A COMPARATIVE-ANALYSIS OF SEX-RATIO INVESTMENT PARAMETERS IN ANTS

1. Accurate estimates of female-to-male cost ratios are essential for testing theories about kin selection and worker control over sexual in vestments in ants. However, obtaining such estimates has proved to be notoriously difficult. 2. Comparative data on dry weight, energy conte nt and respiration in ant sexuals were analysed across species, to exp lore biases following from the use of different female-to-male cost ra tios. 3. Two groups of ants, those with claustral and independent colo ny foundation (without the help of workers; usually species with singl e-queen colonies) and those with non-claustral, dependent colony found ation (with the help of workers; generally species with multiple-queen colonies), showed consistent differences in weight and energetic cost ratios, with only a relatively small range of overlap. 4, The fat acc umulation in females, relative to males, during maturation was a clear power function of sexual weight dimorphism when analysed across all a nt species, but more like a constant fraction when ant species with in dependent and dependent colony founding were analysed separately. 5. F emale-to-male respiration ratios were always lower than female-to-male dry weight ratios. The adult respiration ratio was a power function o f adult sexual weight dimorphism but the pupal respiration ratio was f ound to be a constant fraction of the pupal dry weight ratio across an t species of both categories. 6. The across-species trends confirmed e arlier species-specific findings. Cost ratios expressed as adult femal e-to-male dry weight ratios underestimate the relative energy content but overestimate the cost of respiration of females, relative to males . 7. A complete female-to-male cost ratio could be obtained for the Ar gentine ant, Iridomyrmex humilis, and a similar estimate was available for Lasius niger from a previous study. These estimates plus the less complete data for three other ant species agreed reasonably well with an earlier proposed 0.7 power-conversion factor, both for ants with i ndependent and dependent colony founding.