Among us: How to find an optimal clutch sex ratio when the clutch sex ratios of co-foundress wasps are not known beforehand?

A female-biased clutch sex ratio is selected under local mate competition since it reduces competition between male sibs and provides extra mating opportunities for sons. Theoretical models predict that the brood sex ratio of fig wasps becomes less female-biased as the number of wasps laying eggs in the same fig increases. Empirical data have demonstrated that pollinator females lay most of their male eggs first, followed by the female ones in an oviposition bout (males first rule). As oviposition sites are limited in the fig, the brood sex ratio is positively correlated with the number of wasps laying eggs. To understand the strategy of sex ratio adjustment of Sycobia hodites, a non-pollinating fig wasp associated with Ficus benjamina, we compared observed and simulated data. The female wasp starts oviposition shortly after landing on the fig. This process involves the insertion of the ovipositor through the fig surface and into the flower's ovary via the stigma/style. The brood sex ratio of S. hodites did not significantly correlate with the fig brood size. Brood simulations supported the notion that the sex ratio of S. hodites is automatically determined by the male-first rule, involving no control by the mothers. The simulation model best fitting empirical data considered that: (1) females lay few eggs per fig (six or less) and distribute their eggs among several figs, and (2) the probability of an egg producing a male wasp decreases with its position in the egg sequence. Empirical and simulated data showed a wide variation in both brood size and sex ratio, suggesting that selection for an optimal clutch sex ratio is possibly weak. We argue that when selective pressure for sex ratio adjustment is weak, evolution favors male polymorphism as a strategy to cope with mate competition.