Social structure of the polygynous ant, Crematogaster osakensis

Abstract

The colony structures of social insects vary greatly among species. In ant societies, the number of queens within a colony is variable during colony maturation. We investigated the social structure of a polygynous ant Crematogaster osakensis in a series of field and laboratory experiments. First, the initial colonies headed by multiple queens were found in the field. In laboratory experiments, queens that were artificially cohabited after their nuptial flight harmoniously co-existed even in the presence of newly emerged workers, suggesting that mated queens of this species can establish their colony cooperatively as primary polygynous colonies. In addition, the mating frequency of a queen was typically more than one, estimated from the sperm number stored in field-collected males and queens, and from genetic relatedness among daughters of lab-reared monogynous colonies. Second, our assessment of genetic relatedness in a mature field colony of this species revealed that dealated queens, as well as workers and alates, were relatives. The number of developed oocytes identified reproductive skew in two of five field-collected nests. Moreover, under laboratory conditions, the most fertile egg layer altered over 3 months of observation. Based on these lines of evidence, we propose that in C. osakensis, polygynous foundresses might either be unrelated and subsequently be replaced by daughter queens of particular foundresses, or be related in the first place.