Temporal Variation in Colony Populations of the Ant Myrmica sulcinodis: II. Sexual Production and Sex Ratios

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Abstract
The numbers and sex ratio of reproductive castes reared by two populations of Myrmica sulcinodis Nyl. over 7 years since 1979 are reported. On average, 40% of the colonies were small and reaed no sexuals. In the remainder, sexual production was very variable, having a small significant correlation with worker number (+ve) and queen number (-ve). Sexual production differed significantly from year to year, but not between sites. The colonies from four groups, according to whether they rear gynes, males, both or neither. Total spring production was compared for these. The results are consistent with data for other Myrmica species. The sex ratio varied between years and sites. Both populations had a male bias, which was greatest in highly polygynous colonies and least in large colonies, as is expected under kinship theory. The social regulation of sexual production at the colony level may be difficult to modify by natural selection, which operates instead on the colony structure required to maximize the species'' breeding success in its chosen habitat. If secondary polygyny is an adaptation that ensures a colony''s survival in a variable habitat, then many colonies exist for long periods in sub-optimal nest sites. Male bias is the global cost of the polygymous lifestyle for these species. In such populations only the largest and reproductively most successful colonies might approach the optimal sex ratio; these colonies of M. sulcinodis averaged a 1:1 sex ratio (3:1 females by dry weight).

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