Diploid males and sex determination in a paper wasp, Polistes chinensis antennalis (Hymenoptera, Vespidae)

Abstract

Beyond helping the queen's reproductive function, the worker caste of Polistes wasps is expected to have an alternative reproductive strategy; to become a replacement queen, following copulation with early males that emerge along with the first brood workers. We analyzed genotypes and chromosome numbers of the early males in a natural population of P. chinensis antennalis. The frequency of early-male-producing colonies within a population was 5.2% (4/77) in 1993 through 1995. The numerical sex ratios in the 4 colonies for the 3 years and another early male-producing colony in 1999 were 1:1. For one early-male producing colony in 1995, we genotyped 31 females and all 128 males. All 31 genotyped females out of 67 emerged females showed heterozygosity and 69 out of 128 genotyped males were heterozygous; the remaining 59 males were homozygous or hemizygous. The ratio between the number of females and diploid males in this colony was 67:69, which is almost identical with one-to-one ratio. The cytological analysis of male chromosome for one early-male producing colony in 1999 revealed that the early males laid by a queen had 46 chromosomes, while worker laid males had 23. Our results revealed that the early males in this species are diploid males and eventually sterile. Secondly, the single locus complementary sex determination model is most plausible to explain the diploid male production in this species.