A parent-of-origin effect on honeybee worker ovary size.

Apis mellifera capensis is unique among honeybees in that unmated workers can produce pseudo-clonal female offspring via thelytokous parthenogenesis. Workers use this ability to compete among themselves and with their queen to be the mother of new queens. Males could therefore enhance their reproductive success by imprinting genes that enhance fertility in their daughter workers. This possibility sets the scene for intragenomic conflict between queens and drones over worker reproductive traits. Here, we show a strong parent-of-origin effect for ovary size (number of ovarioles) in reciprocal crosses between two honeybee subspecies, A. m. capensis and Apis mellifera scutellata. In this cross, workers with an A. m. capensis father had 30% more ovarioles than genotypically matched workers with an A. m. scutellata father. Other traits we measured (worker weight at emergence and the presence/absence of a spermatheca) are influenced more by rearing conditions than by parent-of-origin effects. Our study is the first to show a strong epigenetic (or, less likely, cytoplasmic maternal) effect for a reproductive trait in the honeybee and suggests that a search for parent-of-origin effects in other social insects may be fruitful.