Within-colony relatedness and comparison with the literature
At our sites, within-mound relatedness was significantly higher in
monogyne mounds (mean and standard errors: 0.644 ± 0.024) than in
polygyne mounds (0.269 ± 0.037; F1,60 = 75.832, P<0.001). However, relatedness in polygyne mounds at our sites
was significantly greater than zero (t33 = 7.249,P < 0.001; 95% CI: 0.193-0.344). Relatedness in
monogyne mounds 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 S7), as has been reported previously
(Fritz, Vander Meer, & Preston, 2006; Lawson, Vander Meer, &
Shoemaker, 2012). Within-mound relatedness did not vary by site
(F5,60 = 1.781, P = 0.130), nor did the
within-mound relatedness of each social form vary by site
(F3,60 = 0.382, P = 0.766).
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
5). 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 5). Studies conducted on
introduced polygyne populations in Australia and Taiwan were greater
than zero (Richlands, Australia: 0.246; Chiayi, Taiwan: 0.1444; Taoyuan,
Taiwan: 0.1122). Likewise, coefficients of polygyne fire ants in their
native range of Argentina were also greater than zero (Corrientes: 0.24;
Formosa: 0.15).