Male honeybees produce antimicrobial chemicals in their semen to protect new queens from a fungal disease.
Sex always comes with the risk of contracting a sexually transmitted disease, so male honeybees have evolved to produce antimicrobial chemicals in their semen. The fungus Nosema apis is a specialised pathogen of honeybees, which can be transmitted to new queens when they mate, but new research shows that male honeybees’ semen has powerful antifungal activity, disrupting the lifecycle of the Nosema spores and reducing their viability.
Queen honeybees can make with 25 or more males during her nuptial flight, before settling down to raise a colony, so she has plenty of opportunity to come into contact with sexually transmitted diseases like Nosema. Yan Peng and her team of researchers at the University of Western Australia collected semen from male honeybees (Apis mellifera) and tested the viability and germination success of Nosema apis spores when incubated in the semen. They found that honeybee seminal fluid reduced spore viability by over 80% in just 24 hours. Analysing this process under the microscope, the team found that the seminal fluid caused the spores to rupture prematurely. This process mimics the normal process of spore germination, but instead of releasing the spores’ infectious agents to infect the cell, the invading party is met by a second line of immune defence and the fungus is killed.
The team found that when they separated the seminal fluid into proteins and non-proteins, and tested the two halves separately, that both halves of the seminal fluid were equally effective at killing the spores. This suggests that the seminal fluid contains at least two different lines of defence against the fungus, the authors say. The protein half is responsible for rupturing the spore wall, while the non-protein half kills the spores more directly, although we do not yet fully understand how.
The researchers found that the bees’ seminal fluid was extremely specific – it only killed Nosema spores, and not those of other fungal pathogens, suggesting that Nosema has been a serious and ever-present threat to honeybee colonies. Some strains of Nosema may have developed a resistance to the bees’ antifungal semen, which explains why around 20% of spores were able to survive over 24 hours bathing in the stuff. The team now hopes to study the interaction between Nosema strain and honeybee genetics to better understand how different populations of honeybees have adapted to their local strain of STD.
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