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).