Policing behaviour towards virgin egg layers in a polygynous ponerine ant

The majority of colonies of Gnamptogenys menadensis in Sulawesi lack queens and several workers ('gamergates') mate and reproduce instead. Virgin workers lay morphologically specialized trophic eggs which are fed to larvae. Some of these virgins switch to male eggs when gamergates are experimentally removed. Three distinct patterns of oogenesis thus result in: (1) trophic eggs; (2) reproductive eggs (unfertilized) laid by virgin workers; and (3) reproductive eggs laid by gamergates, whose ovarioles are always longer than those of virgin workers. We investigated the behavioural regulation of ovarian activity in virgin workers by temporarily excluding gamergates. In 12 groups of 35-45 virgins, a few workers became dominant and started to lay reproductive eggs. Once gamergates were reintroduced, sterile workers attacked and immobilized workers with enlarged ovaries (confirmed by dissection of 173 individuals), which often died as a result. Gamergates were never aggressive towards new egg layers. Aggression was not triggered by divergence in colony odours, as it was absent in control experiments in which six colonies were divided in half, with each part containing gamergates, and reunited after 50 days. Our results show that sterile workers discriminate against new egg layers, given that their ovaries are not as developed as those of gamergates. Olfactory detection of different levels of ovarian activity thus appears possible. Mesh experiments indicated that the putative pheromones are nonvolatile and require physical contact for transmission. Aggressive behaviour directed at reproducing workers can be interpreted as worker policing. In G. menadensis, worker policing results in virgins laying only trophic eggs. Copyright 1999 The Association for the Study of Animal Behaviour.     

Morphology and reproductive behaviour of intercastes in the ponerine antPachycondyla obscuricornis

Summary Queens are usually the functional reproductives inPachycondyla obscuricornis, but none were found in one colony collected near Brasilia. In this colony, three adults differed morphologically from workers; although wingless, their thorax was more or less like that of winged queens (scutum and scutellum distinct; metanotum larger than that of workers). Another 11 such individuals were found by opening cocoons. We consider that these are intercastes (sensu Peeters, 1991). Two adult intercastes were mated and laid eggs. In contrast, all the workers were virgin, but some laid distinct trophic eggs which were fed to the two reproductives. Following experimental removal of the intercastes, dominance interactions began among the workers, and reproductive eggs were then laid. Intercastes with a reproductive function have not been reported previously in the Ponerinae. They are distinct from ergatoid queens (permanently wingless reproductive caste) or gamergates (mated egglaying workers).     

Reproductive allocation in multinest colonies of the ponerine ant Pachycondyla goeldii

Abstract.  1.  Pachycondyla goeldii constitutes the only recorded case of a monogynous (i.e. one queen per colony) polydomous (i.e. several nests per colony) species in the Ponerinae subfamily. This study examines the impact of polydomy on reproductive allocation between nests (also called 'calies' in polydomous society) in Pachycondyla goeldii Forel, by: (i) recording the number of workers and sexuals in 67 nests belonging to 21 colonies; (ii) dissection of workers in nine nests containing a queen (QR nests), nine nests without a queen but associated to a QR nest (QL nests) and five nests belonging to colonies that permanently lost the queen (OR nests); and (iii) measuring the length of all eggs present in the nests (our laboratory study shows that queen-laid eggs were significantly longer than worker-laid eggs).
2. The number of workers was significantly higher in QR nests than in QL nests, while the number of virgin queens was significantly higher in QL nests compared with QR nests.
3. Worker ovarian activity is inversely related to queen proximity: highest in OR nests, intermediate in QL nests, and lowest in QR nests.
4. Egg length was highest in QR nests, where the queen was most likely the primary egg-layer, intermediate in QL nests, where eggs could have originated from both the queen and workers, and lowest in OR nests, where workers were the sole egg-layers.
5. We postulate that the proximal mechanism explaining differences between QR and QL nests is the pheromonal absence of the queen from QL nests and that the evolutionary reasons of these divergences between nest types are likely to originate from the different conflicts occurring in ant colonies.     

Chemical profiles of mated and virgin queens, egg-laying intermorphs and workers of the ant Crematogaster smithi

Many colonies of the North American ant Crematogaster smithi contain a “third female caste” in addition to queens and workers. These “intermorphs” are morphological intermediate of queens and workers and have well-developed ovaries but lack a spermatheca for the storage of sperm. They are specialised for laying large numbers of unfertilised, viable eggs, most of which serve as food for larvae and adults, though a few may eventually develop into males. Based on the assumption that cuticular hydrocarbons (CHCs) in social insects honestly signal the reproductive status of an individual we investigated the CHC of mated mature queens, virgin queens, intermorphs and workers. We expected intermorphs to show chemical profiles intermediate between those of mated queens and non-reproductive workers. A discriminant analysis of the chemical profiles reliably separated queens, virgin queens, and workers, but failed to distinguish between queens and intermorphs even though workers were apparently capable of doing so.     

Emergence and mating behavior of the oriental fruit moth Cydia molesta (Lepidoptera: Tortricidae) and its potential for reproduction

The Oriental fruit moth, Cydia molesta (Busck, 1916) (Lepidoptera: Tortricidae), is a key pest of fruit and is widely distributed around the world. There are important connections between its behavior and biology and its management in agriculture, but few studies have investigated the associations between adult behaviors and oviposition. In this study, adult emergence, mating, and reproduction were investigated under laboratory and field conditions. The ratio of females to males at eclosion was approximately 1:1. When one virgin female had access to one virgin male, 66% and 34% of the couples copulated just once and twice, respectively; and the infertility rate of eggs (21.39 ± 1.25%) did not vary daily. Males, given access to one new female daily, could copulate multiple times, whereas females seldom mated more than once, indicating a male-biased operational sex ratio, but mating status of the male parent had no effect on progeny egg reproduction. Also, the number of eggs that hatched by all female partners of a male was inversely proportional to copulation duration for the female laying the eggs for total female reproductive success; and the number of eggs laid by all female partners of a male was proportional to their number of matings for total male reproductive success. However, the total number of eggs that hatched did not significantly differ for eggs laid by a female given new virgin males daily for mating (17.75 ± 4.28) versus eggs laid by virgin females (19.17 ± 7.51) presented daily with a male that re-mated daily with the series of females. Therefore, our results showed that females engaged in mate choice and males engaged in mate competition, affecting egg production, a factor that may be used to enhance mating disruption technology against Cydia molesta.     

Worker reproduction and policing in insect societies: an ESS analysis

Insect societies are vulnerable to exploitation by workers who reproduce selfishly rather than help to rear the queen's offspring. In most species, however, only a small proportion of the workers reproduce. Here, we develop an evolutionarily stable strategy (ESS) model to investigate factors that could explain these observed low levels of reproductive exploitation. Two key factors are identified: relatedness and policing. Relatedness affects the ESS proportion of reproductive workers because laying workers generally work less, leading to greater inclusive fitness costs when within-colony relatedness is higher. The second key factor is policing. In many species, worker-laid eggs are selectively removed or 'policed' by other workers or the queen. We show that policing not only prevents the rearing of worker-laid eggs but can also make it unprofitable for workers to lay eggs in the first place. This can explain why almost no workers reproduce in species with efficient policing, such as honeybees, Apis, and the common wasp, Vespula vulgaris, despite relatively low relatedness caused by multiple mating of the mother queen. Although our analyses focus on social insects, the conclusion that both relatedness and policing can reduce the incentive for cheating applies to other biological systems as well.     

Functional Monogyny and Dominance Hierarchy in the Queenless Ponerine Ant Pachycondyla (=Bothroponera) sp. in West Java,Indonesia (Hymenoptera,Formicidae, Ponerinae)

Social organization of the queenless ponerine ant Pachycondyla (Bothroponera) sp. was studied in Bogor, West Java, Indonesia. Colonies had no morphologically distinct queens. Worker number per colony was 11 on average. Most colonies contained multiple mated workers (gamergates), however, only one of them laid eggs, whereas additional gamergates were sterile or ovipositing at a low rate, indicating that this ant species shows functional monogyny. Some virgin workers also developed their oocytes and actually laid eggs. Ritualized dominant — subordinate behavior was frequently observed and a linear dominance hierarchy was established among workers. The topranking individual was a fertile gamergate. Sterile gamergates positioned in lower ranks and they often engaged in foraging. Among virgin workers, callows and young workers monopolized higher ranks.     

Potential and realized reproduction by different worker castes in queen-less and queen-right colonies of <Emphasis Type="Italic">Pogonomyrmex badius</Emphasis>

Workers of the Florida harvester ant (Pogonomyrmex badius), the only North American Pogonomyrmex with a polymorphic worker caste, produce males when colonies are orphaned. In this study,we assessed the reproductive potential of workers of each caste group, minors and majors, in the presence and absence of the queen, and tested whether males produced in natural queen-right colonies are derived from workers. Worker size was positively correlated with ovariole number such that major workers had approximately double the number of ovarioles as minor workers. The number of vitellogenic oocytes, a measure of reproductive potential, was greater in major compared to minor workers and increased in both worker castes when queens were removed. Major workers have greater reproductive potential than minors although they represent a minority within the colony (~5% of workers are majors). Worker produced eggs were visible in colonies 28 – 35 days after queen removal. This time lag, from queen removal to egg production, is similar to other ants and bees. Though workers are capable of producing viable eggs, we found no evidence that they do so in queen-right colonies, suggesting that worker reproduction is controlled via some social mechanism (self restraint, policing, or inhibition). This result supports predictions of kin selection theory – that due to multiple mating by the queen workers are more related to queen-produced males than most worker-produced males and should thus favor reproduction by the queen and inhibit reproduction by other workers. Received 25 January 2007; revised 1 May 2007; accepted 21 May 2007.     

The reproductive cycle of thelytokous colonies of Cerapachys biroi Forel (Formicidae,Cerapachyinae)

Summary: The reproductive cycle of thelytokous colonies of Cerapachys biroi was investigated in laboratory conditions. It included several stages, the duration of which was assessed by direct observation on experimental nests set up by fission of natural, queenless, colonies. The results show that two phases of adult activity alternated while cohorts of brood developed synchronously. During the statary phase, virgin workers laid diploid eggs simultaneously but no foraging activity was observed until the following phase which began after the callow workers of the previous brood cohort emerged and the eggs hatched. During this foraging phase, workers explored intensively for food while larvae matured synchronously. Biometrical measures allowed to determine that three larval instars occurred in this species. While larvae started pupation, workers stopped to forage and the next statary phase took place, during which a new cohort of eggs was laid and pupae matured. This repeated phasic reproductive cycle where adult activity and development of the brood are synchronised reminds that of true army ants (subfamily Ecitoninae), which brings new arguments in favour of a filiation between both groups.     

Reproduction by virgin queen fire ants in queenless colonies: Comparative study of three taxa (Solenopsis richteri,hybridS. invicta/richteri,S. geminata) (Hymenoptera: Formicidae)

Summary In the fire ant,Solenopsis invicta, some winged virgin queens are known to shed their wings (dealate) upon removal of the mated mother queen. These virgin queens then develop their ovaries and begin to lay eggs, thereby foregoing the option of leaving on mating flights and attempting to found their own colonies. Such a response of virgin queens to queenlessness has not been reported for other ants. In order to determine if virgin queens of some other fire ants (subgenusSolenopsis) would respond in the same way, experiments were conducted onS. richteri, hybridS. invicta/richteri andS. geminata, a member of a species complex different from that of the other taxa. Just as inS. invicta, virgin queens ofS. richteri and the hybrid dealated and began to lay eggs within days of the removal of the queen. In addition, workers executed many of the reproductively active virgin queens, a phenomenon also found inS. invicta. In contrast, virgin queens ofS. geminata did not dealate or quickly begin to lay eggs upon separation from the queen. Reasons for the variability in the response of virgin queens of the different species may be 1) higher probability of reproductive success for unmated dealated queens compared to normal claustral founding inS. invicta andS. richteri linked to relatively frequent loss of the mother queen; or 2) phylogenetic constraint.     

Worker reproductive parasitism in naturally orphaned colonies of the Asian red dwarf honey bee, Apis florea

The truce between honey bee (Apis spp.) workers over reproduction is broken in the absence of their queen. Queenright workers generally abstain from personal reproduction, raising only the queen’s offspring. Queenless workers activate their ovaries, produce eggs, and reduce the rate at which they destroy worker-laid eggs, so that some eggs are reared to maturity. Reduced policing of worker-laid eggs renders queenless nests vulnerable to worker reproductive parasitism (WRP), and may result in the colony raising eggs of unrelated (non-natal) workers that parasitize it. Queenless colonies of A. florea are heavily parasitized with the eggs of non-natal workers. However, queenless colonies often abscond upon disturbance and build a small comb in which to rear their own male offspring. We investigated three naturally occurring orphaned colonies to determine if they are also parasitized. We show that WRP is present in orphaned colonies, and non-natal workers have significantly higher rates of ovary activation than natal workers. In contrast to experimentally manipulated colonies, in our samples, natal and non-natal workers had statistically equal reproductive success, but this may have been due to the small number of non-natals present.     

Cheaters sometimes prosper: targeted worker reproduction in honeybee (Apis mellifera) colonies during swarming

Kin selection theory predicts that honeybee (Apis mellifera) workers should largely refrain from producing their own offspring, as the workers collectively have higher inclusive fitness if they rear the sons of their mother, the queen. Studies that have quantified levels of ovary activation and reproduction among workers have largely supported this prediction. We sampled pre‐emergent male pupae and adult workers from seven colonies at regular intervals throughout the reproductive part of the season. We show that the overall contribution of workers to male (drone) production is 4.2%, nearly 40 times higher than is generally reported, and is highest during reproductive swarming, when an average of 6.2% of the males genotyped are worker‐produced. Similarly, workers in our samples were 100 times more likely to have active ovaries than previously assumed. Worker reproduction is seasonally influenced and peaks when colonies are rearing new queens. Not all worker subfamilies contribute equally to reproduction. Instead, certain subfamilies are massively over‐represented in drone brood. By laying eggs within the period in which many colonies produce virgin queens, these rare worker subfamilies increase their direct fitness via their well‐timed sons.     

Some aspects of oögenesis in the stable fly Stomoxys calcitrans (Diptera: Muscidae)

Two distinct patterns of blood ingestion in the female stable fly, Stomoxys calcitrans L. were observed, based on whether or not the female was mated. Mating is not required for oögenesis, but is necessary for oviposition. Virgin females develop eggs but, in the absence of mating, they retain eggs until death. In stable flies, oögenesis appears to be atypical among other dipterans as the penultimate follicles develop and deposit up to 50% yolk before the terminal follicles are matured. Oösorption was seen in the penultimate follicles of virgin females retaining eggs. Accessory-gland implants initiated oviposition in virgin females. However, the total number of eggs laid by such females was 50% less than the number of eggs laid by mated flies.     

Colony structure and reproduction in the thelytokous parthenogenetic ant Platythyrea punctata (F. Smith) (Hymenoptera, Formicidae)

Summary: An important evolutionary characteristic of the formicine subfamily Ponerinae is the occurrence of various alternative reproductive tactics within single species. In Platythyrea punctata Smith, 1858, queens, gamergates and parthenogenetic workers co-occur in the same species. Morphological queens, both alate and dealate, were present in only 29 percent of the colonies collected in Florida, but absent from colonies collected in Barbados and Puerto Rico. One of the six queens which were dissected (three alate and three dealate) was found to be inseminated but not fertile. Instead, in most queenless colonies, a single uninseminated worker monopolized reproduction by means of thelytokous parthenogenesis, i.e., it produced female offspring from unfertilized eggs. A single mated, reproductive worker (gamergate) was found dominating reproduction in the presence of an inseminated alate queen in one of the Florida colonies. Thelytokous parthenogenesis was examined in artificial groups of virgin laboratory-reared workers, where one worker typically monopolized reproduction despite the presence of several individuals with elongated ovaries. In 16 colonies collected in Florida, a total of 66 individuals differed morphologically from queens and workers. Their thorax morphology varied from a worker-like to an almost queen-like structure. We refer to these individuals as "intercastes" (sensu Peeters, 1991a). The remarkable complexity of reproductive strategies renders P. punctata unique within ants.     

Vitellogenin content in fat body and ovary homogenates of workers and queens of Melipona quadrifasciata anthidioides during vitellogenesis

Abstract Vitellogenin (Vg) is an egg yolk protein that is produced primarily in the fat body of most female insects. In the advanced social structure of eusocial honeybees, the presence of the queen inhibits egg maturation in the workers’ ovaries. However in the stingless bee Melipona quadrifasciata, the workers always develop ovaries and lay a certain amount of eggs while provisioning the brood cells with larval food during what is known as the worker nurse phase. The present work is a comparative study of the presence of Vg in homogenates of the fat bodies and ovaries of the nurse workers, and the virgin and physogastric queens of M. quadrifasciata. The presence of Vg was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoblotting using Apis mellifera anti‐egg antibody. Vg was not detected in the fat bodies or ovaries of the workers, but it was found in the ovaries of virgin and physogastric queens and in the fat body of physogastric queens. The results are discussed, taking into account the reproductive state of the individuals and the other possible roles of Vg, such as a storage protein for metoabolism of other organs.     

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.     

Egg-Laying “Intermorphs” in the Ant Crematogaster smithi neither Affect Sexual Production nor Male Parentage

We study male parentage and between-colony variation in sex allocation and sexual production in the desert ant Crematogaster smithi, which usually has only one singly-mated queen per nest. Colonies of this species are known to temporarily store nutrients in the large fat body of intermorphs, a specialized female caste intermediate in morphology between queens and workers. Intermorphs repackage at least part of this fat into consumable but viable male-destined eggs. If these eggs sometimes develop instead of being eaten, intermorphs will be reproductive competitors of the queen but—due to relatedness asymmetries—allies of their sister worker. Using genetic markers we found a considerable proportion of non-queen sons in some, but not all, colonies. Even though intermorphs produce ∼1.7× more eggs than workers, their share in the parentage of adult males is estimated to be negligible due to their small number compared to workers. Furthermore, neither colony-level sex allocation nor overall sexual production was correlated with intermorph occurrence or number. We conclude that intermorph-laid eggs typically do not survive and that the storage of nutrients and their redistribution as eggs by intermorphs is effectively altruistic.     

Morphology of reproductive and trophic eggs and their controlled release by workers in Trigona (Tetragonisca) angustula llliger (Apidae, Meliponinae)

Abstract. To study the reproductive potential of workers in the stingless bee Trigona (Tetragonisca) angustula Illiger (Apidae, Meliponinae), we examined the morphological quality of their eggs. Worker-eggs were all placed on the inside of the upper wall of brood cells. Normally, such eggs are consumed by the queen and are therefore referred to as trophic. The provisioning and oviposition processes in queenright colonies are characterized by the occurrence of circular aggregations of workers, 'rosettes', around the broodcell opening immediately after the release of a worker-egg. The ovaries of 35% of these rosette workers contained mature, chorionated eggs. In a single worker ovary, always only one mature egg was found. Some of the eggs, dissected from the ovarioles, showed a reticulate chorion pattern. Worker-eggs which lacked this pattern were significantly bigger than patterned eggs. Scanning electron micrographs revealed that the patterned worker-eggs are similar in appearance to queen-eggs.
After a worker-egg had been removed experimentally from a broodcell, the same cell could be oviposited by a worker again. Light microscopic analysis revealed that all these worker-eggs lacked the reticulate chorion pattern and were very similar in their morphology. In a colony without a laying queen workers laid eggs which had a reticulate pattern on the chorion. Since these eggs developed into males, we assume that the pattern on the chorion is characteristic for reproductive eggs. We also assume that the queen prevents the release of reproductive eggs by the workers. However, she does not inhibit the development of this type of egg.     

Virgin wasps develop ovaries on par with mated females, but lay fewer eggs

In the primitively eusocial wasp Ropalidia marginata, mating is not necessary for a female wasp to develop her ovaries, lay eggs, and even to become the sole egg layer of her colony despite the presence of other mated nestmates. Here, we show that virgin wasps do not differ from their mated counterparts in the extent and rapidity of their ovarian development, in the proportion of individuals that build a nest and laid eggs, and in the time taken to do so. However, a significantly larger proportion of virgin females showed resorbing oocytes, and laid fewer eggs as compared to mated individuals. Thus, virgin females have the ability to develop ovaries and lay eggs but also to refrain from necessarily laying all mature eggs produced, before mating opportunities arise. This dual ability would be adaptive in haplodiploid, tropical species with perennial nesting cycles and frequent opportunities for workers to become replacement queens or solitary nest foundresses throughout the year.     

Regulation of reproduction in a queenless ant: aggression,pheromones and reduction in conflict

In the monogynous queenless ant Diacamma ceylonense, the future reproductive (future gamergate) is very aggressive towards infertile workers during the first days of her adult life. Overt aggression disappears at about three weeks, when the future gamergate begins to lay male-destined eggs and is ready to mate. Over the same period, her cuticular hydrocarbon profile alters, changing from a chemical signature similar to that of a sterile worker towards that of a gamergate. In nature, these behavioural and chemical changes will coincide with a reduction in conflict within the nest: faced with a virgin future gamergate, infertile workers have an interest in producing male-destined eggs; however, once the gamergate produces female eggs, they have an interest in rearing her offspring. This demonstration of a shift from physical inhibition to chemical signalling is interpreted in terms of sociogenetic theory, the role of cuticular hydrocarbons as an indicator of fertility in insects and the fact that the regulation of reproduction in Diacamma involves mechanisms redolent of both queenless and queenright ant species.