Positive association of queen number and queen-mating frequency in Myrmicaants: a challenge to the genetic-variability hypotheses

Detailed knowledge of the mating system in specific social insect populatio ns is essential for testing general evolutionary hypotheses of multiple pat ernity in eusocial Hymenoptera. We have studied the mating frequency of que ens in a polygynous population of the red ant Myrmica sulcinodis. Genetic m other-offspring analysis showed that double mating occurred at a considerab le frequency, but that the effective number of queen-mates remained close t o one. After quantifying the effects of multiple maternity (polygyny) and m ultiple paternity (polyandry) on the genetic diversity of workers, we concl ude that multiple paternity in M. sulcinodis did not evolve as an adaptatio n to increase genetic variation within colonies. Contrary to the prediction s from 'genetic variability' hypotheses, we found a positive correlation be tween colony-specific queen number and the average number of mates per quee n. Such positive association of queen number and frequency of multiple mati ng was also found after analysing comparative data across six species of My rmica ants. These results suggest that resticted dispersal of young queens may be a common factor promoting both polygyny and polyandry at the same ti me, and that moderate degrees of multiple mating may be an unselected conse quence of (1) mating at low cost when mating occurs close to the nest and ( 2) mating in swarms with a highly male biased operational sex ratio. Future comparative tests of genetic-variability hypotheses should therefore not i nclude species with such evolutionary derived mating system characteristics .