Flow cytometry evidence about sperm competition in honey bee (Apis mellifera)

We tested whether flow cytometry can be used for assessment of viability of honey bee (Apis mellifera) sperm. The method was used to detect possible competition between the sperm of different drones. The flow cytometry analysis of semen stained with SYBR-14/propidium iodide revealed significant differences between fresh and freeze-thawed samples. The identification of populations corresponding to viable and nonviable sperm allowed us to assess the sperm viability. The comparison of single-drone semen with mixed semen of two unrelated drones showed that sperm viability was not affected by mixing, but there were differences between mixed and unmixed semen in side scatter, which correlates with shape and optical homogeneity of particles. The proportion of particles in different populations also was affected by mixing of the semen. The results suggest that there are interactions between ejaculates of different drones, possibly related to sperm competition.