Characterizing the Expression Pattern of Socially-Relevant Candidate Immediate Early Genes in the Common Eastern Bumblebee, Bombus impatiens

Abstract

Social behavior is essential for the organization and survival of social insects, where interactions among individuals enable communication, learning, and coordinated colony function. Despite its importance, the neural mechanisms underlying social behavior in insects remain poorly understood. Immediate early genes (IEGs) provide a powerful tool for investigating the neural basis of behavior, as they are rapidly and transiently expressed following neuronal activation, making them useful markers of neural activity and enabling the mapping of active neural circuits. Although IEGs are widely used in vertebrate systems, their application in insects remains limited. This study examined the relationship between social behavior and activity-dependent gene expression in the common eastern bumblebee, Bombus impatiens, with the goal of identifying candidate IEGs associated with social interaction. This study uses a two part approach. First, as an initial screening, single-nucleus RNA sequencing (snRNA-seq) was performed on central brain tissue following behavioral assays to identify genes differentially expressed in response to social interaction. Differential expression was restricted to specific cell types, particularly large Kenyon cells and class II Kenyon cells, with several genes upregulated in the social condition. Second, a follow-up bulk RNA sequencing experiment was designed using central brain samples collected after behavioral assays across three conditions and multiple time points to test whether these genes exhibit the rapid and transient expression dynamics characteristic of true IEGs. These data were not available for analysis at the time of this thesis. Despite the lack of temporal validation, the snRNA-seq experiment identified candidate immediate early genes upregulated in specific cell types during social interaction, supporting their potential as markers of neural activity. These findings provide a foundation for future studies aimed at validating these markers and expanding activity-dependent labeling tools to map the neural circuits involved in processing social information in the bumblebee brain.