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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGY, GENOMICS, AND INTEGRATED PEST MANAGEMENT OF INVASIVE ANTS

Location: Imported Fire Ant and Household Insects

Title: A Y-like social chromosome causes alternative colony organization in fire ants

Authors
item Wang, John -
item Wurm, Yannick -
item Nipitwattanaphon, Mingkwan -
item Riba-Grognuz, Oksana -
item Shoemaker, David
item Keller, Laurent -

Submitted to: Nature
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 15, 2012
Publication Date: January 1, 2013
Citation: Wang, J., Wurm, Y., Nipitwattanaphon, M., Riba-Grognuz, O., Shoemaker, D.D., Keller, L. 2013. A Y-like social chromosome causes alternative colony organization in fire ants. Nature. 493:664-668.

Interpretive Summary: Fire ants are considered significant ecological, agricultural, and public health pest throughout their invasive range in the U.S.A. A research entomologist at the Center for Medical, Agricultural, and Veterinary Entomology, USDA-ARS, Gainesville, Florida, in collaboration with scientists from the University of Lausanne, Academia Sinica and Queen Mary University describe here the results of a study characterizing the genomic region responsible for two divergent forms of colony social organisation in fire ants. The results demonstrate that this genomic region is part of a pair of heteromorphic chromosomes having many of the key properties of sex chromosomes. The results also reveal that the two variants are characterized by a large region (55% of the chromosome) where recombination is completely suppressed. Importantly, the non-recombining region comprises most of the genes with demonstrated expression differences between individuals of the two social forms. These findings highlight how genomic rearrangements can maintain divergent adaptive social phenotypes involving many genes acting in concert by locally limiting recombination.

Technical Abstract: Intraspecific variability in social organization is common, yet the underlying causes are rarely known1-3. In the fire ant Solenopsis invicta, the existence of two divergent forms of social organisation is under the control of a single Mendelian genomic element marked by two variants of an odorant binding protein (OBP) gene4-8. Here we characterize the genomic region responsible for this important social polymorphism and show that it is part of a pair of heteromorphic chromosomes having many of the key properties of sex chromosomes. The two variants, hereafter referred as the Social B and Social b (SB and Sb) chromosomes, are characterized by a largeregion of ca. 13 Mb (55% of the chromosome) where recombination is completely suppressed between SB and Sb. Recombination appears to occur normally between the SB chromosomes but is impossible between Sb chromosomes because Sb/Sb individuals are non-viable. Genomic comparisons revealed limited differentiation between SB and Sb, with all or at least the vast majority of the 616 genes identified in the non-recombining region present in the two variants. The reduced recombination between the two heteromorphic Social chromosomes can be explained at least partly by the increased number of repetitive elements and insertions in the non-recombining region of Sb compared with the homologous region of SB.Moreover, we identified an inversion on the Sb chromosome, which may further suppress recombination. Importantly, the non-recombining region comprises most of the genes with demonstrated expression differences between individuals of the two social forms. These findings highlight how genomic rearrangements can maintain divergent adaptive social phenotypes involving many genes acting in concert by locally limiting recombination.

Last Modified: 4/19/2014