Alternative reproductive strategies and the evolution and maintenance of multiple-queen societies in the fire ant Solenopsis invicta.

摘要

Multiple-queen or polygyne insect societies present an apparent paradox for kin selection theory because the presence of multiple reproductive individuals within a nest reduces relatedness between workers and the sexual brood that they rear. If, however, workers can make fine scale discriminations between nestmates of variable relatedness, they may still act to increase their inclusive fitness if they feed and care for predominantly closely related nestmates. We tested this in the fire ant Solenopsis invicta using behavioral assays and five allozyme loci to estimate genetic relatedness between workers and the recipients of their altruism. We were unable to detect a positive signal of relatedness between these interactants using two different assays: workers tending reproductive queens and workers feeding virgin queens. Introduced populations of S. invicta, however, may not provide legitimate tests of kin selection theory because recent work indicates they have undergone drastic changes in their social organization when they were introduced into North America.; We show that reproductive strategies are variable among queens in both the monogyne (single-queen) and polygyne forms of S. invicta. Allozyme markers combined with field data collected in other studies reveal that some queens from the monogyne form successfully infiltrate mature nests to reproduce and that this alternative reproductive strategy is comparably successful to the more common reproductive strategy (independent colony founding).; Reproductive tactics of queens also appear to vary in the polygyne form, and this variation is strongly influenced by variation at a single locus, for which we have a protein marker called Gp-9. Heavy Gp-9{dollar}sp{lcub}BB{rcub}{dollar} queens show vagility and habitat selection similar to those seen in monogyne, independent colony founding queens. Lighter Gp-9{dollar}sp{lcub}Bb{rcub}{dollar} and Gp-9{dollar}sp{lcub}bb{rcub}{dollar} queens show a mixed strategy. Some of these skinny queens appear to mate near or return to their natal nest site, where they presumably attempt to infiltrate a mature nest to reproduce. Other skinny queens appear to disperse to other sites, but these emigrating queens appear to be largely unsuccessful at infiltrating nests to reproduce. It may be that dispersing skinny queens also attempt to found new nests like the heavy Gp-9{dollar}sp{lcub}BB{rcub}{dollar} queens: independently of worker aid.