Between-mound sharing and colony genetic structure
All treated mounds showed elevated \(\delta\)15N
values, indicating that our methods were successful in enriching the
isotope values of individual mounds. Counter to our expectations,
treated mounds shared very little with neighboring mounds, regardless of
social form (Fig 3) and within-mound relatedness between workers
(Appendix S5). Six of the 57 untreated mounds showed evidence of sharing
with the treated mound (three monogyne and three polygyne). Sharing was
independent of the social form of the treated mound
(χ2 = 0.0091, df = 1, P = 0.924), the social
form of the untreated mound (χ2 = 0.0001, df = 1,P = 0.992), and by the interaction between these variables
(χ2 = 0.0061, df = 1, P = 0.938). Moreover,
sharing was independent of within-mound relatedness between workers in
the treated mound (χ2 = 0.0681, df = 1, P =
0.794), by relatedness between workers in the untreated mound
(χ2 = 0.7718, df = 1, P = 0.380), and by the
interaction between these variables (χ2 = 0.000, df =
1, P = 1.000).
There was a significant effect of distance on whether or not sharing was
detected in untreated mounds (χ2 = 10.0858, df = 1,P = 0.001). All untreated mounds with elevated\(\delta\)15N values were within 5 m of the treated
mound (Fig 4a). However, not all mounds within 5 m of the treated mound
shared (Appendix S6), indicating that distance was not the only
component influencing sharing between mounds. There were 13 untreated
mounds within 5 m from the treated mound that did not share with the
treated mound, one of which was only 0.4 m from the treated mound.
Sharing between mounds did not vary by site (χ2 =
2.0408, df = 5, P = 0.843).
Treated mounds were more genetically similar to the untreated mounds
with which they shared compared to those with which they did not share.
Pairwise F ST values between the treated and
untreated mounds were significantly lower on average and near zero in
mounds that shared (mean and standard errors: 0.028 ± 0.015) than in
mounds that did not share (0.228 ± 0.021; χ2 =
14.5562, df = 1, P < 0.001; Fig 4b) whereF STs were equivalent toF STs between different colonies. Likewise,
untreated mounds that shared could not be significantly genetically
differentiated from the treated mound according to the log-likelihood
(G)-based test of differentiation. There was no significant interaction
between distance and pairwise F ST values
(χ2 = 0.3395, df = 1, P = 0.560). PairwiseF ST between polygyne mounds within each site was
lower than between monogyne mounds (mean and standard errors of 0.144 ±
0.008 and 0.356 ± 0.010 respectively), but there was no significant
interaction between pairwise F ST and social form
(χ2 = 0.0000, df = 3, P = 1.000) on sharing
between mounds.