “ovarian part of testis” in the gonad and mature-looking eggs appear in a similar reproductive cycle to the female. Vitellogenesis of U. major was investigated focusing on the characterization of vitellogenin (Vg) gene expression and Vg processing. Vg cDNA cloned by PCR-based methods was 7799 bp-long, encoding 2568 amino acids in a single open reading frame. The deduced amino acid sequence shared common characteristics conserved in other shrimp Vgs. The Vg gene was expressed in the hepatopancreas of females and males, the ovary, and the ovarian part of testis. Vitellins (Vns) were detected in the gonads of both females and males as three prominent polypeptides with apparent molecular masses of 82 kDa, 100 kDa, and 115 kDa. N-terminal amino acid sequences determined for the three polypeptides were present in the deduced amino acid sequence, demonstrating that they derived from a single long Vg polypeptide. Immunoblot analysis using polyclonal antibodies raised against two Vns (82 kDa and 100 kDa) confirmed Vg processing in the hepatopancreas, in the hemolymph and possibly in the oocytes, similarly in both sexes.     

Hepatopancreas is the extraovarian site of vitellogenin synthesis in black tiger shrimp, Penaeus monodon

The site of yolk protein synthesis in crustaceans has long been a subject of controversy. The vitellogenin gene structure was partially reported only very recently in Macrobrachium rosenbergii, after which the hepatopancreas was confirmed as the extraovarian site of vitellogenin synthesis in that species. Ovaries are the most frequently reported as the site of yolk protein synthesis in penaeid shrimp. Using cDNA reversed-transcribed from mRNA isolated from the hepatopancreas of vitellogenic female shrimp, Penaeus monodon, we found that its deduced amino acid sequence had high identity of 48% with that from M. rosenbergii vitellogenin. A similar location of the intron in the sequenced region of genomic DNA was also found between these two species. We therefore concluded that the hepatopancreas the extraovarian site of vitellogenin synthesis in P. monodon in vivo. The partial structure of vitellogenin gene is presented in this study.     

Size and fat content of gynes in relation to the mode of colony founding in ants (Hymenoptera; Formicidae)

Summary In ants, there are two main processes of colony founding, the independent and the dependent modes. In the first case young queens start colony founding without the help of workers, whereas in the second case they are accompanied by workers. To determine the relation between the mode of colony founding and the physiology of queens, we collected mature gynes of 24 ant species. Mature gynes of species utilizing independent colony founding had a far higher relative fat content than gynes of species employing dependent colony founding. These fat reserves are stored during the period of maturation, i.e. between the time of emergence and mating, and serve as fuel during the time of colony founding to nurture the queen and the brood. Gynes of species founding independently but non claustrally were found to have a relative fat content intermediate between the values found for gynes founding independently and those founding dependently. This suggests that such gynes rely partially on their fat reserves and partially on the energy provided by prey they collect to nurture themselves and the first brood during the time of colony founding. Study of the fat content of mature gynes of all species has shown that it gives a good indication of the mode of colony founding.     

One-step, non-denaturing purification method of carp (Cyprinus carpio) vitellogenin

A new single-step purification procedure was developed to purify carp (Cyprinus carpio) vitellogenin (VTG), from estradiol-treated carp plasma. This method was performed by high performance liquid weak anion-exchange chromatography, using a discontinuous elution gradient of NaCl (0-0.5 M, steps of 12.5 mM/4 min). SDS and native-PAGE analysis, of treated-fish plasma and purified solution, showed the appearance of a 370 kDa phospholipoprotein, composed of two 130 kDa monomers, with all VTG characteristics. The sequencing of a 130 kDa monomer confirmed that it was carp VTG. Consequently, this procedure is a rapid method, permitting high quantities of non-denatured carp VTG to be obtained.     

Methoprene accelerates age polyethism in workers of a social wasp (Polybia occidentalis)

Abstract. Topical applications of the Juvenile Hormone (JH) analogue methoprene to 1-day-old adult workers of the highly eusocial wasp Polybia occidentalis (Olivier) (Hymenoptera: Vespidae) accelerate the rate of age polyethism. Longevity of laboratory-reared wasps is negatively correlated with dose of topically applied methoprene. Doses of 25 μg methoprene or greater are lethal. Untreated wasps show marked age polyethism in the field. Age of first performance of acts in seven behavioural categories (in-nest, transition to outside, non-task on nest envelope, nest maintenance, foraged material handling, defence, and foraging) is negatively correlated with methoprene dose. Topical applications of methoprene accelerate age polyethism of highly eusocial bee and wasp workers, but do not have this effect on primitively eusocial bees and wasps, suggesting that JH control of age polyethism evolved independently in advanced species of Apidae and Vespidae.     

Polymorphism and oligogyny in the ponerine antCentromyrmex bequaerti (Formicidae: Ponerinae)

Summary Centromyrmex bequaerti is a ponerine ant of the African equatorial forest which nests in the termitaries of diverse Termitinae and Macrotermitinae, occupying several chambers and galleries of the termitaries and preying on their guests. This species presents four traits convergent with termitolestic Myrmicinae: a parasitic nesting habit (but shelters directly in the cavities of the termitaries and not in the walls), blind workers, a strong dimorphism between the queens (20 mm in length) and the workers (from 5.75 to 12 mm total length) and polymorphism in the worker caste. We recorded two other traits considered as evolutionarily-derived: oligogyny, a kind of polygyny (the societies include up to 13 queens, but each queen lives in a separate cavity of the termitary) and large colon size. Behavioural observations show that there is a relationship between worker size and polyethism in this species. Although workers of all size classes participate in hunting, the media are more often engaged in this activity and the largest workers guard the nest entrance.     

Flexibility of first brood production in a claustral ant, Camponotus japonicus (Hymenoptera: Formicidae)

The numbers of first-batch eggs and workers (minims) in a carpenter ant Camponotus japonicus are not fixed but are regulated in response to various internal and external factors of founding queens. The initial body weight of founding queens was positively correlated with the number of minims. The amount of queen weight loss during the founding period was highly correlated with the number of minims. The numbers of first-batch eggs and minims for artificially fed queens were significantly greater than those for control group queens and for unfed queens, respectively. The number of eggs laid by a queen increased when eggs deposited in the early stage of founding were removed. In contrast, artificial addition of alien eggs reduced the number of eggs laid by a queen. The adaptive implications of this flexibility in the production of the first-batch brood in C. japonicus are discussed. Received: December 18, 2000 / Accepted: March 19, 2001     

Ultrastructural immunocytochemical localization of vitellogenin in the fat body of the blowfly,Calliphora vicina Rob.-Desv. (erythrocephala Meig.) by use of the unlabeled antibody-enzyme method

Summary The unlabeled antibody-enzyme method was used to demonstrate ultrastructurally the specific localization of vitellogenin in the fat body of Calliphora. In control flies the binding sites to vitellogenin were localized in secretory granules situated in the Golgi complex, and in larger bodies named composite secretory granules. These composite granules appear to be formed when a part of a Golgi complex containing secretory granules and a number of small vesicles become surrounded by a common membrane. Ovariectomized flies, which apparently do not produce secretory granules, exhibited no immunocytochemical staining. Ovariectomized flies in which the administration of ecdysterone induced formation of secretory granules, also revealed specific staining on these granules. This is the first ultrastructural evidence of: (a) the specific localization of vitellogenin in secretory granules of the fat body of an insect; (b) the relationship between the presence of the ovary, and of ecdysterone, and the synthesis of vitellogenin by the fat body.     

Molecular characterization of the vitellogenin receptor from the tick,Amblyomma hebraeum (Acari: Ixodidae)

We have identified the full-length cDNA encoding a vitellogenin receptor (VgR) from the African bont tick Amblyomma hebraeum Koch (1844). VgRs are members of the low-density lipoprotein receptor superfamily that promote the uptake of the yolk protein vitellogenin (Vg), from the haemolymph. The AhVgR (GenBank accession No. JX846592) is 5703 bp, and encodes an 1801 aa protein with a 196.5 kDa molecular mass following cleavage of a 22 aa signal peptide. Phylogenetic analysis indicates that AhVgR is highly similar to other tick VgRs. AhVgR is expressed in only the ovary of mated, engorged females, and is absent in all other female tissues and in both fed and unfed males. Unfed, adult females injected with a VgR-dsRNA probe to knock-down VgR expression experienced a significant delay in ovary development and started oviposition significantly later than controls. These results indicate that the expression of AhVgR is important for the uptake of Vg and subsequent maturation of the oocytes.