Wang J, Wurm Y, Nipitwattanaphon M, Riba-Grognuz O, Huang YC, Shoemaker D, Keller L.

Nature. 2013 Jan 31;493(7434):664-8. doi:10.1038/nature11832

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

“The lack of recombination over more than half of the two heteromorphic social chromosomes can be explained by at least one large inversion of around 9 megabases, and this absence of recombination has led to the accumulation of deleterious mutations, including repetitive elements in the non-recombining region of Sb compared with the homologous region of SB.”