Krüppel-homologue 1 Mediates Hormonally Regulated Dominance Rank in a Social Bee

Abstract

Dominance hierarchies are ubiquitous in invertebrates and vertebrates, but little is known on how genes influence dominance rank. Our gaps in knowledge are specifically significant concerning female hierarchies, particularly in insects. To start filling these gaps, we studied the social bumble bee Bombus terrestris, in which social hierarchies among females are common and functionally significant. Dominance rank in this bee is influenced by multiple factors, including juvenile hormone (JH) that is a major gonadotropin in this species. We tested the hypothesis that the JH responsive transcription factor Krüppel homologue 1 (Kr-h1) mediates hormonal influences on dominance behavior. We first developed and validated a perfluorocarbon nanoparticles-based RNA interference protocol for knocking down Kr-h1 expression. We then used this procedure to show that Kr-h1 mediates the influence of JH, not only on oogenesis and wax production, but also on aggression and dominance rank. To the best of our knowledge, this is the first study causally linking a gene to dominance rank in social insects, and one of only a few such studies on insects or on female hierarchies. These findings are important for determining whether there are general molecular principles governing dominance rank across gender and taxa.

Kr-h1, a Cornerstone Gene in Insect Life History

“…However, in contrast to the honey bee, bumble bee foragers do not have higher Kr-h1 levels relative to nurses. Instead, in bumble bees, Kr-h1 is associated with JH-mediated division of worker reproduction and dominance rank ( Shpigler et al, 2010 ; Pandey and Bloch, 2021 ). Bumble bees are primitively eusocial insects that there are no obvious morphological differences between the queen and the workers.…”

“…Kr-h1 levels are found to be higher in dominant workers with active ovaries relative to subordinated individuals with undeveloped ovaries in queenless groups ( Shpigler et al, 2010 ). Knockdown Kr-h1 expression in bumble bees by a perfluorocarbon nanoparticles-based RNA interference protocol showed that bees with reduced Kr-h1 transcript abundance exhibited significantly reduced ovarian activity, less dominance behavior, and had lower dominance rank ( Pandey and Bloch, 2021 ). Therefore, Kr-h1 is associated with JH-mediated regulation of social organization in both bees, from labor division in honey bees to reproduction division and dominance rank in bumble bees.…”

Versatile, vigilance, and gut microbiome support the priority of high-ranking hens

“…Social dominance is a ubiquitous phenomenon, which is among social creatures from insects to primates ( 1 , 2 ). Social rank affects the distribution of dominant resources among individuals, and individuals with high rank tend to select areas where dominant resources are densely distributed, thus obtaining more relative resources.…”