Seminal fluid proteins differ in abundance between genetic lineages of honeybees

Seminal fluid is transferred to the females' reproductive tract as part of the ejaculate and contains highly complex molecular machinery that is of central importance for male and female reproductive success. Interspecific studies suggest rapid evolutionary changes in the sequences of some seminal fluid proteins and also highlight the importance of specific seminal fluid proteins for sperm function and paternity success. Much less work has been conducted to study if variation in the steady-state abundance of seminal fluid proteins occurs within a species, which could provide a foundation for future selection to act upon. Here we used a unique breeding program of the honeybee Apis mellifera to provide evidence for quantified differences in seminal fluid protein abundances between three genetic lineages that have been bred for ~20 generations. We found the same subset of seminal fluid proteins to be present in all lines, but protein abundance or protein modification state varied significantly for 16% of the protein spots investigated. Protein spots with changed abundances were identified using mass spectrometry, with the abundance of a number documented from other species to be correlated with male fertility, reproductive success or immune-competence. We conclude that significant alterations in the abundance or modification state of specific proteins in seminal fluid can be linked to different genotypes in honeybees.