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Abstract
Biological complexity evolves via major evolutionary transitions featuring the onset of cooperative reproduction by formerly independent reproducers. Examples include the transition from asexual to sexual reproduction and from solitary to social life. An analogous transition exists in ants, from monogyne (single reproductive queen) to polygyne (multiple reproductive queens) colonies. We investigated this transition in the fire ant Solenopsis geminata and show: 1) polygyne colonies employ a peculiar reproductive mode with queens produced asexually and workers sexually, while monogyne colonies display the typical reproductive mode of Hymenoptera; 2) the polygyne form exploits gene flow from the monogyne form to produce workers and, hence, viable colonies; and 3) two divergent polygyne subpopulations arose independently from a neighboring monogyne population. These instances of an ostensible reduction in complexity on one vector (sexual to asexual reproduction) coupled with an increase in complexity on another (monogyny to polygyny) highlight underappreciated interactions between different biological transitions.