Triploid females and diploid males: underreported phenomena in Polistes wasps?

Abstract

In hymenopteran species, males are usually haploid and females diploid. However, in species that have complementary sex determination (CSD), diploid males arise when a female produces offspring that are homozygous at the sex-determining locus. Although diploid males are often sterile, in some species they have been shown to produce diploid sperm, thus producing triploid daughters if they mate successfully. Diploid males have been observed in very few species of social wasps, and we know of no published reports of triploid females. In this paper, we review the existing literature on diploid males and triploid females in the Hymenoptera, and report the observation of triploid females in three species of Polistes paper wasps. Although polyploid offspring may be produced parthenogenetically, the more likely scenario is that Polistes wasps have CSD and produce diploid males via homozygosity at the sex-determining locus. Therefore, female triploidy indicates that diploid males do exist in Polistes species where they are presumed to be absent, and are likely to be even more frequent among species that have experienced a genetic bottleneck. We conclude by cautioning against the assumption of a selective advantage to the production of early males, and by discussing the implications of male diploidy and female triploidy for measurement of sex ratio investment and assumptions of reproductive skew theory.

Effective population size in Hymenoptera with complementary sex determination

“…Effective sterility of diploid males is thus likely to be more common than inviability, further increasing the effects of diploid male production on reducing N e . This is supported by recent reports of triploid females, the product of matings between females and diploid males, in several hymenopteran species (Krieger et al, 1999;Ayabe et al, 2004; reviewed by Liebert et al, 2004). Failure to incorporate diploid male production into population and conservation genetic models may lead to overestimates of N e , a parameter of great significance to the evolutionary genetics of the Hymenoptera, especially in populations expected to have low allelic diversity at the sex locus.…”

“…Both scenarios have been documented in the Hymenoptera in both natural and laboratory populations (eg Plowright and Pallett, 1979;Agoze et al, 1994;Duchateau et al, 1994;Cook and Crozier, 1995;Holloway et al, 1999;Krieger et al, 1999;Ayabe et al, 2004;Liebert et al, 2004).…”

Diploid males sire triploid daughters and sons in the parasitoid wasp Cotesia vestalis

“…near hebetor, and Polistes dominulus (Holloway et al, 1999;Liebert et al, 2004). The triploid females did not differ morphologically from diploid females and their ovaries appeared normal.…”

Rapid determination of sperm number in ant queens by flow cytometry

“…Because of the complementary sex-determination (csd) system of Hymenoptera, homozygous individuals at the sex-determining loci develop into diploid males (Cook and Crozier, 1995). Diploid males constitute particularly high fitness costs to colonies since they are usually sterile or they father a sterile, triploid female progeny (de Boer et al, 2007;Cournault et al, 2006;Krieger et al, 1999;Liebert et al, 2004). Whether diploid males always produce diploid spermatozoa, or not, remains unclear; FCM could greatly help in this respect.…”