Polygyny in the nest-site limited acacia-ant Crematogaster mimosae

Abstract

Polygyny is common in social insects despite inevitable decreases in nestmate relatedness and reductions to the inclusive fitness returns for cooperating non-reproductive individuals. We studied the prevalence and mode of polygyny in the African acacia-ant Crematogaster mimosae. These ants compete intensively with neighboring colonies of conspecifics and with three sympatric ant species for resources associated with the whistling-thorn acacias in which they all obligately nest. We used the genotypes of alate males at ten microsatellite loci to reconstruct queen genotypes and found that C. mimosae colonies are frequently secondarily polygynous, in that they include multiple closely related (and sometimes full-sib) queens, and (more rarely) unrelated queens. We also found that individual queens in both monogynous and polygynous colonies had mated with multiple males, making C. mimosae an interesting example of simultaneous polygyny and polyandry. The presence of polygyny in C. mimosae and the intense competition for nest-sites between C. mimosae and its conspecifics support the association between nest-site limitation and polygyny. Polygyny may allow for increased worker populations and a competitive advantage, as intercolony conflicts are typically won by the colony with the larger number of workers.

Polygyny does not explain the superior competitive ability of dominant ant associates in the African ant‐plant, Acacia (Vachellia) drepanolobium

“…This was suggested by Rubin et al. for C. mimosae (), and it may also be the case for the rare colonies of C. sjostedti and C. nigriceps for which we found evidence of polygyny (i.e., a Polygyny Index > 1). These Crematogaster colonies also accepted unrelated queens (or at least, accepted the offspring of unrelated queens), although this appeared to be less common in these ant species than in T. penzigi .…”

“…In the A. drepanolobium system, it is unknown whether higher worker populations are the result of polygyny or some other difference(s) among the different ant species. The only research to date on queen number in this system is that of Rubin et al (2013), who used microsatellite markers to show that C. mimosae colonies are commonly polygynous. However, no further work on the remaining three species has been performed to test the hypothesis that queen number underlies competitive ability in these ants.…”

“…The only research to date on queen number in this system is that of Rubin et al. (), who used microsatellite markers to show that C. mimosae colonies are commonly polygynous. However, no further work on the remaining three species has been performed to test the hypothesis that queen number underlies competitive ability in these ants.…”

“…The higher competitive ability of dominant species, in particular, seems to be driven by larger worker populations (Palmer, ; Ruiz‐Guajardo, Grossenbacher, Grosberg, Palmer, & Stanton, ), but the proximate causes of these larger worker populations are unknown. A primary hypothesis proposed is that more competitive species are polygynous, that is, they have multiple queens per colony (Palmer, ; Rubin et al., ). Collectively, these queens are able to lay more eggs, thereby producing larger worker populations that can outcompete their neighbors.…”

The ecological benefits of larger colony size may promote polygyny in ants

“…Another, nonexclusive hypothesis is that the augmentation in colony size that potentially stems from the association of several egg-laying queens could provide a competitive advantage (H€ olldobler & Wilson, 1977;Rubin et al, 2013). However, this hypothesis has seldom been tested.…”