Morphofunctional Changes in Frozen-Thawed Sperm of Apis Mellifera Linnaeus Drones

Instrumental insemination of queen bees using cryopreserved sperm is an important biotechnological tool to address the issues of contemporary beekeeping. Long-term cryopreservation is detrimental to sperm function and drone fertility, killing more than 50% of the sperm during the process. Prediction of cryopreservation damage from freezing drone semen remains elusive. The purpose of this study was to assess the impact of long-term cryopreservation in “Kakpakov diluents” (C46) on morphometric measurements of sperm head of the Apis mellifera L. and ultrastructure. For the experiment, sperm samples from the cryobank of the Federal Beekeeping Research Centre (Russia), frozen since 1993, 2011 and 2013 were used. In the present study, it was found out that cryopreservation had a considerable impact on the drone sperm head morphometry. Sperm head measurements of cryopreserved samples were significantly lower compared with the extended sample for morphometric measurements of the nucleus area 3.55 ± 0.12, 4.07 ± 0.1, 4.31 ± 0.04 (5.57 ± 0.03, respectively); nucleus perimeter 10.57 ± 0.11, 11.11 ± 0.13, 11.59 ± 0.05 (11.72 ± 0.06, respectively); nucleus length 4.66 ± 0.05, 4.82 ± 0.06, 5.07 ± 0.02 (5.22 ± 0.03, respectively); nucleus acrosome length 3.72 ± 0.08, 3.65 ± 0.08, 3.96 ± 0.05 (4.24 ± 0.04, respectively). Cryopreserved and thawed spermatozoa revealed changes in ultrastructure such as vacuolation of the axoneme, intranuclear vacuoles, and loss of the derivative’s mitochondria. These details provide valuable data for further experiments on modification of the composition of cryomedium to minimize cryodamage in the semen of honey bee drones.