Brighter is better, according to a new study linking bill colour to STD status in ducks.
Credit: iStockPhoto
LONDON: Antibacterial activity in the ejaculates of birds has been discovered for the first time, in a new study also showing that bill colouration can be used to predict the antibacterial capacity of semen.
By examining the relationship between the colouration of a duck's sexual ornament - its bill - and the antibacterial activity of its ejaculates, the results could lend support to Darwin's theory of sexual selection, explaining why females are attracted to colourful, extravagant displays.
"Several studies examine the association between general immunity and colouration but as yet no studies have looked at the antibacterial defenses of ejaculates and how this might be correlated with colouration," lead author Melissah Rowe from the University of Oslo in Norway told COSMOS.
Bacterial-induced sperm damage
While it has been known that antibacterial activity exists in the semen of a range of animals, such as cows, insects and crabs, this is the first time that it is has been discovered in ducks.
Antibacterial agents in semen combat pathogens present in the ejaculate and in the female reproductive tract. In birds, gut pathogens from the intestines can mix with the ejaculate in the cloaca - a common opening for the digestive and reproductive tracts - and can be sexually transferred from the male to the female, at a high cost to her health.
Sperm cells can be damaged by microbial exposure as they are not immune, and this can reduce the chances of fertilisation.
Sperm are selfish
"The male has to reduce the bacterial challenges to his own sperm for a couple of selfish reasons," said Tom Pizzari, an evolutionary biologist at the University of Oxford in the UK who was not involved in the study.
"The first is that these bacteria could damage sperm and impair his own ejaculate in sperm competition. The other is that if an ejaculate contains very high levels of bacteria, it might elicit an immune response by the female that might eventually backfire on his own sperm."
"Sperm want to be delivered in a way that is not immunologically challenging to the female so that the immune system does not raise barriers that might impair the success of the ejaculate," Pizzari added.
