Queen-worker Conflict Research Articles

SEX-RATIO DETERMINATION WITHIN COLONIES OF ANTS.

Trivers and Hare (1976) propose that in social Hymenoptera a queen and her daughter workers can be in conflict over the relative amount invested in the two sexes. A worker is three times more related to a full sister than to a brother, while the queen is equally related to both sons and daughters. They present a wide array of evidence which suggests that wherever conflict occurs, the workers are likely to win and produce female-biased sexual investment ratios. Several subsequent studies, however, appear to indicate that, within some individual colonies, queens can exert enough influence to produce sex ratios favorable to their interests (Brian, 1 979; Forsyth, 1981; Pamilo and Rosengren, 1983). Herbers's study (1984) is perhaps the most thorough investigation of worker-queen conflict within a single hymenopteran species. She presents two major lines of evidence suggesting that workers of the ant species Leptothorax longispinosus attempt to maximize inclusive fitness at the expense of their queen's and that an active conflict occurs within colonies. First, proportional investment in females by colonies follows the order predicted by kin selection where, queenless > monogynous > oligogynous (2-4 functional queens) > polygynous (?5 queens). Queenless colonies are the most femalebiased, because the workers could produce their optimal sex ratio without opposition from a queen. Oligogynous and polygynous colonies are the least female-biased, because increasing queen number reduces the asymmetry in relatedness between brothers and sisters, and queen and worker investment equilibria converge (Trivers and Hare, 1976). Also, the queen-to-worker ratio is increased, which should favor the queens doing better in conflict situations. The second line of evidence is that worker number is often correlated negatively with proportional investment in males for monogynous, oligogynous, and polygynous colonies. This supports the conflict hypothesis in that the larger the work force, the more difficult it may be for a queen to affect the sex ratio. Overall, Herbers's results and the variance in investment ratios between colonies found by numerous studies (see Nonacs [ 1986] for a review), appear to suggest that a dynamic conflict occurs between workers and queens over sex ratio. Male production seems to be increased in direct proportion to the ability of queens to succeed in the conflicts. I propose, however, that the sex ratios produced by individual colonies primarily reflect the workers' interests. I will support this hypothesis in two ways. First, I will show that Herbers's study (as the particular case in point) and the variance in investment ratios from many other ant species are equally well (or better) explained by a proximate mechanism of resource availability as by worker-queen conflict. Second, I will argue that because the fitness of any given colony's investment ratio depends on the sex ratio of the interbreeding population, colonies producing male-biased broods can still be harmonious with a hypothesis of total worker control although, superficially, they may appear queen-influenced. The patterns of investment observed by Herbers, particularly in reference to worker number, may also be explained by a resource availability hypothesis. Larger colonies with more workers may generally be expected to collect more food (Oster and Wilson, 1978 pp. 26-74; Brian et al., 1981; Elmes and Wardlaw, 1982). It is reasonable to assume that with more food, sexual production increases. In many species, investment in males is negatively correlated with total sexual production (Nonacs, 1986). In other words, with increasing resources, colonies are more likely to favor female production. Therefore, worker number may be only spuriously correlated to investment ratios due to its relationship to ergonomic efficiency. Available data sets from 18 monogynous, five polygynous, and one slave-making species measure sexual production and worker number. These can be tested as to whether one, both, or neither accurately predicts sex ratio. For each species, I have examined the partial correlations among the total amount of sexuals produced (measured as biomass), the number of adult workers, and the male proportion of the total sexual biomass (R), which was normalized by arcsine square root transformation. The relationship between total sexual biomass and proportion invested in males is strong (Table 1). When worker number is controlled, seven correlations are significantly negative (P < 0.025). In total, 20 of 24 correlations are negative, a significant trend across species (sign test, P < 0.002). With total sexual biomass controlled, however, there is almost no relationship between worker number and proportion invested in males (Table 1). In only two species are the correlations significant, with one being negative and the other positive. Moreover, there is no trend across species as the correlations are equally split between negative and positive (12 of 24 negative). When R is controlled, there are positive corre-

Reproductive Dominance Within Colonies of Bombus Terrestris (L.)

The primitive character of eusociality in bumblebees is expressed in the fact that laying workers appear beside the laying queen and in the severe outbursts of aggression that coincide with this phenomenon. Egg cells of both the queen and the workers are destroyed and in many cases the queen is killed. In the eight colonies that were investigated it was found that the queen switched from laying fertilized eggs to laying unfertilized eggs within a short period. The time when haploid (unfertilized) eggs were produced was derived from the demographic data of the colonies and from our present knowledge of the developmental time of the workers, the queens and the males. Egg laying by workers and overt aggression never occurred until the queen had stopped laying fertilized eggs. As a result, the interests of diploid brood were not affected by the worker-queen conflict in the colonies. The possible meaning of a specific worker display towards the queen, the so-called 'buzzing behaviour', is discussed in terms of the worker-queen relation.

Evolution of sex ratios in social hymenoptera: kin selection, local mate competition, polyandry and kin recognition

A model is constructed to study the effects of local mate competition and multiple mating on the optimum allocation of resources between the male and female reproductive brood in social hymenopteran colonies from the ‘points of view’ of the queen (parental manipulation theory) as well as the workers (kin selection theory). Competition between pairs of alleles specifying different sex investment ratios is investigated in a game theoretic frame work. All other things being equal, local mate competition shifts the sex allocation ratio in favour of females both under queen and worker control. While multiple mating has no effect on the queen’s optimum investment ratio, it leads to a relatively male biased investment ratio under worker control. Under queen control a true Evolutionarily Stable Strategy(ess) does not exist but the ‘best’ strategy is merely immune from extinction. A trueess exists under worker control in colonies with singly mated queens but there is an asymmetry between the dominant and recessive alleles so that for some values of sex ratio a recessive allele goes to fixation but a dominant allele with the same properties fails to do so. Under multiple mating, again, a trueess does not exist but a frequency dependent region emerges. The best strategy here is one that is guaranteed fixation against any competing allele with a lower relative frequency. Our results emphasize the need to determine levels of local mate competition and multiple mating before drawing any conclusions regarding the outcome of queen-worker conflict in social hymenoptera. Multiple mating followed by sperm mixing, both of which are known to occur in social hymenoptera, lower average genetic relatedness between workers and their reproductive sisters. This not only shifts the optimum sex ratio from the workers’ ‘point of view’ in favour of males but also poses problems for the kin selection theory. We show that kin recognition resulting in the ability to invest in full but not in half sisters reverts the sex ratio back to that in the case of single mating and thus completely overcomes the hurdles for the operation of kin selection.

The effects of multiple mating on the worker-queen conflict in Apis mellifera L.

A deterministic model is presented which shows that multiple mating reduces the conflict between workers and queen in the optimal investment ratio in each sex. The natural risk of the nuptual flights of honeybee queens fits well into the theoretically determined risk when queens tend to optimize the numbers of drones with which they mate.

Queen-Worker Conflict and Eusocial Evolution in a Polygynous Ant Species

Queen-Worker Conflict and Eusocial Evolution in a Polygynous Ant Species

Behavioral ecology of Japanese paper wasps,Polistes spp. IV. Comparison of ethograms between queens and workers ofP. chinensis antennalis in the ergonomic stage

Behavioral catalogues, transition matrices between 2 consecutive behavioral acts, and the frequency distribution of time spent in each behavioral act were described for queens and workers of a Japanese paper wasp,Polistes chinensis antennalis in the ergonomic stage (the period from the emergence of the first worker to the emergenece of the first reproductive). The results were; (1) The whole behavior repertoire of queens was completely included in that of workers. Workers oviposited frequently in queen-right colonies. (2) The proportion of off-nest activities to the number of total acts for workers was higher than that for queens. The proportion of time spent off the nest in workers was 5 times as high as that in queens. (3) There was no significant difference in the proportion of number of oviposition to the total number of acts between queens and workers. The oviposition rate was 0.06 eggs/h for workers and 0.37 eggs/h for queens. Queens made more dominance behavior and workers more subordinated behavior. Queens made abdomen wagging more frequently than workers. (4) For behavioral acts common in both queens and workers, the mean duration of a specific act was approximately equal for both. The mean duration of unsuccessful flesh collection for workers was 3.4 times as longs as that for queens. Workers did not search for flesh in 10.1% of duration of flesh collections in the field. (5) The pattern of transitions between 2 consecutive behavioral acts in workers was similar to that in queens. (6) Alien workers approaching a nest with a load were more often accepted by the nest occupants than alien workers with no load. Alien workers with no load were not accepted as often as a legitimate nestmates with no load. The reproductive division of labor between queens and workers inP. chinesis antennalis was incomplete. This suggests worker-queen conflict in different reproductive strategies among colony members. Several behaviors were consistent with the view that they are the behavioral expression of this conflict.

Worker-queen conflict and male parentage in bumble bees

Male parentage in the bumble bee Bombus melanopygus was estimated using a colour dimorphism as a genetic marker. 1491 males from 17 colonies were classified. 19% of the males originated from the workers while the queens were alive; after their death workers continued to lay eggs, thus in total 39% of the males were worker-produced. The sex ratio of reproductive was male biased (1:6.9, F:M) as well as the investiment ratio (1:2.7). The sex and investment ratios of reproductives produced by the queens were also male biased (1:4.4 and 1:1.7) respectively). There was no significant correlation between the proportion of males produced by the workers while the queens were alive and either colony size or queen lifespan. The queens were, on average, significantly more related to the reproductive brood (r=0.469) than were the workers as a group (r=0.380). The average ‘reproductive success’ (the expected number of alleles identical by descent passed on to the next generation) of the queens was significantly greater than that of the workers. Male production by workers appears to be a manifestation of worker-queen conflict and the workers do not seem to be in ‘control’ in the colonies.

Worker-queen conflict in annual social hymenoptera

There is a conflict of interest between the queen and her worker-daughters in social hymenoptera over which party shall lay the haploid eggs which become males and over the ratio of investment in male and female reproductives. A model of this conflict in annual colonies is developed in this paper which can be analysed by mathematical optimisation methods. In the absence of worker-laying the queen prefers a 1:1 investment ratio while the workers prefer a 3: 1 female-biased ratio; it is concluded that the queen is in a strong position to impose her preference because she can lay only haploid eggs in the last generation. If the workers can lay and rear haploid eggs in the last generation (but not in the previous generation because of the danger that physical conflict will destroy the queen together with her contribution to future generations), the queen can gain control of male production by forcing the workers to rear her haploid eggs; but in so doing she must relinquish some control over the investment ratio.

Worker-queen conflict and sex ratio theory in social hymenoptera

There is a conflict of interest between the queen and her worker-daughters in social hymenoptera over the ratio of investment in male and female reproductives. In the absence of worker-laying and inbreeding, the queen prefers a 1:1 (male : female) investment ratio, whereas the workers prefer a 1:3 ratio. Trivers and Hare (1976) suggest that the workers will win this conflict because they control the allocation of care to the young, but this argument ignores the fact that the queen controls the numbers of haploid and diploid eggs laid, and that the workers must operate within this constraint. We have investigated two theoretical models of this situation. We conclude that the queen may have considerable control over the investment ratio; two factors which may act in favour of worker control are a high cost of producing a new queen rather than a worker and the possibility of making a variable investment in a new queen with a concomitant variation in her fitness.

Worker-queen conflict and the evolution of social insects

A general expression for the inclusive fitness of haplodiploids is developed. The optimal investment of colony resources in eusocial Hymenoptera is then derived by maximizing the inclusive fitnesses of workers and queens subject to an ergonomic constraint. Because of assymmetries in the coefficients of relatedness, there is a genotypic “conflict of interest” between the queen and her daughters. We show how the inclusive fitness formula can be used to investigate this situation and to determine who is controlling the colony investment policy. Finally, we show that the optimization of inclusive fitness is consistent with the equilibria of a detailed genetic model.

Haploidploidy and the evolution of the social insect.

Halminton (1) was apparently the first to appreciate that the synthesis of Mendelian genetics with Darwin's theory of natural selection had profound implications for social theory. In particular, insofar as almost all social behavior is either selfish or altruistic (or has such effects), genetical reasoning suggests that an individual's social behavior should be adjusted to his or her degree of relatedness, r, to all individuals affected by the behavior. We call this theory kinship theory. The social insects provide a critical test of Hamilton's kinship theory. When such theory is combined with the sex ratio theory of Fisher (9), a body of consistent predictions emerges regarding the haplodiploid Hymenoptera. The evolution of female workers helping their mother reproduce is more likely in the Hymenoptera than in diploid groups, provided that such workers lay some of the male-producing eggs or bias the ratio of investment toward reproductive females. Once eusocial colonies appear, certain biases by sex in these colonies are expected to evolve. In general, but especially in eusocial ants, the ratio of investment should be biased in favor of females, and in it is expected to equilibrate at 1 : 3 (male to female). We present evidence from 20 species that the ratio of investment in monogynous ants is, indeed, about 1 : 3, and we subject this discovery to a series of tests. As expected, the slave-making ants produce a ratio of investment of 1 : 1, polygynoys ants produce many more males than expected on the basis of relative dry weight alone, solitary bees and wasps produce a ratio of investment near 1 : 1 (and no greater than 1 : 2), and the social bumblebees produce ratios of investment between 1 : 1 and 1 : 3. In addition, sex ratios in monogynous ants and in trapnested wasps are, as predicted by Fisher, inversely related to the relative cost in these species of producing a male instead of a female. Taken together, these data provide quantitative evidence in support of kinship theory, sex ratio theory, the assumption that the offspring is capable of acting counter to its parents' best interests, and the supposition that haplodiploidy has played a unique role in the evolution of the social insects. Finally, we outline a theory for the evolution of worker-queen conflict, a theory which explains the queen's advantage in competition over male-producing workers and the workers' advantage regarding the ratio of investment. The theory uses the asymmetries of haplodiploidy to explain how the evolved outcome of parent-offspring conflict in the social Hymenoptera is expected to be a function of certain social and life history parameters.