Tragedy of the commons in Melipona bees

In human society selfish use of common resources can lead to disaster, a situation known as the ‘tragedy of the commons’ (TOC). Although a TOC is usually prevented by coercion, theory predicts that close kinship ties can also favour reduced exploitation. We test this prediction using data on a TOC occurring in Melipona bee societies

When resistance is useless: policing and the evolution of reproductive acquiescence in insect societies

In social groups composed of kin, inclusive fitness benefits can favor greater cooperation. Alternatively, cooperation can be enforced through the policing of less cooperative individuals. Here, we show that the effect of policing can be twofold: not only can it directly suppress individual selfishness, it can also entirely remove the incentive for individuals to act selfishly in the first place. We term such individual restraint in response to socially imposed policing "acquiescence" and illustrate the concept using examples drawn from the social Hymenoptera (the ants, bees, and wasps). Inclusive fitness models confirm that when a policing system is in place, individuals should be less tempted to act selfishly. This is shown to have important consequences for the resolution of conflict within their societies. For example, it can explain why in many species very few workers attempt to reproduce and why immature females usually do not attempt to develop as queens rather than workers. Although our analyses are primarily focused on the social insects, our conclusions are likely to be general and to apply to other societies as well

Contrasting indirect effects of an ant host on prey–predator interactions of symbiotic arthropods

Indirect interactions occur when a species affects another species by altering the density (density-mediated interactions) or influencing traits (trait-mediated interactions) of a third species. We studied variation in these two types of indirect interactions in a network of red wood ants and symbiotic arthropods living in their nests. We tested whether the ant workers indirectly affected survival of a symbiotic prey species (Cyphoderus albinus) by changing the density and/or traits of three symbiotic predators, i.e., Mastigusa arietina, Thyreosthenius biovatus and Stenus aterrimus, provoking, respectively, low, medium and high ant aggression. An ant nest is highly heterogeneous in ant worker density and the number of aggressive interactions towards symbionts increases with worker density. We, therefore, hypothesized that varying ant density could indirectly impact prey-predator interactions of the associated symbiont community. Ants caused trait-mediated indirect effects in all three prey-predator interactions, by affecting the prey capture rate of the symbiotic predators at different worker densities. Prey capture rate of the highly and moderately aggressed spider predators M. arietina and T. biovatus decreased with ant density, whereas the prey capture rate of the weakly aggressed beetle predator S. aterrimus increased. Ants also induced density-mediated indirect interactions as high worker densities decreased the survival rate of the two predatory spider species. These results demonstrate for the first time that a host can indirectly mediate the trophic interactions between associated symbionts. In addition, we show that a single host can induce opposing indirect effects depending on its degree of aggression towards the symbionts.status: publishe

Joint evolution of multiple social traits: a kin selection analysis

General models of the evolution of cooperation, altruism and other social behaviours have focused almost entirely on single traits, whereas it is clear that social traits commonly interact. We develop a general kin-selection framework for the evolution of social behaviours in multiple dimensions. We show that whenever there are interactions among social traits new behaviours can emerge that are not predicted by one-dimensional analyses. For example, a prohibitively costly cooperative trait can ultimately be favoured owing to initial evolution in other (cheaper) social traits that in turn change the cost-benefit ratio of the original trait. To understand these behaviours, we use a two-dimensional stability criterion that can be viewed as an extension of Hamilton's rule. Our principal example is the social dilemma posed by, first, the construction and, second, the exploitation of a shared public good. We find that, contrary to the separate one-dimensional analyses, evolutionary feedback between the two traits can cause an increase in the equilibrium level of selfish exploitation with increasing relatedness, while both social (production plus exploitation) and asocial (neither) strategies can be locally stable. Our results demonstrate the importance of emergent stability properties of multidimensional social dilemmas, as one-dimensional stability in all component dimensions can conceal multidimensional instability

DNA methylation is associated with codon degeneracy in a species of bumblebee

Social insects display extreme phenotypic differences between sexes and castes even though the underlying genome can be almost identical. Epigenetic processes have been proposed as a possible mechanism for mediating these phenotypic differences. Using whole genome bisulfite sequencing of queens, males, and reproductive female workers we have characterised the sex- and caste-specific methylome of the bumblebee Bombus terrestris. We have identified a potential role for DNA methylation in histone modification processes which may influence sex and caste phenotypic differences. We also find differentially methylated genes generally show low levels of DNA methylation which may suggest a separate function for lowly methylated genes in mediating transcriptional plasticity, unlike highly methylated genes which are usually involved in housekeeping functions. We also examined the relationship between the underlying genome and the methylome using whole genome re-sequencing of the same queens and males. We find DNA methylation is enriched at zero-fold degenerate sites. We suggest DNA methylation may be acting as a targeted mutagen at these sites, providing substrate for selection via non-synonymous changes in the underlying genome. However, we did not see any relationship between DNA methylation and rates of positive selection in our samples. In order to fully assess a possible role for DNA methylation in adaptive processes a specifically designed study using natural population data is needed.</p

The indirect effect of nectar-inhabiting yeasts on olfactory responses and longevity of two stink bug egg parasitoids

Adult parasitoids are well known to feed on sugar-rich resources such as floral nectar. Recently, an increasing body of evidence has shown that nectar is ubiquitously colonized by microorganisms and, as a consequence, microbial metabolic activity can affect several traits of floral nectar. Yet, how the fermentation of nectar by yeasts impacts the olfactory responses and performance of parasitoids is largely understudied, especially in the case of egg parasitoids. In this study, we investigated whether fermentation by the nectar yeasts Metschnikowia gruessii and M.&nbsp;reukaufii affects the olfactory responses of Trissolcus basalis and Ooencyrtus telenomicida, two egg parasitoid species associated with the southern green stink bug Nezara viridula. We also investigated how yeast fermentation affects the longevity and survival of the egg parasitoids. Results of static four-chamber olfactometer tests showed that nectar fermented by M. gruessii (but not by M. reukaufii) was attractive to both egg parasitoid species, whereas no significant yeast-mediated effects were found in terms of wasp longevity. Gas chromatography coupled with mass spectrometry (GC-MS) showed a clear separation of the volatile profiles among M. gruessii, M. reukaufii and non-fermented control nectar supporting the results of the insect bioassays. The results of our study highlight the need to consider the role of microbes when studying interactions between flower nectar and egg parasitoids and could have implications from a conservation biological control perspective

Covert deformed wing virus infections have long-term deleterious effects on honeybee foraging and survival

Several studies have suggested that covert stressors can contribute to bee colony declines. Here we provide a novel case study and show using radio-frequency identification (RFID) tracking technology that covert deformed wing virus (DWV) infections in adult honeybee workers seriously impact longterm foraging and survival under natural foraging conditions. In particular, our experiments show that adult workers injected with low doses of DWV experienced increased mortality rates, that DWV caused workers to start foraging at a premature age, and that the virus reduced the workers’ total activity span as foragers. Altogether, these results demonstrate that covert deformed wing virus infections have strongly deleterious effects on honey bee foraging and survival. These results are consistent with previous studies that suggested DWV to be an important contributor to the ongoing bee declines in Europe and the US. Overall, our study underlines the strong impact that covert pathogen infections can have on individual and group-level performance in bees

Bacterial phylogeny predicts volatile organic compound composition and olfactory response of an aphid parasitoid

There is increasing evidence that microorganisms emit a wide range of volatile compounds (mVOCs, microbial volatile organic compounds) that act as insect semiochemicals, and therefore play an important role in insect behaviour. Although it is generally believed that phylogenetically closely related microbes tend to have similar phenotypic characteristics and therefore may elicit similar responses in insects, currently little is known about whether the evolutionary history and phylogenetic relationships among microorganisms have an impact on insect‐microbe interactions. In this study, we tested the hypothesis that phylogenetic relationships among 40 Bacillus strains isolated from diverse environmental sources predicted mVOC composition and the olfactory response of the generalist aphid parasitoid Aphidius colemani . Results revealed that phylogenetically closely related Bacillus strains emitted similar blends of mVOCs and elicited a comparable olfactory response of A. colemani in Y‐tube olfactometer bioassays, varying between attraction and repellence. Analysis of the chemical composition of the mVOC blends showed that all Bacillus strains produced a highly similar set of volatiles, but often in different concentrations and ratios. Benzaldehyde was produced in relatively high concentrations by strains that repel A. colemani , while attractive mVOC blends contained relatively higher amounts of acetoin, 2,3‐butanediol, 2,3‐butanedione, eucalyptol and isoamylamine. Overall, these results indicate that bacterial phylogeny had a strong impact on mVOC compositions and as a result on the olfactory responses of insects