Evaluating the factors that promote invasive ant abundance is critical
to assess their ecological impact and inform their management. Many
invasive ant species show reduced nestmate recognition and an absence of
boundaries between unrelated nests, which allow populations to achieve
greater densities due to reduced intraspecific competition. We examined
nestmate discrimination and colony boundaries in introduced populations
of the red imported fire ant (Solenopsis invicta; hereafter, fire
ant). Fire ants occur in two social forms: monogyne (colonies with a
single egg-laying queen) and polygyne (colonies with multiple egg-laying
queens). In contrast with monogyne nests, polygyne nests are thought to
be interconnected due to the reduced antagonism between non-nestmate
polygyne workers, perhaps because polygyne workers habituate the colony
to an odor unique to Gp-9-carrying adults.
However, colony boundaries and nestmate discrimination are poorly
documented, particularly for worker-brood interactions. To delimit
boundaries between field colonies, we correlated the exchange of a
N-glycine tracer dissolved in a sucrose solution
with social form. We also evaluated nestmate discrimination between
polygyne workers and larvae in the laboratory. Counter to our
expectations, polygyne colonies behaved identically to monogyne
colonies, suggesting both social forms maintain strict colony
boundaries. Polygyne workers also preferentially fed larval nestmates
and may have selectively cannibalized non-nestmates. The levels of
relatedness among workers in polygyne colonies was higher than those
previously reported in North America (mean ±SE: 0.269 ± 0.037). Our
study highlights the importance of combining genetic analyses with
direct quantification of resource exchange to better understand the
factors influencing ant invasions.
Distinct colony boundaries and larval discrimination in polygyne red imported fire ants (Solenopsis invicta)