title: Gene Expression Dynamics in Major Endocrine Regulatory Pathways along the Transition from Solitary to Social Life in a Bumblebee,Bombus terrestris.
abstract: Understanding the social evolution leading to insect eusociality requires, among other, a detailed insight into endocrine regulatory mechanisms that have been co-opted from solitary ancestors to play new roles in the complex life histories of eusocial species. Bumblebees represent well-suited models of a relatively primitive social organization standing on the mid-way to highly advanced eusociality and their queens undergo both, a solitary and a social phase, separated by winter diapause. In the present paper, we characterize the gene expression levels of major endocrine regulatory pathways across tissues, sexes, and life-stages of the buff-tailed bumblebee,Bombus terrestris, with special emphasis on critical stages of the queen's transition from solitary to social life. We focused on fundamental genes of three pathways: (1) Forkhead box protein O and insulin/insulin-like signaling, (2) Juvenile hormone (JH) signaling, and (3) Adipokinetic hormone signaling. Virgin queens were distinguished by higher expression offorkhead box protein Oand downregulated insulin-like peptides and JH signaling, indicated by low expression ofmethyl farnesoate epoxidase(MFE) and transcription factorKrüppel homolog 1(Kr-h1). Diapausing queens showed the expected downregulation of JH signaling in terms of lowMFEandvitellogenin(Vg) expressions, but an unexpectedly high expression ofKr-h1. By contrast, reproducing queens revealed an upregulation ofMFEandVgtogether with insulin signaling. Surprisingly, the insulin growth factor 1 (IGF-1) turned out to be a queen-specific hormone. Workers exhibited an expression pattern ofMFEandVgsimilar to that of reproducing queens. Males were characterized by highKr-h1expression and lowVglevel. The tissue comparison unveiled an unexpected resemblance between the fat body and hypopharyngeal glands across all investigated genes, sexes, and life stages.
authors.affiliation: Department of Chemistry of Social Insects, The Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences Prague, Czechia.
authors.forename: Pavel
authors.initials: P
authors.lastname: Jedlička
authors.affiliation: Department of Chemistry of Social Insects, The Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences Prague, Czechia.
authors.forename: Ulrich R
authors.initials: UR
authors.lastname: Ernst
authors.affiliation: Agricultural Research Ltd. Troubsko, Czechia.
authors.forename: Alena
authors.initials: A
authors.lastname: Votavová
authors.affiliation: Department of Chemistry of Social Insects, The Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences Prague, Czechia.
authors.forename: Robert
authors.initials: R
authors.lastname: Hanus
authors.affiliation: Research Group of Infochemicals, The Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences Prague, Czechia.
authors.forename: Irena
authors.initials: I
authors.lastname: Valterová
keywords: caste differentiation; diapause; endocrine glands; hormones; reproduction; social evolution; social insects