Abstract
Honeybees are the most important insect to agricultural success worldwide. They are worth billions of dollars per year to agriculture due to their pollination abilities. Hives contain thousands of workers responsible for pollination duties across the world. All of these workers are produced by a single mother - the queen. The decline of honeybee populations in the face of expanding threats presents a risk to the economy and food availability. To address this problem, a project was designed to understand more about honeybee reproduction and development. This project aims to provide developmental targets to support the production of higher-quality hive members and improve their numbers.
The honeybee queen is the sole reproducer of worker bees, so the project Airst investigated the honeybee queen germline. In situ hybridization chain reaction (HCR) revealed that four genes (nanos, vasa, ovo, tapas) are germline-only cell markers in honeybees, while two genes (castor, unzipped) are somatic-only cell markers in honeybees. Immunohistochemistry of dividing cell markers and EdU injections revealed that the germline in honeybee queens are 8-cell clusters that divide and replace themselves, suggesting that eight-cell clusters must be produced during larval development of the honeybee queen.
Using HCR and immunohistochemistry of dividing cells, this thesis explores the production of the honeybee queen ovary and the germline stock. HCRs showed that the ovary has immature terminal Ailament and germarium regions by larval stage 3. Immunohistochemistry revealed interconnected, synchronously dividing germline cells joined by polyfusomes. The germline clusters reach eight cells by pupation. Therefore, the eight-cell germline clusters seen in adult queens are produced during larval stages. This thesis also outlines a novel terminal Ailament cell marker, oddskipped. HCRs also confirmed that the honeybee queen emerges without a developed vitellarium.
Finally, using immunohistochemistry of dividing and apoptosing cells, this thesis explores how the reproductive division of labour impacts honeybee development in caste differentiation of ovaries. Both castes develop ovaries similarly, until larval stage 5.
At this stage, worker ovaries undergo a reduction of ovarioles and polyfusomes. Polyfusomes present again by pupation. There are fewer developing germ-cell clusters in workers across larval stages. These differences may be attributed to the groups of apoptosing cells present in workers, but not queens, at larval stage 4. Finally, newly emerged workers, like queens, lack a developed vitellarium. Notably, the appearance of a newly emerged worker ovary resembles a reproductively repressed mature worker ovary.
Overall, this thesis outlines the honeybee germline and how it is developed in queen and worker larval development. It also describes the developmental timing in both queen and worker ovaries, and how it differs depending on caste. This work provides targets for improving the overall laying success and longevity of honeybee queens. It also gives insight into how the reproductive division of labour impacts honeybee development. This work provides fundamental biology knowledge that will support research into successful population growth of honeybee populations, by informing how to measure the fecundity of queens during breeding and development.