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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. This article is protected by copyright. All rights reserved.
-4.0 -2.0 0.0 2.0 4.0 6.0
PC2 (15.2%)
PC1 (42.8%)
Reproductive workers
Sterile workers
-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4
Ovary Score
0.4 0.5 0.6 0.7 0.8 0.9 1.0
Colony Stage
0 1 2 3 4 5 6
0 1 2 3 4 5 6
Variable Estimate p
(Intercep t) 0.50 0.88 0.384
Ovary Score 0.89 5.81
< 0.001 ** *
Variable Estimate p
(Intercept) Q 8.03 3.26
0.00 3 * *
Colony Stage -5.68 -1.79 0.083
Caste RW -8.47 -3.02
0.00 5 * *
Colony Stage * Caste RW 9.62 2.67
0.01 2 *
Variable p
(Intercep t) Q 21.96 2.63
0.013 *
PC1 -3.88 -1.78 0.084
Caste RW -16.06 -1.82 0.078
PC1 * Caste RW 6.89 2.95
0.006 **
Estimate t
Variable p
(Intercept) Q 100.66 5.44
< 0.001 ** *
PC1 -17.87 -3.71
< 0.001 ** *
Caste RW -65.97 -3.38
0.00 2 * *
PC1 * Caste RW 20.17 3.90
< 0.001 ** *
Estimate t
Peak # Component
GLMM: Q vs. SW, p < 0.01
GLMM: RW vs. SW, p < 0.01
Average Percentage
PC1 loading
PC2 loading
Q vs. SW
RW vs. SW
Q vs. SW
RW vs. SW
Q vs. W - V. crabro
Q vs. W - D. maculata
Q vs. W - V. squamosa
Q vs. W - V. maculifrons
Log2 ratio
1n-C23 >13 >0.3 >3
2 7-,9-,11-MeC23
33-MeC23 0.0 0
b5,x -diMeC23
53,7-diMeC25 0 <-0.3 <-3
d 4-MeC24
7,8 x-C25:1 (+isomer)
10 n-C25
11 7-,9-,11-,13-MeC25
12 5-MeC25
13 3-MeC25
14 5,9-diMeC25
15 n-C26
16 3,9-diMeC25
17 10-,11-,12-,13-MeC26
18 5-MeC26
19 4-MeC26
20,21 x-C27:1 (+isomer)
22 4,y-diMeC26
23 n-C27
24 9-,11-,13-MeC27
25 7-MeC27
26 5-MeC27
27 11,15-diMeC27
28 3-MeC27
29 5,11-diMeC27
30 5,y-diMeC27 + x-C28:1
31 n-C28
32 3,11-, 3,13-diMeC27
33 3,7-diMeC27
34 11-,12-,13-,14-MeC28
35 6-MeC28
36 4-MeC28
37,38 x-C29:1 (+isomer)
39 n-C29
40 9-,11-,13-,15-MeC29
41 7-MeC29
42 5-MeC29
43 9,13-, 11,15-, 13,17-diMeC29
44 3-MeC29
45 5,y-diMeC29
46 3,9-, 3,11-, 3,13-, 3,15-diMeC29
47 3,7-diMeC29
48 12-, 13-, 14-, 15-MeC30
49 4,y-diMeC30
50 x-C31:1
51 unidentified
52 n-C31
53 13-, 15-MeC31
54 11,15-diMeC31
55 3-MeC31 + 7,13-, 7,15-diMeC31
56 5,y-diMeC31
g 13-, 15-MeC33
D. saxonica V. vulgaris Other Vespinae
PCA Log2 ratio Log2 ratio Log2 ratio
... It was amply demonstrated in A. mellifera queen's signals that change according to her mating status and quality and exerting different effects on workers and males [26,59,60]. Honest fertility signaling was also demonstrated in different ant species [61,62] as well as in social wasps [63]. The honesty of queen signals has been debated at length and the view of queen pheromones as manipulative agents was frequently challenged and mostly abandoned [5 ,8 ,9,15]. ...
Pheromones mediating social behavior are critical components in the cohesion and function of the colony and are instrumental in the evolution of eusocial insect species. However, different aspects of colony function, such as reproductive division of labor and colony maintenance (e.g. foraging, brood care, and defense), pose different challenges for the optimal function of pheromones. While reproductive communication is shaped by forces of conflict and competition, colony maintenance calls for enhanced cooperation and self-organization. Mechanisms that ensure efficacy, adaptivity and evolutionary stability of signals such as structure-to-function suitability, honesty and context are important to all chemical signals but vary to different degrees between pheromones regulating reproductive division of labor and colony maintenance. In this review, we will discuss these differences along with the mechanisms that have evolved to ensure pheromone adaptivity in reproductive and non-reproductive context.
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Juvenile hormone (JH) has important functions that regulate insect life. In adult individuals, it induces gonadotropic and behavioral changes. Manipulating JH levels helps to understand how it influences insect physiology. The effects of JH on Epiponini swarm-founding wasps have shown contrasting results, affecting reproduction, chemical compound expression, behavior, and age polyethism. In this study, we investigated whether JH affects reproductive physiology and production of fertility cues in a swarm-founding wasp species Polybia occidentalis in an age-controlled experimental setup. We treated newly emerged females with methoprene (JH analogue) and precocene-I (JH inhibitor) to determine their effects on ovary activation and cuticular hydrocarbon (CHC) expression. Furthermore, we compared the chemical profiles of treated workers with those of queens. Our results show that methoprene and precocene-I affected the CHC production in P. occidentalis. Additionally, females treated with methoprene were chemically more similar to queens than precocene- and acetone-treated females. Methoprene affected ovarian status (increasing ovary activation). These results suggest that different levels of JH reflect changes in chemical and reproductive traits in P. occidentalis females. Furthermore, we point out the existence of fertility cues in this Epiponini wasp.
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Cuticular hydrocarbons (CHCs) are present in several insects. One of the most important functions of these compounds in social insects is the exchange of signals during interactions between nestmates. Although we know about the functions performed by CHCs, we still have little information about how these compounds evolved within different groups of insects, especially among wasps. In this study, we examine the diversity and abundance of the cuticular hydrocarbon profile of 17 species of Epiponini wasps using a phylogenetic approach. We investigated phylogenetic constraints on the evolution of CHCs in Epiponini. We then calculated the phylogenetic signal for all compounds present in the studied species. For several CHC traits, the phylogenetic signal was low, indicating a random expectation. Moreover, within a phylogenetic context, we did not find a pattern of increasing or decreasing number of compounds or structural groups. However, we verified that Epiponini wasps, a tribe that shows colony foundation by swarming, exhibit a smaller number of CHC compounds than the tribes (Mischocyttarini and Polistini) that show an independent foundation. Probably this difference is related to their type of nest and nesting behavior.
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In the highly eusocial wasp, Vespula vulgaris , queens produce honest signals to alert their subordinate workers of their fertility status, and therefore they are reproductively suppressed and help in the colony. The honesty of the queen signals is likely maintained due to hormonal regulation, which affects fertility and fertility cue expression. Here, we tested if hormonal pleiotropy could support the hypothesis that juvenile hormone controls fertility and fertility signaling in workers. In addition, we aimed to check oocyte size as a proxy of fertility. To do that, we treated V . vulgaris workers with synthetic versions of juvenile hormone (JH) analogue and a JH inhibitor, methoprene and precocene, respectively. We dissected the treated females to check ovary activation and analyzed their chemical profile. Our results showed that juvenile hormone has an influence on the abundance of fertility linked compounds produced by workers, and it also showed to increase oocyte size in workers. Our results corroborate the hypothesis that juvenile hormone controls fertility and fertility signaling in workers, whereby workers are unable to reproduce without alerting other colony members of their fertility. This provides supports the hypothesis that hormonal pleiotropy contributes to keeping the queen fertility signals honest.
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The production of royal pheromones by reproductives (queens and kings) enables social insect colonies to allocate individuals into reproductive and non-reproductive roles. In many termite species, nestmates can develop into neotenics when the primary king or queen dies, which then inhibit the production of additional reproductives. This suggests that primary reproductives and neotenics produce royal pheromones. The cuticular hydrocarbon heneicosane was identified as a royal pheromone in Reticulitermes flavipes neotenics. Here, we investigated the presence of this and other cuticular hydrocarbons in primary reproductives and neotenics of this species, and the ontogeny of their production in primary reproductives. Our results revealed that heneicosane was produced by most neotenics, raising the question of whether reproductive status may trigger its production. Neotenics produced six additional cuticular hydrocarbons absent from workers and nymphs. Remarkably, heneicosane and four of these compounds were absent in primary reproductives, and the other two compounds were present in lower quantities. Neotenics therefore have a distinct ‘royal’ blend from primary reproductives, and potentially over-signal their reproductive status. Our results suggest that primary reproductives and neotenics may face different social pressures. Future studies of these pressures should provide a more complete understanding of the mechanisms underlying social regulation in termites.
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Neotropical swarm‐founding wasps are divided into 19 genera in the tribe Epiponini (Vespidae, Polistinae). They display extensive variation in several colony‐level traits that make them an attractive model system for reconstructing the evolution of social phenotypes, including caste dimorphism and nest architecture. Epiponini has been upheld as a solid monophyletic group in most phylogenetic analyses carried out so far, supported by molecular, morphological and behavioural data. Recent molecular studies, however, propose different relationships among the genera of swarm‐founding wasps. This study is based on the most comprehensive epiponine sampling so far and was analyzed by combining morphological, nesting and molecular data. The resulting phylogenetic hypothesis shows many of the traditional clades but still impacts the way certain behavioural characters, such as nest structure and castes, evolved, and thus requires some re‐interpretations. Angiopolybia as sister to the remaining Epiponini implies that nest envelopes and a casteless system are plesiomorphic in the tribe. Molecular dating points to an early tribal diversification during the Eocene (c. 55–38 Ma), with the major differentiation of current genera concentrated in the Oligocene/Miocene boundary.
Cuticular hydrocarbons are chemical compounds present in all insects and primarily involved in preventing water loss and protecting against pathogenic microorganisms. In social insects, cuticular hydrocarbons evolved in cues that provide multilevel information. In this chapter, we review the studies on cuticular hydrocarbons in Neotropical social wasps. So far, the main research exploring the CHCs of independent and swarm-founding wasps demonstrates their importance in mediating interactions between nestmates and also that these compounds may vary within colony members, differences between sexes, reproductive status, fertility, age, and their relationships with social parasitism.
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Wasps are a true model in studies on the origin and evolution of cooperative behavior and the mechanisms that help to stabilize sociality and resolve internal conflicts. Indeed, the wide variety of social organizations found in the group-ranging from solitary to highly social-provides unique opportunities to test how cooperation evolved and how conflicts are suppressed in societies with different degrees of social complexity. As the individuals in wasp colonies are not genetic clones of each other, inclusive fitness theory predicts that there should often be significant scope for conflicts between the queen and worker castes arising from specific genetic relatedness asymmetries within the colony. In many species, for example, the workers retain the ability to develop their ovaries and lay unfertilized male-destined eggs, thereby allowing them to challenge the reproductive monopoly of the queen. The amount of worker reproduction that is tolerated within the colony is a function of the genetic relatedness patterns within the colony and the costs and benefits of cheating, which under some circumstances can drive social enforcement mechanisms, whereby eggs laid by workers are selectively cannibalized or "policed" by the queen herself or by other workers. In some wasp species, such policing is so effective that workers are better off not trying to reproduce in the first place because nearly all the workers' eggs would be policed anyway. The fact that policing can align the evolutionary interests of the queens and workers facilitates the evolution of queen signaling systems (i.e. queen pheromones, that act as honest signals for the presence of a healthy and fertile queen, resulting in workers refraining from reproducing in many social species). In many other species though, queen-worker conflict can be severe, with workers sometimes even engaging in matricide-killing their own mother queen to be able to reproduce without interference. This chapter provides an overview of both current and past research on reproductive conflicts within the Vespidae wasps and how their study has been instrumental in testing some key predictions of inclusive fitness theory.
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The dominance hierarchy in primitively eusocial insect societies has been shown to be mainly regulated through aggressive interactions. Females that are generally more dominant stand out and occupy the queen position, meaning that they monopolize reproduction while others perform other tasks. Chemical communication is important for maintaining social cohesion. Cuticular hydrocarbons are recognized as the main molecules responsible for mediating social interactions, especially nestmate recognition and queen signalling. Many highly eusocial groups have been studied in recent years, but primitively eusocial groups, which are key to understanding the evolution of social behavior, remain unexplored. In this study, we investigated the connection between cuticular hydrocarbons in females expressed in different social contexts in the primitively eusocial wasp Mischocyttarus cerberus. Colonies in two different ontogenetic phases, pre-and post-worker emergence, were used. We observed and categorized behavioral interactions between individual females and collected all individuals in a nest to obtain information on size, ovary activation and chemical composition. Furthermore, we conducted experiments in which the alpha (dominant) females were removed from nests to produce a new dominance hierarchy. We found that females in different hierarchical positions had small chemical difference corresponding with ovary activity. Our results support the hypothesis that cuticular hydrocarbons are associated with social context in this primitively eusocial species, with some compounds being associated with hierarchical position and ovarian activity.
Why workers forfeit direct reproduction is a crucial question in eusocial evolution. Worker reproduction provides an excellent opportunity to understand the mechanism of kin conflict resolution between the queen and workers. We evaluated behavioral and physiological differences among females in the paper wasp Polistes chinensis antennalis to examine why some workers reproduce under queenright conditions. Reproductive workers were old and foraged less early in the season; their cuticular hydrocarbon (CHC) profiles overlapped with those of queens but were significantly different. The distinct CHC profile of the eggs of the queen likely represented a cue for policing against those by workers. Juvenile hormone (JH) and dopamine seemed to be associated with gonadotropic function, and the JH level of reproductive workers was similar to that of the queen. The high JH level of reproductive workers likely facilitated their reproduction even under queenright conditions. Gene expression levels of the queen and reproductive workers differed only in vitellogenin. These results suggest that worker reproduction is facilitated by an increase in JH level; however, CHC is not a fertility-linked signal, but a queen-linked signal; consequently, reproductive workers without a queen-linked signal might be allowed to stay within the colony.
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Ropalidia marginata is a primitively eusocial paper wasp widely distributed in peninsular India, and unlike many other primitively eusocial wasps, where the queen is physically dominant and aggressive, the R. marginata queen is remarkably meek and docile in behaviour. Despite being docile, she is able to maintain reproductive monopoly and is the sole egg-layer in the colony. Upon removal of the queen, one of the workers becomes extremely aggressive but immediately drops her aggression if the queen is returned. If the queen is not returned, this hyper-aggressive individual will develop her ovaries, lose almost all her aggression, and become the next queen of the colony. Hence we call her the potential queen (PQ). Because of the non-aggressive nature of the queen and because the PQ loses her aggression by the time she starts laying eggs, we consider the hypothesis that regulation of worker reproduction in R. marginata is mediated by pheromones rather than by physical aggression. Using the immediate loss of aggression by the PQ upon return of the queen, we develop a bioassay to demonstrate that the queen’s Dufour’s gland is at least one of the sources of the queen pheromone. Extracts of the queen’s Dufour’s gland (but not that of the worker’s Dufour’s gland) mimic the queen in making the PQ drop her aggression. We are also able to correctly classify queens and workers by a discriminant function analysis based on the chemical compositions of their respective Dufour’s glands. Our study sheds light on the unique position held by R. marginata, midway between primitive and highly eusocial species, and provides understanding regarding evolution of primitive to highly eusocial state in general.
The common approach to the multiplicity problem calls for controlling the familywise error rate (FWER). This approach, though, has faults, and we point out a few. A different approach to problems of multiple significance testing is presented. It calls for controlling the expected proportion of falsely rejected hypotheses — the false discovery rate. This error rate is equivalent to the FWER when all hypotheses are true but is smaller otherwise. Therefore, in problems where the control of the false discovery rate rather than that of the FWER is desired, there is potential for a gain in power. A simple sequential Bonferronitype procedure is proved to control the false discovery rate for independent test statistics, and a simulation study shows that the gain in power is substantial. The use of the new procedure and the appropriateness of the criterion are illustrated with examples.
In vivo studies in the 1960s determined that labeled acetate was readily incorporated into insect cuticular lipids, especially hydrocarbons (Vroman et al., 1965; Lamb and Monroe, 1968; Nelson, 1969), establishing the de novo synthesis of insect hydrocarbons. Later studies with specific radio-labeled precursors and careful analysis of metabolic products determined the biosynthetic pathways for the most common components. In vivo experiments with 13C-labeled precursors extended and confirmed the conclusions based on radiochemical data. In vitro studies using microsomal preparations examined the elongation of fatty acyl-CoAs and the conversion of fatty acyl-CoAs to hydrocarbons. The mechanism of how long-chain fatty acyl-CoAs are converted to hydrocarbons has been controversial, and only recently have studies using the powerful techniques of molecular biology been applied to gaining a more complete understanding of the biosynthesis and regulation of insect hydrocarbons (Wicker-Thomas and Chertemps, Chapter 4, this book). The biosynthesis of hydrocarbons has been studied in relatively few insects, including the dipterans Musca domestica (Blomquist, 2003) and Drosophila melanogaster (Jallon and Wicker-Thomas, 2003), and considerable work has been done on cockroaches Periplaneta americana and Blattella germanica, the termite Zootermopsis angusticollis and several other insects (Nelson and Blomquist, 1995; Howard and Blomquist, 2005). Work has been done with the cabbage looper, Trichoplusia ni (Dwyer et al., 1986; de Renobales et al., 1988), southern armyworm Spodoptera eridania (Guo and Blomquist, 1991) and in cockroaches (Young and Schal, 1997) on the timing of hydrocarbon synthesis and its deposition on the insect cuticle. This chapter will concentrate on the biosynthesis of long-chain cuticular hydrocarbons.
Primitive ant societies, with their relatively simple social structure, provide an opportunity to explore the evolution of chemical communication, in particular of mechanisms underlying within-colony discrimination. In the same colony, slight differences in individual odours can be the basis for discrimination between different castes, classes of age and social status. There is some evidence from correlative studies that such inter-individual variation is associated with differences in reproductive status, but direct proof that certain chemical compounds are detected and recognized by ants is still lacking. In the ponerine ant Pachycondyla inversa , fertile queens and, in orphaned colonies, dominant egg-laying workers are characterized by the predominance of a branched hydrocarbon, 3,11-dimethylheptacosane (3,11-diMeC27) on the cuticle. Using electroanntennography and gas chromatography with electroantennographic detection, we show that the antennae of P. inversa workers react to this key compound. 3,11-diMeC27 is correlated with ovarian activity and, because it is detected, is likely to assume the role of a fertility signal reflecting the quality of the sender.
When queens of eusocial Hymenoptera mate ≤2 times (assuming equal sperm contributions from males and random sperm use), the workers are more closely related to the queen's sons than to the sons of a randomly chosen worker. This suggests that workers should try to prevent other workers from reproducing, and hence producing sons, in species with queens that mate ≤2 times. It also provides a possible reason for the absence of reproductive workers in many hymenopteran societies. Reproductive harmony may therefore result from lowered relatedness among workers. The necessary behaviors and discriminatory ability to favor queen-produced over worker-produced males are referred to as "worker policing'. Population-genetics simulations of the fate of a "police allele', which confers any marginal increase in policing behavior to the workers carrying it, indicate that such an allele will invade and spread to fixation provided that queens mate two or more times. This conclusion is supported empirically by what is known about queen mating frequency and worker reproduction in the highly eusocial bees and wasps. Societies typically headed by monandrous queens, eg those of the bumblebee Bombus terrestris and stingless bees (Meliponinae), have reproductive workers in queenright colonies; those with polyandrous queens, as in honey bees Apis and some yellowjacket wasps Vespula, do not. -from Author
Four important points in colony development are distinguished: 1) start of egg laying by the queen, leading to the beginning of the eusocial phase, the emergence of the first workers; 2) the switch point, at which the queen switches from laying diploid eggs (producing workers or queens) to the laying of haploid eggs (producing males); 3) onset of queen production reared from diploid eggs; 4) loss of dominance by the queen, expressed by the beginning of aggression on the part of queen and workers, worker oviposition, oophagy and the functional elimination of the queen. -from Authors