Experimental dissection of acceptance of Sb supergene-carrying queens by workers in the red imported fire ant

The multiple-queen (polygyne) social form of the red imported fire ants (Solenopsis invicta) is associated with the Sb supergene, a Mendelian genetic element formed by chromosomal inversions. When workers carry this Sb supergene, the colony accepts multiple reproductive queens, given the queens also carry Sb. In contrast, when workers lack Sb supergene, such as is the case in single-queen (monogyne) colonies, the colony tolerates only a single reproductive queen. Colonies were shown to display polygyne behavior with as few as 10% to 20% of workers carrying the Sb supergene. However, it remains unknown how such a low proportion of Sb workers affects the collective social phenotype of the whole colony. To identify essential factors in the collective acceptance of Sb queens, we conducted a series of behavioral assays using mixed polygyne-monogyne worker units with the proportion of Sb workers around the threshold level of 20%. We changed the type and amount of interaction between the two worker types in the assays and see which conditions favor acceptance of multiple polygyne queens. Our results showed that Sb-carrying (polygyne) workers can indirectly influence queen preference behavior of monogyne workers without contacting the queens, suggesting that certain non-volatile (likely cuticular) compounds from Sb workers play a critical role in the process.