Intraspecific phenotypic variation offers unique opportunities to understand the contexts in which traits evolve and how they affect fitness. However, relatively little is known concerning the molecular-genetic changes underpinning such processes in ecologically relevant contexts.
The host recently sequenced the genome of the fire ant Solenopsis invicta and subsequently discovered that two distinct forms of social colony organisation in this species are under control of a pair of social chromosomes, SB and Sb, that evolve similarly to X and Y sex chromosomes. Recombination ceased between SB and Sb less than 500,000 generations ago, ie. >10x more recently than the divergence of other extensively-studied supergenes such as sex chromosomes or butterfly wing coloration genes. Furthermore, both variants of the social chromosome are found in multiple closely related species. The fire ant social chromosome thus offers a unique opportunity to gain novel insights on supergene evolution, evolution of heteromorphic chromosomes and the evolutionary transitions in social organisation.
We propose a detailed study of this newly discovered pair of social chromosomes in several closely related socially polymorphic fire ants, using an integrative examination of the social chromosomes combining modern sequencing methods, genetic mapping, structural analyses, population genomics and comparative genomics methods. This will shed light on a major transition in social evolution and have wide-reaching implications on the evolution of supergenes and the spread of novel traits.
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