BackgroundReproductive division of labor in eusocial insects is a striking example of a shared genetic background giving rise to alternative phenotypes, namely queen and worker castes. Queen and worker phenotypes play major roles in the evolution of eusocial insects. Their behavior, morphology and physiology underpin many ecologically relevant colony-level traits, which evolved in parallel in multiple species.ResultsUsing queen and worker transcriptomic data from 16 ant species we tested the hypothesis that conserved sets of genes are involved in ant reproductive division of labor. We further hypothesized that such sets of genes should also be involved in the parallel evolution of other key traits. We applied weighted gene co-expression network analysis, which clusters co-expressed genes into modules, whose expression levels can be summarized by their ‘eigengenes’. Eigengenes of most modules were correlated with phenotypic differentiation between queens and workers. Furthermore, eigengenes of some modules were correlated with repeated evolution of key phenotypes such as complete worker sterility, the number of queens per colony, and even invasiveness. Finally, connectivity and expression levels of genes within the co-expressed network were strongly associated with the strength of selection. Although caste-associated sets of genes evolve faster than non-caste-associated, we found no evidence for queen- or worker-associated co-expressed genes evolving faster than one another.ConclusionsThese results identify conserved functionally important genomic units that likely serve as building blocks of phenotypic innovation, and allow the remarkable breadth of parallel evolution seen in ants, and possibly other eusocial insects as well.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-016-0902-7) contains supplementary material, which is available to authorized users.

Social insect sex and caste ratios are well-studied targets of evolutionary conflicts, but the heritable factors affecting these traits remain unknown. To elucidate these factors, we carried out a short-term artificial selection study on female caste ratio in the ant Monomorium pharaonis. Across three generations of bidirectional selection, we observed no response for caste ratio, but sex ratios rapidly became more female-biased in the two replicate high selection lines and less female-biased in the two replicate low selection lines. We hypothesized that this rapid divergence for sex ratio was caused by changes in the frequency of infection by the heritable bacterial endosymbiont Wolbachia, because the initial breeding stock varied for Wolbachia infection, and Wolbachia is known to cause female-biased sex ratios in other insects. Consistent with this hypothesis, the proportions of Wolbachia-infected colonies in the selection lines changed rapidly, mirroring the sex ratio changes. Moreover, the estimated effect of Wolbachia on sex ratio (~13% female bias) was similar in colonies before and during artificial selection, indicating that this Wolbachia effect is likely independent of the effects of artificial selection on other heritable factors. Our study provides evidence for the first case of endosymbiont sex ratio manipulation in a social insect.

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During colony relocation, the selection of a new nest involves exploration and assessment of potential sites followed by colony movement on the basis of a collective decision making process. Hygiene and pathogen load of the potential nest sites are factors worker scouts might evaluate, given the high risk of epidemics in group-living animals. Choosing nest sites free of pathogens is hypothesized to be highly efficient in invasive ants as each of their introduced populations is often an open network of nests exchanging individuals (unicolonial) with frequent relocation into new nest sites and low genetic diversity, likely making these species particularly vulnerable to parasites and diseases. We investigated the nest site preference of the invasive pharaoh ant, Monomorium pharaonis, through binary choice tests between three nest types: nests containing dead nestmates overgrown with sporulating mycelium of the entomopathogenic fungus Metarhizium brunneum (infected nests), nests containing nestmates killed by freezing (uninfected nests), and empty nests. In contrast to the expectation pharaoh ant colonies preferentially (84%) moved into the infected nest when presented with the choice of an infected and an uninfected nest. The ants had an intermediate preference for empty nests. Pharaoh ants display an overall preference for infected nests during colony relocation. While we cannot rule out that the ants are actually manipulated by the pathogen, we propose that this preference might be an adaptive strategy by the host to “immunize” the colony against future exposure to the same pathogenic fungus.

Background and purpose Real‐world evidence regarding the effectiveness and safety of ocrelizumab for the treatment of multiple sclerosis (MS) is limited. The aim was to evaluate the effectiveness and safety of ocrelizumab treatment for MS in a real‐world setting. Methods A nationwide population‐based cohort study was conducted where clinical and magnetic resonance imaging data of MS patients enrolled prospectively in the Danish Multiple Sclerosis Registry who initiated ocrelizumab treatment between January 2018 and November 2020 were analyzed. Results A total of 1104 patients (85.7% relapsing–remitting MS [RRMS], 8.8% secondary progressive MS [SPMS], 5.5% primary progressive MS [PPMS]) were included, with a median follow‐up period of 1.3 years. At baseline, the mean age was 41.4 years in the RRMS group, 44.5 years in the PPMS group and 50.3 years in the SPMS group. Median Expanded Disability Status Scale score was 2.5, 3.5 and 5.5, respectively. Most RRMS and SPMS patients had received previous disease‐modifying therapies (87.5% and 91.8%, respectively), whereas PPMS patients were mostly treatment naïve (78.7%). After ocrelizumab initiation, 9.3% of the patients experienced a relapse and 8.7% a 24 weeks confirmed disability worsening. Conversely, 16.7% showed a 24 weeks confirmed disability improvement. After ~1 year of treatment, most patients (94.5%) were free of magnetic resonance imaging activity. Ocrelizumab was generally well tolerated, as side effects were only reported for 10% of patients, mostly consisting of infusion‐related reactions and infections. Conclusions It is shown that most MS patients treated with ocrelizumab are clinically stabilized and with an adverse event profile consistent with the experience from the pivotal clinical trials.

SUMMARY Insect social life is governed by chemicals. A great number of studies have demonstrated that the blend of hydrocarbons present on the cuticle (CHCs) plays a pivotal role in intra- and inter-specific communication. It is not surprising, therefore, that social parasites, specialized in exploiting the costly parental care provided by host workers, exploit the host chemical communication system too. Throughout their life cycle, social parasites intercept and break this CHC-based code. Recently, however, several polar compounds (mainly peptides) have been found in addition to CHCs both on the cuticle and on the comb surface of social insects, and their semiochemical role has been demonstrated in some circumstances. In the present study, we used the paper wasp social parasite–host system Polistes sulcifer (Zimmerman)–Polistes dominulus (Christ) to evaluate the relative importance of the CHCs and polar compounds in two different steps of the host exploitation process: host nest detection by the pre-usurping parasite and parasite chemical integration into the host colony. After separating the polar and apolar fractions of the host nest as well as those of pre- and post-usurpation parasites, we carried out laboratory assays based on the binary choice model. Our results show that nest polar compounds neither are used by the parasite to detect the host's nest nor play a role in parasite chemical integration into the host colony. In contrast, we demonstrate that CHCs are fundamental in both steps, thus confirming their primary role in social insect life and consequently in social parasite–host interactions.

A colony of social insects is like a fortress where access is allowed only to colony members. The epicuticular mixture of hydrocarbons has been widely reported to be involved in nestmate recognition in insects. However, recent studies have shown that polar compounds (mainly peptides) are also present, mixed with hydrocarbons, on the cuticle of various insects, including the paper wasps of the genus Polistes. As these polar compounds are variable among Polistes species and are perceived by the wasps, this cuticular fraction could also be involved in nestmate recognition. Through MALDI-TOF (Matrix-Assisted Laser Desorption Ionization Time of Flight) mass spectrometry analysis, we assessed, for the first time, the intercolonial variability of the cuticular polar fraction of Polistes dominulus in order to evaluate its reliability as source of nestmate recognition cues. We then tested through behavioral assays the importance of the 2 isolated fractions (apolar and polar) in nestmate recognition by presenting them separately to colonies of P. dominulus. Our results showed that the cuticular polar compounds are not colony specific and they are not used by paper wasps to discriminate nestmates from non-colony members. On the contrary, we confirmed that the isolated cuticular hydrocarbons are the chemical mediators prompting nestmate recognition in paper wasps.

In social insects, cuticular hydrocarbons function in nest-mate recognition and also provide a waxy barrier against desiccation, but basic evolutionary features, including the heritability of hydrocarbon profiles and how they are shaped by natural selection are largely unknown. We used a new pharaoh ant ( Monomorium pharaonis ) laboratory mapping population to estimate the heritability of individual cuticular hydrocarbons, genetic correlations between hydrocarbons, and fitness consequences of phenotypic variation in the hydrocarbons. Individual hydrocarbons had low to moderate estimated heritability, indicating that some compounds provide more information about genetic relatedness and can also better respond to natural selection. Strong genetic correlations between compounds are likely to constrain independent evolutionary trajectories, which is expected, given that many hydrocarbons share biosynthetic pathways. Variation in cuticular hydrocarbons was associated with variation in colony productivity, with some hydrocarbons experiencing strong directional selection. Altogether, this study builds on our knowledge of the genetic architecture of the social insect hydrocarbon profile and indicates that hydrocarbon variation is shaped by natural selection.