Cell death and ovarian development in highly eusocial bees (Hymenoptera, apidae): caste differentiation and worker egg laying

The development and functioning of the ovary in highly eusocial bees is one of the most prominent differences between the castes in these insects, with queens having very large ovaries and a high capacity to produce eggs while the workers have small, sub-functional ovaries. The differences in ovary size and function are established during larval and pupal development and are hormonally controlled. Differential cell death has a prominent role in modulating the ovarian differences during development and adulthood. In this review, we discuss the forms of cell death, the types of cells affected and the timing of death in relation to the function of the female castes in the colony.

Cell death in the Germline: mechanisms and consequences for reproductive plasticity in social bees

Its serial architecture makes the insect ovary an interesting playground to study the regulation of cell death and identify critical check points along the apical-basal axis of the ovarioles. In Drosophila melanogaster, cell death is observed at two points: (1) in the germarium, where entire germ cell clusters may die in response to environmental conditions, and (2) as an obligatory event at the end of oogenesis, when nurse cells dump their cytoplasm into the oocyte and, subsequently, when the follicle epithelial cells form a chorion. The social organization of bees, wasps and ants depends on the monopolization of reproduction by a queen. This has marked consequences on the ovary phenotype of queens and workers. The role of programmed cell death in larval ovary development and in adult ovary function is best studied in honey bees. During larval development, workers loose over 90% of the ovariole primordia. This cell death is induced by a low juvenile hormone titer causing breakdown of the actin cytoskeleton in germ cell clusters. The actin cytoskeleton also plays a major role in the control of cell death in the ovary of adult bees, where many TUNEL-labeled and pycnotic nuclei are detected in a germarial region rich in actin agglomerates. This suggests that common mechanisms may regulate cell death in the ovaries of bees, both during the shaping of the caste-specific ovary phenotypes during larval development, and during the tuning of reproductive activity in adult bees.