title: Evolutionary constraints shape caste-specific gene expression across 15 ant species.
abstract: Development of polymorphic phenotypes from similar genomes requires gene expression differences. However, little is known about how morph-specific gene expression patterns vary on a broad phylogenetic scale. We hypothesize that evolution of morph-specific gene expression, and consequently morph-specific phenotypic evolution, may be constrained by gene essentiality and the amount of pleiotropic constraints. Here, we use comparative transcriptomics of queen and worker morphs, that is, castes, from 15 ant species to understand the constraints of morph-biased gene expression. In particular, we investigate how measures of evolutionary constraints at the sequence level (expression level, connectivity, and number of gene ontology [GO] terms) correlate with morph-biased expression. Our results show that genes indeed vary in their potential to become morph-biased. The existence of genes that are constrained in becoming caste-biased potentially limits the evolutionary decoupling of the caste phenotypes, that is, it might result in "caste load" occasioning from antagonistic fitness variation, similarly to sexually antagonistic fitness variation between males and females. On the other hand, we suggest that genes under low constraints are released from antagonistic variation and thus more likely to be co-opted for morph specific use. Overall, our results suggest that the factors that affect sequence evolutionary rates and evolution of plastic expression may largely overlap.
authors.affiliation: Centre of Excellence in Biological Interactions, Department of Biosciences, University of Helsinki, Helsinki, Finland.|Tvärminne Zoological Station, University of Helsinki, J.A. Palménin tie 260, FI-10900, Hanko, Finland.
authors.forename: Claire
authors.initials: C
authors.lastname: Morandin
authors.affiliation: Okinawa Institute of Science and Technology, 1919-1 Tancha, Onna-son, Kunigami-gun, Okinawa, 904-0412, Japan.|Research School of Biology, Australian National University, Canberra, ACT, 0200, Australia.
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Mikheyev
authors.affiliation: Centre for Social Evolution, University of Copenhagen, Universitetsparken 15, 2100, Copenhagen, Denmark.
authors.forename: Jes Søe
authors.initials: JS
authors.lastname: Pedersen
authors.affiliation: Centre of Excellence in Biological Interactions, Department of Biosciences, University of Helsinki, Helsinki, Finland.|Tvärminne Zoological Station, University of Helsinki, J.A. Palménin tie 260, FI-10900, Hanko, Finland.
authors.forename: Heikki
authors.initials: H
authors.lastname: Helanterä
mesh_terms: D000818:Animals; D005260:Female; D008297:Male; D001000:Ants / Q000235:genetics; D015870:Gene Expression; D016678:Genome; D010641:Phenotype; D010802:Phylogeny
keywords: Caste differentiation; RNAseq; gene expression; phylogenetic signal; social insects