Tissue-specific regulatory evolution involved in divergent migratory behavior
Authors: Matthew Louder; Hannah Justen; Kira Delmore
Affiliation: Texas A&M University
Keywords: Speciation & hybridization
Behavioral traits are critical for adaptation to different environments and can lead to reproductive isolation. Yet, how the regulation of gene expression is involved in the evolution of behavioral traits and reproductive isolation remains unclear. Here we examine gene expression in two subspecies of Swainson’s thrush (Catharus ustulatus) that take different routes on migration and their hybrids that exhibit intermediate and ecologically-inferior behaviors to pure forms. We use RNAseq data to compare expression patterns between seasons and taxonomic groups, focusing on five brain regions with predicted associations to migratory behavior. We find that the majority of genes are differentially expressed between seasons are specific to a subspecies and brain region, with a large proportion being limited to the cluster N hyperpallium and hypothalamus. Genes that are differentially expressed between subspecies, but not seasonally responsive, are additively expressed in hybrids and exhibit allele specific expression (ASE), indicative of divergence in cis regulatory regions between subspecies. However, seasonally responsive genes that are specific to a subspecies are predominantly regulated by trans mechanisms. Furthermore, genes putatively involved in divergent migratory behavior between subspecies do not exhibit transgressive expression patterns in hybrids. These results indicate that divergence in trans regulation can be important mechanism in the evolution of behavior and reproductive isolation.