Worker policing in the German wasp Vespula germanica

In some ants, bees, and wasps, workers kill or "police” male eggs laid by other workers in order to maintain the reproductive primacy of the queen. Kin selection theory predicts that multiple mating by the queen is one factor that can selectively favor worker policing. This is because when the queen is mated to multiple males, workers are more closely related to the queen's sons than to the sons of other workers. Earlier work has suggested that reproductive patterns in the German wasp Vespula germanica may contradict this theory, because in some colonies a large fraction of the adult males were inferred to be the workers' sons, despite the effective queen mating frequency being greater than 2 (2.4). In the present study, we reexamine the V. germanica case and show that it does support the theory. First, genetic analysis confirms that the effective queen mating frequency is high, 2.9, resulting in workers being more related to the queen's sons than to other workers' sons. Second, behavioral assays show that worker-laid eggs are effectively killed by other workers, despite worker-laid eggs having the same intrinsic viability as queen-laid ones. Finally, we estimate that approximately 58.4% of the male eggs but only 0.44% of the adult males are worker derived in queenright colonies, consistent with worker reproduction being effectively police

Conflict over male production in Vespinae wasps.

Insect societies are well known for their cooperation. However, a number of conflicts do occur within their colonies. The eusocial Hymenoptera (bees, ants and wasps) are no exception, with several reproductive conflicts affecting their societies. One of these conflicts is over male production. This conflict is caused by the fact that the workers in most species, though unable to mate, possess functional ovaries and retain the capacity to lay unfertilized, male eggs. In addition, since both the mother queen and the workers are each most related to their own sons, they would be expected to strongly compete over male production. One important mechanism that can resolve this conflict is policing, whereby workers are prevented to successfully reproduce, thereby maintaining the reproductive primacy of the queen. Policing can be carried out by both the mother queen (queen policing), and by the workers (worker policing), and can occur either via aggression or selective egg eating. In this thesis, we examined the ultimate causes and underlying proximate mechanism that enable worker policing by egg eating in Vespinae wasps.In a first set of studies, we looked at the importance of the relatedness among workers as an ultimate cause for the selection of worker policing in three species of Vespinae wasps, the German wasp Vespula germanica, the Norwegian wasp Dolichovespula norwegica and the Saxon wasp Dolichovespula saxonica. Our data show that patterns of policing can be surprisingly complex. In particular, different evolutionary factors, including relatedness, as well as effects on colony productivity and the sex ratio, are not mutually exclusive and need to be considered together to explain prevailing patterns of worker policing in eusocial Hymenoptera. In addition, we provide evidence for the occurrence of selfish worker policing in D. norwegica. In this type of policing, workers carrying out the policing also occasionally lay eggs themselves, thereby acquiring direct fitness benefits. This finding supports selfish worker policing to be an important mechanism that can greatly facilitate the evolution of worker policing. Inclusive fitness theory and empirical data suggest that in eusocial hymenopteran species where colonies are either headed by a single mated queen or a multiple mated queen, workers should police other workers' eggs only in colonies headed by a multiple mated queen. Despite earlier evidence for facultative worker policing in Dolichovespula saxonica by Foster and Ratnieks (2000), we found no evidence for facultative worker policing but show that seasonal progression of the nest and the location in the nest where males were reared explain the patterns of worker reproduction. Furthermore, we showthat chemical variability in cuticular hydrocarbon profiles among the workers was not significantly correlated with queen mating frequency and, therefore, is likely not used by workers to facultatively police according to the queen mating frequency. Our results suggest that the earlier evidence for facultative worker policing in D. saxonica by Foster and Ratnieks (2000) may have been due to accidental correlations with certain confounding variables, or, alternatively, that there are large interpopulation differences in the expression of worker policing.In another study, we looked at the proximate mechanism that enables workers to selectively police worker-laid eggs. We demonstrate that in the common wasp Vespula vulgaris, surface hydrocarbon profiles of queen-laid eggs and worker-laid eggs can contain the necessary information for workers to effectively police worker-laid eggs.Finally, in a last chapter, our data suggest that the beetle, Metoecus paradoxus, which is known to parasitize Vespula vulgaris colonies, can elude host recognition in the adult stage by mimicking the wasps‟ cuticular hydrocarbon profiles. This study is the first to show chemical mimicry by a non-social insect parasitizing social wasp colonies.Acknowledgments I Summary III Samenvatting V Contents VII Introduction IX Conflicts in insect societies IX Queen-worker conflict over the sex ratio X Conflict over male production XI The basis for the conflict XI Policing as a conflict-reducing mechanism XII Proximate mechanisms involved in policing XIV Chemical mimicry by social parasites in wasp colonies XVI Study organisms XVII Structure and outline of the thesis XXII Chapter 1 1 Worker policing in the German wasp Vespula germanica Chapter 2 17 Co-occurrence of three types of egg policing in the Norwegian wasp Dolichovespula norwegica Chapter 3 33 Seasonal progression and not facultative policing explains pattern of worker reproduction in the Saxon wasp Chapter 4 53 Hydrocarbon signatures of egg maternity, caste membership and reproductive status in the common wasp Chapter 5 69 Chemical mimicry by the beetle Metoecus paradoxus in Vespula vulgaris wasp colonies General conclusions and perspectives 77 References 81nrpages: 118status: publishe

Queen signaling in social wasps

Social Hymenoptera are characterized by a reproductive division of labor, whereby queens perform most of the reproduction and workers help to raise her offspring. A long-lasting debate is whether queens maintain this reproductive dominance by manipulating their daughter workers into remaining sterile (queen control), or if instead queens honestly signal their fertility and workers reproduce according to their own evolutionary incentives (queen signaling). Here, we test these competing hypotheses using data from Vespine wasps. We show that in natural colonies of the Saxon wasp, Dolichovespula saxonica, queens emit reliable chemical cues of their true fertility and that these putative queen signals decrease as the colony develops and worker reproduction increases. Moreover, these putative pheromones of D. saxonica show significant conservation with those of Vespula vulgaris and other Vespinae, thereby arguing against fast evolution of signals as a result of a queen–worker arms race ensuing from queen control. Lastly, levels of worker reproduction in these species correspond well with their average colony kin structures, as predicted by the queen signaling hypothesis but not the queen control hypothesis. Altogether, this correlative yet comprehensive analysis provides compelling evidence that honest signaling explains levels of reproductive division of labor in social wasps.status: publishe

Data from: Queen signalling in social wasps

Social Hymenoptera are characterized by a reproductive division of labour, whereby queens perform most of the reproduction and workers help to raise her offspring. A long-lasting debate is whether queens maintain this reproductive dominance by manipulating their daughter workers into remaining sterile (queen control), or if instead queens honestly signal their fertility and workers reproduce according to their own evolutionary incentives (queen signalling). Here we test these competing hypotheses using data from Vespine wasps. We show that in natural colonies of the Saxon wasp, Dolichovespula saxonica, queens emit reliable chemical cues of their true fertility and that these putative queen signals decrease as the colony develops and worker reproduction increases. Moreover, these putative pheromones of D. saxonica show significant conservation with those of Vespula vulgaris and other Vespinae, thereby arguing against fast evolution of signals as a result of a queen-worker arms race ensuing from queen control. Lastly, levels of worker reproduction in these species correspond well with their average colony kin structures, as predicted by the queen signalling hypothesis but not the queen control hypothesis. Altogether, this correlative yet comprehensive analysis provides compelling evidence that honest signalling explains levels of reproductive division of labour in social wasps

Song stability and neighbour recognition in a migratory songbird, the black redstart

International audienceTerritorial male songbirds have the ability to discriminate between the songs of their neighbours and those of strangers and for a few species it has been shown that they maintain this ability from one breeding season to the next. To better understand the acoustic basis of this long-term discrimination ability we studied song stability across two breeding seasons in a migratory songbird with high inter-annual return rates and territory stability, the black redstart, Phoenicurus ochruros. Strophe repertoires of 14 males (≥2 years old) were stable from one breeding season to the next and high strophe sharing occurred for males within the same group of houses or hamlets (81%) in contrast to only limited sharing between different hamlets (15%). However, subtle differences exist between the renditions of the same strophe sung by neighbouring males and these differences equally show an inter-annual stability, providing an acoustic basis for long-term discrimination abilities. Playback tests showed the existence of a strong dear-enemy effect: males reacted less aggressively to the familiar, often shared song of a neighbour than to a stranger unshared song and this pattern was maintained when birds returned from migration one year later. We discuss on one side the possible mechanisms leading to the observed patterns of song sharing and on the other side the significance of stable vocal signatures for neighbour recognition

Data from: Colony stage and not facultative policing explains pattern of worker reproduction in the Saxon wasp

Inclusive fitness theory predicts that in colonies of social Hymenoptera headed by a multiple mated queen, workers should benefit from policing eggs laid by other workers. Foster & Ratnieks (2000) provided evidence that in the vespine wasp Dolichovespula saxonica, workers police other workers' eggs only in colonies headed by a multiple mated queen, but not in those headed by a single mated one. This conclusion, however, was based on a relatively small sample size and the original study did not control for possible confounding variables such as the seasonal colony progression of the nests. Our aim, therefore, was to reinvestigate whether or not facultative worker policing occurs in D. saxonica. Remarkably, our data shows that in the studied Danish population, there was no correlation between worker-worker relatedness and the percentage of worker-derived males. In addition, we show that variability in cuticular hydrocarbon profiles among the workers did not significantly correlate with relatedness, and that workers therefore probably did not have sufficient information on queen mating frequency from the workers’ cuticular hydrocarbon profiles. Hence, there was no evidence that workers facultatively policed other workers' eggs in response to queen mating frequency. Nevertheless, our data do show that the seasonal progression of the nest and the location in which the males were reared both explain the patterns of worker reproduction found. Overall, our results suggest that the earlier evidence for facultative worker policing in D. saxonica may have been due to accidental correlations with certain confounding variables, or, alternatively, that there are large interpopulation differences in the expression of worker policing

Colony stage and not facultative policing explains patterns of worker reproduction in the Saxon wasp

Inclusive fitness theory predicts that in colonies of social Hymenoptera headed by a multiple-mated queen, workers should benefit from policing eggs laid by other workers. Foster & Ratnieks provided evidence that in the vespine wasp Dolichovespula saxonica, workers police other workers’ eggs only in colonies headed by a multiple-mated queen, but not in those headed by a single-mated one. This conclusion, however, was based on a relatively small sample size, and the original study did not control for possible confounding variables such as the seasonal colony progression of the nests. Our aim, therefore, was to reinvestigate whether or not facultative worker policing occurs in D. saxonica. Remarkably, our data show that in the studied Danish population, there was no correlation between worker–worker relatedness and the percentage of worker-derived males. In addition, we show that variability in cuticular hydrocarbon profiles among the workers did not significantly correlate with relatedness and that workers therefore probably did not have sufficient information on queen mating frequency from the workers’ cuticular hydrocarbon profiles. Hence, there was no evidence that workers facultatively policed other workers’ eggs in response to queen mating frequency. Nevertheless, our data do show that the seasonal progression of the nest and the location in which the males were reared both explain the patterns of worker reproduction found. Overall, our results suggest that the earlier evidence for facultative worker policing in D. saxonica may have been caused by accidental correlations with certain confounding variables, or, alternatively, that there are large interpopulation differences in the expression of worker policing.status: publishe

Worker policing in the German wasp Vespula germanica

In some ants, bees, and wasps, workers kill or "police" male eggs laid by other workers in order to maintain the reproductive primacy of the queen. Kin selection theory predicts that multiple mating by the queen is one factor that can selectively favor worker policing. This is because when the queen is mated to multiple males, workers are more closely related to the queen's sons than to the sons of other workers. Earlier work has suggested that reproductive patterns in the German wasp Vespula germanica may contradict this theory, because in some colonies a large fraction of the adult males were inferred to be the workers' sons, despite the effective queen mating frequency being greater than 2 (2.4). In the present study, we reexamine the V. germanica case and show that it does support the theory. First, genetic analysis confirms that the effective queen mating frequency is high, 2.9, resulting in workers being more related to the queen's sons than to other workers' sons. Second, behavioral assays show that worker-laid eggs are effectively killed by other workers, despite worker-laid eggs having the same intrinsic viability as queen-laid ones. Finally, we estimate that approximately 58.4% of the male eggs but only 0.44% of the adult males are worker derived in queenright colonies, consistent with worker reproduction being effectively policed. Copyright 2008, Oxford University Press.