Exploring Neuromolecular Similarities Underlying the Response to Social Isolation Across Two Vertebrate and Two Invertebrate Species

Abstract

Many animals participate in social interactions with conspecifics, from the transient aggregation of fruit flies collecting on a food source to the development of a more rigid social hierarchy, such as in a bumble bee colony. Engaging with conspecifics shapes the gene expression profiles of neurons in the brains of animals both during early development and in adulthood. Consequently, becoming socially isolated induces a range of aberrant transcriptional profiles and behavioral phenotypes in both vertebrates and invertebrates. It is unknown if these neuromolecular responses are homologous reflections of a shared ancestry of early nervous systems, or instead convergent responses to social isolation-induced stress. Using a comparative transcriptomics approach, this study analyzed publicly-available bulk mRNA sequencing data generated from the neural tissue of four species – house mice (Mus musculus), zebra finch (Taeniopygia guttata), bumble bees (Bombus impatiens) and fruit flies (Drosophila melanogaster) – that had experienced periods of social isolation. Lists of significantly differentially expressed genes associated with experiencing isolation were generated for mice, fruit flies, and bumble bees. A Gene Ontology analysis revealed similar cross-species directional regulation of transcripts associated with metabolism, immune function, and neuronal responsiveness. Gene orthology found groups of conserved genes expressed in neural tissue, though cross-referencing this data with differential gene expression information revealed little significant directionally coherent regulation of these gene groups following social isolation. Finally, an orthologous transcription factor enrichment analysis between the murine medial amygdala, ventral tegmental area, and the whole fly brain demonstrated that ancestral transcription factors were also not expressed in a directionally similar way following isolation. Taken together, these results begin to suggest that the similar response to social isolation in vertebrates and invertebrates is an example of convergent evolution.