The fire ant Solenopsis invicta exists in two alternate social forms: monogyne nests contain a single reproductive queen and polygyne nests contain multiple reproductive queens. This colony-level social polymorphism corresponds with individual differences in queen physiology, queen dispersal patterns, and worker discrimination behaviors, all evidently regulated by an inversion-based supergene that spans more than 13Mb of a "social chromosome," contains over 400 protein-coding genes, and rarely undergoes recombination. The specific mechanisms by which this supergene influences expression of the many distinctive features that characterize the alternate forms remain almost wholly unknown. To advance our understanding of these mechanisms, we explore effects of social chromosome genotype and natal colony social form on gene expression in virgin queens sampled as they embarked on nuptial flights, using RNA-sequencing of two important tissues. We observe relatively minor effects of natal social form, that is, of the social/developmental environment, on gene expression profiles, but substantial effects of genotype, including i) supergene-associated gene upregulation, ii) allele-specific expression, and iii) pronounced extra-supergene trans-regulatory effects. These findings, along with observed spatial variation in differential and allele-specific expression within the supergene region, highlight the complex gene regulatory landscape that emerged following evolutionary divergence of the inversion-mediated Sb haplotype from its homolog that largely retained the ancestral gene order.The distinctive social chromosome-linked gene expression trajectories we document at the onset of a queen's reproductive life expand the known record of relevant molecular correlates of a complex social polymorphism and point to putative genetic underpinnings of the alternate social syndromes.
Indirect genetic effects, where phenotypic variation is influenced by the genotypes of social partners, act as heritable sources of environmental variation in eusocial organisms. In the fire ant Solenopsis invicta, a supergene exhibits striking indirect genetic effects on worker regulation of colony queen number. We assess the direct and indirect genetic effects of this social supergene on gene expression using RNA-seq of brains and abdominal tissues from lab-reared workers and field-collected pre-reproductive queens. We find that direct genetic effects cause larger gene expression changes and are more consistent across tissue types and castes than indirect genetic effects. Indirect genetic effects influence the expression of many loci but are generally restricted to the abdominal tissues. Further, indirect genetic effects were only detected when the genotypic composition of social partners differed throughout the development and adult life of the focal individual, and were often only significant with relatively lenient statistical cutoffs. Our study demonstrates the importance of including diverse sample types and considering the magnitude of changes in gene expression when studying the roles of direct and indirect genetic effects on behavior.
Moncton, ville née des fonctions de relation et surtout du chemin de fer, est aussi la plus grande ville acadienne. Les aspects et les problèmes de la cité dérivent du dépérissement du centre ancien concurrencé par les centres d'achat périphériques, de la gêne de la circulation engendrée par les installations ferroviaires. La coexistence de deux groupes humains : Acadiens francophones et anglophones influence peu les aspects urbains mais pose des problèmes de géographie sociale en voie de règlement.
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