3.2 | Within-colony relatedness and comparison with the literature
At our sites, within-nest relatedness was significantly higher in monogyne nests (mean and standard errors: 0.644 ± 0.024) than in polygyne nests (0.269 ± 0.037; F1,60 = 75.832, P<0.001). However, relatedness in polygyne nests at our sites was significantly greater than zero (t33 = 7.249,P < 0.001; 95% CI: 0.193-0.344). Relatedness in monogyne nests was significantly lower than 0.75 (t35 = -4.368, P < 0.001; 95% CI: 0.595-0.693), consistent with our genetic results showing that some colonies (18/38) were headed by a multiply mated queen (Appendix S8), as has been reported previously (Fritz, Vander Meer, & Preston, 2006; Lawson, Vander Meer, & Shoemaker, 2012). Within-nest relatedness did not vary by site (F5,60 = 1.781, P = 0.130), nor did the within-nest relatedness of each social form vary by site (F3,60 = 0.382, P = 0.766). In all but one nest that were defined as monogyne using Gp-9 , the presence of a single reproducing queen was confirmed using microsatellite markers, as all workers could be assigned to a unique queen. The reproduction of multiple queens was confirmed in all but three polygyne nests.
Based on our analysis of within-colony relatedness coefficients between workers reported in the literature, no other study has analyzed within-colony relatedness between fire ant workers in Texas, USA (Fig 3). Of the five studies conducted in Georgia, USA, four reported coefficients in polygyne populations that were not significantly greater than zero, and one reported a coefficient that was significantly greater than zero (mean: 0.16; Ross et al. 1993; Fig 3). Studies conducted on in introduced polygyne populations in Australia and Taiwan revealed relatedness coefficients higher than zero (Richlands, Australia: 0.246; Chiayi, Taiwan: 0.1444; Taoyuan, Taiwan: 0.1122). Likewise, within-nest relatedness coefficients of polygyne fire ants in their native range of Argentina were also greater than zero (Corrientes: 0.24; Formosa: 0.15).