Polygyne Queens Research Articles

Nuclear and mitochondrial genetic structure in two social forms of the fire ant Solenopsis invicta: insights into transitions to an alternate social organization

We describe genetic structure at microgeographical scales in two social forms of the introduced fire ant Solenopsis invicta using nuclear and mitochondrial markers. Fire ant populations in northern Georgia, U.S.A. are structured in fundamentally different ways at the two genomes. Virtually all nuclear genetic variation resides within sampling sites; no differentiation was apparent between the social forms and only minimal differentiation was found among sites in only one social form (the polygyne form, which has nests with numerous queens). In contrast, substantial mtDNA variation exists at all levels; the forms are significantly differentiated and strong divergence was detected among sites in the polygyne form. No mtDNA differentiation was found among sites in the monogyne form (which has nests with a single queen). These results are predicted on the basis of the social biology of the ants. Monogyne queens and males of both forms presumably disperse widely, and polygyne queens commonly mate with monogyne males, thus explaining the uniformity of nuclear allele frequencies across sampling sites and between the forms. Polygyne queens display habits consistent with limited dispersal, and queens of both forms seem unable to establish themselves as reproductives in nests of the alternate form, thus explaining the strong microgeographical structure within the polygyne form and differentiation between the forms found using mtDNA markers. The mtDNA haplotypes are distributed among sites in a manner that suggests a mechanism for the spread of polygyny in introduced fire ants. Monogyne queens apparently mate occasionally with polygyne males and acquire a Mendelian nuclear factor allowing the expression of polygyny in their sexual daughters.

Competition and relatedness between queens of the facultatively polygynous antMyrmica tahoensis

Reproductive conflicts that arise in multiple-queen (polygynous) social insect colonies often lead to behavioural dominance by one queen. No evidence of dominance was found in an intensive study of queen behaviour patterns in colonies of the facultatively polygynous ant Myrmica tahoensis. Colonies were monitored in artificial nests for 228 hours (432 queen-hours). Observations were divided between seven monogynous colonies, nine polygynous colonies, and seven colonies containing one native queen and an unrelated queen that had recently been transplanted into the colony. Aggression rarely occurred between queens in the polygynous colonies, virtually all queens laid eggs, and there was no sign of skew in egg-laying rates. Overall queen activity levels varied considerably between colonies in the three colony types. Queens in monogynous colonies spent more time antennating workers and were groomed more than polygynous queens, whereas polygynous queens laid eggs, handled brood and moved more often. Introduced queens were groomed at a higher rate than queens in naturally polygynous colonies, and queens from naturally polygynous colonies antennated workers, moved, laid eggs and antennated other queens more frequently. Within the introduced-queen colonies, native queens laid eggs and handled brood more frequently than introduced queens. Following the behavioural study, queen–queen relatedness was estimated within the polygynous colonies by means of microsatellite DNA polymorphisms. Queen behaviour patterns were similar regardless of whether queens were close or distant relatives. These results suggest that queens and workers of M. tahoensis behave differently towards newly introduced queens, but do not respond to queen–queen relatedness levels.

Phenotypic plasticity and ?cultural transmission? of alternative social organizations in the fire ant Solenopsis invicta

We investigated the process of sexual maturation in winged queens of the fire ant Solenopsis invicta, a species with two distinct forms of social organization. We found that queens of the monogynous social form (single reproductive queen per colony) differ little or not at all from queens of the polygynous form (multiple reproductive queens per colony) in weight and fat content when these are pupae or newly-eclosed adults. Furthermore, the size of a sclerotized region of the adult thorax, which is set during larval growth, does not differ between queens of the two forms. In contrast, winged queens of the two social forms differ dramatically in their physiological phenotypes once they have matured, with monogynous queens weighing more and having greater fat reserves than polygynous queens. A crossfostering experiment revealed that the different maturation processes of queens of the two forms are induced largely by the type of colony in which a queen matures (monogynous or polygynous) rather than being due to intrinsic genetic differences between the forms. However, genetic variation at a single locus does appear to play some role in determining physiological phenotype in queens of the polygynous form, providing an example of genotype-environment interaction in the expression of these physiological traits. Differences between the social forms in the mature phenotypes that are produced constrain the reproductive options of queens, so that the characteristic social organization of a colony is perpetuated by virtue of the social environment in which new queens are reared.

A comparison of queen oviposition rates from monogyne and polygyne fire ant, Solenopsis invicta, colonies

Abstract. The oviposition rate of individual queens of Solenopsis invicta Buren (Hymenoptera: Formicidae) in relation to their weight and number of queens present in the colony was investigated by direct 2 h observations. There is a strong positive correlation between the weight of a queen and its oviposition rate in both monogyne and polygyne colonies. However, the number of eggs laid per mg queen is higher for moonogyne queens than for polygyne queens. This difference is more evident when the total weight of queens present in a colony is considered. The individual queen oviposition rate is negatively correlated with the number of queens in the colony. In addition, the weight loss per egg laid is significantly greater for polygyne than for monogyne queens, probably due to differences in egg size. These data suggest that oviposition is more efficient in monogyne than in polygyne queens at the individual level; however, at the colony level, polygyne colonies produce significantly more eggs. Comparison of colony level efficiency predicts that polygyne colonies must have at least nine queens to compete reproductively with a mature monogyne queen. Therefore, oligogyny does not appear to be a viable strategy for S.invicata.