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 value of oviposition timing,queen presence and kinship in a social insect

Reproductive cooperation confers benefits, but simultaneously creates conflicts among cooperators. Queens in multi-queen colonies of ants share a nest and its resources, but reproductive competition among queens often results in unequal reproduction. Two mutually non-exclusive factors may produce such inequality in reproduction: worker intervention or queen traits. Workers may intervene by favouring some queens over others, owing to either kinship or queen signals. Queens may differ in their intrinsic fecundity at the onset of oviposition or in their timing of the onset of oviposition, leading to their unequal representation in the brood. Here, we test the role of queen kin value (relatedness) to workers, timing of the onset of oviposition and signals of presence by queens in determining the maternity of offspring. We show that queens of the ant Formica fusca gained a significantly higher proportion of sexuals in the brood when ovipositing early, and that the presence of a caged queen resulted in a significant increase in both her share of sexual brood and her overall reproductive share. Moreover, the lower the kin value of the queen, the more the workers invested in their own reproduction by producing males. Our results show that both kinship and breeding phenology influence the outcome of reproductive conflicts, and the balance of direct and indirect fitness benefits in the multi-queen colonies of F. fusca.     

Kin structure and colony male reproduction in the hornet<Emphasis Type="Italic"> Vespa crabro</Emphasis> (Hymenoptera: Vespidae)

We estimated queen mating frequency, genetic relatedness among workers, and worker reproduction in Vespa crabro flavofasciata using microsatellite DNA markers. Of 20 colonies examined, 15 contained queens inseminated by a single male, 3 colonies contained queens inseminated by two males, and 2 colonies contained queens inseminated by three males. The genetic relatedness among workers was estimated to be 0.73±0.003 (mean±SE). For this high relatedness, kin selection theory predicts a potential conflict between queens and workers over male production. To verify whether males are derived from queens or workers, 260 males from 13 colonies were genotyped at four microsatellite loci. We found that all of the males were derived from the queens. This finding was further supported by the fact that only 33 of 2,990 workers dissected had developed ovaries. These workers belonged to 2 of the 20 colonies. There was no relationship between queen mating frequency and worker reproduction, and no workers produced male offspring in any of the colonies. These results suggest that male production dominated by queens in V. crabro flavofasciata is possibly due to worker policing.     

The potential for worker reproduction in the ant <Emphasis Type="Italic">Aphaenogaster cockerelli</Emphasis> and its absence in the field

A reproductive division of labor between subordinates and established reproductives is a hallmark of eusociality. In most groups, however, workers retain some reproductive capabilities. Across insect societies, measures of successful worker reproduction in the presence of a queen, with few exceptions, indicate that worker reproduction is kept at very low levels. There are, however, certain colony-level characteristics that may influence the degree to which worker reproduction is promoted, such as queen number, queen mating frequency, and physical presence of a queen in species with multiple nesting sites (polydomy). In this study, the level of worker reproduction in field colonies of the ant species Aphaenogaster cockerelli was measured. A. cockerelli is a monogynous and polydomous species, so worker reproduction across nesting sites was investigated. None of the 297 males sampled provided any evidence of worker reproduction. Worker reproduction would have been detectable if it was present at or above a level of 1.5 % of the total males per colony. An effective mating frequency for queens of this species was found to be 1.03. Although A. cockerelli colonies have many colony-level factors potentially promoting worker reproduction (workers with active, trophic egg-producing ovaries, a single singly-mated queen, workers who are physically separated from the queen), it is evident that worker reproduction is highly regulated. Synthesizing the extensive amount of policing and fertility signaling data previously reported on this species, A. cockerelli is presented as case study for how worker reproduction is repressed and cooperation is maintained in insect societies.     

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.     

Worker interests and male production in Polistes gallicus, a Mediterranean social wasp

The resolution of social conflict in colonies may accord with the interests of the most numerous party. In social insect colonies with single once-mated queens, workers are more closely related to the workers' sons than they are to the queens' sons. Therefore, they should prefer workers to produce males, against the queen's interests. Workers are capable of producing males as they arise from unfertilized eggs. We found Polistes gallicus to have colonies of single, once-mated queens, as determined by microsatellite genotyping of the workers, so worker interests predict worker male production. In colonies lacking queens, workers produced the males, but not in colonies with original queens. Thus worker interests were expressed only when the queen was gone. The high fraction of missing queens and early end to the colony cycle relative to climate so early in the season is surprising and may indicate a forceful elimination of the queen.     

The evolution of worker sterility in honeybees: the genetic basis of failure of worker policing

Worker honeybees (Apis mellifera) usually only lay eggs when their colony is queenless. However, an extremely rare ''anarchistic'' phenotype occurs, in which workers develop functional ovaries and lay large numbers of haploid eggs which develop into adult drones despite the presence of the queen. Studies of such colonies can give important insights into the mechanisms by which worker sterility is maintained in normal colonies. Here we report on the results of a breeding programme which enhanced the frequency of the anarchistic phenotype. Colonies derived from queens inseminated only by worker-laid males showed up to 9% of workers with highly developed ovaries. In these colonies a large proportion of males arose from worker-laid eggs. Colonies headed by queens inseminated with 50% worker-laid drones and 50% queen-laid drones showed variable phenotypes. In most such colonies there was no worker reproduction. In some, many workers had highly developed ovaries, but no worker-laid eggs were reared. In one colony, many worker-laid eggs were reared to maturity. The results suggest that the anarchy phenotype results from a complex interaction of queen genotype, the worker genotype of subfamilies that successfully reproduce and of those that do not, and the external environment.     

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.     

Mating structure and male production in Vespa analis and Vespa simillima (Hymenoptera: Vespidae)

We estimated queen mating frequency, genetic relatedness between workers and worker reproduction in the hornets Vespa analis and Vespa simillima using microsatellite DNA genotyping. The 20 V. analis colonies studied each contained a queen inseminated by a single male. Of the 15 V. simillima colonies studied, nine had a queen inseminated by a single male, four had a queen inseminated by two males, and two had a queen inseminated by three males. The estimated effective number of matings was 1.33 ± 0.74 (mean ± SD), with 75–85% of the offspring of the six multiply mated queens sired by single males. The values for genetic relatedness between the workers of V. analis and V. simillima were 0.739 ± 0.004 and 0.698 ± 0.013 (mean ± SD), respectively. We conclude that V. analis and V. simillima colonies are genetically monogynous and monandrous. When high relatedness between the workers occurs within colonies, kin selection theory predicts a potential conflict between queens and workers over male production. To determine whether males were derived from queens or workers, males from V. analis and V. simillima colonies were genotyped at four microsatellite loci and the level of ovary activation in workers was determined. None of the 787 V. analis workers and only 15 of 3520 V. simillima workers had developed ovaries. Furthermore, the genotyping identified no worker‐produced males in any colony. The presence of reproductive workers correlated positively with the number of workers within the colony. These results suggest that eusocial colonies with an annual life cycle tend to break down socially when they become large and are close to dying.     

The Effect of Queen and Worker Adoption on Weaver Ant (Oecophylla smaragdina F.) Queen Fecundity

Incipient ant colonies are often under fierce competition, making fast growth crucial for survival. To increase production, colonies can adopt multiple queens (pleometrosis), fuse with other colonies or rob brood from neighboring colonies. However, different adoption strategies might have different impacts such as future queen fecundity or future colony size. O. smaragdina queen production was measured in incipient colonies with 2, 3 or 4 founding queens, following the transplantation of 0, 30 or 60 pupae from a donor colony. Pupae developed into mature workers, resulting in increased worker/queen ratios in pupae transplanted treatments and leading to increases in the per capita queen production. Conversely, more queens did not induce increased per capita fecundity. Thus, brood robbing added individuals to the worker force and increased future production of resident queens, whereas queen adoption increased the colony’s future production, but not the production of individual queens.     

Differential time allocation of foraging workers in the subterranean termite

Background

Worker reproduction has an important influence on the social cohesion and efficiency of social insect colonies, but its role in the success of invasive ants has been neglected. We used observations of 233 captive colonies, laboratory experiments, and genetic analyses to investigate the conditions for worker reproduction in the invasive Anoplolepis gracilipes (yellow crazy ant) and its potential cost on interspecific defence. We determined the prevalence of worker production of males and whether it is triggered by queen absence; whether physogastric workers with enlarged abdomens are more likely to be reproductive, how normal workers and physogastric workers compare in their contributions to foraging and defence; and whether worker-produced males and males that could have been queen- or worker-produced differ in their size and heterozygosity.

Results

Sixty-six of our 233 captive colonies produced males, and in 25 of these, some males could only have been produced by workers. Colonies with more workers were more likely to produce males, especially for queenless colonies. The average number of days between the first appearance of eggs and adult males in our colonies was 54.1 ± 10.2 (mean ± SD, n = 20). In our laboratory experiment, queen removal triggered an increase in the proportion of physogastric workers. Physogastric workers were more likely to have yolky oocytes (37–54.9%) than normal workers (2–25.6%), which is an indicator of fertile or trophic egg production. Physogastric workers were less aggressive during interspecific aggression tests and foraged less than normal workers. The head width and wing length of worker-produced males were on average 4.0 and 4.3% greater respectively than those of males of undetermined source. Our microsatellite DNA analyses indicate that 5.5% of worker-produced males and 14.3% of males of undetermined source were heterozygous, which suggests the presence of diploid males and/or genetic mosaics in A. gracilipes.

Conclusions

Our experimental work provides crucial information on worker reproduction in A. gracilipes and its potential cost to colony defence. The ability of A. gracilipes workers to produce males in the absence of queens may also contribute to its success as an invasive species if intranidal mating can take place between virgin queens and worker-produced males.

     

Estimates of Genetic Relatedness Among Males in a Polygynous Wasp

Cyclical oligogyny is considered to be the mechanism that is most likely to be responsible for stabilizing cooperation in polygynous, epiponine wasps, in which single-queen colonies produce new queens and multiple-queen colonies produce males. In contrast with the number of studies on relatedness among adult females, we know little about relatedness among males in polygynous epiponine wasps. We estimated worker and male relatedness in the Brazilian epiponine wasp Polybia paulista Ihering and found that colonies of P. paulista produced males when they contained multiple queens. Although average relatedness within males did not differ significantly from 0.5, the number of alleles observed suggests that there were more than one queen to produce males in each colony. Our data would be helpful to elucidate dynamics of the male production in a colony of epiponine wasps.     

Significant reproductive skew in the facultatively polygynous ant Pheidole pallidula

Reproductive skew - the extent to which reproduction is unevenly shared between individuals in a social group - varies greatly between and within animal species. In this study, we investigated how queens share parentage in polygynous (multiple queen) colonies of the Mediterranean ant Pheidole pallidula. We used highly polymorphic microsatellites markers to determine parentage of gynes (new queens), males and workers in P. pallidula field colonies. The comparison of the genotypes of young and adult workers revealed a very low queen turnover (less than 2%). The first main finding of the study of reproductive skew in these colonies was that there was a significant departure from equal contribution of queens to gyne, male and worker production. Reproductive skew was greater for male production than for queen and worker production. There was no relationship between the magnitude of the reproductive skew and the number of reproductive queens per colony, their relatedness and the overall colony productivity, some of the factors predicted to influence the extent of reproductive skew. Finally, our study revealed for the first time a trade-off in the relative contribution of nestmate queens to gyne and worker production. The queens contributing more to gyne production contributed significantly less to worker production.     

Queen mating frequency and maternity of males in the stingless bee Trigona carbonaria Smith

Summary. Aspects of the sociobiology of the native Australian stingless bee Trigona carbonaria (Hymenoptera, Meliponini) were investigated using highly variable microsatellite markers. The queen mating frequency was estimated by examining genotypes of samples of workers from five colonies across three to five microsatellite loci. In each case, results were consistent with the workers being progeny of a queen mated with a single male. Microsatellite analysis of haploid males from two of the colonies suggested they predominantly arose from queen-laid eggs. As workers are more related to sons-of-workers than to sons-of-queens in monandrous colonies, this is somewhat surprising, and suggests that there may be colony-level costs associated with worker reproduction, or that queens are able to regulate worker reproduction via the ritualized cell provisioning and oviposition process. Males from another T. carbonaria colony were found to be diploid.     

Worker reproduction and related behavior in orphan colonies of a Japanese paper wasp,Polistes jadwigae (Hymenoptera,Vespidae)

Worker reproduction and related behavior in 2 orphan colonies ofPolistes jadwigae, one of which had been maintained by a queen and 5 artificially introduced alien workers, were observed. After the queen loss, a dominance hierarchy was established among workers, and several workers laid eggs without physical interference from other workers. Only males emerged from worker-laid eggs, however, a few new queens were produced from queen-laid eggs. Investment sex ratio of queenright (=normal) colonies (0.27) fell between the 2 theoretical values, corresponding to worker control (0.20 or 0.18) and queen control (0.48 or 0.46) of the sex ratio, both being calculated by considering the excess of males produced in the orphan colonies.     

Control of male production in the swarm‐founding wasp,Polybioides tabidus

In social insect colonies, male production may involve conflicts over the sex ratio, worker vs. queen reproduction, and each queen's contribution to the males when there are multiple queens. We examined male production in the swarm‐founding, multiple‐queened wasp, Polybioides tabidus, for which previous work suggested worker control of the sex ratios. We found that queens produced the males in accord with the collective worker preference. We also found that diploid males were produced, but only in association with haploid males. Simulations show they should have been produced in other colonies as well and their absence indicates that they were killed in some of these other colonies. The pattern of their removal indicates that P. tabidus cannot distinguish diploid from haploid males, and that haploid males would have been removed from these colonies too. This provides evidence that the workers are able to manipulate male production when collective preferences dictate.     

Asexually produced Cape honeybee queens (Apis mellifera capensis) reproduce sexually

Unmated workers of the Cape honeybee Apis mellifera capensis can produce female offspring including daughter queens. As worker-laid queens are produced asexually, we wondered whether these asexually produced individuals reproduce asexually or sexually. We sampled 11 colonies headed by queens known to be the clonal offspring of workers and genotyped 23 worker offspring from each queen at 5 microsatellite loci. Without exception, asexually produced queens produced female worker offspring sexually. In addition, we report the replacement of a queen by her asexually produced granddaughter, with this asexually produced queen also producing offspring sexually. Hence, once a female larva is raised as a queen, mating and sexual reproduction appears to be obligatory in this subspecies, despite the fact that worker-laid queens are derived from asexual lineages.     

No evidence that reproductive bumblebee workers reduce the production of new queens

Kin selection theory predicts potential conflict between queen and workers over male parentage in hymenopteran societies headed by one, singly mated queen, because each party is more closely related to its own male offspring. In ‘late-switching’ colonies of the bumblebee Bombus terrestris, i.e. colonies whose queens lay haploid eggs relatively late in the colony cycle, workers start to lay male eggs shortly after the queen lays the female eggs that will develop into new queens. It has been hypothesized that this occurs because workers recognize, via a signal given by the queen instructing female larvae to commence development as queens, that egg laying is now in their kin-selected interest. This hypothesis assumes that aggressive behaviour in egg-laying workers does not substantially reduce the production of new queens, which would decrease the workers' fitness payoff from producing males. We tested the hypothesis that reproductive activity inB. terrestris workers does not reduce the production of new queens. We used microsatellite genotyping to sex eggs and hence to select eight size-matched pairs of ‘late-switching’ colonies from a set of commercial colonies. From one colony of each pair we removed every egg-laying or aggressive worker observed. From the other colony, we simultaneously removed a nonegg-laying, nonaggressive worker. Removed workers were replaced with young workers from separate colonies at equal frequencies within the pair. There was no significant difference in queen productivity between colonies with reduced or normal levels of egg-laying or aggressive workers. Therefore, as predicted, reproductive B. terrestris workers did not significantly reduce the production of new queens.     

Polygyny in the nest-site limited acacia-ant Crematogaster mimosae

Polygyny is common in social insects despite inevitable decreases in nestmate relatedness and reductions to the inclusive fitness returns for cooperating non-reproductive individuals. We studied the prevalence and mode of polygyny in the African acacia-ant Crematogaster mimosae. These ants compete intensively with neighboring colonies of conspecifics and with three sympatric ant species for resources associated with the whistling-thorn acacias in which they all obligately nest. We used the genotypes of alate males at ten microsatellite loci to reconstruct queen genotypes and found that C. mimosae colonies are frequently secondarily polygynous, in that they include multiple closely related (and sometimes full-sib) queens, and (more rarely) unrelated queens. We also found that individual queens in both monogynous and polygynous colonies had mated with multiple males, making C. mimosae an interesting example of simultaneous polygyny and polyandry. The presence of polygyny in C. mimosae and the intense competition for nest-sites between C. mimosae and its conspecifics support the association between nest-site limitation and polygyny. Polygyny may allow for increased worker populations and a competitive advantage, as inter-colony conflicts are typically won by the colony with the larger number of workers.