Queen Number as an Adaptable Trait: Evidence from Wild Populations of Two Red Ant Species (Genus myrmica)

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Abstract
(1) Data are given for the number of queens in colonies of two species of Myrmica ants: samples of Myrmica rubra were taken in autumn from four populations from Dorset, U.K., one of which was sampled for 18 years; samples of Myrmica limanica spp. jacobsoni were taken continuously throughout the summer for 6 years, from a population living near Warsaw, Poland. Analysis of these data showed that the average number of queens in colonies varied with colony size (worker number). (2) When the variation due to sampling different sized colonies was removed statistically, it was shown that the average number of queens varied significantly between years, between months in the same year, and between sites in the same year. (i) Both species had significant annual differences in the populations studied. In the case of M. rubra this could be explained by climatic variations and the best model was a quadratic function of late-summer temperatures. M. rubra colonies appeared to be at their smallest, with fewest queens, when the temperature averaged 16 degrees C; this coincided with the long-term average late-summer temperature in Dorset. (ii) The data for M. limanica showed that the number of queens can very between different months in the same year. In fact there was a general decline during the summer, which suggested that up to 60% of all queens die each summer and are replaced by new queens in the autumn and following spring. (iii) In any year, M. rubra queen numbers varied significantly and in a consistent manner, between the four nearby sites in Dorset. Each site had the same pattern of annual variation, a result which can be explained by the general influence of climate on these proximate sites. Differences in the average number of queens in the M. rubra colonies, living on the different sites, are probably due to the pattern of variation of microclimate at individual nest spots, but no data was available to test this. (3) The data and analyses are discussed in relation to the general ecology of Myrmica. It is concluded that, in this genus at least, polygyny is an adaptable trait as predicted from theoretical modelling studies.