Abstract
Ants are a highly successful family of insects that thrive in a variety of habitats across the world. Perhaps their best-known features are complex social organization and strict division of labor, separating reproduction from the day-to-day maintenance and care of the colony, as well as strict discrimination against foreign individuals. Since these social characteristics in ants are thought to be mediated by semiochemicals, a thorough analysis of these signals, and the receptors that detect them, is critical in revealing mechanisms that lead to stereotypic behaviors. To address these questions, we have defined and characterized the major chemoreceptor families in a pair of behaviorally and evolutionarily distinct ant species, Camponotus floridanus and Harpegnathos saltator. Through comprehensive re-annotation, we show that these ant species harbor some of the largest yet known repertoires of odorant receptors (Ors) among insects, as well as a more modest number of gustatory receptors (Grs) and variant ionotropic glutamate receptors (Irs). Our phylogenetic analyses further demonstrate remarkably rapid gains and losses of ant Ors, while Grs and Irs have also experienced birth-and-death evolution to different degrees. In addition, comparisons of antennal transcriptomes between sexes identify many chemoreceptors that are differentially expressed between males and females and between species. We have also revealed an agonist for a worker-enriched OR from C. floridanus, representing the first case of a heterologously characterized ant tuning Or. Collectively, our analysis reveals a large number of ant chemoreceptors exhibiting patterns of differential expression and evolution consistent with sex/species-specific functions. These differentially expressed genes are likely associated with sex-based differences, as well as the radically different social lifestyles observed between C. floridanus and H. saltator, and thus are targets for further functional characterization. Our findings represent an important advance toward understanding the molecular basis of social interactions and the differential chemical ecologies among ant species.
Highlights
The family of insects commonly known as ants originated during the Cretaceous period, approximately 140 million years ago [1]
The automated genome annotations of C. floridanus and H. saltator revealed about 100 odorant receptors (Ors) and about 10 gustatory receptors (Grs) genes [46], which is substantially fewer than the number of Or and Gr genes in two other sequenced ant genomes
In order to address this potential discrepancy and comprehensively elucidate the genomic repertoire of chemosensory receptor genes in C. floridanus and H. saltator, we rigorously re-annotated Or, Gr, and ionotropic glutamate receptors (Irs) genes in these two ant species using a custom automated pipeline followed by careful manual inspection
Summary
The family of insects commonly known as ants (family Formicidae) originated during the Cretaceous period, approximately 140 million years ago [1] Since that time, they have established a global presence, with only the most remote locations lacking ant species [2]. Camponotus floridanus (the Florida Carpenter Ant), is a Formicine ant from the South-Eastern United States which belongs to one of the most globally prevalent ant genera [6] These ants feature a rigid caste structure, with strict division of labor between the reproductive queens and the non-reproductive workers that is primarily regulated through pheromones [7,8,9]. When a H. saltator colony loses its queen, one or more of the workers will begin laying eggs and become functional reproductives
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